Adsorption characteristics of carbonized bark for phenol and pentachlorophenol

The potential of using carbonized slash pine bark as a substitute for activated carbon was examined in this study. The bark was carbonized by slow heating in nitrogen for 6.5 h to 672 degrees C. The BET-N-2 surface area, average micropore and mesopore diameter, and micropore volume were 332 m(2) g(-1) 21.7 Angstrom, and 0.125 cm(3) g(-1), respectively. The adsorption capacities for phenol and pentachlorophenol (PCP) at pH 2 and pH 8 were evaluated. The Langmuir equation provided a slightly better fit than the Freundlich equation to two sets of phenol data. The calculated Freundlich constants, K = 0.41 - 0.58 mmol/g/(mmol dm(-3))(1/n) and 1/n = 0.30 - 0.41, were lower and higher, respectively, than literature values for activated carbons. The adsorption capacity of the carbonized bark was much lower for PCP than for phenol. The protonated and anionic PCP isotherms were Type II or III, respectively, in the Brunauer classification. The BET equation provided the best fit to protonated PCP isotherm data. The anionic PCP data were fitted to both the BET model and an equation used in the literature to represent phosphate adsorption on activated carbons. Nonlinear regression of the data for both phenol and PCP adsorption with the Freundlich, Langmuir and BET equations generally gave more accurate parameters, compared with the use of linearized equations to obtain the parameters. (C) 1998 SCI.

Solution structures in aqueous SDS micelles of two amyloid beta peptides of A beta(1-28) mutated at the alpha-secretase cleavage site (K16E, K16F)

NMR solution structures are reported for two mutants (K16E, K16F) of the soluble amyloid beta peptide A beta(1-28). The structural effects of these mutations of a positively charged residue to anionic and hydrophobic residues at the alpha-secretase cleavage site (Lys16-Leu17) were examined in the membrane-simulating solvent aqueous SDS micelles. Overall the three-dimensional structures were similar to that for the native A beta(1-28) sequence in that they contained an unstructured N-terminus and a helical C-terminus. These structural elements are similar to those seen in the corresponding regions of full-length A beta peptides A beta(1-40) and A beta(1-42), showing that the shorter peptides are valid model systems. The K16E mutation, which might be expected to stabilize the macrodipole of the helix, slightly increased the helix length (residues 13-24) relative to the K16F mutation, which shortened the helix to between residues 16 and 24. The observed sequence-dependent control over conformation in this region provides an insight into possible conformational switching roles of mutations in the amyloid precursor protein from which A beta peptides are derived. In addition, if conformational transitions from helix to random coil to sheet precede aggregation of A beta peptides in vivo, as they do in vitro, the conformation-inducing effects of mutations at Lys16 may also influence aggregation and fibril formation. (C) 2000 Academic Press.

Nutritional strategies for the prevention of hypocalcaemia at calving for dairy cows in pasture-based systems

This review considers the current literature on the macro-mineral nutrition of the soon-to-calve, or transition, dairy cow. Calcium is the main focus, since milk fever (clinical hypocalcaemia) appears to be the most common mineral-related problem faced by the transition cow Australia-wide. The importance of minimising calcium intake and optimising the balance of the key dietary electrolytes, sodium, potassium, sulfate, and chloride, in the weeks before calving is highlighted. Excess dietary potassium can, in some situations, induce milk fever, perhaps even more effectively than excess calcium. Excess sodium remains under suspicion. In contrast, excess dietary chlorine and, to a lesser extent, sulfur can improve the ability of the cow to maintain calcium homeostasis. Diets that promote either a hypomagnesaemia or hyperphosphataemia have also the potential to precipitate milk fever at calving. Current prevention strategies focus on the use of forages with moderate to low levels of calcium, potassium, and sodium, and also rely on or utilise addition of chloride and sulfate in the form of 'anionic' feeds. Anionic salts are one example of an anionic feed. However, legitimate questions remain as to the effectiveness of anionic salts in pasture-feeding systems. The causes and prevention of milk fever are considered from the perspective of the variety of Australian feedbases. Impediments to the use of anionic feeds in Australia feeding systems are outlined. The potential for improving maternal reserves of calcium around calving to reduce the risk of milk fever is also discussed.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant

A new cloud-point extraction and preconcentration method, using a cationic, surfactant, Aliquat-336 (tricaprylyl-methy;ammonium chloride), his-been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degreesC. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants: At pH 6-7, it showed an outstanding selectivity in ahalyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was. not cle tectable in.the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degreesC) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR: The cloud-point extraction process can be. completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters, collected from a local river and a local duck pond spiked with realistic. concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.

Comparison of adsorption capacity of p-Cresol & p-Nitrophenol by activated carbon in single and double solute

Adsorption of p-Cresol and p-Nitrophenol by untreated activated carbon in single and multisolute solutions was carried out at 301 K and at controlled pH conditions. In acidic conditions, well below the pK(a) of both solutes, it was observed that the adsorbate solubility and the electron density of aromatic rings influenced the extent of adsorption by affecting the extent of London dispersion forces. The fitted parameters obtained from single-solute Langmuir equation show that Q(max) and the adsorption affinity of carbon for the compound with low pK(a) decrease more significantly. In higher solution pH conditions, on the other hand, it was found that electrostatic forces played a significant role on the extent of adsorption. The presence of another compound decreases Q(max) and the adsorption affinity of carbon for the principal compound. The effect of pH, on the carbon surface and on the solute molecules, must be considered. Adsorption of the solute at higher pH values was found to be dependent on the concentration of anionic form of the solute. The isotherm data were fitted to the Langmuir isotherm equation for both single and double solute solutions.

Synthesis and characterization of mono- and bis-ligand zinc(II) and cadmium(II) complexes of the di-2-pyridylketone Schiff base of S-benzyl dithiocarbazate (Hdpksbz) and the X-ray crystal structures of the [Zn(dpksbz)2] and [Cd(dpksbz)NCS]2 complexes

New mono- and bis-chelated zinc(II) and cadmium(II) complexes of formula, [M(dpksbz)NCS] (dpksbz = anionic form of the di-2-pyridylketone Schiff base of S-benzyldithiocarbazate) and [M(dpksbz)(2)] (M = Zn-II, Cd-II) have been prepared and characterized. The structure of the bis-ligand complex, [Zn(dpksbZ)(2)] has been determined by X-ray diffraction. The complex has a distorted octahedral geometry in which the ligands are coordinated to the zinc(II) ion as uninegatively charged tridentate chelates via the thiolate sulfur atoms, the azomethine nitrogen atoms and the pyridine nitrogen atoms. The distortion from a regular octahedral geometry is attributed to the restricted bite angles of the Schiff base ligands. X-ray structural analysis shows that the [Cd(dpksbz)NCS](2) complex is a centrosymmetric dimer in which each of the cadmium(II) ions adopts a five-coordinate, approximately square-pyramidal configuration with the Schiff base acting as a tetradentate chelating agent coordinating a cadmium(II) ion via one of the pyridine nitrogen atoms, the azomethine nitrogen atom and the thiolate sulfur atom; the second pyridine nitrogen atom is coordinated to the other cadmium(II) ion of the dimer. The fifth coordination position around each cadmium(II) is occupied by an N-bonded thiocyanate ligand. (C) 2003 Elsevier Science Ltd. All rights reserved.

The preparation of zinc(II) and cadmium(II) complexes of the pentadentate N3S2 ligand formed from 2,6-diacetylpyridine and S-benzyldithiocarbazate (H2SNNNS) and the X-ray crystal structure of the novel dimeric [Zn2(SNNNS)2] complex

The pentadentate chelating agent, 2,6-diacetylpyridinebis(S-benzyldithiocarbazate) (H2SNNNS) reacts with zinc(II) and cadmium(II) ions forming stable complexes of empirical formula, [M(SNNNS)] (M=Zn2+, Cd2+; SNNNS2 =doubly deprotonated anionic form of the Schiff base). These complexes have been characterized by a variety of physico-chemical techniques. IR and H-1 NMR spectral evidence indicate that the Schiff base coordinates to the zinc(II) and cadmium(II) ions via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the mercaptide sulfur atoms. The crystal and molecular structure of the zinc(II) complex has been determined by X-ray diffraction. The complex is a dimer in which the pyridine nitrogen atom,the azomethine nitrogen atom and the thiolate sulfur atom from one ligand coordinate to one of the zinc(II) ions whereas the azomethine and thiolate sulfur atoms from another ligand complete pentacoordination around the zinc(II) ion, the ligands being coordinated in their deprotonated forms. The coordination geometry about each zinc(II) can be considered as intermediate between a square-pyramid and trigonal-bipyramid. The cadmium(II) complex is also assigned with a dimeric structure. (C) 2003 Elsevier Ltd. All rights reserved.

Use of anion clay hydrotalcite to remove coloured organics from aqueous solutions

Anion clay hydrotalcite sorbents were prepared to investigate their adsorption capabilities in the removal of coloured organic substances from various aqueous systems. Anion clay hydrotalcite was found to be particularly effective at removing negatively charged species. Its excellent uptake levels of anionic species can be accounted for by its high surface area and anion exchange ability. That is, coloured substances can be adsorbed on the surface or enter the interlayer region of the clay by anion exchange. In the adsorption of Acid Blue 29 on the anion clay hydrotalcite, an equilibrium time of 1 h with dye removal exceeding 99% was obtained. The hydrotalcite was found to have an adsorption capacity marginally below that of commercial activated carbon. It should be noted that the spent sorbents can be regenerated easily by heating at 723 K to remove all adsorbed organics. The reused sorbents displayed greater adsorption capabilities than the newly prepared hydrotalcite. Hence, the anion clay hydrotalcite is easily recoverable and reusable such that it is a promising sorbent for environmental and purification purposes. (C) 2002 Elsevier Science B.V. All rights reserved.

Abolition of valproate-derived choleresis in the Mrp2 transporter-deficient rat

Valproic acid (VPA) is a major therapeutic agent in the treatment of epilepsy and other neurological disorders. It is metabolized in humans and rats primarily along two pathways: direct glucuronidation to yield the acyl glucuronide (VPA-G) and beta-oxidation. We have shown much earlier in the Sprague-Dawley rat that i.v. administration of sodium valproate (NaVPA) caused a marked choleresis ( mean of 3.3 times basal bile flow after doses of 150 mg/kg), ascribed to the passive osmotic flow of bile water following excretion of VPA-G across the canalicular membrane. Active biliary pumping of anionic drug conjugates across the canalicular membrane is now believed to be attributable to transporter proteins, in particular Mrp2, which is deficient in the TR- ( a mutant Wistar) rat. In the present study, normal Wistar and Mrp2-deficient TR- rats were dosed i.v. with NaVPA at 150 mg/kg. In the Wistar rats, there was a peak choleretic effect of about 3.2 times basal bile flow, occurring at about 30 to 45 min postdose ( as seen previously with Sprague-Dawley rats). In TR- rats given the same i.v. dose, there was no evidence of postdose choleresis. The choleresis was correlated with the excretion of VPA-G into bile. In Wistar rats, 62.8 +/- 7.7% of the NaVPA dose was excreted in bile as VPA-G, whereas in TR- rats, only 2.0 +/- 0.6% of the same dose was excreted as VPA-G in bile ( with partial compensatory excretion of VPA-G in urine). This study underlines the functional ( bile flow) consequences of biliary transport of xenobiotic conjugated metabolites.

The preparation and characterization of tin(IV) complexes of 2-quinolinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazates and the X-ray crystal and molecular structures of the 2-quinolinecarboxaldehyde Schiff base of S-benzyldithi

New tin(IV) complexes of empirical formula, Sn(NNS)I-3 (NNS = anionic forms of the 2-quinolinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate) have been prepared and characterized by a variety of physico-chemical techniques. In the solid state, the Schiff bases exist as the thione tautomer but in solution and in the presence of tin(IV) iodide they convert to the thiol tautomer and coordinate to the tin atom in their deprotonated thiolate forms. The structures of the free ligand, Hqaldsbz and its triiodotin(IV) complex, [Sn(qaldsbz)I-3] have been determined by X-ray diffraction. The complex, [Sn(qaldsbz)I-3] has a distorted octahedral structure with the Schiff base coordinated to the tin atom as a uninegatively charged tridentate chelating agent via the quinoline nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The three iodo ligands are coordinated meridionally to the tin atom. The distortion from an ideal octahedral geometry of [Sn(qaldsbz)I-3] is attributed to the restricted bite size of the tridentate Schiff base ligand. (C) 2004 Elsevier Ltd. All rights reserved.

The preparation and characterization of seven-coordinate tin(IV) complexes of the 2,6-diacetylpyridine Schiff bases of S-alkyl/aryl-dithiocarbazates and the X-ray crystal structure of the [Sn(dapsme)I-2] complex (dapsme=doubly deprotonated form of the 2,6

New tin(IV) complexes of empirical formula, Sn(SNNNS)I-2 (SNNNS = anionic form of the 2,6-diacetylpyridine Schiff bases of S-methyl- or S-benzyldithiocarbazate) have been prepared and characterized by a variety of physico-chemical techniques. The structure of Sn(dapsme)I-2 has been determined by single crystal X-ray crystallographic structural analysis. The complex has a seven-coordinate distorted pentagonal-bipyramidal geometry with the Schiff base coordinated to the tin(IV) ion as a dinegatively charged pentadentate chelating agent via the pyridine nitrogen atom, the two azomethine nitrogen atoms and the two thiolate sulfur atoms. The ligand occupies the equatorial plane and the iodo ligands are coordinated to the tin(IV) ion at axial positions. The distortion from an ideal pentagonal bipyramidal geometry is attributed to the restricted bite size of the pentadentate ligands. (C) 2004 Elsevier Ltd. All rights reserved.

The cyclic antimicrobial peptide RTD-1 induces stabilized lipid-peptide domains more efficiently than its open-chain analogue

The effects of a mammalian cyclic antimicrobial peptide, rhesus theta defensin 1 (RTD-1) and its open chain analogue (oRTD-1), on the phase behaviour and structure of model membrane systems (dipalmitoyl phosphatidylcholine, DPPC and dipalmitoyl phosphatidylglycerol, DPPG) were studied. The increased selectivity of RTD-1 for anionic DPPG over zwitterionic DPPC was shown by differential scanning calorimetry. RTD-1, at a molar peptide-lipid ratio of 1:100, induced considerable changes in the phase behaviour of DPPG, but not of DPPC. The main transition temperature, T-m, Was unchanged, but additional phase transitions appeared above T-m. oRTD-1 induced similar effects. However, the effects were not observable below a peptide:lipid molar ratio of 1:50, which correlates with the weaker biological activity of oRTD-1. Small-and wide-angle X-ray scattering revealed for DPPG the appearance of additional structural features induced by RTP-1 above T-m, which were interpreted as correlated lamellar structures, with increased order of the fatty acyl side chains of the lipid. It is proposed that after initial electrostatic interaction of the cationic rim of the peptide with the anionic DPPG headgroups, leading to stabilized lipid-peptide clusters, the hydrophobic face of the peptide assists in its interaction with the fatty acyl side chains eventually leading to membrane disruption. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Synthesis and stabilization of nanocrystalline zirconia with MSU mesostructure

In the presence of nonionic block-copolymer surfactant, nanocrystalline zirconia particles with MSU mesostrucmre were synthesized by a novel solid-state reaction route. The zirconia particles possess a nanocrystalline pore wall, which renders higher thermal stability compared to an amorphous framework. To further enhance its stability, laponite, a synthetic clay, was introduced. Laponite acts as an inhibitor to crystal a growth and also as a hard template for the mesostructure. High surface area and ordered pore structure were observed in the stabilized zirconia. The results show that the formation of the MSU structure is attributed to reverse hexagonal micelles, which are the products of the cooperative self-assembly of organic and inorganic species in the solid-state synthesis system with crystalline water and hygroscopic water present.

Synthesis of wormlike nanoporous nickel oxide with nanocrystalline framework for electrochemical energy storage

In this work, nanoporous nickel oxide was synthesized using anionic surfactant assembly method. Structure characterizations show that this nickel oxide possesses partly-ordered mesoporous structure with nanocrystalline pore wall. The formation mechanism of wormlike nanoporous structure is ascribed to the quasi-reverse micelle system formed by ternary phases of SDS (sodium dodecyl sulfate)/urea/water. Cyclic voltammetry shows that these nickel oxide samples possess both good capacitive behavior due to its unique nanoporous structure and very high specific capacitance due to its high surface area with electrochemical activity.