Application of pulse radiolysis methods to study the reactions and structure of biomolecules

Abstract

T o study reactions occurring on timescales faster than N 10-&lo-3 s, simple mixing of reagents is too slow and other methods of initiating reactions have to be used. Pulses of thermal energy, light quanta or ionising radiation have been used to perturb chemical and biological systems from equilibrium. Pulse radiolysis is the more recent of these three methods of initiating fast reactions, and this review emphasises the versatility of this technique for studying events occurring between 10-11 and 1 0 2 s after energy absorption. The extent and tiniescale of radiation damage in dilute aqueous solutions are outlined and the facile manipulation of experimental conditions to isolate a single reactive species is illustrated. The basic requirements for the radiation pulse and detection system are discussed. T h e experimental techniques which have been used to monitor fast reactions following pulse radiolysis include optical absorption spectroscopy and light scattering, and timeresolved electrical conductivity, polarography, and electron spin resonance spectroscopy. Some applications of pulse radiolysis to study fast reactions of biologically important molecules are illustrated, including the kinetics and thermodynamics of redox processes and electron-transfer reactions, enzymic processes and structural effects which are revealed by physical or kinetic properties.

Recent advances in 1,4-benzoquinone chemistry

“…Predominantly, pulse radiolysis is an established methodology for studying one-electron transfer processes in liquid media. [355][356][357] Rao and Hayon 358 studied in detail the ionization constants, absorption spectra and extinction coefficients of numerous semiquinone radicals in aqueous solution and correlated their increased reduction potential with increased acidity. Shoute and Mittal 359 carried out pulse radiolysis study of one-electron reduction reaction of fluoranil (234) in aqueous solution.…”

Reactions of the nitro radical anion of metronidazole in aqueous and mixed solvent: a cyclic voltammetric study

“…The reactivity of nitro radical anions from most of the nitrocompounds has been studied mainly by the pulse radiolysis [39][40][41][42] technique. Recently electrochemical techniques like cyclic voltammetry [43][44][45][46][47][48][49][50][51][52][53][54][55][56] have been used to study the behaviour of the nitro radical anions.…”

Some Reactions and Properties of Nitro Radical-Anions Important in Biology and Medicine

“…The most powerful and reliable method to determine E(ArNO2/ArNO2-) is from pulse radiolysis measurements of the equilibrium constant for one-electron transfer equilibria involving ArNO2 and a reference compound of known reduction potential such as a quinone or bipyridinium compound (56,57): (5) (6) (7) E(ArNO2/MANO2 ) -E(Q/Q ) -0.059 log K5 (8) if E is in volts. The yields and reactions of the species produced upon radiolysis of aqueous solutions are so well established that the design of such experiments is a matter of routine (5).…”

“…The yields and reactions of the species produced upon radiolysis of aqueous solutions are so well established that the design of such experiments is a matter of routine (5). The radicals: ArNO21, Q are usually generated within a microsecond or so of the end of a radiolysis pulse of equally short duration, and the equilibrium (5) attained and the equilibrium constant K5 measured spectrophotometrically within (typically) 10-200 ,usec, i.e., before the unstable radicals can decay via routes such as (3) (5,56,57).…”