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.     

Phorbasides A-E, cytotoxic chlorocyclopropane macrolide glycosides from the marine sponge Phorbas sp. CD determination of C-methyl sugar configurations

Five new cytotoxic macrolide glycosides phorbasides A-E (3-7), each possessing a macrolide ring appended to a rare ene-yne-trans-2-chlorocyclopropane, were isolated from the same Western Australian sponge (Phorbas sp.) that provided phorboxazoles A and B. The structures of 3-7 were solved by analysis of spectroscopic data including NMR, MS, and CD. A synthesis of methyl 2-O-methyl-alpha-L-evalose from L-rhamnose was completed and used for configurational assignment of the sugar residue in 3. Acid-catalyzed methanolysis of 3 followed by two-step derivatization of the liberated O-methyl glycoside gave a vicinal 4-O-naphthoyl/tertiary 3-N-(2-aminonaphthyl)carbamate derivative that exhibited exciton coupled CD identical with that of the derivative prepared from synthetic 1,2- O-dimethyl-alpha-L-evalose.     

Characterization of organosulfates from the photooxidation of isoprene and unsaturated fatty acids in ambient aerosol using liquid chromatography/(-) electrospray ionization mass spectrometry

In the present study, we have characterized in detail the MS(2) and MS(3) fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2-methyltetrols, 2-methylglyceric acid, 2-methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2-methyltetrols and 2-methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO(4)](-) anion, while the deprotonated sulfate esters of 2-methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS(2), MS(3) and accurate mass data led to the structural characterization of unknown polar compounds in K-puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2-hydroxy-1,4-butanedialdehyde, 4,5- and 2,3-dihydroxypentanoic acids, and 2-hydroxyglutaric acid, and of alpha-pinene, i.e. 3-hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2-methylglyceric acid, 4,5- and 2,3-dihydroxypentanoic acid, and 2- and 3-hydroxyglutaric acids, showed in addition to the [HSO(4)](-) ion (m/z 97) neutral losses of water, CO(2) and/or SO(3), features that are characteristic of humic-like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions.     

H-bonded complexes of aniline with HF/F- and anilide with HF in terms of symmetry-adapted perturbation, atoms in molecules, and natural bond orbitals theories

The hydrogen-bonded isoelectronic complexes of aniline with HF/F- and an ionic form of aniline with HF were investigated by use of computational methods: Symmetry-Adapted Perturbation Theory (SAPT), Atoms in Molecules (AIM), and Natural Bond Orbitals (NBO) approaches. All computations were based on structural models previously generated at the B3LYP/6-311+(d,p) level. The differences between neutral (Ph-NH2...HF)and anionic (Ph-NH2...F- and Ph-NH-...HF) complexes were clearly outlined. The discussed charged complexes serve as Lewis acids and base, HF and F-, respectively. It was found that electrostatic and induction energy terms, obtained as a result of the SAPT method, are most dependent on the type of H-bonding (i.e.,charged or neutral). The electrostatic term is the most distinctive between the neutral and charge-assisted hydrogen bonds in the investigated two-body systems, whereas the latter is more significant in the case of weaker interactions (larger H...B distances). Application of Principal Component Analysis (PCA) to energy components obtained from the SAPT procedure indicated that all of them are relatively well intercorrelated.The above-mentioned terms together with the exchange energy terms are the most important contributions ofthe main principal component, which describes 95% of the total variance. Comparison of AIM parameters in bond critical points for modeled H-bond systems shows a good agreement with those from equilibrium complexes, both experimental and calculated ones. It was found that charged H-bonded complexes exhibit larger fluctuation of electron density and its Laplacian in bond critical points, in line with SAPT analysis. NBO results confirmed the effect of the strength of interaction on property changes both in the region of H-bonding and outside of it. The latter, more distant consequences follow the Bent-Walsh rule for all studied complexes.     

Numerical analysis of the Gran methods. A comparative study

The paper concerns mainly the modified Gran methods, considered as extrapolative standard addition methods. Particularly, the approximation: