Highly enantioselective oxidation of phenyl methyl sulfide and its derivatives into optically pure (S)-sulfoxides with Rhodococcus sp. CCZU10-1 in an n-octane–water biphasic system

Enantiopure sulfoxides can be prepared via the asymmetric oxidation of sulfides using sulfide monooxygenases. The n-octane–water biphasic system was chosen for the bio-oxidation of a water-insoluble phenyl methyl sulfide (PMS) by Rhodococcus sp. CCZU10-1. In this n-octane–water system, the optimum reaction conditions were obtained. (S)-phenyl methyl sulfoxide ((S)-PMSO) with >99.9 % enantiomeric excess formed at 55.3 mM in the n-octane–water biphasic system. Using fed-batch method, a total of 118 mM (S)-PMSO accumulated in 1-L reaction mixture after the 7th feed, and no (R)-PMSO and sulfone were detected. Moreover, Rhodococcus sp. CCZU10-1 displayed fairly good activity and enantioselectivity toward other sulfides. In conclusion, Rhodococcus sp. CCZU10-1 is a promising biocatalyst for synthesizing highly optically active sulfoxides.     

Asymmetric sulfoxidations mediated by alpha-chymotrypsin

The oxidation of aryl alkyl sulfides with H(2)O(2) in aqueous solution is a reasonably facile reaction producing racemic sulfoxides. We show that in the presence of the hydrolytic enzyme alpha-chymotrypsin such a sulfoxidation is accelerated and, more importantly, becomes stereoselective. With phenyl isobutyl sulfide as a model, the chymotrypsin-mediated, highly asymmetric oxidation is shown to occur in the hydrophobic binding pocket of the enzyme active site. The stereoselectivity of the chymotrypsin-mediated sulfoxidations is correctly explained by means of structure-based molecular modeling of the enzyme-sulfide complexes.     

Biotransformation of organic sulfides: Part. 10. Formation of chiral ortho- and meta-substituted benzyl methyl sulfoxides by biotransformation using Helminthosporium species NRRL 4671

Benzyl methyl sulfides substituted with methyl, chloro, cyano, bromo, methoxy, nitro and amino groups in the ortho or meta positions of the aromatic ring have been converted to (S) sulfoxides by biotransformation using the fungal biocatalyst Helminthosporium species NRRL 4671. The enantiomeric excesses for meta-substituted examples were high in those cases where the substituent was of a polar nature, and comparable to those observed for the corresponding para-substituted substrates. With one exception (o-amino), the ortho-substituted examples gave sulfoxides of lower enantiomeric purity. The role of a suitably located polar substituent on an aryl ring of the substrate in ensuring a high enantiomeric excess in sulfoxidation by Helminthosporium species has been confirmed by the biotransformations of 4-(methylthiomethyl)benzyl alcohol and 2-(4-nitrophenyl) ethyl methyl sulfide, which give sulfoxides of much higher optical purity than those obtained from the corresponding unsubstituted substrates.     

Stereoselective oxidation of aromatic sulfides and sulfoxides in the binding domain of bovine serum albumin

The oxidation of aromatic sulfides with achiral oxidizing agents, e.g., sodium metaperiodate (NaIO₄) and hydrogen peroxide (H₂O₂) in the binding domain of bovine serum albumin (BSA), furnished a strong asymmetric bias (max 81%) of the product sulfoxides in fairly high chemical yields. The kinetic resolution of racemic aromatic sulfoxides was also carried out in the chiral binding domain, and the remaining unchanged sulfoxides showed optical purities ranging over 1–33% at ca. 50% completion of oxidation. The combination of the two stereoselective oxidations above mentioned produced several optically active sulfoxides of >90% optical purity in ca. 50% chemical yield. The present method constitutes a successful biomimetic approach to achieving stereoselectivities as high as obtained by sulfur-oxidizing microorganisms.     

Volatile constituents and fatty acid composition of lipids in Durio zibethinus

The predominating flavour compounds in the fruit pulp of Durio zibethinus were hydrogen sulfide, ethyl hydrodisulfide and several dialkyl polysulfides, particularly (C₂H₅)₂S_n, where n = 2 or 3. Ethyl acetate, 1,1-diethoxyethane and ethyl 2-methylbutanoate contribute to an additional fruity odour note. Hydrodisulfides are probably the precursors of the dialkyl sulfides. In the pericarp and seed no volatile sulfur compounds could be detected. The fatty acid composition of the lipids in pericarp, pulp and seed depended on the origin and/or harvest season of the fruit. The main components were oleic and palmitic acids or arachidic acid together with appreciable quantities of palmitoleic, stearic, linoleic and linolenic acids.     

Copper and manganese complexes with C2-multitopic ligands. X-ray crystal structure of [Cu(N,N′-bis[(S)-prolyl]phenylenediamine)H2O]. Catalytic properties

Eight mononuclear complexes with multitopic C₂-symmetry ligands, [Cu(L)]ClO₄, [Mn(L)Cl(H₂O)]PF₆, (L=N,N′-bis[(S)-prolyl]phenylenediamine (1), N,N′-bis[(S)-N-benzylprolyl]phenylenediamine (2), N,N′-bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine (3), N,N′-bis-{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}phenylenediamine (4)) have been prepared and characterised by analytical (elemental analysis, and mass spectroscopy) and FT IR, NMR and electronic spectroscopies. The data show that the ligands are neutral and coordinate to the metal in a tetradentate manner. The N,N′-bis[(S)-prolyl]phenylenediamine ligand also appears as an anionic species, (LH-2), and the single crystal structure determination of the respective complex, [Cu(1)]H₂O, is reported. This new family of Cu-complexes catalyse the cyclopropanation of styrene with ethyl and t-butyl diazoacetate to afford cis/trans 2-phenylcyclopropan-1-carboxylates with good yields and selectivity against dimerisation and low ee (<10%). On the other hand, the manganese and copper complexes also catalyse the oxidation of organic sulfides to sulfoxides with high selectivity, and moderate to low enantioselectivity. If an excess of oxidant were used the reaction yields sulfone as only product with excellent yield.     

Electrochemical behavior of S,S-bridged adducts of square planar metalladithiolene complexes [M(S2C2Ph2)2](M=Ni, Pd, and Pt)

The electrochemical behavior of the S,S^′-bridged adducts of square planar metalladithiolene complexes was investigated by using cyclic voltammetry and electrochemical spectroscopies (visible, near-IR, and ESR). The norbornene-bridged S,S^′-adduct [Ni(S₂C₂Ph₂)₂(C₇H₈)] (2a; C₇H₈=norbornene) formed by [Ni(S₂C₂Ph₂)₂] (1a) and quadricyclane (Q) was dissociated by an electrochemical reduction, and anion 1a⁻ and norbornadiene (NBD) were formed. Q was isomerized to NBD in the overall reaction. The o-xylyl-bridged S,S^′-adduct [Ni(S₂C₂Ph₂)₂(CH₂)₂(C₆H₄)] (3a; (CH₂)₂(C₆H₄)=o-xylyl) was also dissociated by an electrochemical reduction, and this reaction gave the o-xylyl radical (o-quinodimethane). The reduction of complex 3a in the presence of excess o-xylylene dibromide underwent the catalytic formation of o-quinodimethane. The butylene-bridged S,S^′-adduct [Ni(S₂C₂Ph₂)₂(CH₂)₄] (4a; (CH₂)₄=butylene) was stable on an electrochemical reduction. The lifetimes of reduced species of these adducts 2a-4a were influenced by the stability of the eliminated group (stability: NBD > o-xylyl radical (o-quinodimethane) > butylene radical). Therefore, the reduced species are stable in the sequence 4a⁻ > 3a⁻ > 2a⁻. Although the palladium complex [Pd(S₂C₂Ph₂)₂] (1b) was easier to reduce than the nickel complex 1a or the platinum complex [Pt(S₂C₂Ph₂)₂] (1c), their S,S^′-adducts were easier to reduce in the order of Ni adduct > Pd adduct > Pt adduct.     

Sequence analysis and heterologous expression of a new cytochrome P450 monooxygenase from Rhodococcus sp. for asymmetric sulfoxidation

In this study, a 3.7-kb DNA fragment was cloned from Rhodococcus sp. ECU0066, and the sequence was analyzed. It was revealed that the largest one (2,361 bp) of this gene fragment encodes a protein consisting of 787 amino acids, with 73% identity to P450RhF (accession number AF45924) from Rhodococcus sp. NCIMB 9784. The gene of this new P450 monooxygenase (named as P450SMO) was successfully expressed in Escherichia coli BL21 (DE3), and the enzyme was also purified and characterized. In the presence of reduced nicotinamide adenine dinucleotide phosphate, the enzyme showed significant sulfoxidation activity towards several sulfides, with (S)-sulfoxides as the predominant product. The p-chlorothioanisole, p-fluorothioanisole, p-tolyl methyl sulfide, and p-methoxythioanisole showed relatively higher activities than the other sulfides, but the stereoselectivity for p-methoxythioanisole was much lower. The optimal activity of the purified enzyme toward p-chlorothioanisole occurred at pH 7.0 and 30°C. The current study is the first to report a recombinant cytochrome P450 enzyme of Rhodococcus sp. which is responsible for the asymmetric oxidation of sulfides. The new enzymatic activity of P450SMO on the above compounds makes it an attractive biocatalyst for asymmetric synthesis of enantiopure sulfoxides.     

Temperature and pressure dependent equilibrium studies of 1, 4, 8, 11-tetramethyl-1, 4, 8, 11-tetraazacyclotetradecane nickel(ii) in coordinating solvents

In coordinating solvents, the complex 1, 4, 8, 11- tetramethyl-1, 4, 8, 11-tetraazacyclotetradecane nickel(II) bisperchlorate exists as an equilibrium mixture involving four coordinate R,S,R,S-[Ni(tmc)]²⁺ and five coordinate R,S,R,S-[Ni(tmc)(solvent)]²⁺ species. Spectrophotometric measurements of this equilibrium in a number of solvents have been conducted over a range of temperatures and pressures. The stability order for the five coordinate complex in the solvents investigated is CH₃CN>DMF>DMSO>C₆H₅CN> H₂O>ClCH₂CN at 25 °C. Differences in stability are considered in terms of the measured thermodynamic parameters ΔH° and ΔS°. Both steric and electronic factors were found to influence solvent coordination with the macrocyclic complex.For the equilibrium in CH₃CN, C₆H₅CN, DMF and H₂O, reaction volumes, ΔV°, of −3.2±0.5, −4.2±0.5, −0.2±0.5 and −0.5±0.5 cm³ mol⁻¹ respectively have been determined. Each is significantly smaller than the corresponding solvent molar volume. The ΔV° for the equilibrium in CH₃CN is comparable with the previously determined activation volume for exchange of this solvent on R, S, R, S- [Ni(tmc)(CH₃CN)]²⁺. The equilibrium and measured volume parameters are discussed in relation to the mechanism for solvent exchange.     

A convenient synthesis of meso-substituted porphyrins

Acid-catalyzed condensations of 1,19-diunsubstituted 1,19-dideoxybiladiene-ac dihydrobromides with aldehydes, R · CHO, afford the corresponding meso-substituted porphyrins (R = C₆H₅, p-Me·C₆H₄, p-MeO·C₅H₄, p-O₂N·C₆H₄, p-HOC·C₆H₄, p-(MeO)₂CH·C₆H₄, Me, n-Pr, CO₂Et), mostly in good yield.     

A Gaussian-3 theoretical study of the alkylthio radicals and their anions: structures, thermochemistry, and electron affinities

The optimized geometries, electron affinities, and dissociation energies of the alkylthio radicals have been determined with the higher level of the Gaussian-3(G3) theory. The geometries are fully optimized and discussed. The reliable adiabatic electron affinities with ZPVE correction have been predicted to be 1.860 eV for the methylthio radical, 1.960 eV for the ethylthio radical, 1.980 and 2.074 eV for the two isomers (n-C₃H₇S and i-C₃H₇S) of the propylthio radical, 1.991, 2.133 and 2.013 eV for the three isomers (n-C₄H₉S, t-C₄H₉S, and i-C₄H₉S) of the butylthio radical, and 1.999, 2.147, 2.164, and 2.059 eV for the four isomers (n-C₅H₁₁S, b-C₅H₁₁S, c-C₅H₁₁S, and d-C₅H₁₁S) of the pentylthio radical, respectively. These corrected EA_ad values for the alkylthio radicals are in good agreement with available experiments, and the average absolute error of the G3 method is 0.041 eV. The dissociation energies of S atom from neutral C_nH_2n+1S (n?=?1–5) and S^- from corresponding anions C_nH_2n+1S^- species have also been estimated respectively to examine their relative stabilities.     

Fe(III) oxides protect fermenter–methanogen syntrophy against interruption by elemental sulfur via stiffening of Fe(II) sulfides produced by sulfur respiration

Thermosipho globiformans (rod-shaped thermophilic fermenter) and Methanocaldococcus jannaschii (coccal hyperthermophilic hydrogenotrophic methanogen) established H₂-mediated syntrophy at 68 °C, forming exopolysaccharide-based aggregates. Electron microscopy showed that the syntrophic partners connected to each other directly or via intercellular bridges made from flagella, which facilitated transfer of H₂. Elemental sulfur (S⁰) interrupted syntrophy; polysulfides abiotically formed from S⁰ intercepted electrons that were otherwise transferred to H⁺ to produce H₂, resulting in the generation of sulfide (sulfur respiration). However, Fe(III) oxides significantly reduced the interruption by S⁰, accompanied by stiffening of Fe(II) sulfides produced by the reduction of Fe(III) oxides with the sulfur respiration-generated sulfide. Sea sand replacing Fe(III) oxides failed to generate stiffening or protect the syntrophy. Several experimental results indicated that the stiffening of Fe(II) sulfides shielded the liquid from S⁰, resulting in methane production in the liquid. Field-emission scanning electron microscopy showed that the stiffened Fe(II) sulfides formed a network of spiny structures in which the microorganisms were buried. The individual fermenter rods likely produced Fe(II) sulfides on their surface and became local centers of a core of spiny structures, and the connection of these cores formed the network, which was macroscopically recognized as stiffening.     

Amino acid substitutions in naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4 result in regio- and stereo-specific hydroxylation of flavanone and isoflavanone

Wild-type naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 transforms relatively planar flavone and isoflavone to cis-dihydrodiols. However, this enzyme cannot catalyze the transformation of flavanone and isoflavanone in which a phenyl group bonds to the stereogenic C2 or C3 of the C-ring. Protein modeling suggested that Phe224 in the substrate binding site of NDO may play a key role in substrate specificity toward flavanone and isoflavanone. Site-directed mutants of NDO with substitution of Phe224 with Tyr biotransformed only the (S)-stereoisomers of flavanone and isoflavanone, producing an 8-OH group on the A-ring. In contrast, the Phe224Cys and Phe224Gln substitutions, which used (2S)-flavanone as a substrate, and Phe224Lys, which transformed (2S)-flavanone and (3S)-isoflavanone, each showed lower activity than the Phe224Tyr substitution. The remainder of the tested mutants had no activity with flavanone and isoflavanone. Protein docking studies of flavanone and isoflavanone to the modeled mutant enzyme structures revealed that an expanded substrate binding site, due to mutation at 224, as well as appropriate hydrophobic interaction with the residue at 224, are critical for successful binding of the substrates. Results of this study also suggested that in addition to the previously known Phe352, the Phe224 site of NDO appears to be important site for expanding the substrate range of NDO and bringing regiospecific and stereospecific hydroxylation reactions to C8 of the flavanone and isoflavanone A-rings.     

The lysis of isolated fish (Oncorhynchus mykiss) gill epithelial cells by surfactants

1. The interaction of a wide range of surfactants with isolated gill epithelial cells of rainbow trout (Oncorhynchus mykiss) was investigated as a function of the surfactant concentration up to and above the critical micelle concentration (cmc). The surfactants included a homologous series of n-alkyl sulphates, single and double chain tri and dimethylammonium bromides (TABs and DABs), cholates and the nonionics n-octylglucoside and Triton X-100.2. With the exception of the C₂₂ alkyl chain TAB and the double chain [(C₁₂)₂] DAB, the surfactants solubilized between 84 and 100% of the cell protein at high concentrations (>cmc).3. At low concentrations n-dodecyltrimethylammonium bromide and, to a lesser extent, Triton X-100 and sodium n-dodecylsulphate release a larger proportion of cell protein than they solubilize lipid in contrast to sodium cholate which initially preferentially solubilizes cell lipid. This differential pattern of solubilization is similar to that observed for other plasma membranes such as those of human erythrocytes and platelets.4. The surfactant concentration required to solubilize 50% (S_50%) of cell protein increases with the cmc. There is an approximately linear relationship between log(S_50%) and log cmc.5. Light microscopy shows that the surfactants at high concentrations (>cmc) fragment the secondary lamellae of the gill filaments.     

Biochemical constituents of a wild strain of Schizophyllum commune isolated from Achanakmar-Amarkantak Biosphere Reserve (ABR), India

A wild strain of Schizophyllum commune (MTCC 9670) isolated from Achanakmar-Amarkantak Biosphere Reserve of Central India was evaluated for the production of bioactive compounds. The chemical constituents of wild and in vitro grown cultures were compared. Under optimized conditions, different organic and aqueous extracts from mycelia and fruiting bodies were used to extract chemical components from the cultures grown in vitro. The gas chromatography combined wih mass spectrometry analysis of extracts identified two phenolic compounds, namely Phenyl benzoate (C₁₃H₁₀O₂) and 4-(phenyl methoxy) phenol (C₁₃H₁₂O₂) in the ethanolic extract of in vitro grown fruiting bodies and one antibacterial compound Pyrrolo (1, 2-a) piperazine-3, 6-dione (C₇H₁₀O₂N₂) in the methanolic extract of mycelia. High-performance liquid chromatography analysis revealed that the gallic acid and l-ascorbic acid were identifiable antioxidant components in the extracts possessing high free radical scavenging activity. The findings suggest that the wild strain of S. commune may serve as the source of novel bioactive compounds with effective antimicrobial and antioxidant activities.     

The coordination of small molecules by manganese(II) phosphine complexes. Part 12. The synthesis of some tetrahydrofuran/long chain tertiary phosphine complexes of manganese(II) halides,MnX2(phosphine)(THF), and their reaction with molecular oxygen

Manganese(II) complexes of long chain phosphines, MnX₂(phosphine)(THF) XCl, Br, I; phosphine=P(C₁₂H₂₅)₃, P(C₁₄H₂₉)₃, P(C₁₆H₃₃)₃, PPh(C₁₂H₂₅)₂, PPh(C₁₄H₂₉)₂, PPh(C₁₆H₃₃)₂; THF=tetrahydrofuran have been prepared and characterised. These complexes react reversibly with molecular oxygen both in the solid state and in THF and toluene solution forming 1:1 Mn:O₂ adducts. These adducts are monomeric in toluene and THF and molecular weight measurements confirm that the THF ligand remains coordinated in toluene solution leading to the formation of MnX₂(phosphine)(THF)(O₂) species. All the O₂-adducts are highly coloured and binding curves have been constructed and K_o2 values calculated. Based on these K_o2 values the affinity for dioxygen is in the order XCl>Br>I in toluene solution, with Hill coefficient, n, indicating cooperativity (1-1.5). In THF dioxygen binding does not appear to be cooperative.     

Hydrolysis of DMPC or DPPC by pancreatic phospholipase A2 is slowed down when (perfluoroalkyl) alkanes are incorporated into the liposomal membrane

The effect of the incorporation of linear (perfluoroalkyl)alkanes (C_mF_2m+1C_nH_2n+1, FmHn) into liposomes made of DMPC or DPPC on the activity of porcine pancreatic phospholipase A₂ was investigated. A large decrease in enzyme activity and modifications of the kinetic profile, especially at and above the phospholipid's phase transition temperature, were observed; both depend on the relative lengths of the phospholipid's fatty acid chains and of the Hn segment of the FmHn molecule. With DMPC Hn must have a minimum of 10 carbon atoms to be effective, as in F6H10, F8H10 and F4H12; F8H8 had no significant hydrolysis-rate-reducing effect. With DPPC H_n must have a minimum of 12 carbon atoms, as in F4H12, while F8H8, F6H10 and F8H10 were ineffective. The absence of effect when C₁₀H₂₂ or C₁₆H₃₄ was incorporated establishes that the fluorinated segment, although its length (from C₄ to C₈) is not crucial, is required to hinder hydrolysis by PLA₂, indicating that this segment plays an important role in structuring the liposomal membrane.     

Synthetic and mechanistic studies of the addition of 2,6-dimethylaniline to tricarbonyl (1–5-η-dienyl) iron(II) complexes (dienyl=C6H7 or C7H9)

Detailed synthetic and mechanistic studies of the addition of 2, 6-dimethylaniline to the organometallic complexes [Fe(CO)₃(1–5-η-dienyl)]BF₄ (1, dienyl=C₆H₇ or C₇H₉) indicates the general rate law k_obs=k_a [2,6-(Me)₂C₆H₃NH₂]+k_b which is consistent with an equilibrium process. The greater reactivity of the C₆H₇ complex and the low ΔH_a3 and large negative ΔS_a3 values are in accordance with direct addition of the amine to the dienyl rings of 1. On the other hand the relatively much higher ΔH_b 3 values are consistent with bond cleavage in dissociation as is the positive ΔS_b 3 value of +220 J K⁻¹ mol⁻¹ determined for the C₆H₇ reaction. The negative ΔS_b3 value of −43 J K⁻¹ mol⁻¹ found for the C₇H₉ reaction suggests the presence of an ordered transition state through which the starting dienyl complex is reformed via some internal S_N2 process.     

Effect of a phenyl group in quaternary ammonium compounds on thiamine uptake in isolated rat hepatocytes

The inhibitory effect of a phenyl group in quaternary ammonium compounds on thiamine uptake in isolated rat hepatocytes was investigated. The phenyltrimethylammonium ion was a more potent inhibitor than the tetramethylammonium ion, while the dibenzyldimethylammonium ion was the most potent inhibitor of thiamine uptake among those compounds examined. A kinetic study showed that this compound was a competitive inhibitor. The cetyltrimethylammonium ion was a less effective inhibitor than the benzyltrimethylammonium ion, and the palmitoylcholine ion was a weak inhibitor. These results indicate that the lipophilicity of a quaternary ammonium compound is not always correlated with its affinity for thiamine-carrier binding, but the presence of a phenyl group plays a significant role in affinity. The inhibitory effect of the series of (CH₃)₃N⁺(CH₂)_nC₆H₅ (n = 0−6) compounds on thiamine uptake in isolated rat hepatocytes was studied. The maximal inhibitory activity occurred at n = 5. These results suggest that the phenyl group in a quaternary ammonium compound has a specific interaction with the thiamine-binding site in rat liver plasma membrane.     

The reaction of [η:C5H4-(CH2)n-C6H5]2MCl2 complexes (n=1-5; M=Zr, Hf) with EtLi

The reaction of metallocene complexes of the type [η⁵:C₅H₄-(CH₂)_n-C₆H₅]₂MCl₂ (n=1-5; M=Zr, Hf) with EtLi gives the mono nuclear ethyl derivatives [η⁵:C₅H₄-(CH₂)_n-C₆H₅]₂M(Et)Cl and the metallacycles [η⁵:C₅H₄-(CH₂)_n-C₆H₅][η⁵:C₅H₄-(CH₂)_n-η¹:C₆H₄]MEt. A large excess of EtLi affords the dinuclear species [η⁵:C₅H₄-(CH₂)_n-η⁶:C₆H₅]₂M₂Cl₂ (n=2-5). All types of complexes can be activated with methylalumoxane (MAO) and then be used for catalytic polymerization of ethylene.