Mutual Transformations of Polysulfide Chromophore Species in Sodalite-Group Minerals: A DFT Study on S6 Decomposition.

It is known that various polysulfide species determine the color of sodalite-group minerals (haüyne, lazurite, and slyudyankaite), and that heating induces their transformations and color change, but the mechanisms of the transitions are unknown. A prominent example is the decay of cyclic S6 molecule. Using density-functional simulations, we explore its main decay pathways into the most probable final reaction products (the pairs of radical anions S3⋅-+S3⋅- and S2⋅-+S4⋅-). It was found that the most favorable reaction path involves initial capture of one electron by the S6 molecule, which greatly facilitates its decay of S6 and leads to the opening of the S6 cycle, and subsequent decomposition of the thus formed chain radical anion, with a limiting energy barrier of ~0.4 eV. Neutral polysulfide molecules capture one electron with a significant energy reduction. The radical anions Sn⋅- (n=2-6) are the most stable ones among corresponding species with the same n values and different charges. The capture of the second electron by S6⋅- occurs with a huge energy barrier (~2 eV). The results of the DFT calculations are in agreement with experimental data on the products of thermal conversions of extra-framework S-bearing groups in sodalite-group minerals.

Stability of sulfur molecules and insights into sulfur allotropy.

Using ab initio evolutionary algorithm USPEX, we predict structures of sulfur molecules Sn (n = 2 - 21). It is shown that for n ≥ 5 stable structures of sulfur molecules are closed helical rings, which is in agreement with the experimental data and previous calculations. We investigate the stability of molecules using the following criteria: second-order energy difference (Δ2E), fragmentation energy (Efrag) and HOMO-LUMO gaps. The S8 molecule has the highest value of Δ2E and forms the most common allotropic form of sulfur (orthorhombic α-S), into which all other modifications convert over time at room temperature. Commonly found molecules S12 and S6 also have strongly positive Δ2E. Another well-known molecule, S7, has negative Δ2E, but at temperatures above 900 K has positive second-order free energy difference Δ2G. Generally, Δ2E (or Δ2G at finite temperatures) is a quantitative measure of the stability allowing one to predict the ease of formation of molecules and corresponding molecular crystals. Temperature dependence of the above-mentioned measures of stability explains a wide range of facts about sulfur crystalline allotropes, molecules in the gas phase, etc.

The Assessment of Methyl Methanesulfonate Absorption by Amphipods from the Environment Using Lux-Biosensors.

The ability of aquatic mesofauna representatives involved in trophic chains to sorb and accumulate toxicants is important for understanding the functioning of aquatic ecosystems and for fishing industry. This study investigated the capacity of marine amphipod Gammarus oceanicus and freshwater amphipods Eulimnogammarus vittatus and Gammarus lacustris to absorb the DNA-alkylating agent methyl methanesulfonate (MMS). The presence of alkylating agents in the environment and in the tissues of the amphipods was determined using whole-cell lux-biosensor Escherichia coli MG1655 pAlkA-lux, in which the luxCDABE genes from Photorhabdus luminescens, enabling the luminescence of the cell culture, are controlled by the PalkA promoter of DNA glycosylase. It was shown that within one day of incubation in water containing MMS at a concentration above 10 µM, the amphipods absorbed the toxicant and their tissues produce more alkylation damage to biosensor cells than the surrounding water. Concentrations of MMS above 1 mM in the environment caused the death of the amphipods before the toxicant could be significantly concentrated in their tissues. The sensitivity and the capacity to absorb MMS were found to be approximately the same for the marine amphipod G. oceanicus and the freshwater amphipods E. vittatus and G. lacustris.

Two known and one new species of Draconematidae and Epsilonematida (Nematoda, Desmodorida) from the White Sea, North Russia.

Morphological descriptions of three "walking nematode" species found for the first time in the White Sea are presented. Draconema ophicephalum (Claparède, 1863) (Draconematidae) and Epsilonema steineri Chitwood, 1935 (Epsilonematidae), both known from insufficient material and females only, are re-described and problems of their taxonomic identification as well as species compositions of respective genera are discussed. The new species Prochaetosoma marisalbi sp. n. (Draconematidae) differs from other Prochaetosoma species except P. longicapitatum (Allgén, 1935) in that the pharyngeal bulb lumen is not cuticularised, from P. longicapitatum by shape of body and rostrum, greater number of cephalic adhesive tubes, and from P. maertensi Decraemer, 1989 by having a relatively longer tail, fewer anterior adhesive tubes and longer spicules, besides lacking cuticular thickening in the pharyngeal bulb. Draconema hoonsooi, D. youngeouni, P.rochaetosoma beomseomense, P. brevicaudatum, P. byungilli, P. cracense, P. saheungi, P. sujungi, P. supseomense erected by Rho & Min (2011) are considered as invalid species while Prochaetosoma arcticum, P. lugubre and Epsilonema cygnoides are assumed as species inquirenda. From a phylogenetic tree based on the 18S rRNA gene, all three White Sea species adjoin to unidentified species of their respective genera.