H-Bond Network in Amino Acid Cocrystals with H sub(2)O or H sub(2)O sub(2). The DFT Study of Serine-H sub(2)O and Serine-H sub(2)O sub(2)

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 115; no. 46; pp. 13657 - 13663-13657-13663
• Main Authors: Vener, Mikhail V, Medvedev, Alexander G, Churakov, Andrei V, Prikhodchenko, Petr V, Tripol'skaya, Tatiana A, Lev, Ovadia
• Format: Journal Article
• Language: English
• Published: 04-01-2011
• Subjects: Bands; Computation; Crystal structure; Crystals; Networks; Orbitals; Plane waves; Vibration
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp207899z

The structure, IR spectrum, and H-bond network in the serine-H sub(2)O and serine-H sub(2)O sub(2) crystals were studied using DFT computations with periodic boundary conditions. Two different basis sets were used: the all-electron Gaussian-type orbital basis set and the plane wave basis set. Computed frequencies of the IR-active vibrations of the titled crystals are quite different in the range of 10-100 cm super(-1). Harmonic approximation fails to reproduce IR active bands in the 2500-2800 frequency region of serine-H sub(2)O and serine-H sub(2)O sub(2). The bands around 2500 and 2700 cm super(-1) do exist in the anharmonic IR spectra and are caused by the first overtone of the OH bending vibrations of H sub(2)O and a combination vibration of the symmetric and asymmetric bendings of H sub(2)O sub(2). The quantum-topological analysis of the crystalline electron density enables us to describe quantitatively the H-bond network. It is much more complex in the title crystals than in a serine crystal. Appearance of water leads to an increase of the energy of the amino acid-amino acid interactions, up to 50 kJ/mol. The energy of the amino acid-water H-bonds is 30 kJ/mol. The H sub(2)O/H sub(2)O sub(2) substitution does not change the H-bond network; however, the energy of the amino acid-H sub(2)O sub(2) contacts increases up to 60 kJ/mol. This is caused by the fact that H sub(2)O sub(2) is a much better proton donor than H sub(2)O in the title crystals.