Spectroscopically-tested, improved, semi-empirical potentials for biological molecules: Calculations for glycine, alanine and prolineElectronic supplementary information (ESI) available: Geometries (MP2 and PM3) of alanine, glycine and proline conformers I and II. See http://www.rsc.org/suppdata/cp/b3/b315326f/

XRD, thermal, FTIR and SEM studies on gel grown γ‐glycine crystals

“…Characteristic bands with strong intensities for the zwitterionic nature of amino acids occurred at 1595 cm -1 (COO -asymmetric stretching), 1404 cm -1 (COO -symmetric stretching) and 1500 cm -1 (NH 3 + symmetric bending). C-C stretching vibrations (1331, 924 & 897 cm ) were also observed [21]. Intense absorption peak, due to the torsional oscillation of NH 3 + occurred at 507 cm -1 .…”

First-principles anharmonic quantum calculations for peptide spectroscopy: VSCF calculations and comparison with experiments

“…It was applied successfully for several small systems. 26,36 The upgraded potentials constructed here are calculated from the much faster HF method while the harmonic potentials at this level are upgraded by much more accurate MP2 method. We used double-zeta Dunning type cc-pVDZ basis and 8 grid points per normal modes throughout this study and calculated the fundamental bands for all the vibrational modes.…”

“…In the present study, we used quantum chemical full pair-wise coupling potentials considering all the vibrational modes of the three dipeptides. Until now, VSCF-PT2 calculations using quantum chemical potentials of suitable accuracy were carried out for amino acids, 22,36 their complexes with water molecules 37 and other biomolecules 38 of similar sizes. The present paper extends the state-of-the-art quantum VSCF-PT2 calculations to dipeptides.…”

Reducing the vibrational coupling network in N-methylacetamide as a model for ab initio infrared spectra computations of peptides

“…General features of the vibrational spectrum of NMA are discussed in Section 3.1, and some of the problems encountered within the standard VSCF approach are indicated. Dual-level computations which reduce the computational cost of calculating coupling potentials are presented in Section 3.2 and compared to a recently suggested method which is based on scaled semi-empirical potentials [36]. Finally, Sections 3.3 and 3.4 treat the problem of partially decoupling the NMA modes while, at the same time, retaining the spectroscopically relevant coupling terms.…”