Translational diffusion of transient radicals created by the photoinduced hydrogen abstraction reaction in solution: Anomalous size dependence in the radical diffusion

Abstract

Diffusion coefficients ͑D͒ of various radicals created by the photoinduced hydrogen abstraction reactions from alcohols ͑ethanol and 2-propanol͒ are investigated by using the transient grating ͑TG͒ method. In all the reaction systems, D's of the transient radicals, as well as those of the parent molecules, can be measured simultaneously. The results clearly show slower diffusive motions of the radicals, at least of the radicals in the hydrogen abstraction reaction systems, compared with those of the parent molecules. D's of the parent molecules usually agree well with the calculated values based on the Spernol and Wirtz modification of the Stokes-Einstein ͑SE͒ relation. Although the measured D's of the radicals are closer to the values predicted by the simple SE equation, the agreements and the ratio of D between the radicals and its parent molecules depend on the molecular size. The ratio becomes closer to unity as the molecular size becomes large. Possible origins of this dependence are discussed.

Stability of Dimer and Domain–Domain Interaction of Arabidopsis Phototropin 1 LOV2

“…When the molecular diffusion coefficient (D) is time independent, the temporal profile of the species grating signal can be calculated by the molecular diffusion equation and the q-Fourier component of the concentration decays with a rate constant of Dq 2 for the reactant and the product. Hence, the time development of the TG signal for describing the molecular diffusion part can be expressed by: 6,7,29,[41][42][43][44] …”

“…[41][42][43][44] The signal consists of δn due to the temperature change [δn th (t); thermal grating] and that of the created (or depleted) chemical species (the species grating). [41][42][43][44] The species grating signal intensity is given by the difference of the refractive index changes due to the reactant (δn R ) and the product (δn P ). The total TG signal [I TG (t)] is expressed as: 6,7,29,[41][42][43][44] I TG ðtÞ ¼ a dn th ðtÞ þ dn P ðtÞ À dn R ðtÞ f g 2 ð6Þ…”

“…6,7,29,[41][42][43][44] Briefly, a laser pulse from a dye laser (Lumomics, HyperDye 300; wavelength = 465 nm) pumped by an excimer laser (Lambda Physik, XeCl operation; 308 nm) was used as an excitation beam and a diode laser (835 nm) was used as a probe beam. The excitation beam was split into two by a beam splitter and crossed inside a sample cell.…”

Dynamics of Conformational Changes of Arabidopsis Phototropin 1 LOV2 with the Linker Domain

“…In the TG experiment, the excitation beam was split into two by a beam splitter, and crossed inside a quartz sample cell (optical path-length, 2 mm). 13,17,25,26,[35][36][37][38] The excitation laser power was ∼4 μJ/ pulse and the beam was slightly focused to the sample with a 1 mm diameter. The sample solution was not moved at all during the measurement.…”

“…13,17,25,26,[35][36][37][38] Briefly, a laser pulse from a dye laser (Lumonics, HyperDye 300; wavelength, 465 nm) pumped by an excimer laser (Lambda Physik, XeCl operation; 308 nm) was used as an excitation beam for the TG and the TrL experiments. A diode laser (835 nm) was used for the TG experiment and a He-Ne laser for the TrL experiment.…”