Effects of metal salts on polymerization. VI. Photo and thermally catalyzed polymerization of N-vinylimidazole in the presence of metal salts

Polymerization of 2-methyl-1-vinylimidazole (MVI) and 2-ethyl-1-vinylimidazole (EVI) was found to be markedly photosensitized in the presence of oxidizing metal salts such as UO₂(NO₃)₂, Ce(NH₄)₂(NO₃)₆, Hg(CH₃COO)₂, AgNO₃; non-oxidizing metal salts such as Zn^II did not act as photosensitizers. The interaction of monomer with a metal salt is discussed on the basis of infrared and electronic spectroscopy. This photopolymerization is very specific with respect to the kind of monomer. The polymerization of noncomplexing monomer (styrene) is not photosensitized by these metal salts. Consequently, photosensitized electron transfer between monomer and metal salt via complex formation is considered to be the most probable initiation mechanism. Cupric acetate and sodium chlorolaurate, which have been reported as efficient initiators for the polymerization of vinylpyridine and N-vinylcarbazole, respectively, act as linear terminators of growing radicals. The radical polymerizability of the zinc complex of MVI was studied by means of copolymerization with styrene. The reduction of the reactivity of MVI on complexing was explained by correlating with the spectroscopic observations. Because the polymerization system is heterogeneous, a detailed discussion was not possible.     

Colominic acid: a novel chiral selector for capillary electrophoresis of basic drugs

Capillary zone electrophoresis was used for characterising nine samples of natural organic matter (NOM) using phosphate buffer (25 mM, pH 7) and various modifiers; methanol (50 mM), acetonitrile (10%,v/v), dimethyl sulfoxide (5%,v/v), and urea (5 M). Principal component analysis (PCA) was used to examine whether the electrophoretic profiles can be utilised as fingerprints for tracing the NOM samples to their source and/or type of location. It was found that all modifiers except methanol affect the electropherograms. Furthermore, it was found that the PCA analysis carried out on the electrophoretic profiles recorded in buffer solution modified by urea gave the best results for fingerprinting. The distribution of the fingerprints suggests a model for the humic substances in which all samples can be regarded as mixtures between two endmembers: autochtonous and allocthoneous NOM.     

1,2-silyl-migrative cyclization of vinylsilanes bearing a hydroxy group: stereoselective synthesis of multisubstituted tetrahydropyrans and tetrahydrofurans(1)

Acid-catalyzed intramolecular addition of a hydroxy group to alpha-alkylated vinylsilanes has been studied. Treatment of (Z)-5-alkyl-5-silyl-4-penten-1-ols 1 (R = alkyl) with 5 mol % TiCl(4) in CHCl(3) gave trans-2-alkyl-3-silyltetrahydropyrans 2 exclusively (trans/cis = >99/1 to 97/3). The cyclization efficiency and rate strongly depended on the geometry of the C-C double bond and the silyl group. The use of (E)-vinylsilanes resulted in lower yields with poor cis-selectivity. In the cyclization of (Z)-1 (R = Bu), the silyl group used, the reaction time, and the yield of 2 were as follows: SiMe(2)Ph, 9.5 h, 75%; SiMe(3), 7.5 h, 66%; SiMePh(2), 24 h, 58%; SiMe(2)-t-Bu, 0.75 h, 85%; SiMe(2)Bn, 1.5 h, 78%. This 1,2-silyl-migrative cyclization could be applied to stereoselective synthesis of trisubstituted tetrahydropyrans. The acid-catalyzed reaction of 1-, 2-, or 3-substituted (Z)-5-silyl-4-nonen-1-ols 8 gave r-2,t-3,c-6-, r-2,t-3,t-5-, or r-2,t-3,c-4-trisubstituted tetrahydropyrans with high diastereoselectivity, respectively. (Z)-4-Alkyl-4-silyl-3-buten-1-ols 5 as well as 1 underwent the 1,2-silyl-migrative cyclization to give 2-alkyl-3-silyltetrahydrofurans 6 with high trans-selectivity. This silicon-directed cyclization was also available for the stereoselective synthesis of tri- and tetrasubstituted tetrahydrofurans.     

The exponent for the mean square displacement of self-avoiding random walk on the Sierpinski gasket

The authors rigorously prove that the exponent for the mean square displacement of self-avoiding random walk on the Sierpinski gasket is

The structures of macbecin I and II : New antitumor antibiotics

Macbecin I 1, C₃₀H₄₂N₂O₈, and macbecin II 2, C₃₀H₄₄N₂O₈, were shown to be 2,6-disubstituted benzoquinone and hydroquinone derivatives by an oxidation-reduction relationship, UV. ¹H and ¹³C NMR spectra. Alkaline methanolysis of 1 gave a 2-aminobenzoquinone derivative 5, suggesting an ansa-structure for 1, and acid hydrolysis of 1 gave decarbamoyl products 9,10 and 11, indicative of the location of carbamoyloxy group in allylic position. Spin decoupling studies on 1,3 and 5clarified the partial structures [A], [B], [C] and [D]. From their mutual disposition two structures 1a and 1b, were proposed out of which 1a has been selected for the structure of 1 on the basis of the structure of oxidative degradation product 12. X-Ray analysis of the bromoacetyl derivative of 1 confirmed the above proposed structure and determined the absolute stereochemistry of 1 and 2.     

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.     

Efforts to expand the genetic alphabet: identification of a replicable unnatural DNA self-pair

Six unnatural nucleotides featuring fluorine-substituted phenyl nucleobase analogues have been synthesized, incorporated into DNA, and characterized in terms of the structure and replication properties of the self-pairs they form. Each unnatural self-pair is accommodated in B-form DNA without detectable structural perturbation, and all are thermally stable and selective to roughly the same degree. Furthermore, the efficiency of polymerase-mediated mispair synthesis is similar for each unnatural nucleotide in the template. In contrast, the efficiency of polymerase-mediated self-pair extension is highly dependent on the specific fluorine substitution pattern. The most promising unnatural base pair candidate of this series is the 3-fluorobenzene self-pair, which is replicated with reasonable efficiency and selectivity.     

Basic peptides as functional components of non-viral gene transfer vehicles

Improving the performance of non-viral gene-delivery vehicles that consist of synthetic compounds and nucleic acids is a key to successful gene therapy. Supplementing synthetic vehicles with various biological functions by using natural or artificial peptides is a promising approach with which to achieve this goal. One of the obstacles hindering this effort is that some of the potentially useful peptides, especially those with many basic amino acid residues, interfere with the formation of the complex owing to strong electrostatic interactions with the nucleic acid. In this review, we describe our recent work in examining the potential of these peptides in gene delivery, using a recombinant lambda phage particle as the model for the gene-delivery complex. Lambda phage encapsulates large duplex DNA in a rigid polyplex-like shell with a diameter of 55 nm, and can display various peptides on this capsid, independently of particle formation. By examining the expression of marker genes encapsulated in the phage capsid, we have demonstrated that the protein transduction domain of HIV Tat protein and the nuclear localization signal derived from SV40 T antigen can remarkably facilitate the delivery of these marker genes across the two major barriers, the cell membrane and the nuclear membrane, respectively. Our results indicate that these basic peptides can constitute effective components of synthetic gene-transfer complexes, as long as sufficient copies are displayed on the outer surface of the complex.     

Adduct formation properties of mono- and bidentate phosphine oxide compounds in the liquid—liquid extraction of some divalent metals with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

The bidentate phosphine oxide compounds bis(diphenylphosphinyl)methane (BDPPM) and bis(diphenylphosphinyl)ethane (BDPPE) were synthesized and the liquid—liquid extraction equilibria of some divalent metal ions such as Co(II), Ni(II), Zn(II) and Cd(II) with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) and the neutral phosphine oxide compounds were investigated. BDPPM was found to be much more powerful than BDPPE and the monodentate neutral ligand trioctylphosphine oxide (TOPO). The composition of the extracted species were determined by a graphical method to be M(PMBP)₂(TOPO)_s (s = 2 for Co, Ni, Cd and s = 1 for Zn), M(PMBP)₂(BDPPM) and M(PMBP)₂(BDPPE). The adduct formation constants between the acylpyrazolone chelates and the neutral ligands were determined and are discussed in terms of the molecular structure.     

A Convenient Preparation of p-Chloromethyl-Styrene and its Reactions

In the present communication we would like to describe a novel method for the preparation of p-chloromethylstyrene and some reactions of this compound.