Interaction of Rose Bengal with α-chymotrypsin and α- chymotrypsinogen-A

Absorption spectra of aqueous solutions of Rose Bengal—(α-chymotrypsin) and Rose Bengal—(α- chymotrypsinogen-A) measured at different pHs showed that both proteins formed the same complexes. The binding constants for the formation of RB/CHT and RB/CHTGA complexes were of the same order of magnitude. The binding isotherms showed that stoichiometry of RB complexes was 3:1 at pH 4.6 and 1:1 at pH 7.2 for both RB/CHT and RB/CHTGA, respectively. Equal binding between the dye and both proteins eliminated the possibility that RB could interact selectively with the active site of α-chymotrypsin.Charge-charge interaction between the carboxylic group of the dye and the positively charged protein surface was essential for the stability of the complexes. The binding reached its minimum when the pH of aqueous solution was equal to the pI of the protein. The complexes exhibited no CD at any pH and at any KCl concentration varied from 0.0 to 0.5 M, which showed that the complexes were achiral. At pH < 4, both proteins trapped the acidic form of RB in a temperature dependent process.     

Polymerization of linear higher α-olefins with a modified Ziegler catalyst

The polymerization of hexene-1, octene-1 and decene-1 with a modified Ziegler catalyst based on the product of interaction of TiCl₄, Et₂AlCl, and n-Bu₂O in toluene has been studied. Et₂AlCl, i-Bu₂AlCl, and a combination of Et₂AlCl with MgBu₂ were used as cocatalysts. The addition of a small amount of MgBu₂ to Et₂AlCl resulted in a sharp increase in the catalytic system activity along with decreases in the molecular masses of the formed polymers. It has been shown that a change of [Mg]/[Al] ratio makes it possible to produce polyolefins in a wide range of molecular masses with high effectiveness. The above mentioned polymers are amorphous ultrahigh molecular materials with predominantly isotactic structure.     

Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane

Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe₂Si(OSiMe₂) _n H and (-OSiMe₂-)m (n = 2–6, m = 3–7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.     

Graphene oxide as an enzyme inhibitor: modulation of activity of α-chymotrypsin

We have investigated the efficacy of graphene oxide (GO) in modulating enzymatic activity. Specifically, we have shown that GO can act as an artificial receptor and inhibit the activity of α-chymotrypsin (ChT), a serine protease. Most significantly, our data demonstrate that GO exhibits the highest inhibition dose response (by weight) for ChT inhibition compared with all other reported artificial inhibitors. Through fluorescence spectroscopy and circular dichroism studies, we have shown that this protein-receptor interaction is highly biocompatible and conserves the protein's secondary structure over extended periods (>24 h). We have also explored GO-enzyme interactions by controlling the ionic strength of the medium, which attenuates the host-guest electrostatic interactions. These findings suggest a new generation of enzymatic inhibitors that can be applied to other complex proteins by systematic modification of the GO functionality.     

Biosensor for aluminium(III) based on its inhibition of α-chymotrypsin immobilized on a screen-printed carbon electrode modified with gold nanoparticles

We report on an amperometric assay for Al(III) ions that is based on the inhibition of the enzyme α-chymotrypsin. Screen-printed carbon electrodes modified with gold nanoparticles were used as solid supports for the immobilization of the enzyme. The amperometric response of the synthetic enzyme substrate substrate N-benzoyl-L-tyrosine ethyl ester is affected by Al(III) ions, and this leads to a decrease in the amperometric oxidation current. The assay has a detection limit of 3.3?μM of Al(III). The repeatability and reproducibility of the method are 6.9% (n?=?3) and 6.4% (n?=?5), respectively. Main interferents include Mo(VI), W(VI) and Fe(III) ions. The method was successfully applied to the determination of Al(III) in tap water.

Estimation of the intrinsic stresses in α-alumina in relation with its elaboration mode

The specific signatures of α-Al₂O₃ by Fourier transform infrared (FTIR) spectroscopy were investigated to estimate the intrinsic stress in this compound according to its elaboration mode. Thus, α-alumina was prepared either by calcination of boehmite or gibbsite and also generated by oxidation of a metallic FeCrAl alloy. FTIR results were mainly supported by X-ray diffraction (XRD) patterns that allowed to determine the crystallite size and the strain in the various alpha aluminas. Moreover, the infrared peak at 378.7 cm⁻¹ was used as a reference for stress free α-alumina and the shift of this peak allowed to estimate intrinsic stresses, which were related to the morphology and to the specific surface area of aluminas according to their elaboration mode. These interpretations were confirmed by results obtained by cathodoluminescence experiments.     

Quantum-chemical modeling of the mechanism for reaction of arenesulfonyl chlorides with α-amino acids

We have calculated the potential energy surface for arenesulfonylation reactions of a-amino acids and glycine hydrates. We have shown that all the reactions occur via a complicated route, with varying angle of attack by the nucleophile according to an S _N2 mechanism. Hydration of glycine lowers the activation energy compared with the gas phase.     

Theoretical studies on the mechanism of the thermal decarboxylation and decarbonylation of a number of α-keto-acids

Both processes of decarboxylation and decarbonylation of a number of acids including RCOCO2H,R=H,CH3,CH2F,CF3,CH=CH2,Ph,OH have been studied by semi-empirical MO theory AMI method to verify the reaction mechanism of each process and the effect of different substituents on them.The calculated results are consistent with the experimental reports and can be summed up as follows:(1) The decarboxylation of these acids to form aldehydes and carbon dioxide is concerted and takes place through a 4-membered ring transition state in which a partial negative charge develops on the carbon of the α-carbonyl group,so that the inductive effect of some substituents is favourable for this process.(2) Their decarbonylation into carboxylic acids and carbon monoxide however is the attack of the OH on the carbon of the alkyl portion of the acid,forming a 3-membered ring transition state.(3) The activation energy of decarbonylation is lower than that of decarboxylation,since oxygen is more nucleophilic than hydrogen and als     

Does a fluorinated Lewis acid catalyst change the molecular mechanism of the decomposition process of nitroethyl carboxylates?

The molecular mechanism of the decomposition reaction of nitroethyl benzoates catalyzed by Lewis acids based on boron element—BH₃ and BF₃—was studied using density functional theory methods. These reactions take place much faster than the uncatalyzed process. However, the presence of fluorinated Lewis acids has a unique influence on the molecular mechanism. In the case of BF₃, a change from a one-step mechanism to a two-step one involving a zwitterionic intermediate is observed.     

Semi-synthesis of an artificial scandium(iii) enzyme with a β-helical bio-nanotube

We have succeeded in preparing semi-synthesized proteins bound to Sc(3+) ion which can promote an epoxide ring-opening reaction. The Sc(3+) binding site was created on the surface of [(gp5βf)(3)](2) (N. Yokoi et al., Small, 2010, 6, 1873) by introducing a cysteine residue for conjugation of a bpy moiety using a thiol-maleimide coupling reaction. Three cysteine mutants [(gp5βf_X)(3)](2) (X = G18C, L47C, N51C) were prepared to introduce a bpy in different positions because it had been reported that Sc(3+) ion can serve as a Lewis-acid catalyst for an epoxide ring-opening reaction upon binding of epoxide to bpy and two -ROH groups. G18C_bpy with Sc(3+) can accelerate the rate of catalysis of the epoxide ring-opening reaction and has the highest rate of conversion among the three mutants. The value is more than 20 times higher than that of the mixtures of [(gp5βf)(3)](2)/2,2'-bipyridine and l-threonine/2,2'-bipyridine. The elevated activity was obtained by the cooperative effect of stabilizing the Sc(3+) coordination and accumulation of substrates on the protein surface. Thus, we expect that the semi-synthetic approach can provide insights into new rational design of artificial metalloenzymes.     

Translocation of α-helix chains through a nanopore

The translocation of α-helix chains through a nanopore is studied through Langevin dynamics simulations. The α-helix chains exhibit several different characteristics about their average translocation times and the α-helix structures when they transport through the nanopores under the driving forces. First, the relationship between average translocation times τ and the chain length N satisfies the scaling law, τ～N(α), and the scaling exponent α depends on the driving force f for the small forces while it is close to the Flory exponent (ν) in the other force regions. For the chains with given chain lengths, it is observed that the dependence of the average translocation times can be expressed as τ～f(-1/2) for the small forces while can be described as τ～f in the large force regions. Second, for the large driving force, the average number of α-helix structures N(h) decreases first and then increases in the translocation process. The average waiting time of each bead, especially of the first bead, is also dependent on the driving forces. Furthermore, an elasticity spring model is presented to reasonably explain the change of the α-helix number during the translocation and its elasticity can be locally damaged by the large driving forces. Our results demonstrate the unique behaviors of α-helix chains transporting through the pores, which can enrich our insights into and knowledge on biopolymers transporting through membranes.     

Synthesis of electron-deficient dienes bearing a chromonyl moiety via the reaction of 3-formylchromones with ylidenemalononitriles and ethyl α-cyano-β-methylcinnamate

3-Formylchromones react with ylidenemalononitriles in the presence of triethylamine in dichloromethane to produce the target electron-deficient dienes connected to the chromone system with excellent E-selectivity and in good yields. In a similar manner, their reaction with ethyl α-cyano-β-methylcinnamate gave a mixture of E,Z- and E,E-isomeric chromonyl dienes, from which the former could be isolated in a pure state by crystallization.     

Enantioselective synthesis of tertiary alcohols through a zirconium-catalyzed Friedel-Crafts alkylation of pyrroles with α-ketoesters

Chiral complexes of 1,1'-bi-2-naphthol-based ligands with zirconium tert-butoxide catalyze the Friedel-Crafts alkylation of pyrroles with α-ketoesters to afford tertiary alcohols in good yields and ee up to 98%. The reaction is also of application to 4,7-dihydroindole to give C2-alkylated indoles after oxidation with p-benzoquinone.     

Synthesis,antioxidant activity,and α-glucosidase enzyme inhibition of α-aminophosphonate derivatives bearing piperazine-1,2,3-triazole moiety

A novel series of piperazine-1,2,3-triazole bearing dimethyl(((2-(4-((1H-1,2,3-triazole-4-yl)methyl)piperazin-1-yl)ethylamino)(2-hydroxyaryl)methyl)phosphonate derivatives have been prepared via copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) (Click Reaction) and Schiff base reactions. The synthesized compounds were confirmed by spectral characterization (¹H, ¹³C and ³¹P NMR, and mass). The title compounds were evaluated for in vitro alpha glucosidase enzyme inhibition and in vitro antioxidant activity using DPPH and H₂O₂ methods.     

Amberlyst-15: an efficient and reusable catalyst for the Friedel-Crafts reactions of activated arenes and heteroarenes with α-amido sulfones

The heterogeneous Amberlyst-15 catalyst displays efficient catalytic properties for the Friedel-Crafts reactions between an activated arenes or heteroarenes and α-amido sulfones. Various α-amido sulfones on treatment with 1,2,4-trimethoxy benzene give the Friedel-Crafts reaction products in very good yield. The reactions with heteroarenes show moderate yield of the product. The catalyst can be easily recycled without significant loss of activity.     

Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

Functional detergents (FD) based on pyridine and containing aldoximate, ketoximate, and hydroxamate groups were synthesized. Their reactivity in FD/CTAB comicelles toward 4-nitrophenyl 4-toluenesulfonate (NPTS), diethyl phosphate (NPDEP), and diethylphosphonate (NPDEPS) in weakly alkaline media was investigated. Functional detergents based on pyridine are effective in the decomposition of ecotoxicants; the half-lives for the transformation of the substrates into the reaction products in the presence of a functional detergent containing, for example, a ketoximate group amounts to ∼40 s (NPTS), ∼120 s (NPDEP), and ∼5 s (NPDEPS). By analyzing the results it was possible to establish the paths to further modification of the head group of the surfactant, i.e., by varying the structure of the oximate group at various positions of the pyridinium ring aimed at the production of low-basicity functional detergents. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 284–291, September–October, 2008.     

Superparamagnetic iron oxide as an efficient catalyst for the one-pot, solvent-free synthesis of α-aminonitriles

Superparamagnetic Fe₃O₄ is shown to act as a very efficient catalyst for the one-pot, three-component synthesis of α-aminonitriles from aldehydes, amines, and TMSCN. The catalyst is easily recovered by the use of an external magnet and reused in several reactions without any noticeable loss of activity. The products are obtained rapidly at room temperature in good purity upon separation of the catalyst and evaporation of the volatiles of the reaction mixture.     

Relationship between the hydration degree of poly-N-isopropylacrylamide gel and activity of immobilized α-chymotrypsin

The influence of the pH, temperature, and dimethyl sulfoxide concentration on the hydration degree of the poly-N-isopropylacrylamide gel and the activity of -chymotrypsin immobilized into the polymer was studied. The behavior of more hydrophilic preparations based on polyacrylamide and copolymer of acrylamide and acrylic acid was studied for comparison. An increase in both the temperature and dimethyl sulfoxide content decreases the hydration of the poly-N-isopropylacrylamide, which correlates with a decrease in the activity of the immobilized enzyme. The use of substrates with different structures and an irreversible inhibitor proves that the change in the properties of -chymotrypsin immobilized into the poly-N-isopropylacrylamide gel is related to the change in the rate constants of enzymatic reactions. Comparison of all experimental data obtained suggested an opportunity of local interactions between the protein globule and polymeric chains with a change in the hydration degree of poly-N-isopropylacrylamide during its phase transition.