Stabilization of Telomeric I‐Motif Structures by (2′S)‐2′‐Deoxy‐2′‐C‐Methylcytidine Residues

G‐quadruplexes and i‐motifs are tetraplex structures present in telomeres and the promoter regions of oncogenes. The possibility of producing nanodevices with pH‐sensitive functions has triggered interest in modified oligonucleotides with improved structural properties. We synthesized C‐rich oligonucleotides carrying conformationally restricted (2′S)‐2′‐deoxy‐2′‐C‐methyl‐cytidine units. The effect of this modified nucleoside on the stability of intramolecular i‐motifs from the vertebrate telomere was investigated by UV, CD, and NMR spectroscopy. The replacement of selected positions of the C‐core with C‐modified residues induced the formation of stable intercalated tetraplexes at near‐neutral pH. This study demonstrates the possibility of enhancing the stability of the i‐motif by chemical modification.     

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements: numerical simulations

A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from measurements.     

Pore blockage effect of NOM on atrazine adsorption kinetics of PAC: the roles of PAC pore size distribution and NOM molecular weight

Natural organic matter (NOM) in natural water has been found to have negative effects on the adsorption of various trace organic compounds by activated carbon through two major mechanisms: direct competition for sites and pore blockage. In this study, the pore blockage effect of NOM on atrazine adsorption kinetics was investigated. Two types of powdered activated carbon (PAC) and three natural waters were tested to determine the roles of PAC pore size distribution and NOM molecular weight distribution in the pore blockage mechanism. When PAC was preloaded with natural water, the pore blockage effect of the NOM was found to cause a reduction of up to more than two orders of magnitude in the surface diffusion rate of atrazine compared to simultaneous adsorption of atrazine and NOM with fresh PAC. The surface diffusion coefficient of atrazine for preloaded PAC decreased with a decrease in PAC dose or an increase in NOM surface concentration. Because of the pore blockage effect of NOM, a 30% drop in atrazine removal was observed in a continuous flow PAC/microfiltration (MF) system after 7 days of contact compared to the removal predicted from the batch isotherm test. Large micropores and mesopores were found to play an important role in alleviating the effect of pore blockage. A PAC with a relatively large fraction of large micropore and mesopores was shown to suffer much less from the pore blockage effect compared with a PAC that had a much smaller fraction of large pores. Natural waters with different NOM molecular weight distribution caused different extent of pore blockage. The NOM molecules with molecular weight between 200 and 700 Dalton appeared to be responsible for the pore blockage effect.     

Inactivation kinetics of adenovirus serotype 2 with monochloramine

The effect of pH (6-10), temperature (10-30 degrees C), disinfectant concentration (1-11mg/l as Cl(2)), and ammonia nitrogen-to-chlorine molar ratio (1.3-52) on the inactivation kinetics of adenovirus serotype 2 with monochloramine was investigated by performing batch-reactor experiments with synthetic 0.01M buffer (phosphate or borate) solutions. The inactivation kinetics was independent of monochloramine concentration and ammonia nitrogen-to-chlorine molar ratio but had strong pH dependence, with the rate of inactivation decreasing with increasing pH. The kinetics at pH 6 and 8 were consistent with pseudo-first-order kinetics, while curves at pH 10 were characterized by a lag phase followed by a pseudo-first-order phase. The rate of inactivation increased with increasing temperature-activation energies of 56.5kJ/mole (pH 8) and 72.6kJ/mole (pH 10). The results obtained in this study revealed that monochloramine disinfection might not generally provide adequate control of adenoviruses in drinking water at high pH and low temperature.     

Mercury accumulation in upland acid forest ecosystems nearby a coal-fired power-plant in southwest Europe (Galicia, NW Spain)

This study was carried out to determine total Hg concentrations (HgT) in acid soils and main plant species in forest ecosystems located in the river Sor catchment, which is located 20 km to the NE of the biggest coal-fired power-plant in southwestern Europe (Galicia, NW Spain). Mercury enrichment factors and Hg inventories were also determined in the soils, which were regularly sampled between 1992 and 2001. The presence of elemental Hg was estimated by simple thermal desorption at 105 degrees C. The highest HgT concentrations occurred in upper soil layers (O and A horizons) with values up to 300 ng g(-1). HgT decreased with depth, achieving the lowest values in the bottommost horizons (i.e. the soil parent material, <6 ng g(-1)), except in podzolic soils. A similar trend occurred for Hg enrichment factors (HgEF) which showed values from 40 to 76 in topsoils. Upper soil mineral horizons (A or AB) made the largest contribution (>50%) to the HgT inventory despite showing lower concentrations than the organic horizons. The role of vegetation in capturing atmospheric Hg and subsequent deposition to soil agrees with the sequence of HgT in plant material: wood相似文献   

A Daphnia magna feeding bioassay as a cost effective and ecological relevant sublethal toxicity test for Environmental Risk Assessment of toxic effluents

Environmental Risk Assessment of chemical products and effluents within EC countries require the use of cost effective standardized toxicity tests that in most cases are restricted to acute responses to high doses. Thus, subtle ecological effects are underestimated. Here we propose a short-term one day Daphnia magna feeding inhibition test as a cost effective and ecological relevant sublethal bioassay. The sensitivity and reliability of the proposed bioassay was tested in the laboratory against standardized bacteria, algae growth, D. magna and fish acute toxicity test by using 16 chemical mixture x water type combinations that included four different water types fortified with four complex chemical mixtures. Water types included ASTM hard water and three selected effluents diluted 1/10 in water to mimic worse field situations that many overexploited arid river ecosystems suffer during summer months when effluents are discharged into them with little dilution. The results obtained denoted a greater sensitivity of the proposed feeding bioassay in 51 out of 65 tests performed with an average sensitivity 50 fold greater than that of the standardized tests. The greater differences were obtained for mixtures that included narcotic chemicals and the lowest differences for those containing pesticides. Furthermore, feeding responses to the studied contaminant mixtures behaved differently to increasing TOC content than those based on bioluminescent bacteria and algae. Increasing TOC coming from sewage treated effluents decrease toxicity to the latter bioassays but increased those of D. magna feeding bioassays. These results empathize the need to include additional bioassays to monitor more accurately and realistically the toxicity of effluents or surface waters dominated by effluent discharges, a quite common situation in America and Mediterranean arid regions.