Correlation of structure and vibrational spectra of the zwitterion l-alanine in the presence of water: an experimental and density functional analysis

The low-frequency (terahertz) dynamics of condensed phase materials provide valuable insight into numerous bulk phenomena. However, the assignment and interpretation of experimental results requires computational methods due to the complex mode-types that depend on weak intermolecular forces. Solid-state density functional theory has been used in this regard with great success, yet the selection of specific computational parameters, namely the chosen basis set and density functional, has a profound influence on the accuracy of predicted spectra. In this work, the role of these two parameters is investigated in a series of organic molecular crystals, in order to assess the ability of various methods to reproduce intermolecular forces, and subsequently experimental terahertz spectra. Specifically, naphthalene, oxalic acid, and thymine were chosen based on the varied intermolecular interactions present in each material. The results highlight that unconstrained geometry optimizations can be used as an initial proxy for the accuracy of interatomic forces, with errors in the calculated geometries indicative of subsequent errors in the calculated low-frequency vibrational spectra, providing a powerful metric for the validation of theoretical results. Finally, the origins of the observed shortcomings are analyzed, providing a basic framework for further studies on related materials.

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A DFT Analysis of the Molecular Structures and Vibrational Spectra of Diphenylsulfone and 4,4'-Sulfonyldianiline (Dapsone)

Zeitschrift für Naturforschung B ◽

10.1515/znb-2011-0112 ◽

2011 ◽

Vol 66 (1) ◽

pp. 69-76 ◽

Cited By ~ 3

Author(s):

Wolfgang Förner ◽

Hassan M. Badawi

Keyword(s):

Vibrational Spectra ◽

Density Functional ◽

Parent Compound ◽

Harmonic Approximation ◽

Molecular Structures ◽

Spectral Lines ◽

Basis Set ◽

Minor Role ◽

Parent Molecule ◽

Chemical Difference

We have performed density functional calculations with the B3LYP functional and a 6-311G** basis set to obtain the vibrational spectra in harmonic approximation of the anti-leprosy drug Dapsone and the parent compound diphenylsulfone. Although the chemical difference between the two molecules is not that pronounced (Dapsone has amino groups in the para positions in the phenyl rings), Dapsone is an active drug, while to our knowledge diphenylsulfone shows no medical activity. We compared the theoretical results to experimental vibrational spectra found in the literature. With the help of the program GAUSSVIEW we were able to assign the experimentally found spectral lines to specific atomic motions. The remarkable difference between the two molecules, regarding their structural behavior, is that the drug Dapsone has a more flexible structure of the phenyl ring than the parent molecule has. This might contribute to a greater ability of the drug to fit into receptor sites in a cell membrane although one has to be well aware that this plays most propably only a minor role in the drug activity of Dapsone

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