Combined molecular mechanics, molecular dynamics and quantum mechanical study of (+)-multifidene structure and conformation

Molecular mechanics, molecular dynamics and quantum mechanical tools have been used to explore the conformational space of (+)(3S,4S)-multifidene bioactive compounds. All the computations have been performed in the absence and presence of the solvent, simulated by the explicit introduction of a number of water molecules or by the polarized continuum model (PCM). Three conformational minima, both in vacuo and in water (simulated by PCM tool), have been confirmed at ab initio level of theory (B3LYP and MP2). All minima lie in a very narrow range of energy, and the interconversion between them is possible with a small amount of energy expense.     

Inter-simple sequence repeat markers reveal strong genetic differentiation among populations of the endangered mollusc Patella ferruginea (Gastropoda: Patellidae) from two Sardinian marine protected areas

The giant Mediterranean limpet Patella ferruginea Gmelin, 1791 is an endangered marine gastropod, whose range has progressively shrinked to few, restricted areas, due to intense human exploitation. We have studied the genetic structure of the species, in order to (1) gather information about the levels of genetic variability within and between natural populations of P. ferruginea collected in two Sardinian marine protected areas (MPAs) (Penisola del Sinis—Isola di Mal di Ventre and Isola dell’ Asinara), and (2) make an attempt to find relationships between ecological and biological attributes of the species and the genetic differentiation of the populations studied. The genetic study was carried out by means of the analysis of ten inter-simple sequence repeat (ISSR) primers on a total of 40 individuals collected at four localities. Genetic analysis evidenced (1) medium to high levels of within-population genetic variability, (2) a pattern of genetic structuring that varied with spatial scales, and (3) a strong genetic differentiation between the two MPAs. Although preliminary, these results suggest that gene flow may be present only at very small geographic scale, raising concerns on the future of the conservation of the species.     

Optimisation of a microbial bioassay for contaminated soil monitoring: bacterial inoculum standardisation and comparison with Microtox assay

This work represents the first step to set up a toxicity testing procedure and to evaluate the sensitivity of the test microorganism to several classes of environmental pollutants. First, three different techniques were employed to standardise the microbial inoculum, then two different toxicity assessment protocols have been compared: Microtox and a dehydrogenase (DHase) activity inhibition test. The main goal was the optimisation of a microbial bioassay based on the dehydrogenase activity (DHase) inhibition in Pseudomonas fluorescens bacterial strain ATCC 13525. Triphenyl tetrazolium chloride (TTC) was used as electron acceptor and its reduction produces Triphenyl formazane (TPF). The P. fluorescens DHase inhibition bioassay was investigated for being a reliable and rapid method for assessing toxicity. The optimisation of the operating conditions resulted in a repeatable bioassay. Then, P. fluorescens and Vibrio fischeri sensitivity were firstly compared by testing Zn++, one of the reference compounds for Microtox test. In addition, other compounds (Ni++, Cd++, Cu++, phenol) were also tested with both bioassays. A high statistical significance of data was obtained with the logistic curve. The present work has demonstrated that P. fluorescens is as sensitive as Microtox culture (V. fischeri), for some of the metal ions. With reference to organic compounds, the lower sensitivity of P. fluorescens to phenol makes its use difficult in organic polluted samples.     

Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository

The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters.     

Standardization of BOD₅/COD ratio as a biological stability index for MSW

The control of biodegradable substances is the key issue in evaluating the short and long-term emission potential and environmental impact of a landfill.Aerobic and anaerobic indices, such as respirometric index (RI) and biomethane potential production (GB21), can be used in the estimation of the stability of solid waste samples.Previous studies showed different degrees of relationship between BOD₅/COD ratio compared with RI4.Aim of this study is to standardize the parameter BOD₅/COD ratio and to test the methodology under different operating conditions (dynamic or static leaching and leaching duration, 6 and 24-h) keeping constant temperature and liquid/solid ratio (L/S = 10 l/kg_TS), with the introduction of a COD fractioning method. The COD fractioning is based on the differentiation between the soluble fraction (COD_sol) and the colloidal fraction (COD_coll) using a flocculation method.The BOD₅/COD and the BOD₅/COD_sol indices are both consistent and significant and can be used as stability indices.The BOD₅/COD ratio does not seem to be influenced, for the same test duration, by the type of test, static or dynamic. In the same way the longer test duration (24-h) does not influence significantly the values of BOD₅/COD ratio. As a consequence a leaching test duration of 6-h is preferable to avoid the beginning of the hydrolysis and oxidation processes.     

Simultaneous estimation of effective and apparent diffusion coefficients in compacted bentonite

Effective diffusion coefficients (D(e)) are usually measured by means of "through-diffusion" experiments in which steady state is reached, and the "time-lag" methods are used to estimate the apparent diffusion coefficient (D(a)). For sorbing radionuclides (as caesium), the time needed to reach steady-state conditions is very large, and the precision in D(a) determinations is not satisfactory. In this paper, a method that allows determining simultaneously effective and apparent diffusion coefficients in compacted bentonite without reaching steady-state conditions is described. Basically, this method consists of an "in-diffusion" experiment in which the concentration profile in the bentonite sample is used to estimate D(a), and the temporal evolution of the solute concentration in the reservoir is used to estimate D(e). This method has several advantages over the typical "through-diffusion" experiments, in particular: (a) experiment duration is significantly shorter, (b) D(a) values are measured with greater precision and (c) it is not necessary to maintain a constant solute concentration in the reservoir. This new method has been used to estimate the effective and apparent diffusion coefficients for caesium in FEBEX bentonite and in order to validate it, the results have been compared with results previously obtained with standard methods. Experimental results have been satisfactorily modelled using a simple model of diffusion in porewater and the measured value of D(e)(Cs) is very similar to D(e)(HTO) in the same bentonite. There is no evidence of "surface diffusion" in FEBEX bentonite for caesium.