Ultrasonic studies in chemically active liquid media (1) aqueous solution of N2O4

Using a pulse method the ultrasonic absorption has been studied in the frequency range of 2 to 10 Mc/s in dilute aqueous solutions of nitrogen tetroxide gas at room temperature. The absorption peaks (αλ vs frequency) observed in this study are attributed to the ionic dissociation reaction of the nitrous acid into its constituent ions. The rate constants of the forward and backward reactions are calculated using the theory of Tabuchi. The variation of the logarithm of the rate constant of the bimolecular ionic reaction, namely, log10 kb, with the square root of ionic strength qualitatively follows Brönsted's theory for ionic reactions in solutions.

Ultrasonic propagation through aqueous solutions of acetates

Using the pulse method in the range of 2 to 26Mc's the ultrasonic absorption, velocity and the adiabatic compressibility have been studied in eleven aqueous acetate solutions up to a concentration of 1 mole/litre. The substances studied are the acetates of lithium, sodium, potassium, ammonium, magnesium, calcium, strontium, barium, zinc, cadmium and lead. Absorption in mercuric acetate has been studied only at 2 and 6 Mc/s. Two regions of relaxation are noticed, one below 10 Mc/s and the other between 10 and 26 Mc/s. The first relaxation is ascribed to the dissociation reaction of the salt and the second one to the monomerdimer reaction of the acetic acid formed by the hydrolysis of the salt in water.

Anti-amyloidogenic property of leaf aqueous extract of Caesalpinia crista

Amyloid beta (A beta) is the major etiological factor implicated in Alzheimer's disease (AD). A beta(42) self-assembles to form oligomers and fibrils via multiple aggregation process. The recent studies aimed to decrease A beta levels or prevention of A beta aggregation which are the major targets for therapeutic intervention. Natural products as alternatives for AD drug discovery are a current trend. We evidenced that Caesalpinia crista leaf aqueous extract has anti-amyloidogenic potential. The studies on pharmacological properties of C. crista are very limited. Our study focused on ability of C. crista leaf aqueous extract on the prevention of (i) the formation of oligomers and aggregates from monomers (Phase I: A beta(42) + extract co-incubation); (ii) the formation of fibrils from oligomers (Phase II: extract added after oligomers formation); and (iii) dis-aggregation of pre-formedfibrils (Phase III: aqueous extract added to matured fibrils and incubated for 9 days). The aggregation kinetics was monitored using thioflavin-T assay and transmission electron microscopy (TEM). The results showed that C. crista aqueous extract could able to inhibit the A beta(42) aggregation from monomers and oligomers and also able todis-aggregate the pre-formed fibrils. The study provides an insight on finding new natural products for AD therapeutics. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Novel phase-transition behavior in an aqueous electrolyte solution

We have investigated the near-critical behavior of the susceptibility of a ternary liquid mixture of 3-methylpyridine. water, and sodium bromide as a function of the salt concentration. The susceptibility was determined from light-scattering measurements performed at a scattering angle of 90 degrees in the one-phase region near the locus of lower consolute points. A sharp crossover from asymptotic Ising behavior to mean-field behavior has been observed at concentrations ranging from 8 to 16.5 mass% NaBr. The range of asymptotic Ising behavior shrinks with increasing salt concentration and vanishes at a NaBr concentration of about 17 mass%. where complete mean-field-like behavior of the susceptibility is observed. A simultaneous pronounced increase in the background scattering at concentrations above 15 mass%, as well as a dip in the critical locus at 17 mass % NaBr, suggests that this phenomenon can be interpreted as mean-field tricritical behavior associated with the formation of a microheterogeneous phase due to clustering of the molecules and ions. An analogy with tri critical behavior observed in polymer solutions as well as the possibility of a charge-density-wave phase is also discussed. In addition, we, have observed a third soap-like phase an the liquid-liquid interface in several binary and ternary liquid mixtures.

Biosorption of iron(III) from aqueous solutions using the husk of Cicer arientinum

Iron is a major pollutant released as a by-product during several industrial operations especially during acid mining of metal ores. In this paper, the use of Bengal gram husk (husk of channa dal, Cicer arientinum) in the biosorption of Fe(III) from aqueous solutions is discussed. Parameters like agitation time, adsorbent dosage and pH were studied at different Fe(Ill) concentrations. The adsorption data fit well with Langmuir and Freundlich isotherm models. The adsorption capacity (q(max)) calculated from the Langmuir isotherm was 72.16 mg of Fe(III)/g of the biosorbent at an initial pH of 2.5. Desorption Studies were performed at different concentrations of hydrochloric acid showing that quantitative recovery of the metal ion is possible. The infrared spectra of the biomass before and after treatment with Fe(III), revealed that hydroxyl, carboxyl and amide bonds are involved in the uptake of Fe(III) ions.

A novel fiber-coated strong base-type anion exchanger with superfast kinetics. Removal and recovery of silver thiosulfate from aqueous solutions

A commercial acrylic fiber with 92% (w/w) acrylonitrile content was partially hydrolyzed converting a fraction of the nitrile (-CN) groups to carboxylic acid (-COOH) groups, to coat the fiber with polyethylenimine (PEI) resin, which was then crosslinked with glutaraldehyde and further quaternized with ethyl chloroacetate to produce a novel strong-base anionic exchanger in the form of fiber. Designated as PAN(QPEI.XG)(Cl-), the fibrous sorbent was compared with a commercial bead-form resin Amberlite IRA-458(Cl-) in respect of sorption capacity, selectivity, and kinetics for removal of silver thiosulfate complexes from aqueous solutions. Though the saturation level of [Ag(S2O3)(2)](3-) on PAN(QPEI.XG)(Cl-) is considerably less than that on IRA-458(Cl-), the gel-coated fibrous sorbent exhibits, as compared to the bead-form sorbent, a significantly higher sorption selectivity for the silver thiosulfate complex in the presence of excess of other anions Such as S2O32-, SO42-, and Cl-, and a remarkably faster rate of both sorption and stripping. The initial uptake of the sorbate by the fibrous sorbent is nearly instantaneous, reaching up to similar to 80% of the saturation capacity within 10 s, as compared to only similar to 12% on the bead-form sorbent. The high initial rate of uptake fits a shell-core kinetic model for sorption on fiber of cylindrical geometry. With 4M HCl, the stripping of the sorbed silver complex from the fibrous sorbent is clean and nearly instantaneous, while, in contrast, a much slower rate of stripping on the bead-form sorbent leads to its fouling due to a slow decomposition of the silver thiosulfate complex in the acidic medium.

Critical behavior of the aqueous electrolytic system 3-methylpyridine+D2O+NaBr

The system 3-methylpyridine(3MP)+water(H2O)+NaBr has been the subject of an intense scientific debate since the work of Jacob [Phys. Rev. E. 58, 2188 (1988)] and Anisimov [Phys. Rev. Lett. 85, 2336 (2000)]. The crossover critical behavior of this system seemed to show remarkable sensitivity to the weight fraction (X) of the ionic impurity NaBr. In the range X <= 0.10 the system displayed Ising behavior and a pronounced crossover to mean-field behavior in the range 0.10 <= X <= 0.16. A complete mean-field behavior was observed at X=0.17, a result that was later attributed to the existence of long-living nonequilibrium states in this system [Kostko , Phys. Rev. E. 70, 026118 (2004)]. In this paper, we report the near-critical behavior of osmotic susceptibility in the isotopically related ternary system, 3MP+heavy water(D2O)+NaBr. Detailed light-scattering experiments performed at exactly the same NaBr concentrations as investigated by Jacob reveal that the system 3MP+D2O+NaBr shows a simple Ising-type critical behavior with gamma similar or equal to 1.24 and nu similar or equal to 0.63 over the entire NaBr concentration range 0 <= X <= 0.1900. The crossover behavior is predominantly nonmonotonic and is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (gamma(eff)) reveals that the crossover behavior is nonmonotonic for 0 <= X <= 0.1793 and tends to become monotonic for X > 0.1793. The correlation length amplitude xi(o), has a value of similar or equal to 2 A for 0.0250 <= X <= 0.1900, whereas for X=0, xi(o)similar or equal to 3.179 A. Since isotopic H -> D substitution is not expected to change the critical behavior of the system, our results support the recent results obtained by Kostko [Phys. Rev. E. 70, 026118 (2004)] that 3MP+H2O+NaBr exhibits universal Ising-type critical behavior typical for other aqueous solutions.

Aqueous channels within apolar peptide aggregates. Solvated helix of Boc-Aib-Ala-Leu-Aib-Ala-Leu-Aib- -Ala-Leu-Aib-OMe. H2O.CH3OH

Although the peptide Boc-Aibl-Ala2-Leu3- Aib4-Alas Leu'-Aib7-Ala8-Leu9-Aib'0-OMe [with a t-butoxycarbonyl(Boc) blocking group at the amino terminus, a methyl ester (OMe) at the carboxyl terminus, and four a-aminoisobutyric (Aib) residues] has a 3-fold repeat of residues, the helix formed by the peptide backbone is irregular. The carboxyl-terminal half assumes an at-helical form with torsion angles ) and r of approximately -60° and -45°, respectively, whereas the amino-terminal half is distorted by an insertion of a water molecule between the amide nitrogen of Ala5 [N(5)] and the carbonyl oxygen of Ala2 [0(2)]. The water molecule W(1) acts as a bridge by forming hydrogen bonds N(5).W(1) (2.93 A) and W(1)---0(2) (2.86 A). The distortion of the helix exposes the carbonyl oxygens of Aib' and Aib4 to the outside environment, with the consequence that the helix assumes an amphiphilic character despite having all apolar residues. Neighboring helices in the crystal run in antiparallel directions. On one side of a helix there are only hydrophobic contacts with efficient interdigitation of leucine side chains with those from the neighboring helix. On the other side of the helix there are hydrogen bonds between protruding carbonyl oxygens and four water molecules that separate two neighboring helices. Along the helix axis the helices bind head-to-tail with a direct hydrogen bond N(2)-0(9) (3.00 A). Crystals grown from methanol/water solution are in space group P2, with a = 15.778 ± 0.004 A, b = 11.228 ± 0.002 A, c = 18.415 ± 0.003 A, = 102.10 ± 0.02ur and two formula units per cell for C49HON1003 2H2OCH3OH. The overall agreement factorR is 7.5% for 3394 reflections observed with intensities >3a(F), and the resolution is 0.90 A.

Biomimetic synthesis of silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical prediction of particle size

In the present study silver nanoparticles were rapidly synthesized at room temperature by treating silver ions with the Citrus limon (lemon) extract The effect of various process parameters like the reductant con centration mixing ratio of the reactants and the concentration of silver nitrate were studied in detail In the standardized process 10(-2) M silver nitrate solution was interacted for 411 with lemon Juice (2% citric acid concentration and 0 5% ascorbic acid concentration) in the ratio of 1 4(vol vol) The formation of silver nanoparticles was confirmed by Surface Plasmon Resonance as determined by UV-Visible spectra in the range of 400-500 nm X ray diffraction analysis revealed the distinctive facets (1 1 1 200 220 2 2 2 and 3 1 1 planes) of silver nanoparticles We found that citric acid was the principal reducing agent for the nanosynthesis process FT IR spectral studies demonstrated citric acid as the probable stabilizing agent Silver nanoparticles below 50 nm with spherical and spheroidal shape were observed from transmission electron microscopy The correlation between absorption maxima and particle sizes were derived for different UV-Visible absorption maxima (corresponding to different citric acid concentrations) employing MiePlot v 3 4 The theoretical particle size corresponding to 2% citric acid concentration was corn pared to those obtained by various experimental techniques like X ray diffraction analysis atomic force microscopy and transmission electron microscopy (C) 2010 Elsevier B V All rights reserved

Bubble formation at closely spaced orifices in aqueous solutions

A filter cloth with 182 holes per 10−4 m2 has been used to generate air bubbles both in pure water and in aqueous solutions of electrolytes and non-electrolytes at various air flow rates. Potassium bromide and ammonium perchlorate were the electrolytes used, while the non-electrolytes were isopropanol, urea and glycerol. Bubble diameters and their size distribution were measured from photographs. The role of solutes in affecting bubble sizes and their distribution compared to that of pure water is discussed in the light of a hypothesis. This hypothesis assumes that if the final bubble diameter is less than the inter-orifice distance, then bubbles do not coalesce; on the other hand, if it is greater, then coalescence occurs when tf greater-or-equal, slantedti+ts, but does not occur when t

An aqueous-solution based low-temperature pathway to synthesize giant dielectric CaCu3Ti4O12-Highly porous ceramic matrix and submicron sized powder

A simple, cost-effective and environment-friendly pathway for preparing highly porous matrix of giant dielectric material CaCu3Ti4O12 (CCTO) through combustion of a completely aqueous precursor solution is presented. The pathway yields phase-pure and impurity-less CCTO ceramic at an ultra-low temperature (700 degrees C) and is better than traditional solid-state reaction schemes which fail to produce pure phase at as high temperature as 1000 degrees C (Li, Schwartz, Phys. Rev. B 75, 012104). The porous ceramic matrix on grinding produced CCTO powder having particle size in submicron order with an average size 300 nm. On sintering at 1050 degrees C for 5 h the powder shows high dielectric constants (>10(4) at all frequencies from 100 Hz to 100 kHz) and low loss (with 0.05 as the lowest value) which is suitable for device applications. The reaction pathway is expected to be extended to prepare other multifunctional complex perovskite materials. (C) 2010 Elsevier B.V. All rights reserved.