Search

Selectivity between Am3+ and Cm3+ was investigated after their aqueous complexation with three structurally tailored hydrophilic bis-(1,2,4-triazin-3-yl) ligands followed by their extraction with N,N,N′N′-tetraoctyl diglycolamide (TODGA) dissolved in an ionic liquid (C4mim·Tf2N). The three hydrophilic ligands used were SO3PhBTP, SO3PhBTBP, and SO3PhBTPhen. It was evident from the solvent extraction studies that SO3PhBTP formed a stronger complex with Cm3+ than with Am3+, but SO3PhBTPhen showed better complexation ability for Am3+ than for Cm3+, and SO3PhBTBP showed no selectivity for the two actinide ions. DFT calculations indicated that the coordinating ‘N’ atoms in BTP were more co-planar in the complex and this co-planarity was higher in the Cm3+ complex as compared to that in Am3+. In the case of BTBP and BTPhen ligands, on the other hand, the co-planarity was more pronounced in the Am3+ complexes. Mayer's bond order calculations of M–N bonds in the complexes also indicated a reversal of the complexation ability of the BTP and BTPhen ligands for Am3+ and Cm3+. Calculations of the complexation energies further supported the higher selectivity of the BTP ligand for Am3+ by −52.0 kJ mol−1, and better selectivity of the BTPhen ligand for Cm3+ by −24.7 kJ mol−1.

This paper presents the preliminary results obtained in developing a powder metallurgy process involving an approach based on the use of press (compaction) and sintering together with subsequent extrusion on one hand and press and extrusion on the other hand. Two systems have been compared: an unreinforced AA6061 alloy (matrix) and AA6061-2 wt.% fly ash particulate composite. Mechanical mixing of the matrix powder, obtained from elemental powders, and particulate reinforcement was followed by compaction. Pressurisation was carried out at 345 MPa with zinc stearate as die wall lubricant. Some green compacts were extruded subsequently at 5–10 mm min−1 rate with a reduction ratio of 16:1 at 500°C. And some were sintered at 620°C for 4 h before extrusion. From XRD, SEM EDAX and mechanical testing studies it was observed that the press extruded samples were showing improvement in density, hardness, 0·2% proof stress and tensile strength over press sinter extruded samples.

A series of alkyl, alkenyl and β-D-ribofuranosyl derivatives of 7-deazaguanine were synthesized and their ability to inhibit certain RNA virus infections was assessed in mice. 8-Chloro-7-deazaguanosine (6) protected the majority of mice infected intraperitoneally (i.p.) with benzi, encephalomyocarditis, San Angelo, or Semliki Forest virus at doses as low as 50 mg/kg/day. It was also orally active.

The ability of simple azole nucleosides to promote antiparallel triplex formation at non-homopurine duplex targets was explored. It was also shown that spermidine-cholesterol conjugation is effective in enhancing cellular uptake and stability of oligonucleotides.

Triple helix-forming oligonucleotides (TFOs) offer the potential to specifically modulate expression of gene in a sequence dependent manner. TFOs containing G and T residues that bind to duplex DNA, forming a series of GGC and TAT base triplets, have been well studied. It has been observed that T is relatively nonspecific in that it binds with similar affinity to AT, GC, and CG base pairs. This may significantly reduce the specificity of a given TFO, leading to undesired effects on the expression of genes unrelated to the intended target. We have now prepared 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-pyrido[2,3-d]pyrimidine-2,7(8H )- dione (P) and incorporated it into TFOs using the solid-support, phosphoramidite chemistry. It has been demonstrated that a limited substitution of P for T in a G-rich 26-mer TFO can improve binding specificity for AT base pairs in antiparallel motif under certain conditions. The specificity exhibited by P is suggestive of base pair specific interactions that influence the binding strength and consequently enhance the potential therapeutic application of TFOs. However, the effect of substitution of P for T is dependent on the binding conditions, as well as the number of position of substitutions.

In the past few years, chemical beam epitaxy (CBE) has succeeded in producing high purity InP with residual carrier concentrations in the low 10/sup 14/ cm/sup -3/ range and liquid nitrogen temperature mobilities much higher than 10/sup 5/ cm/sup 2//Vs. The authors present the results of a study where they have combined electrical, chemical, and optical measurements to identify the residual impurities in InP layers grown with different growth parameters. It is shown that S and Si are the two major residual donor impurities in InP layers grown by CBE and that they originate from the gas sources. Arsenic contamination of InP layers is a common problem in gas source systems, particularly when a single cracker cell is used for both As and P sources. However this contamination can be greatly reduced with a thorough baking prior to InP growth. The concentration of acceptors is negligible and too low to allow the identification of the residual acceptor impurities. Under optimized growth conditions, InP layers with residual carrier concentrations less than 10/sup 14/ cm/sup -3/ can be routinely grown with 77 K mobilities larger than 2 /spl times/ 10/sup 5/ cm/sup 2//Vs. >

5,6-Dialkylated uridine derivatives were conveniently synthesized in 5 steps starting from 2′,3′-O-isopropylideneuridine (1) in a 43% overall yield. The key reaction is a novel acid catalyzed cyclization reaction of 6-(4-butanal)-2′,3′-O-isopropylideneuridine.

An alternative analogy for the dissociation of oxyhemoglobin to explain why successive oxygen molecules are bound less strongly than preceding ones.

The kinetics of oxidation of L-ascorbic acid by 2,6-dichlorophenolindophenol in aqueous solution has been studied. The rate of the reaction decreases with increasing pH since the hydrogen ascorbate ion is less reactive than the unionized L-ascorbic acid. The rate constants for the oxidation of the two species have been evaluated and a plausible mechanism of the reaction is suggested.

The kinetics of the reaction between has been studied under conditions of production of iodine at a known rate by the persulfate-iodide reaction and its consumption by S2O3 -- . The effective concentration of iodine during the steady state is measured from its reduction potential at a bright platinum foil electrode. The reaction is of first order with respect to I3 - and S2O3 -- individually and hence of over all second order. The specific rate is 1.51 X 105 M -1 sec-1 and the frequency factor is 1.69 × 1012 M -1 sec-1 at 25 °C. The energy of activation for the reaction is 9.58 × 103 cal/mole and the entropy of activation is -2.55 cal/mole deg.

The magnetostriction of polycrystalline mixed nickel-zinc and cobalt-zinc ferrites of different compositions are studied as a function of composition, magnetic field, and temperature, using the strain gauge method. At room temperature it is observed that the values of saturation magnetostriction in both the ferrite systems decrease with the increase of zinc concentration. The anomalous behaviour observed in the variation of saturation magnetostriction with temperature is explained on the basis of magnetic anisotropy energy. Die Magnetostriktion von polykristallinen Nickel-Zink- und Kobalt-Zink-Mischferriten unterschiedlicher Zusammensetzung wird mit der Eichspannungsmethode in Abhangigkeit von Zusammensetzung, Magnetfeld und Temperatur gemessen. Bei Zimmertemperatur wird beobaohtet, das die Werte der Sattigungsmagnetostriktion in beiden Ferritsystemen mit zunehmender Zinkkonzentration abnehmen. Das anomale Verhalten, das bei der Anderung der Sattigungsmagnetostriktion mit der Temperatur beobachtet wird, wird auf der Basis der Energie der magnetischen Anisotropie erklart.

5,6-Dialkylated uridine derivatives were conveniently synthesized in 5 steps starting from 2′,3′-O-isopropylideneuridine (1) in a 43% overall yield. The key reaction is a novel acid catalyzed cyclization reaction of 6-(4-butanal)-2′,3′-O-isopropylideneuridine.

The kinetics of the oxidation of oxalic acid by cerium(IV) in sulfuric acid medium has been studied voltammetrically. The specific reaction rate is 132±4.0 M−1s−1 at 25.0 °C. The energy of activation is 62.6±3.0 kJ mol−1. The entropy of activation is −2.7 J mol−1K−1. The specific reaction rate is influenced by complexation and also by ionic strength (μ). The most likely mechanism has been suggested.

H 2 OX + is one of the prominent but doubtful species suggested in recent years to explain the electrophilic substitution in halogenations of organic substrates. The present studies are aimed at revealing the role of this hypothetical species in such reactions on the basis of related kinetic and conductance data and also on the basis of equilibria affecting the formation of H 2 OX + in aqueous solutions.

The kinetics of the addition of bisulfite to acetone has been studied by the polarographic technique. The specific rate increases with pH and hence the reaction is probably base catalyzed. Mechanisms have been suggested for the reaction in the presence and absence of added base.

Thermoelectric power studies are made of LiNi mixed ferrites over the temperature range 300 to 520 K by thermal probe method. The Seebeck coefficient (Q) is found to decrease while the carrier concentration (n) and the charge carrier mobility (μ) are found to increase with the increasing temperature. On the basis of these results an explanation for the conduction mechanism in LiNi mixed ferrites is suggested. Es wird die Thermospannung in LiNi-Mischferriten im Temperaturbereich von 300 bis 520 K mittels Thermosonde untersucht. Der Seebeck-Koeffizient (Q) nimmt ab, wahrend die Ladungstragerkonzentration (n) und die Ladungstragerbeweglichkeit (μ) mit steigender Temperatur zunehmen. Auf der Grundlage dieser Ergebnisse wird eine Erklarung fur den Leitungsmechanismus in LiNi-Mischferriten vorgeschlagen.

The utility of the rotating platinum electrode for the study of fast reactions has been shown by evaluating the specific reaction rates of brominations of m-acetotoluidide, acetanilide and o-acetotoluidide in aqueous solution.

Theoretical curves of the voltage dependence of cathodoluminescence have been obtained for the case where the intensity of cathodoluminescence varies superlinearly with the net carrier generation rate. Calculations are based on numerical integration of the distribution of excess carriers assuming a Guassian approximation to the distribution of excitation with depth. The theoretical curves make possible the measurement of diffusion lengths using the method of voltage dependence of cathodoluminescence in specimens where the intensity of cathodoluminescence is not linearly proportional to the specimen current (e.g., p‐type GaAs). Experimental results with accelerating voltages of 5–50 kV using a defocused electron beam and selected area technique indicate values of electron diffusion length in p‐type GaAs ranging from 3.2 μ at low carrier concentration (6.9×1016 cm−3) to 0.6 μ at high carrier concentration (3.76×1019 cm−3).