The oxidation number of Fe is +2 (see part a)
The group number of Fe is 8
d-electron count = 8 – 2 = 6
The d-electron count is d
6
(c )
What is the coordination geometry?
The coordination number (CN) is 6, so the geometry is octahedral.
G.
Zinc can act as a Lewis acid, and coordinate amino acids like cysteine by their sulfhydryl
(SH) groups.
Normally, the sulfhydryl group of cysteine has a pK
a
of ~8.
However, the
interaction with zinc can lower the pK
a
of the sulfhydryl group by as much as 4 pH units.
Using your knowledge of acid/base chemistry, estimate the approximate ratio of
protonated to deprotonated cysteine at neutral pH for
(a)
free cysteine (pK
a
of ~
8) and
4

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