Biocoordination Chemistry 1 Flashcards
Ligand Denticity refers to
the number of donor groups in a single ligand that bind to a central metal ion in a coordination complex
H2O, although it contains two lone pairs, cannot be bidentate.
Why?
The two lone pairs are at an angle > 109° relative to each other, and so cannot be donated to the same metal ion
Bridging ligands are
the ligand acts as a bridge between the metal ions
A chelating agent is one where
- it forms two dative bonds with the same metal ion
En forms a ring around the metal ion
The en ligand is called a chelating agent
Chelates are
a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points.
Chelate stability depends on
the size of the ring
Order of chelate stability according to ring size:
3 < < < 4 < < 5 > 6 »_space; 7»_space; 8
Why is chelation therapy used?
To mobilise and remove unwanted or excess metal ions from the body.
Three areas of clinical use of chelating drugs:
i. Removal of metal ions that accumulate in tissues due to genetic disorders.
ii. Treatment of heavy metal (e.g. Pb, Hg, Cd) toxicity due to environmental pollution.
iii. Treatment of degenerative diseases of blood vessels (removal of Ca-containing plaques).
Chelation therapy using EDTA
The sodium salt of this complex, Na2 [Ca(EDTA)], is used as a drug (Calcium disodium versenate® ) to treat lead poisoning
Why do we use [Ca(EDTA)]2- - used to treat lead poisoning?
EDTA4- has a higher affinity for Pb2+ than Ca2+.
Pb2+ is larger than Ca2+ and EDTA4- fits better around it.
How is EDTA is also used to treat some forms of coronary artery disease?
Coronary artery disease generally refers to the build up of plaques in the inside layers of the arteries. As shown above, this will slowly narrow blood flow through the vessel, and the muscle it supplies will not get enough blood. The plaque weakens the wall. As shown in the lower artery, a crack may develop in the plaque and a blood clot may form - this is the mechanism of most heart attacks.
Atherosclerosis is a disease process in which lipids and/or calcium compounds and abnormal cells accumulate in the walls of the coronary arteries, forming plaques, and leading to blockage of the arteries.
How is atherosclerosis treated?
Treated by bypass surgery (expensive) or chelation therapy which can remove calcium containing deposits.
Iron Chelation Therapy – Treatment of Thallassaemia
Iron chelation therapy removes excess iron.
