Effects of Additives on the Laser-Initiated Polymerization of 1,6-Hexanediol Diacrylate

Polymerization exotherms of 1,6-hexanediol diacrylate (HDDA) were generated by a pulsed laser source and recorded on a modified differential scanning calorimeter. Several aromatic carbonyl-based photoinitiators were compared with respect to maximum rate and extent of polymerization in the absence and presence of oxygen. α-Cleavage photoinitiators were more efficient than the hydrogen-abstracting benzophenone. The addition of an amine to a photocleavable initiator improved the polymerization of HDDA under an inert atmosphere, whereas triarylphosphines under similar conditions were effective in reducing the air inhibition. This synergistic effect depends on the type and structure of the additive and the photoinitiator.

The use of benzophenone in combination with an α-cleavage photoinitiator showed no significant effect upon polymerization, while extra thermal energy imposed upon the system slightly improved the polymerization.     

Inverting the G‐Tetrad Polarity of a G‐Quadruplex by Using Xanthine and 8‐Oxoguanine

G‐quadruplexes are four‐stranded nucleic acid structures that are built from consecutively stacked guanine tetrad (G‐tetrad) assemblies. The simultaneous incorporation of two guanine base lesions, xanthine (X) and 8‐oxoguanine (O), within a single G‐tetrad of a G‐quadruplex was recently shown to lead to the formation of a stable G?G?X?O tetrad. Herein, a judicious introduction of X and O into a human telomeric G‐quadruplex‐forming sequence is shown to reverse the hydrogen‐bond polarity of the modified G‐tetrad while preserving the original folding topology. The control exerted over G‐tetrad polarity by joint X?O modification will be valuable for the design and programming of G‐quadruplex structures and their properties.     

Graphene‐like Molecules with Four Zigzag Edges

An efficient synthetic method toward graphene‐like molecules (GLMs), having four zigzag edges, is described. They were obtained as stable materials and their structures were confirmed by X‐ray crystallographic analysis. They exhibit topology‐ and size‐dependent electronic properties and global aromaticity, which are all different from GLMs having either all‐armchair edges, or three zigzag edges, or two armchair/two zigzag edges. They can be reversibly oxidized and reduced into stable charged species, which show fragmental aromatic character to minimize anti‐aromaticity. Our studies give some new insights into the electronic structures and properties of a new type of rarely studied GLMs.     

Synthesis and reactivity of naphthalene sandwich complexes of molybdenum. X-ray structure of [Mo(η6-naphthalene) {P(OMe)3}3] and [Mo(H)(η6-naphthalene){P(OMe)3}3][BF4]

The sandwich complexes bis(η⁶-naphthalene)molybdenum(0) ( 1 ), bis(η⁶-1-methylnaphthalene)molybdenum(0) ( 2 ), and bis(η⁶-1,4-dimethylnaphthalene)molybdenum(0) ( 3 ) are synthesized by cocondensation of Mo-atoms with the naphthalene ligands. Complexes 1–3 are also obtained by reduction of MoCl₅ or MoCl₄. 2THF with highly activated Mg in the presence of the naphthalene ligands. Mg was activated by sublimation of the metal in a simple rotating solution reactor. Complex 2 exists as a mixture of regio- and stereoisomers. Three regioisomers, 3a–c , are formed in reactions of Mo-atoms with 1,4-dimethylnaphthalene, whereas 3a , the isomer with the Mo-atom coordinated to the unsubstituted rings, is formed selectively via the reductive method. The ligands in 1–3 are highly labile. CO displaces both naphthalene rings in 2 and 3 to give [Mo(CO)₆], while PF₃, P(OMe)₃, and PMe₃ displace only one coordinated naphthalene in 1 to yield the [Mo(η⁶-naphthalene)L₃] complexes 4–6 . In toluene, arene exchange is a competitive process in reactions of 1 with PF₃. Complexes 5 (L = P(OMe)₃) and 6 (L = PMe₃) react with HBF₄ to give the cationic metal hydride complexes 8 and 9 . The X-ray crystal structures of [Mo(η⁶-naphthalene) {P(OMe)₃}₃] ( 5 ) and [Mo(H)(η⁶-naphthalene) {P(OMe)₃}₃][BF₄] ( 8 ) are reported.     

The isomeric ratio of fragment 135Xe from photofission of 233U induced by 23.5 MeV bremsstrahlung

The ratio of the probabilities of population of the isomeric and ground states, so called the isomeric ratio is closely connected to the angular momentum of the initial fission fragments that is dissipated at the later stages of gamma ray cascade. This ratio also provides important information on the nuclear level structure as well as the nuclear reaction mechanism involved. In this work, the isomeric ratio in fission fragment ¹³⁵Xe from photofission of ²³³U induced by 23.5 MeV bremsstrahlung has been determined by the method that uses inert gaseous flow. The results have been discussed and compared with that of other authors.     

Synthesis of 2‐amino‐4‐oxo‐5‐substitutedbenzylthiopyrrolo[2,3‐d]‐pyrimidines as potential inhibitors of thymidylate synthase

A series of ten novel 2‐amino‐4‐oxo‐5‐[(substitutedbenzyl)thio]pyrrolo[2,3‐d]pyrimidines 2‐11 were synthesized as potential inhibitors of thymidylate synthase and as antitumor agents. The analogues contain various electron withdrawing and electron donating substituents on the benzylsulfanyl ring of the side chains and were synthesized from the key intermediate 2‐amino‐4‐oxo‐6‐methylpyrrolo[2,3‐d]pyrimidine, 14 . Appropriately substituted benzyl mercaptans were appended to the 5‐position of 14 via an oxidative addition reaction using iodine, ethanol and water. The compounds were evaluated against human, Escherichia coli and Toxoplasma gondii thymidylate synthase and against human, Escherichia coli and Toxoplasma gondii dihydrofolate reductase. The most potent inhibitor, ( 6 ) which has a 4′‐methoxy substituent on the side chain, has an IC₅₀=25 μM against human thymidylate synthase. Contrary to analogues of general structure 1 , electron donating or electron withdrawing substituents on the side chain of 2‐11 had little or no influence on the human thymidylate synthase inhibitory activity.     

Highly efficient utilization of H2O2 for oxygenation of organic sulfides catalyzed by [γ-SiW10O34(H2O)2]

Remarkable efficiency of hydrogen peroxide utilization is reported for oxygenation of four organic sulfides catalyzed by a divacant lacunary silicotungstate, (Bu₄N)₄[γ-SiW₁₀O₃₄(H₂O)₂] (1), under mild conditions. The addition of imidazole, phosphate, or carboxylates significantly enhances the rate of organic sulfide oxygenation. Most notably, use of 1 and imidazole, both at 1% molar concentration, resulted in the quantitative conversion of phenylsulfide to sulfoxide with 1 equiv of H₂O₂ in 3 h, and to sulfone with 2 equiv of H₂O₂ in 6 h.     

A new flavan from the Drynaria bonii H. Christ rhizomes

In Vietnam, the medicinal plant Drynaria bonii H. Christ is used for the treatment of osteoporosis, bone fractures, and stimulate the growth of hair, treat tinnitus (Ho 2002; Loi 2004). In this article, experiments were designed to investigate the proliferation activity of ethanol, n-hexane, chloroform, ethyl acetate and methanol extracts from D. bonii rhizomes on MG-63 human osteoblast-like cells. The results showed that methanol and hexane extracts had the ability to proliferate MG-63 cells at the concentration varying from 0.1 to 0.01 μg/mL. In particular, at the concentration of 0.01 μg/mL, hexane and methanol extracts illustrated the highest proliferation ratio with 9.31% and 6.16%, respectively. By column chromatography, a new compound named drynaether A (1) and five known compounds uracil (2), 4′-hydroxy-7-methoxyflavan (3), kaempferol (4), indole-3-carboxylic acid (5) and protocatechuic acid (6) were isolated and identified from the methanol extract.     

Sol–gel encapsulation of acid phosphatase in the presence of the ionic liquid [BMIM][BF4]

Abstract  

The effect of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) on acid phosphatase (APase) from wheat germ in solution and in the sol–gel-encapsulated form was investigated to explore new methods of enzyme preparation with improved catalytic performance. APase was encapsulated in hydrogel beads made from tetramethyl orthosilicate. Compared with free APase, 20–28% enzymatic activity was retained in over nine catalytic cycles. Sol–gel encapsulation improved the thermal stability of APase. Heat shock exposure at 60 °C for 1 h resulted in activity decreasing by a factor of three, only, for sol–gel-encapsulated APase, in contrast with a factor of nine decrease for free APase. Addition of 10% v/v [BMIM][BF₄] did result in a slight decrease of enzymatic activity for free and sol–gel-encapsulated APase, but resulted in a remarkable increase in alkaline pH tolerance of sol–gel-encapsulated APase.     

Toward Two‐Dimensional π‐Conjugated Covalent Organic Radical Frameworks

Reported is the synthesis, characterization, and material properties of the first π‐conjugated two‐dimensional covalent organic radical framework (CORF), PTM‐CORF , based on the stable polychlorotriphenylmethyl (PTM) radical. The covalent organic framework (COF) precursor ( PTM‐H‐COF ) was first synthesized by liquid/liquid interfacial acetylenic homocoupling of a triethynylpolychlorotriphenylmethane monomer, and showed crystalline features with a hexagonal diffraction pattern matching that of A‐B‐C stacking. Subsequent deprotonation and oxidation of the PTM units in PTM‐H‐COF gave PTM‐CORF . Magnetic measurements revealed that the neighboring PTM radicals in the PTM‐CORF are anti‐ferromagnetically coupled each other, with a moderate exchange interaction (J=?375 cm^?1). The PTM‐CORF has a small energy gap (ca. 0.88 eV) and a low‐lying LUMO energy level (?4.72 eV), and exhibits high electrocatalytic activity and durability toward the oxygen reduction reaction.