Facile access to polymer supported zinc–salen complex: highly efficient heterogeneous catalyst for synthesizing hydantoins,thiohydantoins and Schiff bases in aqueous medium

Research on Chemical Intermediates - The synthesis of polymer supported zinc–salen complex (PS-Zn–salen) is described. The mononuclear zinc(II)–salen complex was characterized by...     

Comparison of Bacterial Communities in the Throat Swabs from Healthy Subjects and Pharyngitis Patients by Terminal Restriction Fragment Length Polymorphism

Terminal restriction fragment length polymorphism (T-RFLP) analysis was applied to characterize bacterial flora present in the throats of healthy subjects and pharyngitis patients. The 16S?rRNA genes of bacteria present in throat metagenome were amplified by PCR with 6-carboxy-fluorescein (6-FAM)-labeled universal forward primer (27?F) and a universal reverse primer (1513R). The 16S rDNAs were digested with restriction enzymes with 4-bp recognition sites (MspI or RsaI) and analyzed by using an automated DNA sequencer. T-RFLP patterns were numerically analyzed using computer programs. From analysis of the throat bacterial community, patterns derived from MspI and RsaI digested samples of healthy subjects and pharyngitis patients were grouped into different clusters, though RsaI digested samples showed some uncertainty. Pharyngitis throats generated an average species richness of 9 [±2.1 (SD)] and 10 (±2.9) for MspI and RsaI digests, respectively, whereas healthy throats generated 6.3 (±1.2) and 6.1 (±1.5) in MspI and RsaI digests, respectively. These results suggest that samples from pharyngitis patients contain an unexpected diversity of causative bacteria. The pharyngitis throats were colonized with a rich diversity of bacterial species than that of healthy throats. Using T-RFLP, we are able to detect a model bacterium, Streptococcus pyogenes SF370, and T-RF patterns were consistent with the Streptococcal T-RFLP patterns. Our study indicates that T-RFLP analysis is useful for the assessment of diversity of throat bacterial flora and rapid comparison of the community structure between subjects with and without pharyngitis.     

Influence of sodium fluoride (NaF) on the crystallization and spectral properties of L-tyrosine

L-Tyrosine (C(9)H(11)NO(3)) is an essential amino acid in living organisms. It is also a building unit in protein, takes part in bio-synthesis of hormones, neurotransmitters, pigments and one of the organic chemical constituents of urinary stones. L-Tyrosine has been crystallized in silica gel by double diffusion technique with and without the addition of NaF. The crystals had rosette-like shape. In case of fluoride addition, two types of crystals have formed: rosette like crystallites, at the gel-solution interface and reticulate type crystallites beneath the interface. XRD results confirmed that both the products are of l-tyrosine with identical crystal structures. Crystal structure, morphology, thermal and spectral properties are analyzed using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR) and UV-vis transmittance studies. The TG-DTA results suggest that the thermal stability of L-tyrosine has markedly improved due to fluoride doping. Optical band gap energy of NaF grown l-tyrosine crystallite is estimated as 4.28eV. Second harmonic generation efficiency test indicates that L-tyrosine crystals can be used for application in nonlinear optical devices.     

Viologen-terminated polyamidoamine (PAMAM) dendrimer encapsulated with gold nanoparticles for nonenzymatic determination of hydrogen peroxide

The development of an accurate and low-cost monitoring technique for hydrogen peroxide (H₂O₂) is a crucial demand in environment, food industry, medicine and biology. Herein, we report the design and synthesis of viologen terminated second (G2.0) and third generation (G3.0) poly(amidoamine) PAMAM dendrimers, followed by encapsulation with gold nanoparticles to form G2.0 and G3.0 Vio-PAMAM-AuNPs. The G2.0 and G3.0 Vio-PAMAM-AuNPs were deposited over glassy carbon electrode (GCE) to form G2.0 and G3.0 Vio-PAMAM-AuNPs/GCE modified electrodes, respectively. The electrochemical behavior of G2.0 and G3.0 Vio-PAMAM-AuNPs/GCEs were investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Both the G2.0 and G3.0 Vio-PAMAM-AuNPs/GCEs showed a pair of well-defined redox peaks in 0.1 M phosphate buffer corresponding to the redox behavior of viologen V²⁺?V^?+ radical. G3.0 Vio-PAMAM-AuNPs/GCE has shown a higher current response than that of the G2.0 Vio-PAMAM-AuNPs/GCE and further the G3.0 Vio-PAMAM-AuNPs/GCE demonstrated impressive electrocatalytic activity towards reduction of H₂O₂, based on which a nonenzymatic sensor for the detection of H₂O₂ has been developed. The developed nonenzymatic sensor has displayed excellent performance towards H₂O₂ detection in the broad linear range of 0.1 mM – 6.2 mM with a low detection limit of 27 μM and high sensitivity of 202.7 μA mM^?1 cm^?2. The G3.0 Vio-PAMAM-AuNPs/GCE modified electrode with its extensive dendritic structure creating tailored sanctuary to accommodate a large number of viologen mediator and AuNPs exhibited good operational and long term stability and further the quantification of H₂O₂ in real samples has been verified by standard addition method.     

Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol‐Gel Thin Film Electrode Derived from 3‐Aminopropyl Trimethoxy Silane

An organically modified sol‐gel electrode using 3‐aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2 V to ?0.6 V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ?0.265 V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ?0.34 V. A good linear working range from 2.94×10^?6 M to 2.11×10^?3 M with a detection limit of 1.76×10^?6 M and quantification limit of 5.87×10^?6 M was obtained for nitrite determination. The stable and quick response (4 s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol‐gel matrix.     

Amperometric hydrogen peroxide sensor based on a sol-gel-derived ceramic carbon composite electrode with toluidine blue covalently immobilized using 3-aminopropyltrimethoxysilane

A carbon composite amperometric hydrogen peroxide sensor has been developed using a sol-gel technique. Toluidine blue (TB), which acts as the redox mediator, was covalently immobilized via glutaraldehyde crosslinking with an organically modified silane, namely 3-aminopropyltrimethoxysilane (APTMOS). Methyltrimethoxysilane (MTMOS) was used as the additional monomer; this controls the hydrophobicity of the electrode surface, thus limiting the wettability. The immobilization of TB within the sol-gel matrix was confirmed with FTIR studies. The sol-gel mixture containing TB immobilized in APTMOS and MTMOS was mixed with graphite powder in order to prepare the carbon composite electrode. The electrode was characterized using voltammetric techniques and its electrocatalytic activity for the reduction of hydrogen peroxide was also studied. The carbon composite electrode has the advantage of sensing H₂O₂ at a lower potential and with a higher sensitivity, and interferences due to ascorbic acid, uric acid and acetaminophen were greatly minimized. The linear range for the determination of H₂O₂ extends from 5.37 × 10⁻⁶ to 6.15 × 10⁻³ M, with a correlation coefficient of 0.9981. The detection limit was found to be 2.15 × 10⁻⁶ M. The covalent immobilization of TB effectively prevents the leakage of the water-soluble mediator during measurements. The modified electrode, aside from electrocatalyzing the reduction of H₂O₂, exhibits distinct advantages in terms of surface renewal in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability, and good reproducibility. Figure Amperometric hydrogen peroxide sensor based on sol-gel-derived ceramic carbon composite electrode with toluidine blue covalently immobilized using 3-aminopropyltrimethoxysilane Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.