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Polar Component (polar + component)
Selected AbstractsFrom quantum chemistry and the classical theory of polar liquids to continuum approximations in molecular mechanics calculations,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Sergio A. Hassan Abstract Biological macromolecules and other polymers belong to the class of mesoscopic systems, with characteristic length scale of the order of a nanometer. Although microscopic models would be the preferred choice in theoretical calculations, their use in computer simulations becomes prohibitive for large systems or long simulation times. On the other hand, the use of purely macroscopic models in the mesoscopic domain may introduce artifacts, with effects that are difficult to assess and that may compromise the reliability of the calculations. Here is proposed an approach with the aim of minimizing the empirical nature of continuum approximations of solvent effects within the scope of molecular mechanics (MM) approximations in mesoscopic systems. Using quantum chemical methods, the potential generated by the molecular electron density is first decomposed in a multicenter-multipole expansion around predetermined centers. The monopole and dipole terms of the expansion at each site create electric fields that polarize the surrounding aqueous medium whose dielectric properties can be described by the classical theory of polar liquids. Debye's theory allows a derivation of the dielectric profiles created around isolated point charges and dipoles that can incorporate Onsager reaction field corrections. A superposition of screened Coulomb potentials obtained from this theory makes possible a simple derivation of a formal expression for the total electrostatic energy and the polar component of the solvation energy of the system. A discussion is presented on the physical meaning of the model parameters, their transferability, and their convergence to calculable quantities in the limit of simple systems. The performance of this continuum approximation in computer calculations of amino acids in the context of an atomistic force field is discussed. Applications of a continuum model based on screened Coulomb potentials in multinanosecond simulations of peptides and proteins are briefly reviewed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Fabrication and characterization of solution cast MWNTs/PEI nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009Lu Shao Abstract Under mild conditions with the aid of ultrasonic, multi-walled carbon nanotubes (MWNTs) have been functionalized by mixed acid treatment which was proved by FTIR and XPS. According to SEM, acid treatment on MWNTs decreased the thickness of the membrane. However, no devastating damage and fracture happened on MWNTs after acid treatment under mild conditions. Precipitation observation illustrated that the enhanced solubility of MWNTs in water, ethanol, and dimethylformaide (DMF). Further, MWNTs/polyetherimide (PEI) nanocomposite films have been prepared by the simple solution casting method. The dispersion of MWNTs in polyetherimide (PEI) matrix was observed by Atomic Force Microscopy (AFM) which illustrated the improved dispersion for acid treated MWNTs in PEI. The adding of MWNTs in PEI decreased the dispersive component of surface energy and increased the polar component of surface energy, which resulted in the decrement of film surface energy. Differential scanning calorimetry showed that the glass transition temperature of PEI increased by about 4°C after the introduction of MWNTs. This improvement was related to the better affinity between MWNTs and PEI matrix, which also resulted in the improvement of mechanical strength in MWNTs/PEI nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] The effect of nitrogen incorporation on surface properties of silicon oxynitride filmsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1 2009Jongin Hong Abstract In order to investigate the surface heterogeneity of silicon oxynitride films, we observed the nanoscale variation of the surface potential by Kelvin probe force microscopy (KFM), the molecular bonding characteristics by Fourier transform infrared spectrometry (FTIR), and the wetting behavior by contact angle measurement. Nitrogen incorporation into silicon oxynitride films influenced the decrease in the surface potential and the polar component of the surface free energy. We present the first correlation between the nanoscale measurement of the surface potential and the macroscopic measurement of the surface free energy in silicon oxynitride films grown by a standard plasma-enhanced chemical vapor deposition (PECVD) technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Physicochemical Properties of Functional Surfaces in Pitchers of the Carnivorous Plant Nepenthes alata Blanco (Nepenthaceae)PLANT BIOLOGY, Issue 6 2006E. V. Gorb Abstract: Pitchers of the carnivorous plant Nepenthes alata are highly specialized organs adapted to attract, capture, and digest animals, mostly insects. They consist of several well distinguishable zones, differing in macro-morphology, surface microstructure, and functions. Since physicochemical properties of these surfaces may influence insect adhesion, we measured contact angles of non-polar (diiodomethane) and polar liquids (water and ethylene glycol) and estimated the free surface energy of 1) the lid, 2) the peristome, 3) the waxy surface of the slippery zone, and 4) the glandular surface of the digestive zone in N. alata pitchers. As a control, the external surface of the pitcher, as well as abaxial and adaxial surfaces of the leaf blade, was measured. Both leaf surfaces, both lid surfaces, and the external pitcher surface showed similar contact angles and had rather high values of surface free energy with relatively high dispersion component. These surfaces are considered to support strong adhesion forces based on the capillary interaction, and by this, to promote successful attachment of insects. The waxy surface is almost unwettable, has extremely low surface energy, and therefore, must essentially decrease insect adhesion. Both the peristome and glandular surfaces are wetted readily with both non-polar and polar liquids and have very high surface energy with a predominating polar component. These properties result in the preclusion of insect adhesion due to the hydrophilic lubricating film covering the surfaces. The obtained results support field observations and laboratory experiments of previous authors that demonstrated the possible role of different pitcher surfaces in insect trapping and retention. [source] Some Effects of Corona Plasma Treatment of Polylactide/Montmorillonite Nanocomposite FilmsPLASMA PROCESSES AND POLYMERS, Issue S1 2009Marian, enkiewicz Abstract Influence of the unit energy (Eu) of corona discharge used for modification of pure polylactide (PLA) and polylactide nanocomposite (PLAC) containing 5 wt% of an aluminosilicate nanofiller (Cloisite 30B) on water (,W) and diiodomethane (,D) contact angles as well as on surface free energy (,s) of these polymers was studied. ,W and ,D as advancing contact angles were measured with use of a goniometer while ,s was calculated by the Owens,Wendt method. It was found that ,W increased with the rising Eu while ,D remained approximately constant. Assuming Eu,=,const, it could be stated that the increase in ,s was much more evident for PLA than for PLAC. This increase resulted practically from the change in the polar component of ,s because the dispersive component for the two materials only slightly decreased with increase in Eu. [source] UV curing behaviors and hydrophilic characteristics of UV curable waterborne hyperbranched aliphatic polyesters,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2003Anila Asif Abstract A series of waterborne hyperbranched polyesters (WBHPs) endcapped with methacrylic and salt-like groups in different ratios have been investigated as UV curable resins. The kinetic studies of the drying step and UV curing were carried out by FT-IR measurements. The drying of the film of 100,,m thickness was completed in less than 6,hr at 70°C or within 10,hr at 50°C in an oven. The influence of different photoinitiators and their concentrations, extent of unsaturation and acid content of WBHP on final unsaturation conversion was studied. The surface free energy is a critical character, which affects the surface properties of a cured film. So one method based on the measurement of contact angle of a pure liquid on a solid surface was applied to determine the polar and dispersive components of the surface energy of UV cured films. The investigations of surface energy of WBHPs illustrated that those with more acid content and thus higher polar component are more sensitive to water, while those containing less acid content and thus lower polar term are less water sensitive. Moreover, the UV cured films of WBHPs and their blends with commercial waterborne resins (trade name EB 210, EB 2002, EB 11 and IRR 160) have acceptable pendulum hardness varying from 55 to 180,sec. Copyright © 2003 John Wiley & Sons, Ltd. [source] Liquid-liquid phase separation in acetone solutions of palm olein: Implications for solvent fractionationEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 4 2007Kevin W. Smith Abstract The quality of palm mid fractions (PMF) obtained by dry fractionation has increased, but the best-quality PMF for application in many confectionery fats are still produced by solvent fractionation. In the present study, liquid-liquid phase separation has been observed in acetone solutions both for pure triacylglycerols and for palm olein. The temperature at which phase separation occurs increases as the oil concentration is increased and linearly as the water content of the system is increased. The triacylglycerol compositions of the two liquid phases that form do not differ. However, the oil-rich phase is depleted with respect to the polar components. The temperature at which liquid-liquid phase separation occurs is reduced by about 0.2 and 0.4,°C per percent of free fatty acids and diacylglycerols, respectively. When oil-rich droplets appear, crystallisation occurs within them rather than in the oil-depleted phase, due to the higher oil concentration. Thus, liquid-liquid phase separation prior to crystallisation raises the nucleation temperature but may lead to a greater concentration of entrained olein in the filter cake, leading to a poorer-quality PMF. [source] Estrogenic activity of Nigella damascena extracts, evaluated using a recombinant yeast screenPHYTOTHERAPY RESEARCH, Issue 5 2002E. Agradi Abstract We used the yeast estrogen screen (YES) containing a human estrogen receptor to evaluate the estrogenic activity of extracts obtained from Nigella damascena seeds. Alcohol extracts obtained by direct extraction of seeds showed a low estrogenic activity, while the alcohol extract obtained after extraction with solvents of increasing polarity showed a strong estrogenic activity. This suggests the presence in Nigella of polar components whose activity can be clearly demonstrated after previous elimination of interacting apolar components that may mask the activity of more polar components. The response of both alcohol fractions follow a bell-shaped curve indicating a concentration-dependent relationship. Copyright © 2002 John Wiley & Sons, Ltd. [source] Perfume fingerprinting by easy ambient sonic-spray ionization mass spectrometry: nearly instantaneous typification and counterfeit detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2008Renato Haddad Perfume counterfeiting is an illegal worldwide practice that involves huge economic losses and potential consumer risk. EASI is a simple, easily performed and rapidly implemented desorption/ionization technique for ambient mass spectrometry (MS). Herein we demonstrate that EASI-MS allows nearly instantaneous perfume typification and counterfeit detection. Samples are simply sprayed onto a glass rod or paper surface and, after a few seconds of ambient drying, a profile of the most polar components of the perfume is acquired. These components provide unique and reproducible chemical signatures for authentic perfume samples. Counterfeiting is readily recognized since the exact set and relative proportions of the more polar chemicals, sometimes at low concentrations, are unknown or hard to reproduce by the counterfeiters and hence very distinct and variable EASI-MS profiles are observed for the counterfeit samples. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||