Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

Nmr spectroscopic studies on the tautomerism in tenuazonic acid analogs

Nmr spectra of structural analogs of tenuazonic acid such as 3-acetyltetramic acid, 3-acetyltetronic acid, 3-acetylthiotetronic acid and others were investigated for elucidation of the tautomeric structures. These compounds have completely enolized β,β′-triketone systems, and the position of the nmr signals for the enolic proton shows that the strength of their intramolecular hydrogen-bonding is weaker than those of acyclic β,β′-triketones and six-membered cyclic triketones. The assignment was made for nmr signals split by the difference of the diamagnetic anisotropic effect in each tautomers. The percentages of each of the tautomers were calculated from the intensities of the corresponding nmr signals. The results were confirmed by means of ¹³C-nmr spectroscopy.     

Synthesis and photochemical properties of a photochromic iron(II) complex of hexaarylbiimidazole

The photochromic ligand bis(terpyridyl)hexaarylbiimidazole (bistpy-HABI) and the Fe(II) complex of bistpy-HABI with formula [{Fe(tpy)}2.bistpy-HABI](PF6)4.4H2O were synthesized and characterized. Bistpy-HABI is readily cleaved into a pair of terpyridyltriphenylimidazolyl radicals (tpy-TPI*) on irradiation with UV light. This photochemical reaction is completely reversible, and the light-induced radicals can thermally recombine to form bistpy-HABI in the dark. [{Fe(tpy)}2.bistpy-HABI]4+ is the first example of a transition-metal complex of an HABI derivative and was found to show photochromic reaction in solution. The spin state of the light-induced radical pair in a frozen matrix was investigated by ESR spectroscopy. The triplet state of the light-induced radical pair from [{Fe(tpy)}2.bistpy-HABI]4+, as well as that from bistpy-HABI, was confirmed to be a ground state or nearly degenerated with a singlet state. Kinetic studies on the radical recombination reaction in solution elucidated the decrease in the activation energy by forming the Fe(II) complex. This is the first observation of a decrease in the activation energy of the radical recombination reaction by the formation of a metal-coordinated radical complex. The syntheses, photochemical properties, and spin states of bistpy-HABI and [{Fe(tpy)}2.bistpy-HABI](PF6)4 are discussed.     

Chemical oxygen-iodine laser: Recent advances as a chemical device

Recent advances in chemical oxygen-iodine lasers (COIL) are reviewed. In this paper, developments of the COIL as a unique chemical device, whose product is not a chemical substance but coherent photons is emphasized. The key component of a COIL is the singlet oxygen generator (SOG). The unique principles of modern SOGs are reviewed. For high-efficiency operation, rapid mixing of oxygen and iodine is of primarly importance. The latest mixing enhancement techniques are reviewed. Applications of ultrahigh-power COILs are presented. The text was submitted by the author in English.     

Amphidinolide T, novel 19-membered macrolide from marine dinoflagellate Amphidinium sp

A novel 19-membered macrolide, amphidinolide T (1), has been isolated from a marine dinoflagellate Amphidinium sp., and the structure was elucidated on the basis of spectroscopic data. Relative stereochemistry at C-7, C-8, and C-10 was deduced from the NOESY correlations, while absolute configurations at C-2, C-13, C-14, and C-18 were assigned on the basis of NMR data of the MTPA esters of 1 and those of degradation products of 1.     

Monomer-isomerization polymerization. XXIII.. Monomer-isomerization polymerization of 5-phenyl-2-pentene with ziegler–natta catalysts

5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl₃–R₃Al (R = C₂H₅ or i-C₄H₉, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl₃ was in the following order: (C₂H₅)₃Al > (i-C₄H₉)₃Al > (C₂H₅)₂AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl₃–(C₂H₅)₃Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)₂], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios.     

Novel pyridinium salts as cationic thermal and photoinitiators and their photosensitization properties

Novel pyridinium salts [N‐(α‐phenylbenzyl)‐, N‐(1‐naphthylmethyl)‐, or N‐cinnamyl p‐ or o‐cyanopyridinium hexafluoroantimonates] were synthesized by the reaction of p‐ or o‐cyanopyridine and the corresponding bromides followed by anion exchange with KSbF₆. These pyridinium salts polymerized epoxy monomers at lower temperatures than previously reported for N‐benzyl‐2‐cyanopyridinium hexafluoroantimonate. The o‐substituted pyridinium salts showed higher activity than the p‐substituted ones, and the crosslinked epoxy polymers cured with these initiators showed higher glass‐transition temperatures. These pyridinium salts photoinitiated radical polymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic ketones as photosensitizers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1037–1046, 2002     

Programmable DNA translation system using cross-linked DNA mediators

The information of template DNA strands was converted into the specific sequences in a programmable way by following the mediation of cross-linked DNAs.     

Emission Mössbauer spectroscopic studies of57Fe atoms produced in57Co-labelled trinuclear cobalt-iron halogenoacetate complexes

Mixed-valence states of⁵⁷Fe atoms produced after EC-decay of⁵⁷Co in a series of trinuclear cobalt-iron halogenoacetate complexes, [Co^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃] (0≤n≤3, X=Cl, Br, and I), were studied by comparing the results obtained by emission Mössbauer spectroscopy with those observed in absorption Mössbauer spectra of analogous trinuclear iron complexes, [Fe^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃]. Some of the emission Mössbauer spectra show a temperature-dependent mixed-valence state as found in the absorption Mössbauer spectra. Others show a somewhat different temperature dependence compared with the absorption Mössbauer spectra. The results were interpreted in terms of after-effects of the EC-decay.     

Trapping effect of eugenol on hydroxyl radicals induced by L-DOPA in vitro

Many researchers have stated that eugenol might inhibit lipid peroxidation at the stage of initiation, propagation, or both, and many attempts have been made to elucidate the mechanism of its antioxidant activity. Nevertheless, details of its mechanism are still obscure. This study was carried out to investigate the trapping effect of eugenol on hydroxyl radical generated from L-3,4-dihydroxyphenylalanine (DOPA) in MiliQ water and the generation mechanism of the hydroxyl radical by this system which uses no metallic factor. This was studied by adding L-DOPA and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to phosphate buffered saline (PBS) or MiliQ water, and the generation of hydroxyl radical was detected on an ESR spectrum. By this method, the effect of antioxidants was detected as a modification of ESR spectra. We found that the eugenol trapped hydroxyl radicals directly, because it had no iron chelating action, did not trap L-DOPA semiquinone radical and inhibited hydroxyl radicals with or without iron ion.