Volume 229, Issue 3

CYPMPO (5-(2,2-dimethyl-1,3-propoxyl cyclophosphoryl)-5-methyl-1-pyrroline N -oxide) is a phosphorus containing spin trap that has been useful in aqueous media. Using a kinetic ESR spin trapping technique, we evaluated free radical trapping rate constants of two newly synthesized CYPMPO-type spin traps, including 2,2-dibutyl-substituted CYPMPO (DBCYP) and 5-phenyl-substituted CYPMPO (PhCYP). We investigated the spin trapping of five free radical species, i. e. , superoxide, hydroxyl radical, alkoxyl radical, alkyl peroxyl radical and methyl radical. Other than superoxide, spin trapping rate constants of DBCYP and PhCYP are comparable to CYPMPO, ranging from 43.9% to 101% of CYPMPO's corresponding rate constants. However, PhCYP's spin-trapping rate constant against superoxide was 44% higher than that of CYPMPO. The results indicate that DBCYP and PhCYP may be the spin traps as useful as CYPMPO either in aqueous or non-aqueous medium.

The kinetic study of reduction of single chain surfactant octahedral cobalt(III) complexes, cis -[Co(en) 2 (4AMP)(DA)](ClO 4 ) 3 and cis -[Co(trien)(4CNP)(DA)](ClO 4 ) 3 (where en = ethylenediamine; trien = triethylenetetramine; 4AMP = 4-aminopyridine; 4CNP = 4-cyanopyridine; DA = dodecylamine) with [Fe(CN) 6 ] 4 – has been carried out by spectrophotometric method under pseudo first order conditions using an excess of a reductant in different media namely, micelles, β -cyclodextrim ( β -CD), liposome vesicles (DPPC) and ionic liquids ((BMIM)Br) at different temperatures in order to have deep insight into the molecular behavior during the electron transfer reaction. The analysis of kinetic results strongly suggests that the reduction reaction between the surfactant complex and [Fe(CN) 6 ] 4 – occurs via a second order outer sphere electron transfer mechanism. The remarkable increase in the rate of electron transfer from the oxidant to reductant is observed in ionic liquid medium as compared to the rest of all other media studied in the present investigation. This can be ascribed due to the fact that the formation of aggregated and constrained geometry of the surfactant cobalt(III) complexes (oxidants) in ionic liquid medium renders the rate of one electron transfer from the oxidants to the reductant, [Fe(CN) 6 ] 4 – to be higher. Furthermore, the rate constant value increases with increase in the concentration of micelles, however in the presence of β -cyclodextrin medium the rate of electron transfer substantially decreases due to the inclusion of long aliphatic chain of the surfactant cobalt(III) complexes into β -cyclodextrin. In liposome media, second order rate constant for this electron transfer reaction from both the oxidants was found to decrease with increase in the concentration of the liposome below the phase transfer temperature of DPPC. However, above the phase transition temperature the reaction was found to increase with increase in the concentration of the DPPC. The main driving force for this phenomenon is considered to be the intervesicular hydrophobic interaction between the surfactant complexes and vesicular surface. The activation parameters ( Δ S ‡ and Δ H ‡ ) of this outer sphere electron transfer reaction have been calculated by varying temperatures and the analysis of the data corroborates the kinetics of the reaction.

The electrochemical behavior of Cu-10Ni-10Zn alloy and Cu was investigated in acidic, neutral and basic solutions. The effect of chloride ions in neutral solutions was also studied. Conventional electrochemical techniques and electrochemical impedance spectroscopy were used. The corrosion rate of these materials in acidic solutions is relatively high compared to that in neutral or basic solutions. The open-circuit potential of the alloy is nearly the same as that of pure copper in the different media, indicating that the processes which occur on the alloy surface are mainly governed by copper dissolution. In chloride solutions the rate of Cu corrosion is remarkably high. In the alloy, the copper dissolution was suppressed by the presence of nickel and zinc, due to the formation of complex oxide layers. The impedance data were fitted to equivalent circuit models that explain the different electrochemical processes occurring at the electrode/electrolyte interface. SEM and EDAX have shown that the alloy surface is enriched with Ni. In neutral solutions the chloride ions are penetrating the metallic surface.

In this research, it was found that following the photo-dissolution of the intermediate product N-bromo-1,4-benzoquinone-4-imine in the bromate – 4-aminophenol reaction, removal of illumination may allow the system to exhibit spontaneous chemical oscillations. This new observation complements the earlier report that the bromate – 4-aminophenol reaction could only oscillate under continuous illumination. Our exploration illustrates that the initial concentrations of bromate, 4-aminophenol and sulfuric acid have great influence on whether or not the system requires constant illumination for exhibiting oscillatory behavior. There is indeed an optimal illumination time interval at which the subsequently un-illuminated system would exhibit a large number of high frequency oscillations with or without an induction time period. Similar influences were also observed in the presence of cerium, in which the system exhibited sequential oscillations. Being able to respond to light in both a negative and constructive way makes this oscillatory system an attractive model for investigating perturbed nonlinear reaction dynamics.

This paper reports the chemical and mechanical stability of Molybdenum (Mo) thin films deposited by direct current magnetron sputtering technique onto soda lime glass substrates. Mo thin films were deposited at various Ar (working) gas pressures to get optimized structural, morphological, adhesive and electrical properties. Mo thin films were further characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction, Hall measurements and the cross hatch tape test. To study their chemical stability the prepared Mo thin films were further dipped in acetic acid and ammonia solution for 6 h. Mechanical stability of Mo thin films was tested by high speed ultrasonication for an hour. Both the chemical and mechanical stability studies showed that Mo thin films were highly stable since morphology, adhesion and electrical properties did not alter significantly. FE-SEM results showed that the grain size of the chemo-mechano stability tested Mo thin films remained significantly similar with an unimportant effect on the film thickness. Electrical properties showed that electrical resistivity and hall mobility for as-deposited Mo thin films were 2.7 · 10 – 5  Ω cm and 5.1 cm 2 /Vs, respectively and remained nearly stable regardless of chemical and mechanical treatment. All of the films passed the cross hatch tape test and showed an excellent adhesion with glass substrates. The wettability investigations showed that all the Mo thin films were hydrophilic in nature and having contact angles in the range of 35 ○ to 40 ○ .

Surfactant solutions in practical applications usually are mixtures of different types, especially ionic and nonionic ones. The mixing behavior of nonionic Cremophor EL-cationic gemini systems was therefore investigated by surface tension measurements. The Gemini surfactants used were of the type alkanediyl – α , ω – bis(dimethylalkylammonium bromide), (alkyl: 14 or 16 and alkane: butane, pentane or hexane), designated in the text as 14-s-14/16-s-16 (where s is the spacer length). The experimental results indicated that the mixed systems of EL with 16-6-16, 14-5-14 and 14-6-14 have lower cmc values than of pure surfactants. Comparison between experimental and calculated values of cmc (cmc and cmc id ) showed that the interaction between the component amphiphiles inside aggregates of EL with RH, 16-4-16, 16-5-16 and 14-4-14 was not ideal but shows antagonism. Such fact was reflected by the values of activity coefficients also. This may be due to the steric repulsions which decrease with the increase in spacer length. The aggregates were mainly comprised of geminis at low stoichiometric mole fraction of EL ( α 1 ) while by EL at high α 1 . The molecular interaction parameter, β m , calculated using Rubingh's approach, was negative for mixed systems of EL with 16-6-16, 14-5-14 and 14-6-14. Surface parameters, evaluated by Rosen's model, also suggested mixed monolayer formation with negative β σ for all 16-s-16, 14-4-14 and 14-6-14 systems.

Chalcones, a group of polyphenolic compounds, has been studied for a long time due to their biological properties and their ability as analytical reagents. In this work the stability and thermodynamic parameters concerning the fotmation in ethanolic medium of two chalcone–aluminium complexes (2′,3-dihydroxychalcone-Al(III) and 2′,4′,3-trihydroxychalcone-Al(III)) were studied and a kinetic study of the formation reaction was aslo performed. Both systems showed 1:1 L : M stoichiometry and stability constants at four temperatures were determined. Thermodynamic parameters indicate that both formation reactions are endothermic and driving force is entropic. Kinetic study revealed that 2′,4′,3-trihydroxychalcone-Al(III) formation is faster than 2′,3-dihydroxyclacone-Al(III), a factor which can be interesting when proposing new analytical reagents.

Oligopeptides containing internal π -system units are shown to self-assemble in water near nanoparticles into fibrillar nanostructures. We have investigated the biopolymer hybrid monomer of the overall structure `peptide- π -system-peptide' with the sequence VDFAG – perylene diimide (PDI) – GAFDV in the presence of Ag-nanoparticles. Unique to these self-assembling monomers is the fact that the π -conjugated unit has been directly embedded within the peptide backbone by way of a special synthetic coupling. The symmetric peptide-based molecular design enforces intimate π - π communication within the aggregates after self-assembly, making these nano structures attractive for optical or electronic applications. The assembly process can in principle be followed by the change in optical spectra of the monomer and ordered monomer π -systems. Here we show that the Ag-nanoparticles act as seeds for the fibrillation, which makes the fibrils grow in a defined fashion and the supramolecular assembly can be followed via the optical spectrum of the plasmon resonances of the silver nanoparticles, which depend sensitively upon the local environment, making the optical plasmon resonance spectra a nice probe for the assembly process, as well as the interaction of monomers and fibrillar structures in contact with the nanoparticles. While it has been known that these systems may aggregate under certain conditions towards nano fibrils the new aspect here is the controlled and accelerated fibrillation near silver nanoparticles, which results in fibrils of 15–150 nm in diameter and up to 10 μm long, partially incorporating the seed nanoparticles. This approach provides a novel avenue to synthesize bioorganic-hybrid systems (in high yields) in contact with Ag metal nanoparticles and possibly enables us to control the location of growth for the materials in future applications.

The interaction of diglycine with sulphamethoxazole drug as a function of temperature and concentration have been investigated by volumetric method. The density of ternary mixture of diglycine (0.002–0.01 mol  ·  kg – 1 ) in aqueous sulphamethoxazole drug (0.001–0.01 mol  ·  kg – 1 ) solution have been measured using Anton Paar DSA 5000 instrument at T  = (288.15  to  308.15) K. The apparent molar volumes V φ , partial molar volume at infinite dilution V φ 0 , transfer partial molar volume Δ tr V φ ○ , partial molar expansibility E 2 o , thermal expansion coefficient α 2 , and Hepler's constant (∂ C P ∞ /∂ P ) T are calculated from density data. The above parameters are used to interpret the solute-solute and solute-solvent interactions of diglycine in aqueous solution of sulphamethoxazole drug. Hydration number and interaction coefficients have also been calculated from these data. Dehydration of diglycine is observed, rising with the temperature and drug molality. These results are explained on the basis of drug-water-amino acid interactions. The data suggest that interaction between ions and charged/hydrophilic groups are predominant.