13 research outputs found
Electron self-exchange kinetics determined by MARY spectroscopy: theory and experiment.
The electron self-exchange between a neutral molecule and its charged radical, which is part of a spin-correlated radical ion pair, gives rise to line width effects in the fluorescence-detected MARY (magnetic field effect on reaction yield) spectrum similar to those observed in EPR spectroscopy. An increasing self-exchange rate (i.e., a higher concentration of the neutral molecule) leads to broadening and subsequent narrowing of the spectrum. Along with a series of MARY spectra recorded for several systems (the fluorophores pyrene, pyrene-d(10) and N-methylcarbazole in combination with 1,2- and 1,4-dicyanobenzene) in various solvents, a theoretical model is developed that describes the spin evolution and the diffusive recombination of the radical pair under the influence of the external magnetic field and electron self-exchange, thereby allowing the simulation of MARY spectra of the systems investigated experimentally. The spin evolution of the radicals in the pair is calculated separately using spin correlation tensors, thereby allowing rigorous quantum mechanical calculations for real spin systems. It is shown that the combination of these simulations with high resolution, low noise experimental spectra makes the MARY technique a novel, quantitative method for the determination of self-exchange rate constants. In comparison to a simple analytical formula which estimates the self-exchange rate constant from the slope of the linear part of a line width vs concentration plot, the simulation method yields more reliable and accurate results. The correctness of the results obtained by the MARY method is proved by a comparison with corresponding data from the well-established EPR line broadening technique. With its less stringent restrictions on radical lifetime and stability, the MARY technique provides an alternative to the classical EPR method, in particular for systems involving short-lived and unstable radicals
MARY spectroscopy: magnetic field effects on fluorescence intensities used for measuring electron transfer rates
Unprecedented ab initio simulations of exchange-affected magnetic field on reaction yield (MARY) spectra of real radical pair (RP) systems are presented which provide a novel, reliable method for the determination of electron self-exchange rate constants by MARY spectroscopy. The MARY technique is an interesting alternative to EPR in the study of short-lived and unstable radicals. A RP lifetime of a few nanoseconds is sufficient compared to at least 100 ms necessary for the CW EPR line broadening technique. © VSP 2005
Recommended from our members
Impacts of abiotic and biotic factors on terrestrial leeches in Indonesian Borneo
Funder: AZA Ape TAG InitiativeFunder: Department of Afroamerican and African Studies, University of Michigan; Id: http://dx.doi.org/10.13039/100005543Funder: Disney Conservation Fund; Id: http://dx.doi.org/10.13039/100012168Funder: Idea Wild; Id: http://dx.doi.org/10.13039/100007142Funder: Leakey Foundation; Id: http://dx.doi.org/10.13039/100005966Funder: Mohamed bin Zayed Species Conservation Fund; Id: http://dx.doi.org/10.13039/501100011672Funder: Victoria University of Wellington; Id: http://dx.doi.org/10.13039/501100001538Abstract: Haemadipsid leeches are ubiquitous inhabitants of tropical and subâtropical forests in the IndoâPacific region. They are increasingly used as indicator taxa for biomonitoring, yet very little is known about their basic ecology. For example, to date no study has assessed the occurrence and distribution of haemadipsid leeches across naturally occurring gradients within intact habitats. We analyzed a longâterm data set (2012â2020) on the closely related tiger (Haemadipsa picta) and brown (Haemadipsa spp.) leech species to investigate if and how abiotic and biotic factors influence their occurrence across a gradient of forest types at an undisturbed tropical rainforest site in Indonesian Borneo. We compared a series of negative binomial mixed models and found that, of the abiotic factors, soil moisture had the largest positive effect on encounter rates of both leech species. Among biotic factors, forest type had differential effects on counts of the two species: while tiger leech counts were greater in low elevation forest types, brown leech counts were greater in high elevation forest types. Additionally, we found that the presence of one species had a positive effect on the presence of the other species. Finally, our results show that the tiger leech has a narrower distribution, being restricted to lower elevation forest types with higher water retention, suggesting that the tiger leech could be more sensitive to lower soil moisture levels. Abstract in Indonesian is available with online material