Enzymatic Catalysis In Organic Solvents Research Articles

Reflections on Charge State Distributions, Protein Structure, and the Mystical Mechanism of Electrospray Ionization

The connection between charge state distributions, protein structure, and mechanistic details of electrospray are discussed in relation to the emerging field of gas phase structural biology. Comparisons are drawn with the established area of enzymatic catalysis in organic solvents, which shares many similar challenges. Charge solvation emerges as a dominant force in both systems that must be dealt with to enable kinetic trapping of native structures in foreign environments. Potential methods for mediating unfavorable charge solvation effects are discussed and, ironically, do not include partial solvation by water. The importance of timescale in relation to the evolution of protein structure during the process of electrospray ionization is discussed. Finally several prospects for future endeavors are highlighted.

A graphene oxide/hemoglobin composite hydrogel for enzymatic catalysis in organic solvents

A graphene oxide/hemoglobin (GO/Hb) composite hydrogel was prepared for catalyzing a peroxidatic reaction in organic solvents with high yields, exceptional activity and stability.

Enantioselective transesterification by Candida antarctica Lipase B immobilized on fumed silica

Enzymatic catalysis to produce molecules such as perfumes, flavors, and fragrances has the advantage of allowing the products to be labeled “natural” for marketing in the U.S., in addition to the exquisite selectivity and stereoselectivity of enzymes that can be an advantage over chemical catalysis. Enzymatic catalysis in organic solvents is attractive if solubility issues of reactants or products, or thermodynamic issues (water as a product in esterification) complicate or prevent aqueous enzymatic catalysis. Immobilization of the enzyme on a solid support can address the generally poor solubility of enzymes in most solvents. We have recently reported on a novel immobilization method for Candida antarctica Lipase B on fumed silica to improve the enzymatic activity in hexane. This research is extended here to study the enantioselective transesterification of (RS)-1-phenylethanol with vinyl acetate. The maximum catalytic activity for this preparation exceeded the activity (on an equal enzyme amount basis) of the commercial Novozyme 435 ® significantly. The steady-state conversion for (R)-1-phenylethanol was about 75% as confirmed via forward and reverse reaction. The catalytic activity steeply increases with increasing nominal surface coverage of the support until a maximum is reached at a nominal surface coverage of 230%. We hypothesize that the physical state of the enzyme molecules at a low surface coverage is dominated in this case by detrimental strong enzyme–substrate interactions. Enzyme–enzyme interactions may stabilize the active form of the enzyme as surface coverage increases while diffusion limitations reduce the apparent catalytic performance again at multi-layer coverage. The temperature-, solvent-, and long-term stability for CALB/fumed silica preparations showed that these preparations can tolerate temperatures up to 70 °C, continuous exposure to solvents, and long-term storage.

Fumed silica activated subtilisin Carlsberg in hexane in a packed‐bed reactor

AbstractEnzymatic catalysis in organic solvents can enable applications, reactivities, and selectivities that are not accessible in water. The use of enzymes for catalysis in organic solvents has been somewhat hampered by their relatively low‐catalytic activity. A new preparation of the enzyme subtilisin Carlsberg (SC) with fumed silica as support (FS) has been developed. This preparation matches and sometimes exceeds the activity of some of the best reported preparations of the same enzyme for use in solvents. The usefulness of our preparation in a packed‐bed reactor is explored here. The catalytic characteristics of our preparation containing 5 wt % of enzyme/95 wt % FS in a packed‐bed reactor for a model transesterification in hexane is determined. Mass‐transfer limitations are explored, and a comparison to batch results is given. The activity of our preparation after prolonged storage as a packed bed is investigated. Our immobilized enzyme preparation may be a step towards more economical enzymatic catalysis in organic solvents. © 2006 American Institute of Chemical Engineers AIChE J 2007

Enzymatic catalysis of formation of Z-aspartame in ionic liquid - An alternative to enzymatic catalysis in organic solvents.

We present the first report of enzymatic catalysis in an ionic liquid. The virtually nonexistent vapor pressure makes ionic liquids an exciting new alternative for enzyme-catalyzed syntheses in environmentally friendly environments. Z-aspartame was synthesized in a thermolysin-catalyzed reaction of carbobenzoxy-L-aspartate and L-phenylalanine methyl ester hydrochloride in 1-butyl-3-methylimidazolium hexafluorophosphate (BP6). Ionic liquids such as BP6 are thermally stable and have a remarkable range of temperatures over which they remain liquid (300 degrees C). With an initial rate of 1.2 +/- 0.1 nmol min(-)(1) mg(-)(1), we observed a competitive rate in comparison to that of enzymatic synthesis in organic solvent. Additionally, the enzyme exhibits outstanding stability, which would normally require immobilization.

Enzymatic catalysis in organic solvents: Polyethylene glycol modified hydrogenase retains sulfhydrogenase activity in toluene

Naturally occurring enzymes may be modified by covalently attaching hydrophobic groups that render the enzyme soluble and active in organic solvents, and have the potential to greatly expand applications of enzymatic catalysis. The reduction of elemental sulfur to hydrogen sulfide by a hydrogenase isolated from Pyrococcus furiosus has been investigated as a model system for organic biocatalysis. While the native hydrogenase catalyzed the reduction of sulfur to H(2)S in aqueous solution, no activity was observed when the aqueous solvent was replaced with anhydrous toluene. Hydrogenase modified with PEG p-nitrophenyl carbonate demonstrated its native biocatalytic ability in toluene when the reducing dye, benzyl viologen, was also present. Neither benzyl viologen nor PEG p-nitrophenyl carbonate alone demonstrated reducing capability. PEG modified cellulase and benzyl viologen were also incapable of reducing sulfur to H(2)S, indicating that the enzyme itself, and not the modification procedure, is responsible for the conversion in the nonpolar organic solvent. Sulfide production in toluene was tenfold higher than that produced in an aqueous system with equal enzyme activity, demonstrating the advantages of organic biocatalysis. Applications of bio-processing in nonaqueous media are expected to provide significant advances in the areas of fossil fuels, renewable feedstocks, organic synthesis, and environmental control technology. (c) 1996 John Wiley & Sons, Inc.

Effect of HY‐zeolites on the performance of tyrosinase‐modified carbon paste electrodes

AbstractThe dependence of electrode response on additive properties in enzyme‐modified carbon paste was studied. Four different HY‐zeolite powders, dealuminated to different extents and characterized by both Si/Al ratio and hydrophilicity, were used as the carbon paste modifiers. The enzyme tyrosinase used in biosensors for the detection of catechol and other phenolic compounds was chosen as the model system for the construction of a composite carbon paste biosensor incorporating different HY‐zeolites as additives. Tyrosinase was trapped on the HY‐zeolite particles from a buffer solution, dried and mixed with graphite powder and a pasting oil. It was found that by incorporating HY‐zeolites into the carbon paste the heterogeneous reaction rate of catechol redox conversion and the signal response for catechol were increased. In the latter case a higher response was observed for increased hydrophilicity, i.e., decreased Si/Al ratio of the HY‐zeolite. The carbon paste/solution interface is considered to be an aqueous/organic phase and the characteristics of the enzyme‐ modified carbon paste electrode are related to theories, explaining enzymatic catalysis in organic solvents.

Enzyme-mediated regioselective acylation of polyhydroxylated natural products

Abstract

Pressure affects enzyme function in organic media

Pressure affects enzyme function in nonaqueous media. Activation volumes have been determined and provide evidence that the primary effect of pressure is to enhance the stripping of water off an enzyme in polar organic solvents and leads to decreased enzymatic activity. Activation volumes of subtilisin Carlsberg in organic solvents, particularly with the enzyme hydrated, have a larger magnitude than activation volumes determined in aqueous solutions. This study provides further evidence that enzymatic activity in polar organic solvents is dominated by the interaction of enzyme-bound water with the solvent. From a practical standpoint, however, the results of this study suggest that enzymatic catalysis in organic solvents may be controlled by the combined effects of pressure and enzyme hydration.

Supported aqueous-phase enzymatic catalysis in organic media

The use of partially hydrated porous silica particles has been studied as a support for cofactor-dependent enzymatic catalysis in organic solvents. At an optimal pore hydration corresponding to 70% pore volume, horse liver alcohol dehydrogenase catalyzes the oxidation and reduction of alcohols and aldehydes, respectively, with rates sixfold higher than with nonporous glass beads as the enzymatic support and with cofactor recycling numbers in excess of 105. Thus, supported aqueous-phase enzymatic catalysis makes highly effective use of the enzyme and cofactor by coimmobilization and by providing a high interfacial area for reactions in organic media.

Enzymatic catalysis in organic solvents

Enzymatic catalysis in organic solvents

Enzymatic catalysis in nonaqueous solvents.

Subtilisin and alpha-chymotrypsin vigorously act as catalysts in a variety of dry organic solvents. Enzymatic transesterifications in organic solvents follow Michaelis-Menten kinetics, and the values of V/Km roughly correlate with solvent's hydrophobicity. The amount of water required by chymotrypsin and subtilisin for catalysis in organic solvents is much less than needed to form a monolayer on its surface. The vastly different catalytic activities of chymotrypsin in various organic solvents are partly due to stripping of the essential water from the enzyme by more hydrophilic solvents and partly due to the solvent directly affecting the enzymatic process. The rate enhancements afforded by chymotrypsin and subtilisin in the transesterification reaction in octane are of the order of 100 billion-fold; covalent modification of the active center of the enzymes by a site-specific reagent renders them catalytically inactive in organic solvents. Upon replacement of water with octane as the reaction medium, the specificity of chymotrypsin toward competitive inhibitors reverses. Both thermal and storage stabilities of chymotrypsin are greatly enhanced in nonaqueous solvents compared to water. The phenomenon of enzymatic catalysis in organic solvents appears to be due to the structural rigidity of proteins in organic solvents resulting in high kinetic barriers that prevent the native-like conformation from unfolding.

ChemInform Abstract: Enzymatic Catalysis in Organic Solvents

ChemInformVolume 18, Issue 17 Reviews ChemInform Abstract: Enzymatic Catalysis in Organic Solvents P. CESTI, P. CESTI Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this authorF. FRANCALANCI, F. FRANCALANCI Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this authorM. FOA, M. FOA Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this author P. CESTI, P. CESTI Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this authorF. FRANCALANCI, F. FRANCALANCI Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this authorM. FOA, M. FOA Ist. Guido Donegani SpV, 28100 Novara, ItalySearch for more papers by this author First published: April 28, 1987 https://doi.org/10.1002/chin.198717390Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue17April 28, 1987 RelatedInformation