Modulation of anionic reverse micellar interface with non-ionic surfactants can regulate enzyme activity within the micellar waterpool

Kinetic Study of SN2 Reaction between Paranitrophenyl Benzoate and Hydrazine in the Presence of CTAB Reverse Micelles

Kinetic study of the reaction between p-Nitrophenyl benzoate (PNPB) by hydrazine (HYN) in the presence of Cetyltrimethylammonium bromide (CTAB)/Chloroform/Hexane reverse micellar medium shows that the reaction obeys first order kinetics with respect to each of the reactants. The rate of the reaction is much slower in reverse micellar medium compared to aqueous medium under identical conditions (kˈAq = 2.84×10−3 sec−1, krm =1.34×10−4 sec−1). The rate constants for the reaction in the reverse micellar medium have been determined at different values of W {W=[H2O]/[CTAB]} and at different concentrations of CTAB. It was found that the observed rate constant decreases with W. This kinetic behaviour was interpreted by using modified Berezin pseudo phase model, taking into consideration the distribution of the reactants, PNPB and hydrazine between the three pseudo phases, i.e., water pool, interface an organic phase. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Mixed micelles and bicontinuous microemulsions: Promising media for enzymatic reactions

Enzymes, the natural catalysts, replace catalysts of chemical origin in a wide spectrum of reactions and generally work under environment friendly conditions. Various strategies are adopted to modify catalytic activities of enzymes further, of which one is application of novel reaction medium. This work reviews applicability of novel media like mixed micelles and bicontinuous microemulsions in enzymatic reactions and points out their capability to play bigger roles in enzyme catalysis. Ionic reverse micelles reduced catalytic activities of enzymes through denaturation. Addition of nonionic surfactant to these reverse micelles led to corresponding mixed micelles and thus restored or sometimes enhanced catalytic abilities of enzymes. Mixed micelles comprising of two nonionic surfactants, bicontinuous microemulsion containing two anionic surfactants also acted as efficient reaction media for enzymes. Even a cationic/anionic/nonionic mixed micelle was found to increase activity of enzyme. Mixed micelles and bicontinuous microemulsions comprising of anionic and zwitterionic surfactants augmented enzyme catalysis. Mixed micelles and bicontinuous microemulsions containing ionic liquid and surfactant also had critical impact on enzyme catalysis. Catalytic abilities of enzymes altered significantly in substrate/surfactant and bile salt/surfactant mixed micelles. Concentrations of individual surfactant, molar ratio of surfactants, and molar ratio of water to total surfactants had notable impacts on enzyme catalysis in those media.

A Molecular Probe with Both Chromogenic and Fluorescent Units for Detecting Serine Proteases

A molecular probe with l-phenylalanine p-nitroanilide and l-lysin 4-methylcoumaryl-7-amide, in which these amino acid derivatives are connected through a succinic-acid spacer, was prepared. Trypsin and papain were detected by blue-fluorescence emission of generated 7-amino-4-methylcoumarin (AMC). α-Chymotrypsin and nattokinase were detected from both the blue-fluorescence emission of AMC and the UV absorbance of p-nitroaniline. In addition, different time courses of p-nitroaniline and AMC were observed between the reaction of P1 with α-chymotrypsin and that with nattokinase. In the case of nattokinase, both the fluorescence emission and UV absorbance slowly increased. In contrast, the increasing UV absorbance was saturated at the early stage of the reaction of the present probe with chymotrypsin, whereas the fluorescence emission continuously increased in the following stages.

The multifaceted effects of DMSO and high hydrostatic pressure on the kinetic constants of hydrolysis reactions catalyzed by α-chymotrypsin

The cosolvent DMSO and high pressure have antagonistic effects on the kinetic constants of α-chymotrypsin-catalyzed hydrolysis reactions.

Structural Characterization of Biocompatible Reverse Micelles Using Small-Angle X-ray Scattering, 31P Nuclear Magnetic Resonance, and Fluorescence Spectroscopy

The most critical problem regarding the use of reverse micelles (RMs) in several fields is the toxicity of their partial components. In this sense, many efforts have been made to characterize nontoxic RM formulations on the basis of biological amphiphiles and/or different oils. In this contribution, the microstructure of biocompatible mixed RMs formulated by sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri- n-octylphosphine oxide (TOPO) surfactants dispersed in the friendly solvent methyl laurate was studied by using SAXS and ³¹P NMR and by following the solvatochromic behavior of the molecular probe 4-aminophthalimide (4-AP). The results indicated the presence of RM aggregates upon TOPO incorporation with a droplet size reduction and an increase in the interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edge excitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the external nonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogen bond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionic surfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches, i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of the interfacial fluidity of RMs, a parameter that is difficult to measure directly.

Enhanced Catalytic Activity of α-Chymotrypsin in Cationic Surfactant Solutions: The Component Specificity Revisited

Enhanced catalytic activity (super activity) of enzymes in the presence of surfactants is of key importance in "micellar enzymology"; such super activity is not very trivial, it is highly system specific, and the mechanism behind the activity enhancement is not always well apprehended. We report the catalytic activity of α-chymotrypsin (CHT) on ala-ala-phe-7-amido-4-methylcoumarin (AMC) in the presence of cationic surfactants of different hydrophobic chain lengths: dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB). It is observed that in comparison to buffer the catalytic activity of CHT is enhanced 5-fold in premicellar DTAB solutions, while negligible changes are observed in CTAB and OTAB. Activity decreases considerably in the post micellar concentration, specifically for the latter two surfactants. A similar trend is also obtained in another substrate 2-napthyal acetate hydrolysis. Such surfactant specific superactivity is intriguing. The protein's secondary and tertiary structures in the presence of these surfactants are determined using circular dichroism (CD) spectroscopy and it is found that both CTAB and OTAB perturb the protein structure significantly, especially in the post micellar concentrations. DTAB, on the other hand, does not produce noticeable changes in the protein structure. The various pairwise interactions present in the system have been underlined using both steady-state and time-resolved fluorescence spectroscopy. Assuming a three-step kinetics model, we determine the free energy changes of the reaction, and the observations have been discussed in the light of the various interactions among the components.