Oxidation-reduction sequential

Preliminary observations of the reactions of Fe(II) and Fe(III) in an ultrasonic field revealed conversion of Fe(II) to Fe(III) and vice-versa, even without any external oxidant/reductant, which were subsequently confirmed experimentally and sequentially through the following four qualitative conversions. The details are available in the literature [35]. 

Epimerization of carbohydrate stractures to the corresponding epi-hydroxy stereoisomers is an efficient means to generate compounds with inverse coirfiguration that may otherwise be cumbersome to prepare. Several different synthetic methods have been developed, including protocols based on the Mitsunobu reaction,sequential oxidation/reduction... 

Medici et al. have used a combined sequential oxidation-reduction to access a range of imsaturated secondary alcohols from their racemates [7] (Scheme 1). Here the S-alcohol 2 is oxidized by B. stereothermophilus which is displaying Prelog specificity leaving the l -enantiomer untouched. The other microorganism, Y. lipolytica contains an anti-Prelog dehydrogenase which is therefore able to reduce the ketone 1 to the l -alcohol 2. Thus the combination of the two steps effects a net deracemization of substrate 2. 

Kroutil et al. have recently reported [18] an elegant one-pot oxidation/reduction sequence for the deracemization of a chiral secondary alcohol using a single biocatalyst. LyophiUzed cells of a Rhodococcus sp. CBS IVJ.Ti converted racemic 2-decanol into the (S)-enantiomer in 82% yield and 92% enantiomeric excess (e.e.). via a non-specific oxidation followed sequentially by an (S)-selective reduction (Scheme 6.5). Acetone was used as the hydrogen acceptor in the first step and isopropanol as the hydrogen donor in the second step. 

Chemical reactions are grouped under reaction types (oxidation, reduction, etc.), and each of the five systems is dealt with sequentially in each subsection. 

Deamination studies have aided attempts to locate the positions of the O-sulfate groups in heparin. From the results of deamination and periodate-oxidation studies, it was concluded239 that half of the uronic acid residues are sulfated at C-2, and sequential periodate oxidation, reduction with sodium borohydride, acid treatment, and deamination gave 2,5-anhydro-D-mannose 6-sulfate.240,241 Sulfated O-(hexosyluronic acid)-2,5-anhydro-D-mannose and sulfated uronic acids were subsequently isolated, and the isolation (in 65% yield) of the disulfated 0-(idosyluronic acid)-2,5-anhydro-D-mannose (137) from heparin, together with the 13C n.m.r. spectra of 137 and heparin, suggested243 that at least two thirds of the heparin structure consists of the repeating unit 138. 

Through a series of oxidation-reduction reactions driven by two light reactions operating in series and involving several hundred chlorophyll molecules, electrons flow from water to NADP. Participating in the overall reaction is a water-splitting complex that includes a mangano-protein and chloride ions. An unidentified chlorophyll a molecule serves as the reaction center of photosystem II, with Q as the primary electron acceptor. Involved sequentially on the electron transport chain are plasto-... 

While the redox titration method is potentiometric, the spectroelectrochemistry method is potentiostatic [99]. In this method, the protein solution is introduced into an optically transparent thin layer electrochemical cell. The potential of the transparent electrode is held constant until the ratio of the oxidized to reduced forms of the protein attains equilibrium, according to the Nemst equation. The oxidation-reduction state of the protein is determined by directly measuring the spectra through the tranparent electrode. In this method, as in the redox titration method, the spectral characterization of redox species is required. A series of potentials are sequentially potentiostated so that different oxidized/reduced ratios are obtained. The data is then adjusted to the Nemst equation in order to calculate the standard redox potential of the proteic species. Errors in redox potentials estimated with this method may be in the order of 3 mV. 

Epoxidation of oxonine 93 with dimethyldioxirane, followed by reduction with diisobutylaluminium hydride (DIBAL-H), resulted in a separable mixture of alcohols 95 and 96, and the side product 94 (Scheme 16). Each of the isomers was submitted to Swern oxidation and sequential stereoselective reduction with L-selectride to achieve desired stereochemistry of the products 97 and 98. Formation of the side product 94 was explained by Lewis acidity of DIBAL-H and confirmed by treatment of oxirane derived from 93 with another Lewis acid, AlMe3, to produce oxocine aldehyde 99 in 35% isolated yield <1997CL665>. Similar oxidative synthetic sequence was utilized for the synthesis of functionalized oxonines as precursors of (-l-)-obtusenyne <1999JOG2616>. 

In the electrochemical reduction of 5-bromo-l-methyl-4-nitroimidazole some cleavage of the C—Br bond is evident giving rise to the debrominated product (79JGU1877). Imidazole itself is not reducible cathodically in aqueous media, but electrons have been attached to imidazole and histidine in aqueous solution the rate of oxidation depends on pH. Protonated or quaternized imidazoles form the neutral conjugate acids of the true anion radical, and a number of anion radicals have been made from nitroimidazoles under various radiolytic conditions (79AHC(25)205). The electrochemical reduction of 2-cyanobenzimidazole 3-oxide gives sequentially 2-cyanobenzimidazole and 2-aminomethylbenzimidazole (80ZC263). 

The majority of such reactions entail the transfer of a functional group, such as a phosphoryl or an ammonium group, from one substrate to the other. In oxidation-reduction reactions, electrons are transferred between substrates. Multiple substrate reactions can be divided into two classes sequential displacement and double displacement. 

The primary process operations are conducted sequentially in the same tungsten crucible. These primary operations are conducted in a circular processing assembly with operating stations dedicated for each operation. Decladding is conducted at the first station, oxide reduction is conducted at the second station, FP-3 donor is conducted at the third station, and U-Pu donor is conducted at the fourth station. Each station has the necessary apparatus to conduct the desired operations (introduction of fuel assembly, stirring, and transfer of molten salt and metal phases into and out of the crucible). Figure 4 gives a cross section view of the turntable. 

In yeast and mycelial fungi, xylose is metabolized via coupled oxidation-reduction reactions . Xylose reductase is the enzyme involved in the reduction of xylose to xylitol. Sequential enzymatic events, through the oxidation of xylitol to xylulose, lead to the utilization of xylose. Many yeast species utilize xylose readily, but the ethanol production capability is very limited. Only a few yeast species effectively produce ethanol from xylose these include Pachysolen tan-nophilus, Candida shihatae and Pichia stipitis [80]. The production of ethanol from xylose by these three yeast strains has been studied extensively in recent years. Recently, genetically engineered yeast strains have been constructed for more effective conversion of xylose to ethanol. 

Semiempirical calculations of free energies and enthalpies of hydration derived from an electrostatic model of ions with a noble gas structure have been applied to the ter-valent actinide ions. A primary hydration number for the actinides was determined by correlating the experimental enthalpy data for plutonium(iii) with the model. The thermodynamic data for actinide metals and their oxides from thorium to curium has been assessed. The thermodynamic data for the substoicheiometric dioxides at high temperatures has been used to consider the relative stabilities of valence states lower than four and subsequently examine the stability requirements for the sesquioxides and monoxides. Sequential thermodynamic trends in the gaseous metals, monoxides, and dioxides were examined and compared with those of the lanthanides. A study of the rates of actinide oxidation-reduction reactions showed that, contrary to previous reports, the Marcus equation ... 

Fig. 18. The model for the redox-driven translocation of a metal ion between a two compartments ligand. The metal center exists in two oxidation states of comparable stability, connected by a fast and reversible one-electron redox change. The two compartments display different coordinating tendencies, e.g., compartment A is hard, compartment B is soft. In these circumstances, the oxidized metal (the smaller ball) will prefer to stay in compartment A, whereas the reduced form (larger ball) will occupy compartment B. Therefore, it is expected that, following consecutive oxidation/reduction, the metal center will translocate sequentially between A and B...

Studies on a sequential oxidative reductive process of degradation of chloro-aliphatics and chloroaromatics have been under investigation since 1995. Anaerobic breakdown of o -chlorophenol (100 mg 1 1) and 2,4-dichlorophenol (100 mg H) into catechol acclimatized upflow fixed bed biroeactor is reported to have reached 75% and 55 % respectively [61,62]. 

The presence of galactofuranose residues in SXA was shown by controlled, periodate oxidation, reduction with borohydride, and mild hydrolysis (with acid) to yield arabinose. Sequential periodate oxidation, reduction with borohydride, and acidic hydrolysis of SXA yielded threitol phosphates. 

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