X-ray structure and NMR assignment of 4-methoxy-4′-methylthio-3,3′-diquinolinyl sulfidea

The title compound (C₂₀H₁₆N₂OS₂) is monoclinic, witha=7.786(3).,b=13.252(3),c=17.162(4) Å, =99.16(3)° and space groupP2₁/n. Two quinoline moieties are nearly perpendicular to each other (112.9(2)°). Both methoxy and methylthio groups are trans-orientated with the respect to the C(3)–S(1)–C(13) plane. Two pairs of the heteroatoms in ortho-positions are in very close contact. The conformation of the molecule explains an unusual¹H NMR spectrum     

Structure of phosphonium rhenates(VII)

Four phosphonium rhenates(VII) were prepared and crystallized: (A) 1,2-bis (triphenylphosphonium)ethane rhenate(VII) (Pī, a=8.298(2), b=10.638(3), c= 11.242(3) ?, α=64.96(2), β=80.49(2), γ=88.17(2)°), (B) methyltriphenylphosphonium rhenate(VII) (Pca2₁, a=15.096(3), b=12.627(3), c=19.353(3) ?), (C) benzyltriphenylphosphonium rhenate(VII) (Pī, a=9.648(2), b=11.689(2), c=20.806(3) ?, α=88.44(2), β=84.63(2), γ=77.33(3)°), and (D) orthorhombic form of (iodomethyl)triphenylphosphonium rhenate(VII) (Pca2₁, a=14.952(3), b=13.120(3), c=20.603(4) ?). Each crystal structure consists of separate phosphonium cations and rhenate(VII) anions. In A centrosymmetric 1,2-bis(triphenylphosphonium)ethane cations form layers perpendicular to [011]. In B the cations are set in chains along [100] forming layers perpendicular to [001]. In C two symmetrically-independent cations form double columns along [100] and these columns are arranged in puckered layers perpendicular to [001]. D is almost isomorphous to B. The crystal structures are stabilised by weak C–H⋯O hydrogen bonds as well as phenyl rings interactions. In all crystal structures supramolecular motifs of phenyl rings embraces could be distinguished.     

Synthesis and X-ray structure of p-tolyl phenylthioglyoxylate

The title compound (C₁₅H₁₂O₂S) is triclinic witha=7.077(10),b=8.825(2),c=11.068(2) Å, =106.66(3)^o, Z=2, and space group P. The significant structural features lies in the two carbonyl groups of the thioglyoxylate which are oriented antiperiplanar to each other [–168.2(2)^o]. The central C(8)–C(9) bond is 1.553(3) Å. The phenyl rings are twisted with respect to the carbonyl groups. Short contacts are present between S and O(1) [2.652(2) Å] and also between S and O(2) [2.758(2) Å].     

Progress in planar electrochromatography

Developments in planar electrochromatography in open (PEC) and closed (PPEC) systems are reviewed. The discussion focuses on progress in chamber construction for planar electrochromatography, separating system performance, equilibration of the PPEC process, separation time and selectivity, and the general advantages, disadvantages and prospects of this separation mode. Presented at the 11th International Conference on Chemistry and the Environment, 9–12 September 2007, Torum, Poland.     

Completions of GBL-algebras: negative results

We provide a simple sufficient criterion to show that a given variety of GBL-algebras does not admit (local) completions. As corollaries, we obtain that no variety of GBL-algebras containing Chang’s chain, no nontrivial variety of ℓ-groups, nor the variety of product algebras admit completions. The first result strengthens a result of Gehrke and Priestley. Received August 10, 2006; accepted in final form March 8, 2007.     

Caesium cis‐tetrachloridodioxidorhenate(VII)

The title crystal structure, Cs[ReCl₄O₂], consists of cis‐tetrachloridodioxidorhenate(VII) anions and caesium cations. The distorted octahedral anion has nearly C_2v symmetry, with a cis arrangement of the oxide ligands. The Re—Cl bond lengths for the Cl atoms trans to the oxide ligands are affected by the trans influence of the Re—O bonds and are longer than for the Cl atoms cis to the oxide ligands [average of 2.472 (2) Åversus average of 2.322 (2) Å, respectively]. There are ten Cl atoms from six cis‐tetrachloridodioxidorhenate(VII) anions in the neighbourhood of the caesium cation.     

Trace estimates for stable processes

In this paper we study the behaviour in time of the trace (the partition function) of the heat semigroup associated with symmetric stable processes in domains of R ^d . In particular, we show that for domains with the so called R-smoothness property the second terms in the asymptotic as t → 0 involves the surface area of the domain, just as in the case of Brownian motion.     

The pro-oxidant effects of interactions of ascorbate with photoexcited melanin fade away with aging of the retina

Photoexcited melanin from retinal pigment epithelium (RPE) has been shown to induce photo-oxidation of ascorbate with concomitant generation of hydrogen peroxide. The aim of this study was to test whether the age-related changes in melanin content and distribution in the RPE affect the susceptibility of RPE cells to ascorbate-mediated photo-oxidation. Our results demonstrate that there is an age-dependent shift in the pathways with which ascorbate interacts in human RPE. In young RPE, melanin-ascorbate interactions may lead to pro-oxidant effects, but in the aged there is no net increase in photo-oxidation in the presence of ascorbate in comparison with samples without ascorbate. However, as ascorbate undergoes light-induced depletion and photogenerates ascorbyl free radical in the old RPE cells with initial yields similar to that observed for young RPE, an influence of ascorbate on oxidation pathways is revealed in the old RPE as well. Interestingly, the pro-oxidant effects of photoexcited melanolipofuscin-ascorbate interactions are greater than for photoexcited melanosomes when normalized to the same melanin content. The pro-oxidant effects of photoexcited melanin-ascorbate interactions are strongly dependent on the irradiation wavelength, this being the greatest for the shortest wavelength studied (340 nm) and steeply decreasing with increasing wavelength but still detectable even at 600 nm.     

Role of ocular melanin in ophthalmic physiology and pathology

The mammalian eye consists of several layers of pigmented tissues that contain melanin. The eye is a unique organ for pigment cell research because one can isolate and compare melanosomes from different tissues and embryonic origins. Retinal, iris and ciliary pigment epithelial cells are derived from the neural ectoderm, more specifically from the extremity of the embryonic optical cup, which is also the origin of the retina. In contrast, the pigment-generating cells in the choroid and in the stroma of the iris and ciliary body, uveal melanocytes, are developed from the neural crest, the same origin as the melanocytes in skin and hair. This review examines the potential functions of ocular melanin in the human eye. Following a discussion of the role of melanins in the pigment epithelium and uveal melanocytes, three specific topics are explored in detail-photo-screening protective effects, biophysical and biochemical protective effects, and the biologic and photobiologic effects of the two main classes of melanins (generally found as mixtures in ocular melanosomes)--eumelanin and pheomelanin.