Enzymatic acylation of hydroxypropyl cellulose in organic media and determination of ester formation by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy

Enzyme biotechnology in degradation and modification of plant cell wall polymers

Lignocelluloses are abundant raw materials for production of fuels, chemicals and materials. The purpose of this paper is to review the enzyme-types and enzyme-technologies studied and applied in the processing of the lignocelluloses into different products. The enzymes here are mostly glycoside hydrolases, esterases and different redox enzymes. Enzymatic hydrolysis of lignocellulosic polysaccharides to platform sugars has been widely studied leading to development of advanced commercial products for this purpose. Restricted hydrolysis or oxidation of cellulosic fibers have been applied in processing of pulps to paper products, nanocelluloses and textile fibers. Oxidation, transglycosylation and derivatization have been utilized in functionalization of fibers, cellulosic surfaces and polysaccharides. Enzymatic polymerization, depolymerization and grafting methods are being developed for lignin valorization.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Green polymer chemistry: enzyme catalysis for polymer functionalization

Enzyme catalyzed reactions are green alternative approaches to functionalize polymers compared to conventional methods. This technique is especially advantageous due to the high selectivity, high efficiency, milder reaction conditions, and recyclability of enzymes. Selected reactions can be conducted under solventless conditions without the application of metal catalysts. Hence this process is becoming more recognized in the arena of biomedical applications, as the toxicity created by solvents and metal catalyst residues can be completely avoided. In this review we will discuss fundamental aspects of chemical reactions biocatalyzed by Candida antarctica lipase B, and their application to create new functionalized polymers, including the regio- and chemoselectivity of the reactions.

Supercritical carbon dioxide biocatalysis as a novel and green methodology for the enzymatic acylation of fibrous cellulose in one step

Aliphatic esters of cellulose have recently raised the interest on the field of biopolymers. The objective of this work is to develop a methodology for the enzymatic acylation of cellulose with long chain fatty groups in one step. Therefore we designed a system at which fibrous cellulose was enzymatically acylated with vinyl laurate in supercritical carbon dioxide (scCO(2)) and as a result cellulose laurate was formed. The biocatalysts used for this reaction were immobilized lipase Candida antarctica, immobilized esterase from hog liver and the immobilized cutinase Fusarium solani. The ester content of the product varied on the specificity of the biocatalyst used, reaching a maximum of 4.1% after 9h of reaction. In our knowledge, it is the first time where fibrous cellulose is enzymatically acylated by a long chain aliphatic group in one step, without the necessity of any pretreatment.

Direct enzymatic acylation of cellulose pretreated in BMIMCl ionic liquid

Cellulose esters are an important class of functional biopolymers with great interest in the chemical industry. In this work the enzymatic acylation of Avicel cellulose with vinyl propionate, vinyl laurate and vinyl stearate, has been performed successfully in a solvent free reaction system. At first cellulose was putted into the ionic liquid BMIMCl (1-n-butyl-3-methylimidazolium chloride) in order to facilitate the unwrap of the structure of the polysaccharide molecule and make it accessible to the enzyme. Thus, after this pretreatment the enzymatic esterification reaction was performed using various hydrolases. The enzymes capable of catalyzing the acylation of cellulose were found to be the immobilized esterase from hog liver and the immobilized cutinase from Fusarium solani, while the lipases used did not show any catalytic activity. Cellulose esters of propionate, laurate and stearate were synthesized with a degree of esterification of 1.9%, 1.3% and 1.0%, respectively. It is the first successful direct enzymatic acylation of cellulose with long chain fatty acids.

Synthesis of esters by immobilized-lipase-catalyzed condensation reaction of sugars and fatty acids in water-miscible organic solvent

A lipase-catalyzed condensation reaction in an organic solvent is a promising means of synthesizing esters. Reaction equilibrium constant, which is usually defined on the basis of reactant concentration, is an important parameter for estimating equilibrium yield. It is shown that the constant is markedly, affected by some factors, such as the hydration of a sugar substrate and the interaction of a reactant with a solvent. To reasonably design the reaction system or determine the reaction conditions, attention should be paid to these factors. From the viewpoint of kinetics, substrate selectivity for carboxylic acids also numerically correlates to the electrical and steric properties of these acids. Reactor systems for continuously producing esters through an immobilized-lipase-catalyzed condensation reaction are developed.

Modification of Cellulose Fiber Surfaces by Use of a Lipase and a Xyloglucan Endotransglycosylase

A strategy for the modification of cellulose fiber surfaces was developed that used the ability of Candida antarctica lipase B (CALB) to acylate carbohydrates with high regioselectivity, combined with the transglycosylating activity of the Populus tremula x P. tremuloides xyloglucan endotransglycosylase 16A (PttXET16A). Xyloglucan oligosaccharides (XGOs) prepared from tamarind xyloglucan were acylated with CALB as a catalyst and vinyl stearate or gamma-thiobutyrolactone as acyl donors to produce carbohydrate molecules with hydrophobic alkyl chains or reactive sulfhydryl groups, respectively. The modified XGOs were shown to act as glycosyl acceptors in the transglycosylation reaction catalyzed by PttXET16A and could therefore be incorporated into high M(r) xyloglucan chains. The resulting xyloglucan molecules exhibited a high affinity for cellulose surfaces, which enabled the essentially irreversible introduction of fatty acid esters or thiol groups to cellulose fibers.

Transacetylations to carbohydrates catalyzed by acetylxylan esterase in the presence of organic solvent

Various conditions were applied to test the ability of acetylxylan esterase (AcXE) from Schizophyllum commune to catalyze acetyl group transfer to methyl beta-D-xylopyranoside (Me-beta-Xylp) and other carbohydrates. The best performance of the enzyme was observed in an n-hexane-vinyl acetate-sodium dioctylsulfosuccinate (DOSS)-water microemulsion at a molar water-detergent ratio (w(0)) of about 4-5. Although the enzyme was found to have a half-life of about 1 h in the system, more than 60% conversion of Me-beta-Xylp to acetylated derivatives was achieved. Under identical reaction conditions, the enzyme acetylated other carbohydrates such as methyl beta-D-cellobioside (Me-beta-Cel), cellotetraose, methyl beta-D-glucopyranoside (Me-beta-Glcp), 2-deoxy-D-glucose, D-mannose, beta-1,4-mannobiose, -mannopentaose, -mannohexaose, beta-1,4-xylobiose and -xylopentaose. This work is the first example of reverse reactions by an acetylxylan esterase and a carbohydrate esterase belonging to family 1.

Fast quantification of humic substances and organic matter by direct analysis of sediments using DRIFT spectroscopy

A simple method based on diffuse reflectance coupled with infrared Fourier transform spectroscopy (DRIFTS) has been developed for the quantification and the characterization of sedimentary (or soil, peat, etc.) humic substances. Under optimized conditions, the quantification of humic substances or total organic matter is possible with DRIFTS at a frequency of 2930 cm(-1) using whole dry sediment samples. A study of the operational parameters that affect the DRIFTS signal shows the importance of normalizing analysis conditions, especially the diffuse reflectance accessory alignment, the particle size and compaction, and the homogeneity of the powdered samples, to obtain reproducible quantitative analyses. The quantification of total humic substances by DRIFTS correlates well with the concentrations determined using classical extraction methods. DRIFTS analysis requires only a few minutes instead of tedious extractions of humic substances. Moreover, the distribution of total organic matter and of fulvic acids, humic acids, and humin can also be obtained. Analysis of natural samples indicates that a calibration using humic material representative of the studied area provides the most accurate quantification. The fast screening of organic matter fractions by DRIFTS on intact natural samples provides useful quantitative and qualitative information that can be used in environmental or monitoring studies.

Reactivity and stability of mycelium-bound carboxylesterase from Aspergillus oryzae

The reactivity and thermostability of a novel mycelium-bound carboxylesterase from lyophilized cells of Aspergillus oryzae are explored in organic solvent. Ethanol acetylation was selected as reference esterification reaction. High carboxylesterase activity cells were used as biocatalyst in batch esterification tests at 12.5 < S(o) < 125 mmol L(-1), 5.0 < X(o) < 30 g L(-1), 0.49 < log P < 4.5 and 30 < T < 80 degrees C, as well as in residual activity tests after incubation at 40 < T < 90 degrees C. The starting rates of product formation were used to estimate with the Arrhenius model the apparent activation enthalpies of the enzymatic reaction (29-33 kJ mol(-1)), the reversible unfolding (56-63 kJ mol(-1)), and the irreversible denaturation (22 kJ mol(-1)) of the biocatalyst.