Application of a new chiral derivatizing agent to the enantioseparation of secondary amino acids

A new chiral derivatizing agent, (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester, (S)-NIFE, was applied for the high-performance liquid chromatographic separation of enantiomers of 19 unnatural secondary amino acids: proline, pipecolic acid analogues, piperazine-2-carboxylic acid, morpholine-3-carboxylic acid, thiomorpholine-3-carboxylic acid and analogues containing the 1,2,3,4-tetrahydroisoquinoline, 1,2,3,4-tetrahydronorharmane, 1,2,3,4-tetrahydro-2-carboline and 2-benzazepine skeletons. Excellent resolutions were achieved for most of the investigated compounds by using a reversed-phase mobile phase system. The conditions of separation were optimized by variation of the mobile phase composition.     

Mesoscopic organization of two-dimensional J-aggregates of thiacyanine in Langmuir-Schaefer films

When dioctadecyl dimethylammonium bromide (DODAB) is compressed on a subphase containing 3,3'-disulfopropyl-5,5'-dichlorothiacyanine (THIAMS), adsorption of the dye to the DODAB monolayer results in the formation of J-aggregates which spontaneously organize into polygonal domains of micron size. The features of the domains depend on the surface pressure. The fluorescence of the individual domains is polarized. The shapes of the domains determined by fluorescence microscopy and atomic force microscopy (AFM) are identical. The domains differ however significantly from those observed after injection of a 3,3'-disulfopropyl-5,5'-dichloro-9-ethylthiacarbocyanine (THIATS) or THIAMS solution below a precompressed DODAB film, as well as from the domains observed upon compression of a DODAB monolayer on a subphase containing 10(-6) M THIATS.     

New Emivirine (MKC-442) Analogues Containing a Tetrahydronaphthalene at C-6 and their Anti-HIV Activity

An 5-ethyl-2-thiouracil derivative with a 6-(tetrahydronaphthalen-1-yl)methyl substituent was synthesized by condensation of thiourea with an adequate β-ketoester which in turn was synthesized in a single step from (tetrahydronaphthalen-1-yl)acetonitrile. The latter starting material was also used to synthesize an analogously substituted tetrahydronaphthalen-1-yl substituted uracil with a locked conformation. Only the non-nucleoside derivatives prepared from the desulfurized substituted 2-thiouracil showed moderate activity against HIV whereas a corresponding non-nucleoside derivative was devoid of activity against HIV.     

An approach to acyclo-1-deazathymidine c-nucleosides via 3,5-dichloro-6-methyl-2H-1,4-oxazin-2-one.

An approach to the synthesis of acyclo-1-deazathymidine nucleosides is described. Diels-Alder reaction of 3,5-dichloro-6-methyl-2H-1,4-oxazin-2-one with acetylenic compounds 4 and 5 yielded the 3-[(tetrahydropyran-2-yl)oxy]-methyl- and 3-bromomethyl-5-methyl-2,6-dichloropyridine intermediates 7 and 8. The bromomethyl group of compound 8 underwent easy substitution with the appropriate nucleophiles, permitting the introduction of acycLo sugar moieties. The resulting 3-substituted 2,6-dichloro-5-methyl pyridines 9a,b - precursors for some acyclo pyridine-C-nucleosides - were treated with sodium phenylmethoride to afford 2,6-dibenzyloxypyridines 10a,b. Debenzylation using a palladium-strontium carbonate catalyst gave the unstable C-nucleosides 2a,b of the 6-hydroxy-1H-pyridin-2-one type. A stable 6-hydroxy-1H-pyridin-2-one 2c, exempt from benzylic oxygen, was obtained via cycloaddition of THP-protected 6-hydroxy-1-hexyne.     

Efficient C2 functionalisation of 2H-2-imidazolines

Alkylation and oxidation of 2H-2-imidazolines, followed by regioselective deprotection, thionation and microwave-assisted Liebeskind-Srogl reaction, efficiently led to 2-aryl-2-imidazolines as new analogues of p53-hdm2 interaction inhibitors (Nutlins).     

Silica filled poly(4-methyl-2-pentyne) nanocomposite membranes: Similarities and differences with poly(1-trimethylsilyl-1-propyne)–silica systems

The performance of poly(4-methyl-2-pentyne) (PMP)/silica nanocomposites was studied for membranes with a filler content between 10 and 40 wt%. An increase in permeability and a constant vapor selectivity were measured with increasing filler content. The constant selectivity was in contrast to earlier published results for silica filled poly(1-trimethylsilyl-1-propyne) (PTSMP) membranes. Therefore, a comparison between both materials was made. Free volume sizes and interstitial mesopore sizes were determined by use of positron annihilation lifetime spectroscopy (PALS) and image analysis was performed on transmission electron microscopy (TEM) pictures of both materials. Although both materials possessed interstitial mesopores, a difference in membrane structure was noticed, explaining the difference in membrane performance.     

Self-consistent field modeling of non-ionic surfactants at the silica-water interface: incorporating molecular detail

We have constructed a model to predict the properties of non-ionic (alkyl-ethylene oxide) (C(n)E(m)) surfactants, both in aqueous solutions and near a silica surface, based upon the self-consistent field theory using the Scheutjens-Fleer discretisation scheme. The system has the pH and the ionic strength as additional control parameters. At high ionic strength, the solvent quality for the surfactant head groups is affected, which changes both the bulk and the adsorption behavior of the surfactant. For example, with increasing ionic strength, the CMC drops and the aggregation increases. Surfactants adsorb above the critical surface association concentration (CSAC). The CSAC is a function of the surfactant and the surface properties. Therefore, the CSAC varies with both the ionic strength and the pH. We predict that with increasing ionic strength, the CSAC will first slightly increase but then drop substantially. The charge on the surface is pH dependent, and as the head groups bind through H-bonding to the silanol groups, the CSAC increases with increasing pH. We focus on adsorption/desorption transitions for the surfactants and compare these to the experimental data. Both the equilibrium predictions and the consequences for the kinetics of adsorption follow experimental findings. Our results show that molecularly realistic models can reveal a much richer interfacial behavior than anticipated from more generic models.     

Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces

The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e(2u)(pi(*)) and b(2g)(pi(*)) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both sigma(*)(Pt-C) and pi(*) characters.     

A multicomponent synthesis of triazinane diones

An efficient, one-pot synthetic protocol toward triazinane diones, a rather unexplored class of heterocyclic scaffolds combining phosphonates, nitriles, aldehydes, and isocyanates is described. The optimization of the reaction, synthesis of a small library of different triazinane diones, as well as alternative routes toward the triazinane dione scaffold are discussed.     

Charge transfer enhanced annihilation leading to deterministic single photon emission in rigid perylene end-capped polyphenylenes

Two new peryleneimide end-capped polyphenylenes are shown to be deterministic single photon sources in PMMA films due to efficient annihilation between charge transfer states.