Dependence of Photochemical Reactivity of the All-trans Retinal Protonated Schiff Base on the Solvent and the Excitation Wavelength

An all-optical experimental technique aimed at measuring photoisomerization quantum yield (ϕ) of the all-trans protonated Schiff base of retinal in solution has been implemented. Upon the increase in the excitation wavelength from 400 to 540 nm a slight increase in ϕ from 0.16 ± 0.03 to 0.20 ± 0.02 is observed in the chromophore dissolved in methanol, whereas the ϕ value of the one dissolved in acetonitrile varies only from 0.22 ± 0.03 (400 nm) to 0.23 ± 0.04 (540 nm). The results suggest that dissipation of the excited-state vibrational energy excess, along with environment-induced modifications of the potential energy surfaces are necessary for an efficient retinal photoisomerization in both solvent and protein environment.     

Constrained stability for biaxial nematic phases

We study the invariance properties of the molecular Hamiltonian interaction put forward by Straley to describe biaxial nematic phases. We show that the reduction to two out of four scalar order parameters, which was accidently remarked upon in the literature, is indeed a rigorous consequence of the Hamiltonian invariance for specific values of the interaction parameters. The stability analysis of the mean-field free energy in the reduction classes for the order parameters reveals a sequence of Landau triple points.     

Clustering states in the62Ni(58Ni,58Ni)62Ni reaction

Excitation function and angular distributions of the⁶²Ni(⁵⁸Ni,⁵⁸Ni)⁶²Ni elastic scattering have been measured at incident⁵⁸Ni energies from 220.0 to 230.0 MeV in steps of 0.5 MeV. Evidence of two structures was found in the excitation function; a statistical analysis suggests a possible nuclear cluster quasi-molecular nature for these structures.     

Damped oscillations in the energy autocorrelation functions of the 58Ni+46Ti elastic and 58Ni+62Ni elastic and inelastic scattering cross sections

Structures of non-statistical character, recently observed in ⁵⁸ Ni +⁴⁶ Ti elastic and ⁵⁸ Ni +⁶² Ni elastic and inelastic excitation functions, produce damped oscillations in the cross section energy autocorrelation functions. The analysis of these damped oscillations in terms of S-matrix spin and parity decoherence indicates, as a possible interpretation, damping of the coherent rotational motion of the intermediate dinuclear system formed in the reaction.     

Synthesis and structural characterization of syndiotactic trans‐1,2 and cis‐1,2 polyhexadienes

The (E) isomer in mixtures of (E) and (Z) 1,3‐hexadiene was polymerized with the system CoCl₂(PⁱPrPh₂)₂‐MAO, a highly active and stereospecific catalyst for the preparation of 1,2 syndiotactic polybutadiene. A new crystalline polymer with a melting point of 109 °C was obtained. The polymer was characterized by IR, NMR (¹³C, ¹H in solution and ¹³C in the solid‐state), X‐ray diffraction, DSC, GPC and it was found to have a trans‐1,2 syndiotactic structure with a 5.18 ± 0.04 Å fiber periodicity. Since only the (E) isomer was polymerized, at the end of the reaction we were able to separate the (Z) isomer, which was ultimately polymerized with CpTiCl₃‐MAO at low temperature, obtaining a low molecular weight, stereoregular polymer that, characterized by IR and NMR methods, was found to exhibit a cis‐1,2 syndiotactic structure, never reported before. Molecular mechanics calculations were carried out on the trans‐1,2 syndiotactic polymer and structural models consistent with the X‐ray diffraction data are proposed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5339–5353, 2007     

Optical Storage in Side-Chain Liquid Crystalline Polyesters

Long-term, high resolution holographic storage has been achieved in side-chain liquid crystalline polyesters with high diffraction efficiency. The information can be completely erased by heating the film to about 80°C. The modular architecture of the polyesters permits a varition in the length of the main- and side-chains and the substituents of the azo chromophore. Each of these has a profound influence on the storage properties of the polyesters. In this article, we examine the influence of the length of the side-chains, the probe-beam-polarization dependence of the observed signal on the interface and the crystalline vs. amorphous nature of the films for optical storage.     

Improvement in underwater phase measurement of an amplitude-modulated laser beam by polarimetric techniques

The phase of the amplitude-modulated radiation reflected by a Lambertian target immersed in water was measured by using a linearly and circularly polarized sounding laser beam. Different values of the water extinction coefficient in the range of 0.06 - 2 m(-1) were realized by adding skim milk as a scattering element. It is shown that very efficient rejection of optical noise, resulting in reliable phase measurements, is accomplished with a cross-polarized and copolarized detection scheme for linear and circular polarization, respectively. The experiment demonstrates that phase measurements are very sensitive to optical noise suppression and that, as far as single scattering is the main involved mechanism, significant improvements can be achieved by adopting a polarization control on both the transmitter and the receiver stages of the apparatus.     

Antioxidant and antifungal activity of different extracts obtained from aerial parts of Inula crithmoides L.

The total phenolic content, antioxidant and antifungal activities of three Inula crithmoides extracts (n-hexane, methylene chloride and MeOH) were investigated. The methanolic extract showed the highest total phenolic content. In the DPPH assay, the methanolic and hexane extracts exhibited the highest DPPH-radical scavenging activity; in the 5-lipoxygenase assay, the hexane extract showed greater inhibitory effect with an IC₅₀ similar to that of Trolox and ascorbic acid. The antifungal activity of the methanolic extract revealed a higher activity against Phytophtora cryptogea and Alternaria solani.