Electron behavior in mixed solvents: optical spectra and reactivities in water/alkane diols

Abstract

Investigation of the effect of solvent structure on the optical absorption spectrum and reactivity of solvated electrons has been extended to diol/water mixed solvents, using 1,2-ethanediol (12ED) and 1,4-butanediol (14BD). The large effects that had been found in mono-ol/water mixed solvents did not occur in diol/water. Although addition of 3 mol% of a diol to water increased the optical absorption energies of e−s by 0.06 eV, similar to the shift caused by addition of 3 mol% of a mono-ol, the variation of the spectrum over the rest of the composition range was nearly ideal in diol/water, in contrast to the very non-ideal variation in mono-ol/water. Reaction rate constants kS at 298 K in the diol/water mixed solvents vary approximately as the inverse viscosity,η−1.0, in the diffusion-controlled limit. However, when reactions are two or three orders of magnitude slower than diffusion controlled, kS at 298 K is independent of η. Toluene reacts with e−s at a 10−3-fold smaller rate than does nitrobenzene; the difference is nearly completely due to a ~50 J/mol K lower entropy of activation of the former reaction.

Oxidation of Bromide Ions by Hydroxyl Radicals: Spectral Characterization of the Intermediate BrOH•–

“…A pseudo-first-order rate constant for the disappearance of e aq – is found to be 6.7 × 10 8 s –1 . Taking into account the concentration of acetone, that corresponds to a bimolecular rate constant of 6.7 × 10 9 dm 3 mol –1 s –1 ; this value is in the range (from 5.6 × 10 9 to 8 × 10 9 dm 3 mol –1 s –1 ) of the reported values − and in good agreement with the average selected value (6.5 × 10 9 dm 3 mol –1 s –1 ) of k 8 . Regarding the signals registered at 360, 305, and 400 nm, i.e., near the absorption maximum and on the blue and red side of the absorption band, the kinetics profiles are clearly wavelength dependent.…”

UV-Absorption Observation of the Silver Bromide Growth from a Single Molecule to the Crystal in Solution

“…It is well-known that the energy deposited in the aqueous solution generates the following radiolytic species from the solvent water: In the presence of an alcohol such as tert -butyl alcohol OH • radicals are scavenged to produce the alcohol radical. The rate constant of this reaction is 6 × 10 8 mol L -1 s -1 . But the reaction between H • atoms and tert -butyl alcohol is very slow, 10 5 mol L -1 s -1 .…”

“…The rate constant of this reaction is 6 × 10 8 mol L -1 s -1 . 27 But the reaction between H • atoms and tert-butyl alcohol is very slow, 10 5 mol L -1 s -1 . 28 Even at high concentration of alcohol, we can almost neglect the reaction between tert-butyl alcohol and H • atoms.…”

Photophysics of indole, tryptophan and N-acetyl-l-tryptophanamide (NATA): Heavy atom effect

“…This aim will be realized applying the heavy atom effect, using the addition of potassium iodide, which is known to be a suitable enhancer of intersystem crossing for indole [17,18] and tryptophan [17]. Applying the heavy atom effect, we hope to increase the probability that intersystem crossing into the triplet state will be the major pathway of indole S 1 decay.…”