Cis-platin (Edexcel A Level Chemistry)

• Sometimes, complexes with four coordinate bonds may adopt a square planar geometry instead of a tetrahedral one
  • Cyanide ions (CN^-) are the most common ligands to adopt this geometry
  • An example of a square planar complex is cisplatin
• The bond angles in a square planar complex are 90^o

Cisplatin is an example of a square planar complex

• In the 1960s the drug cis-platin was discovered, which has been extremely effective in treating a number of different types cancer such as testicular, ovarian, cervical, breast, lung and brain cancer
• Cancer cells grow and replicate much faster than normal cells
• Cis-platin is a square planar molecule that has a geometric isomer with the side groups in different positions

The structures of cis-platin and trans-platin

• The cis-platin works by binding to the nitrogen atoms on the bases in DNA
• The cis-platin passes through the cell membrane and undergoes ligand exchange where the chlorines are replaced by water molecules
• The nitrogen is a better ligand than water and forms dative covalent bonds with the cis-platin
• The cis-platin distorts the shape of the DNA and prevents the DNA from replicating

The process by which cis-platin binds to DNA and prevents replication

Adverse Effects

• Cis-platin binds to healthy cells as well as cancerous cells, but affects cancer cells more as they are replicating faster
• Unfortunately, this means that other healthy cells which replicate quickly, such as hair follicles, are also affected by cis-platin
• This is why hair loss is a side-effect of people undergoing cancer treatment
• Despite this drawback, cisplatin is a highly effective drug and society needs to find a balance between the adverse effects of drugs and their therapeutic value
• New therapeutic pathways are constantly under development that aim to deliver drugs that target cancer cells while leaving healthy cells untouched