the supramolecular chemistry chemistry of non-covalent interactions: host-guest complexes farzad...
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The Supramolecular Chemistry
Chemistry of Non-covalent Interactions:
Host-guest Complexes
Farzad Fani-Pakdel
Outline
• Definition and keywords
• Comparing chemical and biological systems
• Three host-guest chemistry systems will be fully described
• Applications
• Conclusion
Supramolecular Chemistry?!
Jean-Marie Lehn (Nobel Prize 1987):
“Chemistry of Molecular Assemblies and of the Intermolecular Bond.”
“Chemistry Beyond Molecule”
There is not a good general definition for such a broad field.
Intermolecular Forces
: face to face, edge to face cation-
Hydrogen bonding (normally 2-5kcal/mol)
van Der waals ( < 2 kcal/mol)
Coulombic
Agnew. Chem. Int. Ed. 2001, 40, 2382-2426Leonard J. Prins, David N. Reinhoudt, Peter Timmerman
Non-covalent interactions are weak !
DNA:cooperative bondingSelf-assembly
http://www.cstl.nist.gov
In Vivo
Enzyme:Selectivity, Self-assembly
www.ih.navy.mil/environm.htm
Chemists Interested In Such systems
Early 1970 molecular recognition in biological systems attracted synthetic chemists.
1967 discovery of crown ethers.
(Charles Pederson).
As 0.4% impurity !
[18] crown-6 a host for K+
Host-Guest chemistry is an example of supramolecular chemistry.
Molecular assembly!? Human made DNA
Chemical level
Selectivity!? Human made Enzyme
It will be many years before our understanding of molecular structure becomes great enough to encompass in detail such substances as the proteins, but the attack on these substances by the methods of modern structural chemistry can be begun now, and it is my belief that this attack will ultimately be successful.
Linus Pauling, 1939
No more jobs for Biochemists!
Is it hopeless for a chemist to try to design super-molecules?
Host-Guest Chemistry
Host-Guest chemistry is an example of supramolecular chemistry.
Calixarenes:
macrocycles that are made from phenol or P-tert-butylphenol.
Calix[4]arene Calix[8]areneCalix[6]arene
Different views of calix[4]arene
~ 3-7 Å width
An example for anion receptor:
Urea derivative of calix[4]arene.
Urea is a strong hydrogen bond donor
Tetrahedron Letters 42 (2001) 1583-1586V. Michlova, Ivan Stibor, Czech Republic
A Host For Anions
X= t-Bu
41%
n-PrI, Cs2CO3
acetone, reflux
HNO3
CH2Cl2/CH3COOH
rt
80%
SnCl2·2H2O
ethanol, reflux
98%
Ph-N=C=O
CH2Cl2
rt
50%
Complexation With NBu4X An Anionic Guest
X= Cl, Br, I, H2PO4, Acetate, Benzoate
Host
Host + Guest
Urea -NH- Hydrogen
NMR Titration
G
X X
+
Fast enough
x [H] [HG]
[H] [HG]
f [H] [G]
[HG]
H HG
Kf
Formation constants from 1H NMR
titration CHCl3 / CH3CN
selectivity based on the size
Cl- > Br- > I-
One to one complexation
Allosteric effect
Results
11 Å
Confirming Results With a Model Compound
R= -NH-Ph
Association constants with anions are almost the same for this model as well as the original host.
In the case of Benzoate there is a large change from 1800 to 161000!
If R= Ph ( i.e. amide instead of urea the Kf drops significantly.
model
J. Am. Chem. Soc.; 1997; 119(27); 6324-6335J. L. Atwood, University of Missuri@ columbia
[{Ru(6-p-cymene)}4(calix[4]arene-2H)]X6
An Organomethalic Derivative of Calix[4] For Hosting Anions
X= BF4-, CF3SO3
-, PF6-
X-ray crystal structure
X= BF4-
[NBu4]I / CH3NO2
Color change
Iodide inclusion complex
NMR Titration
NaI in water was added to the host (X= CF3SO3-)
Anion to host ratio of 20:1 The chemical shift related to methylene of the calix shifts down field (higher ppm) EQNMR software was used to find and model association constant. K1 = 51 M-1 for Iodide
The same experiment was done for Chloride, Bromide, Nitrate, Acetate, Hydrogen phosphate and sulfate
Results
Concentration of Iodide 0 - 0.025 M
For Host concentration of 0.00125M
Ch
emi c
al s
hi f
t ( 2
- 2
.9 p
pm
)
Binding Constants in water
anion K1 K2 K3
Cl- 551 8.1 0.05
Br- 133 13.6 0.35
I- 51
NO3 - 49 109 0.06
CH3CO2- 0
H2PO4- 0
SO42- 0
~10% error
18-crown-6 ether as a host for Ruthenium-amine Complexes
Second Sphere Coordination
Inorganica Chimica Acta 282 (1998) 247-251 Inorganica Chimica Acta 249 (1996) 201-205Higashi, Fukuoka University, Japan Isao Ando, Fukuoka University, Japan
[Ru(NH3)5(Pz)](PF6)2
[Ru(NH3)5(dampy)](PF6)3
[ (NH3)5 Ru (Pz) Ru(NH3)5](PF6)5
2+ 3+
Ru(II)1 : 1 complex
Ru(III)1 : 2 complex
Cartoon Scheme of the Adducts
The Crown ether was dissolved in 1,2-dichloroethane and stirred with the metal complex after filtration, Ether was added to precipitate the product.
Hydrogen Bonding between first and second Sphere Coordination
18-C
-6
18-C-6
18-C-6
Ru(II) - Ru(III)1 : 3 complex
18-C
-6
18-C-6
18-C-6
Elemental Analysis
Experimental results for H, N, C, Ru elemental analysis is compared to calculated ones.
IR Spectroscopy
N-H stretching of ruthenium complex shifts 30-70 cm-1 to lower frequency.
C-O-C stretching also observed at lower energy.
After addition of crown ether:
Data confirms hydrogen bonding between H of Ru-NH3 and O of crown ether
400-2500 cm -1 KBr disk, 2500-4000 cm -1 in Nujol
After addition of crown ether:
Ru(II) complex shows a red shift ( lower energy)
Ru(III) complex shows a blue shift (higher energy)
UV-Vis
Solvent = CH3CN
Both complexes have charge transfer
LUMO
HOMO
LUMO
HOMO
Ru(II): MLCT Ru(III): LMCT
Ligand
LigandMetal
Metal
Another application for UV Job plot
Since the Maximum is at 0.5 molefraction of the complex it shows the ratio of crown ether to complex is 1:1 for Ru(II) complex.
Mole fraction of complex 0 - 1
.
10 0
Cyclic Voltammetry
After addition of crown ether
0.0 0.2 0.3
Cyclic voltammogram for Ru(II) complex
E/volt
I /
A
20
Change in diagram after addition of crown ether is an evidence for binding.
reversibe
negative shift of E 1/2 shows that Ru(III) makes a more stable adduct with the crown ether
Ru(III) – Ru(II)
After addition of 0.10M crown ether
Another example :
Artificial Enzyme for Cytochrome P-450
Manganese porphyrin attached to four -cyclodextrins
Cyclodextrin
J. Am. Chem. Soc. 1996, 118, 6601-6605
J. Am. Chem. Soc. 1997, 119, 4535-4536 R. Breslow, Columbia University
selective, turnover number 4
Last one:Iron Transfer
Inorg. Chem.; 1995; 34(4); 928-932.A L. Crumbliss, Duke University
Second-Sphere Coordination of Ferrioxamine B
A siderophore
Application in Chemistry
Detection of environmental contaminations such as nitrates, phosphates, chromate, uranyl and heavy metals.
Catalysis
Separations
Application in Biology
Understanding biochemical systems
electron transfer, ion transfer, enzymes
Design: Artificial enzymes, medicinal applications
Conclusion
• Host-guest chemistry is not limited to some special molecules or hosts. We can have Cations, neutral species, anions and even metal complexes as both host and guest.
• All sort of intermolecular interactions are important.• Host-guest interactions influences the chemical and spectroscopic
properties of both host and the guest.• We can use different analytical methods in order to measure or
estimate the strength of such interactions. Association constant is an important factor in this case.
• Selectivity based on intermolecular forces and geometrical effects was observed.
• Solvent has an important role in these interactions.• Reversibility.
References
1. Supramolecular Chemistry, Jonathan W.Stead, Jerry L. Atwood, (2000) J. Wiley and Sons
2. Leonard J. Prins, David N. Reinhoudt, Peter Timmerman; Agnew. Chem. Int. Ed. 2001 40 2382-2426
3. V. Michlova, I. Stibor; Tetrahedron Letters 42 (2001) 1583-15864. J. L. Atwood; J. Am. Chem. Soc. 1997, 119(27), 6324-63355. Higashi;Inorganica Chimica Acta 282 (1998) 247-251 6. Ando; Inorganica Chimica Acta 249 (1996) 201-2057. R. Breslow; J. Am. Chem. Soc. 1996, 118, 6601-66058. R. Breslow; J. Am. Chem. Soc. 1997, 119, 4535-45369. A L. Crumbliss; J. Am. Chem. Soc. 1997, 119, 4535-4536
Acknowledgements
Jason R. Telford Telford’s research group Joe Malandra Department of chemistry, university of Iowa