Solutions Of HgCl Research Articles

Mercury sorption to sediments: Dependence on grain size, dissolved organic carbon, and suspended bacteria

A combination of laboratory scale derived correlations and measurements of grain size distribution, DOC (dissolved organic carbon) concentration, and density of suspended bacteria promises to be useful in estimating Hg(II) sorption in heterogeneous streambeds and groundwater environments. This was found by shaking intact sediment and fractions thereof (<63–2000 μm) with solutions of HgCl 2 (1.0–10.0 ng ml −1). The intact sediment was also shaken with the Hg(II) solutions separately in presence of DOC (6.5–90.2 μg ml −1) or brought in contact with suspensions of a strain of groundwater bacteria (2 × 10 4–2 × 10 6 cells ml −1). Hg(II) sorption was rather weak and positively correlated with the grain size, and the sorption coefficient ( K d) varied between about 300 and 600 ml g −1. By using the relative surface areas of the fractions, K d for the intact sediment was back calculated with 2% deviation. K d was negatively correlated with the concentration of DOC and positively correlated with the number of bacteria. A multiple regression showed that K d was significantly more influenced by the number of bacteria than by the grain size. The findings imply that common DOC concentrations in groundwater and streambeds, 5–20 μg ml −1, will halve the K d obtained from standard sorption assays of Hg(II), and that K d will almost double when the cell numbers are doubled at densities that are common in aquifers. The findings suggest that simultaneous measurements of surface areas of sediment particles, DOC concentrations, and bacterial numbers are useful to predict spatial variation of Hg(II) sorption in aquifers and sandy sediments.

Thermodynamic model for the stabilization of trigonal thiolato mercury(II) in designed three-stranded coiled coils.

A thermodynamic model is presented that describes the binding of Hg(II) to de novo designed peptides, Tri L9C and Baby L9C, which were derived from the Tri family. The Tri peptides are based on the parent sequence Ac-NH-G(LKALEEK)(x)()G-CONH(2) and are known to form two-stranded coiled coils at low pH (pH <4) and three-stranded coiled coils at high pH (pH >7). Tri L9C (x = 4) contains a four heptad repeat sequence with cysteine in position 9 and leucines in the other a and d positions; Baby L9C (x = 3), which also has a cysteine in position 9 but is one heptad shorter than Tri L9C, was designed to form less stable helical coiled coils in solution. The free energies of coiled coil formation for Tri, Tri L9C, Baby Tri, and Baby L9C at pH 2.5 and 8.5 were determined by guanidinium denaturation titrations; Tri L9C was observed to be highly helical in the absence of denaturant at pH 8.5 while Baby L9C contained <20% helical content at pH 8.5, indicating a weakly associated or unassociated coiled coil. Size-exclusion chromatography (SEC) verified that Baby L9C was a monomer at pH 8.5. The helicity of Baby L9C was induced by addition of HgCl(2). The subsequent formation of a trigonal thiolato Hg(II) in the interior of a three-stranded coiled coil was verified by the presence of a characteristic HgS(3) UV band at 248 nm. Titrations of Tri L9C and Baby L9C into solutions of HgCl(2) at pH values between 7 and 9 were performed to extract binding constants. Global fits to the data employed a mechanism that involved initial binding of mercury to the peptides forming a two-stranded coiled coil with linear thiolato Hg(II) at [peptide]/[Hg] <2, followed by addition of a more weakly associated third helix to generate a three-stranded coiled coil. This mechanism would require the deprotonation of the third cysteine thiol to generate the trigonal thiolato Hg(II) at pH >7.5 [the pK(a) of the cysteine thiol in the presence of Hg(II)]. Support for this mechanism was given by the observation of a three-stranded coiled coil by SEC in a solution of Tri L9C at pH 7.0.

Recovery of mercury using an electrochemical flow-by reactor. Part I Reaction rate expression for mercury deposition in the presence ofa side reaction

This paper analyses the deposition of the mercuric complexes from dilute solutions ofHgCl(2−n)n and high concentrations of NaCl, taking into account the reduction of O2 as a simultaneous electrochemical reaction. Studies with a vitreous carbon rotating disk electrode were performed to determine the potential regions where the reactions take place and also to calculate the kinetic parameters under experimental conditions. Reproducible results were obtained only when a mercury film was deposited on the vitreous carbon surface prior to each experiment. Potentiodynamic polarizations were obtained from 5×10−4 M Hg(II) solutions and different NaCl concentrations ranging from 1 M to 4 M, in the presence and absence of dissolved oxygen. The mercuric complex deposition and the oxygen reduction proceeded via mixed control within the first 50 mV overpotential, followed by a diffusion control. After −0.450 V vs sce the H2 evolution started. This reaction occurred at free vitreous carbon left between the liquid mercury droplets where the hydrogen overpotential is smaller. Kinetic parameters as well as the reaction rate expression for mercury deposition from its chloride complexes were obtained.

The synthesis of low crystallinity polyacetylene from the precursor polymer polybenzvalene

The synthesis and properties of the conductive polymer precursor polybenzvalene ( PBV) and its conversion to polyacetylene ( PA) are presented. PBV was synthesized by ring-opening metathesis polymerization ( ROMP) of benzvalene ( BV) with non-Lewis acidic tungsten alkylidene catalysts. Treatment of PBV with solutions of HgCl 2, HgBr 2, ZnI 2 and AgBF 4 results in a CC bond rearrangement, and produces polyacetylene PA. The PA films produced with HgCl 2 displayed the highest conductivities and the best mechanical properties. The PA produced was of low crystallinity and upon treatment with I 2 exhibited conductivities of 1 Ω −1cm −1. Oriented PA was produced by stretching the PBV and converting it to PA. With I 2 doping, the oriented PA ( l/ l 0=6) displayed a conductivity of 49 Ω −1cm −1.

Kinetics of precipitation of Hg 2Fe(CN) 6 from HgCl 2 and K 4Fe(CN) 6 in aqueous solution

When 10 -2 M solutions of HgCl 2 and K 4Fe(CN) 6 are mixed a fine yellow precipitate of Hg 2Fe(CN) 6 is formed. The rate of formation of this was determined at various temperatures. For kinetic measurements using spectometry, mixing of K 4Fe(CN) 6 and HgCl 2 such that the final concentrations of K 4Fe(CN) 6 and HgCl 2 were in the range of 1 to 3 mM and 3 to 10 mM respectively, so that 7 > [HgCl 2]/[K 4Fe(CN) 6] ⩾ 3 was found to be most suitable, in terms of absorbance and induction period. The rate of precipitation is given by dα/ dt = kα 2 2 3 (1 − α), where α is the fraction precipitated at any time. The rat of precipitation increased exponentially with temperature according to k = A exp(- E a/ RT). Precipitation kinetics at different temperatures gave E a = 72.4 ± 2.5 kJ/mole and A = 10 11.5 s -1. The energy barrier to precipitation is higher compared to that for the formation other ionic precipitates, possibly due to some special steric orientation effects.

The hydrolysis of mercury(II) chloride, HgCl 2

The hydrolytic equilibria of HgCl 2 have been studied in 1 M(Na +)ClO 4 − ionic medium at 25°C by potentiometric methods using the cells 1. -RE/test solution/GE+ -RE/test solution, HgCl 2,Cl −,Hg 2Cl 2(S)/Pt+ where GE denotes glass electrode, and RE is the reference half-cell: RE = Ag, AgCl/0·01 M Cl −, 0·99 M ClO 4 −, 1 M Na +/1 M NaClO 4. The test solutions had the general composition: [Hg(II)] tot =B M,[H +] tot =H M,[Hg(l)] tot =M M,[Cl −] tot =A M,[Na +] =(1−H+A−2B−2M) M,[ClO 4 −]=1M . B ranged from 5 × 10 −3 M to 0·2 M, and A−2 B−2 M was kept equal to zero in the majority of experiments. The e.m.f. data, which indicate that in solutions of HgCl 2 hydrolysis becomes appreciable at log [H +] < −3, can be explained by assuming the equilibria HgCl 2+ H 2 O⇆ HgClOH+H ++ 2Cl −, logβ 1,2,2=−19·6±0·1 HgCl 2+ H 2 O⇆ Hg(OH) 2+ 2H ++ Cl −, logβ 1,1,1=−9·56±0·05 The method of study of the system where three species, HgCl 2, H + and Cl −, participate in the hydrolytic equilibria is described in some detail.