Date of Award
Master of Science
Theresa L Windus
Single-point energies resulting from the rotations of free -OH groups in the central residue of a cellulose Iα fragment consisting of nine cellotriose chains were obtained using restricted Hartree-Fock (RHF) with the 6-31G(d,p) basis set, density functional theory with the B3LYP functional using the 6-31G(d,p), and the fragment molecular orbital (FMO) method at the FMO2 method with second order perturbation theory (MP2) and the 6-31G(d) basis set. Potential energy curves calculated using these three methods are in excellent agreement with each other for the dihedral angles corresponding to energy maxima and minima. The calculated relative energies using the DFT/B3LYP and FMO2/MP2 levels of theory differ from each other by an average of 0.5 kcal/mol, 0.5 kcal/mol, and 1.1 kcal/mol when each of the -OH groups attached to the C2, C3, and C6 atoms, respectively, were rotated. The use of the pair interaction energy decomposition analysis (PIEDA) with the pair interaction energies from the dimer part of the FMO2 calculations also allowed the identification of the glucose residues most significantly involved in contributing to the rotational energy barriers. Intrachain and interchain interactions (those occurring between residues found in the same cellulose sheet) were seen to be stronger than intersheet interactions (occurring between residues found in different cellulose sheets) in contributing to the relative energy changes due to the rotations of free -OH groups in cellulose.
Restricted Hartree-Fock (RHF) and density functional theory (DFT) methods were used to determine the energies involved in the acid-catalyzed hydrolysis of cellobiose in the gas phase. A stepwise mechanism for the reaction was used to determine the different species involved. The initial step was protonation of a cellobiose molecule with a hydronium ion, which was followed by removal of a molecule of water to produce protonated cellobiose. Dissociation of the protonated cellobiose followed to produce a β-D-glucose molecule and a glucosyl cation. The cation in turn was hydrated to produce an α-D-glucose molecule. The energy change for the dissociation step was determined to be +36.8 kcal/mol using density functional theory with the B3LYP functional and 6-311+G(d,p) basis set. The calculated value is similar to those obtained from experimental data and from a recent solution phase Car-Parrinello molecular dynamics calculation.
John Ysrael Baluyut
Baluyut, John Ysrael, "Cellulose and cellobiose: adventures of a wandering organic chemist in theoretical chemistry" (2012). Graduate Theses and Dissertations. 12272.