Lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene: synthesis, characterization, and selective recognition of Hg2+ and its sensitivity toward pyrimidine bases

The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest.     

Ferrocene-containing carbohydrate dendrimers

Aliphatic amines, incorporating one or three (branched) acylated beta-D-glucopyranosyl residues, were coupled with the acid chloride of ferrocenecarboxylic acid and with the diacid chloride of 1,1'-ferrocenedicarboxylic acid to afford four dendrimer-type, carbohydrate-coated ferrocene derivatives in good yields (54-92%). Deprotection of the peracylated beta-D-glucopyranosyl residues was achieved quantitatively by using Zemplén conditions, affording four water-soluble ferrocene derivatives. When only one of the two cyclopentadienyl rings of the ferrocene unit is substituted, strong complexes are formed with beta-cyclodextrin in H2O, as demonstrated by liquid secondary ion mass spectrometry (LSIMS), 1H NMR spectroscopy, electrochemical measurements, and circular dichroism spectroscopy. Molecular dynamics calculations showed that the unsubstituted cyclopentadienyl ring is inserted through the cavity of the toroidal host in these complexes. The electrochemical behavior of the protected and deprotected ferrocene-containing dendrimers was investigated in acetonitrile and water, respectively. The diffusion coefficient decreases with increasing molecular weight of the compound. The potential for oxidation of the ferrocene core, the rate constant of heterogeneous electron transfer, and the rate constant for the energy-transfer reaction with the luminescent excited state of the [Ru(bpy)3]2+ complex (bpy = 2,2'-bipyridine) are strongly affected by the number (one or two) of substituents and by the number (one or three) of carbohydrate branches present in the substituents. These effects are assigned to shielding of the ferrocene core by the dendritic branches. Electrochemical evidence for the existence of different conformers for one of the dendrimers in aqueous solution was obtained.     

Recent progress in insertion and cyclopropanation reactions of metal carbenoids from α-diazocarbonyl compounds

Research on Chemical Intermediates - Metal–carbenoids from α-diazocarbonyl compounds are well-known reactive intermediates with a long history of useful applications in synthetic organic...     

Functionalized polynorbornene dielectric polymers: Adhesion and mechanical properties

Within the microelectronics industry, there is an ongoing trend toward miniaturization coupled with higher performance. High glass-transition temperature polynorbornenes exhibit many of the key performance criteria necessary for these demanding applications. However, homopolynorbornene exhibits poor adhesion to common substrate materials, including silicon, silicon dioxide, aluminum, gold, and copper. In addition, this homopolymer is extremely brittle, yielding less than 1% elongation-to-break values. To address these issues, the homopolymer was functionalized to improve adhesive and mechanical properties. Attaching triethoxysilyl groups to the polymer backbone substantially improved the adhesion, but at the cost of increasing the dielectric constant because of the polarity of the functional group. Alkyl groups were also added to the backbone, which decreased the rigidity of the system, and resulted in significantly higher elongation-to-break values and a decrease in residual stress. The addition of an alkyl group slightly decreased the dielectric constant of the polymer as a result of an increase in molar volume. The coefficient of thermal expansion and modulus are also reported for the polynorbornene functionalized with triethoxysilyl groups using a multiple substrate approach. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3003–3010, 1999     

Electron transfer free radical mechanism in the reactions of arenediazonium cations with grignard reagents

The major pathway in the reactions of arenediazonium cations with certain Grignard reagents is found to involve an electron transfer from the latter to the π-system of the former reactant and radicals are the immediate precursors of the final products.     

D-branes on Calabi–Yau Manifolds and Superpotentials

We show how to compute terms in an expansion of the world-volume superpotential for fairly general D-branes on the quintic Calabi-Yau using linear sigma model techniques, and show in examples that this superpotential captures the geometry and obstruction theory of bundles and sheaves on this Calabi-Yau.Louis Michel Professor     

Morphological studies of blends of conjugated polymers and acceptor molecules using langevin dynamics simulations

We use coarse‐grained Langevin dynamics simulations of blends of generic conjugated polymers and acceptor molecules to show how architecture (e.g., side chains, backbone flexibility of oligomers) and the pair‐wise interactions between the constituents of the blend affect morphology and phase transition. Alkyl side chains on the conjugated oligomer backbones shift the liquid crystal (LC) transition temperature from that of bare conjugated backbones and the direction of the shift depends on backbone–backbone interactions. Rigid backbones and constrained side chains cause a layer‐by‐layer morphology of conjugated polymers and amorphous acceptors, whereas flexible backbones and unconstrained side chains facilitate highly ordered acceptor arrangement. Strong backbone–backbone attraction shifts LC transition to higher temperatures than weak backbone–backbone attraction, and strong acceptor–acceptor attraction increases acceptor aggregation. Pure macro‐phase separated domains form when all pair‐wise interactions in the blend are strongly attractive, whereas interconnected domains form at intermediate acceptor–acceptor attraction and strong polymer–polymer attractions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Enantio- and diastereodifferentiating cis,trans-photoisomerization of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid derivatives in organized media

[reaction: see text] Four methods of asymmetric induction in the cis, trans-photoisomerization of 2beta, 3beta-diphenylcyclopropane-1alpha-carboxylic acid derivatives were studied. Best results (ca. 80% de) were obtained by irradiation of chiral esters, amides, and salts in NaY and LiY zeolites and in the pure crystalline state.     

Photolysis of gamma-(alpha-carboxy-2-nitrobenzyl)-L-glutamic acid investigated in the mcrosecond time scale by time-resolved FTIR

The photolytic release of substrates from caged substrates has proven to be an excellent method to generate concentration jumps for kinetic measurements in the microsecond time scale. In this report we use time-resolved FTIR in the step-scan mode to probe the photolysis mechanism of one such caged compound, namely gamma-(alpha-carboxy-2-nitrobenzyl)glutamate, and to obtain a direct measure of the rate of photorelease of the substrate glutamate. The time-resolved difference FTIR spectra exhibit specific signals that can be assigned to the reactant caged glutamate, photolytically released product glutamate, as well as to the aci-nitro intermediate, the key intermediate of the photolysis reaction. Therefore these signals allow the characterization of the kinetics of formation and decay of the intermediate and products. This is the first such report that provides a direct determination of the rate of formation of the photolysis product from a caged compound in the microsecond time scale. Furthermore, the results presented provide a good basis for further time-resolved FTIR studies of molecular reaction mechanisms, such as ligand protein interactions, in the microsecond time scale through the photolytic release of substrates from caged compounds.     

Monte carlo simulations of polydisperse polymers grafted on spherical surfaces

This article presents effects of polydispersity in polymers grafted on spherical surfaces on grafted polymer chain conformations, grafted layer thickness, and free‐end monomer distribution within the grafted layer. At brush‐like grafting densities, as polydispersity index (PDI) increases, the scaling exponent of radius of gyration of grafted chains approaches that of a single chain grafted on the same nanoparticle, because polydispersity alleviates monomer crowding within the brush. At high PDI, the chains shorter than the number average chain length, N_n, have more compressed conformations, and the chains longer than N_n overall stretch less than in the monodisperse case. As seen in polydisperse flat brushes at high grafting densities, the grafted layer thickness on spherical nanoparticle increases with PDI. Polydispersity eliminates the region near the surface devoid of free‐end monomers seen in monodisperse cases, and it reduces the width of free‐end monomer distribution and shifts the free‐end monomer distribution close to the surface. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012