Thiolate Ions Research Articles

Investigation on recycling and reprocessing ability of self-healing natural rubber based on ionic crosslink network

Abstract Natural rubber (NR) is a complex material that is often discarded due to its three-dimensional structure. Recycling of rubber is difficult due to its complex structure, and only 1.7 million tonnes of waste, such as tyres and gloves, are considered recyclable. This study aims to develop self-healing rubber, which allows a product to recover without affecting structural reliability. Commercial NR was ionically crosslinked with zinc thiolate, forming an ionic crosslink network between rubber chains and zinc thiolate ions. The ionic crosslinks allow the rearrangement of rubber molecular chains under external heat, providing self-healing capabilities. The highest ionic crosslink density was found in NR with 35 phr zinc thiolate. The self-healing NR can recover 90 % of its initial properties at room temperature for 10 min and can be reprocessed and recycled three times without compromising its properties. It also shows excellent weldability, making it a promising material for repairing existing rubber products in heavy engineering applications.

Enhancing self‐healing efficiency of natural rubber composites using halloysite nanotubes

AbstractThis study aimed to explore the reinforcement effect of halloysite nanotubes (HNTs) in self‐healing natural rubber based on metal thiolate ion networks. The amount of HNTs was varied at five levels (2, 4, 6, 8, and 10 phr) in order to assess the optimum amount of filler for self‐healing efficiency and mechanical recovery performance. Fourier‐transform infrared (FTIR) provides evidence for the reversible ionic bonding, facilitated by Zn2+ and S− bonding from the metal thiolate vulcanization with rubber molecular chains. Scanning electron microscopy (SEM) revealed that the NR/HNTs composites with lower filler loading exhibited better recovery, as there were no observable gaps between the cut surfaces of the samples. The results also revealed that addition of HNTs resulted in a significant improvement in the mechanical performance, particularly the tensile strength, which increased by approximately 20%–75%. Furthermore, the extent of healing after the broken pieces were brought in contact with each other varied from 87% to 98%, depending on HNT concentration.Highlights Fabrication of self‐healing elastomers based on natural rubber. Self‐healing NR presented enhanced mechanical performance with addition of HNTs. HNTs lumen endows the composites with excellent self‐healing efficiency. Developed NR/HNTs composite exhibited room temperature self‐healing properties. Reversible ionic bonding expedited by Zn2+ contributes in excellent self‐healing.

Click-chemistry and ionic cross-linking induced double cross-linking ionogel electrolyte for flexible lithium-ion batteries

With the expansion of portable devices, high-security and flexible energy storage technologies are gaining popularity. However, because of the use of poisonous, flammable, and unstable organic liquid electrolytes in commercial lithium-ion batteries, they cannot provide sufficient protection for the safety and long-term life of portable devices. A thiolate click reaction and ion interaction are used to successfully create a double cross-linking ionogel electrolyte (DC-Ionogel) by sealing 1-ethyl-3methyimidazolium bis (trifluoromethyl) imide (EMIm(TFSI)) in a double cross-linked network. An ion cross-linking network and a covalent cross-linking network are interlaced in the double cross-linked network, which considerably increased the flexibility and stability of the ionogel electrolyte. As a result, DC-Ionogel outperformed in terms of flame retardancy and thermal dimensional stability and outperformed in terms of electrochemical performance, with higher room ionic conductivity (1.79 × 10−3S cm−1) and a broader electrochemical window (5 V). Due to its excellent performance, it is more likely to be used in flexible energy-storage devices.

Insights into Ubiquitin Product Release in Hydrolysis Catalyzed by the Bacterial Deubiquitinase SdeA

We report the co-crystal structure of the (catalytic Cys)-to-Ala mutant of the deubiquitinase domain of the Legionella pneumophila effector SdeA (SdeADUB) with its ubiquitin (Ub) product. Most of the intermolecular interactions are preserved in this product-bound structure compared to that of the previously characterized complex of SdeADUB with the suicide inhibitor ubiquitin vinylmethyl ester (Ub-VME), whose structure models the acyl-enzyme thioester intermediate. Nuclear magnetic resonance (NMR) titration studies show a chemical shift perturbation pattern that suggests that the same interactions also exist in solution. Isothermal titration calorimetry and NMR titration data reveal that the affinity of wild-type (WT) SdeADUB for Ub is significantly lower than that of the Cys-to-Ala mutant. This is potentially due to repulsive interaction between the thiolate ion of the catalytic Cys residue in WT SdeADUB and the carboxylate group of the C-terminal Gly76 residue in Ub. In the context of SdeADUB catalysis, this electrostatic repulsion arises after the hydrolysis of the scissile isopeptide bond in the acyl-enzyme intermediate and the consequent formation of the C-terminal carboxylic group in the Ub fragment. We hypothesize that this electrostatic repulsion may expedite the release of the Ub product by SdeADUB. We note that similar repulsive interactions may also occur in other deubiquitinases and hydrolases of ubiquitin-like protein modifiers and may constitute a fairly general mechanism of product release within this family. This is a potentially important feature for a family of enzymes that form extensive protein-protein interactions during enzyme-substrate engagement.

An insight into the interaction between α-ketoamide- based inhibitor and coronavirus main protease: A detailed in silico study

The search for therapeutic drugs that can neutralize the effects of COVID-2019 (SARS-CoV-2) infection is the main focus of current research. The coronavirus main protease (Mpro) is an attractive target for anti-coronavirus drug design. Further, α-ketoamide is proved to be very effective as a reversible covalent-inhibitor against cysteine proteases. Herein, we report on the non-covalent to the covalent adduct formation mechanism of α-ketoamide-based inhibitor with the enzyme active site amino acids by QM/SQM model (QM = quantum mechanical, SQM = semi-empirical QM). To uncover the mechanism, we focused on two approaches: a concerted and a stepwise fashion. The concerted pathway proceeds via deprotonation of the thiol of cysteine (here, Cys145 SγH) and simultaneous reversible nucleophilic attack of sulfur onto the α-ketoamide warhead. In this work, we propose three plausible concerted pathways. On the contrary, in a traditional two-stage pathway, the first step is proton transfer from Cys145 SγH to His41 Nδ forming an ion pair, and consecutively, in the second step, the thiolate ion attacks the α-keto group to form a thiohemiketal. In this reaction, we find that the stability of the tetrahedral intermediate oxyanion/hydroxyl group plays an important role. Moreover, as the α-keto group has two faces Si or Re for the nucleophilic attack, we considered both possibilities of attack leading to S- and R-thiohemiketal. We computed the structural, electronic, and energetic parameters of all stationary points including transition states via ONIOM and pure DFT method. Additionally, to characterize covalent, weak noncovalent interaction (NCI) and hydrogen-bonds, we applied NCI-reduced density gradient (NCI-RDG) methods along with Bader's Quantum Theory of Atoms-in-Molecules (QTAIM) and natural bonding orbital (NBO) analysis

Synthesis, characterization, and investigation of the antioxidant activity of some 1,2,4-benzothiadiazine-1,1-dioxides bearing sulfonylthioureas moieties

A series of 1,2,4-benzothiadiazine-1,1-dioxides bearing a sulfonylthiourea moiety were synthesized, characterized, and screened for their antioxidant activity, using six antioxidant analytical assays comparatively to reference compounds, ascorbic acid and quercetin. The results indicated that several compounds demonstrated strong antioxidant activity in DPPH, ABTS, H2O2, and lipid peroxidation assays where some of them were either as active as or more active than reference compounds. However, all compounds were largely less active than references compounds in the reducing power assay. The results indicated that the thiourea moiety probably played a crucial role in the antioxidant activity of the target compounds, as a thiolate ion. The most favorable R1groups were the hydrogen atom and methyl group, followed by phenyl and benzyl groups, whereas the most favorable R2group was iPr, followed by the phenyl and methyl groups. The combination of benzothiadiazine ring with sulfonylthiourea moieties led to valuable new antioxidants, which could be used in the treatment or the prevention of certain diseases or in the field of cosmetics, which needs further investigations in the future.

Modulating Thiol p Ka Promotes Disulfide Formation at Physiological pH: An Elegant Strategy To Design Disulfide Cross-Linked Hyaluronic Acid Hydrogels.

The disulfide bond plays a crucial role in protein biology and has been exploited by scientists to develop antibody-drug conjugates, sensors, and for the immobilization other biomolecules to materials surfaces. In spite of its versatile use, the disulfide chemistry suffers from some inevitable limitations such as the need for basic conditions (pH > 8.5), strong oxidants, and long reaction times. We demonstrate here that thiol-substrates containing electron-withdrawing groups at the β-position influence the deprotonation of the thiol group, which is the key reaction intermediate in the formation of disulfide bonds. Evaluation of reaction kinetics using small molecule substrate such as l-cysteine indicated disulfide formation at a 2.8-fold higher ( k1 = 5.04 × 10-4 min-1) reaction rate as compared to the conventional thiol substrate, namely 3-mercaptopropionic acid ( k1 = 1.80 × 10-4 min-1) at physiological pH (pH 7.4). Interestingly, the same effect could not be observed when N-acetyl-l-cysteine substrate ( k1 = 0.51 × 10-4 min-1) was used. We further grafted such thiol-containing molecules (cysteine, N-acetyl-cysteine, and 3-mercaptopropionic acid) to a biopolymer namely hyaluronic acid (HA) and determined the p Ka value of different thiol groups by spectrophotometric analysis. The electron-withdrawing group at the β-position reduced the p Ka of the thiol group to 7.0 for HA-cysteine (HA-Cys); 7.4 for N-acetyl cysteine (HA-ActCys); and 8.1 for HA-thiol (HA-SH) derivatives, respectively. These experiments further confirmed that the concentration of thiolate (R-S-) ions could be increased with the presence of electron-withdrawing groups, which could facilitate disulfide cross-linked hydrogel formation at physiological pH. Indeed, HA grafted with cysteine or N-acetyl groups formed hydrogels within 3.5 min or 10 h, respectively, at pH 7.4. After completion of cross-linking reaction, both gels demonstrated a storage modulus G' ≈ 3300-3500 Pa, which indicated comparable levels of cross-linking. The HA-SH gel, on the other hand, did not form any gel at pH 7.4 even after 24 h. Finally, we demonstrated that the newly prepared hydrogels exhibited excellent hydrolytic stability but can be degraded by cell-directed processes (enzymatic and reductive degradation). We believe our study provides a valuable insight on the factors governing the disulfide formation and our results are useful to develop strategies that would facilitate generation of stable thiol functionalized biomolecules or promote fast thiol oxidation according to the biomedical needs.

Colorimetric sensing of cyanide ion by pyromellitic diimides synthesized in one step from commercially available reactants

Several pyromellitic diimides (PMDIs) containing different groups including thiol, carboxyl, hydroxyl, and alkyl as N-substituent were synthesized from commercially available reactants in one step, and their interactions with anions like CN¯ and F¯ were studied. The investigation indicated that the anions more basic than RS¯ trigger generation of colorful radical anion in diimides bearing thiol group as N-substituent. The study of mechanism using various techniques such as spectroelectrochemical analysis and UV–vis spectroscopy suggested deprotonation of thiol by anion, followed by electron transfer (ET) from thiolate ion to carbonyl as a probable mechanism. The proposed mechanism was further approved through theoretical study. The geometry optimization of diimide/CN¯ system resulted in complete deprotonation of thiol by CN¯ as a stable structure. Also, the calculation of HOMO and LUMO levels for diimide, its anion, and CN¯ showed that deprotonation make intramolecular ET more feasible, while decreasing the probability of intermolecular ET. Thereafter, in order to develop a new sensor for CN¯, the selectivity and sensitivity of diimides possessing thiol group were tested. The results indicated that although these diimides can be applied as a sensor to differentiate CN¯ from many anions at a micro-level concentration, they undergo the same reaction with any anion more basic than HS¯. The present study did not only introduce a novel indicator for CN¯ (or any anion more basic than RS¯), but also provided new insights into the interaction of anions with aromatic diimides (ADs).

Molecular characterization of two alkylresorcylic acid synthases from Sordariomycetes fungi

Two putative type III polyketide synthase genes (PKS) were identified from Sordariomycetes fungi. These two type III PKS genes from Sordaria macrospora (SmPKS) and Chaetomium thermophilum (CtPKS), shared 59.8% sequence identity. Both, full-length and truncated versions of type III PKSs were successfully cloned and overexpressed in a bacterial host, Escherichia Coli BL21 (DE3) using a N-terminus hexa-histidine tag. The full-length and the truncated construct of PKSs showed similar activity profiles, suggesting that additional amino acid residues at the C-terminal of both SmPKS and CtPKS may not be involved in catalytic functions. We demonstrate that these two recombinant polyketide synthases could efficiently synthesize tri- and tetraketide pyrones, resorcinols and resorcylic acids using various acyl-CoAs (C4–C20) as starter units. The truncated S. macrospora polyketide synthases (TrSmPKS) showed a maximum of 7.0 × 104 s−1 M−1 catalytic efficiency towards stearoyl-CoA.Whereas, truncated C. thermophilum polyketide synthases (TrCtPKS) preferred the long-chain acyl-CoA starter arachidoyl-CoA, to produce pentaketide and hexaketide resorcinols with a high catalytic efficiency of 6.2 × 104 s−1 M−1. Homology model and substrate docking analyses suggest a shorter distance between sulfur of catalytic Cys152 and thioester carbonyl group of arachidoyl-CoA as well as stronger imidazolium–thiolate ion pair distance in TrCtPKS between catalytic Cys152-His309 compared to TrSmPKS- arachidoyl CoA complex. Enhanced binding interactions of CtPKS residues forming intermolecular contacts at the active site could be attributed to its high specificity towards arachidoyl-CoA. This study reports the functional characterization of two fungal type III polyketide synthases, SmPKS and CtPKS with high catalytic efficiency from S. macrospora and C. thermophilum respectively. Furthermore, the results suggested that the both SmPKS and CtPKS could be attractive targets for protein engineering to discern the unique substrate specificity and catalytic efficiency.

One-Step Synthesis of 2-Alkenecarbodithioate Esters from Substituted Propargyl Ethers, and Their Conversion into Isothiazole Ring through a [4+1] Type Oxidative Ring Closure

Treatment of substituted propargyl methyl ethers with a base and elemental sulfur in the presence of a thiolate ion afforded 2-alkenecarbodithioate esters in good yields. The reaction is assumed to proceed through a pathway involving in situ generation of propadienethione intermediates. Further conversion of 2-alkenecarbodithioate esters into 2,3-dihydroisothiazoles were efficiently performed by treating with chloramine-T through a [4+1] type oxidative ring closure via thiocarbonyl S-tosylimides.

Solvent-catalyzed umpolung carbonsulfur bond-forming reactions by nucleophilic addition of thiolate and sulfinate ions to in situ–derived nitrosoalkenes in deep eutectic solvents

The low transition temperature mixture formed by lactic acid and choline chloride proved to be effective for an umpolung carbonsulfur bond formation at the α-position of α-chloro oximes. Aliphatic, aromatic, and heteroaromatic thiolate and sulfinate ions can be smoothly added to in situ–derived nitrosoalkenes affording the corresponding sulfenylated or sulfonylated adducts, respectively, in a very good yield (up to >98%). This methodology offers the advantage of working at room temperature and under air in biodegradable and cost-effective reaction mixtures, which can be used both as solvents and catalysts (20 mol %), thereby avoiding the use of anhydrous, hazardous volatile organic solvents and an inert atmosphere.

Density Functional Theory-Based First Principles Calculations of Rhododendrol-Quinone Reactions: Preference to Thiol Binding over Cyclization

Using density functional theory-based first principles calculations, we investigated the changes in the energetics and electronic structures of rhododendrol (RD)-quinone for the initial step of two important reactions, viz., cyclization and thiol binding, to give significant insights into the mechanism of the cause of cytotoxic effects. We found that RD-quinone in the electroneutral structure cannot undergo cyclization, indicating a slow cyclization of RD-quinone at neutral pH. Furthermore, using methane thiolate ion as a model thiol, we found that the oxidized form of the cyclized RD-quinone, namely RD-cyclic quinone, exhibited a reduced binding energy for thiols. However, this reduction of binding energy is clearly smaller than the case of dopaquinone, which is a molecule originally involved in the melanin synthesis. This study clearly shows that RD-quinone has a preference toward thiol bindings than cyclization compared to the case of dopaquinone. Considering that thiol bindings have been reported to i...

Iron(ii) complexes of 2-mercaptopyridine as rubredoxin site analogues.

The synthesis, characterization and reactivity studies of iron(ii) complexes [FeII(PySH)4](OTf)2, 1-(OTf)2, [FeII(PySH)4](ClO)4, 1-(ClO4)2, and [FeII(PyS)2]n, (2), of a 2-mercaptopyridine (PySH) ligand are discussed. The X-ray crystal structures of both 1-(OTf)2 and 1-(ClO4)2 reveal a distorted tetrahedral geometry at the iron(ii) center with identical constituents. All the pyridine nitrogen atoms are protonated and thiolate ions are coordinated to the iron(ii) center. The structure and function of complex 1-(OTf)2 or 1-(ClO4)2 resembles the active site of rubredoxin. Complex 2 has octahedral geometry at the iron(ii) center forming a 1-D coordination polymer. Complex 1-(OTf)2 exhibits a high positive redox potential (E1/2 = 0.23 V vs. Ag/AgCl) which reduces to -0.12 V in the presence of triethylamine under an inert atmosphere. This change of the redox potential is highly reversible in the presence of a weak acid such as p-toluenesulfonic acid, pTsOH. DFT studies show that the complex cation [FeII(PySH)4]2+ upon treatment with a base converts to its anionic congener, [FeII(PyS)4]2-, via the deprotonation of the pyridinium moiety. The iron(ii) complexes readily react with molecular oxygen to yield the corresponding iron(iii) complex, which rapidly decays to form pyridine disulphide (Py2S2) and an iron(ii) complex.

Inactivation Kinetics and Structural Changes of High Pressure Treated Actinidin

Plant sulfydryl proteases such as actinidin are mainly used as meat tenderisers, milk clotting agents for the development of novel dairy products and proteolytic agents in biotechnological procedures. The main issue with regards their application is the method for the control of their enzymatic activity after the desired extent of proteolysis, considering that thermal treatment is not applicable. High Pressure (HP) processing could be applied for the enzyme activity regulation. Actinidin, extracted from kiwi fruit (Hayward var., A. chinensis), was purified using anion-exchange and gel filtration chromatography. After purification procedure, only one single peak was finally received for this enzyme corresponding to a protein of molecular mass of 24 kDa with an isoelectric point equal to or lower than 3.5. The effect of HP (500–900MPa and 50- 70°C) on the remaining activity of purified actinidin in phosphate buffer solution (pH 6.0) was studied. Inactivation of purified actinidin was described by a first-order kinetic model both for thermal and HP treatment at the studied processing conditions. Aiming at an optimal process design, a composite mathematical model, which describes the actinidin inactivation rate as a function of pressure and temperature conditions, taking into account the dependence of both activation energy and activation volume on the applied pressure and temperature respectively, was used. HP-induced conformational changes of the purified actinidin were also investigated using Circular Dichroism spectroscopy (CD). A direct comparison of the CD results for the treated and the untreated enzymes reveals that reversible changes were depicted in the far- and near-UV. It is suggested that the exposure to HP may affect the linkage between thiolate ion of cysteine group and positively charged nitrogen of the imidazole group of the active site of actinidin leading to the reduction of the enzyme activity.

The paradoxical influence of the pKa on the reactivity of thiols and its biological relevance

Background. Not much is known about the factors that influence thiol reactivity. In this paper we will investigate the paradoxical influence of the acid dissociation constant (pKa). The pKa influences the deprotonation of a compound. This deprotonation gives thiols a negative charge and therefore increases reactivity. Compounds with a low pKa have a higher percentage of deprotonation, this will lead to a higher reactivity. On the other side, thiols with a higher pKa have a higher electron density, and are therefore also more reactive. We want to recognize this paradox and investigate what the exact contribution of these two paradoxical mechanisms is with respect to the reactivity of thiols. Furthermore we will discuss the biological importance of this study with respect to the anti-oxidant system and drug conjugation. Methods. The reactivity of the thiols was determined by calculating the rate constant of these compounds. This was done for different thiols in reaction with 1-chloro-2,4- dinitrobenzene. To do this we created a pseudo first order reaction by adding an excess of CDNB. The thiols we used in this reaction were glutathione, 5-thio-2-nitrobenzoic acid, 2-mercaptoethanol and 2-mercaptobenzothiazole. The reaction rates were measured, using a spectrophotometer and eventually the reaction constant was calculated and transformed into the reactivity of the thiolate ion. Results. The reaction constants from the different thiols are dependent on the fraction thiolate ion. This was converted to the reactivity of the thiolate ion. The reactivity of thiolate ion decreases as pKa value increases. Conclusion. There is indeed a paradoxical influence of the pKa value on the reactivity of thiols. Increases in pKa lead to decreases in reactivity of the thiolate ion but to increases in the fraction of the thiolate ion. Eventually there was no mechanism that had the biggest contribution to the reactivity for all conditions. Apparently this is dependent on the pH. We advice drug researchers to keep this paradox in mind in order to estimate the reactivity of thiols.

A kinetic study of the oxidations of 2-mercaptoethanol and 2-mercaptoethylamine by heteropoly 11-tungsto-1- vanadophosphate in aqueous acidic medium

The kinetics of oxidation of 2-mercaptoethanol and 2-mercaptoethylamine by the heteropoly 11-tungsto-1- vanadophosphate anion, [PVVW11O40]4−, have been studied spectrophotometrically in aqueous perchloric acid at 25 °C. EPR and optical studies show that [PVVW11O40]4− is reduced to the one-electron reduced heteropoly blue, [PVIVW11O40]5−, whilst the thiols are oxidized to the corresponding disulphides, RSSR. Spectrophotometric titrations show that the stoichiometry of both reactions is 1:1. At constant pH, the reactions show simple second-order kinetics with first-order dependence of rate on both [oxidant] and [thiol]. At constant [thiol], the rate of the reaction increases with increasing pH. Plots of kobs/[thiol]t versus 1/[H+] are linear with finite intercepts, showing that both the undissociated thiol (RSH) and thiolate ion (RS−) are reactive species. Generation of RS· from RSH proceeds via a separated-concerted proton–electron transfer mechanism. The reaction of thiolate ion is a simple outer-sphere electron transfer reaction. By applying the Marcus theory, the self-exchange rate constants for the couples HOCH2CH2S·/HOCH2CH2S− and H3N+CH2CH2S·/H3N+CH2CH2S− were evaluated as 3 × 109 and 2.2 × 108 M−1 s−1, respectively, at 25 °C.

Synthesis, structure and reactivity of iron(II) clathrochelates with terminal formyl (acetal) groups

3- and 4-Formylphenylboron-capped aliphatic iron(II) clathrochelates were obtained by direct template condensation of the corresponding α-dioxime with 3- and 4-formylphenylboronic acids on an iron(II) ion as a matrix under mild reaction conditions in methanol or acetonitrile media; with methanol as a solvent, such one-pot reactions gave also their acetals. The latters were converted to the formyl-terminated iron(II) clathrochelates by H+-catalyzed hydrolysis. The reactive formyl-terminated cage complexes obtained underwent their further H+-catalyzed condensation with isoniazid as a hydrazone component giving the hydrazonate cage complexes with vector apical substituents of this type. The formyl-terminated iron(II) hexachloroclathrochelate was synthesized by template reaction of dichloroglyoxime on an iron(II) ion with 3-formylphenylboronic acid. Nucleophilic substitution of its reactive chlorine atoms with thiolate ions generated in situ from para-mercaptobenzoic acid afforded hexasulfide iron(II) cage complex with six ribbed para-mercaptobenzoic substituents and formyl groups in its apical substituents. The iron(II) complexes synthesized were characterized using elemental analysis, MALDI–TOF mass spectrometry, IR, UV–Vis, 1H and 13C{1H} NMR spectroscopies and by X-ray crystallography (for three aliphatic macrobicyclic acetals).

Human furin Cys198 imposes dihedral and positional restraints on His194 for optimal Ser386-proton transfer

Inhibitors of human furin may represent the clinical remedy for very aggressive cancer, viral, and bacterial infections. Most of the currently available inhibitors are weak in terms of potency, drug-likeness, and furin specificity thereby necessitating the development of newer compounds especially mechanism-based inhibitors. Here, the roles of active site Cys198 (C198), His194 (H194), and Ser386 (S386) were investigated using computational-site-directed mutagenesis and molecular dynamics (MD) simulation. Data were obtained from six (6) biosystems: wildtype (C198/S386), furin-C198G (S386), furin-S386G (C198), and their peptide (nascent hydrolyzed peptide H2N-RTRR-CO2) bound complexes. The results strongly supported that in wildtype furin but not S386G and C198G mutants, following S386/scissile carbon attack (4.0 Å), the peptide retracted from the active site, representing peptide release post hydrolysis. Furthermore, in S386G mutant, C194 side chain thiolate ion may act as the nucleophile replacement but competing electron-rich centers (H194, H364) and energetically unattainable geometric strain on the peptide may constitute the limiting factors. In biosystems not complexed with peptide (representative of pre-attack state), C198 preferentially engaged H194 imidazole moiety via sulfur–π bond system causing a dihedral and positional restraints on the imidazole ring for ultimate alignment of its NE2 hydrogen atom with the side chain enolate oxygen of S364 required for optimal proton transfer. In summary, small-molecular-weight compounds with dual serine and cysteine protease inhibitory actions may represent a new class of potent and furin-selective compounds for future clinical applications.

Mathematical model for reactive recovery of invertase by chemical permeabilization of baker's yeast

BACKGROUND Cell permeabilization techniques allow selective release of an enzyme and specific reactions without breaking the cells. A mathematical model has been developed for selective permeabilization of Saccharomyces cerevisiae to recover invertase at high purity. The effect of thiols on the cell walls of S. cerevisiae was studied under different conditions of pH, cysteine concentration, speed of agitation and solid suspension density. RESULT The rate of release of invertase was a function of pH and cysteine (or thiolate ion) concentration.The maximum recovery of invertase was obtained at pH 10.0, 10 mmol dm−3 cysteine concentration and 15% (w/v) yeast loading. CONCLUSION Thiols are capable of permeabilizing the cell walls of S. cerevisiae and releasing the invertase under basic conditions. The insignificant effect of agitation shows that the external mass transfer resistance does not play any role in the release of invertase. © 2015 Society of Chemical Industry

ChemInform Abstract: One‐Pot Synthesis of Functionalized β‐Amino Sulfides/β‐Amino Selenides via Ring Opening of Cyclic Sulfamidates.

AbstractIn—situ formed thiolate ions from rongalite react in a highly stereospecific manner at the C—O bond yielding enantiopure products in good to excellent yields.