Intermolecular vibrations in hydrophobic amino acid crystals: experiments and calculations.
Intermolecular vibrations of amino acid crystals occur in the THz, or far-infrared, region of the electromagnetic spectrum. We have measured the THz and Raman spectra of DL-leucine as well as two polymorphs of DL-valine, the spectroscopic properties of which have not previously been compared. Theoretical modeling of intermolecular vibrations in hydrophobic amino acids is challenging because the van der Waals interactions between molecules are not accounted for in standard density functional theory. Therefore, to calculate the vibrational modes, we used a recently developed approach that includes these nonlocal electron correlation forces. We discuss methods for comparing results from different theoretical models using metrics other than calculated vibrational frequency and intensity, and we also report a new approach enabling concise comparison of vibrational modes that involve complicated mixtures of inter- and intramolecular displacements.
Department of Chemistry, Yale University , P.O. Box 208107, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States.
Michael R C
MR
Williams
Daniel J
DJ
Aschaffenburg
Benjamin K
BK
Ofori-Okai
Charles A
CA
Schmuttenmaer
D003460:Crystallization; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007930:Leucine / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D055672:Static Electricity; D013237:Stereoisomerism; D014633:Valine / Q000737:chemistry*; D014732:Vibration
D007930:Leucine; D014633:Valine