Theoretical Study Of Amino Acids: Conformers And Ionization Energies

Amino acids are basic units of protein and componments reqquried for human nutritionptotein. The researches about amino acid monomers are significative to the cognition ofComplex biological system.In this article, we scan the potential energy surface of phenylalanine and γ-Aminobutyricacid to locate all the feasible stable conformers. All the calculations are subject to Gaussian03program package and the main methods we use in this paper are Density function theory(DFT) and M062X. Amino acid molecules have many rotational degree of freedom and manystable conformers in gas phase and the sablity of those conformers are closely related to theintramolecular hydrogen bond and intra-molecular hyperconjugation. Using Atoms InMolecules (AIM) as well as natural bonding orbital analysis theory (NBO), we study theintramolecular interaction of the stable conformers and give quantitative and qualitativedescriptions. Furthermore, we also analyze the influence of hyperconjugation interaction onthe stable order. The photoelectron spectroscopy can provide direct measurement of molecularorbit and the electronic structure of molecule. It can help us to realize the property ofmolecule. In this paper, we use partial third-order quasipartical approximation to calculate thevertical detachment energies of the two amino acids and simulate the photoelectronspectroscopy. The results indicate that both of them are match experimental data very well.In this paper, Chapter1describes the investigation background, methods and contents;the basic theories of the quantum chemistry including electronic related, density functionaltheory and partial third-order quasipartical approximation are given in Chapter2. In chapter3and chapter4, we study the conformers and intramolecular interaction of phenylalanine andγ-Aminobutyric acid respectively.