Title

Theoretical studies of structural and energetic properties of macromolecules and their intermolecular interactions

Date of Award

2001

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Jeffrey D. Evanseck, Committee Chair

Abstract

Modern computational tools and theories have been used to better understand supramolecular phenomena of aromatic molecules. The energetic and structural preference of a dehydroxylated calix[4]arene with and without alkali metal cations are presented for the first time using density functional theory to isolate the effects of the aromatic core and cation-pi interaction. The partial cone, flattened cone, chair and 1,3-alternate conformers have been identified as ground state structures in vacuum, with the partial cone and the 1,3-alternate as the lowest energy minima in the aromatic model. The C 4v cone conformation is found to be a transition structure separating flattened cone (C2v) conformers. Multiple weaker non-optimal cation-pi interactions contribute significantly to the overall binding strength. This theoretical analysis underscores the importance of neighboring aromatic faces and provides new insight into the significance of cation-pi binding, not only for calix[4]arenes, but for other supramolecular and biological systems.The advantages of multiple cation-pi interactions even at significant deviations from optimal cation-pi geometries prompted a detailed quantum mechanical study of the fundamental forces contributing to the cation-pi interaction. Natural Energy Decomposition Analysis was used to investigate the cation-pi interaction energy and its dependence on angle and distance. The energetic contributions of electrostatics, polarization, charge transfer, exchange and deformation to the total interaction energy are reported for benzene complexed with alkali metal cations, Li+, Na +, and K+. Although polarization energy is larger than electrostatics, the present study confirms that the electrostatics is the differential factor determining the strength of the optimal interaction energy. As the angle between the cation and the benzene C6 normal axis increases, the polarizability contribution to the binding energy increases significantly, responding to the molecular polarizability of benzene, but the overall binding energy decreases.Structural, conformational, and binding studies of a cyclophane derivative were performed with the PM3 semi-empirical method in order to gain a further understanding on macromolecular complexation. Osawa's conformational analysis produced eight distinct conformers and identified the two major structural changes. Binding studies revealed that this cyclophane derivative retained a preference for nitrogen containing disubstituted biphenyls over those containing oxygen substituents.

Keywords

Chemistry, Biochemistry; Chemistry, Physical

Link to Full Text

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