scholarly journals Oxidation of nitrogenase iron protein by dioxygen without inactivation could contribute to high respiration rates of Azotobacter species and facilitate nitrogen fixation in other aerobic environments

1989 ◽  
Vol 261 (1) ◽  
pp. 181-187 ◽  
Author(s):  
R N F Thorneley ◽  
G A Ashby
Keyword(s):  
Azotobacter Chroococcum ◽  
Stopped Flow ◽  
Protein Species ◽  
Respiratory Pathway ◽  
Kinetics Of Oxidation ◽  
Iron Protein ◽  
Respiration Rates ◽  
High Respiration Rate ◽  
Nitrogenase Iron Protein ◽  
Kinetics Of

The kinetics of oxidation of the Fe proteins of nitrogenases from Klebsiella pneumoniae (Kp2) and Azotobacter chroococcum (Ac2) by O2 and H2O2 have been studied by stopped-flow spectrophotometry at 23 degrees C, pH 7.4. With excess O2, one-electron oxidation of Kp2 and Ac2 and their 2 MgATP or 2 MgADP bound forms occurs with rate constants (k) in the range 5.3 x 10(3) M-1.S-1 to 1.6 x 10(5) M-1.S-1. A linear correlation between log k and the mid-point potentials (Em) of these protein species indicates that the higher rates of electron transfer from the Ac2 species are due to the differences in Em of the 4Fe-4S cluster. The reaction of Ac2(MgADP)2 with O2 is sufficiently rapid for it to contribute significantly to the high respiration rate of Azotobacter under N2-fixing conditions and may represent a new respiratory pathway. Excess O2 rapidly inactivates Ac2(MgADP)2 and Kp2(MgADP)2; however, when these protein species are in greater than 4-fold molar excess over the concentration of O2, 4 equivalents of protein are oxidized with no loss of activity. The kinetics of this reaction suggest that H2O2 is an intermediate in the reduction of O2 to 2 H2O by nitrogenase Fe proteins and imply a role for catalase or peroxidase in the mechanism of protection of nitrogenase from O2-induced inactivation.

Kinetics of oxidation of nitrite by aqueous chlorine

1973 ◽  
Vol 26 (9) ◽  
pp. 1857 ◽  
Author(s):  
JN Pendlebury ◽  
RH Smith
Keyword(s):  
Nitrous Acid ◽  
Ionization Constant ◽  
Initial Step ◽  
The Other ◽  
Stopped Flow ◽  
Unimolecular Decomposition ◽  
Solution Ph ◽  
Kinetics Of Oxidation ◽  
Aqueous Acid ◽  
Kinetics Of

The kinetics of oxidation of nitrite to nitrate by chlorine in aqueous acid solution (pH 0-1) have been studied using a spectrophotometric stopped flow technique. The rate law is ���������������� -d[Cl2]a/dt =([Cl2][NO2-]/Ka[Cl-]2)(f+g[HNO2]) where [Cl2]a = [Cl2]+[Cl3-] and where Ka is the ionization constant for nitrous acid. At 298.2 K and ionic strength 2.75M, f = 60.8�0.5 mol2 l-2 s-1 and g = (2.35�0.05)x105 mol l-1 s-1: the associated activation energies are 68�3 and 44�2 kJ mol-1 respectively. A mechanism is proposed involving the reversible initial step: �������������������������� NO2-+Cl2 ↔ NO2Cl+Cl- with the NO2Cl undergoing two parallel subsequent reactions, one a unimolecular decomposition and the other an attack by HNO2 upon NO2Cl. ��� Oxidation of nitrite by the three halogens, Cl2, Br2, I2, is discussed.

Kinetics of oxidation of thiocyanate by aqueous iodine

1973 ◽  
Vol 26 (9) ◽  
pp. 1863 ◽  
Author(s):  
GT Briot ◽  
RH Smith
Keyword(s):  
Rate Constants ◽  
Activation Energies ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
General Base ◽  
Present Rate ◽  
Rapid Equilibrium ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of thiocyanate to sulphate by aqueous iodine in the pH range 9.2-12.5 have been studied using a spectrophotometric stopped flow technique. The reaction is general base-catalysed, having the rate law ��������������������� -d[I2]a/dt = ([SCN-][I3-]/[I-]2)Σ kB[B] where [I2]a is the total analytical concentration of iodine, [B] is the concentration of base, and where the summation is taken over all bases present. Rate constants, kB, and activation energies have been measured for the bases, OH-, PO43- and CO32-. ��� A mechanism involving the initial steps ����������������� I2+SCN- ↔ ISCN+I- �����������������(rapid equilibrium) ������������� ISCN+H2O+B → HOSCN+I- + HB+ �����������(rate determining) followed by rapid reactions of HOSCN with itself or with iodine is proposed.

Kinetics of oxidation of nitrite by aqueous bromine

1973 ◽  
Vol 26 (9) ◽  
pp. 1847 ◽  
Author(s):  
JN Pendlebury ◽  
RH Smith
Keyword(s):  
Perchloric Acid ◽  
Acetate Buffer ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
Rate Laws ◽  
Temperature Dependences ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of nitrite to nitrate by aqueous bromine have been investigated using a spectrophotometric stopped flow technique. In the pH range 4.2-5.8 (acetate buffer) the rate law is: - d[Br21,/dt = [Br21[N02 -I2 (a + b/[Br-1) (where [Br,], = [Br2]+[Br,-1) with a = (4.61-0-1) x lo4 l2 m01-~ s-l and b = (3.3 1-0.1) x lo4 1. mol-l s-l at 298.2 K and with the temperature dependences, - R d(lna)/d(l/T) = (46k 4) kJ mol-l and - R d(ln b)/d(l/T) = (45 k 2) kJ mol-'. In the pH range 0.8-2.5 (perchloric acid) the rate law is : - d[Br2],/dt = [HN0212[Br21 (w + v/[Br-l)/(l+ z[H+ItBr,l,) with w = (5.9+0.2)x lo4 l2 m01-~ s-l, v = (3.41-0.1)~ lo4 1, mol-l s-I, and z = (1.90i 0.06) x lo7 l2 mol-2 at 298.2 K. In addition: - R d ln(w/z)/d(l/T) = (31 1 4 ) kJ mol-I and - R d ln(v/z)/d(l/T) = (46 f 4) kJ mol-l In the pH range 2.8-3.3 (chloroacetate buffer) a combination of these two rate laws adequately describes the kinetic results. These rate laws have been interpreted in terms of two reversible initial reactions: 6) NO2- +Br2 + N02Br +Br- (followed by attack on N02Br by NO2-) (ii) NO2-+NO2- (or HNOJ + N204'- (or HN204-) (followed by attack by Br2 upon N204'- or HNZO4- or upon N203 formed from HN204-).

Spectrocoulometry – a new spectro-electrochemical technique

1987 ◽  
Vol 52 (6) ◽  
pp. 1386-1396 ◽  
Author(s):  
Ján Mocák ◽  
Michal Németh ◽  
Mieczyslaw Lapkowski ◽  
Jerzy W. Strojek
Keyword(s):  
Optical Probe ◽  
Optical Signal ◽  
Open Circuit ◽  
Electrochemical Technique ◽  
Kinetics Of Oxidation ◽  
Hydrolytic Reaction ◽  
Experimental Errors ◽  
Mechanism And Kinetics ◽  
Kinetics Of

A spectrocoulometric macrocell with a direct-view optical probe was designed and constructed, where the optical signal is transferred by light-conducting glass or quartz fibres permitting to work at wavelengths above 410 or 300 nm. The method of measurement on the proposed equipment is described; it was tested in the study of the mechanism and kinetics of oxidation of Fe(bipy)32+ ions (bipy = 2,2'-bipyridyl) with the use of potentiostatic coulometric electrolysis with open-circuit relaxation at a suitable time. The primary product of electrolysis, Fe(bipy)33+, undergoes a follow-up hydrolytic reaction with the formation of a binuclear complex. The rate constant of the reaction of the first order involves the contributions, kBi, from all bases present in solution; the corresponding values for H2O, OH-, bipy, and CH3COO- ions at a ionic strength 0·5 mol dm-3 and 25 °C were determined as kOH = (5·0 ± 0·6) . 105 mol-1 dm3 s-1, kbipy = (1·3 ± 0·2) . 10-1 mol-1 dm3 s-1, kAc = (5·8 ± 1·0) . 10-2 mol-1 dm3 s-1, and kH2O is not significant with respect to experimental errors.

Effects of salts on the kinetics of oxidation of alkenes by thallic salts in aqueous solutions

1981 ◽  
Vol 46 (3) ◽  
pp. 693-700 ◽  
Author(s):  
Milan Strašák ◽  
Jaroslav Majer
Keyword(s):  
Aqueous Solutions ◽  
Phase Transfer ◽  
Heterogeneous Reaction ◽  
Qualitative Model ◽  
Kinetic Effect ◽  
Tetraalkylammonium Salts ◽  
Reaction Conditions ◽  
Kinetics Of Oxidation ◽  
Kinetics Of ◽  
Heterogeneous Reaction Conditions

The kinetics of oxidation of alkenes by thallic sulphate in aqueous solutions, involving the two reaction steps-the hydroxythallation and the dethallation - was studied, and the effect of salts on the kinetics was examined; this made it possible to specify more precisely the reaction mechanism and to suggest a qualitative model of the reaction coordinate. It was found that in homogeneous as well as in heterogeneous reaction conditions, the reaction can be accelerated appreciably by adding tetraalkylammonium salts. These salts not only operate as catalysts of the phase transfer, but also exert a significant kinetic effect, which can be explained with a simplification in terms of a stabilization of the transition state of the reaction.

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