Theoretical Study On Thermodynamic Properties Of Ionic Crystals And MNR Chemical Shift Tensors Of Amino Acids In Crystal State

The present paper consists of two parts: the first part is concerned with calculation on thermodynamic properties of ionic crystals; the latter is about the calculation on I3C NMR chemical shifts of amino acid crystals. In the former part we first review the methods for determining thermodynamic properties of crystals including experimental methods and theoretical methods, and then describe some details of the calculations, including the method for transformation of the crystal coordinates into the desired Cartesian coordinates. For typical NaCl-type crystal systems, we introduced a modified version of Charge Field Perturbation Theory (CFP) and studied the thermodynamic properties of NaCl-type crystals with ab initio quantum mechanical calculations. We also carried out zero-point vibration and/or thermal corrections on Gibbs free energies of gaseous atoms and molecules. Based on the above-mentioned calculations, we further predict the changes of Gibbs free energy from gas-phase atoms to gaseous molecules and from gaseous atoms to the solid-phase molecules. In comparison with available experimental data, the calculated results reveal that the modified CFP method is appropriate for thermodynamic calculations of ionic crystals. In the second part, we first introduce the basic theory of NMR chemical shift and the problem appeared in the calculation on the I3C NMR chemical shift tensors of the carboxyl carbon in crystal amino acids. Then, by analyzing the possible interaction in crystal amino acids, we find out the factors which had been neglected in previous calculation梙ydrogen bonding effect and other short-distance interaction, and propose a supermolecule model to include this interaction. We analyzed the coordinates of nine crystal amino acids and based on this work and found the hydrogen bonds in the crystals. Then we focus our study on the "central molecules" to be calculated with the ab initio methods. In the calculations, the molecules which have hydrogen bonds with central molecules are included in a bigger system-supermolecule system, together with the central molecule. Based on the work above, we obtain nine supermolecules of amino acid in different sizes. At last, by using Hartree-Fock (HF) theory and density functional theory (DFT) using B3LYP functional, we have studied the i3C NMR chemical shift tensors of supermolecules and gaseous amino acids. By comparing the theoretical results between gas-phase calculation and supermolecule calculation, and comparing the Hartree-Fock and DFT results, we demonstrate that the effects of hydrogen bonding and electron correlation are important factors in theoretical calculation on the chemical shifts of amino acid crystals.