Self-Crosslinkable poly(arylene ether)s containing pendent phenylenetriazene groups

Self-crosslinkable poly(arylene ether)s 6 , and 8 , containing pendent triazene groups were prepared by nucleophilic substitution reaction of poly(arylene ether)s 5 , and 7 , respectively, with 1-[4-(4-hydroxyphenoxy)phenylene]triazenes, 4 , in the presence of potassium carbonate in N,N-dimethylacetamide. A series of triazenes 4 containing various substituents have been synthesized. Self-crosslinkable polymer 6e containing phenyl-substituted triazene pendants can be crosslinked at 215°C, which is about 40°C lower than the glass transition temperature of the virgin base polymer 5 . The degree of crosslinking can be tailored by varying the concentration of the pendent phenylenetriazene groups in the polymer. After curing, the flexible polymer films (ca. 10 μm thick) exhibit high gel contents, increased glass transition temperatures, improved resistance to organic solvents, and little change in dielectric constant and thermal stability. These self-crosslinkable poly(arylene ether)s are potential candidates for electronic applications. © 1994 John Wiley & Sons, Inc.     

A novel method for the templated synthesis of homogeneous samples of hollow carbon nanospheres from cellulose chars

A novel method for the production of homogeneous samples of hollow carbon nanospheres is reported from cellulose, an inexpensive and renewable precursor. The nanospheres are of diameter 50 nm, graphitic wall thickness 5-10 nm, and can easily be produced in several hundred milligram batches. The nanospheres are derived from the laser pyrolysis of a nickel chloride templated cellulose char via open Ni-core shells.     

Deuterium nuclear quadrupole coupling in the hydrogen-bound systems ethylene—D35CI and acetylene—D35CI

The deuterium nuclear quadrupole coupling constants in the T-shaped π-complexes ethylene—D³⁵Cl and acetylene—D³⁵Cl have been measured to be x_aa^D = 171.1 (71) kHz for ethylene—DCl and x_aa^D = 146.3(35) kHz for acetylene—DCL. The values of x_aa^D differ from those expected from projecting the free DCl monomer values. Rotational and centrifugal distortion constants are obtained for acetylene—D³⁵Cl confirming the structure given previously for acetylene—HCl.     

Biochemical investigation of pikromycin biosynthesis employing native penta- and hexaketide chain elongation intermediates

The unique ability of the pikromycin (Pik) polyketide synthase to generate 12- and 14-membered ring macrolactones presents an opportunity to explore the fundamental processes underlying polyketide synthesis, specifically the mechanistic details of chain extension, keto group processing, acyl chain release, and macrocyclization. We have synthesized the natural pentaketide and hexaketide chain elongation intermediates as N-acetyl cysteamine (NAC) thioesters and have used them as substrates for in vitro conversions with engineered PikAIII+TE and in combination with native PikAIII (module 5) and PikAIV (module 6) multifunctional proteins. This investigation demonstrates directly the remarkable ability of these monomodules to catalyze one or two chain extension reactions, keto group processing steps, acyl-ACP release, and cyclization to generate 10-deoxymethynolide and narbonolide. The results reveal the enormous preference of Pik monomodules for their natural polyketide substrates and provide an important comparative analysis with previous studies using unnatural diketide NAC thioester substrates.