Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 5(4), 89-91, April (2015) Res. J. Chem. Sci. International Science Congress Association 89 Short Communication Quantum-chemical Modeling of the Cyclic-Pentameric Mechanism for the 1H-3H Proton Transfer in Imidazole Derivatives Kereselidze J1* Kvaraia M and Mikuchadze G1*Department of Chemistry, Ivane Javachishvili Tbilisi State University, 0179, GEORGIA Department of Chemistry, Sukhumi State University, 0186, GEORGIAAvailable online at: www.isca.in, www.isca.me Received 3rd March 2015, revised 9th April 2015, accepted 17th April 2015 AbstractAbout of the cyclic-pentameric model for the 1H-3H proton transfer in the imidazole derivatives is reported. The activation energy () and reaction energy (E) of the proton transfer as well as the bond orders (PNH) and (PN…H) by means of Density Function Theory (DFT) are calculated. It is shown that proton transfer is energetically more advantageous in nitroimidazole. The values , and E from the point of view of chemical transformations vary in rather reasonable limits, what indicates on the competence of the proposed cyclic - pentameric model. It is the new nonionic and oligomeric cyclic model, where 1H-3H proton transfer with one stage occurs. Keywords: Proton transfer, cyclic-pentameric mechanism, imidazole, DFT calculations. Introduction -3 proton transfer in imidazole is one of the basic stages of chemical and biochemical reactions. Collective mechanisms of this process that contain imidazole trimers were proposed in the Zimmerman’s work. However, the existence of the linear oligomeric structure of imidazole seems to be unlikely because the IR spectra have no absorption bands of the NH group, which must be present in this structure. In works Ten G. et. al2,3, intra- and intermolecular mechanisms of 1-3 proton transfer in imidazole are discussed. With using of the quantum-chemical and spectrometric methods, it was demonstrated that the intramolecular 1H-3H proton transfer is energetically less advantageous4,5. A two-dimensional nitrogen-15 exchange NMR study of 15N-labeled imidazole demonstrates that the conduction mechanism does not involve the reorientation of the imidazole ring invoked in current models. Self-association in imidazole and methylimidazole was also studied by the scpectrometric method and dimerization and polymerization tendencies were noted. The intramolecular one-stage 1-3 proton transfer is structurally complicated and therefore a cyclic-trimer model for 4-fluorine-imidazole was built. The opinion about existence of a cyclic-dimer mechanism was also expressed in our work. Mangiatordi et al.10 the 1H-3H proton transfer in protonated imidazole using the quantum-chemical method studied, however, this proposed modeling cannot lead to a stable structure of 3H-imidazole. Iannuzzi and Parrinelo [11] studied proton transfer in crystalline polymer chains of imidazole and notes the ionic nature of this process. Kurzepa et al.12 studied energy characteristics of tautomeric forms of 5-substituted imidazole by spectrometric and quantum-chemical methods. It was shown that COOH and BH groups stabilize the NH tautomer, whereas stabilization of the NH tautomer by F and O groups is not so intensive. This latter conclusion is not consistent with the notion that NH and NO are strong electron donors and electron acceptors, respectively. Quantum-chemical (DFT) calculations were made for different imidazole tautomers and was pointed out that 1H-imidazole is more stable than non-aromatic tautomer13. However, this stability changes completely when hydrogen atom is substituted by O or F groups, for example, the stability of 1-F-1H-imidazole 2-F-2H imidazole. Results and Discussion The purpose of the proposed research is to build a nonionic oligomerous model of imidazole where 1H-3H proton transfer can occur without substantial energy losses. In our opinion this model represents the cycle of five molecules imidazole, along which 1-3 proton transfer may be realized (figure-1). The activation energy () and reaction energy (E) of the proton transfer in the cyclic-pentamer model of the five imidazole derivatives as well as the bond orders (PNH) and (P...) by means of modern quantum-chemical method-Density Function Theory (DFT)14 are calculated. The calculations are executed using the software “Nature” in the reaction coordinate regime15 using the PBE approximation and its modification mPBE16,17. In addition, for comparison the functional BLYP and local density approximations were used18-20. The results of calculation are given in table-1. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(4), 89-91, April (2015) Res. J. Chem. Sci. International Science Congress Association 90 NN H H H NN H H H NN H H H NN H H H NN H H H N H H N HN N H H H NN H H H NN H H H NN H H H 1 3 R R R R R R R R R 3 R R = H, NH, NOFigure-2 Cyclic-pentameric model of the 1H-3H proton transfer in imidazoleThe activation energy () and reaction energy (E) of the proton transfer in the cyclic-pentamer model of the five imidazole derivatives as well as the bond orders (PNH) and (P...) by means of modern quantum-chemical method - Density Function Theory (DFT)14 are calculated. The calculations are executed using the software “Nature” in the reaction coordinate regime15 using the PBE approximation and its modification mPBE16,17. In addition, for comparison the functional BLYP and local density approximations were used18-20. The results of calculation are given in table-1. Table - 1 Energy of activation (DD), energy of reaction (DDE) and bond orders (PN – H , P...R DD # , kJ/mol DDE, kJ/mol N – H P N ... H NH 2 26.2 -8.60 0.96 0.30 H 30.1 0.05 0.67 0.33 NO 2 10.1 -36.70 0.64 0.31 Amino- and nitro-groups were chosen as donor and acceptor of electrons of substitutes that have influence on the bond orders (PNH) and (P...). The analysis of the table shows that 1-3proton transfer in the amino- and nitro-derivatives is an exotermical process and is energetically more advantageous for the nitro-derivatives. Besides, the the nitro-group causes a relaxation the N-H bond and hence promotes a proton transfer over cycle. For the amino-group the opposite effect is observed, as it the electronodonore group increases the NH bond order. On Figure1, a diagram of the 1H-3H proton transfer energy in unsubstituted imedazole is given as an example. Figure-3 Dependency of energy of the 1H-3H proton transfer on the reaction coordinate for unsubstituted imedazoleConclusion As a result of calculations it can be concluded that the activation energy () and reaction energy (E), for the proton transfer in the cyclic-pentamer model of imidazol derivatives as well as bond orders (PNH) vary in rather reasonable limits for chemical processes, which indicates favour of the proposed cyclic- Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(4), 89-91, April (2015) Res. J. Chem. Sci. International Science Congress Association 91 pentamer mechanism. This is a non-ionic oligomeric cycle of five molecules imidazole in which 1H-3H proton transfer is carried out in one step. Acknowledgment The project has been supported by European Commission FP7 Project High-Perfomance Computing Infrastructure for Sout East Europe’s Research Communities”, Grant No: 261 499. References 1.Zimmermann H., Proton Transfer, Acid-Base Catalysis, Z. Electrochim.,65, 821-840 (1961) 2.Ten G., Burova T. and Baranov V., On the Mechanism of proton Transfer in Imidazole, J. Struct. Chem.,48, 623-633 (2007) 3.Nesmeyanov A, Zavelovich E, Babin V., Kochetkova S. and Fedin E, H and 13C NMR Study of tautomerism in azoles, Tetrahedron,31, 1461-1464 (1975)4.Borisov Yu., Vorob’eva N., Abronin I. and Kolomiets A, On the mechanism of proton transfer imidazole, Izv. Akad. Nauk, Ser. Chim.,2779-2783 (1988) 5.Fedorov L., Saverino A., Viskardi G., Rebrov A. andBarni E., 13C NMR Spectroscopy of Tautomeric Conversions in Imidazole Compounds, Izv. Akad. Nauk, Ser. Khim., 2, 299-308 (1992) 6.Hickman B., Mascal M., Titman J. and Wood I., Protonic Conduction in Imidazole: A Solid - State 15 N NMR Study, J. Am. Chem. Soc.,121, 11486-11490 (1999) 7.Peral F. and Gallego E., Self-association of imidazole and its methyl derivatives in aqueous solution A study by ultraviolet spectroscopy, J. Mol. Struct.,415, 187-196 1997) 8.Kikalishvili T. and Kereselidze J., Trimeric Mechanism of propton transfer in Imidazole, Chem. Heter. Comp.,38, 1069-1071 (2002)9.Alkorta I., Goya P., Elguero J. and Singh Sh.A, Simple Approach to the Tautomerism of Aromatic Heterocycles, Proceed. Natl. Acad. Sci. Lett.,30, 139-159 (2007) 10.Iannuzzi M. and Parrinelo M., Proton Transfer in Heterocycle Cristals, Phys. Rev. Lett.,93, 025901-025904 (2004) 11.Iannuzzi M., Proton Transfer inimidazole-based molecular Cristals, J. Chem. Phys.,124, 204710-204717 2006) 12.Nagata N., Kugimiya Sh. and Kobuke Y., Antenna functions of 5.15-bis (imidazol-4-yl)-10.20-bis (4-dodecyloxyphenyl)-porphyrin supramolecular assembly through imidazole-imidazole hydrogen bonding, Chem. Commun., 15, 1389-1390 (2000) 13.Zundel G. and Muehlinghaus J, Simmetry of hydrogen Bonds, Infrared Continuous Absorbtion and proton transfer, Z. Naturforsch.Chem. Sc., 26b, 546 (1971) 14.Kohn W., Becke A. and Parr R., Density Functional Theory of Electronic structure, J. Phys. Chem.,100, 12974 – 12980 (1996) 15.Laikov D., Ustynyuk Yu. and Priroda 04, A quantumchemical program suite, New possibilities in the study of molecular systems with the application of parallel computing, Russ. Chem. Bull., Int. Edn.,54, 820–826 (2005) 16.Perdew J., Burke K. and Ernzerhof M., Generalized Gradient Approximation Made simple, Phys. Rev. Lett., 77, 3865-3868 (1996) 17.Adamo C. and Barone V., Physicaly motivated density functional with improved performances, J. Chem. Phys, 116, 5933-5940 (2002) 18.Becke A, Density functional exchange: Energy approximation with correct asymptotic behavior, Phys. Rev. A, 38, 3098-3100 (1988) 19.Lee C., Yang W. and Parr R., Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density, Phys. Rev. B,37, 785-789 (1988) 20.Perdew J. and Wang Y., Accurate and simple analytic representation of the electron-gas correlation energy, Phys. Rev. B,45, 13244-13249 (1992)