Gel growth of α and γ glycine and their characterization

The microbial free single crystals of α and γ glycine were grown from gel at room temperature in a new chemical route. These crystals showed a superior quality than the solution grown crystals. The metastable α-form and the stable γ-form of glycine were crystallized in silica gel by solubility reduction method. The form of crystallization is confirmed by single crystal and powder X-ray diffraction analyses. The crystals of α and γ glycine were found to crystallize in monoclinic and hexagonal crystal systems, respectively. For analyzing the functional group and thermal stability of α and γ glycine crystals, spectroscopic and thermal analyses have been carried out. The dielectric studies were performed to find the dielectric constant of the grown crystals and the results are discussed. Second harmonic generation efficiency of the crystal was measured by Kurtz’s powder method using Nd:YAG laser and it was found to be 2.68 times that of potassium dihydrogen phosphate crystals.     

Controlled, simultaneous assembly of polyethylenimine onto nanoparticle silica colloids

A novel precision-assembly methodology is described on the basis of the controlled, simultaneous assembly (CSA) of a core nanoparticle substrate and polyelectrolyte solutions. The method is capable of assembly rates at least as fast as 10(16) core particles s(-1) L(-1) and affords concentrated suspensions of stable colloids with an adsorbed polyelectrolyte. The resulting dispersions are highly homogeneous, have a low viscosity and narrow particle-size distribution, and are stable colloids, even at solid concentrations of at least 33 wt %. The adsorption isotherm and the saturation adsorption for polyethylenimine (PEI) assemblies onto a 15 nm silica colloid have been evaluated with 1H NMR spectroscopy. The saturation adsorption is highly dependent upon the pH at assembly and is given by the equation PEIa (micromol m(-2)) = 1.73pH - 1.89, R2 = 0.986, where micromoles refers to the concentration of the EI monomer. The saturation concentration increases from 6.8 micromol m(-2) at pH 5.0 to 13.7 micromol m(-2) at pH 9.0. The adsorbed polyelectrolyte may be cross-linked and thereby permanently fixed to the colloid surface to prepare nanoparticle-polyelectrolyte colloidal assemblies having enhanced colloid stability, high homogeneity, and a high fraction (>80%) of permanently adsorbed polyelectrolyte. These assemblies are stable at physiological pH and ionic strength and may represent ideal substrates for bioconjugation and, ultimately, the design of nanocarriers for in vivo applications.     

Calculating endomorphism valued cohomology: Singlet spectrum in superstring models

We present a computational strategy based on exact sequences for determining the dimension of endomorphism valued cohomology groups for complete intersections in complex projective space. This cohomology group gives rise to part of the gauge singlet spectrum in superstring compactifications. We establish the underlying justification for the known deformation theoretical algorithm, and by comparison with the exact sequence method, indicate its limitations.Work supported in part by NSF contract PHY-82-09011Work supported in part by an NSF Postdoctoral Fellowship and DOE contract DE-FG02-88ER25065Work supported in part by NSF contract PHY-82-15249     

Strongly stable real infinitesimally symplectic mappings

We prove that a mapA εsp(σ,R), the set of infinitesimally symplectic maps, is strongly stable if and only if its centralizerC(A) insp(σ,R) contains only semisimple elements. Using the theorem that everyB insp(σ,R) close toA is conjugate by a real symplectic map to an element ofC(A), we give a new proof of the openness of the set of strongly stable maps. Then we prove that the set of strongly stable maps is the interior of the set of all infinitesimally symplectic maps with purely imaginary or zero eigenvalues, and the connected components of this set are described. Finally, we give a new proof of the analytic conjugacy theorem for an analytic curve through a given strongly stable map.     

Silicon (111) and (100) surfaces and their interactions with Cs,K, Na and Li; phase changes and kinetics of desorption studied by surface ionization

The rates of desorption of Cs, K, Na, and Li atoms from the (100) and (111) surfaces of silicon are followed by surface ionization. In the temperature range of the experiments, 800–1000 K, the surfaces are prepared in two forms. The first are metastable ones produced by cooling the crystals rapidly to temperatures below their surface phase transitions. These are a well-known one for the (111) face at 1120-40 K and one for the (100) face at 980 ± 20 K. The second forms are relatively stable surfaces to which the metastable ones convert spontaneously. On the metastable surfaces the desorption is first order and relatively rapid. Comparison with a model suggests that the atoms are highly mobile. On the more stable surfaces, where the desorption is mixed first and second order, a model fitting the results has the atoms also highly mobile but concentrated at steps or edges between terraces from which most of the desorption occurs. The sticking probability for the atoms is near unity on all the surfaces, and the smaller atoms, Na and Li, penetrate into the bulk to an appreciable extent.     

Mechanism for dehalogenation reactions in fast atom bombardment mass spectrometry

The mechanism of a dehalogenation reaction that occurs during fast atom bombardment (FAB) mass spectrometry was examined using halogenated nucleosides as model compounds. For aglycone-halogenated nucleosides, an inverse linear relationship exists between the extent of FAB dehalogenation and the calculated electron affinity of an individual nucleoside. The degree of dehalogenation for a given nucleoside also varies inversely with the calculated electron affinity of most FAB matrices. The observed dehalogenation reaction can be completely inhibited when matrices with positive electron affinities, such as 3-nitrobenzyl alcohol and 2-hydroxyethyl disulfide, are used. High-performance liquid chromatographic analysis of the bulk glycerol matrix following exposure to the FAB beam indicates measurable amounts of dehalogenated product, suggesting that this reaction occurs in the condensed phase prior to gas-phase ion formation. A dehalogenation mechanism involving thermal electron capture and subsequent negative charge stabilization is consistent with these observations.     

Synthesis of pyridyloxadiazoles 1. Characterization and thermal rearrangement of an unexpected 1,2,4-oxadiazol-5(4H)one

The synthesis of pyridyloxadiazoles by the reaction of acid chlorides with 5-(2-pyrklyl)-tetrazole or 2-pyridineamidoxime was studied. Reaction of 2-pyridineamidoxime with N,N-dimethylcarbamyl chloride produced 3-(2-pyridyl)-4-N,N-dimethylaminocarbony 1-1,2,4-oxadi-azol-5(4H)one instead of the expected oxadiazole. The oxadiazolone underwent thermal rearrangement with expulsion of carbon dioxide to yield the desired 3-(2-pyridyl)-5-N,N-dimethylamino-1,2,4-oxadiazole.     

Synthesis and anticonvulsant activity of 1-benzyl-4-alkylamino-1H-imidazo[4,5-c]pyridines

Four 3-deaza analogues of the potent anticonvulsant purine, BW A78U, were synthesized and tested for anticonvulsant activity. The imidazo[4,5-c]pyridines 9–12 were prepared in two steps from 4-chloro-1H-imidazo[4,5-c]pyridine ( 2 ). The compounds were potent anticonvulsant agents against maximal electroshock-induced seizures in rats with i.p. ED₅₀ ranging from 2 to 3.5 mg/kg. However, these 3-deazapurines were appreciably more toxic than BW A78U, which precluded their development as potential antiepileptic agents.     

Synthesis,stereochemistry and anti-tetrabenazine activity of bicyclo analogues of 2-phenylmorpholines

A series of bicyclo analogues of several 2-phenylmorpholines were synthesized and tested for anti-tetrabenazine activity in mice. Most of the target compounds were prepared by reaction of 2-bromopropio-phenone ( 22 ) with the appropriate amino alcohol to form 2-phenylmorpholinols. Reduction of the 2-phenyl-morpholinols with sodium borohydride gave amino diols, which were cyclized to morpholines with acid. Alternatively, oxazines 17 and 18 were synthesized by alkylation of phenyl-(2-pyrrolo)carbinol (32a) and phenyl-(2-piperidyl)carbinol (32b) with 2-bromoethanol, followed by cyclization of the resulting amino diols with acid. Only the spirocyclic compounds 8 and 9 had i.p. anti-tetrabenazine activity comparable to the non-cyclic compounds 2a-3b , but 8 and 9 were less active by the oral route of administration.