Simultaneous polymerization and formation of polyacetylene film on the surface of concentrated soluble Ziegler-type catalyst solution

A direct method of simultaneously polymerizing and forming acetylene monomer to produce uniformly thin films of polyacetylene was investigated in terms of catalyst system, catalyst concentration, and polymerization temperature. The best catalyst was a Ti(OC₄H₉)₄–Al(C₂H₅)₃ system (Al/Ti = 3–4) and the critical concentration was 3 mmole/l. of Ti(OC₄H₉)₄. Below the critical concentration, only a solid or a powder was obtained. The configuration of the polymers obtained depends strongly upon the polymerization temperature. Thus an all-cis polymer was obtained at temperatures lower than ?78°C, whereas an all-trans polymer resulted at temperatures higher than 150°C. Observations either in an electron microscope by direct transmission or in a scanning electron microscope showed that the film is composed of an accumulation of fibrils about 200–300 Å in width and of indefinite length.     

Cation binding properties of crown ether-modified polyethylenimines

Crown ether-modified polyethylenimines (PEI-CR) were prepared to elucidate their cation binding efficiency and selectivity by liquid-liquid and solid-liquid extraction methods. With alkali metal cations it was found that polyethylenimines containing benzo-15-crown-5 moieties (Ia and Ib) extracted all cations examined more efficiently than their monomeric analogs, especially in the cases of K⁺ and Rb⁺ cations. The solid-liquid extraction revealed clearly that the polymers complexed with K⁺ and Rb⁺ cations according to a 1:2 cation-to-crown stoichiometry. The high selectivities of the polymers for K⁺ and Rb⁺ were interpreted in terms of the favourable conformation of the polymer chain for the formation of intramolecular 1:2 complexes. On the contrary, these polymers bound alkali earth cations less effectively with low selectivities.     

Reaction of tetraazathiapentalene and thiadiazolopyrimidine derivatives with heterocumulenes: Cycloaddition and elimination reactions via hypervalent sulfur intermediates

Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2‐pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a‐b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described.     

THE CONFORMATIONAL ANALYSIS AND PHOTOISOMERIZATION OF RETINOCHROME ANALOGS WITH POLYENALS

Abstract— 3, 7-Dimethyl-2, 4, 6, 8, 10-dodecapentaenal was synthesized for reconstitution of the retinochrome analog. Its opsin shift was 1000 cm ¹ smaller than that of native retinochrome, whose chromophore contains the same number of double bonds. The conformational change from 6-s-trans to 6-s-cis , as figured in a retinal molecule, plays an important role in the formation of the retinochrome analog, based on the estimation of opsin shifts for retinal analogs locked in the 6-s conformation. Thus the conformation of the 6–7 single bond in the native retinochrome was suggested to be 6 -cis . Analysis of the circular dichroic spectra of retinochrome analogs revealed that the 6-s conformation is independent of the appearance of the β-band. The stereoselectivity in the photoisomerization of the retinal analogs by a retinochrome template depends on the hydrophobic binding in the region of the β-ionone ring.     

Triplet-mediated coupling of 5-bromo-1,3-dimetrhyluracil to Nb-methoxycarbonyltryptamine involving a double electron transfer

On acetone-sensitization, 5-bromo-1,3-dimethyluracil ($\text{1}$ reacts with N^b-methoxycarbonyltryptamine ($\text{4}$ under the assistance of an electron carrier such as 2-methoxynaphthalene to give a coupling product $\text{6}$. A mechanism involving a double electron transfer via the triplet state of $\text{1}$ is proposed.     

Efficient photochemical oxetane formation from 1-methyl-2,4,5-triphenylimidazole and benzophenones

In contrast to simple imidazoles, 1-methy1–2,4,5-triphenylimidazole ($\text{1}$) produced stable oxetane photoadducts $\text{3b}$ - $\text{e}$ with good efficiency upon irradiation in the presence of benzophenone derivatives $\text{2b}$ - $\text{e}$ in acetonitrile solution. Irradiation in the solid-phase was also studied. The oxetanes $\text{3b}$ - $\text{e}$ readily underwent cycloreversion by acid catalysis or by heating.     

Wang resin-type linker containing a nitro group for polymer support oligosaccharide synthesis: polymer-supported glycosyl donor

A nitro-introduced Wang resin-type linker for soluble and insoluble polymer support oligosaccharide synthesis is described. The linker was used for connecting glycosyl donors and polymer supports, and was completely stable under the glycosylation conditions tested. The cleavage of the linker was performed under reductive conditions without affecting the protecting groups to release disaccharides.     

Prompt gamma-ray analysis using cold and thermal guided neutron beams

The extraction behavior of uranium(VI), plutonium(IV) and some fission products like zirconium(IV), ruthenium(III) and europium(III) from 3.5M nitric acid with -irradiated organic phase pre-equilibratedn-dodecane solutions of dihexyl derivatives of hexanamide (DHHA), octanamide (DHOA) and decanamide (DHDA) has been investigated as a function of absorbed dose upto 184·10⁴ Gy. The results indicate that the extraction of uranium(VI) decreases gradually with dose upto 72·10⁴ Gy and becomes almost constant thereafter, while, the extraction of plutonium(IV) decreases upto a dose of 20·10⁴ Gy and then increases rapidly up to a dose of 82·10⁴ Gy indicating synergistic effects of radiolytic products formed at higher doses. Extraction of zirconium(IV) increases gradually upto a dose of 72·10⁴ Gy. Europium(III) does not get extracted with any of these amides in the entire dose range (0–184·10⁴ Gy) studied, however, ruthenium shows insignificant increase in extraction with dose. The decrease inD values noticed in the case of plutonium and zirconium after the dose of 72·10⁴ Gy which was attributed to the third phase formation and emulsification. Infrared studies confirm the final products of radiolysis as the respective amines and carboxylic acids. The degraded amide contents have been estimated by quantitative IR spectrophotometric technique. Extraction data obtained for uranium(VI) and plutonium(IV) with TBP/n-dodecane system have also been compared under similar experimental conditions.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C₁₂H₁₇N₄OS⁺·I^– · 1.5 H₂O, monoclinic,P2₁/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) ų,Z=8,D _c=1.606 g cm^–3,R=0.045 for 3328 observed reflections. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages).     

Vibrational spectra and molecular conformations of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes

The Raman and IR spectra of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes have been measured. The normal coordinates have been calculated for these molecules using a consistent set of force constants and the molecular conformations studied by analysing the spectra with reference to the results of the calculations. In the crystalline solid state, 1,5-dichloropentane assumes the trans-trans-trans-gauche form and 1,5-dibromopentane, 1,6-dichloro- and 1,6-dibromohexanes assume the all-trans form. The normal coordinate treatment with the well-established force field was of great help in determining the whole molecular form of the relatively large chain molecules.