Lower proton concentration

A thermonuclear runaway develops near the base of the He envelope. The associated outward-moving detonation wave heats the matter to temperatures around 3 x 10 K, and leads to the ejection of about 0.2 M0 into the interstellar medium. The associated nucleosynthesis is especially complex, and is reviewed in detail by [32]. The situation may be summarized by saying that a quite high neutron density builds up at the beginning of the detonation, and leads to a weak r-process. Subsequently, the nuclear flow is pushed back to the valley of nuclear stability, and eventually into the neutron-deficient region, by photodisintegrations that become more and more efficient as temperature rises. A process coined pn-process by [87] then develops. The associated flow is displayed in Fig. 36. Its main path lies much further away from the proton-drip line than in the classical rp-process, which eases somewhat the nuclear physics problems. This results from the lower proton concentration... 

Fig. 21.11. Dinitrophenol (DNP) is lipid soluble and can therefore diffuse across the membrane. It has a dissociable proton with a pK near 7.2. Thus, in the intermembrane space where [H ] is high (pH low), DNP picks up a proton, which it carries across the membrane. At the lower proton concentration of the matrix, the dissociates. As a consequence, cells cannot maintain their electrochemical gradient or synthesize ATP. DNP was once recommended in the United States as a weight loss drug, based on the principle that decreased [ATP] and increased electron transport stimulate fuel oxidation. However, several deaths resulted from its use.

The presented experimental results did not confirm this charge transfer reaction for the experimental conditions of high proton activities. However, at lower proton activities a change in the mechanism was observed. Reaction Eq. (6.42) can be considered as a charge transfer reaction for lower proton concentration. 

The expression for Teiec embodies two competing trends of the solution phase potential at the reaction plane. An increase in solution phase potential results in a larger driving force for electron transfer in cathodic direction. This effect is proportional to the cathodic transfer coefficient c. At the same time, a more positive value of (y)- (l) - (po) corresponds to lower proton concentration at the reaction plane, following a Boltzmann distribution (Equation 3.77). The magnitude of this effect is determined by the reaction order yh+ K is> therefore, of primary interest to know the difference of kinetic parameters, - yh+ ... 

Protonation of the sulfoxide prior to H atom addition can be probably excluded, at least at lower HC104 concentrations due to a pKb of the DMSO of — 1.54. 

For weak acids, e.g., salicylic acid, the dependency on a pH gradient becomes complex since both the passive diffusion and the active transport process will be dependent on the proton concentration in the apical solution [61, 63, 98, 105] and a lowering of the pH from 7.4 to 6.5 will increase the apical to basolateral transport more than 20-fold. Similarly, for weak bases such as alfentanil or cimetidine, a lowering of the pH to 6.5 will decrease the passive transport towards the basolateral side [105]. The transport of the ionizable compound will, due to the pH partition hypothesis, follow the pKa curve. 

Zeolites exhibit a considerably lower proton (acid site) concentration than liquid acids. For example, 1 g of H2SO4 contains 20 X 10-3 moles of protons, whereas 1 g of zeolite HY, with a Si/Al atomic ratio of five, contain no more than 3 X 10-3 moles of protons. (Note that this is a cmde approximation of the acidic sites available for catalysis, because it assumes that with both materials all protons are available and catalytically active.) Moreover, 1 g of H2SO4 occupies far less volume (i.e., 0.5 cm3) than the equivalent mass of zeolite (4-6 cm3). 

When considering CEC or AEC, the pH of the soil solution is extremely important. There will be competition for binding sites between H30+ and other cations in the soil solution. Therefore, the observed CEC will be lower at high proton concentrations, that is, at low or acid pH levels, and higher at basic pH levels. For analytical measurements, the CEC of soil at the pH being used for extraction is the important value, not a CEC determined at a higher or lower pH. 

In conclusion, oxygen-17 NMR line-broadening provides the unique opportunity to study very fast proton transfer reactions on these metal oxocyano complexes by lowering the concentration of the reacting species through pH manipulation. 

State for proton removal from the open intermediate. At the lower buffer concentration, the proton-transfer step occurs more slowly than closing of the hydrogen bond, and proton transfer is rate limiting. At the higher... 

In the case of Nafion, a similar situation occurs. There is a sharp increase in proton conductivity and proton concentration as a function of water content followed by a decrease at A > 20. At these higher water contents, Nafion undergoes a similar dilution of proton concentration per BAM membrane in conjunction with a lower mobility value versus ETFE-g-PSSA. However,... 

Under some conditions, the rate of glycolysis from glycogen to lactate plus protons can be greater than the capacity of the transporter to transport all the lactate and protons out of the muscle. In this case, they accumulate in the muscle and the pH falls to about 6.5 or even lower (Chapter 13). This can occur, for example, when a muscle is working close to maximum, or when there is a poor blood supply to a working muscle. If this continued for any length of time, the increase in proton concentration could be sufficient to damage some of the proteins in the muscle. Indeed, if this decrease in pH occurred in the blood, it would be very serious and could rapidly lead to death. This is prevented in two ways ... 

S , HS , and H2S are not pertinent species above the gray line that runs from 0.25 V on the left to —0.75 v on the right. Above this line the S , HS , and H2S have been oxidized to Sg and/or 04 and/or HS04, and then to 208 . Therefore, the E-pH diagrams for this Zn/S system will show that the shaded region above this line is irrelevant to sulfide precipitation. It should be noted that the ion is a weak base. Therefore, it is necessary to take into account that as the pH of the solution is lowered, the concentration of the ion will be lowered due to protonation. The pertinent protonation reactions and corresponding AG° values and AG° (reaction) values (in kj/mole) are... 

These K values are often designated as Kp values (protonation constants) and are related to the commonly encountered acid dissociation constants, Ka, by the following relationship Kp = 1/Ka. From the Kp values, it can be seen that below pH values of 12.9 the ion is protonated to HS which lowers the concentration of ion in solution. The concentration of the ion is... 

These can be explained if they involve a third reaction of the protonated ester, i.e. with a molecule or molecules of water, a reaction not, of course, observed in media such as SbF5-FS03H. The activity of water falls rather sharply as the sulphuric acid concentration increases from 60-100%, and we know that most esters become essentially completely protonated in this region. Thus the situation can arise where the increase in the concentration of protonated ester produced by a given increase in acid concentration is proportionately smaller than the concomitant decrease in the activity of water, so that bimolecular (or higher molecularity) hydrolysis goes more slowly as the acidity is increased. Similar behaviour is observed when amides are hydrolyzed in strong acid solutions, but the rate maximum occurs at lower acid concentration, since amides are more basic than esters, and protonation is complete in solutions of lower acidity. 

The dissolution rate of goethite by sulfide was found to increase with surface area and proton concentration. Pyzik and Sommer (21) suggested that HS" is the reactive species that reduces surface ferric iron after exchanging versus OH . A subsequent protonation of surface ferrous hydroxide would lead to dissolution of a surface layer. Elemental sulfur was the prominent oxidation product polysulfides and thiosulfate were found to a lower extent. The dissolution rate R (in moles per square meter per second) of hematite by sulfide was demonstrated to be proportional to the surface concentration of the surface complexes >FeHS and >FeS (22). 

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