Physical properties of drug molecules

Whatever the source is, chemistry is involved in all processes in the discovery phase. For example, if a drug molecule has to he purified from a natural source, e.g. a plant, processes such as extraction, isolation and identification are used, and all these processes involve chemistry. 

All drugs are chemicals, and pharmacy is a subject that deals with the study of various aspects of drugs. Therefore, it is needless to say that to become a good pharmacist the knowledge of the chemistry of drugs is essential. Before moving on to the other chapters, let us try to understand some of the fundamental chemical concepts in relation to the physical properties of drug molecules. 

Drug molecules exist in various physical states, e.g. amorphous solid, crystalline solid, hygroscopic solid, liquid or gas. The physical state of drug molecules is an important factor in the formulation and delivery of drugs. 

Polarity is a physical property of a compound, which relates other physical properties, e.g. melting and boiling points, solubility and intermolecular interactions between molecules. Generally, there is a direct correlation between the polarity of a molecule and the number and types of polar or nonpolar covalent bond that are present. In a few cases, a molecule having polar bonds, but in a symmetrical arrangement, may give rise to a nonpolar molecule, e.g. carbon dioxide (CO2). 

The term bond polarity is used to describe the sharing of electrons between atoms. In a nonpolar covalent bond, the electrons are shared equally between two atoms. A polar covalent bond is one in which one 

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These properties dictate the therapeutic, toxic, and metabolic characteristics of the overall drug molecule. These properties also completely control the ability of the drug to withstand the arduous journey from the point of administration to the receptor site buried deep within the body. These physical properties of drug molecules may be categorized into the following major groupings ... 

The structurally non-specific drugs include general anaesthetics, hypnotics together with a few bactericidal compounds and insecticides. However, it is important to note here that the biologieal characteristic of such drugs is solely linked with the physical properties of the molecules rather than the chemical feature. 

The most commonly used method is to graft cyclodextrins and their derivatives (aza-crown ethers, fullerenes, linear carbohydrate biopolymers and inorganic/organic hybrid networks) onto the textile materials. Cyclodextrins are potential high-performance carrier materials that have the ability to alter physical, chemical and biological properties of drug molecules. This... 

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