Ecofriendly synthesis of substituted pyridine and pyrido[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidine derivatives

An environmentally benign novel one-pot synthesis of pyridines and pyrido[2,3-d]pyrimidines from chalcones and malononitrile was described. In the reaction under neat conditions using microwave irradiation, enhancement in the reaction rate and high yields were observed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1479–1482, June, 2005.     

Interaction between non-heme iron of lipoxygenases and cumene hydroperoxide: basis for enzyme activation, inactivation, and inhibition

Lipoxygenase catalysis depends in a critical fashion on the redox properties of a unique mononuclear non-heme iron cofactor. The isolated enzyme contains predominantly, if not exclusively, iron(II), but the catalytically active form of the enzyme has iron(III). The activating oxidation of the iron takes place in a reaction with the hydroperoxide product of the catalyzed reaction. In a second peroxide-dependent process, lipoxygenases are also inactivated. To examine the redox activation/inactivation dichotomy in lipoxygenase chemistry, the interaction between lipoxygenase-1 (and -3) and cumene hydroperoxide was investigated. Cumene hydroperoxide was a reversible inhibitor of the reaction catalyzed by lipoxygenase-1 under standard assay conditions at high substrate concentrations. Reconciliation of the data with the currently held kinetic mechanism requires simultaneous binding of substrate and peroxide. The enzyme also was both oxidized and largely inactivated in a reaction with the peroxide in the absence of substrate. The consequences of this reaction for the enzyme included the hydroxylation at C beta of two amino acid side chains in the vicinity of the cofactor, Trp and Leu. The modifications were identified by mass spectrometry and X-ray crystallography. The peroxide-induced oxidation of iron was also accompanied by a subtle rearrangement in the coordination sphere of the non-heme iron atom. Since the enzyme retains catalytic activity, albeit diminished, after treatment with cumene hydroperoxide, the structure of the iron site may reflect the catalytically relevant form of the cofactor.     

DTA study of kinetics of transformation of silica gel to cristobalite

The activation energy for the transformation of silica gel to cristobalite, a partial reaction of first order, was determined from a single DTA curve by the methods available in the literature. The values obtained were not in agreement with those obtained by the isothermal method. This suggested that the methods were not applicable to reactions which are partial. A modified equation was derived which could be utilized for the determination of the activation energy of first-order reactions from a single DTA curve, if the fraction transformed during the reaction was known.

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Zusammenfassung Die Aktivierungsenergie der Umwandlung von Kieselgel in Cristobalit, einer Teilreaktion erster Ordnung, wurde aus einer einzigen DTA-Kurve unter Anwendung einer in der Literatur beschriebenen Methode bestimmt. Die erhaltenen Werte standen mit den durch isotherme Methoden ermittelten nicht in Übereinstimmung. Daraus wurde gefolgert, daß die Methoden bei Teilreaktionen nicht einzusetzen sind. Eine modifizierte Gleichung wurde abgeleitet, die sich zur Bestimmung der Aktivierungsenergie von Reaktionen erster Ordnung aus einer einzelnen DTA-Kurve eignet, wenn der während der Reaktion umgewandelte Anteil bekannt ist.

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Résumé On a déterminé à l'aide d'une seule courbe ATD l'énergie d'activation de la transformation du gel de silice en cristobalite, réaction partiellement du premier ordre, en utilisant les méthodes décrites dans la littérature. Les valeurs obtenues ne sont pas en accord avec celles obtenues par la méthode isotherme. On a déduit que les méthodes utilisées ne sont pas valables dans le cas des réactions partielles. On établit une équation modifiée qui permet de déterminer l'énergie d'activation de réactions du I^er ordre à partir d'une seule courbe ATD si les fractions transformées pendant la réaction sont connues.

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The authors thank Shri K. D. Sharma, Director of the Institute, for his kind permission to publish the paper.     

Dependence ofT c on doping in oxygen-hole induced Jahn-Teller mediated superconductors

A bipolaronic model of high-T _c superconductivity, that is based upon the idea that a doped oxygenhole reduces the separation between the and levels of the neighbouring Cu-ion and hence causes a Jahn-Teller mixing between the two levels, is suggested. Within the BCS scheme, the bipolaron Hamiltonian is investigated for the superconducting order parameter and the critical temperatureT _c as a function of hole-doping. Under suitable approximation for the bipolaronic kinetic energy, the hole-doping dependence ofT _c shows a universal behaviour. For temperatures close toT _c and forT _c 1, obeys the BCS type of relation with pre-factor of (1–T/T _c )² related to the range of superconducting-phase against the doping axis.     

Effect of Ca substitution on structural,magnetic and dielectric properties of BiFeO3

Bi_1-xCa_xFeO₃ (x = 0.40, 0.50) compounds are synthesized by conventional solid-state reaction method. The effect of Ca²⁺ substitution is investigated on structural, dielectric and magnetic properties. Rietveld refinement confirms that crystal structures of both the samples are tetragonal with P4mm symmetry. The highest values of remnant magnetization (M_r ) and coercive field (H_c ) are 0.002 emu/g and 0.23 kOe, respectively, for x = 0.50. The electric modulus formalism is used to distinguish and separate out the relaxation process which is dominated by the transport phenomenon. The relaxation process has activation energy ～0.32 eV which is found to be related to both the hopping mechanisms, i.e. electronic and oxide ions.     

Current carrying capability of HTS Roebel cable

We have developed a numerical technique to estimate the current carrying capability of HTS Roebel cable composed from coated conductor strands. The influence of self-field on the critical current density is studied computationally for a Roebel cable using a realistic field and angle dependence behaviour of critical current. The computations are carried out for N/2 (number of strands/strand width in mm), and N/5 Roebel cable for N = 2–15. The local current distribution in each strand satisfies the self-consistent criteria J = J_c(B(J)) except for a small region where the current density is set to zero to maintain the condition of equal currents in all strands. The variation of critical current with vertical and horizontal separation between the strands is also investigated. Results are compared with the measured values of critical current for some of our cables. The comparison shows an error of up to 10% which we attribute mostly to the model not accounting for the spread in I_c values of the constituent strands.     

Weak C—H...O hydrogen bonds in anisaldehyde,salicylaldehyde and cinnamaldehyde

In situ cryocrystallization has been employed to grow single crystals of 4‐methoxybenzaldehyde (anisaldehyde), C₈H₈O₂, 2‐hydroxybenzaldehyde (salicylaldehyde), C₇H₆O₂, and (2E)‐3‐phenylprop‐2‐enal (cinnamaldehyde), C₉H₈O, all of which are liquids at room temperature. Several weak C—H...O interactions of the types C_aryl—H...O, C_formyl—H...O and Csp³—H...O are present in these related crystal structures.     

Polarographic (DCP & DPP) Determination of Ellagic Acid in Strawberries & Pharmaceutical Formulations

Direct Current (DC) and Differential Pulse (DP) Polarographic methods have been developed for the qualitative as well as quantitative analysis of ellagic acid in plant products (i.e. strawberries) and pharmaceutical formulations (Ellagic insurance formula). Ellagic acid produces a well‐defined polarographic wave/peak in pyridine hydrochloride at pH 6.8 ± 0.1 with E_1/2 /Ep = ?1.298 V vs. SCE. The wave/peak height is found to be proportional to the concentration of ellagic acid. The developed procedure was used for the analysis of ellagic acid in an extract of strawberries (Fragaria × ananassa) and pharmaceutical formulations. Statistical treatment of the observed polarographic data revealed high accuracy and good precision of determination. The work has been supplemented by FTIR screening of the sample. The percentage of ellagic acid in pharmaceutical formulations was determined by the developed method, which is in close agreement with the labeled amount.     

Structural and magnetic properties of nano nickel-zinc ferrite synthesized by reverse micelle technique

Nanocrystalline nickel-zinc ferrites (Ni_0.58Zn_0.42Fe₂O₄) at different pH values (less than 9.6, 9.6, 10.96, and 11.40) for the alkali-precipitating reaction were synthesized by reverse micelle technique. X-ray diffraction reveals a well-defined nickel-zinc ferrite crystal phase at pH=9.6. Increase in pH value obstructs pure-phase formation and results in partial formation of α-Fe₂O₃. The magnetic behaviour of the samples was studied by superconducting quantum interference device. All the samples show superparamagnetic behaviour at room temperature (300 K) and negligible hysteresis at low temperature (5 K). The low value of saturation magnetization is explained on the basis of spin canting. The high-field irreversibility and shifting of the hysteresis loop detected in single-phase sample has been assigned to a spin-disordered phase, which has a spin-freezing temperature of approximately 42 K and other two samples have an antiferromagnetic phase (α-Fe₂O₃) coupled to the ferromagnetic phase.     

Third-order three-point fuzzy boundary value problems

In this paper, we shall present a three-point boundary value problem of fuzzy differential equation by means of Green’s function.