Antimicrobial polyacetylenes from Panax ginseng hairy root culture

Two new polyacetylenes, 1-hydroxydihydropanaxacol (3) and 17-hydroxypanaxacol (4), were isolated from Panax ginseng hairy root culture, along with dihydropanaxacol (1), panaxacol (2) and ginsenoyne D (5). Highly hydroxylated compounds 1-4 were isolated from the medium and compound 5, which was a biosynthetic precursor of compound 1, was isolated from the roots. Compounds 1-4 showed antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Cryptococcus neoformans and Aspergillus fumigatus. It is suggested that P. ginseng plants release antimicrobial polyacetylenes into the surrounding soil from the roots as defense compounds.     

Ultrathin polymer gate buffer layer for air‐stable,low‐voltage,n‐channel organic thin‐film transistors

An ultrathin poly(methyl methacrylate) (PMMA) buffer layer was developed to improve the performance of n‐channel organic thin‐film transistors (OTFTs). The 8 nm‐thick PMMA film, prepared by spin‐coating, provided a very smooth surface and a uniform coverage on SiO₂ surface reproducibly, which was confirmed by X‐ray reflectivity (XR) measurement. Then, we fabricated N,N′‐ditridecyl‐3,4,9,10‐perylenetetracarboxylic diimide (PTCDI‐C13) thin‐film transistors with and without this 8 nm‐thick PMMA insulating layer on SiO₂ gate insulators and achieved one‐order increase of field‐effect mobility (up to 0.11 cm²/(Vs) in a vacuum), one‐half decrease of threshold voltage, and reduction of current hysteresis with the PMMA layer. Only TFTs with the PMMA layer displayed n‐channel operation in air and showed field‐effect mobility of 0.10 cm²/(Vs). We consider that electrical characteristics of n‐channel OTFTs were considerably improved because the ultrathin PMMA film could effectively passivate the SiO₂ insulator surface and decrease interfacial electron traps. This result suggests the importance of the ultrathin PMMA layer for controlling the interfacial state at the semiconductor/insulator interface and the device characteristics of OTFTs. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of highly refractive and transparent polyimides derived from 4,4′‐thiobis[2″,6″‐dimethyl‐4″‐(p‐phenylenesulfanyl)aniline]

New sulfur‐containing aromatic diamines with methyl groups at the ortho position of amino groups have been developed to prepare highly refractive and transparent aromatic polyimides (PIs) in the visible region. All aromatic PIs derived from 4,4′‐thiobis[2″‐methyl‐4″‐(p‐phenylenesulfanyl)aniline ( 2 ), 4,4′‐thiobis[2,″6″‐dimethyl‐4″‐(p‐phenylenesulfanyl)aniline ( 5 ), and aromatic dianhydride, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride ( 6 ) were prepared via a two‐step polycondensation. All PIs showed good thermal properties, such as 10% weight loss temperature in the range of 497–500 °C and glass transition temperatures above 196 °C. In addition, the PIs showed good optical properties, such as optical transparency above 75% at 450 nm with a 10‐μm film thickness, high refractive indices ranging from 1.7135 to 1.7301, and small in‐plane/out‐of‐plane birefringences between 0.0066 and 0.0076. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 656–662, 2010     

Proton transfer in phenol–amine complexes: Phenol electronic effects on free energy profile in solution

Free energy profiles for the proton transfer reactions in hydrogen‐bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self‐consistent field method. The reactions in both the electronic ground and excited states are considered. The second‐order Møller‐Plesset perturbation (MP) theory or the second‐order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen‐bonded complexes. To resolve this discrepancy, the effects of chloro‐substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ππ^* excited state of phenol–trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ππ^* electronic excitation. We further examine the possibility of the electron–proton–coupled transfer in the ππ^* state through the surface crossing with the charge transfer type πσ^* state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Indole synthesis by radical cyclization of o-alkenylphenyl isocyanides and its application to the total synthesis of natural products

Development of indole synthesis by tin-mediated radical cyclization of o-alkenylphenyl isocyanide is described. Upon heating o-alkenylphenyl isocyanide in the presence of tri-n-butyltin hydride and AIBN, 2-stannyl-3-substituted indole was formed via 5-exo-trig cyclization of the imidoyl radical intermediate. After acidic workup, 3-substituted indoles were isolated. For substrates bearing simple alkyl groups, a substantial amount of tetrahydroquinoline derivatives were generated through 6-endo-trig cyclization. This undesired cyclization was suppressed by using an excess amount (five equivalents based on o-alkenylphenyl isocyanide) of ethanethiol instead of tri-n-butyltin hydride. The 2-stannylindole intermediates proved to be a suitable substrate for Stille coupling, giving 2,3-disubstituted indoles in a one-pot procedure. In addition, the 2-stannylindole intermediates could be converted to 2-iodoindoles by treatment with iodine or N-iodosuccinimide. The 2-iodoindoles thus obtained served as good substrates for Heck reactions, Stille couplings, Suzuki couplings, and palladium-mediated carbonylations, to afford a variety of 2,3-disubstituted indoles. The utility of this protocol was demonstrated by application to synthetic studies on gelsemine and discorhabdin A, and the total synthesis of an aspidosperma alkaloid, (-)-vindoline.     

Formation of PPy/Ta2O5/Ta structure by electropolymerization

Electropolymerization of pyrrole on tantalum (Ta) electrodes was carried out in buffer solutions (0.04 M phosphoric acid, 0.04 M acetic acid, 0.04 M boric acid and 0.2 M sodium hydroxide) containing 0.1 M sodium ptoluenesulfonate (TsONa) under galvanostatic conditions and it was found that a polypyrrole (PPy) and a tantalum oxide (Ta₂O₅) layer are formed on a Ta electrode by an electrochemical oxidation process. The conditions of this simultaneous formation were studied in respect to current density (i_d), pyrrole concentration ([Py]), pH and the amount of electricity. Under certain conditions ([Py] = 0.25 M, pH = 1.8, i_d = 10–20 mA cm^?2, the amount of electricity = 1 C), 6–8 μm thick PPy films were efficiently formed on homogeneous 30–50 nm thick Ta₂O₅ layers. The PPy film showed a high electrical conductivity (110 s cm^?1), adhered well and covered the Ta₂O₅ layer. The resulting PPy/Ta₂O₅/Ta system is therefore proved to have excellent properties as a capacitor.     

Brine shrimp lethality test active constituents and new highly oxygenated seco-prezizaane-type sesquiterpenes from Illicium merrillianum

In the study of bioactive substances in Illicium plants, the methanol extract of I. merrillianum showed brine shrimp lethality test (BST) activity at 200 microg/ml. Bioassay-guided fractionation of the BST active fractions resulted in the isolation of 4-O-methyleudesm-11-en-4alpha-ol, eudesmol-11-en-4alpha-ol and (-)-hinokinin as potent BST active compounds. On the other hand, four new highly oxygenated seco-prezizaane-type sesquiterpenes, merrilliortholactone (1), 2alpha-hydroxycycloparvifloralone (2), 2alpha-hydroxycycloparviflorolide (3), and 2alpha-hydroxyanisatin (4) were isolated from the BST-inactive polar fractions. The structures of new compounds were elucidated by extensive analyses of spectral data. Furthermore, the absolute configuration of 3 was established by the modified Mosher's method. Compounds 1--4 showed neither BST activity at 100 microg/ml nor neurite outgrowth-promoting activity.     

Orbital magnetic moment of two-dimensional Wigner crystal

The orbital magnetic moment is calculated for the two-dimensional Wigner crystal within the harmonic approximation. It is shown that the temperature dependence of the magnetic moment in the crystalline state is in the marked contrast with that of the liquid state.     

Synthesis and properties of highly refractive polyimides derived from fluorene‐bridged sulfur‐containing dianhydrides and diamines

Highly refractive and transparent polyimides (PIs) based on fluorene‐bridged and sulfur‐containing monomers have been developed. An aromatic dianhydride, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), was polymerized with several fluorene‐containing diamines, including commercially available 9,9′‐bis(p‐aminophenyl)fluorene (APF), 9,9′‐bis[4‐(p‐aminophenoxy)phenyl]fluorene (OAPF), and newly synthesized 9,9′‐bis[4‐(p‐aminophenyl)sulfanylphenyl]fluorene (ASPF) to afford series A PIs. Meanwhile, series B PIs were obtained from a new dianhydride, 4,4′‐[(9H‐fluorene‐9‐ylidene)bis(p‐phenylsulfanyl)]diphthalic anhydride (FPSP) and two aromatic diamines, ASPF and 4,4′‐thiobis[(p‐phenylenesulfanyl)aniline] (3SDA) via a two‐step polycondensation procedure. The PIs exhibit good thermal stabilities, such as relatively high glass transition temperatures in the range of 220–270 °C and high initial thermal decomposition temperatures (T_10%) exceeding 490 °C. The 9,9′‐disubstituted fluorene moieties endow the PI films with good optical transparency. The optical transmittances of the PI films at 450 nm are all higher than 80% for the thickness of about 10 μm. Furthermore, the highly aromatic fluorene moiety and flexible thioether linkages in the molecular chains of the PIs provide them with high refractive indices of 1.6951–1.7258 and small birefringence of 0.0056–0.0070. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1510–1520, 2008     

Determination of optimal vertices from feasible solutions in unimodular linear programming

In this paper we consider a linear programming problem with the underlying matrix unimodular, and the other data integer. Given arbitrary near optimum feasible solutions to the primal and the dual problems, we obtain conditions under which statements can be made about the value of certain variables in optimal vertices. Such results have applications to the problem of determining the stopping criterion in interior point methods like the primal—dual affine scaling method and the path following methods for linear programming.This author's research is partially supported by NSF grant DDM-8921835 and Airforce Grant AFSOR-88-0088.