• Volume 116, Issue 2

      March 2004,   pages  65-129

    • A lanthanum pyromellitate coordination polymer with three-dimensional structure

      S V Ganesan Srinivasan Natarajan

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      A new three-dimensional metal-organic coordination polymer, [La2(H2O)2(H2BTEC)(BTEC)], 1, was hydrothermally synthesized and characterized by single crystal X-ray diffraction. The three-dimensional framework is built up from La2O16 dimers connected by carboxylate anions. The polymer exhibits strong photoluminescence at room temperature with the main emission band at 390 nm (λex = 338 nm). Crystal data: triclinic, space group P(−1),a = 6.4486(3),b = 9.4525(5),c = 9.6238(5) Å, α= 88.24(1), β = 74.67(2), γ= 76.76(1)°,V = 550.45(5)

    • Covalently linked bisporphyrins bearing tetraphenylporphyrin and perbromoporphyrin units: Synthesis and their properties

      Puttaiah Bhyrappa V Krishnan

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      A series of covalently linked bisporphyrins bearingmeso-tetraphenylporphyrin (TPP) and octabromotetraphenylporphyrin (OBTPP) units have been synthesised and characterised. Electrochemical studies on these bisporphyrins showed an anodic shift (∼ 30–60 mV) of the TPP unit and a cathodic shift (∼40-80 mV) of OBTPP in redox potentials. Further, steady-state fluorescence studies on bisporphyrins indicated dramatic decrease in fluorescence quantum yields of the TPP moiety. Electrochemical redox and fluorescence data seem to suggest the possible existence of intramolecular interactions in these bisporphyrins

    • Yamogenin 3-o-β-D-glucopyranosyl (1 → 4)-o-α-D-xylopyranoside from the seeds ofTrigonella foenum-graecum

      V K Saxena Albert Shalem

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      Trigonella foenum-graecum (NO-Leguminosae) is cultivated in many parts of India. It has been found to possess significant medicinal value. Its leaves are used both internally and externally to reduce swelling, prevent falling of hair and in treating burns. Its seeds are carminative, antipyretic, anthelmintic and diuretic, and are also useful in treatment of dropsy, chronic cough, heart diseases, bronchitis, piles and small pox. This plant also possesses antidiabetic property.

      The present communication deals with the isolation and identification of steroidal saponin SA-III, characterised as yamogenin 3-O-β-D-glucopyranosyl (1 → 4)-O-α-D-xylopyranoside, which was isolated from the seeds ofTrigonella foenum-graecum.

    • Molecular orbital studies on the Wagner-Meerwein migration in some acyclic pinacol—pinacolone rearrangements

      Zodinpuia Pachuau R H Duncan Lyngdoh

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      The semi-empirical PM3 SCF-MO method is used to investigate the Wagner-Meerwein migration of various groups during the pinacol-pinacolone rearrangement of some acyclic systems. Pinacol first protonates and dehydrates to form a carbocation that undergoes a 1,2-migration to form a protonated ketone, which then deprotonates to yield the pinacolone product. We study the Wagner-Meerwein migration of hydride, methyl, ethyl, isopropyl,t- butyl, phenyl and heterocylic 2-, 3-and 4-pyridyl groups in various acyclic 1,2-diol (pinacol) systems as they rearrange to pinacolones. This 1,2-migration involves a three-centred moiety in the cationic transition state. The migratory aptitude predicted here follows the order: hydride >t-butyl > isopropyl > ethyl > methyl > phenyl, which accords well with available experimental data and/or chemical intuition, reflecting also on the ability of the group involved to carry positive charge in the transition state. The structure of the migrating group (whether aliphatic or aromatic) within the transition state also supports the stabilising role of delocalisation of positive charge for reaction feasibility. Geometrical and thermodynamic considerations coincide in assigning the following order to relative “earliness” of the transition state along the reaction pathway:t-butyl > isopropyl > phenyl > methyl > 2-pyridyl > 4-pyridyl

    • Topological estimation of cytotoxic activity of some anti-HIV agents: HEPT analogues

      Vijay K Agrawal Kamlesh Mishra Ruchi Sharma P V Khadikar

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      QSAR studies on anti-HIV cytotoxic activities of a series of HEPT(1-[(2-hydroxyethoxy) methyl]-6-(phenylthio)-thymine) analogues have been discussed. The molecular descriptors used being van der Waals volume(Vw) and equalized electronegativity (χeq). Thein vitro cytotoxicities (pCC50) were modelled using these parameters. It was observed that upon introduction of indicator parameters statistically excellent models are obtained. The predictive power of the models was examined using a cross-validation method

    • Kinetics and mechanism of the oxidation of some neutral and acidic α-amino acids by tetrabutylammonium tribromide

      Raghvendra Shukla Pradeep K Sharma Kalyan K Banerji

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      The oxidation of eleven amino acids by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid results in the formation of the corresponding carbonyl compounds and ammonia. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with some of the amino acids while others exhibit second-order dependence. It failed to induce polymerization of acrylonitrile. The effect of solvent composition indicate that the rate of reaction increases with increase in the polarity of the medium. Addition of tetrabutylammonium chloride has no effect on the rate of oxidation. Addition of bromide ion causes decrease in the oxidation rate but only to a limiting value. The reaction is susceptible to both polar and steric effects of the substituents. A suitable mechanism has been proposed

    • Isopropylation of benzene with 2-propanol over substituted large pore aluminophosphate-based molecular sieves

      K Joseph Antony Raj V R Vijayaraghavan

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      Large pore aluminophosphate-based molecular sieves like AlPO4-5, MAPO-5, MnAPO-5 and ZAPO-5 were synthesised hydrothermally using triethylamine as a structure directing agent. These materials were characterised by X-ray diffraction (XRD),27A1 and31P MAS-NMR, ICP-MS,n-butylamine-TPD, BET and SEM. The catalytic performance of these materials was tested for isopropylation of benzene with 2-propanol at 250, 300, 350 and 400°C. The products were cumene,p-DIPB (p-diisopropylbenzene) andm-DIPB (m-diisopropylbenzene). MnAPO-5 was found to be more active than the other catalysts. Maximum conversion (20%) was noted at 350°C over MnAPO-5. The selectivity to DIPB was found to decrease with time on stream but the selectivity to cumene showed an increase after 3 h of time on stream

    • Dye-sensitized photopolymerization of N,N′-methylenebisacrylamide by initiation with eosin-ascorbic acid system

      Parthasarathy Tigulla Uma Vuruputuri

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      The dye-sensitized photopolymerization of N,N′-methylenebisacrylamide (MBA) in aqueous medium initiated by eosin-ascorbic acid (AH2) was studied at 25°C. The polymerization takes place only at higher concentration of AH2 (> 10−3 mol/L) and its rate increases rapidly as [AH2] is increased. The rate of polymerization is proportional to [MBA] and [AH2]. Kinetic results indicate that semi-quinone (DH) dye radical and semi-oxidized form ($$\mathop {\mathop A\limits^ \bullet }\limits^ - $$) of ascorbic acid are unable to initiate polymerization. Formation of H2O2 is proposed and confirmed. A suitable mechanism is proposed in accordance with experimental results obtained

    • Adsorption dynamics and equilibrium studies of Zn (II) onto chitosan

      G Karthikeyan K Anbalagan N Muthulakshmi Andal

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      Batch equilibration studies are conducted to determine the nature of adsorption of zinc (II) over chitosan. The factors affecting the adsorption process like particle size, contact time, dosage, pH, effects of chloride and nitrate are identified. The influence of temperature and co-ions on the adsorption process is verified. The fraction of adsorption,Yt and the intraparticle diffusion rate constant,kp are calculated at different environments and the results are discussed. The nature of adsorption of the zinc (II)-chitosan system is explained using Freundlich, Langmuir isotherms and thermodynamic parameters

    • Erratum

      Amita Wadehra B M Deb

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