Proton transport, long range

As shown by DFTB and CPMD simulations, the principal features of the transport mechanism are rotational diffusion of the protonic defect and proton transfer toward a neighboring oxide ion. That is, only the proton shows long-range diffusion, whereas the oxygens reside in their crystallographic positions. Both experiments " " and quantum-MD simulations, have revealed that rotational diffu-... 

The highest level, at structural scales >10 nm, is that over which long-range transport takes place and diffusion depends on the degree of connectivity of the water pockets, which involves the concept of percolation. The observed decrease in water permeation with decreasing water volume fraction is more pronounced in sulfonated poly(ether ketone) than in Nafion, owing to differences in the state of percolation. Proton conductivity decreases in the same order, as well. 

These devices need long-range transportation of particular carrier cations such as lithium cations or protons between electrodes. These small cations interact with... 

The authors further found that y-subunit rotation was blocked when the Fq complex was modified by dicyclohexylcarbodiimide (DCCD), the lipid-soluble carboxyl reagent that is known to inhibit proton transport by reacting with a carboxylate residue on one of the c-subunits in Fq (Glu in MFo Asp in EcFq). These results demonstrate that the reconstituted EcFi can rebind to Fq to form a functional, membrane-bound EcFo F complex and that y-subunit rotation in F, is functionally coupled to Fq. This is also consistent with the long-held notion of a long-range conformational interaction between Fq within the membrane and the catalytic nucleotide-binding site on the extrinsic F complex. 

Long-range Proton Transport of Protonic Charge Carriers in Homogeneous Media... 

However it turned out that the structural, chemical and dynamical details are essential for complex descriptions of long-range proton transport. These parameters appear to be distinctly different for different families of compounds, preventing proton conduction processes from being described by a single model or concept as is the case for electron transfer reactions in solutions (described within Marcus theory [23]) or hydrogen diffusion in metals (incoherent phonon assisted tunneling [24]). 

The complexity of the above-discussed many-partide conduction mechanisms of excess and defect protons in water reduces the effective activation enthalpy for the long-range transport of protonic defects, but it is also responsible for the relatively low pre-exponential factor of this process, which probably reflects the small statistical probability to form a transition state configuration in this environment. 

Figure 23.4 Proton conduction mechanism in liquid imidazole as obtained by a CP-MD simulation [67], As in water, changes in the second solvation shell of the protonic defect (here imidazolium) drive the long-range transport of the defect.

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