SOME FURTHER CONSIDERATIONS ON THE USE OF REPAIR-DEFECTIVE ORGANISMS AS BIOLOGICAL DOSIMETERS FOR BROAD-BAND ULTRAVIOLET RADIATION SOURCES

Abstract— The extreme variation in biological effectiveness of the various components of solar ultraviolet radiation (solar UV) which reaches the earth's surface, especially photons of wavelengths between 295 and 330 nm, makes the dosimetry of solar UV a complex and, as yet, unresolved problem. A proper weighting of the various components of solar UV would permit expression of expsoure as a single parameter (dose). Weighting could compensate for the variations in composition of solar UV which might occur during exposure or the differences in sources of UV radiations; weighting would permit comparison of exposures at various locations on the earth and extrapolation of laboratory observations to field situations where wavelength composition might be rather different. Various radiation-sensitive microorganisms have been proposed as biological dosimeters. Biological dosimeters automatically weight the subcomponents of solar UV differently than a purely physical irradiance meter. We have examined the available evidence regarding the weighting which repair-defective mutants provide in comparison with response of a number of wild-type organisms and would caution investigators that, for broad-band UV sources, especially those with significant biological actions through the range of 300–330 nm, repair-sensitive mutants may improperly weight the components, leading to errors of dosimetry and thus to possible errors of interpretation of results of solar UV exposure of wild-type organisms     

Counterion dependent dye aggregates: nanorods and nanorings of tetra(p-carboxyphenyl)porphyrin

Atomic force microscopy (AFM) of porphyrin aggregates formed on silica from acidic aqueous solution is used to investigate the basis for the previously reported counterion dependence of the optical spectra of aggregates of H(2)TCPP(2+), the diacid form of tetra(p-carboxyphenyl)porphyrin (TCPP). Resonance light scattering confirms the presence of excitonically coupled porphyrin aggregates in solutions of H(2)TCPP(2+) in both aqueous HCl and HNO(3). Aggregates formed in aqueous HNO(3) solutions show resonance light scattering (RLS) at wavelengths within both the H and J aggregate absorption bands and are imaged on the surface of silica as nanorods about 3 to 4 nm in height. H(2)TCPP(2+) aggregates in aqueous HCl solution exhibit RLS when excited within the blue-shifted Soret band (H band) and produce AFM images on silica of ring-shaped structures ranging from about 200 to 2000 nm in diameter. Fluorescence excitation and emission spectra reveal quenching of the Q-band emission in the aggregates at a pH less than 1 and confirm the existence of a single species, assigned to a dimer, at a pH just above 1. The morphology of the nanostructures as revealed by AFM provides insight into the structural basis for the counterion-dependent optical properties of H(2)TCPP(2+) aggregates.     

Propriétés électriques des gels aqueux d'amphiphile

Summary This paper deals with the calculation of electrical conductivity in soap-water-systems. Two models are discussed and compared with experimental data.

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Zusammenfassung In der vorliegenden Arbeit werden zwei Modelle zur Berechnung der Leitf?higkeit in Seifen-Wasser-Mischungen beschrieben und mit experimentellen Daten verglichen.

     

Biotinyl-Glucose-6-Phosphate Dehydrogenase Preparation,Kinetics, and Modulation by Avidin

The kinetics of free glucose-6-phosphate dehydrogenase (G-6-PDH), biotinylated G-6-PDH, and biotinylated G-6-PDH complexed with avidin were investigated. The kinetics of the free enzyme were consistent with a sequential rather than a ping-pong mechanism. The kinetics of the biotinylated enzyme were similar to that of the free enzyme, but the kinetic constants were different; theK _m value for NADP was halved, whereas theK _m for G-6-P decreased only slightly. In the presence of avidin, theK _m of biotinylated G-6-PDH for G-6-P nearly doubled whereas theK _m for NADP did not change significantly. Avidin complexed with biotinylated G-6-PDH inhibited the enzyme from acting. Based upon these reactions, it was possible to devise assays for either free biotin or free avidin using biotinylated G-6-PDH as the indicator enzyme. Concentrations of biotin between 40 and 60 mg/mL, or of 25–95 Μg/mL of avidin could be measured within 2 min through the use of biotinylated G-6-PDH.     

PHOTOMOVEMENT, PIGMENTATION AND UV-B SENSITIVITY IN PLANARIA

Four differently pigmented species of planarians were examined for UV-B (Λ= 320 280 nm) tolerance and ability to delect and avoid UV-B-exposed areas. It was found that lighter-pigmented species are more UV sensitive and that movement out of the UV-B is directly related to UV sensitivity. Three species showed positioning preference corresponding to their pigmentation; the darker the species, the less avoidance of UV-B. The white (unpigmented) species showed exceptional and very sensitive behavior.     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Repair of the main UV-induced thymine dimeric lesions within Arabidopsis thaliana DNA: evidence for the major involvement of photoreactivation pathways.

The UV-B induced formation of thymine cis-syn cyclobutane dimer and related (6-4) photoproduct was monitored within DNA of cultured cells and plants of Arabidopsis thaliana. This was achieved using a sensitive and accurate HPLC-tandem mass spectrometry assay. It was found that the cyclobutane pyrimidine dimer was formed in a ninefold higher yield than the (6-4) photoproduct. The removal of the lesions was then studied by incubating irradiated cells either in the darkness, under visible light or upon exposure to UV-A radiation. Dark repair of both cyclobutane dimers and (6-4) photoproducts was found to be very ineffective. In contrast, a rapid decrease in the level of photoproducts was observed when UV-B-irradiated cells were exposed to UV-A and, to a lesser extent, to visible light. The removal of (6-4) adducts was found to occur more efficiently. These results strongly suggest that repair of UV-induced photolesions in plants is mainly mediated by photolyases.     

Enzyme immunoassay for semicarbazide--the nitrofuran metabolite and food contaminant

Semicarbazide (SEM), the marker residue for the banned nitrofuran veterinary antibiotic nitrofurazone (NFZ), has been detected regularly in foods (47% of recent nitrofuran EU Rapid Alerts involve SEM). However, the validity of SEM as a definitive marker for NFZ has been undermined by SEM arising from other sources including azodicarbonamide, a plastics blowing agent and flour treatment additive. An inexpensive screening test for SEM in food matrices is needed—all SEM testing currently uses expensive LC-MS/MS instrumentation. We now report the first production of antibodies against derivatised SEM. A novel carboxyphenyl SEM derivative was used to raise a polyclonal antibody that has been incorporated into a semi-quantitative microtitre plate ELISA, validated according to the criteria set out in Commission Decision 2002/657/EC, for use with chicken muscle. The antibody is highly specific for derivatised SEM, cross-reactivity being 1.7% with NFZ and negligible with a wide range of other nitrofurans and poultry drugs. Samples are derivatised with o-nitrobenzaldehyde and simultaneously protease digested before extraction by cation exchange SPE. The ELISA has a SEM detection capability (CC_β) of 0.25 μg kg⁻¹ when a threshold of 0.21 μg kg⁻¹ is applied to the selection of samples for confirmation (lowest observed 0.25 μg kg⁻¹ fortified sample, n = 20), thus satisfying the EU nitrofurans’ minimum required performance limit of 1 μg kg⁻¹. NFZ-incurred muscles (12) containing SEM at 0.5-5.0 μg kg⁻¹ by LC-MS/MS, all screened positive by this ELISA protocol which is also applicable to egg and chicken liver.     

Removal of 2,4-dichlorophenoxyacetic acid by calcined Zn-Al-Zr layered double hydroxide

The adsorption equilibrium, kinetics, and thermodynamics of removal of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solutions by a calcined Zn-Al layered double hydroxide incorporated with Zr(4+) were studied with respect to time, temperature, pH, and initial 2,4-D concentration. Zr(4+) incorporation into the LDH was used to enhance 2,4-D uptake by creating higher positive charges and surface/layer modification of the adsorbent. The LDH was capable of removing up to 98% of 2,4-D from 5 to 400 ppm aqueous at adsorbent dosages of 500 and 5000 mg L(-1). The adsorption was described by a Langmuir-type isotherm. The percentage 2,4-D removed was directly proportional to the adsorbent dosage and was optimized with 8% Zr(4+) ion content, relative to the total metals (Zr(4+)+Al(3+)+Zn(2+)). Selected mass transfer and kinetic models were applied to the experimental data to examine uptake mechanism. The boundary layer and intra-particle diffusion played important roles in the adsorption mechanisms of 2,4-D, and the kinetics followed a pseudo-second order kinetic model with an enthalpy, ΔH(ads) of -27.7±0.9 kJ mol(-1). Regeneration studies showed a 6% reduction in 2,4-D uptake capacity over six adsorption-desorption cycles when exposed to an analyte concentration of 100 ppm.