Retention behaviour of51CrO4 2− species on ignited microcrystalline iodates

Summary Influence of pH and that of added lattice and certain non-lattice ions has been studied towards instantaneous sorption of tracer⁵¹CrO₄ ^2– ionic species on iodates of lead, barium and strontium. Carrying is postulated to take place by surface adsorption. In the presence of lattice ions, the mode of deposition is in accordance with the adsorption rules. However, the presence of certain non-lattice cations with similar charge and ionic dimensions produces different types of behaviour. Thus, it has been found that addition of Ba²⁺ or Sr²⁺ ions causes the carrying to fall on Pb(IO₃)₂ surface, Pb²⁺ ions on Ba(IO₃)₂ carrier show the helpful role whereas Sr²⁺ ions supresse the carrying. Both Pb²⁺ and Ba²⁺ ions augment the deposition on the surface of Sr(I0₃)₂. An attempt has been made to explain these findings as a consequence of postulated masking of active adsorption centres on Pb(IO₃)₂ and Ba(IO₃)₂ surfaces under the given experimental conditions.

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Zusammenfassung Der Einfluß des pH sowie der Zugabe von Gitterionen oder manchen gitterfremden Ionen auf die unmittelbare Sorption von⁵¹CrO₄ ^2– an Blei-, Barium- und Strontiumjodat wurde geprüft. Die Trägerwirkung ist als Folge der Oberflächenadsorption anzusehen. In Gegenwart von Gitterionen folgt die Art der Bindung den Regeln der Adsorption. Die Anwesenheit gewisser gitterfremder Ionen mit ähnlicher Ladung und Dimension führt zu verschiedenen Verhaltensweisen. So wurde gefunden, daß die Zugabe von Ba²⁺ oder Sr²⁺ die Trägerwirkung der Oberfläche von Pb(JO₃)₂ vermindert, Pb-Ionen die Trägerwirkung von Ba(JO₃)₂ fördern, während Sr-Ionen sie unterdrücken. Pb²⁺ und Ba²⁺ vermehren die Bindung an der Oberfläche von Sr(JO₃)₂. — Es wurde versucht, diese Feststellungen als Ergebnis der Maskierung aktiver Adsorptionszentren des Pb(JO₃)₂ und Ba(JO₃)₂ unter den gegebenen Versuchsbedingungen zu deuten.

     

Radiochemical studies on charge and mass distribution in medium energy fission

Present status of work on charge and mass distribution in medium energy fission of compound nuclei produced using various target projectile combinations is reviewed. Systematics of charge distribution parameters and their dependence on excitation energy of the fissioning nucleus is presented. Variation of mass distribution with excitation energy and mass and charge of the fissioning nucleus is discussed. Qualitative explanation of the data has been sought in terms of existing theories of fission. The importance of charge and mass distribution studies in identifying the different reaction mechanisms in heavy ion induced reaction is highlighted.This article is dedicated to the memory of our beloved friend and colleague Dr. Tarun Datta who passed away on April 2, 1995.     

Stereoselective synthesis of conformationally constrained omega-amino acid analogues from pyroglutamic acid

Bicyclic lactams derived from pyroglutamic acid provide a useful scaffold for synthesis of conformationally restricted analogues of lysine, ornithine and glutamine, as well as an Ala-Ala dipeptide analogue. Amino alcohol and carboxylic acid derivatives are accessible from a common intermediate. In this strategy, the bicyclic lactam system not only controls, but also facilitates the determination of the stereochemistry of the synthetic intermediates.     

Design and synthesis of a new binucleating ligand via cobalt-promoted C-N bond fusion reaction. Ligand isolation and its coordination to nickel,palladium, and platinum

A new polydentate bridging ligand, NH(4)C(5)N=NC(6)H(4)N(H)C(5)H(4)N (HL(2)), is synthesized by the cobalt-mediated phenyl ring amination of coordinated NH(4)C(5)N=NC(6)H(5). The green cobalt complex intermediate [Co(L(2))(2)](ClO(4)), [1](ClO(4)), and the free ligand HL(2) were isolated and characterized. The X-ray structure of [H(2)L(2)](ClO(4)) is reported. The ligand, upon deprotonation, behaves as a bridging ligand. It reacts with NiCl(2).6H(2)O and Na(2)[PdCl(4)] to produce dimetallic complexes, [Ni(2)Cl(2)(L(2))(2)], 2, and [Pd(2)(L(2))(2)](ClO(4))(2), [3](ClO(4))(2), respectively. X-ray structures of these two dimetallic complexes are reported. The structure of the dinickel complex, in particular, is unique. In this complex, the two deprotonated secondary amine nitrogens of the two [L(2)](-) ligands bind to two nickel centers simultaneously forming a planar Ni(2)N(2) arrangement. The complex [3](ClO(4))(2) is diamagnetic while the complex 2 is paramagnetic. The results of magnetic measurements on the dinickel complex in the temperature range 1.8-300 K are reported. The system can be described as a single spin S = 2 in the low-temperature range T < J/k whereas at high temperatures, T > J/k, it behaves as two independent spins S = 1.The reaction of [L(2)](-) with K(2)[PtCl(4)], however, yielded a monometallic platinum complex, [PtCl(3)(L(2))], 5, where the pyridyl nitrogen of the aminopyridyl function remained unused. The X-ray structure of the complex 4a is reported. The bond lengths along the ligand backbones in all the complexes indicate extensive pi-delocalization. Spectral data of the complexes are reported and compared.     

Efficient one-pot synthesis of anti-HIV and anti-tumour β-carbolines

Thermal electrocyclisation of the azahexatriene system has been used as a key step for the synthesis of anti-HIV and anti-tumour compounds, harman, derivatives of harman and 1-aryl-β-carbolines. A one-pot reaction sequence was used to furnish these compounds in good yield.     

A proposed k0 based methodology for neutron activation analysis of samples of non-standard geometry

An internal mono-standard method has been proposed for multi element analysis. This method gives the relative concentration of the elements in a sample of non-standard shape and size. It utilizes an in-situ relative efficiency calibration and hence, does not need the cumbersome procedures, otherwise required to correct for -attenuation in the sample. To validate this method, the relative concentration of elements in IAEA RM's SL-3 and Soil-7 were analyzed with sample amounts ranging from a few milligrams to grams. The samples were counted in different non-specific geometries. The results are in good agreement with the recommended values, suggesting that this methodology could be applied for the analysis of samples of non-standard size and shape, and in principle, for the analysis of large samples.     

Synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone

Radical-mediated opening of a chiral trisubstituted epoxy alcohol using cp₂TiCl furnished the ‘2-methyl-1,3-diol’ moiety with the desired stereochemistry, which led to a total synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone 1.     

Kinetic and mechanistic studies on the interaction between glycylglycine and <Emphasis Type="Italic">cis</Emphasis>-diaqua-<Emphasis Type="Italic">bis</Emphasis>-(bipyridine)-ruthenium(II) complex in aqueous medium

The kinetics of interaction between glycylglycine and cis-[Ru(bipy)₂(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Ru(bipy)₂(H₂O) ₂ ²⁺ ], [diglycine] and temperature at a particular pH (4.8), where the substrate complex exists predominantly as the diaqua species and diglycine as the zwitter ion. The reaction has been found to proceed via two consecutive steps. The first step involves the ligand-assisted anation, while the second step involves chelation when the second aqua ligand is displaced. Rate constants have been evaluated and activation parameters calculated. The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both steps.     

Synthesis and biological activity of bridgehead nitrogen heterocycles

The reaction of 3-(2,4-dichlorophenyl)-5-mercapto 1,2,4–1H-triazole with α-haloketones and with 1,2-dibromoethane leading to the formation of fused heterocycles were carried out and the orientation of cyclization was studied. The reaction of 3-(2,4-dichlorophenyl)-5-mercapto-4-amino-1,2,4-s-triazole with α-haloketones     

Computing the maximum clique in the visibility graph of a simple polygon

In this paper, we present an algorithm for computing the maximum clique in the visibility graph G of a simple polygon P in O(n²e) time, where n and e are number of vertices and edges of G respectively. We also present an O(ne) time algorithm for computing the maximum hidden vertex set in the visibility graph G of a convex fan P. We assume in both algorithms that the Hamiltonian cycle in G that corresponds to the boundary of P is given as an input along with G.