Dipole potentials

Su T, Viggiano A A and Paulson J F 1992 The effect of the dipole-induced dipole potential on ion-polar molecule collision rate constants J. Chem. Phys. 96 5550-1... 

D. Water Orientational Polarization and the Membrane Dipole Potential... 

Figure 7 The electric potential relative to the hydrocarbon ( dipole potential) as a function of distance from the center of a fully hydrated DPPC bilayer.

This chapter has given an overview of the structure and dynamics of lipid and water molecules in membrane systems, viewed with atomic resolution by molecular dynamics simulations of fully hydrated phospholipid bilayers. The calculations have permitted a detailed picture of the solvation of the lipid polar groups to be developed, and this picture has been used to elucidate the molecular origins of the dipole potential. The solvation structure has been discussed in terms of a somewhat arbitrary, but useful, definition of bound and bulk water molecules. 

A negative temperature coefficient of the inner-layer potential drop was observed, -0.8 mV KT1. Estimates of dipole potential drops due to solvent molecules22,23,29,30 gave much larger values for DMSO than for H20, which can be explained by a strong preferential orientation of DMSO at the Hg surface.26,8,304... 

Studies of pzc in mixed solvents were also carried out by Blaszczyk etal n using the dipping method. They worked in mixtures offormamide and NMF and estimated the shift of the standard potential of the hydrogen electrode, of the surface dipole potential atHg, and of the liquid junction potential. 

Electrode surface, and dipole potential difference or potential dependence, 15 Electrode systems, unstable, with asymmetrical fluctuations, 255 Electrode-electrite interface, microwave power and its effect on, 439 Electrogenerated films, storage capacity, 321... 

N2 - NO+ + N, compared with a theory (7) based on classical trajectories subject to an ion-induced dipole potential. The assumptions involved in calculating the measured cross-sections are noted in the text... 

The possibility of a barrier which inhibits a reaction in spite of the attractive ion-dipole potential suggests that one should make even crude attempts to guess the properties of the potential hypersurface for ion reactions. Even a simple model for the long range behavior of the potential between neutrals (the harpoon model ) appears promising as a means to understand alkali beam reactions (11). The possibility of resonance interaction either to aid or hinder reactions of ions with neutrals has been suggested (8). The effect of possible resonance interaction on cross-sections of ion-molecule reactions has been calculated (25). The resonance interaction would be relatively unimportant for Reaction 2 because the ionization potential for O (13.61 e.v.) is so different from that for N2 (15.56 e.v.). A case in which this resonance interaction should be strong and attractive is Reaction 3 ... 

Results of parameter optimization and MD simulations of small model compounds have been published, including alcohols [63], alkanes [63], aromatic [64] and heteroaromatic [209] compounds and liquid amides [65], Studies of ions in aqueous solution were also performed [61, 88] and results from an MD simulation on a DPPC lipid monolayer have been reported (Harder, MacKerell, Roux, submitted). Notable from the monolayer study was the reproduction of the dipole potential across the monolayer, a value that cannot be reproduced using non-polarizable models. This exciting, unforeseen observation points to the types of results that may be obtained from polarizable macromolecular force fields that are not accessible to the present additive models. 

Because T -> V energy transfer does not lead to complex formation and complexes are only formed by unoriented collisions, the Cl" + CH3C1 -4 Cl"—CH3C1 association rate constant calculated from the trajectories is less than that given by an ion-molecule capture model. This is shown in Table 8, where the trajectory association rate constant is compared with the predictions of various capture models.9 The microcanonical variational transition state theory (pCVTST) rate constants calculated for PES1, with the transitional modes treated as harmonic oscillators (ho) are nearly the same as the statistical adiabatic channel model (SACM),13 pCVTST,40 and trajectory capture14 rate constants based on the ion-di-pole/ion-induced dipole potential,... 

Clarke RJ (1997) Effect of lipid structure on the dipole potential of phosphatidylcholine bilayers. Biochim Biophys Acta-Biomembr 1327(2) 269-278... 

Vitha MF, Clarke RJ (2007) Comparison of excitation and emission ratiometric fluorescence methods for quantifying the membrane dipole potential. Biochim Biophys Acta-Biomembr 1768(1) 107—114... 

Clarke RJ, Kane DJ (1997) Optical detection of membrane dipole potential avoidance of fluidity and dye-induced effects. Biochim Biophys Acta Biomembr 1323(2) 223-239... 

Keywords Dual-wavelength ratiometry Electrochromism Ion-transporting membrane proteins Membrane dipole potential Phototoxicity... 

Up to now in this chapter, we have concentrated on the measurement via electric field sensitive dyes of the transmembrane electrical potential, which by itself should produce a linear drop in the electrical potential across a membrane. However, at least through the lipid matrix of a cell membrane, the electrical potential, /, at any point does not change linearly across the membrane. Instead, it follows a complex profile (see Fig. 6). This is due to contributions other than the transmembrane electrical potential to /. The other contributions come from the surface potential and the dipole potential. Both of these can also be quantified via electric field sensitive dyes. 

The transmembrane potential, A /, the surface potential, /s, and the dipole potential, /d, can be defined as follows ... 

Fig. 6 The electrical potential, ij/, profile across a lipid bilayer. The transmembrane potential, Aij/, is due to the difference in anion and cation concentrations between the two bulk aqueous phases. The surface potential, ij/s, arises from charged residues at the membrane-solution interface. The dipole potential, J/d, results from the alignment of dipolar residues of the lipids and associated water molecules within the membrane...

Slow dyes that respond via a redistribution across the entire membrane (sometimes called Nemstain dyes) do so because of a change in the transmembrane electrical potential. As such, they can only be used as probes of the transmembrane potential and not as probes of the surface potential or the dipole potential. Dyes whose electric field sensing mechanism involves a movement between the aqueous medium and its adjacent membrane interface on one side of the membrane can, in principle, respond to changes in both the transmembrane electrical potential and the surface potential. Fast dyes that remain totally in the membrane phase (e.g., styrylpyridinium, annellated hemicyanine, and 3-hydroxyflavone dyes) respond to their local electric field strength, whatever its origin. Therefore, these dyes can, in principle, be used as probes of the transmembrane electrical potential, the surface potential, or the dipole potential. 

Klymchenko AS, Duportail G, Mely Y et al (2003) Ultrasensitive two-colour fluorescence probes for dipole potential in phospholipid membranes. PNAS 100 11219-11224... 

Shynkar VV, Klymchenko AS, Duportial G et al (2005) Two-colour fluorescent probes for imaging the dipole potential of cell plasma membranes. Biochim Biophys Acta Biomem 1712 128-136... 

Clarke RJ (2001) The dipole potential of phospholipid membranes and methods for its detection. Adv Colloid Interfac Sci 89-90 263-281... 

Starke-Peterkovic T, Clarke RJ (2009) Effect of headgroup on the dipole potential of phospholipid vesicles. Eur Biophys J 39 103-110... 

Starke-Peterkovic T, Turner N, Vitha MF et al (2006) Cholesterol effect on the dipole potential of lipid membranes. Biophys J 90 4060-4070... 

Clarke RJ, Liipfert C (1999) Influence of anions and cations on the dipole potential of phosphatidylcholine vesicles a basis for the Hofmeister effect. Biophys J 76 2614-2624... 

Here, Ws is the work function of electrons in the semiconductor, q is the elementary charge (1.6 X 1CT19 C), Qt and Qss are charges located in the oxide and the surface and interface states, respectively, Ere is the potential of the reference electrode, and Xso is the surface-dipole potential of the solution. Because in expression (2) for the flat-band voltage of the EIS system all terms can be considered as constant except for tp (which is analyte concentration dependent), the response of the EIS structure with respect to the electrolyte composition depends on its flat-band voltage shift, which can be accurately determined from the C-V curves. 

The inner and outer potential differ by the surface potential Xa — (fa — ipa- This is caused by an inhomogeneous charge distribution at the surface. At a metal surface the positive charge resides on the ions which sit at particular lattice sites, while the electronic density decays over a distance of about 1 A from its bulk value to zero (see Fig. 2.1). The resulting dipole potential is of the order of a few volts and is thus by no means negligible. Smaller surface potentials exist at the surfaces of polar liquids such as water, whose molecules have a dipole moment. Intermolecular interactions often lead to a small net orientation of the dipoles at the liquid surface, which gives rise to a corresponding dipole potential. 

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