ChemInform Abstract: METAL ION-LIGAND REDOX REACTION

1978 ◽  
Vol 9 (33) ◽  
Author(s):  
A. G. LAPPIN
Keyword(s):  
Redox Reaction ◽  
Metal Ion

Metal-ion oxidations in solution. Part XIX. Redox pathways in the oxidation of penicillamine and glutathione by chromium(VI)

1977 ◽  
Vol 55 (18) ◽  
pp. 3335-3340 ◽  
Author(s):  
Alexander McAuley ◽  
M. Adegboyega Olatunji
Keyword(s):  
Ion Exchange ◽  
Redox Reaction ◽  
Metal Ion ◽  
Hydrogen Ion ◽  
Stopped Flow ◽  
Ion Concentrations ◽  
Flow Method ◽  
Chromium Vi ◽  
Reaction Proceeds ◽  
Transient Intermediate

Three moles of penicillamine or glutathione are required to reduce chromium(VI) to chromium(III). The kinetics and mechanism of the redox reaction have been studied using the stopped-flow method. The reaction proceeds via the formation of a transient intermediate (K1) which decomposes either in a proton-catalyzed pathway or by reaction with a second mole of thiol. The rate law[Formula: see text]where n = 1 for penicillamine and 2 for glutathione has been shown to hold over a range of thiol and hydrogen-ion concentrations. At 25 °C k2 = 14.3 ± 1.0 M−1 s−1 for penicillamine (ΔH≠ = 9 ± 2 kcal mol−1, ΔS≠ = −33 ± 6 cal K−1 mol−1) and 12.1 ± 0.4 M−1 s−1 for glutathione (ΔH≠ = 7 ± 2 kcal mol−1, ΔS≠ = −40 ± 5 cal K−1 mol−1). Several chromium(III) products have been identified by ion-exchange methods. The significance of the second-order pathways in these reactions is discussed.

Metal-ion oxidations in solution. Part XX. The mechanism of the reaction of thallium (III) with 2-mercaptosuccinic acid in perchlorate media

1977 ◽  
Vol 55 (20) ◽  
pp. 3575-3580 ◽  
Author(s):  
Zahid Amjad ◽  
John G. Chambers ◽  
Alexander McAuley
Keyword(s):  
Electron Transfer ◽  
Redox Reaction ◽  
Metal Ion ◽  
Reaction Scheme ◽  
Mercaptosuccinic Acid ◽  
Enthalpy Of Activation ◽  
Electron Transfer Pathways ◽  
Intramolecular Transfer ◽  
Mechanism Of The Reaction ◽  
Sphere Mechanism

The oxidation of 2-mercaptosuccinic (thiomalic) acid (HRSH) by thallium(III) proceeds via an inner sphere mechanism. Spectrophotometric and kinetic evidence are provided for the formation of a sulphur-bonded thallium(III) intermediate. The data are consistent with the reaction scheme[Formula: see text]in which the complex decomposes via a one-electron intramolecular transfer k2 = 3.8 × 10−4 s−1 at 25 °C, with K2 = 1650 M−1. The enthalpy of activation ΔH2≠ for the redox reaction (11.8 ± 1.2 kcal/mol) is considerably smaller than for other systems of this type and reflects the greater ease of reaction. Comparison is made of possible one- and two-electron transfer pathways.

Aspects of high-resolution imaging with a scanning ion microprobe

1986 ◽  
Vol 44 ◽  
pp. 750-751
Author(s):  
R. Levi-Setti ◽  
J. M. Chabala ◽  
Y. L. Wang
Keyword(s):  
Metal Ion ◽  
Secondary Ion Mass Spectrometry ◽  
Chromatic Aberration ◽  
Ion Source ◽  
Ion Microprobe ◽  
Emission Pattern ◽  
Intrinsic Resolution ◽  
Resolution Imaging ◽  
20 Nm ◽  
Secondary Ion

We have shown the feasibility of 20 nm lateral resolution in both topographic and elemental imaging using probes of this size from a liquid metal ion source (LMIS) scanning ion microprobe (SIM). This performance, which approaches the intrinsic resolution limits of secondary ion mass spectrometry (SIMS), was attained by limiting the size of the beam defining aperture (5μm) to subtend a semiangle at the source of 0.16 mr. The ensuing probe current, in our chromatic-aberration limited optical system, was 1.6 pA with Ga+ or In+ sources. Although unique applications of such low current probes have been demonstrated,) the stringent alignment requirements which they imposed made their routine use impractical. For instance, the occasional tendency of the LMIS to shift its emission pattern caused severe misalignment problems.

Scanning ion microscopy images

1987 ◽  
Vol 45 ◽  
pp. 180-181
Author(s):  
R. Levi-Setti ◽  
J.M. Chabala ◽  
Y.L. Wang
Keyword(s):  
Metal Ion ◽  
Secondary Emission ◽  
Scanning Method ◽  
Ion Channeling ◽  
Secondary Ions ◽  
High Resolution Images ◽  
Ion Microscopy ◽  
Z Contrast ◽  
Focused Beams ◽  
Microscopy Images

Finely focused beams extracted from liquid metal ion sources (LMIS) provide a wealth of secondary signals which can be exploited to create high resolution images by the scanning method. The images of scanning ion microscopy (SIM) encompass a variety of contrast mechanisms which we classify into two broad categories: a) Emission contrast and b) Analytical contrast.Emission contrast refers to those mechanisms inherent to the emission of secondaries by solids under ion bombardment. The contrast-carrying signals consist of ion-induced secondary electrons (ISE) and secondary ions (ISI). Both signals exhibit i) topographic emission contrast due to the existence of differential geometric emission and collection effects, ii) crystallographic emission contrast, due to primary ion channeling phenomena and differential oxidation of crystalline surfaces, iii) chemical emission or Z-contrast, related to the dependence of the secondary emission yields on the Z and surface chemical state of the target.

Freeze-etch TEM of aqueous polymer gel network morphology

1986 ◽  
Vol 44 ◽  
pp. 796-797
Author(s):  
J. A. N. Zasadzinski ◽  
R. K. Prud'homme
Keyword(s):  
Metal Ion ◽  
Polymer Network ◽  
Polymer Gels ◽  
Polymer Gel ◽  
Deformation History ◽  
Crosslinked Polymer ◽  
Aqueous Polymer ◽  
History Of ◽  
Gel Network ◽  
Network Morphology

The rheological and mechanical properties of crosslinked polymer gels arise from the structure of the gel network. In turn, the structure of the gel network results from: thermodynamically determined interactions between the polymer chain segments, the interactions of the crosslinking metal ion with the polymer, and the deformation history of the network. Interpretations of mechanical and rheological measurements on polymer gels invariably begin with a conceptual model of,the microstructure of the gel network derived from polymer kinetic theory. In the present work, we use freeze-etch replication TEM to image the polymer network morphology of titanium crosslinked hydroxypropyl guars in an attempt to directly relate macroscopic phenomena with network structure.

Structures of c-di-GMP/cGAMP degrading phosphodiesterase VcEAL: identification of a novel conformational switch and its implication

2019 ◽  
Vol 476 (21) ◽  
pp. 3333-3353 ◽  
Author(s):  
Malti Yadav ◽  
Kamalendu Pal ◽  
Udayaditya Sen
Keyword(s):  
Active Site ◽  
Metal Binding ◽  
Metal Ion ◽  
Triosephosphate Isomerase ◽  
Catalytic Mechanism ◽  
Degradation Mechanism ◽  
Structural Basis ◽  
Conserved Residues ◽  
Phosphodiester Bond ◽  
Cyclic Dinucleotides

Cyclic dinucleotides (CDNs) have emerged as the central molecules that aid bacteria to adapt and thrive in changing environmental conditions. Therefore, tight regulation of intracellular CDN concentration by counteracting the action of dinucleotide cyclases and phosphodiesterases (PDEs) is critical. Here, we demonstrate that a putative stand-alone EAL domain PDE from Vibrio cholerae (VcEAL) is capable to degrade both the second messenger c-di-GMP and hybrid 3′3′-cyclic GMP–AMP (cGAMP). To unveil their degradation mechanism, we have determined high-resolution crystal structures of VcEAL with Ca2+, c-di-GMP-Ca2+, 5′-pGpG-Ca2+ and cGAMP-Ca2+, the latter provides the first structural basis of cGAMP hydrolysis. Structural studies reveal a typical triosephosphate isomerase barrel-fold with substrate c-di-GMP/cGAMP bound in an extended conformation. Highly conserved residues specifically bind the guanine base of c-di-GMP/cGAMP in the G2 site while the semi-conserved nature of residues at the G1 site could act as a specificity determinant. Two metal ions, co-ordinated with six stubbornly conserved residues and two non-bridging scissile phosphate oxygens of c-di-GMP/cGAMP, activate a water molecule for an in-line attack on the phosphodiester bond, supporting two-metal ion-based catalytic mechanism. PDE activity and biofilm assays of several prudently designed mutants collectively demonstrate that VcEAL active site is charge and size optimized. Intriguingly, in VcEAL-5′-pGpG-Ca2+ structure, β5–α5 loop adopts a novel conformation that along with conserved E131 creates a new metal-binding site. This novel conformation along with several subtle changes in the active site designate VcEAL-5′-pGpG-Ca2+ structure quite different from other 5′-pGpG bound structures reported earlier.

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