Average protonation state

Fig. 10. Average protonation states of terminal i]-H20 groups on model a-FeOOH nanoparticles having high (a) and low (b) ratios of (110)/(021) surfaces. Blue corresponds to an average protonation state of 1 (FeOH) and red to an average protonation state of 2 (FeOH2).

The average protonation state for site p is found by performing a thermodynamic average over all IN possible vectors... 

The potency of the inhibitors is affected by the pH. Changes in pH affect the protonation state of the guanidine. In conditions of low pH, such as in ischemia-reperfusion, some dtugs such as cariporide work more efficiently because they are on average more positively charged. 

Example The cleavage of disulfide bonds by reduction with 1,4-dithiothreitol causes the unfolding of the protein. This exposes additional basic sites to protonation, and therefore results in higher average charge states in the corresponding ESI spectrum (Fig. 11.14). [88]... 

The resonance frequencies of the C-2 protons of histidyl residues of deoxy-Hb A and HbCO A depend on the pH of the solution (Russu et al., 1980, 1982) because the observed proton chemical shifts are a weighted average of the chemical shifts of the protonated and un-protonated states of histidyl residues in Hb. Due to this exchange,... 

Polyaniline exists in various forms which differ in the oxidation state and degree of protonation of the main chain. The average oxidation state of the polymer main chain can be varied chemically or electrochemically. The structures of several common oxidation states are shown in Fig. 64. The degree of protonation can be varied by treatment with acid or base. In addition to the structure obtained from head-to-tail coupling at the para-position, other structural units can be obtained. These units can be obtained by substitutions at other positions of the phenyl group as well as head-to-head and tail-to-tail coupling (Fig. 65). The polymerization conditions determine the structural characteristics, oxidation state, and... 

Eor the chosen example, the first term arising from thermal H-bond excitation effects on the average squared coupling contributes, as predicted above, the most, 72%, the final term is next in significance at 20%, and the middle term contributes only 8%. The minimal significance of the (middle term) difference in 0-0 reaction barriers reflects the disparity f S > EaL that we have noted above should be expected for PT in a sufficiently polar environment. The increased contribution (third term) of the excited proton state contribution is due to the differential contribution of the 0-0 transition to the total rate, pi < /ip [60]. 

---