Computational Studies of Regularities in Bond Dissociation Enthalpies and Interactions of Acetylthiocholine with Solvent Molecules

Author

Wencui Zheng, Eastern Illinois University

Degree Name

Master of Science (MS)

Semester of Degree Completion

2001

Thesis Director

Carol A. Deakyne

Abstract

This thesis reports the results of two different research projects. One project is an evaluation of the feasibility of applying constant bond dissociation enthalpy ratios to neutral molecules for which one atom is from group 13 or group 17 and the other atom is from group 16. The other project attempts to validate the proposal that the aromatic residues lining the acetylcholinesterase (AChE) gorge will induce entry of acetylthiocholine (ATCh) into the gorge in a manner similar to that of the neural transmitter acetylcholine.

A total of thirty AB₂ and AB molecules have been examined, where A = B, Al, Ga, Cl, Br and B = O, S, Se. After obtaining the bond dissociation enthalpies of these molecules with the G2 and G2(MP2) methods, the ratios D⁰_m(AB₂)/2D⁰_m(AB) are computed. The results show that the most stable structure for all of the group 17 systems is bent, whereas that for the group 13 systems can be linear or bent. A constant value of 0.9 was obtained for the ratios of the bond dissociation enthalpies of the group 13 molecules, although not all of the molecules have the same point group. However, even though the group 17 molecules all have the same symmetry, the ratios for these molecules are separated into two groups (1.0 and 0.6). Good agreement between the G2 and G2(MP2) data and between the calculated and experimental data is observed.

Computational calculations have located four of the five distinct ATCh conformers. Two of them are stabilized by internal C-H···S hydrogen bonds. Three are stabilized by internal C-H···O hydrogen bonds. Each conformer forms a number of stable complexes with water or benzene. The results show that the binding energy of benzene to ATCh is identical to that of water to ATCh, which suggests that the aromatic residues that line the gorge may compete with the water outside the gorge to facilitate the entry of ATCh into the gorge, yet allow ATCh to transit to the acylation site. The essentially identical binding energies also suggest that the cation-π interaction between tryptophan and ATCh at the peripheral site of AChE should be as effective as that between tryptophan and ACh.

Recommended Citation

Zheng, Wencui, "Computational Studies of Regularities in Bond Dissociation Enthalpies and Interactions of Acetylthiocholine with Solvent Molecules" (2001). Masters Theses. 1544.
https://thekeep.eiu.edu/theses/1544