2.8: Solutions for Selected Problems
- Page ID
- 202258
Exercise 2.1.1:
Exercise 2.1.2:
Exercise 2.1.3:
At neutral pH, lysine would normally be protonated. It would noy have a lone pair on the nitrogen to coordinate a metal ion.
Exercise 2.4.6:
The pKa of an α-position is typically about 20, although it can vary depending on what other groups are nearby. That is too high to build up a significant amount of the deprotonated species in water, which has a pKa (in water) of 14.
Exercise 2.4.7:
- The pKa of the side chain of histidine is about 6.0; upon changing from pH 7 to pH 5, this group would become protonated and positively charged. The positive charge would be more stabilising (or less destabilising) toward Fe2+ than Fe3+; the reduction potential would increase.
- The pKa of the side chain of histidine is about 3.7; upon changing from pH 4 to pH 3, this group would become protonated and positively charged. The positive charge would be more stabilising (or less destabilising) toward Fe2+ than Fe3+; the reduction potential would increase.
- The pKa of the side chain of histidine is about 4.2; upon changing from pH 4 to pH 5, this group would become deprotonated and negatively charged. The negative charge would be more stabilising (or less destabilising) toward Fe3+ than Fe2+; the reduction potential would decrease.
Exercise 2.5.1:
Ti4+ and Ca2+
Exercise 2.5.2:
F- and HO-
Exercise 2.5.3:
- Co2+ with NO2-
- Mg2+ with CH3CO2-
- Cu+ with RS-
- Fe2+ with N2
- Zn2+ with imidazole
Exercise 2.5.4:
Choose the best match for the following metal ions.
- Fe3+ with asp
- Cu+ with met
- Zn2+ with his
- Cu2+ with his
- Co3+ with glu
Exercise 2.5.5:
Choose the amino acid residue that would have the effect on the metal ion as described, based on HSAB principles.
- Increase the reduction potential of Cu2+: met.
- Decrease the reduction potential of Fe3+: glu.
- Make Cu+ easier to oxidise: his.
- Make Fe2+ easier to oxidise: asp.
- Make Fe3+ easier to reduce: cys.
Exercise 2.7.1:
a) 0 β b) 1.73 β c) 2.83 β d) 3.87 β e) 4.89 β f) 5.92 β
Exercise 2.7.2:
a) approx. 4 β b) approx. 4 β c) approx. 2 β d) approx. 3 β
e) approx. 5 β f) approx. 0 β g) approx. 6 β