Wednesday, February 3, 2010

Drugs and receptor interaction (ionic, covalence, H and VDN force)


Most drugs combine with specific sites on macromolecules (e.g. cell membrane components, enzymes, proteins) by precise physiochemical and steric interactions between specific chemical groups of the drug. These sites are termed receptors. The interaction need force such as ionic force, covalence force, hydrogen force and van der waal force.


An ionic bond is an electrical attraction between two oppositely charged atoms or groups of atoms. Normally, atoms are neutral and have no charge. However, in order to gain stability they will sacrifice their neutrality by either losing one or more of its outermost electrons thus becoming a positive ion (cation) or they will gain one or more electrons thus becoming a negative ion (anion). Once this has happened, the resulting charged atoms will attract each other. That electrical attraction between two oppositely charged ions is referred to as an ionic bond. All salts are ionic.


Force holding atoms in a molecule together as a specific, separate entity. In covalent bonds, two atoms share one or more pairs of valence electrons to give each atom the stability found in a noble gas. In single bonds, one electron pair is shared. In coordinate covalent bonds, additional electron pairs are shared with another atom, usually forming a functional group, such as sulfate (SO4) or phosphate (PO4).


Hydrogen bonds occur between molecules that have a hydrogen covalently bonded with an oxygen, nitrogen, or fluorine atom. When the other end of that covalent bond is a hydrogen, the electronegative atom is pulling all electrons associated with hydrogen away from it. Hydrogen acts almost as a positive charge. This high charge makes hydrogen bonds a very strong type of dipole-dipole force. Substances which hydrogen bond are typically liquids at room temperature.


Water molecules in liquid water are attracted to each other by electrostatic forces, and these forces have been described as van der Waals forces. Even though the water molecule as a whole is electrically neutral, the distribution of charge in the molecule is not symmetrical and leads to a dipole moment. This leads to a net attraction between such polar molecules which finds expression in the cohesion of water molecules and contributes to viscosity and surface tension.

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