Presence Of Cis Isomers Research Articles

Influence of blue and red light illumination on the holographic storage in an azopolyester–PMMA blend

Volume holographic polarization gratings have been stored in thick films of blends of a side-chain azobenzene polyester and a poly(methyl methacrylate) (PMMA) homopolymers. The azobenzene content in the blend is 0.2wt%, and the holograms are recorded by using 2ms 4mJ/cm2 488nm light pulses. The dependence of holographic storage on the recording condition has been studied. No stable gratings can be recorded in thermally quenched films. The presence of cis isomers that can be induced by blue light irradiation seems to be necessary to store stable gratings. The cis isomer content and consequently the grating efficiency can be changed by blue and red light irradiation. By choosing appropriate conditions stable and rewritable polarization gratings have been recorded. Up to 20 gratings with diffraction efficiency values higher than 5×10−5 have been multiplexed.

Identification of mixed bromidochloridotellurate anions in disordered crystal structures of (bdmim)2[TeX2Y4] (X, Y = Br, Cl; bdmim = 1-butyl-2,3-dimethylimidazolium) by combined application of Raman spectroscopy and solid-state DFT calculations

The discrete mixed [TeBrxCl6−x]2− anions in their disordered crystal structures have been identified by using the phases prepared by the reaction of 1-butyl-2,3-dimethylimidazolium halogenides (bdmim)X with tellurium tetrahalogenides TeX4 (X=Cl, Br) as examples. Homoleptic (bdmim)2[TeX6] [X=Cl (1), Br (2)] and mixed (bdmim)2[TeBr2Cl4] (3), and (bdmim)2[TeBr4Cl2] (4) are formed depending on the choice of the reagents, and their crystal structures have been determined by single-crystal X-ray diffraction. The coordination environments of tellurium in all hexahalogenidotellurates are almost octahedral. Because of the crystallographic disorder, the mixed [TeBr2Cl4]2− and [TeBr4Cl2]2− anions in 3 and 4 cannot be identified in their crystal structures. Pawley refinement of the X-ray powder diffraction patterns of 1–4 indicates the presence of single phases in all four products. The solid state Raman spectra of 1–4 were assigned with help of DFT calculations that were performed both for the discrete anions in vacuum and for the complete crystal structures employing periodic boundary conditions. The fundamental vibrations of the homoleptic [TeX6]2− (X=Cl, Br) anions could be well reproduced by the solid-state DFT computations and enabled a complete assignment of the Raman spectra. While the presence of cis-isomers in both [TeBr2Cl4]2− and [TeBr4Cl2]2− could be inferred by the computed fundamental vibrations, that of trans-isomers among the reaction products is, however, also possible. The pathway of the formation of [TeX4Y2]2− isomers from TeX4 and Y− (X, Y=Cl, Br) was also explored by DFT calculations both in vacuum and in solution and indicated that both reactions afforded 80mol% of cis-isomers and 20mol% of trans-isomers.

Synthesis and structural characterization of cis isomer of 1,2,3-triazol-5-ylidene based palladium complexes

A palladium complex (3) of abnormal N-heterocyclic carbene (NHC) namely, 4-(hydroxymethyl)-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene was prepared via silver carbene transmetalation method and characterized by spectroscopic and single crystal XRD data. Single crystal analysis revealed the structure of the complex 3 to be a cis isomer. The synthesis of palladium complex 6via silver carbene transmetalation method led to a mixture of cis–trans isomers. In this case trans isomer was formed as major product. We have reported earlier the synthesis and structural characterization of trans isomer (trans-6). However, the presence of cis isomer was not recognized until the crude reaction mixture was recrystallized from acetonitrile. Pure cis isomer (cis-6) was obtained by washing the cis–trans mixture with acetonitrile followed by slow evaporation of acetonitrile solution at 35 °C. Structure of cis (cis-6) isomer was unambiguously established by single crystal XRD data.

Sodium crocetinate does not alter gut hypercapnic responses or renal energy stores during transient sub-diaphragmatic ischaemia.

To evaluate the protection afforded by trans-sodium crocetinate against dysoxia in an animal model of recurrent sub-diaphragmatic ischaemia. Prospective experimental animal study. University research laboratory Adult male Sprague-Dawley rats. Twelve adult male Sprague-Dawley rats (340-510 g) were anaesthetised with sodium pentobarbitone 60 mg/kg i.p. and ventilated with oxygen and isoflurane via tracheostomy. Six 2-min episodes of sub-diaphragmatic hypotension (mean pressure 30 mmHg) were induced using a sling around the proximal aorta. Before the third and sixth episodes, saline 1.5 ml/kg was injected into the aortic cannula. In six rats, this saline contained trans-sodium crocetinate 50 microg/ml. Ileal luminal PCO(2) and distal aortic pressure were monitored continuously. Following ischaemic episodes trans-sodium crocetinate had no discernible effect on either degree of PCO(2) elevation or the time to peak PCO(2). No effects on renal energy charge or nucleotide concentrations were detected. UV-visible spectroscopy of the crocetinate preparation showed that some cis isomer was present. The findings, although limited to one drug dosage in one animal model, bring into question whether trans-sodium crocetinate affects plasma oxygen diffusivity in vivo. Alternative explanations for the negative findings include a TSC-induced exacerbation of arterio-venous oxygen shunting, the brevity of the dysoxic episodes, and the presence of cis isomer.

Central-Cis isomers of lutein found in the major light-harvesting complex of Photosystem II (LHC IIb) of higher plants

Lutein (β,∈-carotene-3,3′-diol) is the major carotenoid of the light-harvesting systems of higher plants. Lutein was isolated at 4°C and in complete darkness from the bulk light-harvesting complex of Photosystem II of spinach (LHC IIb) and from BBY particles. Separation using normal-phase HPLC (with 2D detection) in comparison to the authentic isomers (prepared by iodine-sensitised isomerization) showed the presence of a number of geometrical isomers of this xanthophyll in PS II, namely all-trans (the major component); 13-cis, 13′-cis and 15-cis-lutein. Iodine-sensitised photo-isomerization of all-trans lutein produced six geometrical isomers of lutein as determined by HPLC. The configuration of five of these isomers was determined by 1H-NMR to be all-trans, 9-cis, 9′-cis, 13-cis and 13′-cis. In addition, small amounts of another isomer have been tentatively identified to be 15-cis lutein on the basis of its electronic absorption spectrum. The possible functional significance of the presence of cis-isomers of this carotenoid in LHC IIb is discussed.