Coil-to-globule transitions of interfacial copolymers in better than theta-solvents

Experimental studies of the coil-to-globule transitions exhibited in better than -solvents by interfacial copolymers ofN-isopropylacrylamide and acrylamide imply that a lower bound for the value of n in then-clusters of poly(N-isopropylacrylamide) (PNIPAM) is 3. The corresponding upper bound is therefore likely to be 5 or 6. Statistical copolymers of PNIPAM containing upwards of 0.75 mole fraction of acrylamide (whose homopolymer does not itself displayn-clustering) exhibited this transition, which disappeared at higher mole fractions of acrylamide. Interfacial homopolymers ofN-ethylacrylamide and its statistical copolymers withN-isopropylacrylamide exhibitedn-clustering at all compositions.     

Palladium-catalyzed oxidative cyclizations: synthesis of dihydropyranones and furanones

A boron-mediated syn- and anti-stereoselective aldol reaction giving rise to various beta-hydroxyenones was coupled to a Pd((II))-mediated oxidative cyclization to give 2,3,6-trisubstituted syn- and anti-dihydropyranones in good yields. The Pd((II))-mediated oxidative cyclization was expanded to alpha-hydroxyenones leading to furan-3(2H)-one derivatives, which include natural product bullatenone and a known precursor of geiparvarin. The sole product of the oxidative cyclization of alpha,beta-dihydroxyenone was a five-membered furan-3(2H)-one derivative, suggesting that the ring closure of these diols is both chemo- and regioselective.     

The photodissociation of water by doped iron oxides: The unblased p/n assembly

Mott-Schottky capacitance measurements are used to locate semiconductor band edges for a short-circuited p-type/n-type α-Fe₂O₃ assembly in aqueous solution. The thermodynamic feasibility of the catalytic photodiscussion of water without external bias is verified for this assembly from an energy level diagram obtained for the electrode/electrolyte interfaces. Photocurrent stability and Auger analysis of the electrode show no evidence of electrode dissolution. Oxygen evolution is monitored from an assembly using mass spectrometry and H₂¹⁸O enriched water.     

Amperometric titration of boron with fructose

Aqueous solutions of boratei can be titrated amperometrically with standard fi uctose solutions This procedure may be used to determine the boron content of various types of samples after conversion of the boron to the borate form The methode is based upon the observation that the polarographic wave of fructose. in a o I M LiCl, 001 N'LiOH solution is deprcssed by the presence of borate ions Under the prescribed conditions the methode is sensitive to a few hundredths of a milligram of boron The few comnonly occurring intcrferenes can be conveniently removed prior to the titration