Preface

Set-Valued and Variational Analysis -     

SOLAR DOSIMETRY WITH REPAIR DEFICIENT BACTERIAL SPORES: ACTION SPECTRA, PHOTOPRODUCT MEASUREMENTS AND A COMPARISON WITH OTHER BIOLOGICAL SYSTEMS

Abstract— Populations of radiation sensitive spores ( Bacillus subtilis UVSSP), vegetative bacteria ( E. coli K12-AB2480) and bacteriophage ( E. coli phage T4vx) have been considered as possible biological dosimeters to integrate DNA-absorbed solar energy incident on the Earth's surface.
Irradiation of spores of B. subtilis UVSSP with monochromatic far- and near-UV radiation and solar radiation have indicated that these radiations have a similar efficiency in inducing spore photoproducts per lethal event. Action spectra for lethality taken with the three radiation sensitive biological systems show a similar pattern in each case with a broad shoulder in the 334–365 nm wavelength region. This finding indicates a relatively high susceptibility of the DNA to chemical alteration in this wavelength range. Although less sensitive to sunlight than the other biological systems tested, the B. subtilis UVSSP spore mutant has the advantage of temperature independence of inactivation, stability between irradiation and assay and a simple, reproducible irradiation and assay procedure. Field measurements have supported the utility of this mutant as a sunlight dosimeter.     

Dark induction of haem oxygenase messenger RNA by haematoporphyrin derivative and zinc phthalocyanine; agents for photodynamic therapy.

Haematoporphyrin derivative is one of the main drugs currently used in clinical trials involving photodynamic therapy of cancer, and zinc phthalocyanine is being considered as one of several possible alternatives. We show that incubation of cultured human fibroblasts populations with either of the two drugs will lead to a sharp increase in the accumulation of the messenger RNA corresponding to haem oxygenase. Only cells incubated with haematoporphyrin derivative show additional enhancement of expression of this specific gene on exposure to red light. Since haem oxygenase induction appears to be a specific stress response that may be involved in cellular defence, such observations should be confirmed under conditions which would allow the clinical implications to be fully evaluated.     

CORRELATION BETWEEN ENDOGENOUS GLUTATHIONE CONTENT AND SENSITIVITY OF CULTURED HUMAN SKIN CELLS TO RADIATION AT DEFINED WAVELENGTHS IN THE SOLAR ULTRAVIOLET RANGE

Abstract— Glutathione depletion of cultured human skin fibroblasts by treatment with buthionine-S,R-sulfoximine (BSO) sensitises them to radiation at a series of defined wavelengths throughout the solar UV range. We now show that there is a close quantitative correlation between cellular glutathione content (as depleted by BSO) and sensitivity to radiation at 365 nm. A weaker correlation is observed when cells are depleted of glutathione using diethylmaleimide. Both fibroblasts and epidermal keratinocytes derived from the same foreskin biopsy are sensitised to radiation at 313 nm by glutathione depletion. However, the keratinocytes are sensitised to a much lesser extent, an observation which agrees quantitatively with the higher residual levels of cellular glutathione remaining after maximum depletion by BSO (approximately 25% for the keratinocytes vs less than 5% for the fibroblasts). At low to intermediate fluence levels, 10 mM cysteamine present during irradiation at 302 nm is able to almost completely reverse the sensitising effects of glutathione depletion suggesting that the endogenous thiol protects against radiation at this wavelength by a free radical scavenging mechanism. At 313 nm, the sensitisation is not reversed by cysteamine suggesting that glutathione plays a more specific role in protection against radiation at longer wavelengths. Xeroderma pigmentosum group A fibroblasts (excision deficient) are also sensitised to radiation at 313 and 365 nm by depletion of glutathione but since the sensitization is less than that observed for the normal strain, we cannot conclude that glutathione protects against a sector of DNA damage susceptible to excision repair. The results provide further evidence that endogenous glutathione is involved in protecting human skin cells against a wide range of solar radiation damage and suggest that while free radical scavenging is involved at the shortest wavelength (302 nm) tested, a more specific role of glutathione is involved in protection against radiation at longer wavelengths.     

Retention of alkali,alkaline earth and transition metals on an itaconic acid cation-exchange column. Eluent pH,ionic strength and temperature effects upon selectivity

The unusual selectivity of a methylene succinic (itaconic) acid modified polymeric column was investigated for the separation of alkali, alkaline earth, transition and heavy metals employing non-chelating inorganic eluents. The retention of selected metal ions on the column was investigated with simple HNO3 eluents and eluents prepared from KNO3 and KCl salts of varying pH (adjusted using HNO3). From these studies both the effect of eluent ionic strength and pH upon retention was evaluated for the itaconic acid stationary phase. The results obtained showed that despite slow exchange kinetics causing poor efficiencies, acceptable baseline separations of selected alkaline earth and transitions could be obtained under optimum conditions (the baseline separation of Mg(II), Ca(II), Mn(II), Cd(II), Zn(II) and Co(II) was possible using a 15 mM KNO3-5 mM KCl eluent at pH 3.50 in under 25 min). The use of an simple ionic strength step gradient was shown that facilitated the addition of Pb(II) to the above group of metal ions. An investigation into the effect of temperature upon peak efficiency and retention showed increased column temperature could be used to improve the resolution of closely eluting metal ions such as Ca(II) and Sr(II) and Ca(II) and Mn(II).     

REPAIR OF NEAR (365 nm)- AND FAR (254 nm)-UV DAMAGE TO BACTERIOPHAGE OF ESCHERICHIA COLI

Abstract: Intact bacteriophage have been irradiated at 365 nm or at 254 nm and then analysed for DNA photoproducts or injected into their bacterial host to test susceptibility of the damage to both phage and host-cell mediated repair systems. Both thymine dimers and single-strand breaks are induced in the phage DNA by 365 nm radiation. The dimers appear to be the major lethal lesion (approximately 2 dimers per lethal event) in both repair deficient bacteriophage T4 and bacteriophage λ. after irradiation with either 254 nm or 365 nm radiation. Damage induced in T4 by either wavelength is equally susceptible to x -gene reactivation (repair sector approximately 0.5). v -gene reactivation acts on a larger fraction of the near-UV damage (repair sector of 0.82 at 365 nm as against 0.66 at 254 nm). The host-cell mediated photoreactivation system is only slightly less effective for near-UV damage but host-cell reactivation (as measured by comparing survival of phage λ. on a uvr⁺ and a uvr^- host) is effective against a far smaller sector of near-UV damage (0.35) than far-UV damage (0.85). Weigle-reactivation (far-UV induced) of near-UV damage to phage λ is not observed. The results suggest that unless the near-UV damaged phage DNA is repaired immediately after injection. the lesions rapidly lose their susceptibility to repair with a consequent loss of activity of the phage particles.     

REC A +-DEPENDENT SYNERGISM BETWEEN 365 NM AND IONIZING RADIATION IN LOG-PHASE ESCHERICHIA COLI: A MODEL FOR OXYGEN-DEPENDENT NEAR-UV INACTIVATION BY DISRUPTION OF DNA REPAIR

Abstract —The oxygen dependence of 365 nm inactivation of colony-forming ability of Escherichia coli has been investigated in two series of DNA repair-deficient K12 mutants grown to mid-exponential phase. All strains except a uvr A rec A double mutant are more sensitive to inactivation under O₂ and show a lower threshold dose. The inactivation of photoreactivating enzyme in a crude cell extract and DNA repair disruption are both reduced when irradiation is carried out under nitrogen. The rec A gene-dependent synergism between 365 nm and ionising radiation is reversible if cells are incubated in full growth medium before ionising radiation treatment. In a wildtype strain, incubation for 2.5 h in full growth medium after 10⁶ J m^-2 365 nm radiation changes a sensitised response to a protection from ionising radiation. Protection is not seen at 1.5 times 10⁶ J m^-2. A tentative model for near UV lethality in logarithmic phase cells is suggested which proposes two classes of lesions. One requires oxygen for it's induction, is rapidly fixed as a lethal event as a result of repair disruption, and is primarily responsible for cell death after aerobic 365 nm irradiation. The other lesion, possibly pyrimidine dimers, may lead to cell death under anaerobic conditions.     

Molecular rectification: self-assembled monolayers in which donor-(pi-bridge)-acceptor moieties are centrally located and symmetrically coupled to both gold electrodes

Self-assembled monolayers (SAMs) obtained from 1-(10-acetylsulfanyldecyl)-4-[2-(4-dimethylaminophenyl)vinyl]quinolinium iodide exhibit asymmetric current-voltage (I-V) characteristics. The rectification may be reversibly switched: it is suppressed when the film is exposed to HCl vapor, the intramolecular charge-transfer axis being inhibited by protonation, but restored when exposed to NH(3). The behavior is intrinsic to the donor-(pi-bridge)-acceptor moiety, and ambiguity in the assignment has been excluded by matching the alkyl tails on the substrate and contacting STM tip to locate the chromophore midway between the electrodes: Au-S-C(10)H(21)//D-pi-A-C(10)H(20)-S-Au. Films contacted by gold tips exhibit rectification ratios of ca. 18 at +/-1 V, whereas those contacted by pentanethiolate (Au-S-C(5)H(11))- and decanethiolate (Au-S-C(10)H(21))-coated tips have corresponding ratios of ca. 11 and 5, respectively. The I-V curves are different, but when adjusted for thickness the current versus electric field dependence is indistinguishable. Seven dyes are reported: SAMs with sterically hindered D-pi-A moieties, in which the donor and acceptor are twisted out of plane, exhibit rectification, whereas those that are planar or have a weak donor-acceptor combination do not.     

Nonclassical titanocene silyl hydrides

The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction.