The dependence of the rates of reduction of cobalt(III)-μ-peroxo complexes on isomeric structure

1984 ◽  
Vol 62 (11) ◽  
pp. 2127-2130 ◽  
Author(s):  
Steve C. F. Au-Yeung ◽  
Donald R. Eaton
Keyword(s):  
Rate Constants ◽  
Chemical Shifts ◽  
Cobalt Complex ◽  
Stopped Flow ◽  
Ferrous Ions ◽  
Point Charge Model ◽  
Isomeric Structure ◽  
Initial Reduction ◽  
Charge Model ◽  
Flow Experiments

The reaction of μ-peroxybis(ethylenediamine)bis(diethylenetriamine)cobalt(III) with ferrous ions has been studied by stopped flow spectrophotometry and by 59Co nmr. Two separate initial reduction steps with second order rate constants of 1.07 and 3.04 M−1 s−1, respectively, can be discerned in the stopped flow experiments. These two rate constants are assigned to inner sphere reduction of the aef,cd,b and edf,ac,b isomers of the peroxy cobalt complex, respectively. The different isomers can be distinguished by 59Co nmr. If there is insufficient Fe2+ present to completely reduce the complex to Co(II) and water, the change in the relative intensities of the 59Co resonances after partial reduction shows that one isomer has reacted faster than the other. The 59Co resonances can be assigned to the different isomers on the basis of a point charge model for the chemical shifts and line widths. Based on this model it is concluded that the isomer with the central NH of the diethylenetriamine trans to the peroxy ligand reacts faster. This result is compared to literature reports on the relative rates of substitution of isomers of Co(III) complexes with ethylenediamine and diethylenetriamine ligands.

Octahedral point-charge model and its application to fragment molecular orbital calculations of chemical shifts

2014 ◽  
Vol 593 ◽  
pp. 165-173 ◽  
Author(s):  
Qi Gao ◽  
Satoshi Yokojima ◽  
Dmitri G. Fedorov ◽  
Kazuo Kitaura ◽  
Minoru Sakurai ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Point Charge ◽  
Chemical Shifts ◽  
Molecular Orbital Calculations ◽  
Point Charge Model ◽  
Fragment Molecular Orbital ◽  
Charge Model

scholarly journals Inhibitory efficiencies for mechanism-based inactivators of sialidases

2015 ◽  
Vol 93 (11) ◽  
pp. 1207-1213 ◽  
Author(s):  
Kobra Khazaei ◽  
Juliana H.F. Yeung ◽  
Margo M. Moore ◽  
Andrew J. Bennet
Keyword(s):  
Sialic Acid ◽  
Aspergillus Fumigatus ◽  
Kinetic Parameters ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Fluoride Ion ◽  
Stopped Flow ◽  
Leaving Group ◽  
Inhibitory Efficiency ◽  
Flow Experiments

Here we describe the measurement of the inactivation rate constants for the mechanism-based inactivator 2,3-difluorosialic acid acting upon the sialidase from Micromonospora viridifaciens. Using double mixing stopped-flow experiments conducted in a 3-(N-morpholino)propanesulfonic acid buffer (100 mmol/L, pH 7.00) at 25 °C, the derived kinetic parameters are kinact/Ki = (3.9 ± 0.8) × 106 (mol/L)–1 s–1 and Ki = 1.7 ± 0.4 μmol/L. We demonstrate that the inhibitory efficiency of the inactivation event is similar to the catalytic efficiency for this sialidase acting upon a typical substrate, 4-methylumbelliferone α-d-sialoside, kcat/Km = (7.2 ± 2.8) × 106 (mol/L)–1 s–1. Furthermore, we show that the catalytic efficiencies for inactivation and hydrolysis by the Kdnase from Aspergillus fumigatus are similar for the corresponding Kdn-analogues. We conclude that the deactivating effect of incorporating an axial 3-fluoro substituent onto the sialic acid scaffold is comparable to the enhanced activation that occurs when the 4-methylumbelliferone leaving group is changed to the more nucleofugal fluoride ion.

A model for estimating 59Co nmr chemical shifts and line widths and its application to cobalt dioxygen complexes

1983 ◽  
Vol 61 (10) ◽  
pp. 2431-2441 ◽  
Author(s):  
Steve C. F. Au-Yeung ◽  
Donald R. Eaton
Keyword(s):  
Chemical Shift ◽  
Line Width ◽  
Point Charge ◽  
Chemical Shifts ◽  
Shift Parameter ◽  
Point Charge Model ◽  
Additional Information ◽  
Charge Model ◽  
Line Widths ◽  
Experimental Values

A simple point charge model has been developed for calculating the chemical shifts and line widths obtained from the 59Co nmr spectra of Co(III) complexes. The chemical shift calculations assume the predominance of the paramagnetic term in the Ramsey equation and the relationship of this term to the energies of the d–d electronic transitions. The line width calculations assume the predominance of quadrupolar broadening and use a point charge model to calculate electric field gradients in a manner previously used to interpret Mössbauer spectra. The model is tested by application to some fifty known Co(III) complexes. Most of the 59Co spectra have been remeasured for this purpose. One chemical shift parameter and one line width parameter are required for each different type of ligand. These parameters are related to each other and to the crystal field splitting parameters of the ligands. The calculations can be readily applied to complexes of any symmetry and differentiate between different isomers of the same complex. The calculated chemical shifts cover a range of more than 14 000 ppm and the standard deviation between the calculated and experimental values is 108 ppm. Relative chemical shifts between complexes with similar ligands are calculated with considerably higher accuracy. The agreement between calculated and experimental line widths is only qualitative but the line width calculations provide valuable additional information for making assignments. The model is applied to the assignment of different isomers of cobalt dioxygen compounds and to the identification of products from oxygenation reactions.

scholarly journals Determination of the kinetics underlying the pKa shift for the 2-aminoanthracenium cation binding with cucurbit[7]uril

2015 ◽  
Vol 185 ◽  
pp. 381-398 ◽  
Author(s):  
Suma S. Thomas ◽  
Cornelia Bohne
Keyword(s):  
Rate Constants ◽  
Cation Binding ◽  
Stopped Flow ◽  
Ph Values ◽  
Pka Shift ◽  
Changes Over Time ◽  
Initial Binding ◽  
Flow Experiments ◽  
Over Time

The binding dynamics of the 2-aminoanthracenium cation (AH+) and 2-aminoanthracene (A) with cucurbit[7]uril (CB[7]) was studied using stopped-flow experiments. The kinetics was followed by measuring the fluorescence changes over time for AH+ and A, which emit at different wavelengths. The studies at various pH values showed different mechanisms for the formation of the AH+@CB[7] complex, with this complex formed either by the binding of AH+ or by the initial binding of A followed by protonation. In the latter case, it was possible to determine the protonation ((1.5 ± 0.4) × 109 M−1 s−1) and deprotonation (89 ± 7 s−1) rate constants for complexed A/AH+, which showed that the pKa shift of +3.1 for A/AH+ in the complex is mainly due to a lower deprotonation rate constant.

Ground configuration splitting in UCl5

1977 ◽  
Vol 55 (10) ◽  
pp. 937-942 ◽  
Author(s):  
A. F. Leung ◽  
Ying-Ming Poon
Keyword(s):  
Crystal Field ◽  
Energy Levels ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Coupling Constant ◽  
Point Charge Model ◽  
X Ray Crystallography ◽  
Charge Model ◽  
Crystal Field Parameters

The absorption spectra of UCl5 single crystal were observed in the region between 0.6 and 2.4 μm at room, 77, and 4.2 K temperatures. Five pure electronic transitions were assigned at 11 665, 9772, 8950, 6643, and 4300 cm−1. The energy levels associated with these transitions were identified as the splittings of the 5f1 ground configuration under the influence of the spin–orbit coupling and a crystal field of C2v symmetry. The number of crystal field parameters was reduced by assuming the point-charge model where the positions of the ions were determined by X-ray crystallography. Then, the crystal field parameters and the spin–orbit coupling constant were calculated to be [Formula: see text],[Formula: see text], [Formula: see text], and ξ = 1760 cm−1. The vibronic analysis showed that the 90, 200, and 320 cm−1 modes were similar to the T2u(v6), T1u(v4), and T1u(v3) of an UCl6− octahedron, respectively.

Parametrizing a polarizable force field from ab initio data. I. The fluctuating point charge model

1999 ◽  
Vol 110 (2) ◽  
pp. 741-754 ◽  
Author(s):  
Jay L. Banks ◽  
George A. Kaminski ◽  
Ruhong Zhou ◽  
Daniel T. Mainz ◽  
B. J. Berne ◽  
...  
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Point Charge ◽  
Point Charge Model ◽  
Polarizable Force Field ◽  
Charge Model

scholarly journals Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

Synthesis ◽  
2019 ◽  
Vol 51 (05) ◽  
pp. 1157-1170 ◽  
Author(s):  
Artem Leonov ◽  
Daria Timofeeva ◽  
Armin Ofial ◽  
Herbert Mayr
Keyword(s):  
Rate Constants ◽  
Correlation Equation ◽  
Stopped Flow ◽  
Quinone Methides ◽  
Enol Ethers ◽  
Reactivity Descriptors ◽  
Silyl Enol Ethers ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Least Squares Minimization

The kinetics of the reactions of trimethylsilyl enol ethers and enamines (derived from deoxybenzoin, indane-1-one, and α-tetralone) with reference electrophiles (p-quinone methides, benzhydrylium and indolylbenzylium ions) were measured by conventional and stopped-flow photometry in acetonitrile at 20 °C. The resulting second-order rate constants were subjected to a least-squares minimization based on the correlation equation lg k = s N(N + E) for determining the reactivity descriptors N and s N of the silyl enol ethers and enamines. The relative reactivities of structurally analogous silyl enol ethers, enamines, and enolate anions towards carbon-centered electrophiles are determined as 1, 107, and 1014, respectively. A survey of synthetic applications of enolate ions and their synthetic equivalents shows that their behavior can be properly described by their nucleophilicity parameters, which therefore can be used for designing novel synthetic transformations.

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