INCORPORATION OF 11,12-DIHYDRORETINAL INTO THE RETINAE OF VITAMIN A DEPRIVED RATS

Abstract— The incorporation of 11,12-[15–³H]-dihydroretinal, a retinal in which the crucial 11-ene is saturated, into the retinae of vitamin A deficient rats as a result of intraperitoneal injection of the corresponding alcohol was shown by the presence of the tritium label in the rod outer segments and by identification of the extracted retinals using high pressure liquid chromatography. The amplitude of the electroretinogram (ERG) b-wave, diminished as the result of vitamin A deprivation, was not affected by administration of the analogue, although similar treatment of deprived litter mates with trans retinal restored the ERG b-wave amplitude to a normal level.
The evidence that the analogue is bound to opsin forming 11,12-dihydrorhodopsin is as follows: (1) when incubated with 11- cis retinal, extracts from vitamin A deficient rats regenerate 1.4 nmol rhodopsin while extracts from rats deficient in vitamin A and supplemented with 11,12-dihydroretinal regenerate 0.6 nmol rhodopsin indicating binding of the dihydroretinal blocks rhodopsin regeneration. (2) 11,12-dihydroretinal is shown to remain unchanged in hexane-washed retinae after extraction with methylene chloride and (3) injection of retinal into animals previously injected with 11,12-dihydroretinal also fails to restore visual sensitivity as measured by the ERG b-wave. Our results indicate that the dihydro-chromophore occupies the same binding site as the natural 11- cis retinal and that occupation of the chromophore binding site of opsin is not sufficient to restore the visual sensitivity in a vitamin-A-deprived animal.     

Shaping non-noble metal nanocrystals via colloidal chemistry

Non-noble metal nanocrystals with well-defined shapes have been attracting increasingly more attention in the last decade as potential alternatives to noble metals, by virtue of their earth abundance combined with intriguing physical and chemical properties relevant for both fundamental studies and technological applications. Nevertheless, their synthesis is still primitive when compared to noble metals. In this contribution, we focus on third row transition metals Mn, Fe, Co, Ni and Cu that are recently gaining interest because of their catalytic properties. Along with providing an overview on the state-of-the-art, we discuss current synthetic strategies and challenges. Finally, we propose future directions to advance the synthetic development of shape-controlled non-noble metal nanocrystals in the upcoming years.

This minireview describes the state-of-the-art of shape-controlled nanocrystals of third raw transition metals and discusses future directions to advance their synthetic development, which is important for many applications.     

Catalytic regiodivergent kinetic resolution of allylic epoxides: a new entry to allylic and homoallylic alcohols with high optical purity

A novel regiodivergent kinetic resolution of a series of allylic epoxides with alkylzinc reagents is described. Results demonstrate the potential of chiral copper-phosphoramidite catalysts for enantiomer differentiation of allylic epoxides, allowing a chiral catalyst-stereoregulated synthesis of cyclic allylic and homoallylic alcohols with high optical purities.     

Simultaneous determination of sorbic and benzoic acids in commercial juices using the PLS-2 multivariate calibration method and validation by high performance liquid chromatography

A new method to determine a mixture for preserving sorbic and benzoic acids in commercial juices is proposed. The PLS-2 model was obtained preparing 40 standard solutions adding concentration of sorbic and benzoic acid to filtered natural juices of apple, lemon, orange and grapefruit. The concentration of analytes in the commercial samples was evaluated using the obtained model by UV spectral data. The PLS-2 method was validated by high performance liquid chromatography (HPLC), finding a relative error less than 12% between the PLS-2 and HPLC methods in all cases.     

Three-step solution-phase combinatorial access to 1,2-disubstituted and 1,2,5-trisubstituted pyrroles from carboxylic esters

An efficient diversity-oriented strategy has been developed for the solution-phase parallel synthesis of di- and trisubstituted pyrrole libraries. Methyl esters 1 were effectively converted to 1,2-di- and 1,2,5-trisubstituted pyrroles 5 and 6 in three steps. Treatment of ester 1 with vinylmagnesium bromide in the presence of copper (I) cyanide yielded the corresponding homoallylic ketone 2, which was subjected to ozonolysis or Tsuji-Wacker oxidation to yield the respective cyclization precursors 3 and 4 after aqueous workup. Compounds 3 and 4 were condensed without further purification with a primary amine to afford the desired 1,2-di- or 1,2,5-trisubstituted pyrroles 5 and 6 in good yield and purity.     

Capillary electrophoretic study of the binding of zinc(II) ion to bacitracin A1 in water-2,2,2-trifluoroethanol

Binding of Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A(1) in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn(2+) ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn(2+) ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A(1) towards its biologically active structure.*     

Gauge invariance and asymptotic behavior for the Ginzburg-Landau equations of superconductivity

In this paper we study the gauge invariance of the time-dependent Ginzburg-Landau equations through the introduction of a model which uses observable variables. We observe that the various choices of gauge lead to a different representation of such variables and therefore to a different definition of the weak solution of the problem. With a suitable decomposition of the unknown fields, related to the choice of London gauge, we examine the Ginzburg-Landau equations and deduce some energy estimates which prove the existence of a maximal attractor for the system.     

Mixed integer formulations for the probabilistic minimum energy broadcast problem in wireless networks

In this paper we study a new variant of the minimum energy broadcast (MEB) problem, namely the probabilistic MEB (PMEB). The objective of the classic MEB problem is to assign transmission powers to the nodes of a wireless network is such a way that the total energy dissipated on the network is minimized, while a connected broadcasting structure is guaranteed by the assigned transmission powers. In the new variant of the problem treated in this paper, node failure is taken into account, aiming at providing solutions with a chosen reliability level for the broadcasting structure. Three mixed integer linear programming formulations for the new problem are presented, together with efficient formulation-dependent methods for their solution. Computational results are proposed and discussed. One method emerges as the most promising one under realistic settings. It is able to handle problems with up to fifty nodes.     

Mechanical Switches of Fluorescence

Fluorescence switches are molecular systems containing a light-emitting fragment whose activity can be quenched/revived reversibly, at will,through an external parameter, i.e., a change of pH or the variation of the redox potential.Fluorescence switches can be static (the emission of the fluorophore isswitched ON/OFF by a bistable covalently linked control unit) or dynamic(the change in fluorescence is accompanied by an oriented molecular motion). Of the latterclass of switches, we will consider the cases (i) of a metal scorpionate and (ii) ofsystems in which a metal is reversibly translocated between two nonequivalent compartmentsof a ditopic ligand.     

Particle Systems Characterization Using a Flat Cell Static Light Scattering Apparatus

In this work a light scattering apparatus for the study of heterogeneous liquid systems of evolving morphology is presented. A Fraunhofer configuration consisting of a linear array of photodiodes is used to detect the light scattered by thin samples illuminated by a He‐Ne laser light. Temperature control is available. The instrument is tested with the polymerization induced phase separation of a thermosetting polymer formulated with a divinylester resin copolymerized with styrene and modified with poly(methylmethacrylate). The system is successfully modeled as an arrangement of particles growing in size and number, and varying in composition. The ability of the experimental setup to provide results that can be quantitatively analyzed is checked using microspherical polystyrene standards. Different samples with nominal sizes of 0.5, 1 and 2 μm are used in different combinations of sample thickness and concentration. The analysis of the light scattering spectra is performed using inverse techniques to estimate the particle size distribution of the microspheres. The results agree with previous knowledge of the parameters of the samples.