Micellization and related behavior of sodium dodecylsulfate in mixed binary solvent media of tetrahydrofuran (Tf) and formamide (Fa) with water: a detailed physicochemical investigation.

The detailed aggregation behavior of sodiumdodecyl sulfate (SDS) in tetrahydrofuran (Tf)-water (W) and formamide (Fa)-water (W) media at varied volume percent compositions has been investigated. Surface tension (ST), conductance (Cond), viscosity (Visc), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) were used in this study. The presence of nonaqueous solvents affected the critical micelle concentration (CMC) of SDS, the counter-ion binding of the micelle, the energetics of the air/water interfacial adsorption and micellization of the amphiphiles in the bulk, the ion-association (ion-pair, triple-ion, quadruple, etc. between Na(+) and DS(-) ions) as well as the weakly soluble (aggregation less) amphiphile solution. Tf has been observed to produce a "dead zone" or "non-micelle formation zone" in the mixed Tf-W domain of 10-40 vol%. Fa influenced the SDS aggregation up to 70 vol%, at higher proportions (below the Krafft temperature (K(T))), instead of the micelle, "randomly arranged globular assembly" (RAGA) was formed. The correlation of the standard free energy of micellization (ΔG(m)(0)) with different solvent parameters (1) dielectric constant (ε), (2) viscosity (η0), (3) Reichardt parameter (E(T)(30)), (4) Gordon parameter (G), and (5) Hansen-Hildebrand hydrogen bonding parameter (δ(h)) has been attempted. It has been found that δ(h) produced a master correlation between ΔG(m)(0) and δ(h) for different binary mixtures such as Tf-W, Fa-W, Ml-W and Dn-W.

Amphiphile behavior in mixed solvent media I: self-aggregation and ion association of sodium dodecylsulfate in 1,4-dioxane-water and methanol-water media.

Mixed aquo-organic solvents are used in chemical, industrial, and pharmaceutical processes along with amphiphilic materials. Their fundamental studies with reference to bulk and interfacial phenomena are thus considered to be important, but such detailed studies are limited. In this work, the interfacial adsorption of sodium dodecylsulfate (SDS, C12H25SO4(-)Na(+)) in dioxane-water (Dn-W) and methanol-water (Ml-W) media in extensive mixing ratios along with its bulk behavior have been investigated. The solvent-composition-dependent properties have been identified, and their quantifications have been attempted. The SDS micellization has been assessed in terms of different solvent parameters, and the possible formation of an ion pair and triple ion of the colloidal electrolyte, C12H25SO4(-)Na(+) in the Dn-W medium has been correlated and quantified. In the Ml-W medium at a high volume percent of Ml, the SDS amphiphile formed special associated species instead of ion association. The formation of self-assembly and the energetics of SDS in the mixed solvent media have been determined and assessed using conductometry, calorimetry, tensiometry, viscometry, NMR, and DLS methods. The detailed study undertaken herein with respect to the behavior of SDS in the mixed aquo-organic solvent media (Dn-W and Ml-W) is a new kind of endeavor.

Aqueous synthesis of ZnTe/dendrimer nanocomposites and their antimicrobial activity: implications in therapeutics.

The present strategy proposes a simple and single step aqueous route for synthesizing stable, fluorescent ZnTe/dendrimer nanocomposites with varying dendrimer terminal groups. In these hybrid materials, the fluorescence of the semiconductor combines with the biomimetic properties of the dendrimer making them suitable for various biomedical applications. The ZnTe nanocomposites thus obtained demonstrate bactericidal activity against enteropathogenic bacteria without having toxic effects on the human erythrocytes. The average size of the ZnTe nanoparticles within the dendrimer matrix was in the range of 2.9-6.0 nm, and they have a good degree of crystallinity with a hexagonal crystal phase. The antibacterial activities of the ZnTe/dendrimer nanocomposites (ZnTe DNCs) as well other semiconductor nanocomposites were evaluated against enteropathogenic bacteria including multi-drug resistant Vibrio cholerae serogroup O1 and enterotoxigenic Escherichia coli (ETEC). ZnTe DNCs had significant antibacterial activity against strains of V. cholerae and ETEC with minimum inhibitory concentrations ranging from 64 to 512 µg ml(-1) and minimum bactericidal concentrations ranging from 128 to 1000 µg ml(-1). Thus, the observed results suggest that these water-soluble active nanocomposites have potential for the treatment of enteric diseases like diarrhoea and cholera.

Probing of ascorbic acid by CdS/dendrimer nanocomposites: a spectroscopic investigation.

The gamma irradiation method has provided a route for synthesis of highly water-soluble, good-quality luminescent CdS/dendrimer nanocomposites with amino- or carboxyl-terminated PAMAM dendrimer. An attempt has been made to probe ascorbic acid with the as-synthesized CdS/dendrimer nanocomposites (DNC). Ascorbic acid (AA) is an important biological antioxidant and marker for different diseases in clinical chemistry as well as in quality control in the food industry. Micromolar concentrations of AA significantly quenched the photoluminescence (PL) of both amino (-NH(2)) and carboxylic (-COOH) functionalized semiconductor nanocomposites. The quenching followed a linear Stern-Volmer equation and time-resolved photoluminescence spectroscopy confirmed its static nature. A strong size dependence of the quenching pattern was observed. The binding constants, and the corresponding thermodynamic parameters DeltaG(theta), DeltaH(theta), DeltaS(theta) at different temperatures were calculated. CdS DNC showed selectivity towards ascorbic acid even in the presence of possible interfering molecules, such as uric acid, tartaric acid and citric acid. Nanocomposites-based assay techniques could override the complications involved in multitudes of assay procedures, providing a simple and fast new strategy for the quantification of Ascorbic acid in the range of 16.6 to 100 microM (R=0.998, n=9). The proposed method was applied to the detection of ascorbic acid in Vitamin C tablets with satisfactory results.

Supersaturation driven tailoring of photoluminescence efficiency and size distribution: a simplified aqueous approach for producing high-quality, biocompatible quantum dots.

Supersaturation was found to play a pivotal role during nanoparticle-synthesis and its subtle variation helped achieve two prime objectives: (a) high photoluminescence quantum efficiency (PLQE) and (b) narrow size distribution, thereby obviating the need for post-preparative treatments. Degree of supersaturation of initial synthetic mixture was varied by changing the concentration of reagents while keeping their molar ratio constant at 1:2.5:0.5 for [Cd(2+)]:[cysteine]:[chalcogenide]. An eight-fold increase in supersaturation caused a sharp focusing of size distribution by 64% for CdS quantum dots (QDs). The as-prepared CdS and CdTe QDs were found to have size distribution as low as 4% at higher supersaturation. For a four-fold increase in supersaturation, PLQE of as-prepared CdTe QDs (4.3 nm) rose by 5 times to a remarkably high value of 54%. The focusing of size distribution with increasing supersaturation was found to work well even in the absence of any stabilizer. A substantial overlap of nucleation and growth was found at low supersaturation (0.5S(CdTe)), whereas a good separation of the two events is achieved at a higher supersaturation (4S(CdTe)). This study provides a simplified aqueous route for producing highly monodisperse, photoluminescent and biocompatible nanoparticles.

Physicochemical studies on goat pulmonary surfactant.

The large aggregate (LA) fraction of goat pulmonary surfactant (GPS) was isolated and characterized. Goat lung surfactant extract (GLSE) was obtained by chloroform-methanol extraction of the saline suspended LA fraction. Total phospholipid (PL), cholesterol (CHOL), and protein were biochemically estimated. It was composed of approximately 83% (w/w) PL, approximately 0.6% (w/w) CHOL and approximately 16% (w/w) protein. CHOL content was found to be lower while the protein content was found to be higher than other mammalian pulmonary surfactants. Electrospray Ionization Mass Spectrometry (ESIMS) of GLSE confirmed dipalmitoylphosphatidylcholine (DPPC) as the major phospholipid species, with significant amounts of palmitoyl-oleoyl phosphatidylcholine (POPC), palmitoyl-myristoyl phosphatidylcholine (PMPC) and dioleoylphosphatidylcholine (DOPC). Functionality of the solvent spread GLSE film was carried out in a Langmuir surface balance by way of surface pressure (pi)-area (A) measurements. A high value of pi (approximately 65 mN m(-1)) could be attained with a lift-off area of approximately 1.2 nm(2) molecule(-1). A relatively large hysteresis was observed during compression-expansion cycles. Monolayer deposits at different pi, transferred onto freshly cleaved mica by Langmuir-Blodgett (LB) technique, were imaged by atomic force microscopy. DPPC-enriched domains (evident from height analyses) showed dimensions of 2.5 microm and underwent changes in shapes after 30 mN m(-1). Functionality and structure of the surfactant films were proposed to be controlled by the relative abundances of protein and cholesterol.