Synthesis, characterization, photoluminescence and EPR investigations of Mn doped MgAl2O4 phosphors

MgAl₂O₄:Mn phosphors have been prepared at 500 °C by combustion route. Powder X-ray diffraction (XRD) indicated the presence of mono-MgAl₂O₄ phase. Scanning electron microscopy showed that the powder particle crystallites are mostly angular. Fourier transform infrared spectroscopy confirmed the presence of AlO₆ group which makes up the MgAl₂O₄ spinel. Photoluminescence studies showed green/red emission indicating that two independent luminescence channels in this phosphor. The green emission at 518 nm is due to ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions. The emission at 650 nm is due to the charge-transfer deexcitation associated with the Mn ion. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. The g≈2.00 is due to Mn²⁺ ion in an environment close to tetrahedral symmetry. It is observed that N and χ increase with decrease of temperature obeying the Boltzmann law. The variation of zero-field splitting parameter (D) with temperature is evaluated and discussed.     

Tetrachloroferrate(III)-selective liquid membrane electrode based on crystal violet

An extract of crystal violet-tetrachloroferrate(III) in nitrobenzene was used to prepare a tetrachloroferrate(III)-selective liquid membrane electrode with a poly(vinyl chloride) support. The optimal conditions to determine 2.5 × 10^–5 – 5.0 × 10^–2 M iron(III) as tetrachloroferrate(III) (anionic slope 56 mV/decade, detection limit 7.9 × 10^–6 M) were found to be 4.0–5.5.M total chloride in 0.75–1.5M hydrochloric acid. The electrode was reliably applied to determine iron in human blood, haematite and mineralized vitamin syrup by direct potentiometry, standard and sample additions as well as standard subtraction techniques.     

Selective Spectrophotometric Determination of Copper in Milk with Phenanthraquinone Monothiosemicarbazone

The red complex formed by copper (II) and phenanthraquinone monothiosemicarbazone has an absorption maximum at 530 nm with a molar absorptivity of 14000 cm^?1 mole^?1. The pH range for the determination is 1.1–6.6. Optimum range of concentration for accurate determination is 0.50–3.47 ppm of copper (II) in 50% methanol medium. The limits of interference due to foreign ions have been studied. The method has been successfully employed for the determination of copper in various samples of milk.     

Potentiometric studies in oxidation-reduction reactions: Oxidation with chloramine-b. indirect determinations

Chloramine-B has been used as an oxidising agent to determine indirectly potassium iodate, potassium metaperiodate, potassium, bromate, potassium dichromate, hydrogen peroxide, chloramine-T and potassium permanganate by a potentiometric method. An excess of potassium iodide added to each of the substances in an acid medium is titrated back with a standard solution of chloramine-B, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

o-hydroxylmethylphenylchalcogens: synthesis, intramolecular nonbonded chalcogen...OH interactions, and glutathione peroxidase-like activity

[Structure: see text]. The synthesis and characterization of a series of organochalcogen (Se, Te) compounds derived from benzyl alcohol 13 are described. The synthesis of the key precursor dichalcogenides 15, 22, and 29 was achieved by the ortho-lithiation route. Selenide 18 was obtained by the reaction of the dilithiated derivative 14 with Se(dtc)2. Oxidation of 15 and 22 with H2O2 afforded the corresponding cyclic ester derivatives 17 and 24, respectively. Oxidation of selenide 18 with H2O2 affords the spirocyclic compound 19. The presence of intramolecular interactions in dichalcogenides 15 and 22 has been proven by single-crystal X-ray studies. The cyclic compounds 17 and 19 have also been characterized by single-crystal X-ray studies. GP(X)-like antioxidant activity of selenium compounds has been evaluated by the coupled bioassay method. Density functional theory calculations at the mPW1PW91 level on ditelluride 22 have identified a fairly strong nonbonding interaction between the hydroxy oxygen and tellurium atom. The second-order perturbation energy obtained through NBO analysis conveys the involvement of n(O) --> sigma(Te-Te) orbital overlap in nonbonding interaction. Post wave function analysis with the Atoms in Molecules (AIM) method identified distinct bond critical point in 15 and 22 and also indicated that the nonbonding interaction is predominantly covalent. Comparison between diselenide 15 and ditelluride 22 using the extent of orbital interaction as well as the value of electron density at the bond critical points unequivocally established that a ditelluride could be a better acceptor in nonbonding interaction, when the hydroxy group acts as the donor.     

Thermodynamics of molecular interactions in ethyl iodide+toluene mixtures

The excess Gibb's free energy of mixing, G^E, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The H^E and G^E values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and G^E>H^E. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A₂B molecular species describes well (within±10 J-mol^–1 in the worst case) the general dependence of H^E on X_A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA₂B reactions along with the enthalpies of formation of AB and A₂B molecular species have been calculated.     

Hot atom chemistry in oxyanion targets,part II1: Recoil behaviour of56Mn in permanganates

Fractional precipitation techniques have been utilized to separate the lower valent and parent forms of⁵⁶Mn in permanganate targets and an attempt is made to study a few aspects of chemical stabilization of recoil⁵⁶Mn in permanganates. Ammonium permanganate, recoil behaviour of which has not been studied previously, is chosen as one of the targets along with the potassium permanganate for initial retention and also for isothermal annealing.⁵⁶Mn initial retentions of about 12% and about 4% are obtained for potassium and ammonium permanganate, respectively, by activation from a Ra–Be neutron source. A usual trend for KMnO₄ and the reduction of recoil fragments by ammonium ions in NH₄MnO₄ are seen through the isothermal annealing study.     

Spectrophotometric determination of platinum with substituted pyrimidine-2-thiol

The yellow complex of Pt(IV) with 1-pyridyl-4,4,6-trimethyl-1H,4H-pyrimidine-2-thiol (PyTPT) which has maximum absorbance at 430 nm, is studied for the spectrophotometric determination of the metal. Molar absorptivity is 5000 liters mol^?1 cm^?1 and Sandell's sensitivity is 0.039 μg/cm². The determination of Pt(IV) (2.8–8.4 ppm) in the presence of diverse ions is described.     

Photocatalysed eosin Y mediated C(sp3)-H alkylation of amine substrates via direct HAT

A visible light promoted, photoredox catalysed, green one-pot approach for the alkylation of amine substrates with sp² carbon has been developed. This eosin Y based organic transformations, can behave as an effective direct hydrogen-atom transfer catalyst for coupling reaction. The proposed strategy includes simple procedure which can make adduct product with sp² carbon. This eosin Y based photocatalytic hydrogen-atom transfer strategy may hold great potential for diverse functionalization of a wide range of native CH bonds in an economical and sustainable manner.     

Efficient transesterification/acylation reactions mediated by N-heterocyclic carbene catalysts

Imidazol-2-ylidenes, a family of N-heterocyclic carbenes (NHC), are efficient catalysts in the transesterification involving numerous esters and alcohols. Low catalyst loadings of aryl- or alkyl-substituted NHC catalysts mediate the acylation of alcohols with enol acetates in short reaction times at room temperature. Commercially available and more difficult to cleave methyl esters react with primary alcohols in the presence of alkyl-substituted NHC to efficiently form the corresponding esters. While primary alcohols are selectively acylated over secondary alcohols with use of enol esters as acylating agents, methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts. The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ.