Date of Award

12-2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor

Raymond C. Fort, Jr.

Second Committee Member

Barbara J.W. Cole

Third Committee Member

Joseph M. Genco

Abstract

Hemicelluloses represent a potential feed stock for various valuable chemicals and fuels. Due to the presence of covalently linked lignin they are underutilized. Enzymes may be used for the delignification instead of chemicals, since the process is environmentally friendly. An advantage of the enzymatic process is their selectivity towards the substrate without any degradation. The objective of this work was to investigate the delignification of model lignin carbohydrate complexes (LCC) by laccase without using any mediators. Molecular docking methods were used to learn that the substrate binds tightly to the active site of the enzyme and can be readily oxidized. Model lignin carbohydrate compounds with glycosidic linkages, 4-methoxyphenyl-| 3-D-glucopyranoside and coniferin, were synthesized and characterized using NMR and IR. The laccase of the fungal species Trametes versicolor was used to determine whether enzymes can selectively cleave the lignin without the degradation of the carbohydrate. The products produced from the enzymatic oxidation were identified using GC/MS. The percentage yield of the sugar produced at different time intervals was calculated. A maximum yield of around 90% of the sugar from both compounds was observed. A molecular modeling study was performed on 4-methoxyphenyl-|3-Dglucopyranoside radical-cation in order to understand the bond length differences with that of neutral molecule. The experimental studies were performed to observe that the enzymatic oxidation of model lignin carbohydrate compounds by laccase was efficient in the cleavage of glycosidic bond without any degradation of the sugar. From previous studies on the model compounds, we can predict the possible dimers with 4-0-5 type and 5-5 type of linkage produced from 4-methoxyphenol. Identification of 4-methoxyphenol and the dimers produced by the oxidation of 4-methoxyphenyl-P-D-glucopyranoside were done from their mass spectra. Coniferylaldehyde was identified as one of the products produced from the oxidation of coniferin by laccase.

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