Synthesis and characterization of the aqueous solution chemistry of the food-derived carcinogen model N-acetoxy-N-(1-methyl-5H-pyrido[4,5-b]indol-3-yl)acetamide and its N-pivaloyloxy analogue

We report the synthesis of N-acetoxy-N-(1-methyl-5H-pyrido[4,5-b]indol-3-yl)acetamide, 7, its N-pivaloyloxy analogue, 9, and improved synthesis of indole-2-acetonitrile, 3 (70% in five steps from indole-2-carboxylic acid), the carcinogenic amine Trp-P-2, 4 (40% from 3), and the nitro compound, 5 (40% from 4 by oxidation with H₂O₂ using Mo(CO)₆ catalyst). In aqueous solution at neutral pH, 7 primarily undergoes C-O bond cleavage to yield the hydroxamic acid, 8, but under the same conditions the sterically hindered 9 decomposes predominately by N-O bond cleavage with a pH independent rate constant that is 7.5-fold smaller than that for 7. In the pH range 0.5-7.0 three different processes for the decomposition of 9 were detected by kinetics. Only the process that dominates at neutral pH generates a nitrenium species that can be trapped by N₃⁻.     

Free-radical distributions in emulsion polymerization which employs oil-soluble radical generators

The use of oil-soluble radical generators for emulsion polymerization is considered. When radicals are formed in pairs within particles of a seed latex, the occurrence of radical desorption leads to complex kinetics. Use of radical balances and realistic simplifications produce a method for a relatively simple calculation of radical populations in the particles. Examples are restricted, for illustration purposes, to cases where the average number of radicals per particle, n , is less than one. Very low rates of radical desorption cause a substantial increase in n . As the desorption rate increases, the value of n decreases. n increases slowly with radical generation rate. Large decreases in the chain termination rate coefficient (which may accompany a gel effect) can have a negligible effect on the value of n . Radical distributions obtained from oil-soluble initiators can be slightly broader than those expected from the use of water-soluble initiators. The kinetics of emulsion polymerization will be similar for the two types of radical generator when radicals from oil-soluble generators can desorb from the polymer particles.     

Determination of cibenzoline in plasma and urine by high-performance liquid chromatography

A rapid, sensitive and selective high-performance liquid chromatographic (HPLC) assay was developed for the determination of cibenzoline (CipralanTM) in human plasma and urine. The assay involves the extraction of the compound into benzene from plasma or urine buffered to pH 11 and HPLC analysis of the residue dissolved in acetonitrile-phosphate buffer (0.015 mol/l, pH 6.0) (80:20). A 10-microns ion-exchange (sulfonate) column was used with acetonitrile-phosphate buffer (0.015 mol/l, pH 6.0) (80:20) as the mobile phase. UV detection at 214 nm was used for quantitation with the di-p-methyl analogue of cibenzoline as the internal standard. The recovery of cibenzoline in the assay ranged from 60 to 70% and was validated in human plasma and urine in the concentration range of 10-1000 ng/ml and 50-5000 ng/ml, respectively. A normal-phase HPLC assay was developed for the determination of the imidazole metabolite of cibenzoline. The assays were applied to the determination of plasma and urine concentrations of cibenzoline and trace amounts of its imidazole metabolite following oral administration of cibenzoline succinate to two human subjects.     

Hydrogen Bond Cooperativity and the Three‐Dimensional Structures of Water Nonamers and Decamers

Broadband rotational spectroscopy of water clusters produced in a pulsed molecular jet expansion has been used to determine the oxygen atom geometry in three isomers of the nonamer and two isomers of the decamer. The isomers for each cluster size have the same nominal geometry but differ in the arrangement of their hydrogen bond networks. The nearest neighbor O? O distances show a characteristic pattern for each hydrogen bond network isomer that is caused by three‐body effects that produce cooperative hydrogen bonding. The observed structures are the lowest energy cluster geometries identified by quantum chemistry and the experimental and theoretical O? O distances are in good agreement. The cooperativity effects revealed by the hydrogen bond O? O distance variations are shown to be consistent with a simple model for hydrogen bonding in water that takes into account the cooperative and anticooperative bonding effects of nearby water molecules.     

First measurement of the double spin asymmetry in (-->)e(-->)p-->e(prime)pi(+)n in the resonance region

The double spin asymmetry in the (-->)e(-->)p --> e(prime)pi(+)n reaction has been measured for the first time in the resonance region for four-momentum transfer Q2 = 0.35-1.5 GeV(2). Data were taken at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH3 target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with Q(2) of the helicity asymmetry A1 for the F(15)(1680) resonance than expected from the analysis of the unpolarized data.