Molecular mechanics force fields from ab initio calculations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87595/2/224_1.pd

Optical nonlinearity and charge transfer analysis of 4-[(E)-2-(2,4,6-Trinitrophenyl) ethylidene] benzonitrile adsorbed on silver nanoparticles : Computational and experimental investigations

The search for a potential nonlinear optical (NLO) material has led to the investigation of an organic compound 4-[(E)-2-(2,4,6-Trinitrophenyl)ethylidene]benzonitrile (TEB), which has a possibility of enhancing the NLO properties by the charge transfer mechanism if metal atoms are adsorbed on it. The experimental characterization of TEB is done using Fourier Transform Infrared (FT-IR), Fr-Raman, Ultraviolet-visible (UV-Visible), Photoluminescence (PL), Thermogravimetric/Differential Thermal Analysis (TG/DTA) and Z-scan techniques. The third order NLO properties evaluated using Z-scan technique proves that the material can be used as a good optical limiter. TEB is attached with silver atoms and the theoretical studies including geometry optimization, NBO analysis and hyperpolarizability calculations are carried out. The TEB molecule with silver atoms adsorbed is found to have increased hyperpolarizability values. The charge transfer from the metal atom to the nitrile group of the molecule is evident from the Surface Enhanced Raman Scattering (SERS) spectra using the silver nanoparticles. (C) 2018 Elsevier Ltd. All rights reserved.Peer reviewe

Qualitative and quantitative approach towards the molecular understanding of structural, vibrational and optical features of urea ninhydrin monohydrate

In this study, single crystals of urea ninhydrin monohydrate (UNMH) have been grown by slow evaporation method. The grown crystals were characterized by FT-IR, FT-Raman and UV-Vis-NIR spectroscopies. The Kurtz and Perry powder method was employed to confirm the near-zero SHG efficiency of the as-grown centrosymmetric UNMH crystal. The third order nonlinearity of the crystal has been studied by the open aperture Z-scan method. The nonlinear absorption coefficient is calculated and the potentiality of UNMH in optical limiting applications is identified. The molecular geometry and the origin of optical non-linearity at the molecular level have been investigated by the density functional theory. The normal coordinate analysis was carried out to assign the molecular vibrational modes. Vibrational spectral studies confirms the presence of weak O-H ... O and moderate O-H ... O type hydrogen bonds in the molecule as well as O-H ... O, N-H ... O and blue-shifted C-H ... O type H-bonds in the crystal. The intramolecular charge transfer interactions and the electronic absorption mechanisms have been discussed. The static and the dynamic values of hyperpolarizabilities for UNMH were estimated theoretically by DFT methods. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Vibrational analysis of crystalline triglycine

We have refined vibrational force fields for polypeptides that permit excellent reproduction of the normal mode frequencies of such molecules. This is demonstrated in the present study, in which 80 IR and Raman bands of crystalline triglycine between 1800 and 200 cm-1 are reproduced with an average error of 6 cm-1. A deuterated sample is shown by normal mode analysis to have remained protonated at the C-terminal peptide group. Such results show that normal mode analysis can now provide a rigorous base for spectral studies of conformation in peptides and proteins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27648/1/0000029.pd