Proton potential

Basic Idea Obviously, the protons in acid-base reactions are simply transferred from one base B to another B  

This is also referred to as a proton transfer reaction. The older but ambiguous name protolytic reaction is not recommended. According to the general conversimi formula, the reaction between gaseous hydrochloric acid and ammonia vapor produces a sal-ammoniac fog, a mist of finely distributed ammonium chloride 

This means that the definitions given here also hold when no solvent is present. 

Most acid-base reactions, however, take place in aqueous solutions. In this case, the second acid-base pair is provided by the solvent water itself (H30 /H20 or H2O/OH ). Despite this, it is possible to assign a chemical potential to the bonded yet exchangeable protons. This is the value established in the equilibrium of the reaction Ad Bs -b Vp p, where p denotes protons from any external source. In this particular case we have 

Experiment 7.1 Formation of sal-ammoniac fog from vapors of hydrochloric acid and ammonia Concentrated hydrochloric acid is poured in one of the gaswashing bottles concentrated ammonia solution is poured in the other. By pressing the rubber ball both gases (HCl and NH3) are unified and the resulting sal-ammoniac fog emerges from the small tube. 

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Fig. 2. The fluctuating difference between the proton potential at the product side relative to that at the reactant side (the difference between the two wells in a double-well proton potential). Whenever this difference is close to zero, tunneling conditions are favourable.

Tapia, O., Poulain, E. and Sussman, F. Hydrogen Bond. Environmental effects on proton potential curves. An SCRF MO CNDO/2 calculation of a water dimer, Chem.Phys.Lett, 33 (1975), 65-70... 

G. Steinberg-Yfrach, P. A. Liddell, S. C. Hung, A. L Moore, D. Gust, T. A. Moore, Conversion of Light Energy to Proton Potential in Liposomes by Artificial Photosynthetic Reaction Centres , Nature 1997,385,239-241. 

Fig. 16 Temperature dependence of the P isotropic chemical shift (top) and line width (bottom) for RbH2P04 (left panel). The right panel shows the temperature-dependent asymmetry of the normalized proton potential (solid lines) in comparison to the normalized data shown in the right panel of Fig. 16 [25]...

Another question we might pose to ourselves is whether the neutron and proton distributions in nuclei are the same Modern models for the nuclear potential predict the nuclear skin region to be neutron-rich. The neutron potential is predicted to extend out to larger radii than the proton potential. Extreme examples of this behavior are the halo nuclei. A halo nucleus is a very n-rich (or p-rich) nucleus (generally with low A) where the outermost nucleons are very weakly bound. The density distribution of these weakly bound outermost nucleons extends beyond the radius expected from the R °c A1 /3 rule. Examples of these nuclei are nBe, nLi, and 19C. The most well-studied case of halo nuclei is 1 Li. Here the two outermost nucleons are so weakly bound (a few hundred keV each) as to make the size of 11 Li equal to the size of a 208Pb nucleus (see Fig. 2.12). 

On the other hand, if we bring a proton up to the same nucleus, we will have a slightly different behavior. At first, the nucleus will repel the proton due to the long-range Coulomb force. Then, as we bring the proton very near to the surface, the same nuclear attraction will begin to overcome the repulsion. The nuclear attraction will increase until the proton is surrounded by nucleons as in the neutron case, but there will always be a net repulsion from the other protons. The repulsion decreases the overall attraction, and the proton potential energy well will not be... 

The conflicting results are obtained at solving the question if H+ ions are mixed with aqueous medium or, vice versa, are transported by the membrane-water interface (or inside the membrane) to the nearest A/ZH consumer, what the accurate value of proton potential decrease on H+-ATP-synthase molecule is, and if unmixed layers are present at the interface, and what the membrane profile complexity is [22],... 

This is also confirmed by the fact that ATP splitting by H+-ATP-synthase is constrained by generated proton potential [22] ATP hydrolysis on catalytic site F is performed via direct interaction between the water molecule and anhydride bond of ATP, i.e. which intermediate formation. It should also be noted that A/ZH+ is of higher importance for ATP removal from / j than for ATP synthesis. 

Fig. 20 Bicyclic sidechain analogs test role of nitrogen. Analogs described in Scheme 6 were built onto EC template and optimized in MOE 2007 [44]. Calculation of 3D protonation potential predicts different protonation states for His227 upon binding of the different analogs, a Compound la shown H-bonding to His227. b Compound lb packs firmly against surface of opposite tautomer of His227...

It is also usual to classify the H-bonds according to the property of the one dimensional (ID) proton potential function, although there are no clear discontinuities in the evolution of the properties with the increase of bond enthalpy. According to this finding, H-bonds can be classified into ... 

The solubility of metal-phosphates in soils is highly pH dependent because of the protonation potential of the phosphate species, and the various Kip values of a number... 

SQR (respiratory complex II) is involved in aerobic metabolism as part of the citric acid cycle and of the aerobic respiratory chain (Saraste, 1999). QFR participates in anaerobic respiration with fumarate as the terminal electron acceptor (Kroger, 1978 Kroger etal., 2002) and is part of the electron transport chain catalyzing the oxidation ofvarious donor substrates (e.g., H2 or formate) by fumarate. These reactions are coupled via an electrochemical proton potential (Ap) to ADP phosphorylation with inorganic phosphate by ATP synthase (Mitchell, 1979). 

The proton-tunnelling mechanism in tautomerism 222 The potential profile of the tautomerization of malonaldehyde 225 Molecular symmetry vs. shape of proton potential 227 Photo-induced tautomerization of salicylates 228... 

Fig, 5 Symmetric and asymmetric double minimum proton potentials derived from the rotation of methyl group of 2-methylmalonaldehyde [7]. 

Even though a proton potential for tautomerization is unsymmetrical, the tautomerization can be promoted by thermal or photochemical excitation. For... 

Even though rapid tautomerization is observed in an isolated system, it is not necessarily the case in the solid state, in which the symmetrical proton potential is sometimes deformed by an environmental effect. Therefore, the... 

The difference in the temperature dependence of the dielectric constant is also rationalized by the proton potential along the intramolecular hydrogen bond. As discussed in the case of 2-methylmalonaldehyde [7] in Section 2, the proton potential of 5-methyl-9-hydroxyphenalenone is considered to be unsymmetrical, when the conformation of the methyl group is taken into account (Busch and de la Vega, 1986). As a result, proton tunnelling is less... 

On the other hand, the proton potential of the 5-bromo compound is exactly symmetrical with reference to the reaction coordinate of the tautomerization. Consequently, the proton transfer can proceed through the tunnelling mechanism. This is the reason why the paraelectric behaviour is maintained even at 4 K. The suppression of the antiferroelectric phase transition may be derived from a quantum tunnelling effect. Such paraelectric behaviour can be regarded as quantum paraelectricity , which is a notion to designate the phenomenon that (anti)ferroelectric phase transitions are suppressed even at cryogenic temperatures due to some quantum-mechanical stabilization, proton tunnelling in this case. 

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