Photoacoustic studies on two new organic NLO materials: L‐threonine and L‐prolinium tartrate

Photoacoustic spectroscopy (PAS) is a non‐destructive testing (NDT) tool and used here for analyzing the physical properties such as thermal diffusivity, thermal diffusion length, thermal conductivity and thermal effusivity of L‐Threonine and L‐Prolinium tartrate. These two crystals belong to a group of recently developed NLO materials, in our laboratory. The single crystals of the two compounds were grown by using submerged seed solution growth method. Characterization of the crystals was made by using single crystal X‐ray diffraction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Visual observation of avidin-biotin affinity by fluorescent G4.5 poly(amidoamine) dendrimer

An air-treated G4.5 poly(amidoamine) (PAMAM) dendrimer displayed the enhanced fluorescence enough to be utilized as a fluorescence marker to visualize avidin-biotin affinity: On a fluorescence microscopic image, the avidin labeled by a fluorescent G4.5 PAMAM dendrimer was observed to be selectively bound on the biotin pattern that was prepared by amide-bonding of biotin on a carboxylic acid-terminated self-assembled monolayer and in turn by UV-irradiation with a photomask on the monolayer.     

Exhibition of low hyperfine coupling constant for copper(II) in magnesium rubidium sulphate hexahydrate

Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g₁₁=2.133, g₂₂=2.137, g₃₃=2.327, A₁₁=0.01, A₂₂=1.44 and . The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx²-y² ground state with dz² excited state. Bonding parameters, κ=0.254, , α²=0.706, α=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example.     

The role of crosslinking and polarity in the dark relaxation of azobenzene-based,polymer-stabilised cholesteric liquid crystals

Prior examinations have reported that polymer stabilisation of azobenzene-based cholesteric liquid crystal (CLC) mixtures can reduce the time necessary for complete colour restoration in the dark from three days to as few as five minutes. This work extends upon these prior examinations by exploring and elucidating the role of crosslinker concentration and monomer polarity on the colour restoration of a representative CLC mixture composed of a high HTP bis(azo) binapthanyl chiral dopant (QL76) mixed into the cyanobiphenyl nematic liquid crystal host MDA-00-1444. The impact of these variables was unexpectedly convoluted. In all the formulations examined here, polymer stabilisation dramatically reduces the time for complete colour restoration of the starting reflection notch. In mixtures based on nonpolar liquid crystal monomers, increasing the crosslinker concentration reduces the time necessary for complete colour restoration. However, the dependence on crosslinker concentration reverses in mixtures composed from polar liquid crystal monomers in which increasing the crosslinker concentration serves to increase the time necessary for complete colour restoration.     

Synthesis and Crystal Structure of [C10N2H10]2[P2Mo5O21(OH)2]·2H2O

The crystal structure of [C₁₀N₂H₁₀]₂[P₂Mo₅O₂₁(OH)₂] · 2H₂O, contains the heteropolyanion, [P₂Mo₅O₂₁(OH)₂]^4—, together with diprotonated 4, 4′‐bipyridine. The heteropolyanion is built up from five MoO₆ octahedra sharing four common edges and one common corner, capped by two PO₃(OH) tetrahedra. The structure is stabilized by hydrogen bonds involving the hydrogen atoms of the 4, 4′‐bipyridine, water molecules and the oxygen atoms of the pentamolybdatobisphosphate. This is the first example that this kind of cluster could be isolated in the presence of a poly‐functional aromatic molecule ion. Crystal data: triclinic, P1¯ (No. 2), a = 9.983(2)Å, b = 11.269(2)Å, c = 17.604(4)Å, α = 73.50(3)°, β = 84.07(3)°, γ = 67.96(3)°; V = 1760.0(6)ų; Z = 2; R₁ = 0.037 and wR₂ = 0.081, for 9138 reflections [I > 2σ(I)].     

Redox and antimicrobial studies of transition metal(II) tetradentate Schiff base complexes

Neutral tetradentate chelate complexes of Cu^II, Ni^II, Co^II, Mn^II, Zn^II and VO^II have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, i.r., u.v.–vis., ¹H-n.m.r. and e.s.r. spectral techniques were used to confirm the structures of the chelates. Electronic absorption and i.r. spectra of the complexes suggest a square-planar geometry around the central metal ion, except for VO^II and Mn^II complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the Cu^II complexes in MeCN show two waves for copper(II) copper(III) and copper(II) copper(I) couples, whereas the VO^II complexes in MeCN show two waves for vanadium(IV) vanadium(V) and vanadium(IV) vanadium(III) couples. The e.s.r. spectra of the Cu^II, VO^II and Mn^II complexes were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the investigated compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae, Bacillus subtilis, Shigella flexneri, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands.     

Interfacial regions governing internal cavities of dendrimers. Studies of poly(alkyl aryl ether) dendrimers constituted with linkers of varying alkyl chain length

This report deals with a study of the properties of internal cavities of dendritic macromolecules that are capable of encapsulating and mediating photoreactions of guest molecules. The internal cavity structures of dendrimers are determined by the interfacial regions between the aqueous exterior and hydrocarbon like interior constituted by the linkers that connect symmetrically sited branch points constituting the dendrimer and head groups that cap the dendrimers. Phloroglucinol-based poly(alkyl aryl ether) dendrimers constituted with a homologous series of alkyl linkers were undertaken for the current study. Twelve dendrimers within first, second, and third generations, having ethyl, n-propyl, n-butyl, and n-pentyl groups as the linkers and hydroxyl groups at peripheries in each generation, were synthesized. Encapsulation of pyrene and coumarins by aqueous basic solutions of dendrimers were monitored by UV-vis and fluorescence spectroscopies, which showed that a lower generation dendrimer with an optimal alkyl linker presented better encapsulation abilities than a higher generation dendrimer. Norrish type I photoreaction of dibenzyl ketone was carried out within the above series of dendrimers to probe their abilities to hold guests and reactive intermediate radical pairs within themselves. The extent of cage effect from the series of third generation dendrimers was observed to be higher with dendrimers having an n-pentyl group as the linker.     

The Bott-Borel-Weil Theorem for direct limit groups

We show how highest weight representations of certain infinite dimensional Lie groups can be realized on cohomology spaces of holomorphic vector bundles. This extends the classical Bott-Borel-Weil Theorem for finite-dimensional compact and complex Lie groups. Our approach is geometric in nature, in the spirit of Bott's original generalization of the Borel-Weil Theorem. The groups for which we prove this theorem are strict direct limits of compact Lie groups, or their complexifications. We previously proved that such groups have an analytic structure. Our result applies to most of the familiar examples of direct limits of classical groups. We also introduce new examples involving iterated embeddings of the classical groups and see exactly how our results hold in those cases. One of the technical problems here is that, in general, the limit Lie algebras will have root systems but need not have root spaces, so we need to develop machinery to handle this somewhat delicate situation.

     

Gibbs Sampling with Diffuse Proper Priors: A Valid Approach to Data-Driven Inference?

Abstract

This article demonstrates by example that the use of the Gibbs sampler with diffuse proper priors can lead to inaccurate posterior estimates. Our results show that such inaccuracies are not merely limited to small sample settings.     

Implementation of the virtual element method for coupled thermo-elasticity in Abaqus

Numerical Algorithms - In this paper, we employ the virtual element method for the numerical solution of linear thermo-elastic problems in two dimensions. The framework is implemented within the...