Incorporation of flexible alkyl chains into polyaniline was accomplished through an N-alkylation method with the leucoemeraldine form in order to maximize the degree of alkylation. The number of carbons varied from butyl to octadecyl, and with dodecylated samples, the degree of substitution was also controlled. The solubility in common organic solvents improved remarkably with the alkylation. The polymers displayed interesting solvatochromism and thermochromism, which result from the conformational changes induced by the interactions between the polymer and the solvent molecules and from the cooperation of disordering of the side chains and twisting in the main chain upon heating. In the solid state, the polymers form a layered structure in which the distance between the backbones depends on the length of alkyl side chain as recorded by the d spacing in WAXD patterns. DSC studies revealed that glass and melting transitions decreased systematically by increasing the length of substituents. With increasing side-chain length, the degree of interdigitation increases and the side chains begin to crystallize in a hexagonal packing array as determined by DSC, WAXD, and FT-IR data. The critical length n for side-chain crystallization is a minimum of 14 carbons, which is much larger than in the case of polyacrylates and polythiophenes, indicating the more rodlike character of polyaniline backbones. In addition, with polymers of n > 16, a mesophase transition after melting of the side-chain crystallites can be detected by optical microscopy and DSC.* To whom the correspondence should be sent.

SUMMARY:An electroactive material with remarkable solubility, processibility as well as mechanical properties has been developed by complexation (thermal doping) of polyaniline (PANi) emeraldine base with dodecylbenzenesulfonic acid (DBSA) in the solid state. Isothermal treatment of such a mixture was found to promote the complex formation. Optimum conditions of complexation were established with respect to the formation of layered structure, electrical conductivity and solubility. The optimal temperature for the doping process was found to be in a range of 100-120°C while the best ratio of DBSA to PANi was between 3 : 1 and 4 : 1 by weight, a nearly stoichiometric equivalence of aniline repeat units and DBSA molecules. The time of isothermal treatment should be controlled within 30 min. Thermal doping induced orientation to polymer chains in a layered structure, whereby the hydrophobic tails of the surfactants function as spacers between parallel stacks of the main chains. This anisotropy was achieved by the self-assembly during the thermal doping rather than ordinary drawing or stretching of the polymers. A unique liquid crystalline mesophase with a smectic-like optical texture was observed for the soluble portions of some specimens. The excess DBSA in the samples is considered to function as a solvent and to give rise to the liquid crystalline fluidity of the phase. The scanning tunneling microscopy (STM) image 5000 x 5000 A on a submicrometer scale obtained from a P+Ni/DBSA thin film exhibit! a surface morphology with a granular size of 200-300 A. The image of 150 x 150 A on a molecular scale obtained from multilayer PANiIDBSA deposited on a highly oriented pyrolytic graphite (HOPG) surface provides a direct observation of a self-assembled structure and close layer packing of the polymer backbone with dimensions in accord with the results found by X-ray diffraction. Our results indicate that the thermal doping process of polyaniline by DBSA offers new possibilities to obtain optimal structures through a self-assembly.

Filamentous fungal pathogens secrete effectors that modulate host immunity and facilitate infection. Fusarium graminearum is an important plant pathogen responsible for various devastating diseases. However, little is known about the function of effector proteins secreted by F. graminearum. Herein, we identified several effector candidates in the F. graminearum secretome. Among them, the secreted ribonuclease Fg12 was highly upregulated during the early stages of F. graminearum infection in soybean; its deletion compromised the virulence of F. graminearum. Transient expression of Fg12 in Nicotiana benthamiana induced cell death in a light-dependent manner. Fg12 possessed ribonuclease (RNase) activity, degrading total RNA. The enzymatic activity of Fg12 was required for its cell death-promoting effects. Importantly, the ability of Fg12 to induce cell death was independent of BAK1/SOBIR1, and treatment of soybean with recombinant Fg12 protein induced resistance to various pathogens, including F. graminearum and Phytophthora sojae. Overall, our results provide evidence that RNase effectors not only contribute to pathogen virulence but also induce plant cell death.

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