Exploring the Biocatalytic Scope of Alditol Oxidase from Streptomyces coelicolor

The substrate scope of the flavoprotein alditol oxidase (AldO) from Streptomyces coelicolor A3(2), recombinantly produced in Escherichia coli, was explored. While it has been established that AldO efficiently oxidizes alditols to D ‐aldoses, this study revealed that the enzyme is also active with a broad range of aliphatic and aromatic alcohols. Alcohols containing hydroxy groups at the C‐1 and C‐2 positions like 1,2,4‐butanetriol (K_m=170 mM, k_cat=4.4 s⁻¹), 1,2‐pentanediol (K_m=52 mM, k_cat=0.85 s⁻¹) and 1,2‐hexanediol (K_m=97 mM, k_cat=2.0 s⁻¹) were readily accepted by AldO. Furthermore, the enzyme was highly enantioselective for the oxidation of 1,2‐diols [e.g., for 1‐phenyl‐1,2‐ethanediol the (R)‐enantiomer was preferred with an E‐value of 74]. For several diols the oxidation products were determined by GC‐MS and NMR. Interestingly, for all tested 1,2‐diols the products were found to be the α‐hydroxy acids instead of the expected α‐hydroxy aldehydes. Incubation of (R)‐1‐phenyl‐1,2‐ethanediol with ¹⁸O‐labelled water (H₂¹⁸O) revealed that a second enzymatic oxidation step occurs via the hydrate product intermediate. The relaxed substrate specificity, excellent enantioselectivity, and independence of coenzymes make AldO an attractive enzyme for the preparation of optically pure 1,2‐diols and α‐hydroxy acids.     

Engineering a Highly Active Sucrose Isomerase for Enhanced Product Specificity by Using a “Battleship” Strategy

The sucrose isomerase SmuA from Serratia plymuthica efficiently catalyses the isomerisation of sucrose into isomaltulose, an artificial sweetener used in the food industry. However, the formation of a hygroscopic by-product, trehalulose, necessitates additional separation to obtain a crystalline product. Therefore, we have improved the product specificity of SmuA by first introducing a few exploratory amino acid exchanges around the active site and investigating their influence. Then, we devised a second set of mutations, either at promising positions from the preceding cycle, but with a different side chain, or at alternative positions in the vicinity. After seven iterative cycles involving just 55 point mutations, we obtained the triple mutant Y219L/D398G/V465E which showed 2.3 times less trehalulose production but still had high catalytic efficiency (k_cat/K_M=11.8 mM⁻¹ s⁻¹). Not only does this mutant SmuA appear attractive as an industrial biocatalyst, but our semirational protein-engineering strategy, which resembles the battleship board game, should be of interest for other challenging enzyme optimization endeavours.     

Acyl-peptide releasing enzyme from Sulfolobus tokodaii (ST0779) as a novel promiscuous biocatalyst for aldol addition

This work, for the first time, demonstrated the catalytic promiscuity of an acyl-peptide releasing enzyme from Sulfolobus tokodaii (ST0779) for aldol addition reaction, which shows accelerated activity at elevated temperature. The turnover number k_cat (s^− 1) of this thermostable enzyme at 55 °C is 7.78-fold higher than that of porcine pancreatic lipase (PPL) at its optimum temperature of 37 °C, which is one of the best reported enzymes for promiscuous catalysis of aldol reaction; and the molecular catalytic efficiency k_cat/K_m (M^− 1 s^− 1) adds up to 140 times higher than PPL.     

Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPS^T in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 10¹⁰ M⁻¹ s⁻¹. The CH₂C(CH₃)₂OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 10⁹ M⁻¹ s⁻¹) with ZnTPPS^T to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH₃)₂COH radical reduces both ZnTPPS (k = 1 × 10⁸ M⁻¹ s⁻¹) and ZnTPPS^T (k = 3 × 10⁹ M⁻¹ s⁻¹) to the anion radical (ZnTPPS)⁻. The radical Br⁻₂ oxidizes both states to the cation radical (ZnTPPS)⁺ with k = 8 × 10⁸ M⁻¹ s⁻¹ for the ground state and 5 × 10⁹ M⁻¹ s⁻¹ for the triplet. The transient cation Cd⁺ reduces both states with a diffusion-controlled rate (k = 1 × 10¹⁰ M⁻¹ s⁻¹) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.     

A Single Second Shell Amino Acid Determines Affinity and Kinetics of Linagliptin Binding to Type 4 Dipeptidyl Peptidase and Fibroblast Activation Protein

Drugs targeting type 4 dipeptidyl peptidase (DPP-4) are beneficial for glycemic control, whereas fibroblast activation protein alpha (FAP-α) is a potential target for cancer therapies. Unlike other gliptins, linagliptin displays FAP inhibition. We compared biophysical and structural characteristics of linagliptin binding to DPP-4 and FAP to better understand what differentiates linagliptin from other gliptins. Linagliptin exhibited high binding affinity (K_D) and a slow off-rate (k_off) when dissociating from DPP-4 (K_D 6.6 pM; k_off 5.1×10⁻⁵ s⁻¹), and weaker inhibitory potency to FAP (K_D 301 nM; k_off>1 s⁻¹). Co-structures of linagliptin with DPP-4 or FAP were similar except for one second shell amino acid difference: Asp663 (DPP-4) and Ala657 (FAP). pH dependence of enzymatic activities and binding of linagliptin for DPP-4 and FAP are dependent on this single amino acid difference. While linagliptin may not display any anticancer activity at therapeutic doses, our findings may guide future studies for the development of optimized inhibitors.     

A potential antitumor drug (arginine deiminase) reengineered for efficient operation under physiological conditions

Arginine deiminase (ADI, EC 3.5.3.6) is a potential antitumor drug for the treatment of arginine‐auxotrophic tumors such as hepatocellular carcinomas (HCCs) and melanomas, and studies on human lymphatic leukemia cell lines have confirmed that ADI has antiangiogenic activity. Recent studies showed that a combination of taxane and ADI‐PEG20, which induces caspase‐independent apoptosis, is more effective than taxane monotherapy for prostate cancer. The main limitation of ADI from Pseudomonas plecoglossicida (PpADI) and of many other ADI enzymes lies in their pH‐dependent activity profile. PpADI has a pH optimum at 6.5 and a pH shift from 6.5 to 7.5 results in an ～80 % activity drop (the pH of human plasma is 7.35 to 7.45). In 2010, we reported a proof of concept for ADI engineering by directed evolution that resulted in variant M2 (K5T/D44E/H404R). M2 has a pH optimum of pH 7.0, a fourfold higher k_cat value than the wild‐type PpADI (pH 7.4, 0.5 M phosphate buffer), and an increased K_m value for substrate arginine. In our latest work, variants M5 (K5T/D38H/D44E/A128T/H404R) and M6 (K5T/D38H/D44E/A128T/E296K/H404R) were generated by directed evolution by employing PBS buffer (pH 7.4), which mimics physiological conditions. The S_0.5 value of parent M3 (K5T/D44E/A128T/H404R) decreased from 2.01 to 1.48 mM (M5) and 0.81 mM (M6). The S_0.5 value of M6 (0.81 mM ) is lower than that of wild‐type PpADI (1.30 mM ); the k_cat values improved from 0.18 s^?1 (wild‐type PpADI) to 17.56 s^?1 (M5, 97.6‐fold) and 11.64 s^?1 (M6, 64.7‐fold).     

Discovery and Engineering of a Novel Baeyer-Villiger Monooxygenase with High Normal Regioselectivity

Baeyer-Villiger monooxygenases (BVMOs) are remarkable biocatalysts for the Baeyer-Villiger oxidation of ketones to generate esters or lactones. The regioselectivity of BVMOs is essential for determining the ratio of the two regioisomeric products (“normal” and “abnormal”) when catalyzing asymmetric ketone substrates. Starting from a known normal-preferring BVMO sequence from Pseudomonas putida KT2440 (PpBVMO), a novel BVMO from Gordonia sihwensis (GsBVMO) with higher normal regioselectivity (up to 97/3) was identified. Furthermore, protein engineering increased the specificity constant (k_cat/K_M) 8.9-fold to 484 s⁻¹ mM⁻¹ for 10-ketostearic acid derived from oleic acid. Consequently, by using the variant GsBVMO_C308L as an efficient biocatalyst, 10-ketostearic acid was efficiently transformed into 9-(nonanoyloxy)nonanoic acid, with a space-time yield of 60.5 g L⁻¹ d⁻¹. This study showed that the mutant with higher regioselectivity and catalytic efficiency could be applied to prepare medium-chain ω-hydroxy fatty acids through biotransformation of long-chain aliphatic keto acids derived from renewable plant oils.     

Comparative Biochemistry of Four Polyester (PET) Hydrolases**

The potential of bioprocessing in a circular plastic economy has strongly stimulated research into the enzymatic degradation of different synthetic polymers. Particular interest has been devoted to the commonly used polyester, poly(ethylene terephthalate) (PET), and a number of PET hydrolases have been described. However, a kinetic framework for comparisons of PET hydrolases (or other plastic-degrading enzymes) acting on the insoluble substrate has not been established. Herein, we propose such a framework, which we have tested against kinetic measurements for four PET hydrolases. The analysis provided values of k_cat and K_M, as well as an apparent specificity constant in the conventional units of M⁻¹s⁻¹. These parameters, together with experimental values for the number of enzyme attack sites on the PET surface, enabled comparative analyses. A variant of the PET hydrolase from Ideonella sakaiensis was the most efficient enzyme at ambient conditions; it relied on a high k_cat rather than a low K_M. Moreover, both soluble and insoluble PET fragments were consistently hydrolyzed much faster than intact PET. This suggests that interactions between polymer strands slow down PET degradation, whereas the chemical steps of catalysis and the low accessibility associated with solid substrate were less important for the overall rate. Finally, the investigated enzymes showed a remarkable substrate affinity, and reached half the saturation rate on PET when the concentration of attack sites in the suspension was only about 50 nM. We propose that this is linked to nonspecific adsorption, which promotes the nearness of enzyme and attack sites.     

Biochemical Characterization of Purified Esterase from Soybean (Glycine max) Seed

Alkaline esterase (carboxylic‐ester hydrolases; EC 3.1.1.1) extracted from germinated soybean seeds (Glycine max) was purified approximately 3.6 times by chromatography in a DEAE‐cellulose anion exchange column and filtration in Sephadex G100 gel. The molecular mass of the enzyme was estimated at 45 kDa by gel electrophoresis (SDS‐PAGE). The purified enzyme showed a specific activity of 5.6 U mg^?1 using p‐nitrophenyl butyrate as substrate. The esterase showed optimal activity at 47 °C in moderately alkaline pH, low stability in temperatures higher than 50 °C, and high stability at pH values between 6 and 9.5. The Ca²⁺ and Co²⁺ ions proved to have a positive effect on enzyme activity; however, Hg²⁺ completely inhibited esterase activity. Using p‐nitrophenyl butyrate as substrate, the enzyme showed a K_m of 0.39 mM, V_max of 31.5 mM mg^?1 min^?1 and k_cat 7.60 × 10⁶ s^?1. Regarding substrate affinity, the enzyme showed greater activity for substrates containing short‐chain fatty acids, especially p‐nitrophenyl acetate. Such characteristics give the enzyme great potential for application in the production of low molecular weight esters, in the food industry, and in chemical products. This enzyme is another new member of the family of lipases and esterases from vegetable seeds with high activity and stability in alkaline pH.     

α-Multistriatin: The First Total Synthesis of a Natural Product via Antibody Catalysis

The relevance of antibody catalysis to synthetic organic chemistry is demonstrated here by an efficient total synthesis of (–)-α-multistriatin, the aggregation pheromone of the European elm bark beetle, Scolytus multistriatus, which is the principal vector of the Dutch elm disease, responsible for the severe devastation of the elm population in Europe and North America. The key step in our synthesis of this natural product is an antibody-catalyzed, enantioselective protonolysis of an enol ether to produce a branched ketone. The latter is obtained with an (S) configuration in greater than 99% enantiomeric excess. Catalysis follows Michaelis-Menten kinetics (K_m = 230 μM, k_cat = 0.36 min⁻¹) and useful rate enhancement (k_cat/k_un = 65,000 at pH 6.5). This abzymic step is followed by twelve chemical steps, with all four asymmetric centers originating from the chirality achieved in the antibody-catalyzed reaction. That specific step is a unique example of a chemical transformation which is difficult to achieve either by an available synthetic methodology or via catalysis with a known enzyme. The synthetic pheromone has been checked in field experiments and found as active as the naturally occurring compound in attracting the European elm bark beetles.     

Hydrogen Atom Attack on Fluorotoluenes: Rates of Fluorine Displacement

Rates of hydrogen atom attack on o-fluorotoluene (o-FTOL) and m-fluorotoluene (m-FTOL) at temperatures of 988–1144 K and pressures of 2–2.5 bar have been determined in a single-pulse shock tube study. Hydrogen atoms, generated from the decomposition of hexamethylethane, were allowed to react with the substrates and the characteristic products observed. Rate constants for two reaction channels, displacement of fluorine or methyl, were determined relative to displacement of methyl from 1, 3,5-trimethylbenzene (135TMB). Evidence is presented that abstraction of F is unimportant over the studied temperature range. With k(H + 135TMB → m-xylene + CH₃) = 6.7 × 10¹³ exp(–3255/T) cm³ mol⁻¹s⁻¹, the following rate expressions have been derived: k(H + o-FTOL → C₆H₅CH₃ + F) = 8.38 × 10¹³ exp(–6041/T) cm³ mol⁻¹s⁻¹; (1012–1142 K) k(H + o-FTOL → C₆H₅F + CH₃) = 2.37 × 10¹³ exp(–2938/T) cm³ mol⁻¹s⁻¹; (988–1142 K) k(H + m-FTOL → C₆H₅CH₃ + F) = 1.33 × 10¹⁴ exp(–6810/T) cm³ mol⁻¹s⁻¹; (1046–1144 K) k(H + m-FTOL → C₆H₅F + CH3) = 2.04 × 10¹³ exp(–3104/T) cm³ mol⁻¹s⁻¹; (1008–1144 K) Uncertainties in the relative rate constants are estimated to be factors of about 1.1, while the above absolute values have estimated expanded uncertainties of about a factor of 1.4 in rate, 10 kJ mol⁻¹ in the activation energy, and a factor of 3 in the A-factor. The present data are compared with relevant literature data. From our data and the thermochemistry, a model of the elementary steps comprising displacement of F is developed. On the basis of the model fit to our data, rate constants for the addition of atomic fluorine to toluene at 1100 K are derived. Rate expressions for fluorination reactions of toluene are also determined. The significance of the present results is discussed in the context of the formation of fluorinated byproducts in high-temperature systems.     

Catalysis by Dihydrofolate Reductase from the Psychropiezophile Moritella profunda

The influence of temperature and pH on the stability and catalytic activity of dihydrofolate reductase (MpDHFR) from the cold‐adapted deep‐sea bacterium Moritella profunda was studied. The thermal melting temperature was found to be ～38 °C and was not affected by pH, while activity measurements demonstrated that its stability was maximal at pH 7 and was reduced dramatically below pH 6 or above pH 8. The steady‐state rate constant (k_cat) was maximal at neutral pH and higher temperatures, while the Michaelis constants (K_M) for both substrate and cofactor were optimal at lower temperatures and at elevated or reduced pH. For both temperature and pH, any change in k_cat was therefore offset by a similar change in K_M. Both the activation enthalpy and entropy of the MpDHFR‐catalysed reaction were lower than those of DHFR from E. coli leading overall to a very small difference in activation free energy and therefore similar steady‐state rate constants at the same temperature. The chemical step of the reaction is not rate limiting at pH 7, but becomes progressively more rate limiting as the pH increases. These results demonstrate adaptation of MpDHFR to its environment and show compromises between enthalpic and entropic contributions to the reaction, and between k_cat and K_M.     

A novel non-enzymatic hydrogen peroxide sensor based on single walled carbon nanotubes–manganese complex modified glassy carbon electrode

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20–100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1–12). The surface coverages and heterogeneous electron transfer rate constants (k_s) of immobilized Mn-complex were approximately 1.58 × 10⁻¹⁰ mole cm⁻² and 48.84 s⁻¹. The modified electrode showed excellent electrocatalytic activity toward H₂O₂ reduction. Detection limit, sensitivity, linear concentration range and k_cat for H₂O₂ were, 0.2 μM and 692 nA μM⁻¹ cm⁻², 1 μM to 1.5 mM and 7.96(±0.2) × 10³ M⁻¹ s⁻¹, respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability.     

Synthesis and Characterization of Pyridine Compounds for Amperometric Measurements of Leukocyte Esterase

We introduce a new class of substrates (compounds I – III ) for leukocyte esterase (LE) that react with LE yielding anodic current in direct proportion to LE activity. The kinetic constants K_m and k_cat for the enzymatic reactions were determined by amperometry at a glassy carbon electrode. The binding affinity of I – III for LE was two orders of magnitude better than that of existing optical LE substrates. The specificity constant k_cat/K_m was equal to 2.7, 3.8, and 5.8×10⁵ m ^?1 s^?1 for compounds containing the pyridine ( I ), methoxypyridine ( II ), and (methoxycarbonyl)pyridine ( III ), respectively, thus showing an increase in catalytic efficiency in this order. Compound III had the lowest octanol/water partition coefficient (log p=0.33) along with the highest topological surface area (tPSA=222 Ų) and the best aqueous solubility (4.0 mg mL^?1). The average enzymatic activity of LE released from a single leukocyte was equal to 4.5 nU when measured with compound III .     

A Shock Tube Study of the Reactions of H Atoms with COS,CS2, and H2S

Reactions of H atoms with COS, CS₂, and H₂S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurements of H atoms at L_α. The thermal decomposition of a few ppm ethyl iodide (C₂H₅I) was used as a H-atom source. In the presence of a large excess of the molecular reactant COS, CS₂, or H₂S, a consumption of H was observed which follows a pseudo first-order rate law. Rate coefficients for the reactions: were determined to be: k₁ = 2.4 × 10¹⁴exp(–3415 K/T) cm³mol⁻¹s⁻¹ k₂ = 1.4 × 10¹⁵exp(–9250 K/T) cm³mol⁻¹s⁻¹ k₃ = 2.5 × 10¹⁴exp(–2890 K/T) cm³mol⁻¹s⁻¹     

Immobilization of carbonic anhydrase on polyethylenimine/dopamine codeposited membranes

Carbonic anhydrase (CA) catalyzing CO₂ hydration has an important application in carbon capture, and its immobilization is very significant. Here, CA was covalently linked by glutaraldehyde (GA) to the surface of poly(vinylidene fluoride) (PVDF) and polyethylene (PE) membranes, which were previously modified via a simple codeposition of polyethyleneimine (PEI) and dopamine (DA). The effects of the modification conditions were investigated, and the membranes were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The immobilization process was optimized, and the catalytic properties of immobilized CA were studied. The results show that the optimal mass ratio of PEI and DA was 1:1 and the deposition time was 10–12 h, at which the surface amino group density could reach 1.278 × 10⁻⁷ and 1.397 × 10⁻⁷ mol/cm² for PVDF and PE, respectively. For enzyme immobilization, the optimal CA and GA concentrations were 0.2 mg/mL and 0.1 wt %, and a maximum activity recovery of about 53% and 76% could be achieved for PVDF-attached CA and PE-attached CA, respectively. Their K_m values were 10.62 mM and 8.6 mM, and the corresponding K_cat/K_m values were 132.2 M⁻¹ s⁻¹ and 312.9 M⁻¹ s⁻¹. After immobilization, the storage stability and reusability of CA were much improved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47784.     

New Insights into the Biosynthesis of Prenylated Xanthones: Xptb from Aspergillus nidulans Catalyses an O‐Prenylation of Xanthones

Gene‐inactivation experiments have indicated that the putative prenyltransferase XptB from Aspergillus nidulans was likely to be responsible for the prenylation of 1,7‐dihydroxy‐6‐methyl‐8‐hydroxymethylxanthone. Recently, it was suggested that this enzyme might also accept as substrate the benzophenone arugosin H, which is assumed to be a precursor of prenylated xanthones. In this study, five benzophenones and ten xanthones were incubated with purified recombinant XptB in the presence of dimethylallyl diphosphate (DMAPP). XptB accepted four xanthones as substrates, including the proposed natural substrate, and catalysed regiospecific O‐prenylations at C‐7 of the xanthone core. K_m values in the range of 0.081–1.1 mM and turnover numbers (k_cat) between 0.02 and 0.5 s^?1 were determined for the accepted xanthones. The kinetic parameters for DMAPP were found to be 0.024 mM (K_m) and 0.13 s^?1 (k_cat). Arugosin H was not accepted by XptB under the tested conditions. XptB was relatively specific towards its prenyl donor and did not accept geranyl or farnesyl diphosphate as substrate. Mn²⁺ and Co²⁺ strongly enhanced XptB activity (up to eightfold); this has not been reported before for prenyltransferases of the DMATS superfamily.     

Mechanistic Insights from Substrate Preference in Unsaturated Glucuronyl Hydrolase

Natural and synthetic unsaturated glucuronides were tested as substrates for Clostridium perfringens unsaturated glucuronyl hydrolase to probe its mechanism and to guide inhibitor design. Of the natural substrates, a chondroitin disaccharide substrate with sulfation of the primary alcohol on carbon 6 of its N‐acetylgalactosamine moiety was found to have the highest turnover number of any substrate reported for an unsaturated glucuronyl hydrolase, with k_cat=112 s^?1. Synthetic aryl glycoside substrates with electron‐withdrawing aglycone substituents were cleaved more slowly than those with electron‐donating substituents. Similarly, an unsaturated glucuronyl fluoride was found to be a particularly poor substrate, with k_cat/K_m=44 nM ^?1 s^?1—a very unusual result for a glycoside‐cleaving enzyme. These results are consistent with a transition state with positive charge at carbon 5 and the endocyclic oxygen, as anticipated in the hydration mechanism proposed. However, several analogues designed to take advantage of strong enzyme binding to such a transition state showed little to no inhibition. This result suggests that further work is required to understand the true nature of the transition state stabilised by this enzyme.     

Production and characterization of laccase and manganese peroxidase from the ligninolytic fungus Fomes sclerodermeus

Fomes sclerodermeus was grown on semi‐defined media based on yeast extract, peptone and glucose (YPG). The fungus produced a minimum basal level of laccase activity irrespective of culture medium. The highest laccase production (20 U cm^?3) was obtained in cultures supplemented with CuSO₄. Manganese peroxidase (MnP) could only be detected when MnSO₄ was added to the medium. None of the aromatic compounds tested stimulated further laccase or MnP production. Laccase and MnP stimulated by Cu²⁺ or Mn²⁺ respectively were purified. Two different laccase isoenzymes with the same molecular mass (67 kDa) and N‐linked carbohydrate content (3%) and a slight difference in their pI values (3.41 and 3.48) were characterized. In addition, two different MnP isoenzymes with the same molecular mass (47 kDa) and N‐linked carbohydrate content (4%) and different pI values (3.35 and 3.45) were characterized. Both enzymes showed good stability at 25 °C and over a wide range of pH. Both laccases oxidize ABTS (2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid) more efficiently than 2,6‐dimethoxyphenol (DMP) with similar efficiency values (K_cat/K_m) while the MnP I, the major peroxidase isoenzyme in the studied conditions, oxidizes the Mn²⁺ and Mn‐mediated activity on DMP more efficiently than MnP II. Copyright © 2006 Society of Chemical Industry     

Radical polymerization in disperse systems,by J. Bartoň, I. Capek. Ellis Horwood Ltd,Chichester/VEDA,Bratislava, 1994. pp. 352, price £68. ISBN 0-13-752353-X

Radical copolymerization of zinc acrylate (ZnA₂) with acrylonitrile (AN), initiated by As₂S₃–styrene complex(I), in dimethyl Sulphoxide (DMSO) at 90 ± 0.1°C for 1.0h under inert atmosphere, yields non-alternating copolymers. The kinetic expression is R_p ∝ [I]^0.33 [ZnA₂]^0.25 [AN]^0.44, i.e. the system follows non-ideal kinetics, which is due to primary radical termination as well as degradative chain transfer reactions. The values for activation energy (E) and k²_p/k_t are 128kJ mol⁻¹ and 8.57 × 10⁻⁷ litre mol⁻¹ s⁻¹, respectively. Thermal stability, solubility in different solvents, and IR and NMR spectra have been evaluated.