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?! There is not a good general definition for such a broad field. Jean-Marie Lehn (Nobel Prize 1987): “Chemistry of Molecular Assemblies and of the Intermolecular Bond.” “Chemistry Beyond Molecule”

Intermolecular Forces Hydrogen bonding (normally 2-5kcal/mol) van Der waals ( < 2 kcal/mol) Coulombic cation- P P-P: face to face, edge to face

Non-covalent interactions are weak ! Agnew. Chem. Int. Ed. 2001, 40, 2382-2426 Leonard J. Prins, David N. Reinhoudt, Peter Timmerman

In Vivo http://www.cstl.nist.gov www.ih.navy.mil/environm.htm DNA: cooperative bonding Self-assembly Enzyme: Selectivity, Self-assembly

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+

Chemical level Molecular assembly!? Human made DNA Host-Guest chemistry is an example of supramolecular chemistry. Selectivity!? Human made Enzyme

Is it hopeless for a chemist to try to design super-molecules? 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!

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[6]arene Calix[8]arene

Different views of calix[4]arene ~ 3-7 Å width

An example for anion receptor: A Host For Anions Urea derivative of calix[4]arene. Urea is a strong hydrogen bond donor Tetrahedron Letters 42 (2001) 1583-1586 V. Michlova, Ivan Stibor, Czech Republic

X= t-Bu n-PrI, Cs2CO3 HNO3 acetone, reflux rt SnCl2·2H2O 41% 80% n-PrI, Cs2CO3 acetone, reflux HNO3 CH2Cl2/CH3COOH rt X= t-Bu SnCl2·2H2O ethanol, reflux Ph-N=C=O CH2Cl2 rt 50% 98%

Complexation With NBu4X An Anionic Guest X= Cl, Br, I, H2PO4, Acetate, Benzoate Host Urea -NH- Hydrogen Host + Guest

NMR Titration d1 d2 H HG G + X X [H] d 1 + [HG]d2 [HG] Kf = dx = Fast enough H HG G + X X [H] d 1 + [HG]d2 [HG] Kf = dx = [H] + [HG] [H] [G]

Results Kf Formation constants from 1H NMR titration CHCl3 / CH3CN selectivity based on the size Cl- > Br- > I- One to one complexation Allosteric effect 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.

An Organomethalic Derivative of Calix[4] For Hosting Anions [{Ru(h6-p-cymene)}4(calix[4]arene-2H)]X6 X-ray crystal structure X= BF4-, CF3SO3-, PF6- J. Am. Chem. Soc.; 1997; 119(27); 6324-6335 J. L. Atwood, University of Missuri@ columbia

Iodide inclusion complex [NBu4]I / CH3NO2 Color change X= BF4- 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 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 Chemical shift (2 - 2.9 ppm) Concentration of Iodide 0 - 0.025 M For Host concentration of 0.00125M ~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) 201-205 Higashi, Fukuoka University, Japan Isao Ando, Fukuoka University, Japan

2+ 3+ [Ru(NH3)5(dampy)](PF6)3 [Ru(NH3)5(Pz)](PF6)2 [ (NH3)5 Ru (Pz) Ru(NH3)5](PF6)5

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) 1 : 1 complex Ru(III) 1 : 2 complex

18-C-6 18-C-6 18-C-6 Ru(II) - Ru(III) 1 : 3 complex

Elemental Analysis Experimental results for H, N, C, Ru elemental analysis is compared to calculated ones.

IR Spectroscopy After addition of crown ether: N-H stretching of ruthenium complex shifts 30-70 cm-1 to lower frequency. C-O-C stretching also observed at lower energy. 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

UV-Vis After addition of crown ether: Both complexes have charge transfer After addition of crown ether: Ru(II) complex shows a red shift ( lower energy) Ru(III) complex shows a blue shift (higher energy) Solvent = CH3CN

Ru(III): LMCT Ru(II): MLCT LUMO LUMO HOMO Metal Ligand HOMO Ligand Metal

Another application for UV Job plot Since the Maximum is at 0.5 mole fraction of the complex it shows the ratio of crown ether to complex is 1:1 for Ru(II) complex. DA . 100 Mole fraction of complex 0 - 1

Cyclic Voltammetry After addition of crown ether 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 20 I / m-A 0.0 0.2 0.3 E/volt Cyclic voltammogram for Ru(II) complex

After addition of 0.10M crown ether Ru(III) – Ru(II)

Another example : Artificial Enzyme for Cytochrome P-450 Cyclodextrin Manganese porphyrin attached to four b-cyclodextrins 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 Second-Sphere Coordination of Ferrioxamine B A siderophore Inorg. Chem.; 1995; 34(4); 928-932. A L. Crumbliss, Duke University

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 Supramolecular Chemistry, Jonathan W.Stead, Jerry L. Atwood, (2000) J. Wiley and Sons Leonard J. Prins, David N. Reinhoudt, Peter Timmerman; Agnew. Chem. Int. Ed. 2001 40 2382-2426 V. Michlova, I. Stibor; Tetrahedron Letters 42 (2001) 1583-1586 J. L. Atwood; J. Am. Chem. Soc. 1997, 119(27), 6324-6335 Higashi;Inorganica Chimica Acta 282 (1998) 247-251 6. Ando; Inorganica Chimica Acta 249 (1996) 201-205 7. R. Breslow; J. Am. Chem. Soc. 1996, 118, 6601-6605 8. R. Breslow; J. Am. Chem. Soc. 1997, 119, 4535-4536 9. 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