Remarks on the algebraic approach to intersection theory

The purpose of this paper is to study the solutions ofr algebraic (homogeneous) equations in projectiven-space counted with multiplicities given by the length of well-defined primary ideals. Hence we need an extension of the algebraic approach to the intersection theory given in [20]. Also, we will prove that our intersection numbers of irreducible components coincide with the multiplicities of the obvious primary ideals in the obvious local ring of the join-variety.     

Self-consistent calculation of 1s2s3S state of helium and heliumlike ions

In this paper we present a simple method within the coupled Hartree–Fock framework to calculate the 1s2s ³S state of helium and heliumlike ions. The results are in very good agreement with those obtained by the use of multiterm correlated wave functions. Some interesting observations associated with the wave function are presented.     

Thermodynamics of Aqueous Solutions of 18-Crown-6 at 298.15 K: Enthalpy and Entropy Effects

We reported previously activity and activity coefficient data for aqueous solutions of 18-crown-6 (18C6) in the concentration range of 0.1–2.0 mol-kg⁻¹ at 298.15 K. The results were interpreted in terms of the binding of four water molecules (two bridged and two singly H-bonded) inside the 18C6 cavity having a D_3d conformation. In this work, we report our thermodynamic analysis of the Gibbs energy and enthalpy data (obtained using enthalpy virial data from literature) in aqueous solutions of 18C6 at 298.15 K. The excess enthalpy and Gibbs energy parameters are computed and further used to obtain excess entropies of solutions as a function of 18C6 concentration. The same data are utilized to compute the partial molar entropies of solvent and solute at finite, as well as at infinite, dilution of 18C6 in water. It is observed that ΔG_mix, ΔH_mix and TΔS_mix values are all negative, whereas ΔG^E values show a slightly positive variation as a function of the 18C6 concentration. The partial molar excess entropy of water, ( , decreases (becomes negative) whereas that of 18C6, ( , increases with a increase in the 18C6 concentration. These results are explained in terms of various effects, which include water structure making, incorporation of water molecules in the crown cavities and crown–crown hydrophobic interactions, which persist even at the lowest concentration studied.     

1,3-Dipolar cycloaddition reaction of D-glucose-derived nitrone with allyl alcohol: synthesis of 2-hydroxy-1-deoxycastanospermine analogues

[reaction: see text] The synthesis and evaluation of glycosidase inhibitory activity of polyhydroxylated indolizidine alkaloids namely 2-hydroxy-1-deoxycastanospermine 3a,b and 2-hydroxy-1-deoxy-8a-epi-castanospermine 3c,d is reported. The key step involves the intermolecular 1,3-dipolar cycloaddition of allyl alcohol to d-glucose-derived nitrone 4, followed by tosylation, that afforded four diastereomeric sugar-substituted isoxazolidines 5a-d with the desired regioselectivity. The one-pot conversion of 5a-d to pyrrolidines 8a-d by hydrogenolysis, removal of 1,2-acetonoide functionality, and hydrogenation afforded corresponding target molecules 3a-d.     

Benzophenone-sensitized photopolymerization of methyl methacrylate using dimethyl aniline–maleic acid combination as photoinitiator

Benzophenone (BP)-sensitized photopolymerization of methyl methacrylate (MMA) in near UV/visible light was studied at 40°C using dimethylaniline maleic acid (DMA—MA) combination as the photoinitiator. An instantaneous 1:1 complexation between DMA and MA takes place when they are mixed together in acetonitrile. Also, instantaneous complex formation occurs between DMA and MMA and between MA and MMA when they are dissolved in MMA in low concentrations, separately. Interestingly, when equimolar proportions of DMA and MA are mixed together in MMA, there is indication for further instantaneous complexation between (DMA—MMA) complex and (MA—MMA) complex forming the actual initiating species in the photopolymerization system. Initiator exponent was 0.28 and monomer exponent varied between 0.0 to 1.8 depending on the nature of the solvent and range of dilution used. Analysis of kinetic data indicates a free radical mechanism for the polymerization with initiator-dependent termination. Chain termination via degradative initiator transfer is quite significant; but the degradative effect becomes much less prominent in the higher range of initiator concentration indicating that the reinitiation reaction following the initiator transfer process assumes more proportionate significance as the initiator concentration is increased, probably as a result of higher reinitiation efficiency. Polymers obtained gave evidence for the incorporation of aromatic (amine) end groups in them.     

Redox reactions of uranium hexafluoride. Comparison with phosphorus pentafluoride and preparation of copper(I) hexafluorouranate(V) [1]

Molecular iodine is oxidised by phosphorus pentafluoride in iodine pentafluoride at room temperature giving I₂⁺, PF₆^?, and PF₃. I₂⁺ is formed from uranium hexafluoride under similar conditions, but further oxidation occurs depending on the reaction stoicheiometry used. In all cases uranium pentafluoride is formed. Copper(II) fluoride reacts with UF₅ in acetonitrile at room temperature to give copper(II) hexafluorouranate(V), which is reduced by copper metal to give the copper(I) salt. The latter compound is formed from UF₆ and Cu metal, via the Cu^II salt, only if a fresh Cu surface is used for the reduction step.     

Selective sulfonylation of 4-C-hydroxymethyl-β-l-threo-pento-1,4-furanose: synthesis of bicyclic diazasugars

Hydroxymethylation of α-d-xylo-pentodialdose 6 using excess formaldehyde and sodium hydroxide in THF-water (one pot aldol and crossed Cannizzaro reactions) followed by hydrogenolysis of C3-O-benzyl group afforded triol 8. The regio-selective α- and β-sulfonylation of hydroxymethyl groups in 8 afforded 9a (α-sulfonylation) and 14 (β-sulfonylation) in good yield. The cleavage of the 1,2-acetonide functionality, individually in 9a and 14, followed by reaction with 1,3-diaminopropane gave in situ formation of sugar aminals, that undergo concomitant nucleophilic displacement of the sulfonyloxy group by amino functionality to give hitherto unknown bicyclic diazasugars 4 and 5, respectively, with a hydroxymethyl substituent at C-7.     

Investigations of the solvent polarity effect on the photophysical properties of coumarin-7 dye

Photophysical investigations of coumarin-7 (C7) dye in different solvents using absorption, steady-state fluorescence and time-resolved fluorescence measurements reveal the behavioral changes of the dye in nonpolar and other solvents. In moderate to higher polarity solvents, the experimental parameters such as fluorescence quantum yield (Phif), fluorescence lifetime (tauf), radiative rate constant (k(f)), nonradiative rate constant (k(nr)) and Stokes' shift (Deltav) follow almost linear correlations with the Lippert-Mataga solvent polarity parameter Deltaf but show unusual deviations in nonpolar solvents. From the observed results, it is inferred that the dye exists in a planar intramolecular charge transfer structure in moderate to higher polarity solvents, but in nonpolar solvents, the dye exists in a nonplanar structure with its 7-NEt2 group adopting a pyramidal type of configuration. Unlike some of the other coumarin dyes, namely coumarin-120 (C120) (4-CH3-7-NH2-1,2-benzopyrone) and coumarin-151 (C151) 4-CF3-7-NH2-1,2-benzopyrone), which also show similar structural changes in nonpolar and other solvents, the C7 dye does not show any activation-controlled deexcitation process in nonpolar solvents. This is attributed to the very slow flip-flop motion of the 7-NEt2 group of the C7 dye in comparison with the very fast flip-flop motion of the 7-NH2 group in the C120 and C151 dyes. Qualitative potential energy diagrams are presented to rationalize the observed results of C7 dye and to compare these with those of the other dyes such as C120 and C151. A support for the observed results and interpretation has also been obtained from quantum chemical calculations on the structures of the C7 dye.     

Effect of fluorine substitution on the OH-radical-induced electron-transfer reaction in aqueous solutions of fluorinated alkyl iodides

The transient optical absorption bands formed at λ_max=340 and 435 nm, on reaction of ^√OH radicals in aerated acidic aqueous solutions of 1,1,1-trifluoro-2-iodoethane at low and high solute concentration, have been assigned to monomer and dimer radical cations, respectively. The deprotonation of the solute radical cations is the rate-determining step for the decay of the dimer radical cations. The stability constant for the dimer radical cation is determined to be 50 dm³ mol⁻¹ at 25°C. The dimer radical cation is a strong one-electron oxidant. Quantum chemical calculations and experimental results confirm that fluorine reduces the electron density at iodine and the ^√OH-radical-induced oxidation of fluoroiodoalkanes becomes a difficult process compared to iodoalkanes.     

Synthesis and evaluation of the glycosidase inhibitory activity of 5-hydroxy substituted isofagomine analogues

An efficient strategy for the synthesis of 5-hydroxy substituted isofagomine analogues and , having both -CH2OH/CH3 and -OH functionality at the C-5 position, and evaluation of their inhibitory potency is reported. The synthetic methodology involves the aldol-Cannizzaro reaction of easily available alpha-d-xylopentodialdose followed by hydrogenolysis to afford the triol . Selective amidation of the alpha- and beta-hydroxymethyl group at C-4, deprotection of the 1,2-acetonide group and hydrogenation gave the target molecules, which were found to be potent against beta-glycosidases with IC50 values in the micro molar range. Compound showed excellent potency against glycosidases and human salivary amylase.