Reactions of substituted furan-2-carboxaldehydes and furo[b]pyrrole type aldehydes with benzothiazolium salts

A series of new push-pull compounds were synthesised by reaction of 5-aryl- furan-2-carboxaldehydes and furo[b]pyrrole type aldehydes with benzothiazolium salts. These new condensation products represent highly conjugated systems that have potential biological activity. The reaction of furo[b]pyrrole type aldehydes with benzothiazolium salts give potential precursors of cyanine dyes.     

Molecular Chirality in Meteorites and Interstellar Ices,and the Chirality Experiment on Board the ESA Cometary Rosetta Mission

Life, as it is known to us, uses exclusively L ‐amino acid and D ‐sugar enantiomers for the molecular architecture of proteins and nucleic acids. This Minireview explores current models of the original symmetry‐breaking influence that led to the exogenic delivery to Earth of prebiotic molecules with a slight enantiomeric excess. We provide a short overview of enantiomeric enhancements detected in bodies of extraterrestrial origin, such as meteorites, and interstellar ices simulated in the laboratory. Data are interpreted from different points of view, namely, photochirogenesis, parity violation in the weak nuclear interaction, and enantioenrichment through phase transitions. Photochemically induced enantiomeric imbalances are discussed more specifically in the topical context of the “chirality module” on board the cometary Rosetta spacecraft of the ESA. This device will perform the first enantioselective in situ analyses of samples taken from a cometary nucleus.     

Two-photon photodynamic therapy of C6 cells by means of 5-aminolevulinic acid induced protoporphyrin IX

Photodynamic therapy (PDT) has received increased attention as a treatment modality for malignant tumors as well as non-oncologic diseases such as age-related macular degeneration (AMD). An alternative to excite the photosensitizer by the common one-photon absorption is the method of two-photon excitation (TPE). This two-photon photodynamic therapy has the potential of improving the therapeutic outcome due to a highly localized photodynamic effect. The present study investigated the two-photon excited PDT performing in vitro experiments where C6 rat glioma cells were irradiated with a pulsed and focused fs Ti:sapphire laser emitting light at 800 nm. The irradiance distribution of the laser beam was carefully analyzed before the experiment and the applied irradiance was known for each position within the irradiated cell layer. Cells were divided into four groups and one group was incubated with 5-ALA and irradiated 4-5h later. The survival of this group was tested after irradiation by means of ethidium bromide and acridine orange staining and compared to a control group, which was irradiated under the same conditions, but not incubated with 5-ALA before. Both groups showed necrotic areas depending on the applied irradiance, the value of which at the margin of the necrotic area could be deduced from its size. 5-ALA incubated cells became necrotic after irradiation with a mean irradiance above 6.1 x 10(10) W/cm(2), while non-incubated cells remained viable. Cells of both groups became necrotic when treated with an irradiance above 10.9 x 10(10) W/cm(2). The observed affected area of the cell layers was between 0.13 mm(2) and 1.10 mm(2). Since the irradiation of non-incubated cells below the mean power density of 10.9 x 10(10) W/cm(2) induced no necrosis, apparently no thermal damage was induced in the cells and necrosis of the 5-ALA incubated cells can be ascribed to the photodynamic effect induced by two-photon excitation. The successful photodynamic treatment of a large area of a monolayer cell culture induced by two-photon excitation offers new perspectives for photodynamic treatment modalities.     

Vapor phase tin diiodide: its structure and thermodynamics,a computational study

The molecular structure and vibrational characteristics of monomeric and dimeric tin diiodide, SnI₂ and Sn₂I₄, were determined by high-level computational methods. For the dimer molecule two low-energy geometries were found, one with C _s and the other with C _2v symmetry, the former with somewhat lower energy; their relative energy is strongly dependent on the computational method. Thermodynamic functions for both species and their dimerization reaction were calculated based on the computed structures.

Zinc(II) binding ability of tri-, tetra- and penta-peptides containing two or three histidyl residues

Macroscopic and microscopic protonation processes and zinc(II) complexes of a series of multihistidine peptides (Ac-HGH-OH, Ac-HGH-NHMe, Ac-HHGH-OH, Ac-HHGH-NHMe, Ac-HVGDH-NH(2), Ac-HHVGD-NH(2), Ac-HVHAH-NH(2), Ac-HAHVH-NH(2), Ac-HPHAH-NH(2) and Ac-HAHPH-NH(2)) were studied by potentiometric, NMR and ESI-MS spectroscopic techniques. Protonations of histidyl imidazole-N donor functions were not much affected by the number and location of histidyl residues, but the presence of C-terminal carboxylate groups had a significant impact on the basicities of the neighbouring histidyl sites. The formation of 2N(im) and 3N(im) macrochelates with the stoichiometry of [ZnL] was the major process in the complexation reactions of all peptides followed by the formation of hydroxo or amide bonded species. Thermodynamic stabilities of the zinc(II) complexes were primarily determined by the number of histidyl residues, but the presence of C-terminal carboxylate functions has also a significant contribution to metal binding. The stabilizing effect of the aspartyl beta-carboxylate group was also observed, but its extent is much weaker than that of the C-terminal carboxylate with a neighbouring histidyl residue. Zinc(II) promoted peptide amide deprotonation and co-ordination was observed only in the zinc(II)-Ac-HHVGD-NH(2) system above pH 8.     

Electrospray ionization mass spectrometric analysis of highly reactive glycosyl halides

Highly reactive glycosyl chlorides and bromides have been analysed by a routine mass spectrometric method using electrospray ionization and lithium salt adduct-forming agents in anhydrous acetonitrile solution, providing salient lithiated molecular ions [M+Li]?, [2M+Li]? etc. The role of other adduct-forming salts has also been evaluated. The lithium salt method is useful for accurate mass determination of these highly sensitive compounds.     

Enzymic Hydrolysis of Methyl 2,3-O-Acetyl-5-Deoxy-α and β-D-Xylofuranosides - An Active-Site Model of Pig Liver Esterase

Abstract

The regioselective enzymic hydrolysis of methyl 2,3-di-O-acetyl-5-deoxy-α-D-xylofuranoside (1) and methyl 2,3-di-O-acetyl-5-deoxy-β-D-xylofuranoside (2) in the presence of pig liver esterase (PLE) was studied by GLC. Diacetate 2 gave exclusively methyl 3-O-acetyl-5-deoxy-β-D-xylofuranoside (6) while diacetate 1 produced both methyl 2-O-acetyl-5-deoxy-α-D-xylofuranoside (3) and methyl 3-O-acetyl-5-deoxy-α-D- xylofuranoside (4) in low yield. At high conversion, methyl 5-deoxy-α-D-xylofuranoside (7) was the only product. The first-order rate constants, Michaelis constants, and maximal velocities were determined for 1, 2, and the monoacetates 3 - 6. The results were interpreted on the basis of a recent active-site model for PLE.     

Syndiotactic poly(propylene)/organoclay nanocomposite fibers: influence of the nano‐filler and the compatibilizer on the fiber properties

Melt spinning of nanocomposites prepared from syndiotactic poly(propylene) (sPP) and organolayered silicate (M‐ODA), containing bound octadecyl ammonium chains, was investigated. The influence of the nano‐filler reinforcement and the role of the addition of maleic anhydride grafted isotactic poly(propylene) (iPP‐g‐MA) as compatibilizer with respect to the fiber proportion was examined. The presence of nano‐filler, the drawing ratio, and the compatibilizer addition afforded increased tenacity of the fibers. Only in the presence of the compatibilizer high drawing ratio of the sPP nanocomposite fibers was achieved. Transmission electron microscopy (TEM) was applied to monitor morphology development during nanocomposite fiber spinning in the presence and the absence of the compatibilizer. Copyright © 2005 John Wiley & Sons, Ltd.     

Substituent effects in the ring-chain tautomerism of 4-aryl-1,3,4,6,7,11b-hexahydro-2H-pyrimido[6,1-a]isoquinolines

By condensation of 1-(2′-aminoethyl)-1,2,3,4-tetrahydroisoquinoline derivatives with substituted benzaldehydes, 1,6-unsubstituted and diastereomers of 1-methyl- or 6-methyl-substituted 4-aryl-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrimido[6,1-a]isoquinolines were prepared. The ring-chain tautomeric equilibria of most of these compounds in CDCl₃ at 300 K were found to be shifted nearly totally towards either the cyclic or the open tautomeric forms, while the (6R*,11bR*)-6-methyl substituted compounds proved to be three-component tautomeric mixtures, the equilibria of which could be characterized by a Hammett-type equation. The conformational equilibria of the cyclic forms turned out to be strongly influenced by the 1- and 6-methyl substituents and the configurations of the substituted carbons (C-1 or C-6 and C-4) relative to C-11b.     

Infrared and Raman bands of phytantriol as markers of hydrogen bonding and interchain interaction

Hydrogen bonding and interchain interactions in phytantriol, 3,7,11,15-tetramethyl-1,2,3-hexadecanetriol, have been studied by Fourier transform infrared (FT-IR) and Raman spectroscopies. Assignments of the bands were performed based on the OH/OD isotopic substitution, molecular modeling, and measurements of polarized Raman spectra. Marker bands were evaluated from the temperature-dependent spectral changes. It is shown that Raman spectroscopy provides sensitive markers, namely I(delta(CH2))/I(deltas(CH3)), tau(CH)2, I(nus(CH3)(FR))/I(nus(CH2)), and nus(CH2) for probing the interactions between the hydrocarbon chains. Hydrogen bonding interaction might be studied through the difference Raman spectroscopy by the analysis of polarized band at 811 cm-1. Relationship is found between the frequencies of IR bands at 883-873 and 1097-1086 cm-1, associated with the vibrations localized at the primary COH site, and the frequencies of OH stretching mode, making these bands specific markers in the analysis of hydrogen bonding. Evaluated marker bands may be of utility to probe the interchain and hydrogen bonding interaction of phytantriol with guest molecules in the practically important aqueous liquid-crystalline phases of this lipid.