Sensitive flotation-spectrophotometric method for the determination of vanadium (IV) with 3,5-dinitrosalicylic acid and rhodamine B

Vanadium(IV) is determined by reaction with 3,5-dinitrosalicylic acid and rhodamine B in weakly acidic medium. The flotation of the ternary ion-association complex is carried out with cyclohexane followed by dissolution in acetone for subsequent spectrophotometric determination. The molar absorptivity is 5.91×10⁵ l mole^–1 cm^–1 at 555 nm. Beer's law is obeyed in the range 0.05–1.5 g vanadium(IV) in 25 ml. The method is selective for vanadium(IV) in the presence of sodium fluoride and has been applied to standard reference materials.     

Oriented binding of the His6-tagged carboxyl-tail of the L-type Ca2+ channel alpha1-subunit to a new NTA-functionalized self-assembled monolayer

Oriented stable binding of functional proteins on surfaces is of fundamental interest for receptor/ligand studies in atomic force microscopy (AFM) and surface plasmon resonance (SPR) experiments. Here we have chosen the His6-tagged carboxyl-tail (C-tail) of the alpha1c-subunit of the L-type Ca2+ channel and calmodulin (CaM) as its cognitive partner as a model system to develop a new functional surface. Covalently attached self-assembled monolayers on ultraflat gold containing NTA-thiols to which the His6-tagged C-tail was bound and thiols with triethylene-glycol groups as matrix-thiols represented the system of choice. The topography of this surface was characterized using AFM; its ability to bind C-tail proteins oriented and stable was confirmed by SPR measurements and by complementary force spectroscopy experiments with a CaM4-construct covalently attached to the tip. The developed anchoring strategy can now be used to study receptor/ligand interactions in general applying force spectroscopy and SPR on His6-tagged proteins oriented immobilized onto this new NTA-functionalized self-assembled monolayer.     

On demand release of ionic silver from gold-silver alloy nanoparticles: fundamental antibacterial mechanisms study

Synthesis and biomedical research of bimetallic gold-silver nanoparticles (Au–Ag NPs) have gained much attention due to their unique properties. Antibacterial mechanism of gold-silver nanoparticles is a current topic of interest in nanomedicine engineering. We used three routes in the synthesis of Au–Ag NPs alloy: i) Co-reduction of [HOOC-4-C₆H₄NN]AuCl₄/AgNO₃, ii) Seeding of AuNPs-COOH/AgNO₃ and iii) immobilization of AgNPs over the parent AuNPs-COOH. Two mild reducing agents, NaBH₄ and 9-BBN (9-borabicyclo(3.3.1)nonane), were used. Colloidal alloy nanoparticles structure was confirmed using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The particles reduced using NaBH₄ were larger (~20 nm) than those synthesized using 9-BBN (<10 nm). The synthesized nanoparticles showed high stability under notoriously leaching conditions of chloride-containing electrolytes. Moreover, we studied the Au–Ag NPs antibacterial activity against the growth of Gram-negative Escherichia coli ATCC strain 25922 and Gram-positive Staphylococcus aureus ATCC strain 29213. The antibacterial mechanisms were evaluated by studying the time-dependent generation of reactive oxygen species (ROS). A major destruction of the bacterial cell wall and leakage of cell components were observed by scanning electron microscopy (SEM), which is clearly visible towards E. coli more than S. aureus bacterial strain. The destruction of the bacterial cell wall was further confirmed by detecting the DNA leakage using gel electrophoresis. The synergistic effect of gold enhanced the antibacterial properties, however, with low cytotoxicity to human dermal fibroblast cells. This study deals with the important aspects of time-dependent mechanisms of the antibacterial action of Au–Ag NPs since the leaching out of Ag ion is slow compared to AgNPs. The Au–Ag NPs alloy efficiently tackles microbial activity that can be controlled to minimize cytotoxicity and thus opens their future applications as antibacterial agents.     

Atomic layer deposition of Al2O3, ZrO2, Ta2O5, and Nb2O5 based nanolayered dielectrics

Ta₂O₅, Ta-Nb-O, Zr-Al-Nb-O, and Zr-Al-O mixture films or solid solutions were grown on Si(1 0 0) substrates at 300 °C by atomic layer deposition. The equivalent oxide thickness of Ta₂O₅ based capacitors was between 1 and 3 nm. In Zr-Al-O films, the high permittivity of ZrO₂ was combined with high resistivity of Al₂O₃ layers. The permittivity, surface roughness and interface charge density increased with the Zr content and the equivalent oxide thickness was between 2.0 and 2.5 nm. In the Zr-Al-Nb-O films the equivalent oxide thickness remained at 1.8-2.0 nm.     

FT-IR, FT-Raman and FT-SERS spectra of 4-aminosalicylic acid sodium salt dihydrate.

FT-IR, FT-Raman and FT-SERS spectra of 4-aminosalicylic acid sodium salt dihydrate (4ASAS) have been recorded and analysed. The vibrational bands due to NH2, OH, carboxyl group, and the benzene ring are identified. The CX ipb(17a, 17b), CC ipb(6,18a) and CH ipb (3,14a, 14b) bands are more enhanced in SERS. Broadening of the inplane carboxyl bend indicates interaction with the silver surface. Further the vC=O, v(C-O)c and v(C-O)h are intense in the SERS spectrum. The rocking and wagging modes of NH2 also show up in SERS. The molecule (O, N donor ligand) is thought to adsorb through the carboxyl oxygen atom with the benzene ring in a 'perpendicular side on orientation' with respect to the silver surface.     

Spectroscopic investigations and computational study of sulfur trioxide–pyridine complex

The Fourier transform infrared (FT‐IR) and FT‐Raman spectra of sulfur trioxide‐pyridine complex were recorded and analyzed. The potential‐dependent surface‐enhanced Raman scattering (SERS) was recorded from an electrochemically roughened silver electrode. The vibrational wave numbers of the compound were computed using the Hartree–Fock/6‐31G* basis and compared with the experimental values. The presence of strong pyridine ring vibrations in the SERS spectrum reveals the interaction between the pyridine ring and the silver surface. The molecule is adsorbed on the silver surface with the pyridine ring in a tilted orientation. The direction of charge‐transfer contribution to the SERS is discussed from the frontier orbital theory. The value of the calculated first hyperpolarizability is comparable to those reported for similar structures, which makes this molecule an attractive object for future studies of nonlinear optics. The optimized geometrical parameters of the title compound are in agreement with similar reported structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyvinyl alcohol/acrylamide based photopolymer composition as recording medium for high‐resolution volume‐phase holograms

A polyvinyl alcohol/acrylamide based photopolymer composition that can be used to record holograms (at 532 nm) with ~92% diffraction efficiency and stability extending over a period of several months has been prepared. This system has been investigated earlier but with limitations of diminishing grating efficiency as a function of time and humidity. In the present work, we have successfully addressed these problems. In this work, crosslinkers have been added both for monomer and binder, and the effect of this addition and concentrations of various components of the composition on the diffraction efficiency and recording energy has been studied. It was found that an optimum concentration exists for each component at which diffraction efficiency is the maximum and recording energy the minimum. It was also observed that addition of a crosslinking monomer improved the grating efficiency. Crosslinking of the binder further improved the grating efficiency and its stability over time and under high humidity conditions. Maximum possible resolution for this photopolymer has been found to be 2000 lines/mm. Copyright © 2011 John Wiley & Sons, Ltd.     

Ultrasonication--a complementary 'green chemistry' tool to biocatalysis: a laboratory-scale study of lycopene extraction

Lycopene is bequeathed with multiple bio-protective roles, primarily attributed to its unique molecular structure. The concomitant exploitation of two of the green chemistry tools viz., sonication and biocatalysis is reported here for the laboratory scale extraction of lycopene from tomato peel. The coupled system improved the extraction by 662%, 225% and 150% times over the unaided, only cellulase ‘Onozuka R-10’ treated and only sonication treated samples respectively. The sonication parameters (duration, cycle and amplitude) during the coupled operation were optimized using response surface methodology (RSM). Derivative UV-visible spectra (i.e., dA/dλ and d²A/dλ² against λ), FTIR analysis, and DPPH scavenging test suggested that the reported extraction protocol did not affect the molecular structure and bioactivity of the extracted lycopene. The influence of sonication on the probable structural modulation (through UV-visible spectral analysis) and activity of the enzyme were also analyzed. A plausible mechanism is proposed for the enhanced extraction achieved via the coupled system.     

Vibrational spectroscopic studies and ab initio calculations of sulfanilamide

FT-Raman and FT-IR spectra of sulfanilamide were recorded and analyzed. The vibrational frequencies of the compound have been computed using the Hartree-Fock/6-21G(*) basis and compared with the experimental values. The assignments of the observed bands were made on the basis of available literature.