Quintus Fernando

A review of arsenic (III) in groundwater

Abstract Recent improvements in sample collection and analytical techniques have suggested that As(III) is more prevalent in groundwater than previously believed. Indeed, reducing conditions in alluvial aquifers supplying single families may result in significant exposures to naturally occurring As(III). These results are noteworthy because As(III) is both more toxic and more mobile in the environment than As(V). The literature contains contradictory information concerning the appropriate preservation and analytical techniques for determining As(III). It appears that several previously reported occurrences of As(V) may have been predominantly As(III), but the samples were either not preserved or analyzed properly. For example, separation of arsenic species by ion exchange is apparently necessary to obtain reliable analytical results for certain environmental samples. The problems encountered with investigating As(III) in the environment are due to the complex series of geochemical reactions undergone by a...

Reduction of nitrate to ammonia by zero-valent iron

Abstract The reduction of nitrate to ammonia occurs with nearly complete conversion at room temperature and pressure under aerobic conditions in the presence of iron and either HCl or a pH buffer. A 50.0 mL solution of 12.5 millimolar nitrate is rapidly reduced to ammonia when exposed to 4.00 g of 325 mesh iron at pH 5.0, 0.05 M sodium acetate/acetic acid. The pseudo-first order rate constant was 0.053 min −1 , Under conditions of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjusted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.0408 min −1 and 0.0143 mint, respectively. In unbuffered solutions there was no loss in nitrate and no production of ammonia. A more concentrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also reduced to ammonia in the presence of 2.5 M HCl with the slow addition of 50.0 g of 325 mesh iron.

A method for the rapid dechlorination of low molecular weight chlorinated hydrocarbons in water

1,1,2-Trichloroethylene (TCE), 1,1-dichloroethylene, cis and trans-1,2-dichloroethylene and tetrachloroethylene (PCE), at concentrations of 20 ppm in aqueous solutions were rapidly hydrodechlorinated to ethane (in a few minutes), on the surface of palladized iron in batch experiments that were performed in closed vials. No intermediate reaction products such as 1,1-dichloroethylene, 1,2-dichloroethylenes and vinyl chloride were detected at concentrations > 1 ppm either in the headspace or in solution. The chloromethanes, CCl4, CHCl3 and CH2Cl2 were also dechlorinated to methane on palladized iron; the CCl4 was dechlorinated in a few minutes, the CHCl3, in less than an hour and the CH2Cl2, in 4–5 h. These results indicate that an above-ground treatment method can be designed for the treatment of groundwater contaminated with low molecular weight chlorinated hydrocarbons.

Human Studies with the Chelating Agents, DMPS and DMSA

Meso-2,3-dimercaptosuccinic acid (DMSA) is bound to plasma albumin in humans and appears to be excreted in the urine as the DMSA-cysteine mixed disulfide. The pharmacokinetics of DMSA have been determined after its administration to humans po. For the blood, the tmax and t1/2 were 3.0 h + 0.45 SE and 3.2 h + 0.56 SE, respectively. The Cmax was 26.2 microM + 4.7 SE. To determine whether dental amalgams influence the human body burden of mercury, we gave volunteers the sodium salt of 2,3-dimercaptopropane-1-sulfonic acid (DMPS). The diameters of dental amalgams of the subjects were determined to obtain the amalgam score. Administration of 300 mg DMPS by mouth increased the mean urinary mercury excretion of subjects over a 9 h period. There was a positive correlation between the amount of mercury excreted and the amalgam score. DMPS might be useful for increasing the urinary excretion of mercury and thus increasing the significance and reliability of this measure of mercury exposure. DMSA analogs have been designed and synthesized in attempts to increase the uptake by cell membranes of the DMSA prototype chelating agents. The i.v. administration of the monomethyl ester of DMSA, the dimethyl ester of DMSA or the zinc chelate of dimethyl DMSA increases the biliary excretion of platinum and cadmium in rats.

Determination and metabolism of dithiol chelating agents: VIII. Metal complexes of meso-dimercaptosuccinic acid

Metal complexes of meso-dimercaptosuccinic acid (DMSA) with Pb2+, Cd2+, and Hg2+ were studied by potentiometric and infrared methods. This dimercapto metal-binding agent was found to form complexes whose structures are dependent on the metal ion to be complexed. In the cases of Pb2+ and Cd2+, one oxygen and one sulfur act as the donor atoms; in the case of Hg2+, two sulfur atoms act as the donors. The solubilities of all metal chelates were found to be pH dependent. Complexes of cadmium and lead are insoluble in the pH range 1.0 to 7.1, but are solubilized when the noncoordinated sulfhydryl and carboxylic acid groups are ionized. The mercury complex is insoluble in the pH range 1.0 to 3.0. It dissolves when one of the noncoordinated carboxylic acid groups is ionized. The dimethyl ester of meso-DMSA (DiMe-meso-DMSA) was synthesized and its acid dissociation constants were determined (pK1 = 6.38 and pK2 = 8.00). Esterification of the carboxyl groups of meso-DMSA changes its coordination properties in that the two sulfur atoms of DiMe-meso-DMSA are used to coordinate with Hg2+, Cd2+, or Pb2+. Esterification of meso-DMSA also changes its biological properties. DiMe-meso-DMSA, when given to rats 3 days after Cd administration, greatly increased the excretion of Cd via bile. In contrast, meso-DMSA was devoid of such activity.

The crystal and molecular structure of bis-(O,O′-diethyldithiophosphato) nickel (II)

Abstract The crystal and molecular structure of bis-(O,O′-diethyldithiophosphato) nickel (II), Ni[S 2 P(OC 2 H 5 ) 2 ] 2 , has been established by a single crystal three dimensional X-ray study. The monoclinic unit cell, a = 10·48 A , b = 10·22 A , c = 8·62 A , and β = 102·5° has two formula units in the space group P2 1 c . Each nickel atom occupies a centre of symmetry and forms a planar tetracoordinated chelate with the sulphur atoms of two ligand molecules. The disruption of the chelate rings in solvents of high dielectric constant has been attributed to the presence of an ionic nickel-sulphur bond.

Potentiometric and 1H NMR studies of complexation of Al3+ with (−)-epigallocatechin gallate, a major active constituent of green tea

The acid dissociation of (-)-epigallocatechin gallate (abbreviated as egcg) and its complexation with Al(3+) were studied by potentiometric titrations, and were compared with those of (-)-epicatechin (ec) and (-)-epigallocatechin (egc). In Al(3+)-ec and Al(3+)-egc reaction systems, [Al(LH(-2))](+), [Al(LH(-2))(OH)](0), and [Al(LH(-2))(2)](-) are formed, as reported for Al(3+)-catechin (c). Reactions between Al(3+) and egcg at pH <4.1 yield AlLH(-2) and AlLH(-3) species. The 1H NMR studies have shown that two hydroxyl groups of the gallate (D) ring are deprotonated and coordinated to an Al(3+) ion in [Al(egcgH(-2))](+). The AlLH(-3) species of egcg is supposed to be formulated as [Al(egcgH(-3))](0) in which one hydroxyl group of the pyrogallol (B) ring and two hydroxyl groups of the D ring are deprotonated; an Al(3+) ion is coordinated to two oxygen atoms of the D ring and one oxygen atom from the B ring of the neighboring chelate molecule, resulting in the formation of a polymeric structure. In the Al(3+) complex of egcg, the gallate group forms major coordinate bonds and results in solution properties that are different from those of ec, egc and c which have no gallate group.

Complexation of electroconducting polypyrrole with copper

Abstract A copper complex of polypyrrole is obtained when the polymer perchlorate is treated with a Cu(II)-containing alkaline solution. The X-ray photoelectron spectrum of the resulting polymer material shows that the copper atoms are coordinated to pyrrole nitrogen. The ESR signal of copper ions and that of the pyrrole rings are observed independently of each other; there is no appreciable magnetic interaction between the two paramagnetic species. The room-temperature conductivity is 4 × 10−4 S cm− and the temperature dependence shows semiconductive behavior with an activation energy of 0.11 eV. The degradation of conducting polypyrrole in aqueous solution is suppressed by the presence of copper: the stabilization is attributed to CuN bond formation.

Binuclear structure in the ammonium salt of gadolinium(III) diethylenetriaminepentaacetate, (NH4)4[Gd2(DTPA)2]·6H2O

Abstract A single crystal X-ray analysis of the ammonium salt of Gd 3+ diethylenetriaminepentaacetate has shown that the compound has a binuclear structure in contrast to the corresponding sodium salt that has a mononuclear structure. Five oxygen atoms and three nitrogen atoms from a ligand molecule construct a distorted square antiprism around a Gd 3+ ion. One of the square planes is capped by an oxygen atom from the adjacent metal chelate molecule, resulting in the formation of a binuclear metal chelate. The coordination polyhedron including this oxygen atom is described as a tricapped trigonal prism. The binuclear structure is the result of well-developed hydrogen bonds that involve the ammonium ions.

The crystal and molecular structure of the pentacoordinated copper(II) complex, bis(acetylacetonato)quinolinecopper(II)

The crystal and molecular structure of bis(acetylacetonato) quinolinecopper(II), [Cμ (C5HO2)2(C9H7N)], has been determined by three dimensional methods. The cell dimensions are a = 14·23 A, b = 8·66 A, c = 8·02 A, α = 94·0°, β = 89·0°, γ = 110·8°, the space group P1 and Z = 2. The intensities of 2005 reflections were obtained visually from equi-inclination Weissenberg photographs. The structure was refined by least-squares methods with individual atom isotropic temperature factors, to a conventional R value of 0·138. The structure consists of discrete molecules containing a pentacoordinated copper atom. The donor atoms are arranged in a pyramidal configuration with four equal copper-oxygen bonds. (1·95 ± 0·01 A), directed towards the concerns of the base of a square pyramid and a fifth copper-nitrogen bond, (2·36 ± ·01 A), directed towards the apex of the pyramid.