Molecular imprinting in ultrathin titania gel films via surface sol-gel process

Recent progresses of molecular imprinting in metal oxide matrices were summarized. Application of the surface sol-gel process to mixtures of organic carboxylic acids and titanium alkoxide provides ultrathin layers of titania gel (10-20 nm thick), in which molecule-sized cavities are kept intact upon removal of the organic templates. The imprinted cavity reflects the structural and functional features of the template molecule, and the enantioselective imprinting of dipeptide isomers is observed. Robustness and flexibility of the ultrathin titania layer is demonstrated by the formation of interconnected titania hollow structures. Possible practical applications and unsolved problems of this technique are discussed.     

Radical cyclocopolymerization of divinyl ether and maleic anhydride. A 13C-NMR study of the polymer structure

The structure of the 1:2 copolymer of divinyl ether and maleic anhydride was investigated by ¹³C-NMR spectroscopy. The polymer contains the bicyclic unit composed of one molecule of each monomer and the maleic anhydride unit. The carbon chemical shift for these units was calculated on the basis of the chemical shift of many model compounds. The major peaks of the cyclopolymer prepared in chloroform were consistent with the presence of the symmetrical bicyclic unit with cis junction and the trans monocyclic anhydride unit. The carbonyl carbon spectrum for the copolymer obtained in a mixed solvent of acetone and CS₂ suggested the predominant formation of the unsymmetrical bicyclic unit. The polymerization process was discussed on the basis of these results.     

Self-assembling molecular wires of halogen-bridged platinum complexes in organic media. Mesoscopic supramolecular assemblies consisting of a mixed valent Pt(II)/Pt(IV) complex and anionic amphiphiles

A novel class of supramolecular assemblies in organic media consisting of a molecular wire of a halogen-bridged platinum complex [Pt(en)2][PtCl2(en)2]4+ (en = 1,2-diaminoethane) and anionic amphiphiles is developed. When double-chained phosphates or sulfonates are employed, the resultant [Pt(en)2][PtCl2(en)2](4+)-lipid complexes displayed intervalence charge transfer (CT) absorption bands in the crystalline state. They are soluble in organic solvents because of the amphiphilic superstructure, in which the solvophobic one-dimensional platinum complex is surrounded by solvophilic alkyl chains. CT absorption bands of halogen-bridged linear complexes are maintained in organic media, with varied colors that depend on the chemical structure of constituent amphiphiles. Monoalkylated phosphates failed to form colored, halogen-bridged ternary complexes probably because of their coordination to the axial position of PtII(en)2. Formation of mesoscopic supramolecular assemblies in organic media was confirmed for the [Pt(en)2][PtCl2(en)2] complexes by electron microscopy. Interestingly, a supramolecular complex consisting of dihexadecyl sulfosuccinate and [Pt(en)2][PtCl2(en)2]4+ displayed clear, indigo solutions that are distinct from the yellow color observed for those of [Pt(en)2][PtCl2(en)2]/dialkyl phosphate complexes. The indigo color of the former complex disappeared upon heating the solution to 60 degrees C, whereas it reappeared reversibly by cooling the solution to room temperature. In electron microscopy, rodlike nanostructures with a minimum width of 18 nm and lengths of 700-1700 nm were observed after cooling, though not at elevated temperatures. Apparently, the lipid-[Pt(en)2][PtCl2(en)2]4+ complex undergoes reversible dissociation and reassembly processes in chloroform, and it becomes better dispersed after the reassembling process. The present finding opens a general route to solution chemistry of low-dimensional inorganic complexes and enables rational design and control of self-assembling inorganic molecular wires.     

Facile fabrication of composites of platinum nanoparticles and amorphous carbon films by catalyzed carbonization of cellulose fibers

Composites of platinum nanoparticles and amorphous carbon films have been facilely fabricated by catalyzed carbonization of cellulose fibers.     

A proposal on the steric course of propagation in the homogeneous cationic polymerization of vinyl and related monomers

A stereochemical scheme of propagation was proposed for polymerizations of vinyl and related monomers by Friedel-Crafts catalysts. For the cationic propagation proceeding via the simple carbonium ion pair, the following two factors were considered to be of primary importance in determining the steric course of propagation: (1) the conformation of the last two units of the propagating polymer segment and the direction of approach of the incoming monomer; (2) the tightness of the growing ion pair. Thus, the front-side (less hindered site) attack to the carbonium ion gives rise to a syndiotactic placement and the back-side attack an isotactic placement. The present model can satisfactorily explain the effects of substituents, catalysts, polymerization media, and polymerization temperature on the steric structure of polymers in cationic polymerization of vinyl ethers. Extension of the scheme to polymerization of the β-substituted vinyl ethers in nonpolar solvents predicts formation of the diisotactic structures consistent with the experimental result. The influences of the polymerization condition on the steric structure of polymer were studied for cationic polymerizations of α-methylstyrene at low temperatures. Highly syndiotactic polymers were obtained for homogeneous reactions in toluene-rich media. The isotactic unit increased by increasing the content of methylcyclohexane in the solvent mixture. The effect of catalysts, though insignificant in toluene-rich media, was clearly noted in methylcyclohexane-rich media, less active catalysts (e.g., SnCl₄) yielding higher amounts of the isotactic unit than more active catalysts (e.g., AlCl₃). These results can be readily accommodated in the present model.     

Perfluoroalkylated eight- and nine-membered benzoheterocycles from F-2-methyl-2-pentene

The reactions of $\text{F}$-2-methyl-2-pentene (1) with several $\text{ortho}$- difunctional benzenes afforded eight- and nine-membered benzoheterocyclic compounds carrying perfluoroalkyl groups. Salicylic acid, salicylaldehyde, and their methyl or chloro derivatives reacted in triethylamine-acetonitrile system giving perfluoroalkylated 2H,6H-1,5-benzodioxocin-2,6-dione (8) and 4H,6H-1,5-benzodioxocin (9) compounds respectively, while phthalyl alcohol and o-hydroxyphenethyl alcohol in triethylamine-diethyl ether system gave perfluoroalkylated 1H,3H,7H-2,6- and 4H,6H,7H-1,5-benzodioxonin compounds, (10) and (11). o-Aminobenzyl alcohol and (1) in diethyl ether afforded a perfluoroalkylated benzoxazocinobenzoxazocinone compound (15).     

Synthesis and properties of thermoplastic propyl-etherified amylose

Amylose was etherified with 1-bromopropane in DMSO. The degree of substitution (DS) was varied by altering the feed ratio of 1-bromopropane. The structures of the products were characterized by IR and 1H-NMR spectroscopy. When the molar feed ratio of 1-bromopropane to hydroxyl groups of amylose was beyond 7.5, the hydroxyl groups were completely substituted with propyl ether groups. The etherified amylose with DS 1.9 showed a glass transition temperature (T_g), and that with DS 2.3 or 3.0 showed both T_g and melting temperature (T_m) (DS 3.0 means complete substitution). The etherification imparted melt processability and solubility in nonpolar organic solvent to amylose.     

The Steric Course of the Cationic Polymerization of Vinyl and Related Monomers. The Counterion Effect

Polymerization with many triphenylmethyl salts was conducted for α-methylstyrene, isobutyl vinyl ether, t-butyl vinyl ether, and spiro[2,4]hepta-4,6-diene (SHD). The variation of polymer structure (the isotactic unit content for the first three monomer systems and the amount of the 1,4-addition structure for SHD) showed fairly simple correlations with the counteranion size. The results can be interpreted in terms of the tightness of the propagating ion pair within the framework of a theory of the cationic propagation which had been proposed. When the counteranion radius was greater than 3.5 Å, the counteranion exerts a parallel influence on the tightness of the growing ion pair without regard to the monomer structure. However, in the case of smaller counterions, the tightness appears to be determined by the relative sizes of counteranion and monomer. The penta-coordinated counteranions gave rise to the polymer structure which would arise from tighter ion pairs than expected from their sizes alone. The polymer structure was also affected by the initiator concentration in these cases. These results are attributed to peculiar characteristics of penta-coordinated anions.     

Permselective monolayer membrane based on two-dimensional cross-linked polysiloxane LB films for hydrogen peroxide detecting glucose sensors

Novel two-dimensional (2D) cross-linked polysiloxane LB films were prepared and applied for glucose sensing as H2O2-permselective films in order to block other electroactive interferences, such as L-ascorbic acid, L-cysteine, uric acid and acetaminophen; the 2D cross-linked polysiloxane monolayers were remarkably effective in eliminating interfering responses and had a rapid response for glucose, even though the films were only a monolayer thick.     

Molecular Dispersion of Chains in the Mixed-Valence Complexes

A way to prepare molecular electronic wires in organic media is the solubilization of one-dimensional mixed-valence complexes with varied metal species through the formation of amphiphilic supramolecular assemblies (see picture). Dissociation and reassembly of the complex was detected as thermochromism in the intervalence (M(II)-->M(IV)) absorption bands.