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Hopping Mechanism (hopping + mechanism)
Selected AbstractsNMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells,FUEL CELLS, Issue 3-4 2008H. A. Every Abstract This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks , poly(2,6-diphenylphenol) (P3O) and an imidazole functionalised poly(2,6-dimethylphenol) (imi-PPE) , and subsequently doped with polyphosphoric acid (PPA). From 1H and 31P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi-PPE and the imi-block copolymer, but not of P3O. The similarity in 1H T2 values between imi-PPE and the imi-block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi-PPE phase. 1H diffusion in P3O and the imi-block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi-PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the 31P T2 relaxation behaviour and inability to measure 31P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism. [source] Distance dependence of long-range electron transfer through helical peptides,JOURNAL OF PEPTIDE SCIENCE, Issue 2 2008Minako Kai Abstract Helical peptides of 8mer, 16mer, and 24mer carrying a disulfide group at the N -terminal and a ferrocene moiety at the C -terminal were synthesized, and they were self-assembled on gold by a sulfur,gold linkage. Infrared reflection,absorption spectroscopy and ellipsometry confirmed that they formed a monolayer with upright orientation. Cyclic voltammetry showed that the electron transfer from the ferrocene moiety to gold occurred even with the longest 24mer peptide. Chronoamperometry and electrochemical impedance spectroscopy were carried out to determine the standard electron transfer rate constants. It was found that the dependence of the electron-transfer rates on the distance was significantly weak with the extension of the chain from 16mer to 24mer (decay constant , = 0.02,0.04). This dependence on distance cannot be explained by an electron tunneling mechanism even if increased hydrogen-bonding cooperativity or molecular dynamics is considered. It is thus concluded that this long-range electron transfer is operated by an electron hopping mechanism. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Synthesis, characterization, and hoping transport properties of HCl doped conducting biopolymer- co -polyaniline zwitterion hybridsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2008A. Tiwari Abstract A series of electrically conductive zwitterion hybrid materials were facilely synthesized with anionic acacia gum (AG) and cationic HCl doped polyaniline (PANI) through radical copolymerization method. A representative acacia gum-polyaniline hybrid (AG-PANI) was characterized using UV-vis, FTIR, 1H NMR, and SEM. HCl doped AG-PANI possesses zwitterion character due to the presence of NH on PANI and COO, of AG. The cyclic voltammogram of AG-PANI showed three anodic peaks at 0.20,V, 0.58,V, and 0.64,V along with two cathodic peaks at 0.50,V and 0.40,V with large capacitive background currents. AG-PANI exhibited electrical conductivity that was found dependent on the ratio of aniline to AG, temperature, and pH. Its electrical conductivity versus temperature plot indicated Mott's nearest-neighbor hopping mechanism at the temperature range 83,323,K. The hybridization of AG and PANI yielded eco-friendly advanced functional materials for technological applications. Copyright © 2008 John Wiley & Sons, Ltd. [source] Anion,, Slides for Transmembrane TransportCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Jiri Mareda Dr. Abstract The recognition and transport of anions is usually accomplished by hydrogen bonding, ion pairing, metal coordination, and anion,dipole interactions. Here, we elaborate on the concept to use anion,, interactions for this purpose. Different to the popular cation,, interactions, applications of the complementary ,-acidic surfaces do not exist. This is understandable because the inversion of the aromatic quadrupole moment to produce ,-acidity is a rare phenomenon. Here, we suggest that ,-acidic aromatics can be linked together to produce an unbendable scaffold with multiple binding sites for anions to move along across a lipid bilayer membrane. The alignment of multiple anion,, sites is needed to introduce a cooperative multi-ion hopping mechanism. Experimental support for the validity of the concept comes from preliminary results with oligonaphthalenediimide (O-NDI) rods. Predicted by strongly positive facial quadrupole moments, the cooperativity and chloride selectivity found for anion transport by O-NDI rods were consistent with the existence of anion,, slides. The proposed mechanism for anion transport is supported by DFT results for model systems, as well as MD simulations of rigid O-NDI rods. Applicability of anion,, slides to achieve electroneutral photosynthesis is elaborated with the readily colorizable oligoperylenediimide (O-PDI) rods. To clarify validity, scope and limitations of these concepts, a collaborative research effort will be needed to address by computer modeling and experimental observations the basic questions in simple model systems and to design advanced multifunctional anion,, architectures. [source] | ||||||||||