Computer simulation of the infrared spectra of synthetic melanoidin monomers using hyperchem software

Date

10-1999

Degree

Bachelor of Science in Chemistry

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Ernesto J Del Rosario

Abstract

SILVANIA DESQUITADO RODULFO. University of the Philippines Los Banos. October 1999. Computer Simulation of the Infrared Spectra of Synthetic Melanoidin Monomers Using Hyperchem Software

Adviser: Dr. Ernesto J. del Rosario.

Members: Dr. Cleofe A Calanasan, Dr. Jose H. Santos.

The infrared (IR) spectra of synthetic melanoidins were simulated using Hyperchem sofware in order to elucidate the molecular structures of these dark-colored polymeric compounds which are obtained from the Maillard reaction of carbohydrates and amines followed by Amadori rearrangement. Eleven probable structures of melanoidin were evaluated computationally based on their elemental composition, which agreed with the experimental values, starting with the structure suggested by Kato and Tsuchida (1981). The geometry of each probable molecular structure of melanoidin was optimized using the MM+ force field and PM3 (a semi-empirical method). The vibrations of the optimized structure were analyzed using PM3. The computer-generated wavenumbers and modes of vibration, the probable melanoidin structures were evaluated and compared with those corresponding to the experimental spectra of melanoidins based on the assignment of the modes of vibration (rather than on the exact assignment of frequencies). Discrepancies in the frequencies/wavenumbers of the experimental and computer-generated IR spectra of melanoidin especially for the C=0 and C=C stretching frequencies show the need to correct the computed IR frequencies, for example by using artificial neural networks.

The heats of combustion of synthetic and natural melanoidins were determined experimentally using a Parr bomb calorimeter. Benzoic acid was used as standard and the corresponding heats of formation of the two melanoidins were calculated. These experimental heats of combustion were compared with the computer-calculated vanes for the probable melanoidin structures. The IR spectra, total energy, heat of combustion and electrical charge properties were used as criteria to evaluate the eleven probable monomer structures of melanoidin giving points for each criterion. Based on total points for all criteria, the two most probable synthetic melanoidin monomer structures (C1 and C3) were selected which differed from that postulated by Kato and Tsuchida (1981) primarily in having carboxylic rather than carbinol groups and the absence of hemiacetal groups.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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