Time-resolved Fourier-transform and continuous-wave ESR studies on photo-initiated polymerization

Radical polymerization of vinyl monomers as initiated by the diphenylphosphinoyl (DPO) radical which is formed by the photo-cleavage of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TMDPO) was investigated by continuous-wave electron spin resonance (cw ESR) and Fourier-transform (FT) ESR. Well-resolved hyperfine structures (hfs’s) of the starting radicals were observed by the time-resolved cw ESR for vinyl acetate, ethyl vinyl ether, styrene, methyl methacrylate (MMA), and isoprene. The rates of formation and the spin-lattice relaxation were determined by time-resolved FT ESR for these starting radicals. In the polymerization of MMA and isoprene the primary propagating radicals were found for the first time by the observation of their well-resolved hfs’s with timeresolved cw ESR. On the basis of the kinetic analysis including the spin-lattice relaxation, the rates of formation and the spin-lattice relaxation were determined by simulation of the time profile of FT ESR for the primary propagating radicals of MMA and isoprene. The rate of the primary propagating step was found to be by two orders greater than an average value of whole propagating steps as obtained by a steady-state measurement.     

Thermal modulated interaction of aqueous steroids using polymer-grafted capillaries

Poly(N-isopropylacrylamide) (PIPAAm) of controlled molecular weight was densely grafted onto glass capillary lumenal surfaces using surface-initiated atom transfer radical polymerization (ATRP). Temperature-dependent changes of these thermoresponsive brush surfaces with hydrophobic steroids were investigated by exploiting thermoresponsive aqueous wettability changes of the polymer-modified surfaces in microfluidic systems. IPAAm was polymerized on ATRP initiator-immobilized glass surfaces using CuCl/CuCl(2)/tris(dimethylaminoethyl)amine (Me(6)TREN) as an ATRP catalyst in water at 25 degrees C. PIPAAm graft layer thickness and its homogeneity on glass surfaces are controlled by changing ATRP reaction time. Aqueous wettability changes of PIPAAm-grafted surfaces responses drastically changed to both grafted polymer layer thickness and temperature, especially at lower temperatures. Temperature-responsive surface properties of these PIPAAm brushes within capillary inner wall surfaces were then investigated using capillary chromatography. Effective interaction of hydrophobic steroids with dehydrated, hydrophobized PIPAAm-grafted capillary surfaces was observed above 30 degrees C without any column packing materials. Steroid elution behavior from PIPAAm-grafted capillaries contrasted sharply with that from PIPAAm hydrogel-grafted porous monolithic silica capillaries prepared by electron beam (EB) irradiation wherein significant peak broadening was observed at high-temperature regardless of sample hydrophobicity factors (log P values), indicating multistep separation modes in coated monolithic silica capillaries. In conclusion, thermoresponsive polymer-grafted capillary inner wall surfaces prepared by ATRP exhibit useful temperature-dependent surface property alterations effective to regulate interactions with biomolecules without requirements for separation bed packing materials within the capillary lumen.     

Synthesis of Four- and Five-Membered Heterocycles Derived from an Iminophosphorane

Reactions of an iminophosphorane bearing the Martin ligand with a ketone, an isothiocyanate, and an alkyne gave the corresponding cycloadducts, 1,3,2 u 5 -oxazaphosphetidine, 1,3,2 u 5 -diazaphosphetidine-4-thione, and 1,2 u 5 -azaphosphetine, respectively, while that with dimethyl acetylenedicarboxylate (DMAD) and successive hydrolysis afforded the 1,2 u 5 -oxaphosphole-(2 H )-one. Thermal reactions of the cycloadducts were also studied.     

Thermal and photocontrol of the equilibrium between a 2-phosphinoazobenzene and an inner phosphonium salt

The reversible conversion between a phosphine and a phosphonium salt has been achieved by external stimuli of light and heat. Two 2-phosphinoazobenzenes were successfully synthesized by desulfurization of the corresponding phosphine sulfides. One of the phosphines bearing an azo group was in equilibrium with an inner phosphonium salt and showed thermochromism, which is derived from the change of the equilibrium constant depending on the temperature. While the 2-phosphinoazobenzene reacted as a usual triarylphosphine, its reaction with water gave phosphine oxide bearing a hydrazine moiety via a mechanism similar to the Mitsunobu reaction. The 2-phosphinoazobenzene bearing a methyl group at the 4'-position of azobenzene was isomerized to the Z-isomer by irradiation. The Z-isomer was neither in equilibrium with an inner phosphonium salt nor hydrolyzed, in contrast to the E-isomer, because its geometry is difficult for an intramolecular nucleophilic attack. Photoisomerization caused the switching of the unique reactivity toward water. Such phosphines in equilibrium with the inner phosphonium salts are expected to be useful to control organic reactions by taking advantage of the photoisomerization of the azobenzene moiety.     

The preparation of di- and tri-phenylstannyl esters of aromatic dithio acids,and some of their reactions

Some crystalline di- and tri-phenylstannyl esters [ArCS₂SnPh₃ and (ArCS₂)₂SnPh₂] of aromatic dithio acids have been prepared in good yields and characterized. Preferential cleavage of the SnS bond of the ester was observed by treating them with primary and secondary amines as well as with phenacylidenetetramethylenesulfurane.     

Synthesis and properties of a pyrrole-imidazole polyamide having a ferrocene dicarboxylic amide linker

A new minor groove binder 1 having a redox active ferrocene dicarboxamide linker was synthesized. The affinity of the newly synthesized compound to the target DNA was confirmed by CD titration experiments. Moreover, the redox property of 1 was also demonstrated by cyclic voltammetry. These results suggest the potential of 1 as a new tool for electrochemical gene detection technology.