Functional monomers and polymers. LXXI. Conformation and interaction studies of poly-L-lysine derivatives with pendant nucleic acid bases

Copolymers of L -lysine and L -lysine derivatives which contained nucleic acid bases substituted on the N^ε position were synthesized by grafting nucleic acid derivatives onto poly-L -lysine. The conformation and interaction of these copolymers in solution were studied by using spectroscopic measurements. They existed in helical conformation at neutral pH values, and the polymer complex formation among them was examined by ultraviolet (UV) measurements in organic solvents. A decrease in the nucleic acid base content of the copolymers resulted in a decrease in helical structures and also in interactions with the polymer-containing complementary bases.     

FLAVIN-PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMER IN THE PRESENCE OF MAGNESIUM PERCHLORATE

We have investigated the photosensitized monomerization of the cis,syn -cyclobutane dimer of 1,3-di-methylthymine using riboflavin tetraacetate and a 5-deazaflavin derivative as photosensitizer. Although little monomerization of the dimer is induced by photoexcitation of the flavins in the absence of any additives, the flavins can function as an efficient photosensitizer in the presence of magnesium perchlorate. Mechanistic studies involving spectroscopic, quantum-yield and flash-photolysis measurements demonstrated that the photosensitized monomerization exclusively proceeds through electron transfer from the dimer to the triplet flavins complexed with Mg²⁺. The effects of magnesium perchlorate are compared with those on the chloranil-photosensitized monomerization and also with the effects of HClO₄ on the flavin-photosensitized reaction.     

Self-assembly patterning of colloidal crystals constructed from opal structure or NaCl structure

We developed a novel self-assembly process to fabricate an orderly array of particle wires constructed from a close-packed colloidal crystal without preparation of patterned templates. A substrate was immersed vertically into a SiO2 colloidal solution, and the liquid surface moved downward upon evaporation of solution. Particles formed a mono-/multiparticle layer, which was cut by the periodic drop-off of solution. The orderly array of particle wires was successfully fabricated, showing the suitability of the self-assembly process for the fabrication of nano-/microstructures constructed from nano-/microparticles or blocks. The mechanism of the assembly process and control of thickness, width, and interval of particle wires were further discussed. Moreover, an array of particle wires constructed not from close-packed face-centered cubic (or hexagonal close packed) structure but from two kinds of particles was realized to fabricate an array of particle wires with NaCl structure by this self-assembly process.     

Vinylpolymerisation mit Metall-Komplexen. 27. Mitt. Mechanistische Untersuchung der Vinylpolymerisation mit Polyvinylamin-Cu-(II)-Chelaten in Dimethylsulfoxid-Lösung

Ohne Zusammenfassung     

Functional monomers and polymers. LXI. Photochemical reactions on the synthetic polymers containing thymine bases

Photodimerization of N-2-isobutyloxyethyl thymine (T-M), bis[2-(5-methyl-1-primidinyl)-ethyl] glutarate (T-T), poly(N-2-methacryloyloxyethyl thymine) (polyMAOT), and poly(N-2-acryloyloxyethyl thymine) (poly AOT) was studied in dimethylformamide solution. The rate of intramolecular photodimerization of polyMAOT and polyAOT was 5.7 and 7.2 times faster, respectively, than that of T-T. In T-M, however, intermolecular photodimerization did not occur under the reaction condition used. Quenching studies with isoprene suggest that the photodimerization of T-T occurs predominantly in an excited triplet state, whereas that of polyMAOT and polyAOT occur in singlet and triplet states. It was concluded that the photodimers of T-T, polyMAOT, and polyAOT are two syn-fused cyclobutane-type dimers (cis-syn and trans-syn). Quantum efficiencies of thymine base disappearance were determined by ultraviolet (UV) analysis to be 0.0012 for T-T, 0.0084 for polyMAOT, and 0.010 for polyAOT.     

Polymerization of cyclic derivatives of uracil and thymine

Cyclic derivatives of uracil and thymine were synthesized from their corresponding 1-(2′-chloroethyl) derivatives by dehydrochlorination. These compounds were found to undergo a variety of reactions, giving many valuable derivatives of uracil and thymine. The cyclic derivatives, as monomers, were polymerized with a cationic initiator by a unique ring-opening process. The polymerization proceeded by ring opening with isomerization of the pyrimidine ring to give a polymer in which pyrimidine rings were connected with ethylene between N-1 and N-3 or O-4 in the pyrimidine ring. The structure of these polymers was determined by nuclear magnetic resonance (NMR), ultraviolet (UV), infrared (IR), and mass spectra. The structure was affected by polymerization temperature.     

Self-assembly patterning of silica colloidal crystals

We developed a self-assembly process of silica particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. This result is a step toward the realization ofnano/micro periodic structures for next-generation photonic devices by a self-assembly process.     

Functional monomers and polymers 159 synthesis and photochemical reactions of polymers containing thymine photodimer units in the main chain

Polyamides containing thymine photodimer units in the main chain were synthesized, and their photolysis by ultraviolet irradiation below 260 nm were studied in film state. Photodimers of thymine derivatives were obtained by photochemical reaction of the carboxylic acid derivatives of thymine in aqueous solution irradiated above 270 nm. An attempt was made to resolve the isomers of the photodimers, and the two kinds of cis isomers [cis–syn(head to head), and cis–anti(head to tail)] were isolated successfully. The polyamides were prepared by condensation of the photodimers with diamine using an activated ester method. The photodissociation of the thymine photodimer in the polymer main chain caused the breakage of the polymer chains, leading to the production of oligomers and dimer compounds containing thymine bases at the ends of the molecule. The dissociation rate of the polymer did not depend on the kind of the thymine photodimer which was in the main chain of the polymer.     

Theoretical prediction of the damping of a railway wheel with sandwich-type dampers

This paper presents a procedure for predicting the damping added to a railway wheel when sandwich-type dampers are installed. Although there are different ways to reduce the noise generated by a railway wheel, most devices are based on the mechanism of increasing wheel damping. This is why modal damping ratios are a clear indicator of the efficiency of the damping device and essential when a vibro-acoustic study of a railway wheel is carried out. Based on a number of output variables extracted from the wheel and damper models, the strategy explained herein provides the final damping ratios of the damped wheel. Several different configurations are designed and experimentally tested. Theoretical and experimental results agree adequately, and it is demonstrated that this procedure is a good tool for qualitative comparison between different solutions in the design stages.