Fast and highly efficient solid state oxidation of thiols

A fast and efficient solid state method for the chemoselective room temperature oxidative coupling of thiols to afford their corresponding disulfides using inexpensive and readily available moist sodium periodate as the reagent is described. The reaction was applicable to a variety of thiols giving high yields after short reaction times. Comparison of yield/time ratios of this method with some of those reported in the literature shows the superiority of this reagent over others under these conditions.     

Investigation of hydrothermal routes to mixed-metal cerium titanium oxides and metal oxidation state assignment using XANES

The reaction between TiF(3) or TiO(2) and Ce(3+) in sodium hydroxide solutions yields highly crystalline NaCeTi(2)O(6) at room temperature and under mild hydrothermal conditions (T < or = 240 degrees C). There is no evidence for the formation of ternary Ce-Ti-O materials by this method, and the use of bases other than NaOH always produces poorly crystalline materials. The material NaCeTi(2)O(6) has a distorted perovskite structure with sodium and cerium ions randomly occupying the A sites: Pnma, a = 5.4517(8) A, b = 7.7292(6) A, c =5.4573(3) A. XANES spectroscopy at the Ti K edge and Ce L(III) edge, with reference to crystalline model compounds, reveals that cerium is found solely as Ce(III) and titanium as Ti(IV) in NaCeTi(2)O(6). Isomorphous substitution of Ce(3+) by Nd(3+) or Ti(4+) by V(4+) is found to be very facile under hydrothermal conditions (at a temperature of 240 degrees C), by addition of appropriate amounts of metal salts to the hydrothermal reaction mixtures. The series NaCe(1-x)Nd(x)Ti2O6 (0 < or = x < or = 1) and NaCeTi(2-x)V(x)O6 (0 相似文献   

XANES determination of the platinum oxidation state distribution in cancer cells treated with platinum(IV) anticancer agents

Here we describe the use of X-ray absorption near edge spectroscopy (XANES) to provide information about the relative proportions of platinum(II) and platinum(IV) complexes by analyzing the XANES edge height. The intracellular reduction of platinum(IV) complexes in cancer cells has been observed directly, and the proportion of reduction after 2 h was found to correlate with the reduction potentials of the complexes.     

Correlation of the oxidation state of cerium in sol-gel glasses as a function of thermal treatment via optical spectroscopy and XANES studies

Sol-gel glass matrices containing lanthanides have numerous technological applications and their formation involves several chemical facets. In the case of cerium, its ability to exist in two different oxidation states or in mixed valence state provides additional complexities for the sol-gel process. The oxidation state of cerium present during different facets of preparation of sol-gel glasses, and also as a function of the starting oxidation state of cerium added, were studied both by optical spectroscopy and X-ray absorption near-edge structures (XANES). The findings acquired by each approach were compared. The primary focus was on the redox chemistries associated with sample preparation, gelation, and thermal treatment. When Ce3+ is introduced into the starting sols, the trivalent state normally prevails in the wet and room temperature-dried gels. Heating in air at >100 degrees C can generate a light yellow coloration with partial oxidation to the tetravalent state. Above 200 degrees C and up to approximately 1000 degrees C, cerium is oxidized to its tetravalent state. In contrast, when tetravalent cerium is introduced into the sol, both the wet and room temperature-dried gels lose the yellow-brown color of the initial ceric ammonium nitrate solution. When the sol-gel is heated to 110 degrees C it turns yellowish as the cerium tends to be re-oxidized. The yellow color is believed to represent the effect of oxidation and oligomerization of the cerium-silanol units in the matrix. The luminescence properties are also affected by these changes, the details of which are reported herein.     

Study of oxidation state of plutonium in solution by flow-coulometric method

Reduction rates of Pu(IV) and oxidation rates of Pu(III) have been studied in sulphuric acid and nitric acid media, as functions of acid concentration, plutonium concentration and kind of acid. A flow-coulometric method was used in this work. This procedure has many merits, namely, the sample size required is very small, special reagents are not used, fewer limitations are imposed by the type and concentration of acid, and the method is rapid.     

A high-throughput LC-MS/MS method suitable for population biomonitoring measures five serum folate vitamers and one oxidation product

Small specimen volume and high sample throughput are key features needed for routine methods used for population biomonitoring. We modified our routine eight-probe solid phase extraction (SPE) LC-MS/MS method for the measurement of five folate vitamers [5-methyltetrahydrofolate (5-methylTHF), folic acid (FA), plus three minor forms: THF, 5-formylTHF, 5,10-methenylTHF] and one oxidation product of 5-methylTHF (MeFox) to require less serum volume (150 μL instead of 275 μL) by using 96-well SPE plates with 50 mg instead of 100 mg phenyl sorbent and to provide faster throughput by using a 96-probe SPE system. Total imprecision (10 days, two replicates/day) for three serum quality control pools was 2.8–3.6 % for 5-methylTHF (19.5–51.1 nmol/L), 6.6–8.7 % for FA (0.72–11.4 nmol/L), and ≤11.4 % for the minor folate forms (<1–5 nmol/L). The mean (±SE) recoveries of folates spiked into serum (3 days, four levels, two replicates/level) were: 5-methylTHF, 99.4?±?3.6 %; FA, 100?±?1.8 %; minor folates, 91.7–108 %. SPE extraction efficiencies were ≥85 %, except for THF (78 %). Limits of detection were ≤0.3 nmol/L. The new method correlated well with our routine method [n?=?150, r?=?0.99 for 5-methylTHF, FA, and total folate (tFOL, sum of folate forms)] and produced slightly higher tFOL (5.6 %) and 5-methylTHF (7.3 %) concentrations, likely due to the faster 96-probe SPE process (1 vs. 5 h), resulting in improved SPE efficiency and recovery compared to the eight-probe SPE method. With this improved LC-MS/MS method, 96 samples can be processed in ～2 h, and all relevant folate forms can be accurately measured using a small serum volume.

Determination of the local structure and parameters of the one-electron potential from XANES data (inverse problem of XANES theory)

A method of obtaining complex information on the structure of polyatomic systems using experimental data for one-electron quasistationary state (shape resonance) is developed. The method involves the equation for S-matrix poles in the muffintin (MT) approximation. The parameters of the model (intemuclear distances, valence angles, and potential characteristics) are fitted in such a way that the S-matrix poles in a complex energy plane be maximally close to {E-iГ/2}, where E and Fare the energies and widths of the XANES maxima of one-electron origin. Testing the method on a number of objects shows that it determines internuclear distances with an accuracy of 1% and valence angles with an accuracy of 3%. Among the potentials of this type, the empirical potentials obtained are the best for describing shape resonances. The suggested scheme is applicable in determining the microstructure and in the cases where the diffraction methods of structural analysis do not work (unordered systems, molecular adsorption on the surface of solids, etc.). Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1013–1017, November–December, 1998.     

Fast drug-receptor mapping by site-directed distances: a novel method of predicting new pharmacological leads

The searching and characterization of large chemical databases has recently provoked much interest, particularly with respect to the question of whether any of the compounds in the database could serve as new leads to a compound of pharmacological interest. This paper introduces a fast and novel method of determining whether any of a given series of compounds are able, on geometrical grounds, to interact with an active site of interest. The C program written to implement the method is able to make a qualitative prediction for a given compound in about 1 s per structure (for drug-sized molecules), while still permitting the compound complete conformational freedom. However, the algorithm is sufficiently flexible to permit distance constraints to be placed on the molecules while docking. The test system studied was a family of Baker's triazines docking into the active site of dihydrofolate reductase (DHFR), as defined by a methotrexate/NADPH complex.     

Windows-based guided data capture software for mass-scale thermophysical and thermochemical property data collection

Guided data capture software (GDC) is described for mass-scale abstraction from the literature of experimental thermophysical and thermochemical property data for organic chemical systems involving one, two, and three components, chemical reactions, and chemical equilibria. Property values are captured with a strictly hierarchical system based upon rigorous application of the thermodynamic constraints of the Gibbs phase rule with full traceability to source documents. Key features of the program and its adherence to scientific principles are described with particular emphasis on data-quality issues, both in terms of data accuracy and database integrity.     

Triplet state mechanism for electron transfer oxidation of DNA

The interaction of anthraquinone-2-sulfonate with nucleotides and DNA in acetonitrile and acetonitrile water solvent mixture have been studied using KrF laser photolysis aimed at elucidation of the reaction mechanism. Laser spectroscopy directly demonstrates that the initial species from interaction of anthraquinone-2-sulfonate with nucleotides are radical cations of nucleotides and radical anion of anthraquinone-2-sulfonate. In addition, formation of ion pair from interaction of any of nucleotides with anthraquinone-2-sulfonate is synchronous with decay of triplet anthraquinone-2-sulfonate, which has provided dynamic evidence for initiation of electron transfer from DNA bases to triplet anthraquinone-2-sulfonate. Moreover, direct observation of stabilized DNA guanyl radical cation from interaction of anthraquinone-2-sulfonate with DNA has provided initial evidence for selective cleavage of DNA at guanine moiety. The solvent-separated ion pairs in acetonitrile have evidently dissociated into free ions, thereby enabling independent study of the behavior of guanyl radical cations and radical anion of anthraquinone-2-sulfonate.     

A simple method for evaluation of parameters of the Bender equation of state from experimental data

A simple numerical method for evaluation of parameters (constants) of Bender equation of state for pure fluids is proposed. The minimisation of the objective function leads to a set of linear equations. The method employs experimental data on state behaviour (p–ρ–T) of fluid phases, vapour–liquid equilibrium data (saturated vapour pressures and orthobaric densities), second virial coefficients, and the coordinates of the gas–liquid critical point. Results of the tests using data for two fluids (methane and n-pentane) are presented.     

Fast mapping of protein-protein interfaces by NMR spectroscopy

Identifying the interface of protein complexes can represent a difficult task in structural biology. Here, we report a method for the fast mapping of interfaces of protein complexes by NMR without the need for the assignments of the proteins involved.     

A comprehensive critical collection of electrochemical data

Ready access to the data embodied in the scientific literature is essential for those attempting to devise new applications for analytical methods. Many of the compilations of polarographic data which have been made in the past are now incomplete and obsolete. A more comprehensive and enduring database for polarography is now being compiled.     

Considerations for the automated collection of thermodynamic data in gas chromatography

Thermodynamic modeling of retention times in gas chromatography depends on the accurate estimation of thermodynamic parameters. Previous research has used manual injections of samples with coinjection of a dead time marker to obtain accurate measurements of the retention factor of analytes. Ideally this process would be automated. Herein an approach is presented by which thermodynamic parameters can be estimated both autonomously and accurately. This method also allows for a consistent estimation of thermodynamic parameters regardless of factors such as data system delays and the nature of the void time marker employed. Ignoring these factors can lead to significant errors in the prediction of retention times when using thermodynamic models.     

Native red electrophoresis--a new method suitable for separation of native proteins

A new type of native electrophoresis was developed to separate and characterize proteins. In this modification of the native blue electrophoresis, the dye Ponceau Red S is used instead of Coomassie Brilliant Blue to impose uniform negative charge on proteins to enable their electrophoretic separation according to their relative molecular masses. As Ponceau Red S binds less tightly to proteins, in comparison with Coomassie Blue, it can be easily removed after the electrophoretic separation and a further investigation of protein properties is made possible (e.g. an enzyme detection or electroblotting). The tested proteins also kept their native properties (enzyme activity or aggregation state).     

Variations in electronic state of silver catalysts for methanol oxidation

Variations in the electronic state of silver catalysts for methanol oxidation under the effect of the reaction medium have been studied, using diffuse reflectance spectroscopy. The nature of active centers-Ag⁺ cations, Ag _n ⁺ complexes and clusters of various sizes for bulk and supported catalysts are shown to be identical.

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. - Ag⁺, Ag _n ⁺ .