D.8.1+Drug+Action


 * D.8.1 Describe the importance of geometrical isomerism in drug action **

Geometrical Isomerism -- molecules with a carbon-carbon double bond which prevent the rotation around a bond so that the position of the atoms can change.

There are 2 important isomers - **trans** and **cis** isomers.

Cis isomer
 * two functional groups will be on the same side of the double bond and bonded to two different carbon atoms.

Trans isomer Usually the trans isomer will have a higher melting point because the molecules are able to pack more closely together causing the forces of attaction betwen the molecules to increase. Therefore more energy needs to be absorbed in order to break them, increasing the melting point.
 * two functional groups bonded to opposite sides of the double bond.
 * Physical properties of cis and trans isomers**


 * Cis and trans diamminedichloroplatium (II)**
 * Both isomers exhibit different properties.
 * The cis isomer called cisplatin is an effective treatment of testicular and ovarian cancer while transplatin is not.
 * Both molecules have no overall charge which enables them to diffuse through the cancer cell membrane.
 * Once inside the cell, the two isomers will lose a chlorine molecule and gain a molecule of water to form the complex ion [Pt(NH3)2Cl(H2O)]+.
 * This complex ion will then enter the cancer cells' nucleus but due to the orientation of the two different isomers, only the cis isomer will be able to bind to two guanine molecules in the cell's DNA, exchanging another chloride ion to form [Pt(NH3)2(DNA)]2+. This alters the cancer cell's DNA, so that when the cell replicates it will be unable to 'copy' itself correctly and will die. The two isomers are shown below.


 * Trans isomer** **(on the left)** and **Cis isomer (on the right)**

Image Source:http://www.chem.shef.ac.uk/chm131-2002/cha02cs/platin.gif