The present study involves the fabrication of a novel photoanode comprising oxygen-deficient porous structured hematite nanorods (Vo-α-Fe2O3 PNRs), which was subsequently employed as the support for Pt anchoring to catalyze methanol oxidation reaction (MOR). Interestingly, the catalytic characters of the proposed photoanodes towards MOR displayed notable disparities upon Pt decoration via electrodeposition in comparison to photoreduction. The electrode after Pt modification through photoreduction (Vo-α-Fe2O3 PNRs/Ptphotoreduction) demonstrated a cyclic voltammetry hysteresis pattern towards methanol typical oxidation catalysis, exhibiting a peak current density of 2.46 mA/cm2 at 0.71 VRHE in the forward scan. While the electrode after Pt electrodeposition (Vo-α-Fe2O3 PNRs/Ptelectrodeposition) showed a robust photocurrent lift as the voltage increases in the voltammogram, achieving 2.5 mA/cm2 at 0.7 VRHE. The product generated at the latter electrode was identified to be formaldehyde with an impressive Faradaic efficiency of 95%. The detailed study revealed that the distinct catalytic behavior of the two electrodes may be attributed to their disparate reaction kinetics on the electrode surface, which is mainly influenced by their charge transfer resistance and consequently leads to different reaction pathways. This study proposed a novel strategy for the synthesis of Pt-metal oxide photoelectrochemical catalysts utilized as a tunable efficient photoelectrocatalyst for methanol utilization.
[62535-08-4] C4H16N4Cl2Pt (MW 386.19) InChI = 1S/2C2H8N2.2ClH.Pt/c2*3-1-2-4;;;/h2*1-4H2;2*1H;/q;;;;+4/p-2 InChIKey = VWAWJCIOMHLCCV-UHFFFAOYSA-L (reagent used for highly selective and rapid formation of intramolecular disulfide bonds in peptides) Alternate Name: dichlorobis(1,2-ethanediamine-N,N′)platinum(IV). Physical Data: 1H NMR (D2O) δ 2.87 ppm, J(1H-195Pt) = 26 Hz; 13C NMR (D2O) δ 47.6 ppm.1 Solubility: soluble in H2O and some solvent mixtures such as water–methanol, water–acetonitrile; insoluble in most organic solvents. Form Supplied in: this is a complex cation, existing in different forms when isolated with different counter-ions; with chloride as counter-ions, two forms of the Pt(IV) complex, [Pt(en)2Cl2]Cl2 and [Pt(en)2Cl2]Cl2·2H2O, can be prepared. Both forms are a slightly yellowish white powder; they are not commercially available. Preparative Methods: the title reagent can be prepared by heating bis(ethylenediamine)platinum(II) chloride (commercially available) and excess hydrogen peroxide in aqueous HCl solution to 80–100 °C.2, 3 Handling, Storage, and Precautions: solid forms of [Pt(en)2Cl2]Cl2 and [Pt(en)2Cl2]Cl2·2H2O are stable at room temperature and can be handled in the open. Solutions of the complex containing some NaCl or dilute HCl are stable for weeks to months.
Spectrophotometric equilibrium measurements indicate formation of the complexes [Pd(H2O)(3)HSO4](+) and [Pd(H2O)(3)SO4] in the reaction between [Pd(H2O)(4)](2+) and hydrogen sulfate/sulfate in the region: 0.10 less than or equal to [H+] less than or equal to 0.80 M. The stability constants are 0.7 +/- 0.2 and 19 +/- 6 M-1, respectively, at 25 degrees C and 1.00 M ionic strength. The protolysis constant for coordinated hydrogen sulfate, i.e. the equilibrium constant for the reaction [Pd(H2O)(3)HSO4](+) +H2O reversible arrow[Pd(H2O)(3)SO4] + H3O+, is 2.5 +/- 1.0 M. The stability constant for [Pd(H2O)(3)HSO4](+) and the protolysis constant for coordinated HSO4- are also derived from kinetic measurements as 0.6 +/- 0.2 M-1 and 2.3 +/- 1.3 M, respectively. The kinetics for the reversible complex formation reaction, studied by use of stopped-flow spectrophotometry, is first order with respect to palladium complex and total concentration of sulfate, [S(VI)], with an observed pseudo-first-order rate constant k(obsd) = k(f)[S(VI)] + k(r) for excess sulfate. Here k(f) and k(r) denote observed forward second-order and reverse first-order rate constants, respectively. The kinetic data are interpreted in terms of a reaction mechanism which involves parallel and reversible reactions between [Pd(H2O)(4)](2+) and HSO4- and SO42-, respectively, and between [Pd(H2O)(3)OH](+) and HSO4-. Forward and reverse rate constants for complex formation between [Pd(H2O)(4)](2+) and HSO4- are 119 +/- 6 M-1 s(-1) and 210 +/- 60 s(-1) at 25 degrees C, indicating that HSO4- has a similar nucleophilicity as other oxygen-donor ligands. The rate constants for the reactions of [Pd(H2O)(4)](2+) with SO42- and of [Pd(H2O)(3)OH](+) with HSO4- cannot be resolved because of a proton ambiguity. The mononuclear protolysis constant of [Pd(H2O)(4)](2+) is pK(h) = 3.0 +/- 0.1 at 25 degrees C and 1.00 M ionic strength as determined from rapid spectrophotometric equilibrium measurements. (Less)
In this study, we developed an efficient approach for disulfide bond formation in peptides utilizing the Pt(IV) complex trans-[PtBr2(CN)4]2– to mediate Acm and Thz deprotections. [PtBr2(CN)4]2– can oxidatively deprotect two Acm groups or deprotect one Thz group and one Acm group to directly form an intramolecular disulfide bond in peptides. Several disulfide-containing peptides with excellent yields were achieved via the deprotection method in an aqueous medium under aerobic conditions. Kinetic studies indicated that the dominant path of the reaction is of first-order in both [Pt(IV)] and [peptide]; moreover, the deprotection rate increased dramatically with the addition of NaBr. A mechanism including a bromide-bridge-mediated electron transfer process was proposed. Apamin, α-conotoxin SI, and the parallel homodimer of oxytocin, all containing two disulfide bonds, were synthesized regioselectively through a one-pot method by the combined use of the above deprotection approach with oxidants l-methionine selenoxide and [PtBr2(CN)4]2–. All of the reactions were completed within 30 min to afford good yields for these peptides.
cis hat Bestand: Die Population mit cis-Konformation der Cys-Pro-Imidbindung in der cyclischen Disulfidform der Peptide Ac-Cys-Pro-(Xaa)m-Cys-NH2 (Xaa=Phe, Ala) beträgt 9.3 bis 76.9 %. Dabei zeigt sich klar eine Periodizität bezüglich der Anzahl von Aminosäuren im Peptid.
An anthraquinone dye underwent supramolecular polymerization, affording 2D-monolayered nanosheets in a kinetically controlled state. The nanosheets then transformed into hierarchically chiral aggregates in a thermodynamically controlled step. The unanticipated role played by pathway complexity was clearly unravelled in this work, highlighting the diversified pathways in the supramolecular polymerization of various building blocks.
The kinetics and mechanism for substitution reactions on tetraaquapalladium(II) by an extended series of thioethers, a great number of carboxylic acids, and olefins have been studied by use of UV-VIS, stopped-flow, and high-pressure stopped-flow spectrophotometry and NMR spectroscopy. Second-order rate constants k and activation parameters (activation enthalpies, entropies, and volumes) for formation of monodentate 1:1 complexes have been determined. The reactivity of thioethers toward the metal center can be described by a 3-term equation, in while the electronic effects and steric requirements are expressed by the sum of Taft constants and the ligand cone angle, respectively. The reactivity trends of thioethers toward other square-planar complexes reported in literature can be given a general interpretation. Neither basicity nor steric factors of carboxylic acids influence their reactivities toward the Pd(II) complex in a significant extent due to an excellent isokinetic relation between activation enthalpies and and entropies. Analysis of volume profiles for the carboxylic acid reactions and a linear relation between logk and logK observed for all experimental data so far for tetraaquapalladium(II) complex formation reactions support an Ia mechanism. Reaction between maleic acid and the metal complex results in a chelate with one carboxylate group and the carbon-carbon double bond coordinated to the metal center. The complicated kinetics has been analyzed in terms of a reaction mechanism involving several consecutive and parallel pathways. The kinetics and mechanism for reduction of trans-dichlorotetracyanoplatinate(IV) (as a model compound for Pt(IV) antitumor prodrugs) by l-methionine and thiols (thioglycolic acid, l-cysteine, dl-penicillamine, and glutathione) have been studied in a wide pH range by use of stopped-flow spectrophotometry. Reduction proceeds via parallel pathways involving various protolytic species and via transition states where electron transfer is mediated by coordinated halide. Two types of Bronsted correlations have been found for the thiol reactions, suggesting that the basicity is the predominant factor in determining the reactivity of thiols toward the Pt(IV) complex. This has been interpreted in terms of different transition states. The present work demonstrates that Pt(IV) complexes are reduced rapidly at physiological pH, implying that Pt(IV) antitumor prodrugs are very likely being reduced to their Pt(II) analogues before interaction with DNA. Several structure-reactivity correlations have been derived and a number of experimental relations have been examined, enabling rationalization and systematization of reactivity in a broad sense and also improving the understanding of the reaction mechansims. (Less)
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