Spatial distribution of electrical conductivity and stable isotopes in groundwater in large catchments: a geostatistical approach in the Quequén Grande River catchment,Argentina

Stable isotopes and electrical conductivity in groundwater were used as natural tracers to adjust the hydrogeological conceptual model in one of the largest catchments within the inter-mountainous Pampa plain, Argentina. Geostatistical tools were used to define the model that best fitted the spatial distribution of each tracer, and information was obtained in areas where there was a lack of data. The conventional isotopic analysis allowed the identification of three groundwater groups with different isotopic fingerprints. One group containing 56?% of the total groundwater samples suggested a well-mixed system and soil infiltration precipitation as the main recharge source to the aquifer. The other two groups included samples with depleted (25.5?%) and enriched (18.5?%) isotopic compositions, respectively. The combination of δ¹⁸O, δ²H and electrical conductivities maps suggested ascending regional flows and water transfer from the Quequén Grande River catchment to the Moro creek. The spatial interpretation of these tracers modified the conceptual hydrogeological model of the Quequén Grande River.     

Conformational analysis of model compounds of vitamin D by theoretical calculations

A conformational analysis of two model compounds of vitamin D was carried out by means of theoretical computations, Ab initio calculations were carried out using the standard 6-31G* basis set at the Hartree–Fock (HF) level of theory. In addition, the Møller–Plesset (MP2) correlation treatment was applied on the simplest model. Semiempirical calculations were also performed using the AM1 Hamiltonian. The results predict stable A-ring twist forms with energies in the order of 4–6 kcal/mol relative to the global minimum, significantly higher than those reported from molecular mechanics calculations. In addition, a folded conformation was found by the HF optimizations; however, its stability is predicted to be very poor. Comparison of the theoretical results with experimental data is discussed. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1647–1655, 1997     

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

The photocatalytic and electrocatalytic conversion of CO₂ has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO₂ to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed.     

A value for multichoice games

A multichoice game is a generalization of a cooperative TU game in which each player has several activity levels. We study the solution for these games proposed by Van Den Nouweland et al. (1995) [Van Den Nouweland, A., Potters, J., Tijs, S., Zarzuelo, J.M., 1995. Cores and related solution concepts for multi-choice games. ZOR-Mathematical Methods of Operations Research 41, 289–311]. We show that this solution applied to the discrete cost sharing model coincides with the Aumann-Shapley method proposed by Moulin (1995) [Moulin, H., 1995. On additive methods to share joint costs. The Japanese Economic Review 46, 303–332]. Also, we show that the Aumann-Shapley value for continuum games can be obtained as the limit of multichoice values for admissible convergence sequences of multichoice games. Finally, we characterize this solution by using the axioms of balanced contributions and efficiency.     

Preparation and characterization of a copper(II) compound with a new glycine Schiff base containing an ester function

Summary A new Schiff base was obtained from glycine and ethyl--ketocyclopentylcarboxylate. This forms a potassium salt K(Rgly)·H₂O, where Rgly=C₁₀H₁₄O₄N. From this salt a new copper(II) complex was prepared, Cu(Rgly)·2H₂O, where Rgly=C₁₀H₁₃O₄N (deprotonated Schiff base). The compounds were characterized by i.r. spectroscopy, differential thermal analysis (d.t.a.) and thermogravimetric analysis (t.g.). The activation energy corresponding to the dehydration process for compounds was determined. On the basis of spectral data, the copper compound is believed to be pentacoordinate and square pyramidal.     

Variation of the ground spin state in homo- and hetero-octanuclear copper(II) and nickel(II) double-star complexes with a meso-helicate-type metallacryptand core

Homo- and heterometallic octanuclear complexes of formula Na?{[Cu?(mpba)?][Cu(Me?dien)]?}-(ClO?)?·12H?O (1), Na?{[Cu?(Mempba)?][Cu(Me?dien)]?}(ClO?)?·12H?O (2), Na?{[Ni?(mpba)?]-[Cu(Me?dien)]?}(ClO?)?·12H?O (3), Na?{[Ni?(Mempba)?][Cu(Me?dien)]?}(ClO?)?·9H?O (4), {[Ni?(mpba)?][Ni(dipn)(H?O)]?}(ClO?)?·12.5H?O (5), and {[Ni?(Mempba)?][Ni(dipn)-(H?O)]?}(ClO?)?·12H?O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me?dien = N,N,N',N',N'-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the "complex-as-ligand/complex-as-metal" strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5 show cationic M(II)?M'(II)? entities (M, M' = Cu and Ni) with an overall double-star architecture, which is made up of two oxamato-bridged M(II)M'(II)? star units connected through three meta-phenylenediamidate bridges between the two central metal atoms leading to a binuclear metallacryptand core of the meso-helicate-type. Dc magnetic susceptibility data for 1-6 in the temperature range 2-300 K have been analyzed through a "dimer-of-tetramers" model [H = - J(S(1A)·S(3A) + S(1A)·S(4A) + S(1A)·S(5A) + S(2B)·S(6B) + S(2B)·S(7B) + S(2B)·S(8B)) - J'S(1A)·S(2B), with S(1A) = S(2B) = S(M) and S(3A) = S(4A) = S(5A) = S(6B) = S(7B) = S(8B) = S(M')]. The moderate to strong antiferromagnetic coupling between the M(II) and M'(II) ions through the oxamate bridge in 1-6 (-J(Cu-Cu) = 52.0-57.0 cm?1, -J(Ni-Cu) = 39.1-44.7 cm?1, and -J(Ni-Ni) = 26.3-26.6 cm?1) leads to a non-compensation of the ground spin state for the tetranuclear M(II)M'(II)? star units [S(A) = S(B) = 3S(M') - S(M) = 1 (1 and 2), 1/2 (3 and 4), and 2 (5 and 6)]. Within the binuclear M(II)? meso-helicate cores of 1-4, a moderate to weak antiferromagnetic coupling between the M(II) ions (-J'(Cu-Cu) = 28.0-48.0 cm?1 and -J'(Ni-Ni) = 0.16-0.97 cm?1) is mediated by the triple m-phenylenediamidate bridge to give a ground spin singlet (S = S(A) - S(B) = 0) state for the octanuclear M(II)?Cu(II)? molecule. Instead, a weak ferromagnetic coupling between the Ni(II) ions (J'(Ni-Ni) = 2.07-3.06 cm?1) operates in the binuclear Ni(II)? meso-helicate core of 5 and 6 leading thus to a ground spin nonet (S = S(A) + S(B) = 4) state for the octanuclear Ni(II)? molecule. Dc magnetization data for 5 reveal a small but non-negligible axial magnetic anisotropy (D = -0.23 cm?1) of the S = 4 Ni(II)? ground state with an estimated value of the energy barrier for magnetization reversal of 3.7 cm?1 (U = -DS2). Ac magnetic susceptibility data for 5 show an unusual slow magnetic relaxation behaviour at low temperatures which is typical of "cluster glasses". The temperature dependence of the relaxation time for 5 has been interpreted on the basis of the Vogel-Fulcher law for weakly interacting clusters, with values of 2.5 K, 1.4 × 10?? s, and 4.0 cm?1 for the intermolecular interaction parameter (T?), the pre-exponential factor (τ?), and the effective energy barrier (U(eff)), respectively.     

Perfusion in rat brain at 7 T with arterial spin labeling using FAIR-TrueFISP and QUIPSS

Measurement of perfusion in longitudinal studies allows for the assessment of tissue integrity and the detection of subtle pathologies. In this work, the feasibility of measuring brain perfusion in rats with high spatial resolution using arterial spin labeling is reported. A flow-sensitive alternating recovery sequence, coupled with a balanced gradient fast imaging with steady-state precession readout section was used to minimize ghosting and geometric distortions, while achieving high signal-to-noise ratio. The quantitative imaging of perfusion using a single subtraction method was implemented to address the effects of variable transit delays between the labeling of spins and their arrival at the imaging slice. Studies in six rats at 7 T showed good perfusion contrast with minimal geometric distortion. The measured blood flow values of 152.5±6.3 ml/100 g per minute in gray matter and 72.3±14.0 ml/100 g per minute in white matter are in good agreement with previously reported values based on autoradiography, considered to be the gold standard.     

Identification of structural alerts for liver and kidney toxicity using repeated dose toxicity data

Background

The potential for a compound to cause hepatotoxicity and nephrotoxicity is a matter of extreme interest for human health risk assessment. To assess liver and kidney toxicity, repeated-dose toxicity (RDT) studies are conducted mainly on rodents. However, these tests are expensive, time-consuming and require large numbers of animals. For early toxicity screening, in silico models can be applied, reducing the costs, time and animals used. Among in silico approaches, structure–activity relationship (SAR) methods, based on the identification of chemical substructures (structural alerts, SAs) related to a particular activity (toxicity), are widely employed.

Results

We identified and evaluated some SAs related to liver and kidney toxicity, using RDT data on rats taken from the hazard evaluation support system (HESS) database. We considered only SAs that gave the best percentages of true positives (TP).

Conclusions

It was not possible to assign an unambiguous mode of action for all the SAs, but a mechanistic explanation is provided for some of them. Such achievements may help in the early identification of liver and renal toxicity of substances.

     

New approach based on fuzzy logic and principal component analysis for the classification of two-dimensional maps in health and disease. Application to lymphomas

Two-dimensional (2D) electrophoresis is the most wide spread technique for the separation of proteins in biological systems. This technique produces 2D maps of high complexity, which creates difficulties in the comparison of different samples. The method proposed in this paper for the comparison of different 2D maps can be summarised in four steps: (a) digitalisation of the image; (b) fuzzyfication of the digitalised map in order to consider the variability of the two-dimensional electrophoretic separation; (c) decoding by principal component analysis of the previously obtained fuzzy maps, in order to reduce the system dimensionality; (d) classification analysis (linear discriminant analysis), in order to separate the samples contained in the dataset according to the classes present in said dataset. This method was applied to a dataset constituted by eight samples: four belonging to healthy human lymph-nodes and four deriving from non-Hodgkin lymphomas. The amount of fuzzyfication of the original map is governed by the sigma parameter. The larger the value, the more fuzzy theresulting transformed map. The effect of the fuzzyfication parameter was investigated, the optimal results being obtained for sigma = 1.75 and 2.25. Principal component analysis and linear discriminant analysis allowed the separation of the two classes of samples without any misclassification.