: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Supramolecular chemistry has expanded dramatically in recent years both in terms of potential applications and in its relevance to analogous biological systems. The formation and function of supramolecular complexes occur through a multiplicity of often difficult to differentiate noncovalent forces. The aim of this Review is to describe the crucial interaction mechanisms in context, and thus classify the entire subject. In most cases, organic host-guest complexes have been selected as examples, but biologically relevant problems are also considered. An understanding and quantification of intermolecular interactions is of importance both for the rational planning of new supramolecular systems, including intelligent materials, as well as for developing new biologically active agents.

Binding Mechanisms in Supramolecular Complexes

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. Sulfate is a major component of fine haze particles. Record sulfate concentrations of up to ~300 μg m −3 were observed during the January 2013 winter haze event in Beijing. State-of-the-art air quality models that rely on sulfate production mechanisms requiring photochemical oxidants cannot predict these high levels because of the weak photochemistry activity during haze events. We find that the missing source of sulfate and particulate matter can be explained by reactive nitrogen chemistry in aerosol water. The aerosol water serves as a reactor, where the alkaline aerosol components trap SO 2 , which is oxidized by NO 2 to form sulfate, whereby high reaction rates are sustained by the high neutralizing capacity of the atmosphere in northern China. This mechanism is self-amplifying because higher aerosol mass concentration corresponds to higher aerosol water content, leading to faster sulfate production and more severe haze pollution.

Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China

http://library.um.ac.id/free-contents/downloadpdf.php/buku/complexation-reactions-in-aquatic-systems-an-analytical-approach-j-buffle-translators-s-p-kounaves-a-kounaves-and-r-s-altman-12623.pdf

Complexation reactions in aquatic systems : an analytical approach / J. Buffle, translators S.P. Kounaves, A. Kounaves and R.S. Altman

Methylmercury is a potent neurotoxin produced in natural environments from inorganic mercury by anaerobic bacteria. However, until now the genes and proteins involved have remained unidentified. Here, we report a two-gene cluster, hgcA and hgcB, required for mercury methylation by Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. In either bacterium, deletion of hgcA, hgcB, or both genes abolishes mercury methylation. The genes encode a putative corrinoid protein, HgcA, and a 2[4Fe-4S] ferredoxin, HgcB, consistent with roles as a methyl carrier and an electron donor required for corrinoid cofactor reduction, respectively. Among bacteria and archaea with sequenced genomes, gene orthologs are present in confirmed methylators but absent in nonmethylators, suggesting a common mercury methylation pathway in all methylating bacteria and archaea sequenced to date.

The Genetic Basis for Bacterial Mercury Methylation

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution

Binding of tripolyphosphate by aliphatic amines : Formation, stability and calculation problems

This paper describes a modified version of the SIT (Specific ion Interaction Theory) method and its use in determining the dependence on ionic strength of activity coefficients In the new approach

A new approach in the use of SIT in determining the dependence on ionic strength of activity coefficients. Application to some chloride salts of interest in the speciation of natural fluids

Both mercury(II) and monomethyl mercury(II) poisonings are of great concern for several reasons. As it happens for other metals, chelation therapy is the most indicated treatment for poisoned patients. The efficacy of the therapy and the reduction of side-effects can be sensibly enhanced by an accurate knowledge of all the physiological mechanisms involved in metal uptake, transport within and between various tissues, and (possibly) clearance. All these aspects, however, are strictly dependent on the chemical speciation (i.e., the distribution of the chemical species of a component in a given system) of both the metal and the chelating agent in the systems where they are present. In this light, this review analyzes the state of the art of research performed in this field for mercury(II) and methylmercury(II). After a brief summary of their main sources, the physiological patterns for the treatment of mercury poisoning have also been considered. The binding ability of various chelating agents toward mercury has been then analyzed by modeling the behavior of the main classes of ligands present in biological fluids and/or frequently used in chelation therapy. Their sequestering ability has been successively evaluated by means of a semiempirical parameter already proposed for its objective quantification, and the main characteristics of an efficient chelating agent have been evaluated on this basis.

Chelating agents for the sequestration of mercury(II) and monomethyl mercury(II).

The empirical parameters of a two-parameter SIT equation were determined for some 1:1 electrolytes: chlorides, bromides, iodides, nitrates, perchlorates and carboxylates of alkali metals, inorganic acids and bases, and tetralkylammonium halides. A wide range of ionic strengths were considered. Canonical correlation analysis identified correlations between the SIT and Pitzer interaction coefficients for different classes of 1:1 type electrolytes.

Claudia Foti

Papers

Weak alkali and alkaline earth metal complexes of low molecular weight ligands in aqueous solution

Binding of tripolyphosphate by aliphatic amines : Formation, stability and calculation problems

A new approach in the use of SIT in determining the dependence on ionic strength of activity coefficients. Application to some chloride salts of interest in the speciation of natural fluids

Chelating agents for the sequestration of mercury(II) and monomethyl mercury(II).

SIT Parameters for 1:1 Electrolytes and Correlation with Pitzer Coefficients