Problem 14
Which amino acid contains a weakly acidic phenol-like R group?
Problem 15
Which of the following amino acids have \(\mathrm{R}\) groups that have hydrogen-bonding potential? Ala, Gly, Ser, Phe, Glu, Tyr, Ile, and Thr.
Problem 16
For an amino acid such as alanine, the major species in solution at \(\mathrm{pH} 7\) is the zwitterionic form. Assume a \(\mathrm{p} K_{\mathrm{a}}\) value of 8 for the amino group and a \(\mathrm{p} K_{\mathrm{a}}\) value of 3 for the carboxylic acid. Estimate the ratio of the concentration of the neutral amino acid species (with the carboxylic acid protonated and the amino group neutral) to that of the zwitterionic species at \(\mathrm{pH}\) 7.
Problem 18
The R group of lysine has an amino group that can be positively charged or lose a proton to become neutral. The \(p K_{a}\) of the amino group is \(10.8 .\) Determine the fraction of amino group that is protonated at \(\mathrm{pH}=9.8\) and at \(\mathrm{pH}=11.8\).
Problem 19
Glutamic acid has an R group that contains a carboxyl group whose \(\mathrm{p} K_{\mathrm{a}}=4.1 .\) What fraction of the R group carboxylic acid is protonated at \(\mathrm{pH}=2.1\) and \(\mathrm{pH}=7.1 ?\)
