Glycine titration curve

FIGURE 27 2 The titration curve of glycine At pH values less than pKs H3NCH2CO2H is the major species present At pH values between pKs and pK z the principal species is the zwitter... 

With multiple ionizable groups, such as in amino acids and proteins, each group titrates separately according to its pKa. The titration curves shown in Fig. 23-5 are for the amino acids glycine, histidine, and glutamate. 

Relationship between the Titration Curve and the Acid-Base Properties of Glycine A 100 mL solution of 0.1 m glycine at pH 1.72 was titrated with 2 m NaOH solution. The pH was monitored and the results were plotted on a graph, as shown at right. The key points in the titration are designated I to V. For each of the statements (a) to (o ), identify the appropriate key point in the titration and justify your choice. 

Using the pKa values from problem 3, construct the theoretical titration curve showing the equivalents of H+ or OH reacting with 1 mol of glycine as a function of pH. Note that the shape of this curve is independent of the pfCa. Sketch similar curves for glutamic acid (pK./s equal 2.19,4.25, and 9.67), histidine (pfCa s equal 1.82,6.00, and 9.17) and lysine (pfCa s equal 2.18,8.95, and 10.53). 

Fig. 2. Ionization of glycine, (a) Titration curve of glycine, (b) dissociation of glycine. Numbers in bold in parentheses in (a) correspond to the structures in (b).

You will obtain a titration curve of an amino acid with a neutral side chain such as glycine, alanine, phenylalanine, leucine, or valine. If pH meters are available, you read the pH directly from the instrument after each addition of the base. If a pH meter is not available, you can obtain the pH with the aid of indicator papers. From the titration curve obtained, you can determine the pK values and the isoelectric point. 

Relationship between the Titration Curve and the Acid-Base Properties of Glycine A 100 mL... 

Figure 3.2 Titration curves for several acids. We are titrating 25 ml of 0.1 M acid with 0.1 M NaOH. Note that H3P04 has three plateau regions, and therefore, phosphoric acid may serve as a buffer at three pH ranges, 1-3, 5.7-7.7, and 11-13 for example, an amino acid, glycine, has two plateau (buffering regions). The numbers at the inflection points of each plateau region indicate the pK values.

The pH at which the molecule carries no net charge is called the isoelectric point. For glycine the isoelectric point is pH 6.0. Of course, in a solution of glycine at pH 6, at any instant there will be some molecules that exist as COOH—CH2— NH3, and an equal number as COO-—CH2—NH2, and even fewer of COOH—CH2—NH2. Because of the symmetry of the titration curve around the isoelectric point, it is possible to calculate the pH of the isoelectric point, given the individual pKa values. 

How do the true titration curves of aspartic acid and lysine differ from that of glycine Explain your answer. 

Figure 2-6. Titration curves for glycine (A) and histidine (6). The molecular species of glycine present at various pHs are indicated by the molecules above the curve. For histidine, pKa is the dissociation constant of the imidazole (side chain) group.

Ref. 96, l5N spectra of doubly labelled glycy 1-glycine, originally referred to external 4 m NHf NOp in 2 m HNO +359 06 ppm from neat CH,N02, Table VII the entire titration curves are reported. 

The answer is c. (Murray, pp 15-26.) The figure in the question shows the titration curve of glycine, an amino acid with two dissociable protons—one from the a-carboxyl group and the other from the a-amino group. The maximum buffering capacity of any ionizable function is at the... 

Fig. 7. Potentiometric titration curves of free and glycine (G)-conjugated ursodeoxycholic (UDC) and chenodeoxycholic (CDC) acids. Inset in D represents typical titration curve for free and glycine-conjugated bile acids with notations as explained in the text. The arrows on the GCDC curves indicate the points of bile acid precipitation. (From ref. 35 with permission.)...

Figure 6.12 shows the titration curves for glycine and m-aminophenol. Both show two separated end-points with only the first one being well defined. At 25°C the titration curves furnish the following pK values ... 

See also - Table 5.1, Genetic Code, Glutathione, Metabolism of Serine, Glycine, and Threonine, Essential Amino Acids, Titration Curve of Glycine... 

Titration curve of glycine. At pH values lower than 2.34, H3NCH2CO2H is the major species. At pH = 2.34 [H3NCH2CO2H] = [H3NCH2CO2 ]. Between pH = 2.34 and 9.60, H3NCH2C02 is the major species. 

Figure 4. Titration curves of glutamic acid, glycine, histidine, and lysine. The three amino acids whose titration curves sharply cut the zero-charge-horizontal-line also have a net charge apart from zero in the vicinity of the pH where they cut the zero line, i.e., the pi. That means that they have buffering capacity and conductance in the neighborhood of the isoelectric point and therefore are useful as carrier ampholytes. Glycine, on the other hand, with its extended horizontal part of the curve is not suitable. (Svensson, 2.)...

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