The aqueous cationic system sodium undecenoate-dodecyltrimethylammonium bromide at low concentration

The aqueous sodium undecenoate (SUD) –dodecyltrimethylammonium bromide (DTAB) catanionic system was studied at low concentration. The system did not precipitate, even at a 1:1 SUD:DTAB proportion, but showed the formation of a coacervate in a range of surfactant mixture compositions. Micelles have a preferential composition of 0.37 mole fraction of SUD. This behavior is attributed to the presence of the double bond at the distal extreme of the SUD molecule, which can form hydrogen bonds with water. Consequently, the –CH=CH₂ group is situated at the interface between the hydrocarbon micelle core and water, reducing the interfacial free energy. Structural computations demonstrate that the mentioned SUD proportion produces complete coverage of the micelle surface by the double bonds.     

INSTRUMENTATION FOR FLUORESCENCE MICROSCOPY WITH PICOSECOND TIME RESOLUTION

Abstract— Time-resolved fluorescence microscopy using excitation by actively mode-locked dye lasers and analysis by time-correlated single photon counting is shown to be an effective way of obtaining a high degree of spatial and temporal resolution. The imaging capabilities of the microscope make for optimal instrument response functions even with inexpensive photomultiplier tubes. Thus far limited (by the laser source) to long wavelength visible excitation, the excellent light collection and imaging, coupled with the sensitivity of single photon counting make it highly probable that the much weaker U-V second harmonics of the visible dyes will be useable. Certainly the potential of using the third harmonic line (355 nm) of a mode-locked c.w. Nd: YAG laser, or fundamental lines from mode-locked c.w. ion lasers as excitation sources will enhance the technique. Nevertheless, with visible-absorbing dyes only it is possible to excite such fluorochromes as chlorophylls, porphyrins, xanthenes (rose bengal, erythrosin B), phycobiliproteins, thionine dyes, ethidium bromide, and so on. Furthermore, this technique can be straightforwardly extended for polarized light measurements thereby allowing determinations of rotational diffusion of fluorochromes in cells and organelles. The extension to variable temperature situations is easy to conceive. In addition to its use for examination of cellular and sub-cellular entities, the equipment described can be profitably employed wherever spatial resolution may provide extra information, such as studies of powders and the structures of surfaces and interfaces.     

The reaction of 2-picoline N-Oxide with o-substituled benzoates and lsatoic anhydrides

The reaction of 2-picoline N-Oxide anion with o-substituted henzoates and isatoic anhydrides to give synthetically useful l-(2-methoxyphenyl)-2-(2-pyridinyl)ethanone N-oxides, I-(2-hydroxy-phenyJ)-2-(2-pyridinyl)ethanone N-oxides and I -(2-arninopheny])-2-(2-pyridinyl)ethanone N-oxides is described.     

Effect of molecular weight on the exponential growth and morphology of hyaluronan/chitosan multilayers: a surface plasmon resonance spectroscopy and atomic force microscopy investigation

The layer-by-layer growth of multilayer assemblies of two polysaccharides, the polyanion hyaluronan (HA) and the polycation chitosan (CH), was investigated using atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy, with primary emphasis on the effect of the polysaccharide molecular weights on the film thickness and surface morphology. The HA/CH multilayers exhibit an exponential increase of the optical film thickness with the number of deposited bilayers. We show that the multilayer thickness at a given stage depends on the size of both CH, the diffusing polyelectrolyte, and HA, the non-diffusing species. Assemblies (12 bilayers) of high molecular weight polysaccharides (HA, 360,000; CH, 160,000) were twice as thick (approximately 900 nm vs approximately 450 nm) as those obtained with low molecular weight polymers (HA, 30,000; CH, 31,000), as assessed by AFM scratch tests. The exponential growth rate is the same for the high and low molecular weight pairs; the larger film thicknesses observed by SPR and by AFM arising from an earlier onset of the steep exponential growth phase in the case of the high molecular weight pair. In all cases, isolated islets form during the deposition of the first CH layer onto the underlying HA. Upon further film growth, individual islets coalesce into larger vermiculate features. The transition from distinct islands to vermiculate structures depends on the molecular weights of the polysaccharides and the lower molecular weight construct presents larger worm-like surface domains than the high molecular weight pair.     

Complex emulsion inversion pattern associated with the partitioning of nonionic surfactant mixtures in the presence of alcohol cosurfactant

Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three-phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composition effects.     

Determination of 22 triazole compounds including parent fungicides and metabolites in apples, peaches, flour, and water by liquid chromatography/tandem mass spectrometry

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the determination of 14 parent triazole fungicides and 8 of their metabolites found in apples, peaches, flour, raw water, and tap water. The triazole fungicides chosen for this multiresidue method development project included propiconazole, fenbuconazole and its RH-9129 and RH-9130 metabolites, cyproconazole, difenoconazole, tebuconazole and its HWG 2061 metabolite, hexaconazole, bromuconazole (both stereoisomers), epoxiconazole, tetraconazole, triticonazole and its RPA-404886 and RPA-406341 metabolites, triadimefon, triadimenol, and myclobutanil. Of special concern to the U.S. Environmental Protection Agency were the metabolites common to all triazole fungicides: free triazole, 1,2,4-triazole (T), and its 2 conjugates: triazolylalanine (TA) and triazolylacetic acid (TAA). These metabolites were the primary focus of this project. All samples we cleaned up by a combination of C18 solid-phase extraction (SPE), mixed-mode cationic SPE, and mixed-mode anionic SPE columns. A triple-stage quadrupole mass spectrometer, equipped with electrospray ionization in the positive-ion mode, was used to determine the compounds of interest. T, TA, and TAA were quantitated using isotopically labeled internal standards (IS), in which the 1,2,4-triazole ring had been synthesized by using 13C and 15N (IS_T, IS_TA, and IS_TAA). These isotopically labeled internal standards were necessary to correct for matrix effects. The T, TA, and TAA metabolites were quantitated at the 25-50 parts-per-billion (ppb) level in food commodities and at 0.50 ppb in water. Recoveries were 70-101% from apples, 60-121% from peaches, 57-118% from flour, 75-99% from raw water, and 79-99% from tap water.     

Determination by capillary electrophoresis of total and available niacin in different development stage of raw and processed legumes: comparison with high-performance liquid chromatography

The available and total niacin evolution during maturation of yellow pea lupine (Lupinus luteus L., cv. Juno), pea (Pisum sativum L., cv. Ergo), faba bean (Vicia faba sp. minor Harz, cv. Tibo) and in germinated and high-pressure heated peas (Pisum sativum L., cv. Esla) have been determined by capillary electrophoresis (CE). The results have been compared with those obtained by high-performance liquid chromatography (HPLC). The values obtained by CE were similar to those obtained by HPLC. Maturation of seeds significantly reduced the available and total niacin content in legumes. The available/total niacin ratio during seed maturation depends on the type of legume. In faba beans and peas, a reduction was observed which was more pronounced in the case of peas. For lupine seeds, the ripening produced an increase (34%) in the available/total niacin ratio 50 days after flowering (DAF). Pea germination produced an overall increase in available and total niacin content although the available/total niacin ratio decreased. High pressure heating of pea yielded an increase in the available niacin content and available/total niacin ratio but the total niacin content did not change.     

The synthesis and thermal curing parameters of a novel quinoxaline monomer with terminal ethynyl thermoset and phenylethynyl intramolecular cycloaddition postcure capability

The Synthesis of 3,3′-bis(4-[3-ethynylphenoxy]phenyl)-7,7′-bis(phenylethynyl)-2,2′-diphenyl-6,6′-biquinoxaline (I) was accomplished by the reaction of 2,2′-bis(phenylethynyl)-5,5′-diaminobenzidine (II) and 4-(3-ethynylphenoxy)benzil. Thermal analysis of I indicated a softening temperature of 107°C, followed by an exotherm above 150°C that corresponded to a independent crosslinking reaction of the terminal acetylene groups and an intramolecular cycloaddition (IMC) reaction of the 2,2′-bis(phenylethynyl)biphenyl moieties. In the synthetic work substantial improvements were made in the synthesis of II. The sample of I was cured at 200°C and the maximum partially cured transition temperature attained was 280°C. A sample of 3,3′-bis(4,[3-ethynylphenoxy]phenyl)-2,2′-diphenyl-6,6′-biquinoxaline (IV) was similarly tested as a model without IMC capability and its corresponding value was 250°C. The difference between these two values is discussed briefly.     

Photosensitization of DNA damage by a new cationic pyropheophorbide derivative: sequence-specific formation of a frank scission

Pyropheophorbides are red-absorbing porphyrin-like photosensitizers that may interact with DNA either by intercalation or by external binding with self-stacking according to the value of the nucleotide to chromophore molar ratio (N/C). This article reports on the nature and sequence selectivity of the DNA damage photoinduced by a water-soluble chlorhydrate of aminopyropheophorbide. First, this pyropheophorbide is shown to induce on irradiation the cleavage of phiX174 DNA by both Type-I and -II mechanisms, suggested by scavengers and D2O effects. These conclusions are then improved by sequencing experiments performed on a 20-mer oligodeoxynucleotide (ODN) irradiated at wavelengths >345 nm in the presence of the dye, N/C varying from 2.5 to 0.5. Oxidation of all guanine residues to the same extent is observed after piperidine treatment on both single- and double-stranded ODN. Moreover, unexpectedly, a remarkable sequence-selective cleavage occurring at a 5'-CG-3' site is detected before alkali treatment. This frank break is clearly predominant for a low nucleotide to chromophore molar ratio, corresponding to a self-stacking of the dye along the DNA helix. The electrophoretic properties of the band suggest that this lesion results from a sugar oxidation, which leads via a base release to a ribonolactone residue. The proposal is supported by high-performance liquid chromatography-matrix-assisted laser desorption-ionization mass spectrometry experiments that also reveal other sequence-selective frank scissions of lower intensity at 5'-GC-3' or other 5'-CG-3' sites. This sequence selectivity is discussed with regard to the binding selectivity of cationic porphyrins.     

Structure and oxidation at quasicrystal surfaces

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f vs. 5f surfaces), and with bulk composition (e.g. i-Al–Pd–Mn vs. i-Al–Cu–Fe). We have also compared our results for the quasicrystals with results for crystalline approximants and other related crystalline phases. Our main conclusions are that, under specific conditions of sputter-annealing, the bulk atomic and electronic structures of the clean quasicrystal propagate to the surface. Also, the oxidation chemistry is dominated by that of the primary constituent, aluminum.