The seasonal variations of arsenic species in lake water were studied in the mesotrophic northern and eutrophic southern basins of Lake Biwa in Japan. Within the euphotic zone, arsenite [As(III)] increased in spring and fall, and dimethylarsinic acid [DMAA(V)] became the dominant form in summer. Measurable concentrations of monomethylarsonic acid [MMAA(V)] and trivalent methylarsenic species [monomethylarsonous acid, MMAA(III), and dimethylarsinous acid, DMAA(III)] also appeared, although they were always minor fractions. The total arsenic concentration in the euphotic zones remained constant in the northern basin throughout the year. However, it was increased by 2−4 times in the southern basin in summer. The enhancement was caused by the increase of As(V), which was accompanied by the increase of iron, manganese, and phosphorus. The concentration of methylarsenicals per chlorophyll a was lower in the southern basin. These results indicate that the variations of arsenic species in lake water largely depend on biological processes, such as the metabolism of phytoplankton, decomposition of organic matter by bacteria, and microbial reduction of iron and manganese oxides in sediments. Moreover, they show that eutrophication affects the concentration and speciation of arsenic in the lake water.

The effects of salts, acids, and phenols on the hydrogen-bonding structure of water in 20% (v/v) EtOH−H2O solution were investigated on the basis of 1H NMR chemical shifts of the OH of water and ethanol. It was found that many salts caused structure breaking of water while a few metal salts, such as MgCl2 and KF, had a strengthening effect. The OH proton chemical shifts caused by the presence of alkali-metal and alkaline-earth-metal ions or anions (halides, NO3 -, ClO4 -, SO4 2-) from strong acids were related to the sizes and charges of the ions. Not only acids (H+ and HA, undissociated acids) but also bases (OH- and A-, conjugate-base anions from weak acids) had the effect of strengthening the structure of water; the degree of the effect was dependent on the acid strength (pK a). The proton exchange between water and ethanol molecules in 60% (v/v) EtOH−H2O solution was examined, on the basis of the coalescence of two signal peaks of water and ethanol as well as the further low-field shift in 1H NMR spectra with increasing concentration of solutes. Although it has been already reported that the proton exchange between water and ethanol molecules is promoted by strong acids and bases, a distinct proton exchange was also observed in the neutral solution, i.e., by the addition of phosphate pH buffer solution (pH 6.86). It was also discovered that NaCl had the effect of breaking the structure of water in 20% (v/v) EtOH−H2O solution; however, in 60% (v/v) EtOH−H2O solution the same salt at lower concentrations strengthened the water−ethanol structure, promoting the proton exchange between water and ethanol molecules. Hydrogen bond donors as well as acceptors seemed to cause the intimate (or tight) interaction between H2O and EtOH molecules even in alcoholic beverages.

Electrochemical reduction of elemental sulfur (S8) has been carried out in acetonitrile using a platinum electrode. The products were identified by means of spectrophotometry and ESR. Sulfur is reduced voltammetrically in two steps: S_8+2e→S_8^2-, S_8^2-+2e→2S_4^2- These products turns into more stable species by the succeeding chemical reactions in a bulk solution as follows: 2&S_8^2\oversetK\ightleftarrowsS_6^2-+1/4S_8& &(K=1.6×10^-2) &S_6^2-\oversetK_d\ightleftarrows2S_3^\ewdot& &(K_d=1.2×10^-3) The S42− species was enough active to react with S8 into S82−, which was regarded as the cause of a current maximum on the current-time curve in a controlled potential coulometry of S8 at a potential of the second reduction step.

A new approach is described for the speciation of arsenic species including trivalent methyiarsenicals in natural waters. Arsenious acid [As(m)], monomethylarsonous acid [MMAA(III)], and dimethylarsinous acid [DMAA(III)] are separated from pentavaient species by solvent extraction using diethyiammonium diethyldithiocarbamate (DDDC) and determined by hydride generation atomic absorption spectrometry (HG-AAS) after cold trapping and chromatographic separation. The

in the mole fraction range A^Os = 0.22-0.33 is considered a realistic description of the catalyst. However, the temperature of the melt should be in the range 400-500 °C, and furthermore the melt should be in contact with an S02/02/S03 gas mixture in order to correspond to the conditions of operation. Even in the absence of this redox mixture the complexes of vanadium(V) in the V205-K2S207 binary system might very well be analogous to the complexes formed during operation of the catalyst. The present results show that the dominating vanadium(V) complex in solution in the mole fraction range AV2o5 = 0.22-0.33 is probably the dimer (V02)2(S04)2S2074-. Furthermore, the results for the ternary V205-K2S207-K2S04 system show that the S2072-group is labile and that a ligand exchange forming (V02)2(S04)34-can take place. This lability might lead to an exchange of S2072-with S02 during the catalytic reaction, giving rise to the formation of the complex (V02)2(S04)2S022-as the initial step in the catalytic cycle. In this complex a two-electron transfer from S02 to the vanadium central atoms forming S03 and possibly a V(IV) complex might take place simultaneously.The redox and complex chemistry of vanadium in similar melts is under investigation.25-27 Furthermore, an extended calorimetric (25) Fehrmann, R.; Hansen, N. H.; Bjerrum, N. J.; Phillipsen, J.; Pedersen, E., to be submitted for publication.study involving temperatures other than 430 °C in the range 400-450 °C is under way;28 conductivity and density measurements are in progress.18

Conductivities of a number of uni-univalent salts, including tetrabutylammonium and lithium nitrophenolates, were measured at 25.0 °C in low-permittivity solvents such as tetrahydrofuran (THF, εr = 7.58), 1,2-dimethoxyethane (DME, 7.2), chloroform (4.8), and ethyl acetate (6.0). Minima in the conductometric curves (Λ−C 1/2) were observed for concentrations which were dependent upon both the salt and the solvent, C min = 1.73 × 10-4 mol dm-3 for 2,4-(NO2)2C10H5OLi (lithium 2,4-dinitro-1-naphtholate) in THF and 2.56 × 10-2 mol dm-3 for LiPic (lithium picrate) in DME. The observed molar conductivities including C min could be completely explained by the formation of ion pairs (M+ + X- ⇌ MX, K 1), “symmetrical” triple ions (2M+ + X- ⇌ M2X-, K 2; M+ + 2X- ⇌ MX2 -, K 3; K 2 = K 3), and (in some cases) additional formation of quadrupoles (2MX ⇌ M2X2, K 41). A linear relationship (the slope of −1) between the triple ion formation constants (log(K 2/K 1)) and the salt concentrations at the minimum (log C min) was given for all the salts in the various solvents, except for some systems in which a distinct formation of quadrupole takes place, e.g., LiNO3 in DME (K 1 = 3.16 × 1010, K 2 = 4.5 × 1013, and K 41 = 35). The formation of triple ions might be attributed to the ion sizes in solutions in which Coulombic interactions were the only main forces between ions (R4N+···X-). However, coordination (or covalent) bonding forces as well as Coulombic forces had to be considered for the lithium salts except for LiClO4 and LiBF4). Gutmann's donor and acceptor numbers of solvents (and not the permittivity) accounted for the larger difference of C min of lithium salts in THF and DME. In mixed solvents of THF and 2-ethyl-1-hexanol (εr = 7.58), the C min values of LiNO3 and 2,4-(NO2)2C10H5OLi increased with increasing contents of the hexanol, whereas the C min values of LiClO4 and Bu4NX (X- = NO3 -, 2,4-(NO2)2C10H5O-, and ClO4 -) remained constant for 0−30 vol % hexanol added to THF. The positive shifts in C min were explained quantitatively by the decrease in triple ion formation constants and/or by an increase in the quadrupole formation constants.

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