Photophysical properties of N-acylated linear polyethylenimine and dehydroalanine main-chain polymers containing carbazole or pyrene groups in side chains

A comparison of the UV absorption spectra of a carbazole-substituted N-acylated linear polyethylenimine (PEI) ( 5, 6 ) with its monomer ( 1, 2 ) and dimer ( 3, 4 ) model compounds shows the presence of local conformational order of the carbazole groups in 3, 5 , and 6 since these compounds exhibit hypochromism. The UV absorption spectra of carbazole-substituted N-acrylated dehydroalanine main-chain polymer (PDA) ( 12, 13 ) and monomer ( 10, 11 ) model compounds indicate that the extent of local conformational order of the carbazole groups is reduced in 12 and 13 compared to that in 5 and 6 . The UV absorption spectra of a pyrene-substituted PEI ( 9 ) and PDA ( 15 ) and those of their monomer model compounds ( 7, 14 ) indicate that the extent of local conformational order of the pyrene groups is greater in 9 than in 15 and furthermore the pyrene-substituted polymers ( 9, 15 ) show more local conformational order than analogous carbazole-substituted polymers ( 5, 12 ). The emission spectra of 5 and 12 show carbazole monomer emission, while those of 9 and 15 are dominated by pyrene excimer emission. The formation of excimer emission is more efficient in 9 than in 15 . Fluorescence lifetime measurements indicate interactions of excited carbazole groups in 5 and 13 but not in 12 . The quenching of carbazole fluorescence by dimethyl terephthalate is more efficient in 5 than that in 12 , indicating more efficient transfer of electronic energy in 5 . These measurements show that the PEI main-chain polymers are conducive to interactions of the pendant groups.     

Phototransformations of some 3-alkoxy-2-styrylchromones: type II cyclisations of 1,4- and 1,6-biradicals

3-Alkoxy-2-styrylchromones on photo-irradiation with UV-light transform into oxetanopyrananones, pyranopyrones, pyranopyrananones and pyranoalcohols. The products formed have been found to depend upon the structure of alkoxy group (methyl, benzyl and allyls). Alkoxychromones containing a heterocyclic ring (thiophene, furan) in place of phenyl in the styryl group produced only pyranoalcohols as the photoproducts. The photo-conversions have been rationalized through an initial H-abstraction by the CO group producing a 1,4-biradical. In allyloxy derivatives, cyclisations involve both 1,4- and 1,6-biradicals.     

Kinetics and mechanism of oxidations by metal ions. Part 16. Oxidation of 4-oxopentanoic acid by aquomanganese(III) ions

Summary The outer-sphere oxidation of 4-oxopentanoic acid (4-OPA) to MeCO₂H by aquomanganese(III) ions exhibits a first-order dependence on [4-OPA] and [Mn(III)](aq). The observed pseudo first-order rate constant k _obs ([4-OPA] [Mn^III](aq)) is independent of [Mn^II] but decreases with increasing [H⁺]. The retarding effect of [H⁺] on the observed rate could be explained by considering either the reaction between MnOH⁺(aq) and MeCOCH₂— CH₂CO₂H or between Mn³⁺(aq) and MeCOCH₂CH₂-COO^– ions. The rate constant for the latter pair of reactants is much higher than the rate constant for the reaction between the first pair. Since the activation enthalpy for the first pair is about 14 kJ mol^–1 less than that of the second pair, it is concluded that the reactive species are MnOH²⁺(aq) and MeCOCH₂CH₂CO₂H or that the preferred oxidant is MnOH²⁺(aq) ion.     

Localization of separated protein bands in unstained electrophoresed polyacrylamide gradient slab gel.

Polyacrylamide gel electrophoresis has become the most widely used separation method in biological science. Once electrophoresis is complete the protein bands must be localized prior to excision. A zig-zag gel cutter is described which cuts a strip of gel from the side of a slab gradient gel or a gel of uniform concentration in peaks and valleys. The location of the protein of interest is determined by counting the number of peaks on the stained side strip. The portion of the unstained gel corresponding to the same count (number of valleys) is cut to recover the protein of interest from the main gel for further manipulations.     

Direct resolution of (+/-)-ephedrine and atropine into their enantiomers by impregnated TLC

Direct resolution of (+/-)-ephedrine and atropine into their enantiomers was achieved by normal-phase thin layer chromatography on silica gel plates impregnated with optically pure L-tartaric acid and L-histidine, respectively, as chiral selectors. The mobile phases enabling successful resolution were different combinations of acetonitrile-methanol-water. The spots were detected with iodine vapours and the detection limits were 2 and 6 microg, respectively, in terms of the racemate. The effects of concentration of the impregnating reagent, temperature and pH on resolution have been studied.     

Syntheses and crystal structures of three novel Cu(II) coordination polymers of different dimensionality constructed from Cu(II) carboxylates (carboxylate = malonate (mal), 2 acetate (ac), fumarate (fum)) and conformationally flexible 1,4-bis(imidazole-1-yl-methylene)benzene (IX)

We herein report three new coordination polymers generated from Cu(II) carboxylates (mal, 2ac, fum) and conformationally flexible bifunctional IX as building blocks. All the three complexes adopt unique structures in the solid state. The complex [Cu₂(mal)₂(IX)₂(H₂O)₆]_n crystallizes as orthorhombic co-linear rods with space group P2(1) P2(1) P2(1). Each rod is further formed of two tightly intertwined strings. The second polymer [Cu₂(ac)₄(IX)₂]_n crystallizes with space group P1 which consists of two sets of intersecting 2D sheets composed of parallel rods which interpenetrate to form a fully interlocked 3D structure. In both these complexes IX coordinates in the anti mode. The third polymer [Cu₂(fum)₂(IX)₂(H₂O)₂]_n possesses a monoclinic crystal system with space group C₂/c and crystallizes as 1D straps. Cu–fum–Cu forms the base of the string which is alternatively garlanded by a macrocycle derived from Cu₂(IX)₂ unit, where IX coordinates in the syn fashion. The present study suggests that the use of a rigid building block with a flexible organic ligand leads to a better prediction of the final structure of the polymeric array.     

A rational study of crystal engineering of supramolecular assemblies of 1,2,4,5-benzenetetracarboxylic acid

Supramolecular assemblies of 1,2,4,5-benzenetetracarboxylic acid, 1, with aza donor molecules such as 1,10-phenanthroline, 2, 1,7-phenanthroline, 3, phenazine, 4, 4-(N,N-dimethylamino)pyridine, 5, 1,2-bis(4-pyridyl)ethene, 6, and 1,2-bis(4-pyridyl)ethane, 7, have been synthesized and characterized by single-crystal X-ray diffraction methods. All the complexes crystallize in the triclinic, Ponemacr; space group. In the complexes of 2 and 4, water is also present in the resultant assembly, but the complexes of 5, 6, and 7 crystallize without any water molecules or solvent of crystallization. However, 3 forms two types of complexes, a hydrate and a nonhydrate complex, depending upon whether water is used as a solvent or not. These assemblies divide into two classes, host-guest systems (with aza molecules being in the channels created by the acid molecules) and assemblies with infinite molecular tapes. While the assemblies of the compounds 2, 4, and 5 belong to the former class, the assemblies of compounds 6 and 7 form molecular tapes, which are arranged in two dimensions to form sheet structures. The two structures of 3, in fact, bridge the two classes with each one falling into different categories.     

Direct enantiomeric resolution of (+/-)-atenolol, (+/-)-metoprolol,and (+/-)-propranolol by impregnated TLC using L-aspartic acid as chiral selector

Resolution of three commonly used beta-blockers, (+/-)-atenolol, (+/-)-metoprolol and (+/-)-propranolol, into their enantiomers has been achieved using normal-phase TLC on silica gel plates impregnated with L-aspartic acid as the chiral selector. Different combinations of acetonitrile-methanol-water as mobile phase were found to be successful in resolving the enantiomers. The spots were detected with iodine and the detection limits were found to be 0.26 microg for atenolol and 0.23 microg for each of metoprolol and propranolol as racemate.     

High-performance liquid chromatographic separation of bile acids and bile alcohols diastereoisomeric at C-25

The high-performance liquid chromatographic separation of the 25R and 25S diastereoisomers of the bile alcohols 5 beta-cholestane-3 alpha,7 alpha,26-triol and 5 beta-cholestane-3 alpha,7 alpha, 12 alpha, 26-tetrol and the bile acids, 3 alpha,7 alpha-dihydroxy-5 beta-cholestane-26-oic acid and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestane-26-oic acid is described. A Radial-Pak microBondapak C18 reversed-phase cartridge was used for the separations and elutions were carried out with acetonitrile-water-methanol-acetic acid mixtures. All eight diastereoisomeric compounds showed baseline separation when up to 200 micrograms of the isomeric mixtures were injected into the column and the method can be used for isolation of pure diastereoisomers of these bile acids and bile alcohols.