UV Radiation Effects on SiO2 Gels Doped with Organic Dyes

Silica gels prepared by the sol-gel method with TEOS as a precursor and doped with the organic dyes rhodamine B, Na fluoresceine and eosine G were exposed to UV radiation pulses from a nitrogen laser. The absorption, luminescence and IR spectra were taken as a function of the exposure time. The absorption and the luminescence curves show successive maxima and minima. The same response is observed when the exposure procedure is repeated. These results are explained in terms of the cyclic filling and depletion of the long-lived triplet excited electronic state. At short exposure times, the data can be fitted with a Lorentzian curve and the corresponding parameters are given.     

Amperometric PMMA-microchip with integrated gold working electrode for enzyme assays

The use of a gold film in-channel detector combined with a poly(methyl methacrylate) (PMMA) CE microchip has been tested for alkaline phosphatase (AP) enzymatic assays. Tris-borate or Tris-Gly (pH 9.0, 50 mmol L^–1) buffer solutions were appropriate as running buffer. Signals for three common AP products: -naphthol, p-nitrophenol, and ascorbic acid, were obtained. They were reproducible (RSD 4.4% for six successive electropherograms corresponding to 5 mmol L^–1 -naphthol solution) and the response was dependent on concentration (linear relationship for ascorbic acid solutions between 5 and 20 mmol L^–1 concentration). Use of an end-channel gold film electrode was also investigated. If one of the reagents (substrate or enzyme) is included in the running buffer, two different types of enzymatic assay are feasible in less than 3 min.     

Potential energy surfaces in algebraic molecular models using coherent states

The potential energy surfaces provided by the coherent states formalism for the case of interacting one-dimensional oscillators is investigated. The case of two interacting oscillators modelled with Morse potentials are considered in detail. First the traditional treatment is presented in order to identify the need to establish a new transformation between the parameters and the classical variables that allow the full Hamiltonian to be recovered. To this end the connection between the su(2) algebraic model and the usual treatment in configuration space was taken into account. It is shown that the coherent state approach when applied to recover the potential energy surface (PES) from a polyad preserving Hamiltonian is viable only in systems with a local mode behaviour. For molecules with a normal mode behaviour the approach is still valid, but the polyad must be broken in order to recover the PES. Our approach is evaluated through the calculation of the force constants for H₂O and CO₂, representative examples of local and normal behaviours.     

Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates: Inversion and Enhanced Chirality Based on Spatial Arrangements and Self-Assembly

We synthesized two bichromophoric difluoroboron-β-diketonates (DFB) connected in para and meta positions by using cyclohexane diamine as a chiral bridge ( para and meta (R/S)-CyDFB ). TD-DFT calculations revealed that the variation in connectivity of the DFB units leads to different spatial arrangements and a chirality inversion of the bichromophoric DFB. Higher g_abs values were obtained in (R/S)-CyDFB connected in para as compared to meta position. Aggregation of para (R/S)-CyDFB in mixture of solvents increase the g_lum values as compared to its monomeric form. Ultrasonication and heating induced the formation of highly ordered nano-helical wires of para (R/S)-CyDFB that increased the g_lum values to 0.015. On the other hand, meta (R/S)-CyDFB failed to form highly ordered self-assembled wires due to hindered H-binding sites. These observations indicate that the chiroptical properties of DFB bi-chromophore system can be modulated with self-assembly and spatial arrangement of the chromophores.     

Guayulin B

The sesquiterpene guayulin B, C₂₃H₃₀O₃, 1, crystallizes with two independent molecules in monoclinic space group P2₁ with a = 18.099 (1), b = 6.0649(6), c = 19.126(1) Å, = 100.82(1)°, V = 2062.1(5) ų, and Z = 4. The double bonds of the cyclodecadiene ring are E, both methyl groups on the 10-membered ring are -oriented. The cyclopropane ring at C6 and C7 also has the orientation, while the anisoyloxy group is oriented . The 10-membered rings of the two independent molecules have the same conformation as that of guayulin A.     

The pseudoguaianolide isoconfertiflorin

The sesquiterpene lactone isoconfertiflorin, C₁₇H₂₂O₅, 1, crystallizes in trigonal space group P3₁ with a = 10.4498(5), c = 12.7516(8) Å, V = 1205.9(2) ų, and Z = 3. It differs from confertiflorin in having an endocyclic C=C bond in the lactone ring, which carries an exocyclic methyl group. The seven-membered ring adopts an approximate twist-chair conformation with C10 lying in the local two-fold axis, and asymmetry parameter C₂ = 5.8°. The cyclopentanone ring has the half-chair conformation with C4 on the local two-fold axis, and C₂ = 0.9°. The lactone ring is almost planar with maximum deviation 0.014(2) Å. Both methyl groups on the 7-membered ring are –oriented. The acetyl group at C8 has an orientation.     

Crystal and molecular structure of tetraiodo (1,8-di-2-pyridyl-3,6-dithiaoctane-N,S,S′,N′)dimercury(II)

Summary The X-ray crystal structure of the title compound, [Hg₂(C₁₆H₂₀N₂S₂)I₄], has been determined. The crystals are monoclinic (space groupP2₁/c), with cell dimensionsa=15.016(2),b=6.201(3),c=15.273(2) Å,=115.18(1)°;V _o =1287.0(7) ų,M _r =1213.266,Z=4,D _x =6.26mg m^–3, MoK radiation (graphite crystal monochromator, ),(MoK)=336 cm^–1,F(000)=4272, andT=290°K. The final conventionalR factor=0.054, andR _w =0.062 for 2799 observed reflections. The structure was solved by Patterson and Fourier methods and refined by block-diagonal least-squares methods. The coordination around the mercury atoms is approximately tetrahedral, although with considerable distortion, with two iodine atoms and the N and S atoms of one-half of the ligand molecule.     

Photophysical characterization of a highly conjugated bipyridyl-based dye synthesized by a unique two-step approach

In this article, we present a new and simple, yet efficient, two-step approach to synthesize 4,4'-bis(dibutylaminostyrylstyryl)-2,2'-bipyridine with high yield, as well as its linear and nonlinear optical characterizations in THF and toluene solutions. We show that its one- and two-photon absorption spectra are similar in both solvents. Nevertheless, the relaxation processes of this compound exhibit dependence on the solvent polarity. The one- and two-photon induced fluorescence signal of this molecule in solution reveals that its excited state is highly stabilized in THF solution rather than in toluene. Analysis of the fluorescence quantum yield, lifetime, and radiative and nonradiative decay rates are in agreement with Lippert's model for solute-solvent interactions. The optical measurements demonstrate that this dye is a promising candidate for multiphoton fluorescence imaging, optical limiting, and dye lasers.