Ability of poly(vinyl alcohol) fibers to initiate graft copolymerization

It was noted in a graft copolymerization reaction involving a system of poly(vinyl alcohol) fibers (PVA fibers), methyl methacrylate, and water that fibers oxidized with hydrogen peroxide or sodium hypochlorite or ferric ion-adsorbing fibers effectively initiate the reaction as in the case of cellulose fibers. The initiation reaction of the sample was markedly activated by the presence of a pretreatment with an oxidizing agent at a concentration on the order of 10^?9 mole/l., but the oxidized samples were sharply deactivated by such means as reduction and oximation. Since model initiators for the present system, such as iron(III) acetylacetonate-adsorbing PVA fibers or ferric ion-adsorbing fibres, with the co-existence of acetylacetone were observed to initiate graft copolymerization effectively, it is believed that carbonyl groups in modified PVA fibers could be a major factor for initiating copolymerization through interaction with metallic ions.     

Stabilization of DNA triplexes by dangling aromatic residues

Novel nucleoside analogues containing 2^′-deoxyinosine and aromatic rings, which are connected by short linker groups, were synthesized and incorporated into oligodeoxyribonucleotides (ODNs). ODNs containing the nucleoside analogues formed stable duplexes and triplexes with target nucleic acids. The stacking interaction between base residues in the nucleoside analogues appears to be a major cause of stabilization.     

Temperature stabilized optical waveguide modulator

A low drive-voltage optical modulator using a Ti-diffused UNbO₃ optical waveguide has been fabricated. Stabilization against ambient temperature change was realized by using a miniature halfwave plate. The halfwave voltage, 3 dB bandwidth, optical insertion loss and extinction ratio were 3·8 V (at 1·06m wavelength), 850 MHz, 10 dB and 13 dB, respectively. A reduction scheme for the optical absorption caused by metallic electrodes, and an analysis of the modulator high frequency response are also reported.     

Solubilization of oleyl alcohol by pure and mixtures of surfactants

The solubilization behavior of oleyl alcohol by pure and mixtures of surfactants systems have been studied in terms of the maximum additive concentration (MAC), the solubilizing power, and the particle sizes of micelles with or without oleyl alcohol. The surfactants used are amphoteric (N,N-dimethyl-N-lauroyl lysine, DMLL; N,N,N-trimethyl-N-lauroyl lysine, TMLL; N,N-dimethyl-N-(carboxymethyl)-lauryl ammonium, DMCL), anionic (sodium dodecyl sulfate, SDS) and nonionic (alkyl polyoxyethylene ethers).The maximum additive concentration of oleyl alcohol by pure surfactants is larger by nonionic surfactants than by others.For a nonionic surfactant system mixed with DMLL, the mixing effect of surfactant on the increase in the MAC is not recognized. While, for DMLL mixed with SDS, the MAC becomes larger than that by pure surfactants. This may be attributed to the fact that the large micellar size will result in increasing the maximum additive concentration.     

Studies on reactions of the N-phosphonium salts of pyridines. XIII. Direct polycondensation reaction of carbon dioxide or disulfide with diamines under mild conditions

Polyureas of high molecular weight were obtained by the direct polycondensation reaction of carbon dioxide with diamines at 40°C for several hours under a pressure of carbon dioxide (below 30 atm) by use of diphenyl phosphite in pyridine. Optimal temperature and pressure were 40°C and 20 atm of carbon dioxide. The polycondensation reaction was also affected by solvents and type and amounts of tertiary amines. Pyridine was most effective as tertiary amine and solvent as well. Of the phosphorous compounds used, triaryl phosphites and diphenyl phosphite were most effective, but trialkyl phosphites failed to give polymer. The reaction was assumed to proceed via a carbamyl N-phosphonium salt of pyridine formed by dephenoxylation of phosphites. Similarly, polythioureas were prepared by heating a mixture of carbon disulfide, diamines, and diphenyl phosphite in pyridine at 40°C for 6 hr under nitrogen.     

Effects of carbonyl and aldehyde groups in the graft copolymerization of methyl methacrylate on cellulose with a ceric salt

Graft copolymerization of methyl methacrylate on cellulosic materials of various carbonyl and aldehyde contents with the use of a ceric salt as an initiator was studied. It was found that the concentration of the ceric salt which gives the maximum per cent grafting is in good agreement with the equivalent of total carbonyl content in the cellulosic material, and the number of grafted chains in copolymers is roughly proportional to it. However, the molar ratio of the number of grafted chains to total carbonyl content is quite small, being approximately 1:50, and the graft copolymerization can be explained kinetically on the assumption that the number of radicals produced on cellulose by the ceric salt leading to branching is very much smaller than the number of radicals destroyed by the ceric salt, and growing radicals can be stabilized by the termination reaction with the ceric salt or with a cellulose radical. Although both aldehyde and carbonyl groups contribute to the formation of grafted chains, the former are effective mainly at low concentrations of the ceric salt; both groups participate in the production of graft copolymers showing the maximum per cent grafting.     

Reagentless biosensor for isocitrate using one step modified Pt-Ir microelectrode

The Pt-Ir microelectrode modified through one step electropolymerization is proposed for the isocitrate amperometric biosensor construction. The enzyme (isocitrate dehydrogenase-ICDH), coenzyme (NADP(+)) and mediator (Meldola's Blue) were immobilized onto the microelectrode surface in one step from a PIPES buffer solution containing pyrrole. The optimized experimental conditions were 25 cycles of cyclic voltammetric in a solution containing 3.58 10(-5) mol l(-1) of mediator, 3.51 10(-4) mol l(-1) of coenzyme and 2.68 U ml(-1) of enzyme. In contrast to the biosensor for isocitrate reported in literature, just one enzyme was immobilized and no coenzyme addition in the solution of analysis was necessary. Catalytic currents were proportional to the isocitrate concentration between 7.7 10(-6) and 1.04 10(-4) mol l(-1), showing good repeatability. The detection limit of the proposed biosensor was 3.50 10(-6) mol l(-1), the response time was lower than 20 s, the lifetime was about 30 determinations and no significant interference of sugars and citric acid was verified. Orange juice samples were analysed by both methodology biosensor and spectrophotometric commercial kit, and the obtained results presented a good correlation. The data demonstrated that the developed biosensor is suitable for isocitrate determination in orange juice without matrix interferences.     

Photo-induced cellulose radicals capable of initiating graft copolymerization

The decay behavior of cellulose radicals produced by photo-irradiation at room temperature and the characteristics of photo-irradiated cellulose samples to initiate graft copolymerization of methyl methacrylate (MMA) were investigated. ESR spectra of such untreated, swollen, oximated, and ferric ion-sensitized samples irradiated at room temperature were constructed mainly of a single absorption line with a line width of 20 to 22 gauss and a g value of 2.003, and it is surely conceivable that the radicals showing a singlet spectrum should agree with those of alkoxy end produced at either the C₁ or C₄ position of the glucose unit by the scission of glucosidic bonds. The decay of radicals was accelerated by contact of various solvents with the samples, the activity decreasing in the order, water ≈ methanol ? acetone > dioxane. On the other hand, the decay of radicals by vinyl monomers became smaller in the order, methacrylic acid > MMA ≈ styrene. Graft copolymerization of MMA by a photo-irradiated sample was effectively initiated with the use of a certain amount of water or methanol, but not with acetone and dioxane. As no initiation can occur with the unirradiated sample, it is concluded that the initiation of graft copolymerization on the photo-irradiated sample is attributable to cellulose radicals showing a singlet spectrum which are formed in photo-irradiation at room temperature.     

Studies on reactions of the N-phosphonium salts of pyridines. XIV. Wholly aromatic polyamides by the direct polycondensation reaction by using phosphites in the presence of metal salts

Poly-p-benzamide of high molecular weight (η_inh = ～ in H₂SO₄) was obtained by the direct polycondensation reaction of p-aminobenzoic acid (p-ABA) by means of diphenyl and triaryl phosphites in N-methylpyrrolidone (NMP)-pyridine solution containing lithium and calcium chlorides. Molecular weight of polymer varied with the amount of these salts, showing maximum values at the concentration of about 4 wt-% of LiCl or about 8 wt-% of CaCl₂ in the reaction mixture. The reaction temperature at around 80°C gave a polymer of the highest viscosity. The polycondensation reaction was also affected by monomer concentration, solvents, and tertiary amines like pyridine. Similarly, aromatic polyamides with high molecular weight (η_inh values up to 1.34 in H₂SO₄) were prepared from isophthalic acid and aromatic diamines, whereas terephthalic acid gave only low-viscosity polymers.