Determination of the Rate Constants of the Intersystem Crossing Processes to the Individual Zero‐Field Levels of the Lowest Triplet State

1969 ◽  
Vol 50 (7) ◽  
pp. 3113-3114 ◽  
Author(s):  
M. A. El‐Sayed ◽  
L. Hall
Keyword(s):  
Triplet State ◽  
Rate Constants ◽  
Intersystem Crossing ◽  
Zero Field ◽  
The Individual

Triplet-State Electron Spin Resonance of Chlorophyll a and b Molecules and Complexes in PMMA and MTHF. I: Experimental Determination of Fine-Structure and Rate Constants

1978 ◽  
Vol 33 (1) ◽  
pp. 83-93 ◽  
Author(s):  
W. Hagele ◽  
D. Schmid ◽  
H. C. Wolf
Keyword(s):  
Triplet State ◽  
Chlorophyll A ◽  
Rate Constants ◽  
Resonance Field ◽  
Zero Field ◽  
Chlorophyll B ◽  
Low Concentrations ◽  
Spin Resonance ◽  
Chlorophyll A And B

The triplet state zero-field splittings and the rate constants for the population and depopulation of the triplet spin sublevels have been investigated for chlorophyll a and chlorophyll b in polymethylmethacrylate (PMMA) and methyltetrahydrofurane (MTHF) as a function of the concentration. In PMMA both chlorophyll a and chlorophyll b yielded only one ESR spectrum in the entire range of concentration which could be covered (1.5 × 10-5 - 1 × 10-3 mole/1). In MTHF the results were more complicated. At low concentrations (up to 103 mole/1) only one spectrum was observed, at higher concentrations additional spectra were detectable (all together two for chlorophyll a and five for chlorophyll b at 10-1 mole/1). The assignment of these spectra was facilitated by observing the "triplet resonance-field identity" which connects the resonancefield strengths for the canonical orientations of one particular species. Furthermore, the rate constants for some of these species could be determined.

Photophysics of the lowest triplet state in 2-benzoylpyridine crystals. II. Optically detected e. p. r. in zero and high magnetic fields

1979 ◽  
Vol 369 (1737) ◽  
pp. 187-206 ◽  
Keyword(s):  
Triplet State ◽  
Rate Constants ◽  
Radiative Decay ◽  
Dynamic Properties ◽  
Deep Trap ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Spin Lattice ◽  
Optically Detected

Optically detected zero-field resonance has been used to characterize the intrinsic and deep trap 3 nπ * states in single crystals of 2-benzoylpyridine at 4.2 K. The dynamic properties of these states were studied by means of time-resolved modulated phosphorescence (t. r. m. p.) and estimates for the rate constants for depopulation and spin-lattice relaxation of the magnetic sub-levels obtained by computer simulation. For all species, depopulation from ז z dominates, having rates of order 100 s -1 , but the ז x and ז y sub-states have substantial radiative activity. The orientations of the fine-structure tensors of the magnetic species were determined from high-field e. p. r. spectra. Assuming that z is parallel to C = O, excitation causes the C = O direction to change by 8 ± 2° for the intrinsic species and by an in-significant amount for the deep trap. These spectra also demonstrated that the intrinsic triplet state is mobile. This species is believed to be a polaron with slow intersite hopping rate. A maximum energy transfer rate of 10 4 -10 5 s -1 was found for transfer between translationally inequivalent sites symmetry-related by twofold rotation about the crystal b -axis. Rate estimates for transfer to the other two translationally inequivalent sites established the two dimensional nature of the polaron. The sign and shape of the zero-field resonances for the intrinsic species were found to depend on whether excitation was through S 1 or T 1 . From the parameters required to simulate the corresponding t. r. m. p. signals it is inferred that the changes are largely due to differences in the rate constants for non-radiative decay. The deep trap was shown to have an orientation and magnetic properties similar to those of the intrinsic species, and is believed to be a physical defect. It has radiative activity from the ז x sub-level which is significantly less than for the intrinsic species. Spin-lattice relaxation is fast for the mobile intrinsic species ( ca . 10 4 s -1 ) compared with the deep trap rate ( ca . 50 4 s -1 ). For the intrinsic species a field dependence for spin-lattice relaxation is apparent.

scholarly journals Isomerization of an enzyme-coenzyme complex in yeast alcohol dehydrogenase-catalysed reactions

2003 ◽  
Vol 68 (2) ◽  
pp. 77-84 ◽  
Author(s):  
Vladimir Leskovac ◽  
Svetlana Trivic ◽  
Draginja Pericin
Keyword(s):  
Alcohol Dehydrogenase ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Kinetic Mechanism ◽  
Yeast Alcohol Dehydrogenase ◽  
Catalyzed Reactions ◽  
The Individual ◽  
Individual Rate ◽  
Catalyzed Oxidation

In this work, all the rate constants in the kinetic mechanism of the yeast alcohol dehydrogenase-catalyzed oxidation of ethanol by NAD+, at pH 7.0, 25 ?C, have been estimated. The determination of the individual rate constants was achieved by fitting the reaction progress curves to the experimental data, using the procedures of the FITSIM and KINSIM software package of Carl Frieden. This work is the first report in the literature showing the internal equilibrium constants for the isomerization of the enzyme-NAD+ complex in yeast alcohol dehydrogenase-catalyzed reactions.

Determination of absolute rate constants for an excited triplet state

1978 ◽  
Vol 68 (1) ◽  
pp. 327 ◽  
Author(s):  
Willem R. Leenstra ◽  
Martin Gouterman ◽  
Alvin L. Kwiram
Keyword(s):  
Triplet State ◽  
Rate Constants ◽  
Excited Triplet State ◽  
Absolute Rate ◽  
Excited Triplet

scholarly journals The linkage between binding of the C-terminal domain of hirudin and amidase activity in human α-thrombin

1993 ◽  
Vol 289 (2) ◽  
pp. 475-480 ◽  
Author(s):  
R de Cristofaro ◽  
B Rocca ◽  
B Bizzi ◽  
R Landolfi
Keyword(s):  
Rate Constants ◽  
Binding Constant ◽  
Amidase Activity ◽  
Equilibrium Binding ◽  
Viscosity Effects ◽  
The Individual ◽  
Individual Rate ◽  
Hydrolysis Of ◽  
Equilibrium Binding Constant

A method derived from the analysis of viscosity effects on the hydrolysis of the amide substrates D-phenylalanylpipecolyl-arginine-p-nitroaniline, tosylglycylprolylarginine-p-nitroanaline and cyclohexylglycylalanylarginine-p-nitroalanine by human alpha-thrombin was developed to dissect the Michaelis-Menten parameters Km and kcat into the individual rate constants of the binding, acylation and deacylation reactions. This method was used to analyse the effect of the C-terminal hirudin (residues 54-65) [hir-(54-65)] domain on the binding and hydrolysis of the three substrates. The results showed that the C-terminal hir-(54-65) fragment affects only the acylation rate, which is increased approx. 1.2-fold for all the substrates. Analysis of the dependence of acylation rate constants on hirudin-fragment concentration, allowed the determination of the equilibrium binding constant of C-terminal hir-(54-65) (Kd approximately 0.7 microM). In addition this peptide was found to competitively inhibit thrombin-fibrinogen interaction with a Ki which is in excellent agreement with the equilibrium constant derived from viscosity experiments. These results demonstrate that binding of hir-(54-65) to the fibrinogen recognition site of thrombin does not affect the equilibrium binding of amide substrates, but induces only a small increase in the acylation rate of the hydrolysis reaction.

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