Resonance Raman and surface-enhanced resonance Raman studies of polymer-modified electrodes which mimic heme enzymes

Iron-5,10,15,20-tetraphenylporphyrin (FeTPP) has been incorporated into films of a coordinating hydrogel polymer support medium, poly(gamma-ethyl-L-glutamate) (PEG) functionalised with imidazole pendant arms (PEG-Im), and studied in situ on silver electrodes using a combination of both resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spectroscopy. The SERR spectra give information on the portion of the film close to the electrode surface while RR spectra probe the

Faint supernovae and supernova impostors: case studies of SN 2002kg/NGC 2403-V37 and SN 2003gm

Photometric and spectroscopic observations of the faint Supernovae (SNe) 2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334, respectively, are presented. The properties of these SNe are discussed in the context of previously proposed scenarios for faint SNe: low-mass progenitors producing underenergetic SNe; SNe with ejecta constrained by a circumstellar medium; and outbursts of massive Luminous Blue Variables (LBVs). The last scenario has been referred to as 'Type V SNe', 'SN impostors' or 'fake SNe'.

Further evidence for double-strand breaks originating from a paired radical precursor from studies of oxygen fixation processes

By using a fast reaction technique which employs H2S gas as a fast-reacting chemical repair agent, it is possible to measure the competition kinetics between chemical repair reactions and oxygen fixation reactions in model DNA and cellular systems. In plasmid pBR322 DNA irradiated with electrons, we have compared the oxygen fixation reactions of the free radical precursors that lead to the production of single-strand (SSBs) and double-strand breaks (DSBs). For the oxygen-dependent fixation of radical damage leading to SSBs, a second-order rate constant of 2.3 x 10(8) dm(3) mol(-1) s(-1) was obtained compared to 8.9 x 10(7) dm(3) mol(-1) s(-1) for DSBs. The difference is in general agreement with predictions from a multiple-radical model where the precursor of a DSB originates from two radicals. The fixation of this precursor by oxygen will require both radicals to be fixed for the DSB to be formed, which will have slower kinetics than that of single free-radical precursors of SSBs. (C) 1999 by Radiation Research Society.

A review of studies of ionizing radiation-induced double-strand break clustering

Underpinning current models of the mechanisms of the action of radiation is a central role for DNA damage and in particular double-strand breaks (DSBs). For radiations of different LET, there is a need to know the exact yields and distributions of DSBs in human cells. Most measurements of DSB yields within cells now rely on pulsed-field gel electrophoresis as the technique of choice. Previous measurements of DSB yields have suggested that the yields are remarkably similar for different types of radiation with RBE values less than or equal to1.0. More recent studies in mammalian cells, however, have suggested that both the yield and the spatial distribution of DSBs are influenced by radiation quality. RBE values for DSBs induced by high-LET radiations are greater than 1.0, and the distributions are nonrandom. Underlying this is the interaction of particle tracks with the higher-order chromosomal structures within cell nuclei. Further studies are needed to relate nonrandom distributions of DSBs to their rejoining kinetics. At the molecular level, we need to determine the involvement of clustering of damaged bases with strand breakage, and the relationship between higher-order clustering over sizes of kilobase pairs and above to localized clustering at the DNA level. Overall, these studies will allow us to elucidate whether the nonrandom distributions of breaks produced by high-LET particle tracks have any consequences for their repair and biological effectiveness. (C) 2001 by Radiation Research Society.

In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.