Anion induced capsular self-assemblies

Researchers world-wide have employed diverse strategies to achieve various anion binding hosts and anion induced supramolecular architectures due to the increasing appreciation of anion receptor chemistry. Intellectual discovery of molecular capsules for the recognition of different guest species has opened up a new field of research in the area of supramolecular chemistry. This feature article aims to provide an overview of the current status and recent achievements made by us and others in the last decade in the area of anion induced construction of supramolecular capsules and anion binding in molecular capsules.     

N,N′-Dihydrogenpiperazonium dichloridobis(dimethylglyoximato-k2N,N′)cobaltate(III) Dihydrate

Abstract  

The title complex: C₄H₁₂N₂[Co(C₄H₇N₂O₂)₂Cl₂]₂·2H₂O, viz., PpH₂[Co(dmgH)₂Cl₂]₂·2H₂O, where, dmgH⁻ = dimethylglyoximate and Pp = piperazine was synthesized and analyzed by single crystal XRD studies. The complex was grown as brown crystals by the slow evaporation method in ethanol. The complex crystallizes as triclinic with the space group p[`1] p\overline{1} and unit cell parameters a = 8.4521 (10) Å, b = 10.0999 (11) Å, c = 10.8952(13) Å; α = 94.066(6)°, β = 106.047(6)° and γ = 100.901(6)°. There are two complex molecules present in the unit cell. The short intra molecular O–H···O hydrogen bonds link the glyoximate moieties in the crystal.     

Low-temperature synthesis of Zn2SiO4:Mn green photoluminescence phosphor

Zn₂SiO₄:Mn green phosphor having comparable photoluminescence (PL) efficiency with commercial phosphor has been synthesized at 1000 °C using solid state reactions involving ZnO, silicic acid and manganese acetate. The water of crystallization attached to SiO₂ in silicic acid whose dissociation at 1000 °C seem to promote the sintering efficiency of Zn₂SiO₄:Mn. Incremental ZnO addition and re-firing at 1000 °C promote the diffusion rate of ZnO and SiO₂. The formation of a single crystalline phase of willemite structure in the samples was confirmed by powder XRD measurements. The phosphor exhibit an intense excitation band centered around 275 nm and a relatively weak excitation centered around 380 nm while the broad band green emission peaks at 524 nm. Other parameters studied include PL spectra, grain morphology, ZnO/SiO₂ molar ratio, Mn concentration, co-dopant/flux and the effect of chemical forms of Mn dopant as well as silica on the PL efficiency.     

Fluorescence properties of the anti-tumour alkaloid luotonin A and new synthetic analogues: pH modulation as an approach to their fluorimetric quantitation in biological samples

Luotonin A is an alkaloid structurally related to the natural anti-tumour agent camptothecin. The fluorescence behaviour of luotonin A and a series of six analogues is described in the present work. The influence of solvent polarity and pH on the native fluorescence properties of these alkaloids was studied, finding that in organic solvents or in aqueous solutions (pH 5.5–7.2) the neutral form of the luotonin derivatives emit in the region of 410–450 nm but, in both media, acidification to pH values below 3.0 causes a new emission band to appear at about 500 nm. An ESPT reaction occurs due to the protonation of the basic nitrogen atoms of the pentacyclic ring. Acid-base titrations of luotonin A and its derivatives in aqueous and acetonitrile media were carried out in order to determine their pK_a^? values which were around 2, showing these compounds to be very weak bases. In aqueous media, the absence of an iso-emissive point in the emission spectra suggests the existence of more than two species in the proton transfer equilibria. The basicity of the luotonin A derivatives is increased in organic media, and a good correlation between the pK_a^? values and the chemical structure was found. The protonation of luotonin A was also studied by ¹H-NMR and ¹³C-NMR experiments, which proved the protonation of the nitrogen atoms at the positions 5 and 6 of the pentacyclic ring. The fluorescence quantum yields were determined in ethanol and in aqueous solutions under neutral and acidic conditions. The fluorescence quantum yields were higher in water for the case of the more polar compounds, and the opposite result was obtained for the more hydrophobic ones. The remarkable and interesting fluorescence properties of luotonin A prompted the development of its fluorimetric analytical quantitation, obtaining very good analytical features.     

Weak n-injective and weak n-fat modules

Czechoslovak Mathematical Journal - We introduce and study the concepts of weak n-injective and weak n-flat modules in terms of super finitely presented modules whose projective dimension is at...     

Neutron activation analysis of lithium niobate

A radiochemical neutron activation analysis procedure for the determination of Ta, W, Ir, Pt, Au, Cu, Cr, Co and Zn in lithium niobate has been developed. The method involves a one-step removal of radioactive nuclides of Nb, Ta and W representing the dominating radioactivity of the irradiated sample. After irradiation, the sample is fused with inactive carriers and Na₂O₂ in a nickel crucible. The fused cake is dissolved in HCl–H₂O₂ and Nb, Ta and W are homogeneously precipitated. The impurities are separated by combinations of precipitation and ion-exchange separations for precise -ray measurements with an overall chemical yield of 70% to 90%. The results are discussed.     

Determination of vanadium: an optimization of the gallic acid persulphate method

An optimization procedure for the gallic acid-persulphate method for the ultratrace determination of vanadium is reported. The optimization step has improved the sensitivity by a factor of three. The linearity range of the calibration graph is also extended.