Substitution reactions under NH3 chemical ionization conditions in cis-/trans-1,2-dihydroxybenzosuberans

The nucleophilic substitution reaction under NH₃ chemical ionization (CI) conditions in cis- and trans-1,2-dihydroxybenzosuberans (1–4) has been studied with the help of ND₃ CI and metastable data. The results indicate that in the parent diols 1 (cis) and 2 (trans), the substitution ion [M_sH]⁺, is produced mainly by the loss of H₂O from the [MNH₄]⁺ ion (S_Ni reaction) while in their 7-methoxy derivatives 3 and 4, the ion-molecule reaction between [M? OH]⁺ and NH₃ seems to be the major pathway for the formation of [M_sH]⁺. The substitution ion from 1 and 2 and the [MH]⁺ ion from trans-1-amino-2-hydroxybenzosuberan give similar collision-induced dissociation mass-analysed ion kinetic energy spectra. Interestingly, their diacetates do not undergo the substitution reaction.     

Membrane oscillations involving electrokinetic phenomena

Semi theoretical models have been proposed to account for the mechanism of membrane oscillations involving, electrokinetic phenomena in systems where (i) concentration difference deltaC is finite and deltaP is varying but the current is fixed, and (ii) deltaC=0, pressure difference deltaP is fixed across the membrane and imposed current is fixed. The formalism leads to the van der Pol equation in both cases. Computer simulation has also been attempted, which indicates oscillations in the former case.     

Organic solid-state reactions

The role of voids and cracks in solid-state reaction between 8-hydroxyquinoline and phthalic anhydride has been investigated. 8-hydroxyquinoline reacts with phthalic anhydride both in solution and in solid state, forming a 1:1 yellow-colored complex. X-ray diffraction studies prove that the complex obtained from the solid-state reaction is the same as that obtained from solution. Several techniques have been used to study the kinetics of the reaction in the solid state. Kinetic studies by capillary technique showed that surface migration is the mode of diffusion of reactant concerned. Dilatometric technique confirms the formation of cracks and voids in the systems and shows that the reaction is propagated through the channels.     

Identification of novel alpha-glucosidase inhibitors by screening libraries based on N- [4-(benzyloxy) benzoyl] alanine derivatives

A library of 72 compounds related to N- [4-(benzyloxy) benzoyl]alanine (I) was synthesized, prepared and screened for alpha-glucosidase inhibitory activity. Four compounds showed potent inhibition, six compounds moderate inhibition, and 16 were weak inhibitors. One compound, N- [4-(benzyloxy) benzoyl] serine, was found to be a potent inhibitor of alpha-glucosidase with 100% inhibition at 1 micro M. This inhibitor was at least five times more potent than the lead compound I.     

α-Hydroxymethylation of conjugated nitroalkenes via the Morita-Baylis-Hillman reaction

The Morita-Baylis-Hillman reaction (MBHR) of conjugated nitroalkenes has been successfully carried out for the first time. A variety of aromatic and heteroaromatic nitroalkenes react with formaldehyde at room temperature in the presence of stoichiometric amounts of imidazole and catalytic amounts of anthranilic acid in THF providing moderate to good yields of the multifunctional adducts in most of the cases.     

Identification of inhibitors of DNA topoisomerase II from a synthetic library of glycoconjugates

A library of 24 glycoconjugates related to glycosylated beta-amino acid derivative (I) was been prepared and screened against DNA topoisomerase-II of the filarial parasite S. cervi. Among these, compound 6 was found to be a potent inhibitor of DNA topoisomerase-II with 95% inhibition at 1.09 microM. Furthermore, compound 6 was at least three times more potent than the lead compound, glycosylated beta-amino acid derivative I.     

An experimental and theoretical study of excited-state dipole moments of some flavones using an efficient solvatochromic method based on the solvent polarity parameter, E(N)(T)

The electronic absorption and fluorescence spectra of some biologically active natural flavones have been recorded at room temperature (298 K) in solvents of different polarities. The effects of the solvents upon the spectral properties are discussed. Difference in fluorescence intensity of flavones has been explained on the basis of intersystem crossing and degree of non-planarity calculated theoretically using Austin Model 1 (AM1) method. Excited-state dipole moments have been determined using the solvatochromic method based on the microscopic solvent polarity parameter, E(N)(T). A reasonable agreement has been observed between experimental and AM1 calculated dipole moment changes. Our results are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with microscopic solvent polarity parameter, E(N)(T) is superior to that obtained using bulk solvent polarity functions for all the systems studied here.     

Normal vibrations and their dispersion in syndiotactic polystyrene

Normal modes and their dispersion are obtained for syndiotactic polystyrene (sPS) in the planar zigzag and s(2/1)2 helical conformations. Comparison is made with the spectra of isotactic polystyrene (ips) to identify the conformation-sensitive modes; for example, the 1221 cm^?1 mode is identified as a skeletal mode sensitive to chain structure and it also shows maximum dispersion. Bunching of dispersion curves and their intersection are among the characteristic features which are discussed. A check on the dispersion curves below 400 cm^?1 is made from the spectra of polystyrene oligomers.     

Substituted Diorganotin(IV) O,O’-Alkylene Dithiophosphates: Synthesis and Spectral Aspects

Six new substituted diphenyltin(IV) O,O′-alkylene dithiophosphates, (C₆H₅)₂Sn(X)S(S) POGO [G = —CH₂C(CH₃)₂CH₂—, X = Cl (1), SCN (3), ClO₄ (5); G = —CH₂C (C₄H₉)(C₂H₅)CH₂—, X = Cl (2), SCN (4), ClO₄ (6)], were synthesized by the reaction of the corresponding ammonium salts of the O,O’-alkylene dithiophosphates with an appropriate organotin(IV) chloride. The compounds were characterized on the basis of elemental and spectral analyses (ESI mass spectrometry, IR, ¹H, ¹³C, ³¹P, and ¹¹⁹Sn NMR). The presence of a four-coordinated Sn atom and monodentate O,O’-alkylene dithiophosphate moiety in compounds 1–4 as well as bidentate O,O’-alkylene dithiophosphate unit in compounds 5,6 is established.     

A Hemi‐metallocene Chromium Catalyst with Trimethylaluminum‐Free Methylaluminoxane for the Synthesis of Disentangled Ultra‐High Molecular Weight Polyethylene

Recently, it has been shown that by using a single‐site catalytic system having titanium as a metallic center, it is possible to tailor the entanglement density in the amorphous region of a semi‐crystalline ultra‐high molecular weight polyethylene (UHMWPE). This route provides the possibility to make high‐modulus, high‐strength uniaxially and biaxially drawn tapes and films, without using any solvent during processing. In this publication, it is shown that a single‐site catalyst having chromium as metallic center, proposed by Enders and co‐workers, can also be tuned to provide control on the entanglement density during synthesis of the UHMWPE. However, to achieve the goal some modifications during the synthesis are required. The synthesized polymers can be processed in the solid state below the equilibrium melting temperature, resulting in uniaxially drawn tapes having tensile strength and modulus greater than 3.5 N/tex and 200 N/tex, respectively. Rheological studies have been performed to follow the increase in entanglement density in melt state with time.