Glycine dissociations

What is the pH of a glycine solution in which the a-NHj group is one-third dissociated ... 

If the a-amino group is one-third dissociated, there is one part Gly for every two parts Gly°. The important is the for the amino group. The glycine a-amino group has a of 9.6. The result is... 

Table 9 includes data on the first dissociation constants of seven weak acids it will be recalled that we expect these to fall into class III. The table includes the second dissociation constants of five acids, phosphoric, sulfuric, oxalic, malonic, and carbonic, which fall into class IV, while the amino acids glycine and alanine provide four examples that should fall into class II. 

Using these acid dissociation constants for glycine, calculate the ratios [Z]/[C+] and [Z]/[A-] at pH... 

The larger molecular entity need not be a macromolecule. Consider the proton dissociation steps of the simplest amino acid, glycine. The dissociation of the first proton (i.e., the most acidic proton) can be represented by... 

Because dissociation constants vary with temperature, the zwitterion/uncharged ratio may also vary with temperature. For glycine , the temperature dependencies are dpKJdT = 0.0020 and dpA 2/dT = -0.025. 

Electroreduction of Cd(II)-nitrilotriace-tic acid and Cd(II)-aspartic acid systems was studied on DME using SWV [73]. The CE mechanism in which the chemical reaction precedes a reversible electron transfer was established. Also, the rate constants of dissociation of the complexes were determined. Esteban and coworkers also studied the cadmium complexes with nitrilotriacetic acid [74, 75] and fulvic acid [76]. The complexation reaction of cadmium by glycine was investigated by different electrochemical methods using HMDE and mercury microelectrode [77, 78]. 

It has been tacitally assumed in this discussion that the second-order formation rate constants measure the simple water substitution process. Although this must apply when unidentate ligands replace coordinated water, a composite process could describe the replacement by multidentate ligands. However, consideration of rate constants for successive formation and dissociation processes suggests that the overall rate of complex formation with flexible bidentate (and probably multidentate) ligands such as diamines, dipyridyl, glycine is probably determined by the rate of expulsion of the first water molecule from the metal aqua ion (56, 80, cf. 3 and 84). 

The result for glycine is comparable to that of Hammes and Steinfeld and the water dissociation rate constant is probably about 10 times 12. As the charge decreases from +1 to —2 there is a decrease in the kn value rather than the very large increase which would be expected if a charge decrease made the coordinated water much more labile. In fact, the rate drops more or less in order of the statistical number of coordinated water available for substitution. On the other hand, with the +2 polyamines the dien complex shows a substantial increase in rate of water substitution. The individual coordinated water appears to be about 100 times more labile than in Niaq+2. 

Water dissociation rate constant, 25°C. b Sum of rate constants for solvation and desolvation 25°C for polyethylene glycol, 4°C for glycine, diglycine, triglycine. 

Classification of the twenty amino acids found in proteins, according to the charge and polarity of their side chains is shown here and continues in Figure 1.3. Each amino acid is shown in its fully protonated form, with dissociable hydrogen ions represented in red print. The pK values for the a-carboxyl and a-amino groups of the nonpolar amino acids are similar to those shown for glycine. (Continued on Figure 1.3.)... 

Wash the affinity column with PBS. Pre-elute with dissociating buffer, e.g, 0. M glycine-HCl, pH 2.5. Wash with PBS check that the pH of the eluate is the same as the pH of the PBS (see Note 21). 

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