Magnetic fields and radical reactions: recent developments and their role in nature.

Recombination of pairs of radicals is exceptional in being affected by magnetic fields. The mechanism has been known for some thirty years, but recently new applications have appeared and research has been extended to very high fields (up to 30 Tesla). Claims that low electromagnetic fields damage health have led to extensive medical, chemical and physical research: no firm evidence of hazards has emerged; on the other hand, migrating birds orient themselves in the earth's field (50 microT): radical pairs may provide the mechanism.

Radiation damage in DNA: possible role of higher triplet states.

Triplet states of deoxyribose are expected to dissociate efficiently into radicals, leading to strand breaks. Such states could be excited by slow secondary electrons (A) or result from ion recombination in spurs containing two or more ion pairs (B). Estimates of the efficiencies of these processes are presented and the mechanisms discussed in the light of recent work with electrons, vacuum ultraviolet (VUV) photons, and X rays.

The effects of weak magnetic fields on radical recombination reactions in micelles.

Purpose: To demonstrate the effects of weak magnetic fields (> approximately 1 mT) on chemical reactions involving free radicals, in the context of possible effects of environmental electromagnetic radiation on biological systems.

Materials And Methods: Transient absorption, flash photolysis experiments have been performed to study the kinetics and yields of radical reactions. The triplet state of benzophenone has been used as a convenient source of radical pairs, whose identity is largely immaterial to the investigation of the so-called Low Field Effect.

Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum.

Purpose: To measure action spectra for the induction of single-strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage.

Materials And Methods: Plasmid pMSG-CAT was irradiated as a monolayer, under vacuum, with 7 150eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms by gel electrophoresis.

Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons: an arrangement for irradiating dry or hydrated DNA with monochromatic photons.

Purpose: Theoretical modelling techniques are often used to simulate the action of ionizing radiations on cells at the nanometre level. Using monoenergetic vacuum-UV (VUV) radiation to irradiate DNA either dry or humidified, the action spectra for the induction of DNA damage by low energy photons and the role of water and can be studied. These data provide inputs for the theoretical models.