Question

[e] The following shows the chemical structure of aspartic acid and the Ka values for its respective bolded protons (Ka = 1.02 x 10-2) NH CHCH,COOH (Ka = 1.26 x 10-4) COOH (Ka 9.95 x 10-11) ) 12 marks] Give the structure of the most predominant species and the second predominant species at pH3.5. Most predominant species Second predominant species (ii) 12 mark] Give the structure of the most predominant species and the second predominant species at pH 5.5 Most predominant species Second predominant species

Answer 1

(i) structure of the most predominant species and the second predominant species at pH 3.5. at a pH between pKa1 and pKa2. The net charge is about 0. Hence, Most predominant species Second predominant species COOH O0 CH2 COOH CH2 COOH (ii) the structure of the most predominant species and the second predominant species at pH5.5 at pH above pKa2. The net charge is about -1. Hence, Most predominant species Second predominant species coo coo CH2 COO CH 2 COOH