| Hydrogen bonding plays a critical role in a wide range of chemical and biological phenomena. Therefore the hydrogen bond complexes have received the more extensively theoretical study. The amino group is of great importance because it is the fundamental group combing peptides and proteins. Glycine is the simplest of the roughly 21 amino acids common in nature, which is usually chosen as model for studying biological systems exhibiting the amino acid type of bonding and DNA structures. In addition, due to its simplicity, formic acid is also chosen as model for studying biological systems exhibiting the organic acidic type of bonding. In this paper, we choose these two typical organic acids (formic acid and glycine) to theoretically investigate the hydrogen bond interaction of complexes between them and H2Ox molecules (H2O and H2O2) by using high-level ab initio and density functional theory. Some beneficial results have been obtained.The whole paper consists of six chapters. The first chapter can be divided into three parts. The first part briefly introduces the theoretical background and related contents of the hydrogen bond interaction. The second part narrates the development and research status of the vibrational spectrum theory resumptively. The third part expounds the primary work of this paper. The second chapter introduces the related calculating methods which are used in this paper. By comparing the methods, finally we thought that the DFT method is the best and we used it throughout the research. The third chapter introduces the harmonic oscillator model, normal mode vibration types and frequency characteristics of infrared spectra. In brief, the former three chapters are the basis and background of our studies, which offer us with useful and reliable quantum methods.On the basis of these theories, using density functional theory (DFT) and second-order Moller-Plesset Perturbation (MP2) method, the hydrogen bondingof the complexes formed between formic acid and water molecules (with up two water) has been completely investigated in the fourth part. Twelve reasonable geometries on the potential energy hypersurface of the formic acid and water system are calculated by the large basis sets 6-311++G(d,p) and 6-31 l++G(2d,2p) and the results agree with the experimental values. Of these twelve complexes, six are with one water molecule, and six are with two water molecules. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The infrared spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. Finally the solution phase studies are also carried out using the Onsager reaction field model in water solvent at B3LYP/6-311 ++G(d,p) level.In the fifth part, we investigate the hydrogen bonding of 1:1 complexes formed between glycine and water molecule. We employed the same method and calculated the equilibrium structures, total energies and vibrational frequencies of all the species. Four reasonable geometries on the potential energy hypersurface of glycine and water system are considered with the global minimum being a cyclic double-hydrogen bonded structure. At the same time, the optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported. Finally the solvent effects on the geometries of the glycine-water complexes have also been investigated using self-consistent reaction-field (SCRF) calculations at the B3LYP/6-311++G(d,p) level. The results indicate that the polarity of the solvent has played an important role on the structures and relative stabilities of different isomers.On the basis of the foresaid parts, it is concluded that B3LYP is superior to other methods of DFT because its results are the best agreement with the experimental values. Therefore, B3LYP is used to study the hydrogen bonding of 1:1 complexes formed between formamide and glycine molecule in the sixth... |
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