The influence of pentafluorophenyl groups on the nonlinear optical (NLO) performance of high generation dendrons and dendrimers
With the aim to make the influence of pentafluorophenyl groups in the periphery of high generation dendrons and dendrimers on their NLO performance clearly, some NLO dendrons and dendrimers with different chromophore moieties or different end-capped groups were carefully designed and investigated in detail. The results demonstrated that some strong Ar-ArF interactions between the pentafluorophenyl groups in the periphery and the normal phenyl rings of the donors, could influence the topological structures of dendrons or dendrimers, and then affect their NLO performance. Furthermore, the optical transparency and the stability of the dendrons and dendrimers with pentafluorophenyl groups as end-capped moieties were all improved, in comparison with normal dendrons and dendrimers containing phenyl ones as the end-capped groups.
Dendronized hyperbranched polymers containing isolation chromophores: design, synthesis and further enhancement of the comprehensive NLO performance
Dendronized hyperbranched polymer (DHP) combining the structure of a dendrimer and a hyperbranched polymer, is a new kind of polymer, with some advantages as summarized from the few examples reported so far. Herein, three second-order nonlinear optical (NLO) functional dendronized hyperbranched polymers, DHP-NN, DHP-NS and DHP-SS, were prepared in satisfactory yields through the click chemistry reaction, by using two kinds of low generation dendrimers as the monomers. Due to its particular branched structure, these DHPs with high molecular weights exhibit good solubility, processability, and good nonlinear optical performance. All the DHPs can keep their NLO performance at relatively high temperatures (∼100 °C). In particular, the introduced isolation chromophore could further enhance the thermostability of the NLO performance: DHP-NS and DHP-SS exhibit no obvious decay of their NLO coefficient when the thin films are heated to 125 °C.
Cytoplsmic uridine phosphorylase of rat liver. Characterization and kinetics.
Abstract Uridine phosphorylase (uridine:orthophosphate ribosyltransferase, EC 2.4.2.3) of rat liver cytoplasm has been purified 1900-fold. Initial velocity patterns of the phosphorolysis of uridine or deoxyuridine and of the synthesis of uridine indicated a sequential mechanism. Product inhibition patterns with uracil or ribose 1-phosphate as inhibitors were consistent with an "ordered Bi Bi" reaction in which inorganic phosphate is the first substrate to bind to the enzyme and ribose 1-phosphate the last product to leave the enzyme. The most highly purified enzyme fractions still retained uridine-, deoxyuridine-, and thymidine-cleaving activities in the ratio of 10:7:1 at pH 7.4. The fractions separated into a major and a minor band of protein on electrophoresis in phosphate buffer. Aging of the enzyme with loss of activity resulted in an increase in the proportion of the minor band. The pH optimum of the enzyme for uridine cleavage was 8.2, for deoxyuridine cleavage, 6.5, and for uridine synthesis, 8.5. Uridine or deoxyuridine synthesis was inhibited 50% in the presence of 1 mm uracil. The enzyme did not catalyze the direct transfer of ribose from uridine to uracil in the absence of phosphate. Uridine protected the enzyme to a greater degree than phosphate against inhibition by o-iodosobenzoate. Thus, at least one sulfhydryl group and possibly three are present at or near the active site. Uridine cleavage, uridine synthesis, and deoxyuridine cleavage were inhibited by deoxyglucosylthymine. The phosphorolysis of deoxyuridine and thymidine by thymidine phosphorylase, also purified from rat liver cytoplasm, was not inhibited by deoxyglucosylthymine. The molecular weights of both uridine and thymidine phosphorylases were estimated to be 110,000.