Theoretical Study Of The Amino Acid, Dipeptide Crystal Structure And Vibrational Spectra

Amino acid is the basic unit of protein in human body. The study of the structures and characters of amino acids has important theoretical and practical significance in further studying the structures and characters of proteins, and the biological processes. The short peptides are a kind of very important small biological molecules. To grasp the low-energy conformation stability of short peptides will be of benefit to people to correctly know the reciprocity between the short peptide molecules and the acceptors, and can provide rational way to design medicines. At present, people get the data about short peptide from NMR and a few other experimental methods aided with theoretical simulation. What is used to study the molecule conformation of short peptides is of two kinds. One is ab initio Hartree-Fock(HF) method and the other is molecular quantum chemistry method. The accuracy of ab initio Hartree-Fock(HF) method is higher and its reliability is better than the other. Therefore, the former may be preferably applied to study short peptide molecule systems.Quantum chemistry is becoming increasingly important within the field of chemistry. Its steady growth, application and influence are proved by modern chemical attitudes and approaches as well as the continuous increase in the sophistication of computational techniques, In present study, we began with experiments to prepare amino acid crystals and measure their the crystal data, and then made use of theoretical method to research the molecular structures and vibration frequencies and their corresponding vibration patterns.The whole paper consists of four chapters. The first chapter briefly introduces the present situation about the research on amino acids and peptides, and introduces the related calculation methods and infrared spectra which are used in this paper. The last part of this chapter introduces the main work and practical meanings of this paper.In Chapter Two and Chapter Three, the single crystals of glycin and alanine were prepared and their structures were measured by x-ray single crystal diffraction. The configuration and vibration frequency of glycin and alanine were optimized employing density functional theory (B3LYP) with 6-311++G** and 6-311G** basis sets, respectively. Their infrared intensities corresponding to various frequencies of their most stable conformations were obtained, and their infrared spectra were analyzed. In Chapter Four, glycylglycine was synthesized by a simple and convenient method, and its single crystal was obtained, and then its structure was measured by x-ray single crystal diffraction. On the basis of the previous work, we studied the structure and infrared spectra, and achieved the anticipative purpose.In conclusion, the study began with experiments and got the first-hand information by cultivating crystal and detecting the data of crystal and infrared spectra. And then, the study adopted quantum chemistry calculation method to study the structures and infrared spectra of amino ands and short peptide, and analyzed and compared the data obtained from calculation with the experimental data. In the work we can find out the effective theoretical method to study the structure and infrared spectra of amino acids and short peptides.