Zn, Cd and Hg

Question 1

Why is it difficult to study the chemistry of Zinc complexes?

Answer 1

• do not absorb in the visible region (unlike many transition metal complexes)
• do not have isotopes that can be studied using NMR
• diamagnetic - if you put a zinc complex in a magnetic field, they are weakly repelled

Question 2

What are the characteristics of Zinc?

Answer 2

• readily available in natural waters
• exhibits no redox chemistry in nature
• has a preference for o and N donors
• catalyses acid-base reactions
• Allows HO- to act as a base in biological systems

Question 3

An example of a Zn enzyme

Answer 3

Carbonic anhydrase (CA)
• enhance transport if CO2

Question 4

What is the main cause of symptoms in Alzheimer’s disease?

Answer 4

• alzheimer’s precursor protein - may be a copper protein which degrades into small pieces which ‘precipitate’ in the brian

Question 5

How are chelating ligands different from their counterparts of lower denticity?

Answer 5

• chelating ligands generally form more stable complexes
• e.g. catecholate and enterobactin
• also, Ni2+ complexes with NH3 and dien

Question 6

Why may metal ions be toxic?

Answer 6

1. involved in production of radicals
2. cause precipitation of insoluble salts
3. bind to proteins (enzymes) and disrupt their function
4. displace essential metals from proteins - disruption of function

Question 7

What is the criteria for an effective chelating agent?

Answer 7

• must be soluble and non-toxic
• should reach the tissue where metal toxicity is of concern
• metal ligand complex formed should be stable and non-toxic
• it should be selective for the metal of concern

Question 8

How can metal ion toxicity effects be remediated?

Answer 8

the use of chelating agents

Question 9

What is an example of a chelating agent?

Answer 9

H4EDTA - ethylenediamine tetraacetic acid

Question 10

What is H4EDTA and describe its role

Answer 10

• hexadentate chelating agent - used to treat Pb poisoning

Question 11

What is the problem with H4EDTA?

Answer 11

• Binds to metals as the anion EDTA4-
• bind to metals other than Pb such as Ca2+
• hence, administered as the CaNa2EDTA to reduce calcium depletion

Question 12

What is thalassemia?

Answer 12

A genetic disorder involving abnormal haemoglobin production

Question 13

Treatment for thalassemia?

Answer 13

• often requires blood transfusions leading to iron overload

* desferasirox in current clinical use to remove excess iron

Question 14

How does desferasirox work?

Answer 14

• it is a tridentate ligand - 2 ligands bound per iron atom
• Fe3+ centre is octahedral
• ONO chelating agent with both OH groups being deprotonated upon chelation

Question 15

Denticity of desferasirox?

Answer 15

tridentate

Question 16

What is the structure of the Fe3+ desferasirox complex?

Answer 16

• Fe3+ centre - octahedral

* ONO donor atoms (O and N)

Question 17

Desferasirox function

Answer 17

Removes excess iron