Hydrophobicity and freezing of a water droplet on fluoroalkylsilane coatings with different roughnesses

Smooth (Ra approximately 0.1 nm) and rough (Ra approximately 20 nm) coatings of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17) were prepared by controlling process conditions. The water contact angles for the smooth and rough coatings were similar (107 degrees and 110 degrees, respectively), but their sliding angles differed considerably (10 degrees and 27 degrees, respectively). The surface potential on the smooth coating, assessed using Kelvin force microscopy, showed a sharp distribution, but that on the rough coating ranged widely, implying large chemical heterogeneity including residual SiOH groups. The freezing temperature of a supercooled water droplet on the rough coating was higher than that on the smooth coating.     

Effect of TiO2 powder addition on sonochemical destruction of 1,4-dioxane in aqueous systems

Effects of TiO(2) powder addition on sonochemical destruction of 1,4-dioxane in water were investigated through comparison of a SiO(2) powder that had similar specific surface area. Results show that addition of TiO(2) is more effective for decomposition of 1,4-dioxane in water than addition of SiO(2). The contribution of photocatalytic destruction through sonoluminescence is not a dominant mechanism for acceleration of sonochemical reactions by adding TiO(2). Sonication of TiO(2)-added water generated thermally excited holes in this case. Moreover, intrinsic oxygen vacancies in TiO(2) surface play an important role in achieving high decomposition efficiency by producing cavitation. The addition of reduced TiO(2) powder increases both the ultrasonication energy that is consumed in water and the destruction efficiency of 1,4-dioxane.     

Formation of 1,4-diphosphinobenzenes via tele-substitution on fluorobenzenechromium complexes

The meta-tele-substitution of 2-(boranatophosphino)fluorobenzenechromium complexes took place with various lithiated secondary phosphine-boranes as nucleophiles to give para-substituted bis(boranatophosphino)benzenechromiums. It was revealed that the yield of the tele-substitution product was strongly affected by the strength of a proton acid. Isotope labeling experiments indicated that 1,5-hydrogen migration was involved in this transformation.     

Three new polyketide-terpenoid hybrids from Penicillium sp

Three novel hybrid polyketide-terpenoid metabolites were isolated from a Penicillium minioluteum strain. Their structures were determined by NMR spectroscopic analyses and X-ray crystallography. The proposed biosynthetic pathway including a unique retro-Claisen migration of methyl carbonate correlates the three compounds with berkeleydione and berkeleytrione.     

New preparation method for Vilsmeier reagent and related imidoyl chlorides

An environmentally benign and inexpensive preparation method is described of some imidoyl chlorides, including the Vilsmeier reagent (VR), by using phthaloyl dichloride. Synthetic applications were demonstrated using the isolated VR or VR prepared in situ for the transformation of acids to acid chlorides, alcohols to chlorides, and the formylation of dimethylaminobenzene.     

Synthesis and chemosensing behavior of fluorene‐based alternating copolymers containing ether side chains and Si–vinylene units in the main chain

Alternating copolymerization of 9,9‐bis(3,6,9‐trioxadecyl)‐2,7‐dibromofluorene (ODFl) or 9,9‐bis(3,6‐dioxaheptyl)‐2,7‐dibromofluorene with Si containing divinyl compounds, divinyldiphenylsilane (VPS), or divinyldimethylsilane (VMS) is investigated using the Mizoroki–Heck reaction with palladium(II) acetate. The corresponding alternating copolymer is obtained in the copolymerization of ODFl with VPS. The copolymerization of ODFl with VMS yields low molecular weight oligomers. Optical properties of the ODFl–VPS copolymer have been investigated with UV–vis absorption and photoluminescence (PL) spectroscopy. The ODFl–VPS copolymer shows absorption peaks due to π–π* transition and intramolecular charge transfer through σ–π moiety at around 330 and 360–400 nm, respectively. An emission peak is observed at 450 nm in the PL spectrum of the ODFl–VPS copolymer, and the PL quantum yield is 0.19. The PL spectroscopy of ODFl–VPS copolymer is investigated in the presence of Li⁺, Na⁺, and K⁺, and the intensity of emission peak is decreased by those metal cations, especially by Na⁺. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Spectrophotometric determination of spermine and related compounds using o-hydroxyhydroquinonephthalein and manganese(II).

A simple and highly sensitive spectrophotometric method for the determination of spermine (Spm) was established based on the ternary complex formation reaction of Spm with o-hydroxyhydroquinonephthalein (QP) as a xanthene dye and manganese(II) as a metal ion in the presence of a dispersion agent. The apparent molar absorptivity at 555 nm and the relative standard deviation of the proposed method were 1.4 x 10(5) dm(3) mol(-1) cm(-1) and 0.50% (n = 10), respectively. In the method for flow-injection analysis (FIA), which employs a single-channel flow manifold system, a good linear relationship was observed over the 2 - 20 pg microl(-1) range of Spm by direct injection.     

Concentration and temperature dependency of regio- and stereoselectivity in a photochemical [2 + 2] cycloaddition reaction (the Paternò-Büchi reaction): origin of the hydroxy-group directivity

A set of photochemical oxetane formation reactions, i.e., the Paterno?-Bu?chi (PB) reactions, of tetrahydrobenzofuranol derivatives 1a-d with benzophenone (BP) was investigated to examine poorly understood hydroxy-group directivity on regio- and stereoselectivity. The selectivities of the PB reactions for allylic alcohols 1a,d were found to be largely dependent upon the concentration of the allylic alcohols and the reaction temperature. The temperature-dependent change of the regioselectivity at high concentrations of allylic alcohols was similar to that of the hydroxy-protected methyl ether 1b and tetrahydrobenzofuran (1c). The effect of concentration on regioselectivity can be explained by the hydrogen-bonded aggregates, which mimic the selectivities observed during the PB reaction of 1b,c. The hydroxy-directed cis-selectivity of the higher-substituted oxetane 3a,d formed at low concentration of 1a,d was found to be larger than that at the higher concentration of 1a,d. The cis-selectivity of 3a,d was found to be higher than that of the lower-substituted oxetane 2a,d. The regioselectivity of the cis-configured oxetanes was higher than that of the trans-configured oxetanes. These experimental results strongly suggest that hydroxy-group directivity, induced by hydrogen-bonding stabilization, plays a role in controlling the regio- and stereoselectivity of the PB reactions. The steric effect was also responsible for the diastereoselectivity, as shown by the fact that the cis selectivity in 3d was higher than that in 3a. Computational studies at the (U)MP2 and (U)DFT level of theory revealed that hydrogen-bonding stabilization becomes important only in the excited complex (exciplex) between the triplet excited state of carbonyls and alkenes, in which the charge transfer occurs from the alkene to the excited carbonyl to make the carbonyl oxygen nucleophilic. No significant stabilization energy was found in the intermediary triplet state of biradicals. The combined experimental and computational studies have clarified the origin of the poorly understood hydroxy-group effect on a high degree of regio- and stereoselectivity, i.e., the cooperative effect of hydrogen-bonding stabilization in exciplexes and the steric bulk of the substituents.     

Occurrence of C-glucoside of resveratrol oligomers in Hopea parviflora

Investigation of the highly polar chemical constituents in the stem of Hopea parviflora (Dipterocarpaceae) resulted in the isolation of four new resveratrol derivatives, hopeasides A and B (1, 2) (resveratrol pentamers), C (3) (resveratrol trimer), and D (4) (resveratrol dimer) together with nine known resveratrol oligomers (5-13). The new structures have a common partial structure of the 1-hydroxy-1-(3,5-dihydroxy-2-C-glucopyranosylphenyl)-2-(4-hydroxyphenyl)ethane-2-yl group after oxidative condensation of (E)-resveratrol-10-C-β-glucopyranoside (14). The structures were determined by spectroscopic analysis including 2D-NMR and computer-aided molecular modeling. The biogenetic relationship of the isolates and NMR characteristics caused by steric hindrance are also discussed in this paper.