Spectroscopic (UV-VIS and IR) and computational (hyperchem) studies on the molecular structure of natural melanoidin

Date

4-2000

Degree

Bachelor of Science in Chemistry

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Ernesto J Del Rosario

Abstract

ABSTRACT

NATANAUAN, NIÑA D. University of the Philippines Los Banos, April, 2000. Spectroscopic (UV-Vis and IR) and Computational (HYPERCHEM) Studies on the Molecular Structure of Natural Melanoidin,

Adviser: Dr. Ernesto J. del Rosario

Committee members: Dr. Cleofe A. Calanasan Dr. Evamarie P. Capareda

The infrared (1R) and electronic spectra of the repeating unit of natural melanoidin (NM) were simulated using Hyperchem software in order to have an insight on the molecular structure of this dark-colored polymeric compound obtained from the non-enzymatic Maillard reaction of carbohydrates and amino compounds. Five probable structures of melanoidin were evaluated computationally in terms of their IR spectra and fifteen in terms of their UV-Visible spectra starting with the structures suggested by Kato and Tsuchida (1981), Yaylayan and Kaminsky (1998) and Rodulfo (1999). The geometry of each probable molecular structure was optimized using the WA+ forcefield and PM3, a semi-empirical method. The vibrations of the optimized structure were investigated using PM3. The probable melanoidin repeating unit structures were evaluated based on the comparison between the computer-calculated wavenumbers and modes of vibration with those expected from the experimental spectra. The ZINDO/S semi-empirical calculation was used to calculate the UV-Visible spectral frequencies. Lack of complete agreement between the computer-generated and experimental data indicates the need to correct the computed IR frequencies (for example by using artificial neural networks) and to evaluate the semi-empirical methods of calculation.

The molecular weight (MW) of NM was determined experimentally using gel permeation chromatography. Two fractions were obtained with MW values of 28.5 and 20 5 kDa. Electrophoretic behavior of the NM was also studied using Polyacrylamide Gel Electrophoresis (PAGE). Based on the results, NM has a lower electrophoretic mobility towards the anode indicating a smaller net electrical charge compared to synthetic melanoidin (SM).

Based on the computer calculation and IR and UV-Visible spectra, the most probable structure of the repeating unit of natural melanoidin was proposed which is similar to that suggested by Yaylayan and Kaminsky (1998)

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 993.5 2000 C4 N38

Document Type

Thesis

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