Neural-network analysis of the vibrational spectra of N-acetyl L-alanyl N '-methyl amide conformational states - art. no. 021905

Density-functional theory (DFT) calculations utilizing the Becke 3LYP hybri d functional have been carried out for N-acetyl L-alanine N'-methylamide an d examined with respect to the effect of water on the structure, the vibrat ional frequencies, vibrational absorption (VA), vibrational circular dichro ism (VCD), Raman spectra, and Raman optical activity (ROA) intensities. The large changes due to hydration in the structures, and the relative stabili ty of the conformer, reflected in the VA, VCD, Raman spectra, and ROA spect ra observed experimentally, are reproduced by the DFT calculations. A neura l network has been constructed for reproducing the inverse scattering data (we infer the structural coordinates from spectroscopic data) that the DFT method could produce. The purpose of the network has also been to generate the large set of conformational states associated with each set of spectros copic data for a given conformer of the molecule by interpolation. Finally the neural network performances are used to monitor a sensitivity analysis of the importance of secondary structures and the influence of the solvent. The neural network is shown to be good in distinguishing the different con formers of the small alanine peptide, especially in the gas phase.