Thermal decomposition and carbonization mechanism of poly-para-phenyleneoxadiazole

Thermal decomposition and carbonization mechanism of poly-para-phenylene-1,3,4-oxadiazole were investigated using FT-IR, thermogravimetry, gas-analysis, XPS, ¹³C-CP/MASFT-NMR, and elemental analysis. At temperatures above 500°C, the decomposition reaction proceeds preferentially on the oxadiazole ring, eliminating p-aminocyanobenzene and p-dicyanobenzene. Formation of carbodiimide compounds and their coupling followed in residual compounds, whose products are important intermediates leading to a planar and polyconjugated nitrogen-containing (e.g., graphite-like) carbon precursor.     

The Diameters of Some Transition Graphs Constructed from Hamilton Cycles

 A complete undirected graph of order n has Hamilton cycles. We consider the diameter of a transition graph whose vertices correspond to those Hamilton cycles and any of two vertices are adjacent if and only if the corresponding Hamilton cycles can be transformed each other by exchanging two edges. Moreover, we consider several transition graphs related to it. Received: November 4, 1999 Final version received: August 28, 2000     

L-lysine based gemini organogelators: their organogelation properties and thermally stable organogels

Novel gemini organogelators based on L-lysine, in which two L-lysine derivatives are linked by different alkylene chain lengths through the amide bond, have been simply and effectively synthesized, and their organogelation abilities and thermal stabilities have been investigated. In a series of L-lysine ethyl ester derivatives, the organogelation abilities decreased with increasing alkylene spacer length. In particular, bis(N(epsilon)-lauroyl-L-lysine ethyl ester) oxalyl amide is a good organogelator that gels most organic solvents such as alcohols, cyclic ethers, aromatic solvents and acetonitrile. Various oxalyl amide derivatives with different alkyl ester groups such as hexyl, decyl, dodecyl, 2-ethyl-1-hexyl and 3,5,5-trimethylhexyl also showed good organogelation abilities. Furthermore, it was found that the cyclohexane gels formed by some oxalyl amide derivatives have a high thermal stability.     

Production, analysis, and application of spatially resolved shells in solid-phase polymer spheres

Two-photon fluorescence microscopy has been used to interrogate the interior functionality of polymer resin beads. By employing this technique, the spatial distribution of the initial functionality contained within the polymer matrix has been determined. Spatially resolved, concentric shells were then produced synthetically in these polymer spheres via a series of protection/deprotection reactions in which two-photon fluorescence microscopy was employed to monitor each successive step. To demonstrate the potential utility of these techniques in combinatorial screening, a set of beads was prepared containing a unique tripeptide sequence in each of the three concentric shells within each individual bead. The set was then screened for the binding affinity of each tripeptide toward a fluorescent ligand.     

CONFIGURATIONS OF NEUROSPORENE ISOMERS ISOLATED FROM THE REACTION CENTER AND THE LIGHT-HARVESTING COMPLEX OF Rhodobacter spheroides G1C. A RESONANCE RAMAN, ELECTRONIC ABSORPTION, AND 1H-NMR STUDY

Abstract— HPLC analysis of neurosporene extracted from the chromatophore membranes of Rhodobacter spheroides G1C showed two isomeric components 1 and 2. Extract from the light-harvesting complex (LH) gave only component 2, while extract from the reaction center (RC) mainly gave component 1. Both components were isolated, and their configurations were determined by means of (1) resonance Raman, (2) electronic absorption, and (3) ¹H-HMR spectroscopy. The configuration of component 2 originating from LH was determined to be all -trans and that of component 1 from RC was determined to be 15- cis . Thus, our previous configurational prediction of this particular carotenoid bound to RC, by means of resonance Raman spectroscopy, to be 15-cis [Y. Koyama, T. Takii, K. Saiki and K. Tsukida, Photobiochem. Photobiophys. 5 (1983)139–150] is confirmed.     

Thermoplasticization of cellulose acetates by grafting of cyclic esters

A plasticization method for cellulose acetates (CAs) based on the selective grafting of caprolactone (CL) and L-lactide (LACD) has been developed. The selectivegrafted products could be prepared by ring opening polymerization in the melt state at 140°C using stannous octoate as catalyst, where CAs with remaining hydroxyl groups worked as initiator. Plasticization of CAs by this selective grafting can solve the problem encountered in the previous reports (Yoshioka et al., 1996, 1998) that the bleeding of unreacted monomers and homooligomers from the inside of molded articles to their surface was often found. By using adequate reaction conditions, the grafting reaction proceeded rapidly and could be completed within 10–30min. LACD is grafted more rapidly than CL onto CAs, producing relatively rigid and brittle products in the earlier stages and elastomerlike ones in the later stages. Transparent amorphous molded articles were obtainable depending on the reaction conditions. The analysis of the structure of the grafted side chains by means of high resolution NMR spectroscopy showed that, although the grafted side chains are composed of large amounts of oxycaproyl or lactidyl block polymer portions depending on the reaction conditions, a large amount of randomly polymerized parts coexist in the grafted chains, which confer high thermoplasticity, elasticity and amorphous nature to the grafted products obtained.     

l-Lysine-based supramolecular hydrogels containing various inorganic ions

The preparation of supramolecular hydrogels containing various inorganic acids and salts using L-lysine-based hydrogelators is conducted and their thermal stabilities, gel strengths, FT-IR spectra, and electron micrographs are measured. These hydrogelators can form supramolecular hydrogels over a wide pH range and contain inorganic acids and salts. The supramolecular hydrogels based on ester-type hydrogelators have good thermal stabilities (high Tgel), while the hydrogelator with a carboxyl group forms a thermally sensitive gel with high mechanical strength. Furthermore, the gelation mechanism is discussed using FT-IR spectroscopy and TEM observations.     

Determination of dissociation constants of sparingly soluble phenothiazine derivatives by second-derivative spectrophotometry

The dissociation constants (pK_a) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pK_a values were calculated from the pH dependence of the D values. The pK_a values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined.     

Synthesis and reactions of a monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide

A 3-monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide, was prepared for the first time, by the reaction of (9-triptycyl)diazomethane and S₈O. The dithiirane 1-oxide was obtained as cis- and trans-isomers, and the structure of the trans-isomer was verified by X-ray crystallography. The cis-isomer isomerized gradually to the trans-isomer in solution. The divalent sulfur atom of the cis- and trans-dithiirane 1-oxides were removed on treatment with triphenylphosphine to give the corresponding Z- and E-sulfines, respectively. The reaction of the trans-dithiirane 1-oxide with (Ph₃P)₂Pt(C₂H₄) provided the (sulfenato-thiolato)Pt^II complex, and that with Lawesson's reagent yielded the 1,3,4,2-trithiaphospholane and 1,2,4,5,3-tetrathiaphosphorinane derivatives.