Fluorescence spectroscopy of a naturally occurring carbazole alkaloid: murrayanine

The fluorescence properties of a naturally occurring carbazole alkaloid, murrayanine, have been studied in various polar solvents and micellar systems. It was found that fluorescence peak position and intensity are extremely sensitive to the nature of the solvent medium. Murrayanine fluorescence has been further utilized to determine the critical micellization concentration of Pluronic F68, an amphiphilic copolymer with potential applications in drug-delivery. Time-resolved fluorescence and fluorescence anisotropy decay of murrayanine measured in several n-alcohols display a monotonic retardation with increasing chain-lengths of the alcohols.     

Polarization-maintaining photonic crystal fibers with near-zero flattened dispersion in 1.06 μm waveband for medical applications

In this paper we present the design of a modified hexagonal photonic crystal fiber (PCF) having high birefringence and a near-zero flattened dispersion. Using the finite-difference method (FDM), it is shown that the proposed multiple Gedoped core hexagonal PCF exhibits a high birefringence of order 10⁻³ and a nearly zero flattened dispersion in the optical coherence tomography (OCT) waveband. In addition, the proposed PCF has a confinement loss of less than 10⁻⁸ dB/m at 1.06 μm. PCFs with such properties are considered suitable for both endoscopic OCT and other experimental setups employing 1.06 μm lasers.     

Core-shell microgel stabilized silver nanoparticles for catalytic reduction of aryl nitro compounds

Silver nanoparticles loaded into shell of poly (styrene-N-isopropylmethacrylamide-co-acrylic acid) core shell [P (SNA-CS)] gel particles were synthesized and analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis) and dynamic light scattering (DLS). Catalytic activity of Ag@P (SNA-CS) particles was investigated by reducing p-nitroaniline (p-NA) into p-aminoaniline (p-AA) in the presence of sodium borohydride (NaBH₄) reductant. Molecules of the substrate adsorbed on the surface of silver nanoparticles interact with borohydride ions (BH₄⁻) to form p-AA. Other nitroarenes like o-nitroaniline (o-NA), p-nitrophenol (p-NP) o-nitrophenol (o-NP), 2,4-dinitrophenol(2,4-DNP) were also reduced into their corresponding aryl amines using Ag@P (SNA-CS) composite microgels as catalyst. Reported catalyst efficiently reduced the nitro aromatic compounds individually as well as simultaneously at ambient temperature. Effect of different reaction conditions (catalyst dose, concentration of NaBH₄ and concentration of p-NA) on reaction completion time, value of apparent rate constant (k_app) and reduction efficiency of the catalyst for reduction of p-NA was also demonstrated. Ag@P (SNA-CS) catalyst was found to be able to retain activity up to four cycles.     

Synthesis,Characterization, Antimicrobial Activity Screening,and Molecular Docking Study of Pyrimidine Carbonitrile Derivatives

Russian Journal of Organic Chemistry - The present work describes the synthesis of 4-amino-6-(2-benzylidenehydrazinyl)-pyrimidine-5-carbonitrile derivatives,...     

Synthesis and antimycobacterial activity of some beta-carboline alkaloids

In view of the attributed medicinal properties of beta-carboline alkaloids, some new O-acyl derivatives of beta-carboline alkaloid--harmol, were prepared and tested for possible antimycobacterial activity against Mycobacterium tuberculosis H37Rv.     

Surface ion engineering of Mn2+-doped ZnS quantum dots using ion-exchange resins

We report the engineering of surface ions present as defects in doped quantum dots (Qdots) following their synthesis. This was achieved by treating the Qdots with cation-exchange resin beads (CB). An aqueous dispersion of Mn(2+)-doped ZnS Qdots, when treated with different amounts of CB, resulted in two kinds of changes in the emission due to Mn(2+) ions. First, the intensity increased in the presence of a smaller amount of CB, to the extent of a doubled quantum yield. With increased CB as well as incubation time, the emission intensity decreased systematically, accompanied by an increasing blue shift of the peak emission wavelength. Electron spin resonance results indicated the removal of clusters of Mn(2+) present in the Qdots by the CB, which has been attributed to changes in the emission characteristics. Transmission electron microscopy studies revealed that for smaller amounts of CB there was no change in the particle size, whereas for greater amounts the particle size decreased. The results have been explained on the basis of the removal of Mn(2+) (and also Zn(2+)) ions present on the surfaces of Qdots in the form of clusters as well as individual ions.     

Preconcentration of trace silver with yeast for river water analysis

A new preconcentration method with yeast is presented. The method was evaluated for the determination of trace silver in river waters by graphite furnace atomic absorption spectrometry (GFAAS). A suitable cultivation bed for preconcentration of silver was 1.75 mg ml-1 2-ammonium hydrogen phosphate. The optimal cultivation time and temperature were 2 h and 25 degrees C. Under optimal conditions, silver in aqueous sample was concentrated to 6.9-fold by yeast. The detection limit was 4.6 pg ml-1 (3S/N) for silver in river water. The yeast preconcentration method was applied to the determination of silver in river waters. The recovery of spiked silver was in the range of 89 to 110%. By the preconcentration, it was found that ultra trace silver in river waters could be determined without interferences of matrix elements, after only the cultivation and with no chemical treatment.     

Structure Breaking/Making Property of Acefylline Piperazine in Aqueous,Aqueous Methanol,and Aqueous Ethylene Glycol Systems

Densities of acefylline piperazine (AP) in aqueous, aqueous methanol, and aqueous ethylene glycol (10% v/v) systems are determined in the concentration range 0.04-0.14±0.001 mol/dm³ at different temperatures (298.15-318.15 K) with the interval of 5 K. The apparent molar volume (φv), the partial molar volume \((\phi_v^0)\), and the ion-ion interaction parameter (S_v) are calculated using the Masson equation. Partial molar expansibilities \((\phi_E^0)\), which indicate the presence or absence of the caging or packing effect, are also evaluated and discussed. The results are interpreted in terms of solute-solvent and solute-solute interactions of AP in aqueous, aqueous methanol, and aqueous ethylene glycol systems. The structure-breaking and structure-making properties of AP are inferred by the sign of Hepler′s criterion \((\partial^2\phi_v^0/\partial{T}^2)_p\), i.e. the second derivative of the partial molar volume with respect to the temperature at the constant pressure.     

Initiation of polymerization of methyl methacrylate by oxalic acid and iron(III) mixtures

The polymerization of methyl methacrylate either by free radical or charge transfer mechanism has been studied in dimethyl sulphoxide at 60° in the presence of oxalic acid and hexakis dimethylsulphoxide iron(III) perchlorate, [Fe(DMSO)₆](ClO₄)₃. Increased rate was noticed for 1:1 mole ratio of oxalic acid to Fe³⁺ for charge transfer polymerization; a well defined induction period was found for free radical polymerization in the same systems. Mechanisms for the two types of reaction are proposed. The rate constant for the interaction of poly(methyl methacrylate) radical with the iron-oxalate complex was found to be 1.52 × 10⁵ l. mol^?1 sec^?1 at 60°.