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An insight into the kinetics, mechanism and optimum reaction conditions of the Julia-Colonna epoxidation has been gained using a soluble polyleucine catalyst.

The surface differential reflectivity (SDR) and photoemission methods were used to study surface electronic structure of CdTe and ZnTe (1 1 0) surface. The changes of reflectivity coefficient were caused by the changes of electric field (band bending) induced at the surface region by high power laser illumination of the sample. The SDR spectra were obtained as a function of laser power illumination. The shift of the surface potential was estimated on photoemission spectra as a shift of the Cd 4d level position caused by the laser illumination of the sample. The exponential time decay of the amplitude of SDR spectra were measured after turning of the laser illumination. The decay time constant was estimated at 22 min for clean surface of CdTe and 60 min for real surface of ZnTe. The attempts were done to discuss obtained results in the frame of the Franz–Keldysh effect description.

—Cyclohexanone monooxygenase from Acinetobacter calcoaceticus catalyzed the oxidation of tertiary and secondary amines toN-oxides and nitrones, respectively. The formation of a hydroxylamine intermediate was involved with secondary amines as startingsubstrates.q 2003 Elsevier Ltd. All rights reserved. 1. IntroductionThe increasing demand for enantiomerically pure com-pounds for the pharmaceutical and agrochemical industriesimplies a great incentive for the study of the biotransform-ations. Oxidative biotransformations are amongst the mostuseful of all identified biologically mediated conversions. 1 They usually involve monooxygenases or dioxygenases,that catalyze the insertion of one oxygen or two oxygenatoms at a specific point of a molecule, often with highstereo and/or regioselectivity. The cyclohexanone mono-oxygenase from Acinetobacter calcoaceticus NCIMB 9871(CHMO) (EC 1.14.13.22) is an interesting enzyme for itsapplication in the manufacture of fine chemicals and inorganic synthesis.

An insight into the kinetics, mechanism and optimum reaction conditions of the Julia-Colonna enantioselective epoxidation has been gained using a soluble polyleucine catalyst (PLL), chalcone as the substrate, and hydrogen peroxide (HOO − ) as the oxidant. PLL shows saturation kinetics for both chalcone and HOO − and has a behaviour that fits a steady state random bireactant system with one of the pathways (HOO − binding first) being kinetically preferred to the other (chalcone binding first) in the formation of the ternary complex PLL:HOO − :Chalcone.

Sol–gel routes were used to prepare Ta 10 at% and Nb 5 at% and 10 at% doped titania nanosized powders. When fired between 410°C and 850°C the doped titania powders are in the anatase phase; further heating up to 1050°C is required to obtain the rutile phase. The presence of dopant atoms delays the rate of transformation as compared with pure titania powders. Doping also affects the rate of grain growth and increases the conductance response to gas. To better understand the role played by dopant atoms in inhibiting both phase transformation to rutile and grain growth, X-ray Absorption Spectroscopy measurements were performed at the L III – L I absorption edges of Ta and Nb K absorption edge. Analysis was restricted to the anatase phase because the transformation to rutile phase, obtained by firing at 1050°C, is accompanied by the formation of undesired Ta and Nb oxides (Ta 2 O 5 and Nb 2 TiO 7 , respectively). Extended X-ray Absorption Fine Structure and X-ray Absorption Near-Edge Spectroscopy analysis results indicate that in nanostructured anatase both tantalum and niobium atoms substitute Ti cations with +5 valence state.

The thermal decomposition of transition metal trifluorides MF3 (M = Mn, Fe, Co) was studied by collecting sequences of very-high-energy (89 keV) synchrotron radiation diffraction patterns. The real-time evolution of the crystal lattices was followed as a function of temperature and it was observed that the transition from MF3 to MF2 is generally accompanied by the formation of intermediate short-living phases –M2F5. One of them –Co2F5– is a phase which had never been observed before.

The catalytic oxidation of ortho- and para-alkylthiophenols, carrying methyl or ethyl substituents at sulfur, by lactoperoxidase (LPO), horseradish peroxidase (HRP) or chloroperoxidase (CPO), in the presence of hydrogen peroxide, has been investigated. HPP and CPO are active toward these substrates, whereas LPO is only active with the ortho-substituted compounds. The enzymatic solutions containing ortho-alkylthiophenols develop an intense blue color (with optical absorptions near 400 and 600nm) that is attributed to the formation of relatively stable dimeric three-electron bonded complexes resulting from the association of enzyme-derived radical cations with the phenolic sulfide. The products of the enzymatic reactions by HRP and LPO are oligomers resulting from phenol oxidative coupling reactions and the sulfoxide, with minor amounts of oligomers containing mono or disulfoxide functionalities. With CPO the major product is always the sulfoxide, while phenol coupling products are formed in minor amounts. The selectivity exhibited by LPO toward 2- and 4-methylthiophenol has been investigated through binding experiments, NMR relaxation measurements of LPO-substrate complexes and docking calculations. The para-isomer binds much more strongly than the ortho-isomer to the enzymes. The stronger binding depends on the establishment of hydrogen bonding interactions with protein residues in the active site. (C) 2003 Elsevier Science B.V. All rights reserved.

The performance, in Baeyer-Villiger and heteroatom oxidations, of a partially purified preparation of cyclohexanone monooxygenase obtained from an Escherichia coli strain in which the gene of the enzyme was cloned and overexpressed was investigated. As model reactions, the oxidations of racemic bicyclo[3.2.0]hept-2-en-6-one into two regioisomeric lactones and of methyl phenyl sulphide into the corresponding (R)-sulphoxide were used. Enzyme stability and reuse, substrate and product inhibition, product removal, and cofactor recycling were evaluated. Of the various NADPH regeneration systems tested, 2-propanol/alcohol dehydrogenase from Thermoanerobium brockii appeared the most suitable because of the low cost of the second substrate and the high regeneration rate. Concerning enzyme stability, kosmotropic salts were the only additives able to improve it (e.g., half-life from 1 day in diluted buffer to 1 week in 1 M sodium sulphate) but only under storage conditions. Instead, significant stabilization under working conditions was obtained by immobilization on Eupergit C (half-life approximately 2.5 days), a procedure that made it possible to reuse the catalyst up to 16 times with complete substrate (5 g x L(-1)) conversion at each cycle. Reuse of free enzyme was also achieved in a membrane reactor but with lower efficiency. Water-organic solvent biphasic systems, which would overcome substrate inhibition and remove from the aqueous phase, where reaction takes place, the formed product, were unsuccessful because of their destabilizing effect on cyclohexanone monooxygenase. More satisfactory was continuous substrate feeding, which shortened reaction times and, very importantly, yielded in the case of bicyclo[3.2.0]hept-2-en-6-one (10 g x L(-1)) both lactone products with high optical purity (enantiomeric excess > or = 96%), which was not the case when all of the substrate was added in a single batch.

The enantiomers of chiral (arene)tricarbonylchromium ketones and alcohols were separated by high-performance liquid chromatography with a Chiralcel OD column. The absolute configuration of the ketones was assigned on the basis of the sign of optical rotation determined with an on-line detector.

Enantiomerically pure sulfoxides are excellent chiral auxiliaries for asymmetric synthesis and in the preparation of several enantiopure biologically active compounds. For these reasons we have explored biocatalytic approaches for the synthesis of sulfoxides based on the use of heme peroxidases and flavin monooxygenases, such as chloroperoxidase (CPO) and cyclohexanone monooxygenase (CMO), respectively. By using isolated enzymes or whole-cell biotransformations, we have prepared alkyl aryl sulfoxides, 1,3-dithioacetal-1-oxides and dialkyl sulfoxides in high enantiomeric excess (ee). Recent experiments from our and other laboratories have shown that chloroperoxidase is also able to catalyze a broad spectrum of stereoselective epoxidation reactions. The substrate repertoire includes substituted styrenes, straight chain aliphatic and cyclic cis-olefins. The enzyme is also able to perform benzylic hydroxylation and hydroxylation of alkynes with high ee.

Peroxidases are ubiquitous oxidoreductases that use hydrogen peroxide or alkyl peroxides as oxidants. Advances have recently been made in using them to prepare, under mild and controlled conditions, chiral organic molecules that are valuable for the chemoenzymatic synthesis of a wide range of useful compounds. Horseradish peroxidase can be converted into a peroxygenative enzyme by molecular engineering. Chloroperoxidase, the most versatile peroxidase, behaves like a 'true' monooxygenase in sulfoxidations with molecular oxygen and an external reductant, with substantial increases in enantioselectivity and enzyme stability.

At pH 3, chloride dramatically influenced both the Km of chloroperoxidase (CPO) for methyl p-tolyl sulfide, which decreased, and its activity, which increased. The Km value changed from 75 microM in the absence of chloride toor = 1.2 microM inor = 0.9 mM chloride, and the kcat from 53 s-1 in 0 to 1750 s-1 in 50 mM halide. The kcat/Km value at 0.9 mM chloride was 414 microM -1s-1 compared to 0.7 microM-1s-1 in the absence of the halide. At pH 5, the activating effect was less pronounced. Chloride also acted as inhibitor versus hydrogen peroxide. The data are consistent with a reaction mechanism in which, on hand, chloride competes with hydrogen peroxide for the native enzyme and, on the other hand, activates sulfide oxidation by binding to CPO Compound I to give a CPO-chlorinating intermediate (EOCl-). However, contrary to what happened in the absence of chloride, where the oxidation was enantioselective and an oxygen atom of H2O2 was incorporated in the sulfoxide (from experiments with 18O-labeled H2O2), in the presence of the halide the oxidation was not enantioselective and there was no incorporation of oxygen from H2O2. The data suggest that sulfide oxidation takes place through an enzyme-generated freely dissociable oxidized halogen intermediate formed by the interaction of EOCl- with Cl-.

In situ diffraction studies of structural transformations occurring during thermal decomposition of a cobalt fluoride-CoF3-were performed using a very-high-energy (89 keV) synchrotron radiation. The real-time evolution of the crystal lattice was followed as a function of temperature. A new compound appearing as intermediate in the course of the decomposition from CoF3 to CoF2 was discovered.

Peroxidases catalyze the oxidation of a wide variety of organic compounds using hydrogen peroxide or other peroxides [1]. Reactions of peroxidases with H2O2 yield compound I structures that are two oxidizing equivalents above the resting ferric state. CompoundIVI of horseradish peroxidase (HRP) has been identified as a ferryl (Fe = 0) porphyrin radical cation [2] and is reduced by two single-electron transfers, first to compound II by the reduction of the porphyrin and subsequently to the resting ferric state.

A population-based case-control study of 260 patients (74 males and 186 females, mean age = 56) with cutaneous malignant melanoma and 416 controls (211 males and 205 females, mean age = 55) was conducted in Turin, north-west Italy, to examine the relation between timing of sunburns and sun exposure and melanoma risk within a southern European population, which is still relatively little investigated. Particularly elevated risk was associated with history of sunburns in childhood [odds ratio 5.9; 95% confidence interval (CI) 3.6-9.5], and such risk elevation persisted after allowance for other major melanoma risk covariates. Conversely, risk increase from history of severe sunburns lifelong was lower (odds ratio = 1.7; 95% CI: 1.1-2.4) and was eliminated by allowance for type of skin reaction to sun exposure and history of sunburns in childhood. A significant increase in the risk of cutaneous malignant melanoma was also associated with number of weeks spent on holiday at the beach not only as an adult, but also as a child.

It has often been debated whether the presence of persulfate in a polyacrylamide gel could lead to the oxidation of cysteine (Cys) in proteins to cysteic acid. In fact, direct incubation of bovine serum albumin (BSA) with peroxodisulfate and periodate barely alters the isoelectric point (pI) and does not produce any cysteic acid. In contrast, caroate (peroxomonosulfate) and perphthalate strongly lower the pI of BSA. In the former case it as demonstrated that 4-Cys (of a total of 35) were converted into cysteic acid. Perphthalate was found to be, by far, the strongest oxidant: 15 (of 35) Cys residues were oxidized to cysteic acid and all methionine groups were destroyed.

The role of hormonal and reproductive factors as risks for cutaneous malignant melanoma (CMM) was explored by means of a population-based case-control study conducted in Turin, north-western Italy, on 186 female CMM cases and 205 controls. Past use of oral contraceptives (OC) did not seem to exert any effect on CMM risk odds ratio (OR) = 1.12, 95% confidence interval (CI): 0.56-2.24). No association was found even for the longest duration of use, for superficial spreading melanoma cases and for CMM of lower limbs only. While age at first birth did not affect CMM risk, women who had had three or more children seemed to be significantly protected as compared to nulliparous ones. The association was, however, substantially diminished by adjustment for education and other CMM risk correlates (OR for at least three children versus none = 0.62; 95% Cl: 0.29-1.31).

Unsymmetrical teriary amines were oxidized with a few oxidants in the presence of bovine serum albumin to give the corresponding N-oxides of the highest optical purity ever reported (up to 66%) for the reaction of asymmetric oxidation of amines via their kinetic dynamic resolution.

Enantiomerically pure S-alkyl-S-[(4S)-4-benzyl-2-oxo-1,3-oxazolidin-3-yl]-N-tosylsulfimides react with Grignard reagents affording dialkyl and alkyl aryl sulfimides in high chemical yield and enantiomeric excess.

An insight into the kinetics, mechanism and optimum reaction conditions of the Julia-Colonna epoxidation has been gained using a soluble polyleucine catalyst.

Microperoxidase-11 catalyzed oxidation of alkyl aryl sulfides by H 2 O 2 preferentially give the (−)-(S)-sulfoxides (e.e. 16 – 25 %).

This review article briefly introduces the applications of bacterial cyclohexanone monooxygenases to the enantioselective oxidations of organic sulfur compounds to sulfoxides. High enantioselectivities are observed in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, cyclic and acyclic 1,3-dithioacetals. The oxidation of alkyl aryl sulfides with flavin dependent microorganisms extends the synthetic interest of this class of enzymes.

Cyclohexanone monooxygenase catalysed oxidation of dithioacetals in combination with kinetic resolution gives enantiomerically pure (R)-monosulfoxides.

Horseradish peroxidase catalysed oxidation of aryl methyl sulfides by H2O2 preferentially gives (–)-(S)-sulfoxides, enantiomeric excess 30–68%.

α-Halogenation of benzyl t-butyl sulphoxide (2) by electrophilic halogenating agents in pyridine affords a mixture of the diasteroisomeric α-halogenobenzyl t-butyl sulphoxides in the ratio 5:1. In the case of the (R)-sulphoxide (2), chlorination involves selective replacement of the pro-R-hydrogen atom and occurs both with inversion at sulphur and retention at carbon (major path) and with retention at both sulphur and carbon (minor path).

Optically pure αβ-unsaturated sulphoxides have been synthesised.Addition of piperidine to (–)-(R)-(Z)-propenyl p-tolyl sulphoxide gives a quantitative yield of adduct with an optical yield of 70%. The absolute configuration of the asymmetric carbon centre (β-induction) of the major diastereoisomer is assigned by comparison of the rotation of the derived sulphide with that of a specimen synthesised from (+)-alanine. A lower optical yield is obtained in addition of piperidine to (+)-α-methylvinyl p-tolyl sulphoxide (α-induction). No discernible α-induction is found in additions of PhSD to p-tolyl vinyl sulphoxide.Addition of bromine to (+)-p-tolyl vinyl sulphoxide gives the dibromide with an optical yield (α-induction) of 32%. The absolute configuration of the new asymmetric centre at carbon is assigned by using Brewster's rules. (+)-α-Methylvinyl p-tolyl sulphoxide gives a higher degree of asymmetric induction but yields of dibromide are low.The relationship of the optical yields and absolute configurations of the adducts obtained in these nucleophilic and electrophilic additions is discussed with respect to the mechanisms and steric courses of the reactions.

Representative oxovanadium(IV), oxotitanium(IV), and dioxomolybdenum(VI) complexes of N-salicylidene-L-amino acids (the amino acids are: valine, leucine, except for Mo(VI), and histidine) have been synthesized and characterized by various spectroscopic techniques. It has been found that while in the histidine complexes of titanium(IV) and vanadium(IV) the amino acid residue is bound in the expected glycine-like mode, in the molybdenum(VI) complex it is bound in the unusual histamine-like mode. Also, the structure of this molybdenum(VI) complex contains imidazolate-bridged polymeric units in the solid state, while the carboxyl group of the amino acid residue is protonated. In solution the polymeric structure is cleaved and the monomers contain carboxylate and protonated imidazole groups at the histidine residue. The histamine-like structure of the histidine complex was probcd by comparison with that of the chiral dioxomolybdenum(VI) complex of N -salicylidene-L-histidinol. While the structure of the metal centers is six-coordinate for the dioxomolybdenum(VI) complexes and the histidine complexes of oxotitanium(IV) and oxovanadium(IV), it is likely that the complexes of the latter metals derived from nonpolar amino acids do not achieve coordination numbers higher than five. The present oxometal complexes are catalytically active in the sulfoxidation of sulfides and in the epoxidations of activated olefins by tert-butyl hydroperoxide, but in general exhibit a low degree of asymmetric induction in these reactions.

More than 98 % of A.I. is obtained during addition of TosMic with chiral complexes 2 and 3. The diastereoselectivity of the formation of the oxazolines is studied and the diastereomers clearly assigned. Orbital-interactions and electronic repulsions seem to be responsable for the presence of the cis isomers.

Oxidation of sulphides by in situ generated dioxiranes in buffered (pH 7.5) aqueous solutions, using bovine serum albumin (BSA) as a chiral auxiliary, affords the corresponding sulphoxides in up to 89% enantiomeric excess (e.e.).

Some chiral catalysts have been tested in the reaction of ethyl 2-bromopropionate with potassium phthalimide and in the borohydride reduction of phenyl t-butyl ketone under phase-transfer conditions. The mechanism of the N-alkylation reaction and the influence of the molecular structure of the catalysts on stereoselectivity are analysed.

The addition of thiophenol to α, β, unsaturated ketones in the presence of different proteins gives optically active adducts with enantiomeric excess up to 29%.

The asymmetric epoxidation of chalcone and other electron-poor olefins in a triphase system (water-organic solvent-polyaminoacid) affords optically active oxiranes. The influence of the molecular structure of catalysts and of their secondary conformation on the enantioselectivity of the reaction has also been examined.

The epoxidation of 2 and 2,3-substituted naphthoquinones with t-BuOOH in aqueous buffer solutions, in the presence of bovine serum albumin (BSA) as chiral catalyst, affords the corresponding epoxynaphthoquinones with enantiomeric excess (e.e.) up to 79%. The influences on the enantioselectivity of the pH of the buffer solution, of the oxidizing agent, and of inorganic salts have also been examined.