Characterization of a Novel Mannose Isomerase from Stenotrophomonas rhizophila and Identification of Its Possible Catalytic Residues

D-Mannose has great value in the treatment of chronic diseases. D-Mannose isomerase can catalyze the bioconversion of D-fructose to D-mannose. Therefore, a novel D-mannose isomerase gene (Strh-MIase) from Stenotrophomonas rhizophila strain IS26 was expressed, purified, and characterized for the industrial production of D-mannose. The specific activities of the Strh-MIase for D-mannose and D-fructose were 437.5 ± 0.8 U/mg and 267.2 ± 0.7 U/mg. Its optimal temperature and pH were 50 °C and 7.0. The enzymatic bioconversion produced 25 g/L D-mannose from concentration D-fructose (100 g/L) in 6 h by recombinant Strh-MIase, resulting in a final yield of 25%. Sodium phosphate inhibition has little influence on D-mannose production when a high concentration of D-fructose is used as substrate. We demonstrate that the metal ions improve the efficiency of D-mannose isomerase because of the enhancement of its thermostability. Moreover, the possible catalytic residues of Strh-MIase were identified by site-directed mutagenesis.

A Review on Micellar Catalyzed Oxidation Reactions of Organic Functional Groups in Aqueous Medium Using Various Transition Metals

The current requirement for science and research concerns the absolute sustainable development of a chemistry that is inherently safer, smarter and more environmentally friendly. The oxidation reaction is a very fundamental transformation reaction in organic synthesis and likely plays a significant role in the production of various value-added chemicals from biomass and others precursors. In the focus of making kinetic experiments greener several modified methodologies and safe chemicals have been employed. Surfactants are such suitable alternate that go with the requirments. Surfactant aggregates i. e. micelles are nano-sized supra molecules, able to act as catalysts. They can be used to catalyze the organic functional group transformation reactions mediated with transition metals and promoted with various aromatic bases. This allowed water to be used as a solvent, where the reactions became more sustainable. The recyclability of used surfactants, enhancement of reaction kinetics and speed of reaction with no consumption of energy has added more value to this type of catalytic oxidation. This article aims to contribute to the discussion of the mechanistic aspects of various types of surfactant-catalyzed oxidation of organic functional groups.

Solvent-Free Acetalization of Glycerol with n-Octanal using Combined Brønsted Acid-Surfactant Catalyst

Glycerol, derived from biodiesel production, is a renewable feedstock for the production of value-added chemicals. Herein, we report an investigation of the acetalization of glycerol with n-octanal by homogeneous acid catalysis in the absence of a solvent, using p-dodecylbenzenesulfonic acid, p-toluenesulfonic acid, and sulfuric acid, respectively, as catalysts. p-Dodecylbenzenesulfonic acid, a surfactant-type Brønsted acid, proved to be an excellent catalyst capable of efficiently promoting the reaction under solvent-free conditions, and the yields of glycerol acetals reached 99% under the optimal conditions. The distribution of five- and six-membered cyclic acetal regioisomers varied depending on the reaction time and temperature. Moreover, the amphiphilic properties of the products, with different ratios of five- to six-membered cyclic acetals, have been evaluated by surface tension measurements.

Picolinic Acid Promoted Permanganate Oxidation of D-Mannitol in Micellar Medium

Kinetics of permanganate oxidation of D-mannitol have been investigated spectrophotometrically under pseudo-first-order conditions in aqueous acidic media at 30 °C. The spectral analysis of hydrazone derivative of the product indicates the product to be an aldehyde. The observed rate constant value was found to be relatively slow in the uncatalyzed path, which increases by the presence of four isomeric promoters: 2-picolinic acid (2-PA), 4-picolinic acid (4-PA), 2,3-dipicolinic acid (2,3-diPA) and 2,6-dipicolinic acid (2,6-diPA). The catalytic effect of sodium dodecylbenzene sulfonate (SDBS) surfactant on the permanganate oxidation of D-mannitol has been also studied in the presence of the promoters. The critical micelle concentration (CMC) of SDBS alone and in presence of D-mannitol was determined by conductometry and spectrophotometry. The aggregation and morphological changes during reaction were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The variation of the reaction rates for the different promoters in the presence and absence of SDBS micellar catalyst is discussed qualitatively in the terms of partitioning nature of substrate, charge of surfactant and reactants. 2,3-diPA in association with SDBS as micellar catalyst accelerated the reaction velocity compared to the uncatalyzed path.

A Mechanistic Approach to the Influence of Surfactants on the Oxidation of Ethyl Mercaptan and its Dimer Ethyl Mercaptan Disulfide by Hexacyanoferrate(III) Ions in Aqueous Medium

In this paper we report on the rate of oxidation of ethyl mercaptan and its dimer ethyl mercaptan disulfide by alkaline hexacyanoferrate(III) along with its mechanistic pathway, spectrophotometrically. The influence of different experimental parameters, such as change in concentration of EtSH, HCF, OH− and reaction temperature was studdie. It was observed that the order of reaction decreases in [EtSH] or [OH−] from first order to higher concentration, but it certainly did not tend towards zero order. The effect of surfactants on the rate of reaction was observed at the critical micelle concentration (CMC) of the surfactant and reported to be below the CMC. The investigators, thus, concluded that the added products have an insignificant effect on the reaction rate. Further, the activation parameters were evaluated which lend support to the proposed mechanism. The thermodynamic quantities were also determined and the binding parameters have also been evaluated using the Menger and Portnoy model.

Kinetics of Cetyltrimethylammonium Bromide Catalysed Oxidation of Cyclopentanone by N-Bromophthalimide in Acidic Medium

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulphate (SDS) on the kinetics of oxidation of cyclopentanone by N-bromophthalimide (NBP) was studied iodometrically at 308 K. In addition to the kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties. The kinetic observations indicate fractional order and first order dependence with respect to [cyclopentanone] and [NBP] respectively. Cationic surfactant (CTAB) strongly catalyses the oxidation of Cyclopentanone in aqueous acetic acid medium. Typical kobs and [CTAB] profile were observed i. e. with the progressive increase in [CTAB], the reaction rate increased and at higher concentration of CTAB, constancy in kobs was observed. Anionic surfactant (sodium dodecylsulphate, SDS), mercuric acetate and phthalimide did not influence the reaction rate. The presence of inorganic salts (KCl, KBr) exhibits a severe hike in the reaction rate. The various activation parameters in the presence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed.