146 research outputs found
Supercooled confined water and the Mode Coupling crossover temperature
We present a Molecular Dynamics study of the single particle dynamics of
supercooled water confined in a silica pore. Two dynamical regimes are found:
close to the hydrophilic substrate molecules are below the Mode Coupling
crossover temperature, , already at ambient temperature. The water closer
to the center of the pore (free water) approaches upon supercooling as
predicted by Mode Coupling Theories. For free water the crossover temperature
and crossover exponent are extracted from power-law fits to both the
diffusion coefficient and the relaxation time of the late region.Comment: To be published, Phys. Rev. Lett., 4 pages, 3 figures, revTeX, minor
changes in the figures, references added, changes in the tex
Experimental evidence of the ferroelectric phase transition near the point in liquid water
We studied dielectric properties of nano-sized liquid water samples confined
in polymerized silicates MCM-41 characterized by the porous sizes \sim 3-10nm.
We report the direct measurements of the dielectric constant by the dielectric
spectroscopy method at frequencies 25Hz-1MHz and demonstrate clear signatures
of the second-order phase transition of ferroelectric nature at temperatures
next to the \lambda- point in the bulk supercooled water. The presented results
support the previously developed polar liquid phenomenology and hence establish
its applicability to model actual phenomena in liquid water.Comment: 4 pages, single figur
Enzymatic oligomerization and polymerization of arylamines: state of the art and perspectives
The literature concerning the oxidative oligomerization and polymerization of various arylamines, e.g., aniline, substituted anilines, aminonaphthalene and its derivatives, catalyzed by oxidoreductases, such as laccases and peroxidases, in aqueous, organic, and mixed aqueous organic monophasic or biphasic media, is reviewed. An overview of template-free as well as template-assisted enzymatic syntheses of oligomers and polymers of arylamines is given. Special attention is paid to mechanistic aspects of these biocatalytic processes. Because of the nontoxicity of oxidoreductases and their high catalytic efficiency, as well as high selectivity of enzymatic oligomerizations/polymerizations under mild conditions-using mainly water as a solvent and often resulting in minimal byproduct formation-enzymatic oligomerizations and polymerizations of arylamines are environmentally friendly and significantly contribute to a "green'' chemistry of conducting and redox-active oligomers and polymers. Current and potential future applications of enzymatic polymerization processes and enzymatically synthesized oligo/polyarylamines are discussed
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