Reactivity in Chemistry

Reduction Potentials of Metal Ions in Biology

MB7. Solutions for Selected Problems

Problem MB1.1.

Problem MB1.2.

Problem MB1.3.

At neutral pH, lysine would normally be protonated.  It would noy have a lone pair on the nitrogen to coordinate a metal ion.

 

Problem MB4.6.

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.

Problem MB4.7.

a) 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.

b) 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.

c) 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.

 

Problem MB5.1.

Ti4+ and Ca2+

Problem MB5.2.

F- and HO-

Problem MB5.3.

a)  Co2+ with  NO2-

b)  Mg2+ with CH3CO2-

c)  Cu+ with RS-

d)  Fe2+ with N2

e)  Zn2+ with  imidazole

Problem MB5.4.

Choose the best match for the following metal ions.

a)  Fe3+ with asp

b)  Cu+ with met

c)  Zn2+ with his

d)  Cu2+ with his

e)  Co3+ with glu

Problem MB5.5.

Choose the amino acid residue that would have the effect on the metal ion as described, based on HSAB principles.

a) Increase the reduction potential of Cu2+: met.

b) Decrease the reduction potential of Fe3+: glu.

c) Make Cu+ easier to oxidise: his.

d)  Make Fe2+ easier to oxidise:  asp.

e)  Make Fe3+ easier to reduce:  cys.

Problem MB7.1.

a) 0 β            b) 1.73  β        c) 2.83  β        d) 3.87   β       e)  4.89  β       f)  5.92  β

Problem MB7.2.

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

 

 

This site is written and maintained by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (with contributions from other authors as noted).  It is freely available for educational use.

Creative Commons License
Structure & Reactivity in Organic, Biological and Inorganic Chemistry by Chris Schaller is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License

Send corrections to cschaller@csbsju.edu

This material is based upon work supported by the National Science Foundation under Grant No. 1043566.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

 

Navigation:

Back to Redox Metals in Biology

Back to Reactivity Index

Back to Structure & Reactivity