Reversibility of Electron Transfer in Tryptophan−Tyrosine Peptide in Acidic Aqueous Solution Studied by Time-Resolved CIDNP

2005 ◽  
Vol 109 (8) ◽  
pp. 3668-3675 ◽  
Author(s):  
Olga B. Morozova ◽  
Alexandra V. Yurkovskaya ◽  
Renad Z. Sagdeev
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Time Resolved ◽  
Acidic Aqueous Solution

scholarly journals Time-Resolved Spectroscopic Study of N,N–Di(4–bromo)nitrenium Ions in Acidic Aqueous Solution

2019 ◽  
Vol 20 (21) ◽  
pp. 5512 ◽  
Author(s):  
Lili Du ◽  
Zhiping Yan ◽  
Xueqin Bai ◽  
Runhui Liang ◽  
David Lee Phillips
Keyword(s):  
Aqueous Solution ◽  
Transient Absorption ◽  
Function Theory ◽  
Spectroscopic Properties ◽  
Time Resolved ◽  
Nitrenium Ions ◽  
Acidic Aqueous Solution ◽  
Nitrenium Ion ◽  
Femtosecond Transient Absorption ◽  
Aqueous Conditions

Nitrenium ions are common reactive intermediates with high activities towards some biological nucleophiles. In this paper, we employed femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) as well as nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy and density function theory (DFT) calculations to study the spectroscopic properties of the N(4,4′–dibromodiphenylamino)–2,4,6–trimethylpyridinium BF4− salt (1) in an acidic aqueous solution. Efficient cleavage of the N–N bond (4 ps) to form the N,N–di(4–bromophenyl)nitrenium ion (DN) was also observed in the acidic aqueous solution. As a result, the dication intermediate 4 appears more likely to be produced after abstracting a proton for the nitrenium ion DN in the acid solution first, followed by an electron abstraction to form the radical cation intermediate 3. These new and more extensive time-resolved spectroscopic data will be useful to help to develop an improved understanding of the identity, nature, and properties of nitrenium ions involved in reactions under acidic aqueous conditions.

Kinetics of self-exchange of bis(1,4,7-trithiacyclononane)iron(III)/(II) in acetonitrile and in acidic aqueous solution

1990 ◽  
Vol 68 (12) ◽  
pp. 2228-2233 ◽  
Author(s):  
Hideo Doine ◽  
Thomas W. Swaddle
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Ionic Strength ◽  
Line Broadening ◽  
Acidic Water ◽  
Exchange Reactions ◽  
Acidic Aqueous Solution ◽  
Spontaneous Reduction ◽  
Kinetics Of ◽  
C Nmr

The rate constant kex of the [Formula: see text] self-exchange reaction cannot be measured in most common solvents because of spontaneous reduction of the [Formula: see text] ion, which is also sensitive to photolysis by visible light. However, in CD3CN at −41 to −19 °C, reproducible proton-decoupled 13C NMR line broadening measurements are possible, and give kex = (5.3 ± 0.3) × 104 kg mol−1s−1 at 0 °C, ΔH* = 10.3 ± 1.8 kJ mol−1, and ΔS* = −116 ± 7 J K−1 mol−1, at ionic strength I = 0.1 mol kg−1. Proton NMR line broadening experiments are marginally practicable in very acidic water (2.0 mol kg−1 D2SO4/D2O) near 0 °C, and give kex = 3.2 × 106 kg mol−1 s−1 at 1 °C. The relative kex values of these and other low-spin/low-spin FeIII/II self-exchange reactions follow the predictions of the Marcus–Hush theory at least qualitatively. The effect of ionic strength, however, is less than predicted, probably because of the formation of less reactive anion–cation pairs. Keywords: electron transfer kinetics, crown thioether complexes.

Radiation Chemical Studies of the Oxidation of Aniline in Aqueous Solution

1985 ◽  
Vol 40 (10) ◽  
pp. 1026-1039 ◽  
Author(s):  
Ling Qin ◽  
G. N. R. Tripathi ◽  
Robert H. Schüler
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Radical Cation ◽  
Time Scale ◽  
Radical Cations ◽  
Oh Radicals ◽  
Basic Solution ◽  
Direct Oxidation ◽  
Time Resolved ◽  
Radiation Chemical

Oxidation of aniline in aqueous solution by ·OH radicals proceeds predominantly via addition to the ring followed by elimination of OH- on the microsecond time scale to form the aniline radical cation. Direct oxidation by electron transfer accounts for less than 4% of the ·OH reactions. The different hydroxycyclohexadienyl isomers produced by ·OH addition decay at different rates with this decay catalyzed both by protons and phosphate. In basic solution the resultant radical cation deprotonates to form the anilino radical. The p Ka for the equilibrium between the acidic and basic forms of this radical is 7.05 ± 0.05. Secondary radicals such as Br2·- or N3· oxidize aniline directly by electron transfer and allow rapid preparation of the radical cation even in basic solution, as is conclusively demonstrated by observation of the Raman spectrum of the radical cation on the nanosecond time scale at pH 10.4. The deprotonation process can be followed directly by time resolved absorption spectrophotometry in the pH range of 9 - 11 and is shown to occur via reaction of the radical cation with OH- at a rate constant of 2.2 x 1010 M-1 s-1. Reaction of anilino radical with water is relatively slow (k ~ 2 x 103 s-1). Time resolved Raman methods show that benzidine radical cation is an important tertiary transient, indicating that second order reaction between radical cations results to an appreciable extent from coupling at ring positions.

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