Radical Pairs in Solution

Abstract

Radical pairs (RPs) are important reaction intermediates generated whenever two radicals encounter one another, a bond is cleaved homolytically or electron transfer between non-radical species takes place. The concept of a radical pair as a reaction intermediate is introduced and developed through simple pictorial analogies, indicating how RP behaviour is governed by interplay of spin and spatial motion. Such analogies are then extended to describe the experimental consequences of RPs in magnetic resonance and magnetochemistry experiments, including reference to the relevance of RPs in biological systems. Finally experimental techniques by which RPs can be observed directly are introduced and described in the context of the developed models.

Optical Absorption and Magnetic Field Effect Based Imaging of Transient Radicals

“…Furthermore spin-correlated radical pairs (RPs) have been extensively studied for the last four decades. [1][2][3] In recent years they have returned to the spotlight, primarily due to their proposed role in animal magnetoreception, [4] their importance in solidstate devices involving electron-hole recombination [5] and renewed interest in quantum information related phenomena in the physics community.Surprisingly,with few exceptions, [6] the study of RPs in as patially resolved manner has been largely ignored. In recent years,arange of sophisticated fluorescence-based microscopy methods have been developed and have received much attention.…”

“…In recent years,arange of sophisticated fluorescence-based microscopy methods have been developed and have received much attention. [7] However,f luorescence is not an ideal method for the study of photochemically generated radicals or RPs.P hotochemically generated free radicals in general do not fluoresce.F urthermore,a lthough there are many examples of the use of fluorescence detection to study RP dynamics, [1][2][3] such measurements are typically only possible in spin-selective reactions from singlet RPs to fluorescing exciplexes.Inparticular, to study RPs proposed in biological magnetoreception, an alternative approach is desirable.Infunctioning cryptochrome photochemistry,electron transfer to the photoexcited singlet state of FAD( from an eighboring tryptophan residue) is sufficiently rapid to make fluorescence signals extremely weak. In addition, fluorescence only tracks ground state FADm olecules, whose concentration is not magnetic field-sensitive in flash photolysis experiments.I ng eneral, transient absorption spectroscopy is the best optical spectroscopic method for studying transient radicals and RPs.…”

Chemical magnetoreception in birds: The radical pair mechanism

“…Experimental and theoretical studies of the ''radical pair mechanism'' over the last 30 years have given an extraordinary variety of information on the magnetic properties, kinetics, and dynamics of radicals and their reactions (reviewed in refs. [9][10][11][12][13]. This field of endeavor has come to be called ''spin chemistry.…”

Is There a Dynamic Protein Contribution to the Substrate Trigger in Coenzyme B12‐Dependent Ethanolamine Ammonia Lyase?

“…Alex R. Jones,* Samantha J. O. Hardman, Sam Hay, and Nigel S. Scrutton* Coenzyme B 12 , or 5'-deoxyadenosylcobalamin (AdoCbl), acts as cofactor to a number of enzymes from a range of organisms. [1,2] In all cases, the CoÀC bond in the cofactor undergoes homolysis upon substrate binding, generating a singlet-born, Cbl II /adenosyl radical pair (RP) and thus initiating radical-mediated catalysis.…”

“…If the geminate RP re-encounter, only those in the singlet state will recombine, whereas triplet pairs will separate again. [12] The extent to which the spin-states mix can be altered by the application of external magnetic fields (MFs). [13,14] For increasing MFs of moderate strength (tens to hundreds of mT) the T AE1 levels are gradually removed in energy and ultimately only S and T 0 interconvert.…”