UV-Vis SPECTROSCOPY, UV-Vis SPECTROSCOPY, CHEMOMETRICS AND NON-CHEMOMETRICS AND NON-BONDING INTERACTIONS IN BONDING INTERACTIONS IN

SOLUTION: SOLUTION: qualitative conclusions qualitative conclusions

and and quantitative estimationsquantitative estimations

• UV-Vis Spectroscopy background UV-Vis Spectroscopy background (structural information, (structural information, quantitative analysis)quantitative analysis)

• Crown ethers complex formationCrown ethers complex formation

• Self-association of dyesSelf-association of dyes

• Difficult cases for quantitative Difficult cases for quantitative analysis of equilibria in solution analysis of equilibria in solution (chemometrics)(chemometrics)

Lecture Outline:

What is Optical Spectroscopy?What is Optical Spectroscopy?The study of molecular structure and

dynamics through the absorption, emission and scattering of light.

UV-Vis Spectroscopy:

Maxwell: The light is an electromagnetic field characterized by a frequency , and wavelength .

Light obeys the relationship

c = . With energy of photons

E = h .

The Electromagnetic Spectrum: The Electromagnetic Spectrum:

UV-Vis Spectroscopy:

= c / E = h .

The Electromagnetic Spectrum: The Electromagnetic Spectrum:

UV-Vis Spectroscopy:

= c /

E = h .

1020 1018 1016 1014 1012 108

Cosm

ic

rays

-rays X-rays UV Vis

ible

Infrared Microwave

Electronic excitation

Bond breaking and ionization Vibration Rotation

Visible Spectrum

400 500 600 700

Hz

Molecular Spectroscopy: Molecular Spectroscopy:

UV-Vis Spectroscopy:

Optical Spectroscopy and Non-Optical Spectroscopy and Non-Bonding Interactions (IR vs UV-Bonding Interactions (IR vs UV-Vis): Vis):

IR Spectroscopy:IR Spectroscopy: Vibrational motion (Vibrational motion ( > 1000 nm); > 1000 nm); More suitable for structural More suitable for structural

identification;identification;High concentration range (> 10High concentration range (> 10-3-3 mol/l); mol/l);Limited number of solvents;Limited number of solvents;

UV-Vis Spectroscopy:

Optical Spectroscopy and Non-Optical Spectroscopy and Non-Bonding Interactions (IR vs UV-Bonding Interactions (IR vs UV-Vis): Vis):

UV-Vis Spectroscopy:UV-Vis Spectroscopy:Electronic transitions (200 – 1000 nm)Electronic transitions (200 – 1000 nm)More suitable for quantitative analysis;More suitable for quantitative analysis;Low concentration range (< 10Low concentration range (< 10-4-4 mol/l) mol/l)Large number of solvents, including Large number of solvents, including

water;water;Simple instrumentation, low running Simple instrumentation, low running

costscosts

1940 - Single beam 1940 - Single beam Beckman BBeckman B UV-Vis spectrometerUV-Vis spectrometer1941 - Dual beam scheme Cary & 1941 - Dual beam scheme Cary & BeckmanBeckmanBeckman DU-2 UV-Vis spectrometer Beckman DU-2 UV-Vis spectrometer (1941-1975, 35 000 units produced)(1941-1975, 35 000 units produced)

UV-Vis Spectroscopy:

UV-Vis Spectroscopy:

UV-Vis Spectroscopy:

Frank-Condon principle:Frank-Condon principle:

Describes the intensities of vibronic Describes the intensities of vibronic transitions, or the absorption or transitions, or the absorption or emission of a photon. When a emission of a photon. When a molecule is undergoing an molecule is undergoing an electronic transition the nuclear electronic transition the nuclear configuration experiences no configuration experiences no significant change. This is due in significant change. This is due in fact that nuclei are much more fact that nuclei are much more massive than electrons and the massive than electrons and the electronic transition takes place electronic transition takes place faster than the nuclei can respond. faster than the nuclei can respond. When the nucleus realigns itself When the nucleus realigns itself with the new electronic with the new electronic configuration, the theory states that configuration, the theory states that it must undergo a vibration.it must undergo a vibration.

ENERGY

ABSO

RBAN

CEUV-Vis Spectroscopy:

Amax

Amax /2

1/2

max

position of the band – energy of the transition

integral intensity (area) – oscillator strength (not molar absorptivity)

Spectral shape:

- position of the band

- intensity

- half-band width

Structural Structural information: information:

- chromophore is chromophore is needed needed (conjugation and/or (conjugation and/or auxochrome(s))auxochrome(s))

- broad bands broad bands (usefulness for (usefulness for identification is identification is limited)limited)

UV-Vis Spectroscopy:

Quantitative analysis: Quantitative analysis:

Single compound: Single compound: Beer-Lambert’s lawBeer-Lambert’s law

Mixture:Mixture:Additivity principleAdditivity principle

UV-Vis Spectroscopy:

lcA ..

n

iii clA

1

..

Fathers of Modern Fathers of Modern Supramolecules:Supramolecules:

Charles J. Donald J. Jean-Charles J. Donald J. Jean-MarieMarie

Pedersen Cram LehnPedersen Cram LehnNobel Prize in Chemistry 1987Nobel Prize in Chemistry 1987

Crown Ethers:

Modern Supramolecules:Modern Supramolecules:

crown container crown container cryptandscryptands

ethersethers moleculesmoleculesCharles J. Donald J. Jean-Charles J. Donald J. Jean-

MarieMariePedersen Cram LehnPedersen Cram Lehn

Crown Ethers:

Crown Ethers:Crown Ethers:

Charles J. 12-Charles J. 12-Crown-4 Crown-4

PedersenPedersenJACS 89, 7017 (1967) JACS 89, 7017 (1967)

Crown Ethers:

Crown Ethers:Crown Ethers:- flexible ring structure, containing flexible ring structure, containing

several ether groups;several ether groups;- size fit effect of complex formation with size fit effect of complex formation with

metals (very strong complexes: 18-metals (very strong complexes: 18-crown-6 has high affinity for potassium crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, cation, 15-crown-5 for sodium cation, and 12-crown-4 for lithium cation);and 12-crown-4 for lithium cation);

Crown Ethers:

Crown Ethers:Crown Ethers:- the oxygen atoms are well situated to the oxygen atoms are well situated to

coordinate with a cation located at the coordinate with a cation located at the interior of the ring, whereas the interior of the ring, whereas the exterior of the ring is hydrophobic. The exterior of the ring is hydrophobic. The resulting cations often form salts that resulting cations often form salts that are soluble in nonpolar solvents, and are soluble in nonpolar solvents, and for this reason crown ethers are useful for this reason crown ethers are useful in phase transfer catalysis.in phase transfer catalysis.

Crown Ethers:

Crown Ethers:Crown Ethers:- contain electron-rich atoms (O,S,N) contain electron-rich atoms (O,S,N)

crown aza-crown cyclen crown aza-crown cyclen

Crown Ethers:

Crown Ethers:Crown Ethers:BUT: no spectra, no possibilities for BUT: no spectra, no possibilities for

optical sensorsoptical sensorsSOLUTIONS:SOLUTIONS:- crown ether becomes part of a crown ether becomes part of a

chromophorechromophore- aza-crown ether linked to a aza-crown ether linked to a

chromophore through N-atomchromophore through N-atom

Crown Ethers:

- crown ether becomes part of a crown ether becomes part of a chromophore, butchromophore, but

reduced flexibility;reduced flexibility;reduced electron density at O-atomsreduced electron density at O-atoms

Crown Ethers:

- a distinct and specific interaction a distinct and specific interaction between the nitrogen(s) and cations between the nitrogen(s) and cations may improve the selectivity of may improve the selectivity of ionophores based on size-fit effect; ionophores based on size-fit effect;

- the ionophore nitrogen may be a part the ionophore nitrogen may be a part of the conjugated system improving the of the conjugated system improving the potential of the whole molecule to act potential of the whole molecule to act as a sensor; as a sensor;

- the nitrogen may facilitate the the nitrogen may facilitate the synthesizing of three-dimensional synthesizing of three-dimensional cavities, which improve the receptor cavities, which improve the receptor selectivity.selectivity.

Aza Crown Ethers:

UV-Vis spectroscopy:UV-Vis spectroscopy:- quantitativequantitative (spectral shift upon (spectral shift upon

complexation or/and change in the complexation or/and change in the quantum yield); quantum yield);

- qualitativequalitative (stoichiometry of the (stoichiometry of the complex complex in solutionin solution; binding constant, ; binding constant, which might be used as measure for which might be used as measure for sensitivity (one ion) and selectivity (set sensitivity (one ion) and selectivity (set of ions));of ions));

Ligand + Metal Salt Ligand + Metal Salt Complex Complex

Crown Ethers:

saltL

K

CC

C

.

Spectrophotometric titration:Spectrophotometric titration:- quantitativequantitative - qualitativequalitative

Ligand + Metal Salt Ligand + Metal Salt Complex Complex

Crown Ethers:

saltL

K

CC

C

.

Aza Crown Ethers:Aza Crown Ethers:direct part of direct part of

conjugated donor-conjugated donor-acceptor systemacceptor system

Crown Ethers:

210 310 410 510WAVELENGTH [nm]

0

10000

20000

30000

40000

MO

LA

RA

BS

OR

PT

IVIT

Y

Aza Crown Ethers:Aza Crown Ethers:linked to conjugated linked to conjugated

donor-acceptor donor-acceptor system via spacersystem via spacer

Crown Ethers:

300 400 500 600

/ nm

05,

000

10,0

0015

,000

20,0

00

7 1

Aza Crown Ethers: Aza Crown Ethers: non-conjugated donor-acceptor systemnon-conjugated donor-acceptor system

Crown Ethers:

Crown Ethers & UV-Vis Crown Ethers & UV-Vis spectroscopy: spectroscopy:

Relatively simple case for studyRelatively simple case for studyIF:IF:

- The binding constant is large enough;The binding constant is large enough;- The complex stoichiometry is simple;The complex stoichiometry is simple;- The process of complexation is simple The process of complexation is simple as a mechanism;as a mechanism;

- The binding site is linked to a donor-The binding site is linked to a donor-acceptor system and the complexation acceptor system and the complexation influence either donor or acceptor; influence either donor or acceptor;

Crown Ethers:

Beer-Lambert’s law: Beer-Lambert’s law:

Aggregation:

lcA .. Ax

4

3

2

2 3

A

A

A

C1 C C

Concentration

Ab

sorb

an

ce

C4

1A

Deviations:Deviations: in in the textbooks is the textbooks is

written – at written – at high high

concentrationsconcentrationsWRONG!WRONG!

Beer-Lambert’s law: Beer-Lambert’s law:

Aggregation:

..

..

constlc

lcA

path lengthpath lengthfrom 0.01 mm from 0.01 mm

to 100 mmto 100 mm

350 400 450 500 550 600

0

4000

8000

12000

16000

20000

350 400 450 500 550 600

0

4000

8000

12000

16000

20000

Aggregation of dyes:Aggregation of dyes:

- affecting their colouristic and spectral properties- affecting their colouristic and spectral properties- increases with an increase of dye concentration or - increases with an increase of dye concentration or

ionic strength; ionic strength; - decreases with temperature rising or organic - decreases with temperature rising or organic

solvents adding; solvents adding; - addition to the dye structure of ionic solulilizing - addition to the dye structure of ionic solulilizing

groups (as sulphonate group) decreases aggregation;groups (as sulphonate group) decreases aggregation;- inclusion of long alkyl chains increases aggregation - inclusion of long alkyl chains increases aggregation

because of higher hydrophobic interaction in solutionbecause of higher hydrophobic interaction in solution

Aggregation:

Exciton theory:Exciton theory:

spectral changes observed upon spectral changes observed upon aggregation are caused by aggregation are caused by

electronic interactions between the electronic interactions between the dye molecules in the aggregatedye molecules in the aggregate..

Simple Dimer Model:Simple Dimer Model:

Aggregation:

0 1 2 .

1

2 1 2 1 2.( . . )' '

1

2 1 2 1 2.( . . )' '

Exciton theory:Exciton theory:transition dipolstransition dipols

parallel (sandwich)parallel (sandwich)in-line (head-to-tail)in-line (head-to-tail)

Aggregation:

Exciton theory:Exciton theory:transition dipolstransition dipols

parallel (sandwich)parallel (sandwich)in-line (head-to-tail)in-line (head-to-tail)

Aggregation:

J-Aggregates:J-Aggregates:

Aggregation:

- red (bathochromic) shift in the absorption - red (bathochromic) shift in the absorption with increased intensity;with increased intensity;

- red shift in the emission;red shift in the emission;- aggregation caused by concentration, aggregation caused by concentration, solvent or salt addition; solvent or salt addition;

- typical example: cyanine dyes (non-planar typical example: cyanine dyes (non-planar structures) forming helix paternstructures) forming helix patern

H-Aggregates:H-Aggregates:

Aggregation:

- blue (hypsochromic) shift in the - blue (hypsochromic) shift in the absorption;absorption;

- weak or no emission;weak or no emission;- aggregation caused by concentration, aggregation caused by concentration, solvent or salt addition; solvent or salt addition;

- typical example: ionic planar dyes forming typical example: ionic planar dyes forming rods (rarely, mainly dimers)rods (rarely, mainly dimers)

350 400 450 500 550 600

0

4000

8000

12000

16000

20000

UV-Vis Spectroscopy and UV-Vis Spectroscopy and Dimerization:Dimerization:

Aggregation:

- determination of the - determination of the type of aggregate;type of aggregate;

- estimation of the estimation of the distance between distance between monomer molecules in monomer molecules in the dimer;the dimer;

- estimation of the angle estimation of the angle of transition dipols in of transition dipols in the dimerthe dimer

Structural Parameters of The Structural Parameters of The Dimers:Dimers:

Aggregation:

- require finding the - require finding the constant of constant of dimerization and the dimerization and the spectra of the spectra of the monomer and dimermonomer and dimer

2)( Mi

Di

D c

cK

iDi

Di

Mi

Mi lclcA ....*

2)( Mi

Di

D c

cK

iDi

Di

Mi

Mi lclcA ....*

Difficult cases for quantitative UV-Difficult cases for quantitative UV-Vis spectral analysis:Vis spectral analysis:

Chemometrics:

- complexation with low stability constant of the complexation with low stability constant of the complex, which does not allow to obtain complex, which does not allow to obtain experimentally the pure spectrum of the experimentally the pure spectrum of the complex with addition of metal salt;complex with addition of metal salt;

- dimerization with large dimeric constant, which dimerization with large dimeric constant, which does not allow to obtain experimentally the pure does not allow to obtain experimentally the pure monomer spectrum upon dilutionmonomer spectrum upon dilution

- dimerization with low dimeric constant, which dimerization with low dimeric constant, which does not allow to obtain the pure dimer does not allow to obtain the pure dimer spectrumspectrum

Soft & Hard Modeling:Soft & Hard Modeling:

Chemometrics:raw spectral data

set of spectra

concentrations ofthe components and individual spectra

model definition

Beer's law

mass balance

Beer's law

mass balance

assumptions assumptions

optimization

RESULTS: fundamental

process constants

optimization

RESULTS: components'

concentrations and individual spectra

fitting the model

fundamentalprocess constants

Variant I Variant II

non linearmodeling

non linearmodeling

comp

si

osskik clA

1, )(..)(

Soft Modeling (dimerization):Soft Modeling (dimerization):

strongly bound to the modelstrongly bound to the model

Chemometrics:

mp

AAAKc

KcA

S

p

i

m

j

Dj

Dj

Mj

Di

Diji

.

).(..4

1..812

1 1*

**,

22

2)( Mi

Di

D c

cK i

Di

Di

Mi

Mi lclcA ....*

Hard Modeling (complexation):Hard Modeling (complexation):

gives flexibility and might be used for gives flexibility and might be used for complicated equilibriacomplicated equilibria

Chemometrics:

NH

NH

NH

NH

O O

COOH COOH

NH

N NH

NH

O O

COOH COOH

Bilirubin (BR)

Biliverdin (BVD)

BR BVD

AuBR AuBVD

k1

1 2

UV-Vis spectroscopy is very suitable UV-Vis spectroscopy is very suitable for study of equilibria in solution, for study of equilibria in solution, but has some limitations in both but has some limitations in both

quantitative and qualitative quantitative and qualitative analysis.analysis.

Always use in combination with Always use in combination with other instrumental methods for other instrumental methods for

analysis. Do not forget theoretical analysis. Do not forget theoretical approaches.approaches.

Conclusions: