An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In a mixture of trifluoroacetic acid and water, the combination of metallic palladium and copper chloride catalyzes the hydroxylation of remote primary C−H bonds of a variety of acids, alcohols, and aliphatic halides, in the presence of carbon monoxide and dioxygen. Experiments suggest that the principal role of metallic palladium is to generate hydrogen peroxide in situ and that the species responsible for the remote hydroxylation of the substrate by hydrogen peroxide is copper chloride. The unusual preference for the catalytic hydroxylation of primary C−H bonds was also found in an experiment involving competition between ethane and either cumene or p-isopropylbenzoic acid: even though the solution concentration of ethane was significantly lower than the competing substrate, the vast majority of the oxidation product (ethanol) was derived from ethane. In the reactions studied, acetic acid and formic acid were formed through C−C cleavage steps. An examination of the site of C−C cleavage in propionic acid indicated that both C−C bonds were being broken.
Journal Article A Note on Rupe's Rearrangement Get access W H Linnell, W H Linnell Pharmaceutical Chemistry Research Laboratories of the School of Pharmacy, University of London Search for other works by this author on: Oxford Academic Google Scholar C C Shen C C Shen Pharmaceutical Chemistry Research Laboratories of the School of Pharmacy, University of London Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 2, Issue 1, September 1950, Pages 13–16, https://doi.org/10.1111/j.2042-7158.1950.tb12897.x Published: 12 April 2011 Article history Received: 14 October 1949 Published: 12 April 2011
Silica hydrogel (glass) was doped with native (iron-containing) cytochrome c and with its zinc derivative. Ultraviolet−visible, circular dichroism, and resonance Raman spectra of both proteins and the lifetime of the triplet state of the zinc protein show that encapsulation in the sol-gel glass only slightly perturbs the polypeptide backbone and does not detectably perturb the heme group. Because thermal (ground-state) redox reactions of the encapsulated native cytochrome c are very slow, we take advantage of the transparency of the silica to study, by laser flash spectrometry, photoinduced (excited-state) redox reactions of zinc cytochrome c, which occur in milliseconds. The triplet state, 3Zncyt, is oxidatively quenched by [Fe(CN)6]3-, dioxygen, and p-benzoquinone. These reactions are monophasic in bulk solutions but biphasic in solutions confined in glass. Changes in ionic strength and pH differently affect the kinetics in these two environments. Adsorption of cytochrome c, which is positively charged, to the pore walls, which are negatively charged at pH 7.0, affects the kinetics in the doped glass. Exclusion of the [Fe(CN)6]3- anions from the glass interior also affects the kinetics. Even at equilibrium the anion concentration is lower inside the glass than in the external solution. This exclusion can be lessened or eliminated by raising ionic strength and lowering the pH value. The electroneutral quenchers are not excluded from the glass. Diffusion of all three quenchers is slower in the confined solution than in the bulk solution, as expected. The smaller the molecule, the lesser this hindrance by the glass matrix. In light of these findings, the assumption that porosity of sol-gel glasses ensures uniform penetration of relatively small molecules into the pores must be taken skeptically and tested for each solute (or analyte) of interest, especially for the charged ones. These considerations are important in the design of sensors.
The long-lived triplet state of zinc cytochrome c, designated 3Zn(cyt), has often been used as a reductant, in oxidative-quenching reactions. This article seems to be the first report of the use of 3Zn(cyt) as an oxidant, in two reductive-quenching reactions. Conjugate bases (anions) of ethylenediaminetetraacetic acid (EDTA) quench 3Zn(cyt) at pH 6.5 with the observed rate constant that is 2 times greater than the rate constant for natural decay of this excited state. Electrostatic attraction between these quenchers and Zn(cyt) is a necessary but not sufficient condition for quenching. A transient species observed at 690 nm has the absorbance and the time profile expected of the anion radical Zn(cyt)-. Detection of this species is possible because of the rapid decomposition of EDTA upon oxidation. The complex [Fe(CN)6]4- quenches 3Zn(cyt) at pH 7.0 with the rate constant of (1.5 ± 0.3) × 108 M-1 s-1. This fast quenching is not caused by electrostatic association of 3Zn(cyt) and [Fe(CN)6]4- nor by energy transfer from the former to the latter. The complex [Fe(CN)6]4- is not detectably contaminated by the similar complex [Fe(CN)6]3-, which might act as an oxidative quencher. The evidence supports reductive quenching of 3Zn(cyt) by the [Fe(CN)6]4- ion. The anion radical Zn(cyt)- is not detected, probably because it is rapidly consumed in the back-reaction with the [Fe(CN)6]3- ion. To act as reductive quenchers for 3Zn(cyt), chemicals must have favorable electrostatic properties, redox potential, and reactivity. These requirements are discussed so that further studies of this new reaction may be possible.
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