Cisplatin is extremely important in the medical field as a drug approved by the FDA to treat bladder cancer, ovarian cancer, testicular cancer, squamous cell carcinoma of the head and neck, cervical cancer, malignant mesothelioma, and non-small cell lung cancer. This is obviously an extremely important chemotherapy drug in the fight against a variety of serious cancers. The brand name for this drug is Platinol and is used in hospitals and cancer treatment centers across the world. Cisplatin works by binding to DNA to interfere with cellular growth, stopping cancer cells. Although there are side effects associated with this powerful medicine, cisplatin is a lifesaving drug that is indispensable in the treatment of life-threatening cancers.
Figure 1: Cisplatin injection used to treat cancer
Molecular Information
Cisplatin, also called cis-diamminedichloroplatinum(II), is a molecule made up of 11 atoms. Cisplatin's chemical formula is H6Cl2N2Pt. The molecular shape is square planar, with the bond angles around the center molecule (which is Pt) equaling 90 degrees (see Figure 2). The bond angles between the nitrogen and hydrogen atoms are approximately 109.5 degrees (see Figure 2).
What type of molecule is cisplatin?
Cisplatin is a polar molecule (a molecule with unevenly charged sides). This is displayed in the above image with the plus and minus signs at the positive and negative ends of the molecule. The 3 unshared electron pairs on chlorine make that side of the molecule more negatively charged in relation to the side of the molecule with 6 hydrogen atoms (which hold no unshared electron pairs). This causes the molecule to have a negative side and a positive side, making cisplatin a polar molecule.
Bond Information
In the cisplatin molecule, the atoms H, Cl, N, and Pt are involved in bonds. H is bonded with N, Pt is bonded with B, and Pt is bonded with Cl. The eletronegativity values for these atoms are as follows: hydrogen (H) is 2.2, nitrogen (N) is 3, platinum (Pt) is 2.3, and Chlorine (Cl) in 3.2. The nature of the bonds is described by the arrows (see Figure 2). Arrows are drawn for each bond from the lower electronegativity value to the higher electronegativity value. All of the bonds in a cisplatin molecule are polar covalent (they are covalent but not absolutely covalent) because the difference in electronegativity between the two atoms involved in each bond is greater than zero (absolutely covalent) but less than 1.7 (neutral).
Please note: Because the above image is 3-Dimensional, it was not possible to draw arrows for all of the hydrogen and nitrogen bonds. Every arrow for these bonds would be drawn from the hydrogen atom to the nitrogen atom.
When two cisplatin molecules bond together, two forces of attraction are present. The first force of attraction is london dispersion forces. These forces are present between every two molecules that come in contact with each other. They are caused by the temporary uneven distribution of electrons in a bond and create a temporary, extremely weak dipole (polar molecule). The other force of attraction present in this situation is dipole dipole forces. This force is a result of an electrostatic attraction between the negative end of one molecule and the positive end of another. With two cisplatin molecules, the negative end (with the electron pairs from the chlorine atoms) of one molecule would attract to the positive end (with the 6 hydrogen atoms) of the other molecule. This is an example of dipole dipole forces. The third type of intermolecular forces (hydrogen bonding) would not be present between two cisplatin molecules. Hydrogen bonding is a special case of dipole dipole where hydrogen makes a temporary covalent bond with an adjacent oxygen, nitrogen, or fluorine atom. In the case of two cisplatin molecules, there are no oxygen or fluorine atoms present. While there are two nitrogen atoms in each cisplatin molecule, hydrogen bonding could not occur because each of the nitrogen atoms are completely surrounded by 3 hydrogen and one platinum atom.
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