PROJECT REPORT

on

SYNTHESIS AND CHARACTERISATIONAL STUDIES OF PORPHYRINS, METALLOPORPHYRINS AND THEIR

NANOPARTICLES

(Summer Internship May-July 2012)

BACHELOR OF TECHNOLOGY + MASTERS OF TECHNOLOGY (DUAL DEGREE COURSE)

In

NANOTECHNOLOGY

Under the guidance of:

Prof. S. M. S. Chauhan

HOD, Chemistry,

Delhi University.

Submitted by: Deepti rana, 7th Semester

B.Tech.+M.Tech(2009-14)

Enl No. A1223309036

CERTIFICATE

This is to certify that Deepti Rana is a B.Tech. + M.Tech. in Nanotechnology (Dual) Degree

course student of Amity Institute of Nanotechnology, Amity University, Noida and has

sucessfully underdone Summer Internship on the topic on “Synthesis and Characterisation

studies of Porphyrins, Metalloporphyrins and their Nanoparticles” during the period

May 2012 to July 2012 at Delhi University, North Campus.

The information submitted is true and original to the best of our knowledge.

Prof. S. M. S. Chauhan Ms Deepti Rana

HOD Chemistry, B.Tech+M.Tech (Nanotech.)

Delhi University Amity University, Noida

Declaration

I, Deepti Rana, student of B.Tech + M.Tech. in Nanotechnology (Dual), batch 2009-2014, 7th

semester, studying at Amity University hereby declare that the project training report entitled

“Synthesis and Characteisational studies of Porphyrins, Metalloporphyrins and their

Nanoparticles” is an authentic record of my own work carried out at Delhi University,

Chemistry Department, North Campus as per requirements of the Six Weeks Internship

Project for the award of degree of B.Tech + M.Tech. in Nanotech. (Dual) from Amity

Institute of Nanotechnology, Amity University, Noida, under the guidance of Prof. S. M. S.

Chauhan, HOD Chemistry, Delhi University from May-July 2012.

Deepti Rana

Enl no A1223309036

Date: 30/Oct/2012

Certified that the above statement made by the student is correct to the best of my knowledge

and belief.

Prof. S. M. S. Chauhan

HOD, Chemistry

Delhi University

Acknowledgement

It is my pleasure to be indebted to various people, who directly or indirectly contributed in

the development of this work and who influenced my thinking, behavior and acts during the

course of study.

First of all I would like to thank my guide, Prof. S M S Chauhan, H.O.D Chemistry,

Delhi University, for providing me with valuable insights and support which helped me

throughout my Internship. However, it would not have been possible without the kind support

and help of Ms Renu Guatam, PhD scholar in Chemistry, Delhi University. Furthermore my

senior lab mates and PhD scholars were also proved to be helpful and very supportive during

my internship. I would like to extend my sincere thanks to all of them.

I am highly indebted to University Science Instrumentation Centre (USIC)

Characterization Lab, Delhi University for their guidance and constant supervision as well as

for providing necessary information regarding the characterization details of project.

I would also like to heartily thank Dr. R P Singh, Director, Amity Institute of

Nanotechnology, for permitting me in achieving and completing the objectives for my

Internship.

Lastly, I would like to thank the almighty and my parents for their moral support and

my friends with whom I shared my day-to-day experience and received lots of suggestions

that improved my quality of work.

TABLE OF CONTENTS

CHAPTERS

1. Porphyrin

1.1. Porphyrin Chemistry

1.2. Properties of Porphyrins

1.2.1. Electronic Properties

1.2.2. Explanation of their Optical Absorption spectra

1.3. Biological importance of Porphyrins

1.3.1. Hemoglobin and myoglobin

1.3.2. Chlorophyll

1.3.3. Enzymes

1.3.4. Oxygenases

1.3.5. Peroxidases and Catalase

1.3.6. Cytochromes

1.4. Applications

1.5. Experimental

1.5.1. Synthesis of 5,10,15,20-tetraphenyl porphyrin [H2TPP]

1.6. Characterization

1.6.1. 1H NMR

1.6.2. UV-Vis Spectroscopy

1.7. Conclusion

1.8. References

2. Meso-substituted Symmetrical Porphyrins

2.1. Synthesis methods

2.1.1. Alder and Longo method

2.1.2. [2+2] Condensation

2.2. Application

2.3. Experimental

2.3.1. Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’,-pentafluorophenyl) porphyrin

[F20TPP] by Alder and Longo method

2.3.2. Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’,-pentafluorophenyl) porphyrin

[F20TPP] by [2+2] Condensation

2.3.2.1. Synthesis of 5-(pentafluorophenyl) dipyrromethane (DPM) by

Amberlyst-15

2.3.2.2. Synthesis of F20TPP by [2+2] condensation of 5-(pentafluorophenyl)

dipyrromethane

2.4. Characterisation

2.4.1. 1H NMR

2.4.2. UV-Vis Spectroscopy

2.5. Conclusion

2.6. References

3. Metalloporphyrins

3.1. Introduction

3.2. Properties

3.3. Experimental

3.3.1. Synthesis of Iron(III) 5,10,15,20-tetraphenyl porphyrin [H2TPPFe(III)Cl]

3.3.2. Synthesis of Zinc 5,10,15,20-tetraphenyl porphyrin [TPPZn]

3.3.3. Synthesis of Iron(III) 5,10,15,20-tetra (2’,3’,4’,5’,6’-pentafluorophenyl)

porphyrin [F20TPPFe(III)Cl]

3.3.4. Synthesis of Zinc 5,10,15,20-tetra)2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPPZn]

3.4. Characterization

3.4.1. UV-Vis Spectroscopy

3.5. Conclusion

3.6. References

4. Porphyrin Nanoparticles

4.1. Introduction

4.2. Properties

4.3. Application

4.4. Experimental

4.4.1. H2TPP Nanoparticles

4.4.1.1. Synthesis of H2TPP nanoparticles by Solvent Mixing Techniques

4.4.2. F20TPP Nanoparticles

4.4.2.1. Synthesis of F20TPP Nanoparticles by Sonication Technique

4.5. Characterization

4.5.1. TEM

4.5.2. UV-Vis Spectroscopy

4.6. Conclusion

4.7. References

SYNTHESIS AND

CHARACTERIZATION STUDIES OF

PORPHYRINS,

METALLOPORPHYRINS AND THEIR

NANOPARTICLES

CHAPTER 1

PORPHYRINS

Porphyrins are one of the vital chemical units essential for several life processes on the earth.

Many biological molecules function with prosthetic groups essentially made of these units.

Chlorophylls of chloroplasts which drive photosynthesis, heme as a component of

hemoglobin that transports oxygen to animal tissues and as the central unit of myoglobin

ensures the storage of oxygen - all these have active sites essentially made of porphyrin core

[1-3]. Over the years, a great deal of concerted efforts have brought to light substantial

understanding of the structure-function relationship in these natural porphyrins[4-10].

A large variety of synthetic porphyrins and their metalloderivatives were made over the years

to study the porphyrin based natural systems. The search for anti-cancer drugs, useful

catalysts, semiconductors and superconductors, electronic materials with novel properties has

also made this synthetic porphyrin chemistry a very actively probed one by chemists,

biologists and physicists alike. The synthetic meso-substituted porphyrins offer a great

advantage to study the physical and chemical properties of the porphyrin nucleus

quantitatively by a judicious choice of the substituents that may be attached on the periphery.

Metalloporphyrins are widely and intensely investigated in the area of catalysis and also as

models and mimics of enzymes lie catalase, peroxidases, P450 cytochromes or as

transmembrane electron transport agents [11-13]. They have also been used as NMR image

enhancement agents [14], Nonlinear optical materials [15] and DNA-binding or cleavage

agent [16,17].

Currently there is interest in using chelated radioactive metal isotopes as diagnostic imaging

and therapeutic agents. In that context pophyrins are excellent compounds because of their

extremely high stability constants with many metal ions.

1.1 Porphyrin Chemistry

Porphyrins are a group of organic compounds, many naturally occurring. One of the best

known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein

hemoglobin. Porphyrins are aromatic and obey Hückel's rule for aromaticity, possessing 4n+2

π electrons (n=4 for the shortest cyclic path) delocalized over the macrocycle. Thus porphyrin

macrocycles are highly conjugated systems. As a consequence, they typically have very

intense absorption bands in the visible region and may be deeply coloured; the

name porphyrin comes from a Greek word for purple. The parent porphyrin is porphine, and

substituted porphines are called porphyrins. The specific porphyrin in heme B is

called protoporphyrin IX and has 4 methyl, two vinyl, and two propionic acid substituents at

the indicated positions.

Porphine Heme group B of Hemeoglobin

The porphyrin macrocycle is an aromatic system consisting of four “pyrrole-type” rings

joined by four methine (meso) carbons. Although a porphyrin ring has a total of 22-π

electrons, only 18 of them participate in any one of the several delocalization pathways. Due

to the anisotropic effect from the porphyrin ring current, the shielded N-H protons appear at

very high field (-2 to -4 ppm) in the 1H-NMR spectrum, whereas the peripheral protons show

up at low field (8-10 ppm) due to the presence of the deshielding environment resulting from

the aromatic ring current [18]. In the visible absorption spectra, porphyrins usually show an

intense Soret band [19] at around 400 nm, which results from the delocalized cyclic

electronic pathway of porphyrins. Several weaker absorption bands between 450 nm and 800

nm, which are responsible for the rich colour of porphyhrins, are also observed and known as

Q bands.

Porphyrin macrocycle

Besides many synthetic and naturally occurring ones with the core structure mentioned

above, there are many biologically active systems which also have porphyrin-like structures

which are given in [2-7].

Central metal and porphyrin ligand bond nature

The nature of bonding between a central metal and the porphyrin ligand is found to be

originating essentially from the following two types of primary interactions: a-coordination

of nitrogen lone pairs directed towards the central metal atoms and π-interaction of metal pπ

or dπ orbitals with nitrogen-based π orbitals [20]. The appropriate symmetry-adapted linear

combinations of prophyrin-ligand orbitals involved in the bonding with metal orbitals are

shown in Figure 1.

Figure 1 The symmetry adapted linear combination of porphyrin-ligand orbitals involved in the

bonding with metal orbitals (a) are suitable for σ-interactions and (b) for π-interaction

In the σ-system the prophyrin is clearly a donor to the metal while in the π-system porphyrin

has the appropriate orbitals to act both as a π-donor and as a π-acceptor. The versatile

characteristics of the ubiquitous porphyrin molecules can be attributed largely to the

extensively delocalised π-system which is electronically very sensitive and tunable.

1.2 Properties of Porphyrins

They can form a dianion as well as a dication.

The porphyrin ring is generally stable under strongly acidic and basic conditions. Strong

bases, such as alkoxides can remove the two protons (pKa ~16) on the inner nitrogen atoms

of porphyrin to form a dianion.

On the other hand, the two free pyrrolenine nitrogen atoms (pKb ~9) can be easily

protonated with acids such as trifluoroacetic acid, to form a dication.

The inner protons can also be replaced by a metal. Various types of metals (e.g., Zn, Cu, Ni,

Sn) can be inserted into the porphyrin cavity by using various metal salts (Metalloporphyrins)

[21]. Demetalation of metalloporphyrins can usually be achieved by the treatment with acids,

and different types of acids are required for the removal of different types of metals. All

nitrogen atoms [22] can also be achieved in a similar way to protonation and metalation.

They have usual Planar structures; although some exceptions are possible.

Aromatic compounds such as porphyrins used to be assumed to be planar. Although previous

reported X-ray structures of simple porphyrins showed the ring to be planar, recently, there

have been tremendous numbers of nonplanar porphyrins reported in the literature [23,24].

Nonplanar porphyrins have intriguing physical and biological properties due to the distortion

of the porphyrin ring. Many different factors such as metallation, peripheral substitutions,

alkylation of the pyrrolenine nitrogen atoms, and even protonation, can distort the nominally

planar structure of the porphyrin macrocyle.

Highly conjugated systems, thus are coloured compounds.

Due to the high conjugation of the porphyrin ring, its band gap reduces and comes in the

region of visible range imparting the ring its usual purple colour.

1.2.1 Electronic properties

The electronic heart of a porphyrin is the inner 16-membered ring with 18-π electrons. The

ring is structured with basic fourfold symmetry, including four nitrogen atoms directed

towards the center. The optical absorptions of porphyrin are determined essentially by the

nelectrons on the porphyrin ring, with only minor perturbation from the electrons of the

central substituents.

The optical absorption spectra is an important spectral phenomenon to distinguish between

the free-base porphyrins and their metalloderivatives. The spectrum changes from four-

banded to a two-banded spectrum on metallation. This dramatic effect is attributed to the

enhancing of the D2h symmetry of the free-base porphyrin to D4h on metallation [25].

Majority of metal-free porphyrins shows very characteristic absorption, which consist of two

sets of bands in the ranges of 400-450 nm and 550-700 nm. The first sets of bands are called

the B band or Soret band (strongly allowed) and the lower energy set are the Q bands (quasi-

allowed).

Figure 2 Electronic absorption spectra of (a) free-base porphyrin and (b) its metalloderivative.

1.2.2 Explanation of its Optical Absorption spectra

The Q bands of free-base porphyrins are a set of four absorptions arising from HOMO to π*

transition. Of these, the first set of two lines is x-component of Q while the second set is its y-

component. Both these Qx and Qy components are composed of two types of vibrational

excitations too, the lower energy one being Q(0,0) and the higher energy one Q(1,0). Thus

the four lines in the set are Q,(0,0), Q,(1,0), Qy(0,0) and Qy(1,0) in the increasing order of

energy.

On metallation, the spectrum shows an intense B (Soret) band at 420 nm and two weaker Q

bands at 550-600 nm [26,27]. These spectral absorptions arise from π-π* transitions of the

aromatic porphyrin ligand.

The widely accepted model to fit this spectrum, the four-orbital model, treats the porphyrin as

a cyclic polyene and emphasizes the transition between the two highest filled bonding

molecular orbital levels, a1u, a2u and the lowest empty doubly degenerate antibonding

molecular orbital levels eg*. The allowed transitions, a1u eg* and a2u eg* are assumed to

be degenerate in energy. As a consequence, the states undergo configuration interaction and

give rise to new states. The resulting spectrum shows a high energy band B in which the

transition dipoles add and a low-energy band Q in which the transition dipoles cancel. The

two Q bands are vibronic components of the same transition [28].

1.3 Biological importance of Porphyrins

Metal complexes of porphyrins and related compounds are important prosthetic groups that

assemble to form a wide variety of proteins and enzymes working as redox and

rearrangement catalysts [29]. The nature being a master designer, has chosen and retained the

best choice of molecular assemblies in living systems to carry out very specifically the

functions they are intended for and also to achieve them with the maximum efficiency.

A large number of naturally occurring porphyrin have been isolated and characterized. Of

these protoporphyrins are the most abundant and widely characterized ones. It is found in

hemoglobin, myoglobin, heme enzymes and most of the cytochromes [5].

The biological and chemical importance of metalloporphyrins has brought to focus intense

interest in the nature of the metal ligand linkages in such complexes as well as all the

physicochemical properties of the macrocycles. The macrocycle has the ability to function as

a reservoir of electrons and control the reactivity at the axial position of metal, which usually

serves as a catalytic site in heme enzyme. Because of their ubiquitousness and the variety of

their natural functions, heme proteins have been investigated on multi- and interdisciplinary

levels. These proteins all containing an iron porphyrin as the prosthetic group, are responsible

for oxygen transport and storage (hemoglobin and myoglobin) [30], electron transport

(cytochromes) [31], oxygen reduction (cytochrome oxidase), hydrogen peroxide utilization

and destruction (peroxidases and catalases), and hydrocarbon oxidation (cytochrome, P.450)

[32].

Also the various functions of heme proteins in the transport, storage and reactions with

dioxygen are made possible by different and selective interactions of diverse proteins with

the heme groups [10]. These differences are brought about largely by the axial ligands

provided by ancillary groups of the protein and from the nature of the pockets on either side

of the porphyrin. Important porphyrin based natural systems are the hemoglobin, myoglobin,

chlorophyll, heme enzymes and the cytochromes.

1.3.1 Hemoglobin and myoglobin

Hemoglobin and myoglobin are high molecular weight protein systems containing iron(II)

protoporphyrin IX units. They are responsible for oxygen transport and storage in higher

animals [9]. Hemoglobin transport dioxygen from its source to the site of use inside the

muscle cells. There the oxygen is transferred to myoglobin for use in respiration. Myoglobin

which is responsible for storing oxygen in cells, has high affinity for the dioxygen even at

low partial pressure but in lungs, hemoglobin takes up high amount of oxygen at high partial

pressure. This special property of hemoglobin is attributed to the 'cooperative effect" caused

by the decrement in size of Fe2+ in central hole due to spin change (from high spin to low

spin) on dioxygen complexation [33,34].

The iron in hemoglobin and myoglobin is in the ferrous state and has to have an N-base

(histidine) coordinated to the metal from one of the sides of the plane to have dioxygen bound

at the vacant sixth coordination site. The oxidized form of iron, i.e., ferric state, called

metmyoglobin and methemoglobin will not bind oxygen. The free heme is immediately

oxidized in the presence of oxygen and water and thus renders useless for O2 transport.

Myoglobin exhibits greater affinity of O2 than hemoglobin and it is largely converted to

oxymyoglobin even at low O2 concentration in order to affect the transport of O2 at the cell

[9]. Upon the oxygenation of hemoglobin, two of the heme groups move about 100 pm

towards each other while two others separate by about 700 pm due to the action of protein

envelope. The net result of this combined movement is that hemoglobin can exhibit relatively

low affinity for binding the fit one or two oxygen molecules. But once they are bound, the

binding of subsequent O2 molecule is greatly enhanced. Conversely the loss of one oxygen

molecule from fully oxygenated hemoglobin causes the rest to dissociate more readily when

the oxygen pressure is decreased [35].

1.3.2 Chlorophyll

Chlorophyll is the green colouring matter of leaves and green stems, and its presence is

essential for photosynthesis. In green plants it is the chlorophyll which absorbs the light

energy. Chlorophyll is basically magnesium derivative of porphyrins and some slight

structural changes in porphyrin moiety results in different classes of chlorophyll with slight

difference in photocatalytic properties [5]. All of the chlorophylls absorb light very intensely

particularly at relatively long wavelength regions [36]. The light energy absorbed by a

chlorophyll molecule become delocalised and spread throughout the entire electronic

structure of the excited molecule.

The photosynthetic pigments in the chloroplasts of plants consists of two functional units

namely photo system I and photo system II [37]. Photo system I contain chlorophyll, p-

carotene and a single molecule of P-700, a specialised chlorophyll a which serves as an

energy trap. Photo system II has a characteristic reactive centre namely P-680 a specialized

chlorophyll-protein complex. Photo system I absorbs light at longer wavelength. Photo

system II is activated by shorter wavelength, i.e., 670 nm and below and it is responsible for

oxygen evolution.

Both the photo systems contain chlorophyll a and chlorophyll b. In photo system I, the ratio

of chlorophyll a to chlorophyll b is higher than in photo system II [5]. These two photo

systems must cooperate to yield maximum result in photosynthesis.

1.3.3 Enzymes

Enzymes are biological catalysts that govern, initiate and control biological reactivity

important for the life processes. They are produced by the living organism and are usually

present in only very small amounts in the various cells. All known enzymes are proteins and

some contain non-protein moieties termed prosthetic groups that are essential for the

manifestation of catalytic activities [4,5,9]. In several natural enzymes, metalloporphyrins

constitute these prosthetic groups.

1.3.4 Oxygenases

There are various enzymatic reactions in which one or both atoms of O2 are directly inserted

into the organic substrate molecule to yield hydroxyl groups. Enzymes catalyzing such

reactions are called oxygenase, of which there are two classes - the dioxygenase catalyzes

insertion of both atoms of the O2 molecules into the organic substrate, whereas the

monooxygenase inserts only one [4].

The most important monooxygenase is cytochrome P-450 found in the microsomes of liver

cells [38]. Cytochrome P-450 contains protoheme. The CO derivative of its reduced form

absorbs maximally at 450 nm, hence the name cytochrome P-450. During the enzyme

reaction the ferric P-450 first combines with a substrate followed by a one electron reduction

to form a ferrous P-450 substrate complex. The reduced Fe(II) form of P-450 reacts with

molecular O2 in such a way that one of the O-atoms is reduced to water and the other is

introduced into the organic substrate.

Cytochrome P-450 enzymes catalyze hydroxylation of many different kinds of substrates

including steroids, fatty acids, certain amino acids etc and thus making them more water-

soluble. They also promote hydroxylation of various drugs.

1.3.5 Peroxidases and Catalase

Peroxidases are enzymes catalyzing the oxidation of a variety of organic and inorganic

compounds. Peroxidases obtained from plants contain hemine groups. The different types of

peroxidases are horseradish peroxidase, myloperoxidase, chloroperoxidase etc [8].

Catalase is also a heme enzyme which catalyze the dismutation of H2O2 generated during

various life processes. Catalase is made up of four identical sub-units each containing one

heme group. The axial metal sites appear to be occupied by water and an amino acid residue.

1.3.6 The Cytochromes

The cytochromes are electron transferring proteins, containing iron porphyrin, found in

aerobic cells. Some cytochromes found in endoplasmic reticulam, play a role in specialized

hydroxylation reactions [30]. All cytochromes undergo reversible Fe(III)-Fe(II) valency

changes during their catalytic cycles. In almost all the cytochromes both the fifth and sixth

positions of the iron are occupied by the R groups of specific amino acid residue of the

proteins [39]. Therefore, these cytochromes cannot bind with ligands like O2, CO or CN-. An

important exception is cytochrome oxidase that normally binds O2 in its biological function.

The iron protoporphyrin group of cytochrome c is covalently linked to the protein by

thioether bridges between the prophyrin ring and two cysteine residue in the peptide chain

whereas in other cytochromes the porphyrin ring is non-covalently bound. Cytochrome c is

the only common heme moiety in which the heme is bound to the protein by a covalent

linkage.

1.4 Applications

Porphyrins and related macrocycles provide an extremely versatile synthetic base for a

variety of material applications. The broadly defined porphyrin research area is one of the

most exciting, stimulating and rewarding for scientists in the field of chemistry, physics,

biology and medicine. The beautifully constructed porphyrinoid ligand, perfected over the

course of evolution, provides the chromophore for a multitude of iron, magnesium, cobalt

and nickel complexes which are primary metabolites and without which life itself could not

be maintained. The field is spreading rapidly in every direction across the whole spectrum

[40].

Diverse applications of porphyrins and metalloporphyrins to materials chemistry have been

developed over the past decade, both for their optical properties and their applications as

sensors. Notably, porphyrins and metalloporphyrins have found applications as field-

responsive materials, particularly for optoelectronic applications, including mesomorphic

materials and optical-limiting coatings. For example, the facile substitution of the periphery

of various porphyrins has generated a series of unusual liquid crystalline materials. The

porphyrin ligand serves as a platform on which one can erect desirable molecular and

materials properties.

The nonlinear optical properties of these materials are of special interest, in part for energy

transfer with molecular control, and in part for potential application in optical

communications, data storage and electro optical signal processing. The stability of mono-

and di-cation porphyrin π-radicals makes these systems especially interesting for

photoionization processes. Porphyrins and metalloporphyrins can also be used as nonlinear

optical materials. They have desirable properties for use in optoelectronics. They have greater

thermal stability and their extended π-conjugated macrocycle ring give large nonlinear optical

effects and subtle variation in their physical properties can be made easily through chemical

modification of their periphery [41-45].

They also play key roles in adsorbing light energy over a wide spectral range and converting

it into the highly directional transfer of electrons [46-50]. It is a marvellous but highly

complex process that has inspired considerable interest in the synthesis of porphyrin arrays. A

bio mimetic approach to the photosynthetic apparatus may also lead to applications of similar

systems as optoelectronic devices.

Because of their inherent stability, unique optical properties, and synthetic versatility,

porphyrins and metalloporphyrins are excellent candidates for a variety of sensing-materials

applications. Research in this area has focussed on incorporation of synthetic porphyrins and

metalloporphyrins into a variety of material matrices, such as polymers, glasses and films [3].

The unique spectral characteristics and synthetic versatility of porphyrins allow a variety of

sensing applications. They are also used in the detection of organic vapours and ionic species

in solution.

Photochemical reduction of water utilizes only a limited portion of sun ray. Porphyrins,

whose absorption spectra over an appreciable portion of the spectrum of sunlight, are of great

interest in this respect. Also metalloporphyrins exhibit very high photochemical stability [51].

Large attempts are also made to utilize the photochemical properties of metalloporphyrins in

organic synthesis.

Metalloporphyrins of aluminium, zinc, manganese, cobalt and rhodium complexes have been

demonstrated to serve as excellent initiators for controlled anionic and free radical

polymerizations [52]. The discovery of these metalloporphyrins-based initiators has led to

significant contributions to the progress of precision macromolecular synthesis via "living

polymerization" (i.e., growth pattern of the macromolecule can be viewed as analogous to the

growth of a biological organism) [53-55].

The worldwide approval of Photofibrin [a purified version of Hematoporphyrin derivative

(HpD); a complex mixture of dimers and oligomers in which porphyrin units are joined by

ether, ester and carbon-carbon bonds] for the treatment of various types of cancers has

created enormous interest among physicians, chemists, biologists and physicists [56,57].

During the early and mid 1970s, several groups together has realized that together HpD and

light (Photo dynamic therapy) had a potential capability for tumor destruction. This is now

one of the accepted modalities for the treatment of cancer [58,59].

In addition to its use for cancer treatment, Photo dynamic therapy has also shown a potential

for applications in other areas: They have found applications in molecular recognition, boron

neutron capture therapy, virus destruction, DNA cleavage, data storage, nonlinear optics and

electrochromism treatment of aged-related macular degeneration, Psoriasis, bone marrow

purging, arthritis and purification of blood infected with various viruses including HIV.

Due to their selective localization in tumor cells, synthetic tetrapyrrole pigments have

tremendous applications in PDT (photodynamic therapy) and BNCT (boron neutron capture

therapy) [18]. PDT and BNCT are both binary cancer therapies and their side effects are

limited. PDT involves the irradiation of a photosensitizer with light of a specific wavelength,

which is absorbed by the photosensitizer and subsequently causes the excitation of the

photosensitizer to its excited singlet state, then through intersystem crossing, to reach to its

excited triplet state. The resulting excitation energy is absorbed by the triplet ground state of

dioxygen (found in all living cells) and the highly toxic singlet dioxygen (1O2) is generated;

this kills the tumor cells. BNCT involves the capture of thermal neutrons by boron-10 nuclei,

which have been selectively delivered to tumor cells. The captured neutron releases 7Li and 4He nuclei with kinetic energy (~ 2.4 Mev). These two particles are extremely cytotoxic but

can only travel a distance of about one cell diameter in tissues, thus it can selectively kill the

tumor cell containing it.

At present, all the photosensitizers in clinical trials are based on tetrapyrroles (porphyrins,

chlorins, bacteriochlorins and pthalocynanines), and it seems that porphyrin in general will

show continued interest in the exiting area of photodynamic therapy.

Porphyrins and metalloporphyrins are also ideal model compounds for studying light

harvesting, energy and electron transfer, and multi electron redox catalysis [19]. Porphyrin-

based multi porphyrin arrays and molecular wires have received much interest. In these

model systems, it is important to know how individual molecules within arrays communicate

with each other. So far, factors such as distance, orientation and geometry have been

recognized to be important factors to control this intercommunication.

1.5 Experimental

1.5.1 Synthesis of 5,10,15,20-tetraphenyl porhyrin [H2TPP]

A 500 ml three neck round bottom flask, equipped with dropping funnel and a condenser was

charged with propionic acid (250 ml). The propionic acid was brought to reflux and

benzaldehyde (5.3 g, 0.05 mole) and freshly distilled pyrrole (3.35 g, 0.05 mole) were

simultaneously added to refluxing propionic acid and the refluxing was continued for 30

minutes. The reaction mixture was left at room temperature over night. The glistering purple

crystals were filtered off, washed with water and the mixture was refluxed for 3 hours. The

hot solution was filtered under suction through a sintered glass funnel containing alumina (15

g), which had a filter paper on top of it. The alumina was thoroughly washed with

Dichloromethane (100 ml). The combined filterate was concentrated to about 20 ml and

methanol (10 ml) was added. The mixture was cooled and the resulting purple crystals were

filtered to give 5,10,15,20-tetraphenyl porphyrin [H2TPP].

1.6 Characterisation:

1.6.1 1H NMR spectroscopy

1H NMR spectrum of H2TPP

1H NMR (CDCl3) δ ppm: 8.85 (s, 8H, β-pyrrolic-H), 8.23 (m, 8H, o-phenyl H), 7.76 (m, 12H,

m- & p- phenyl H), -2.77 (brs, 2H, internal NH).

1.6.2 UV-Vis spectrum

UV-Vis spectrum of H2TPP in CHCl3

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 417.90 (1.77), 515.00 (0.11), 549.92 (0.05),

588.27(0.04), 647.22 (0.04).

1.7 Conclusion

Due to the various uses in natural and synthetic systems discussed above we have synthesized

Tetraphenyl porphyrin [H2TPP] which was purple in colour and characterized this sample

through H1 NMR and UV-Vis spectra.

1.8 References

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Structure and Synthesis 1978,1.

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(Eds), Pergamon Press, Oxford, 1987,2.

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oxidative DNA cleavage. Chem Rev., 1992,92(6),1411-1456.

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compounds as synthetic models of the reaction centre in photosynthesis. Russ Chem

Rev.,1989,58(6),602-619.

[14] K E Keller, N Foster. Relaxation enhancement of water protons by manganese(III)

porphyrins: influence of porphyrin aggregation. Inorg Chem., 1992,31(8),1353-1359.

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cancer recent progress. Curr Med Chem–Anti Cancer Agents.,2001,1,175-194. (b) V I

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and phthalocyanines. Porphyrins Phthalocyanines.,2001,5(11),767-781.

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Light-Harvesting Multiporphyrin Arrays. Angew Chem Int Ed., 2003,43(2),150-158.

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Multielectron Redox Reactions of Small Molecules: The “Cofacial

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Academic Press, San Diego, CA, 2000,3,347.

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triatom-bridged porphyrin dimmers. J Am Chem Soc., 1981,103(12),3328-3341.

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reactivity profiles. Curr Org Chem., 2000,4,139-174.

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Soc., 1935,57(10),2010-2011. (b) G P Arsenault, E Bullock, S F MacDonald.

Pyrromethanes and Porphyrins Therefrom. J Am Chem Soc., 1960,82(16),4384-4389. (c)

L T Nguyen, M O Senge, K M Smith. Simple Methodology for Syntheses of Porphyrins

Possessing Multiple Peripheral Substituents with an Element of Symmetry. J Org

Chem., 1996,61(3),998-1003.

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conditions. J Org Chem., 1987,52(5),827-836.

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poiphin. J Chem Phys.,1959,30,1139-1161.

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Physical Chemistry, 1978,111.

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nucleic acids and polypeptides. J Am Chem Soc., 1991,113(20), 7799-7800.

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implications for the hemoproteins. Chem Rev.,1981,81(6),543-555.

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haemoglobin. Nature.,1970,228,726-734.

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Handbook", K M Kadish, K M Smith, R Guillard (Eds),Academic Press, New York, 2000,3.

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Miyata (Eds) CRC Press, Boca Raton, FL, 1997,61,1.

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Nalwa (Ed) John Wiley & Sons, Chichester, 1997,1-4,261.

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B P Lever (Eds), 1996,4,79.

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Mater.,1993,5,341-358.

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Chem.,1991,5,349-377.

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Crystals", Academic Press, Orlando, 1987.

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Biochem.,1987,15,299-317.

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photosynthetic reaction centers and their mechanistic implications.

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Bacterial Reaction Centers: Replacement of Glu 212 in the L Subunit by Glutamine

Inhibits Quinone (QB) Turnover. Proc Natl Acad Sci USA.,1989,86,6602-6606.

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photosynthetic reaction centres. Nature.,1989,339,111-116.

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photosyntheic purple bacteria. Photosynth.,1987,13,225-260.

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response times of oxygen‐quenched luminescent coatings. Rev Sci Instrum.,1993,64,3394-

3402.

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Rev.,1993,125,129-141.

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Polymerizations. Acc Chem Res., 1996,29(1),39-48.

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monomer. A new method of formation of Block Polymers. J Am Chem Soc.,

1956,78(11),2656-2657.

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York 1992;33.

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an overview. J Clin Laser Med Surg.,1996,14(5),223-233.

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bronchogenic carcinoma. J Clin Laser Med Surg.,1996,14(5),235-238.

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Laser Med Surg.,1996,14,219-221.

CHAPTER 2

MESO SUBSTITUTED

PORPHYRINS

Meso-substituted porphyrins bearing specific patterns of functional groups are valuable

components in the synthesis of porphyrin-based biomimetic systems and crucial building

blocks for applications in material chemistry. With regard to possible types of meso-

substituted porphyrins, the most widely studied synthetic porphyrin group encompasses the

symmetrical 5,10,15,20-tetraarylporphyrins like 5,10,15,20-tetraphenylporphyrin (H2TPP)

(A4 -porphyrin 1) [1]. Additionally, symmetrical trans-substituted porphyrins (trans-A2 2 or

trans-A2B2 porphyrins 4) have recently found much use due to their simple synthesis. Less

symmetrical representatives of the meso substituted porphyrin family have been studied only

infrequently based on the absence (e.g. for mono-substituted porphyrins) or complexity (e.g.

for ABCD-porphyrins) of the necessary synthesis (Scheme 2.1).

Scheme 2.1 Meso Substituted Porphyrins

2.1 Synthesis methods

In the past 100 years, porphyrin syntheses have been developed dramatically [2]. Today,

virtually any porphyrin can be synthesized from known synthetic methodology. For example,

tetramerization of pyrroles, [3 + 1] condensation and [2 + 2] condensation are common

methodologies [3]. Tetraarylporphyrins are synthetic porphyrins and have various

applications.

2.1.1 Alder and Longo method

A simple way to obtain symmetrical porphyrins (such as the tetraarylporphyrins) is the acid-

catalyzed condensation reaction of pyrrole with specific aldehyde, followed by oxidation of

the resulting colorless porphyrinogen. This procedure, originally developed by Rothemund

and Menotti [4], has been refined by Adler and Longo [5]. It generally gives around 20%

yields for tetraarylporphyrins (Scheme 2.2). Despite the modest yields, the relative simplicity

of this method has made it well suited for preparation of large amounts of tetraarylporphyrins

(i.e., >1 g of porphyrin). Later, the Lindsey group developed higher yielding and milder

reaction conditions by using a Lewis acid (TFA or BF3) as the catalyst [6]. Subsequently,

Lindsey’s group also developed higher concentration conditions (0.1-0.3 mol L-1). Despite the

slightly lower yields, this improved synthesis is more practical for larger scale preparations of

tetraarylporpyrins. Also, the Lindsey method has the advantage that it can be used to prepare

porphyrins that required the use of acid-unstable aldehydes not generally employed under

Adler-Longo conditions.

Scheme 2.2 Reaction conditions: propionic acid, reflux.

The yields are reduced due to the formation of oligomers and this call for stringent

purification methods to remove the by-products.

2.1.2 [2+2] Condensation Method

Meso or 5-substituted dipyrromethanes are important precursors for the synthesis of meso -

substituted porphyrins by [2+2] condensation. These are used as key building blocks in the

synthesis of linear porphyrin arrays.

Synthesis of meso-substituted dipyrromethanes

The condensation of pyrrole with benzaldehyde in the presence of various cation exchange

resins afforded very good yields of meso-phenyldipyrromethane. This resin is of

macroreticular type, having a styrene divinylbenzene co-polymer matrix (15–17%

crosslinking) and the exchange capacity is in the range of 4.5–4.7 mequiv./g.

Dipyrromethanes were prepared by condensation of substituted aromatic aldehydes in neat

excess pyrrole (1:20). Most of the dipyrromethanes were readily crystallized after removal of

pyrrole. The use of macroporous cation exchange resins has the advantages of controlled

acidity due to site isolation of sulphonic acid groups, high selectivity and purity of the

product due to trace side reactions and easy work-up procedures, which was evidently proven

by the reduction of oligomer formation and the production of excellent yields of meso-

substituted dipyrromethanes in pure forms. This refined process enabled the straightforward

preparation of multi-gram batches of 5-substituted dipyrromethanes.

Scheme 2.3 Synthesis of meso substituted dipyrromethane.

A facile efficient synthetic strategy for preparing 5-substituted dipyrromethanes in excellent

yields using cation exchange resins as heterogeneous acid catalysts (Scheme 2.3). These

dipyrromethanes are subsequently transformed to symmetrical and mixed porphyrins by

[2+2] condensation.

These cation exchange resins are the functional resins with a styrene divinylbenzene

copolymer matrix having sulfonic acid groups. Macroporous (or macroreticular) functional

resins (present on the market mostly as polystyrene crosslinked with divinylbenzene) are

isotropic materials formed by chemically interconnected polymer chains, normally insoluble

in any conceivable solvent. Each resin particle can be viewed as a mini reactor filled with a

solution of functional polymer chains with pendant arms bearing sulfonic acid groups [7].

Functional synthetic cation exchange resins serve as efficient industrial heterogeneous

catalysts, potentially useful in the area of fine chemical synthesis. They offer an environment

for the catalytic reaction quite different from that of a free solution or the surface of

conventional heterogeneous catalysts based on inorganic supports. The mechanism of ion

exchanger catalysed reaction in a non-aqueous environment is similar to that operating for

conventional heterogeneous catalysts (adsorption–surface reaction–desorption). An important

consequence of the catalysis being a multiplet of sulfonic acid groups is that it shows more

than a proportional dependence of the reaction rate on the concentration of acidic centres. In

this connection, the environment of a catalytic site embedded in the polymer network can

almost be considered as a micro reactor.

Formation of symmetrical meso-substituted porphyrins

The ‘2+2 synthesis’ using dipyrromethanes as intermediates, forms the backbone of the

building block approach towards the synthesis of porphyrins. Cation exchange resins has

been used as acid catalysts in the preparation of symmetrical and mixed porphyrins

incorporating various functional groups from aryldipyrromethanes (Scheme 2.4). Aryl

dipyrromethanes (A) with aromatic aldehydes give rise to porphyrinogens, which

subsequently get oxidized to the corresponding meso-substituted porphyrins (B) by means of

p-chloranil.

Scheme 2.4 Synthesis of symmetrical meso substituted porphyrin by [2+2] condensation

2.2 Application

Meso-substituted asymmetric porphyrins (A3B) have recently found specific biomedical

applications, particularly in the field of detection and treatment of neoplastic tissue (PDT)

and also labeling and analysis of nucleic acids [8a]. Not only have they found use in the

medicinal field, but they also display unique properties and find application in several,

optoelectronics, catalysis, biomimetic and material chemistry [8b]. The availability of

suitable building blocks through synthetic methodologies that have the flexibility for

structural modification is closely tied to the level of architectural sophistication achieved in

such systems. 5-Substituted dipyrromethanes are important synthetic intermediates and are

well-established precursors for the synthesis of symmetric and asymmetric meso substituted

porphyrins, expanded porphyrins, and other porphyrin analogues [9a]. Not only are they key

precursors to meso-substituted asymmetric porphyrins, but also calix[4]pyrroles and

calix[4]phyrin macro cycles, which are well established as redoxactive or optical sensors for

anions [9b].

2.3 Experimental

2.3.1 Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin [F20TPP]

by Alder and Longo Technique

Dry chloroform (1.5 litres) was taken in 3 litres three necks round bottom flask fitted with

nitrogen inlet tube, a reflux condenser and a septum. The chloroform was degassed with a

steam of nitrogen for 10 minutes. Freshly distilled pyrrole (1.0 ml, 14.5 mmol) and 2,3,4,5,6-

pentafluorobenzaldehyde (2.85 g, 14.5 mmol) were added to chloroform with stirring. The

reaction mixture was bought to reflux under nitrogen and boron trifluoride etherate (2.5 M

solution in chloroform, 3.88 ml, 4.6 mmol) was injected through septum. The reaction

mixture was refluxed with stirring, under nitrogen atmosphere for 1 hour during which the

colour changed from dark yellow to dark brown. After 1 hour, nitrogen flow was shut off and

DDQ (2.64 mmol) was added to the reaction, and the reaction mixture was refluxed for

additional 1 hour, after which it was cooled to room temperature and triethylamine (0.58 ml,

4.6 mmol) was added with stirring. The solvent was then evaporated to dryness in rotatory

evaporator. The product was chromatographed silica gel column using petroleum ether as

eluent. The evaporation of the eluent of the third fraction of the column gave the required

porphyrin as brown crystals.

2.3.2 Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPP] by [2+2] Condensation

2.3.2.1 Synthesis of 5-(pentafluorophenyl)dipyrromethane by Amberlyst-15:

A solution of pentafluorobenzaldehyde (2.0 mL, 16.2 mmol) and pyrrole (50 mL, 720 mmol)

was degassed by bubbling the mixture with argon for 10 min. Cation exchange resin

amberlyst-15 (2 g) was added to this mixture. The solution was stirred at room temperature.

After 12 hr, the reaction mixture was diluted with CH2Cl2 (400 ml), 100 ml of triethylamine

was added to prevent acidolysis of the mesophenyl dipyrromethane and filtered. The filtrate

was washed with water (400 ml) and the organic layer was dried over Na2SO4. The solvent

was removed under reduced pressure and the unreacted pyrrole was removed by vacuum

distillation (5–8 mm/30–358C). The resulting pale yellow amorphous solid was purified by

crystallization or flash chromatography using pet ether–ethylacetate–triethylamine (85:14:1)

to give (pentafluorophenyl) dipyrromethane as white crystals (70–80%).

2.3.2.2 Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPP] by using 5-(pentafluorophenyl) dipyrromethane

A mixture of 5-(pentafluorophenyl) dipyrromethane (2 mmol) and pentafluoro benzaldehyde

(2 mmol) in 1:1 ratio for (2+2) condensation of DPM ,was stirred under a nitrogen

atmosphere in dichloromethane [CH2Cl2] (50 ml) in presence of a cation exchange resin i.e.,

amberlyst-15 (1 g) at 258 C for 12 hr. DDQ was then added and the reaction mixture was

further refluxed for 3 h, cooled and filtered. The filtrate was concentrated and the crude

product was subjected to soxhlet purification using methanol. The methanol insoluble product

was then purified by flash chromatography on silica gel to afford pink crystals of porphyrins.

2.4 Characterisation

2.4.1 H1 NMR

1H NMR of Pentafluoro dipyrromethane

1H NMR (400 MHz,CDCl3) δ ppm: 5.87 (1H, s, CH), 6.00 (2H, m, ArH), 6.13– 6.16 (2H, m,

ArH), 6.70 – 6.71(2H, m, ArH), 8.14 (2H, brs, NH).

1H NMR of F20TPP

1H NMR (CDCl3) δ ppm: 8.92 (s, 8H, β-pyrrole H). -2.92 (s, 2H, N-pyrrole H)

2.4.2 UV-Vis Spectroscopy

UV-Vis spectra of F20TPP

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 412.44 (1.01), 506.43 (0.09), 583.48 (0.03).

2.5 Conclusion

Here we have synthesized one meso-substituted symmetrical porphyrin i.e., 5,10,15,20-tetra-

(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin [F20TPP] by two different techniques. First by

Alder and Longo technique and secondly by [2+2] condensation of Dipyrromethane (DPM)

by using acid catalyst resin (Amberlyst-15) and studied the products with H1 NMR and UV-

Vis spectra.

2.6 References

[1] J S Lindsey,“The Porphyrin Handbook”, K M Kadish, K M Smith, R Eds Guilard,

Academic Press,San Diego, 2000,46.

[2] M G H Vicente, K M Smith. Porphyrins and derivatives: Synthetic strategies ad

reactivity profiles. Curr Org Chem.,2000,4,139-174.

[3] (a) P Rothemund. Formation of Porphyrins from Pyrrole and Aldehydes. J Am Chem

Soc.,1935, 57(10),2010-2011. (b) G PArsenault, E Bullock, S F MacDonald. Pyrromethanes

and Porphyrins Therefrom. J Am Chem Soc.,1960,82,4384-4389. (c) L T Nguyen, M O

Senge, K M Smith. Simple Methodology for Syntheses of Porphyrins Possessing

Multiple Peripheral Substituents with an Element of Symmetry.J Org

Chem.,1996,61(3),998-1003.

[4] M O Senge, W W Kalisch, I Bischoff. The Reaction of Porphyrins with

Organolithium Reagents. Chem Eur J., 2000,6(15),2721-2738.

[5] X Feng, I Bischoff, M O Senge. Mechanistic Studies on the Nucleophilic Reaction of

Porphyrins with Organolithium Reagents. J Org Chem.,2001,66(26),8693-8700.

[6] R P Brinas, C Bruckner. Synthesis of 5,10-diphenylporphyrin. Tetrahedron.,

2002,58(22),4375-4381.

[7] B Corain, M Kralik. Dispersing metal nanoclusters inside functional synthetic resins:

scope and catalytic prospects. J Mol Catal A:Chem., 2000,159(2),153-162.

[8] (a) L I Grosseweiner. Photodynamic therapy, Chap 8, in “The Science of Phototherapy”,

CRC Press, London, 1994, 139-155. (b) J S McCaughan Jr. Photodynamic Therapy: A

Review. Drugs & Aging.,1999,15,49-68.

[9] (a) J S Lindsey. In “Metalloporphyrins Catalysed Oxidations”, Kluwer Academic

Publishers, The Netherlands, 1994, 49-86. (b) A Jasat, D Dolphin. Expanded porphyrins

and their heterologs. Chem Rev.,1997,97,2677-2340.

CHAPTER 3

METALLOPORPHYRINS

3.1 Introduction

The prophyrin ring provides a vacant site at its centre, ideally suited for metal incorporation.

The NH protons inside the ring of porphyrins possess acidic character and hence can get

deprotonated to give porphyrinato ions. These dianion species with their electronically

sensitive planar n-framework and central cavity with more or less rigid size exhibit

remarkable ligation characteristic towards metal ions. Thus derivatives of porphyrins with

almost all metals and semimetals have been synthesised [1].

A crucial factor to form stable metalloporphyrins seems to be the compatibility of porphyrin

ring size with the ionic radii of the metal cations [2]. Hence stable complexes generally result

when these two sizes match while their instability tends to increase when the size of the

cation is too big or too small with very few exceptions. The porphyrinato dianion is ideally

suited to act as a tetradenate ligand with metal ions [3]. Thus the minimum coordination

number of the metal ion possible in a metalloporphyrin is four. A size matching divalent

metal ion would give neutral complex, while a higher valent cation would carry with it

balancing anion(s) mostly covalently bound with the metal, in addition to the

porphyrinato ion.

The normal coordination geometry around the metal ion in the former species would be

square planar, while in the latter case the coordination geometry would be square pyramidal.

Coordination number greater than four is also possible. The two ligands of the six coordinate

metalloporphyrins are found on the opposite sides of the porphyrinato plane yielding

complexes with tetragonal or octahedral geometries [3]. Ability to exhibit variable oxidation

states of metals in their metalloporphyrins is another important feature in this class of

compounds. They are also capable of stabilizing metal ions in their unusual oxidation states,

which have resulted in extensive studies revealing interesting chemistry.

3.2 Properties

Metalloporphyrins can be divided into two groups based on their UV-vis and fluorescence

properties [4]. Regular metalloporphyrins contain closed-shell metal ions (d 0 or d 10 )—for

example Zn II , in which the d π (dxz , dyz ) metal-based orbitals are relatively low in energy.

These have very little effect on the porphyrin π to π* energy gap in porphyrin electronic

spectra (Figure 1). Hypsoporphyrins are metalloporphyrins in which the metals are of d m , m

= 6–9, having filled d π orbitals. In hypsoporphyrins there is significant metal d π to

porphyrin π* orbital interaction (metal to ligand π- backbonding) [Figure 2]. This results in

an increased porphyrin π to π* energy separation causing the electronic absorptions to

undergo hypsochromic (blue) shifts.

Figure 1 Molecular Orbital Diagram for metalloporphyrins. Interactions between dπ and π* occur in

hypsoporphyrins.

Figure 2 The dπ metal orbital overlap with the π system of the porphyrin ring.

The lowest energy excited singlet states of porphyrins can be thought of as being formed

from the molecular orbitals you examined above. An excited singlet state with an a1ueg

configuration is formed by promoting an electron from the a1u orbital to an eg orbital.

Likewise, an excited singlet state with an a2ueg configuration is formed by promoting an

electron from the a2u orbital to an eg orbital. These excited singlet states mix to two new

singlet states that are nearly 50:50 mixtures of the unmixed states. The closer in energy the

unmixed states, the greater the degree of mixing.

An electronic transition to the higher energy mixed state, the S2 state, is strongly allowed,

whereas an electronic transition to the lower energy mixed state, the S1 state, is only

weakly allowed. The band in the UV-Vis absorption spectrum due to a transition to the S2

state is the Soret band, and the band due to a transition to the vibration less S1 state is the

α band. The greater the degree of mixing, the less intense the α band relative to the Soret

band.

In the UV-visible spectrum of porphyrin (Figure 3), there is also a vibronic band, the β band,

that appears at slightly lower wavelengths than the α band. The β band is due to transitions to

higher vibrational levels in the S1 state and serves as a "normalization band" in porphyrin

absorption spectra. As a result, the intensity of the α band relative to the β band can serve as a

measure of how close in energy the a2u and a1u orbitals are to each other. For example, if the

a2u and a1u orbitals have essentially the same energy, the degree of mixing will be large, the α

intensity will be small, and, therefore, the α/β intensity ratio will be small. On the other hand,

if the a2u and a1u orbitals are well separated in energy, the degree of mixing will be smaller,

and the α/β intensity ratio will be larger [5].

Figure 3 Typical UV-Visible absorption spectrum of a porphyrin

3.3 Experimental

3.3.1 Synthesis of Iron(III)5,10,15,20-tetraphenyl porphyrin [H2TPPFe(III)Cl]

The metallization of 5,10,15,20-tetraphenylporphyrin (H2TPP) by iron metal is done by

taking 5,10,15,20-tetraphenylporphyrin (H2TPP) (1.2 g, 1.95 mmol) and FeCl2.4H2O (3.0 g,

15.8 mmol) salt and dissolving in DMF (250 ml). This reaction mixture was refluxed for 3 h.

The hot solution was filtered, cooled and diluted hydrochloric acid was added to it in small

portions. The precipitated complex was separated by filtration and was crystallized twice

from a mixture of 1,2-dichloroethane and n-hexane to get iron (III)-5,10,15,20-

tetraphenylporphyrinate chloride.

3.3.2 Synthesis of Zinc 5,10,15,20-tetraphenyl porphyrin [ZnTPP]

The metallation of 5,10,15,20-tetraphenylporphyrin (H2TPP) was done by zinc metal in a

similar fashion as was done for above. The 5,10,15,20-tetraphenylporphyrin (H2TPP) (1.2 g,

1.95 mmol) and zinc acetate [Zn(O Ac)2] (3.0 g, 15.8 mmol) as a metal salt precursor were

taken and dissolved in DMF (250 ml). This reaction mixture was refluxed for 3 h. The hot

solution was filtered, cooled and diluted hydrochloric acid was added to it in small portions.

The precipitated complex was separated by filtration and was crystallized twice from a

mixture of 1,2-dichloroethane and n-hexane. A magenta coloured zinc-5,10,15,20-

tetraphenylporphyrin was thus obtained.

3.3.3 Synthesis of Iron (III) 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPPFe(III)Cl]

The 5,10,15,20-tetrakis(2’,3’,4’,5’,6’-pentaflourophenyl) porphyrin (H2F20TPP) (49 mg, 0.50

mmol) and FeCL2.H2O (40 mg, 2.0 mmol) were taken in refluxing DMF (40 ml) and

refluxed for 3 hours. The hot solution was filtered and worked up as above. The crude

porphyrin was recrystallized from dichloromethane:hexane solvent mixtures to obtain

iron(III) 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluoro phenyl) porphyrin [F20TPPFe(III)Cl].

3.3.4 Synthesis of zinc 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[ZnF20TPP]

The 5,10,15,20-tetrakiis(2’,3’,4’,5’,6’-pentaflourophenyl) porphyrin (H2F20TPP) (100 mg,

0.25 mmol) and zinc acetate ( 100 mg, 1.0 mmol) were taken in refluxing DMF (20 ml) and

refluxed for 3 hours at 140 C. The hot solution was filtered and worked up as above. The

crude porphyrin was recrystallized from dichloromethane:hexane solvent mixtures to obtain

zinc 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluoro phenyl) porphyrin [ZnF20TPP].

3.4 Characterisation

3.4.1 UV-Vis spectroscopy

UV-Vis spectrum of H2TPPFe(III)Cl

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 377 (0.603), 415.88 (0.94), 510.26 (0.13), 576.55

(0.040).

UV-Vis spectra of ZnH2TPP

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 413.71 (0.82), 544.29 (0.04).

UV-Vis spectrum of F20TPPFe(III)Cl

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 411.74 (0.81), 505.47 (0.15), 561.07 (0.08).

UV-Vis spectrum of ZnF20TPP

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 429.99 (1.99), 555.18 (0.11), 595.5 (0.06).

3.5 Conclusion

Here we have synthesized two different metalloporphyrins. Firstly the simple 5,10,15,20-

tetraphenyl porphyrin [H2TPP] made to metallated with Iron and Zinc salts to form

Iron(III)5,10,15,20-tetraphenyl porphyrin [H2TPPFe(III)Cl] and Zinc 5,10,15,20-tetraphenyl

porphyrin [ZnH2TPP]. Secondly a meso substituted symmetrical porphyrin i.e., 5,10,15,20-

tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin [F20TPP] also metallated with Iron and Zinc

salts to form Iron (III) 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPPFe(III)Cl] and Zinc 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[ZnF20TPP]. These compounds were studied by UV-Vis Spectroscopy.

3.6 References

[1] J W Buchler, "The Porphyrins" D Dolphin (Ed), Academic, New York, Part A,

Structure and Synthesis 1978,1.

[2] J W Buchler, "Porphyrins and Metalloporphyrins", K M Smith (Ed),Elsevier, 1975.

[3] W R Scheidt. Trends in metalloporphyrin stereochemistry. Acc Chem Res.,

1977,10(9),339-345.

[4] D F Marsh, L M Mink. Microscale Synthesis and Electronic Absorption Spectroscopy

of Tetraphenylporphyrin H2(TPP) and Metalloporphyrins ZnII(TPP) and NiII(TPP). J

Chem Ed.,1996,73,1181.

[5] http://www.molecules.org/experiments/Walters/Walters.html

CHAPTER 4

PORPHYRIN NANOPARTICLES

4.1 Introduction

Many of the unique properties of nanoscaled materials, especially their electronic, photonic

and magnetic properties cannot be achieved using the corresponding atomic, molecular,

polymeric or macroscopic materials. Porphyrins are representative of photofunctional

organics, and they show remarkable photo-, electro- and biochemical properties that

contribute to light harvesting [1]. Hence, meso/nano-scaled porphyrin assemblies or particles

are expected to be promising candidates for use in photonic devices [2]. To fabricate organic

nano-architectures composed of porphyrins, it should be recognized that van der Waals

intermolecular and hydrogen-bonding interactions as well as the electrostatic attraction are

responsible for the specific electronic/optical properties that are fundamentally different from

those of inorganic metals or semiconductors [3]. The formation of nanoscaled colloidal

particles of porphyrins can be accomplished by adding water to a solution of a hydrophobic

porphyrin in water-miscible organic solvents such as THF, DMSO, DMF, or CH3CN with a

few percent of a low molecular weight polyethylene glycol (PEG). This mixed solvent

approach is an efficient means to make large quantities of nanoparticle colloids (20–500 nm

diameter) of a variety of porphyrins [4–5].

4.2 Properties

The properties of many nanoscaled particles are substantially different than those of bulk

materials composed of the same atoms or molecules. Nanometer-scale particles composed of

metals, metal oxides, and other inorganic materials have been reported as have a few

composed of organic molecules [6-11]. Organic molecules also are used in self-assembling

processes to prepare “soft” nanostructures such as spheres and tubes [12,13]. Thus,

nanoscaled particles composed of porphyrins are expected to have chemical activities

significantly different from those of the free porphyrins or of those immobilized onto/into

supports. Porphyrin nanoparticles are promising components of advanced materials because

of the rich photochemistry, stability, and proven catalytic activity [14]. In analogy to

inorganic and other organic nanoparticles, it is expected that nanoparticles of porphyrins will

have unique photonic properties not obtainable by larger-scaled materials containing the

macrocycle, or by the molecules themselves [15] the formation of nanoparticles of catalytic

porphyrins will enhance stability and catalytic rate because of the structure of the aggregate

and the greater surface area.

The UV-vis spectra of porphyrin nanoparticles are significantly different compared to the

spectra of the corresponding porphyrin solutions (Figure 1). Soret bands are found to be

broadened and/or split. The arrangement of macrocycles in aggregates generally fall into two

types, ”J”(edge-to-edge) interactions are characterized by red shifts and “H” (face-to-face)

interactions are characterized by blue shifts. The optical spectra suggest both types of

interactions in the nanoparticles and are well understood to be indicative of electronic

coupling of the chromophores. The extent of J versus H aggregation depends on the specific

porphyrin used.

Volume of water did not have major effect on the positions of the Soret and Q bands of the

porphyrin nanoparticles, but with increasing volume of water as a guest solvent, the

absorbance of the porphyrin nanoparticles decreased. By increasing the volume of the guest

solvent, just the solution of the nanoparticles become more diluted and the intensities of the

absorption become less but the position of the spectra did not change; this shows that the

volume of the guest solvent did not affect the shape of the nanoparticles.

4.3 Application

There are a variety of possible applications of porphyrin nanoparticles that derive from the

photonic properties of both the component molecule and the nanoscaled dimensions of the

particle. Many of these nanoparticles, when the porphyrin contains a redox-active transition

metal (e.g., Fe,Co.Mn) are more efficient catalysts on a per porphyrin basis than the

individual porphyrins adsorbed onto supports. The fluorescence properties of nanoparticles

containing the free base or closed-shell metalloporphyrins or the phosphorescence of these or

other metalloderivatives such as the Pd(II) and Pt(II) can be exploited for sensors and

displays.

The agent used to prevent agglomeration can be covalently attached to the dye forming the

particle or as part of the solvent system. It also demonstrates that these and other types of

dyes with a range of photonic properties do not need to be prepared by encapsulation in

matrices or by designed self-assembly a priori. The matrix may severely limit the

functionality of the particles in the former case, and at present, this size of particle is difficult

to achieve in the latter. A “green” synthesis of porphyrins will also make these materials

more economically feasible.

4.4 Experimental

4.4.1 H2TPP Nanoparticles

The formation of nanoscaled colloidal particles of hydrophobic porphyrins such as

5,10,15,20-tetraphenylporphyrin (H2TPP) and many of the metallo derivatives can be

accomplished by adding water (guest solvent) to a solution of a hydrophobic porphyrin in

THF, DMSO, DMF, or CH3CN (host solvent) with a few percent of a low molecular weight

PEG such as HO(C2H4O)4CH3 [16] or a non-ionic surfactant. Stabilizers such as PEG are

essential for the formation of stable colloidal systems by host–guest solvent methods; reports

on nanoparticle systems of porphyrinoids without this component are misleading or

inaccurate since the porphyrins rapidly and quantitatively precipitate [17]. Other inquiries

into the formation and activity of nanoparticles of dyes such as phthalocyanines have been

reported [18]. The mixed solvent approach is an efficient means to make large quantities of

nanoparticles colloids of a variety of porphyrins. In terms of scale-up, the particle size and

distribution of batches using 20 g of porphyrin correlate well with the small batches of 20

mg.

4.4.1.1 Synthesis of 5,10,15,20-tetraphenyl porhyrin [H2TPP] nanoparticles by Mixing

Solvent technique

By dissolving hydrophilic 5,10,15,20-tetraphenyl porhyrin [H2TPP) ( 2 mg) of porphyrin in

0.5 mL of water, followed by rapid addition of 5 mL of CH3CN. For nanoparticles composed

of hydrophobic/amphipathic porphyrins, 25 µL of (triethyleneglycol)monomethyl ether was

mixed into a 0.2 mL (0.1mM) solution of the porphyrin in DMSO, and then 2.5 mL of water

was added rapidly (Scheme 4.1).

The four ethyleneglycol monomethyl ether derivatives appended to porphyrin Fe(III) adds in

the formation and stabilization of nanoparticles. Consistent with other nanoparticle

preparations, the stabilizer prevents agglomeration and is a factor in determining nanoparticle

size [19].

Scheme 4.1 Synthesis of H2TPP nanoparticles

4.4.2 5,10,15,20-Tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin [F20TPP]

nanoparticles

Colloidal nanoparticles of F20TPP are of interest because of the diverse photonic and catalytic

applications. the particle size and stability depends on the structure of the

porphyrin/metalloporphyrin, the exact preparative procedures, and conditions in which they

are examined (e.g. in solution, concentration, on a surface). The perfluorophenyl groups of

5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl) porphyrin, (F20TPP) are widely recognized

to impart stability to redox catalysts of the metallo derivatives [20-22] and to enhance the

luminescence properties of especially the Pd(II) and Pt(II) species in applications such as

organic LEDs and oxygen sensors [23-25]. F20TPP forms stable nanoparticles under a wide

variety of conditions: stabilizer type and concentration, host solvents, and solvent : water

ratios. One reason for the wide range of processing conditions that yield stable colloids of

F20TPP may be attributed to the unique solvation properties of the perfluoro-phenyl moieties.

Porphyrins bearing only hydro- or fluoro-carbon groups (e.g. F20TPP, TPP) tend to form

nanoparticles with sizes and distributions that are modestly dependent on the exact

chemical structure and concentration of the stabilizer. Conversely, porphyrins with polar

functional groups (e.g. meso pyridyl groups, and hydroxy, carboxy, amino, or sulfonato

groups on the phenyl) exhibit a greater range of particle size with different kinds and amounts

of the stabilizer. This latter observation is likely due to the stronger interactions between the

solute and the solution components (host and guest solvents, and stabilizer). Thus for polar

porphyrins it is possible to tune the sizes and morphology of particles over a greater range by

changing the chemical nature and the quantity of the stabilizer. The complex intermolecular

interactions between amphipathic molecules such as the polyethylene glycols with water, the

polar host solvent, and the porphyrin solute are essential for the formation of stable colloids.

4.4.2.1 Synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin

[F20TPP] nanoparticles by Sonication method

The 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl) porphyrin [F20TPP] nanoparticles

were prepared by means of a sonication technique. Triethylene glycol monomethyl ether (100

μL) as a stabilizer was added to stock solution of F20TPP in THF (1.22 mM for F20TPP, 200

μL) followed by addition of 20 ml water with vigorous mixing and after that was sonicated

for 50 min at 60˚C (Scheme 4.2).

Scheme 4.2 Synthesis of F20TPP nanoparticles

4.5 Characterization

4.5.1 TEM

TEM image of H2TPP nanoparticles

TEM image of F20TPP

TEM images revealed the speherical morphology of the synthesized Organic nanoparticles.

4.5.2 UV-Vis Spectroscopy

UV-Vis spectrum of H2TPP bulk in DMF

UV-Visible [CHCl3, λmax/ nm, (Amax)]: 416.43 (1.75), 513.36 (0.07), 547.82 (0.03), 590.41

(0.01), 645.67 (0.01).

UV-Vis of H2TPP nanoparticles in water

UV-Visible [ λmax/ nm, (Amax)]: 424.97 (0.38), 520.97 (0.10), 554.19 (0.05), 594.32 (0.04),

651.10 (0.03).

UV-Vis spectrum of F20TPP Nanoparticles

UV-Visible [ λmax/ nm, (Amax)]: 424.97 (0.49), 567.97 (0.56), 556.19 (0.36), 629.10 (0.31).

4.6 Conclusion

Here we synthesized two organic nanoparticles by two different techniques. Firstly we did

synthesis of 5,10,15,20-tetraphenyl porhyrin [H2TPP] nanoparticles by solvent mixing

method and secondly synthesis of 5,10,15,20-tetra-(2’,3’,4’,5’,6’-pentafluorophenyl)

porphyrin [F20TPP] nanoparticles by sonication technique. Results were examined through

TEM images and characteristic UV-Vis spectra.

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