The 99.99%: Part 2

Ever noticed that your hands feel cold after using a hand sanitizer such as Purell? This is caused by the evaporation of alcohol from your skin, which pulls body heat from your hands to convert liquids from the sanitizer into their gaseous form. In this second installment of the 99.99% we'll be discussing another major component found in today's cleaners and disinfectants: alcohols. Similar to phenolics, alcohols have several modes of action which lead to their disinfectant capabilities. 

In the field of chemistry, alcohols are organic (carbon-containing) molecules in which a hydroxyl group (-OH) is bound to a carbon. In nomenclature, the suffix -ol (i.e. ethanol, methanol, etc.) is used to denote an alcohol containing molecule. In fact, phenolics (or phenols) (the compounds described in The 99.99%: Part 1) are examples of alcohols. For the purposes of disinfection, however, only ethanol, methanol, and isopropanol are primarily used. 

Courtesy of http://www.innovateus.net

As for their mechanism of action, alcohols work in three ways: dehydration of cells, membrane disruption, and protein denaturation. Dehydration is a process in which an organism loses water. Typically, this process is caused by osmotic pressure differences between the interior and exterior of the specimen. Within the cytosol of a cell, which is primarily water, the concentrations of various compounds are highly regulated by a myriad of mechanisms. In addition, the cell wall of many organisms is permeable to water, meaning that water can move freely across it. When a cell is surrounded by a solution of higher concentration of certain compounds, called a hypertonic solution, water begins to diffuse out of the cell in an effort to equalize the concentration of the compound across the membrane (see above). As water leaves the cell, the cell membrane becomes shrunken and the concentrations of vital compounds within the cell become greatly disrupted, eventually leading to cell death. For the purposes of disinfection, a 70% alcohol solution is typically used. 

Similar to phenolics, alcohols also have a denaturation effect on proteins. As mentioned previously, protein folding is a complicated factor which is dependent on a wide range of cellular factors. One of these factors, is hydrogen bonding, a type of bonding between a polar hydrogen with an electronegative atom; typically nitrogen, oxygen or fluorine. Hydrogen bonding affects both the secondary and tertiary structures of proteins helping provide their distinctive three-dimensional shape. Due to their polar hydroxyl groups, alcohols can also participate in hydrogen bonding. Once the alcohols are within the cell, they disrupt the native hydrogen bonding, leading to the denaturation (inactivation) of proteins, disrupted cellular function and cell death.

Alcohols also take the place of water within the cell membrane. In doing so, the alcohol molecules break down the orderly arrangement of the phospholipids, making the membrane more liquid like and more permeable to certain compounds. Additionally, alcohols affect the shape and function of proteins within the cell membrane in the same way they affect proteins within the cell.

All combined, these affects make alcohols a powerful antiseptic agent, effective against a broad range of bacteria, viruses, and fungi. So next time you lather up, think of all those alcohol molecules swooping in to save the day!

References:

• http://www.ou.edu/research/electron/bmz5364/prepare.html
• http://peer.tamu.edu/curriculum_modules/cell_biology/module_2/hazards2.htm
• http://www.microrao.com/micronotes/sterilization.pdf
• http://www.elmhurst.edu/~chm/vchembook/568denaturation.html
• http://www.cliffsnotes.com/study_guide/Chemical-Methods-of-Control.topicArticleId-8524,articleId-8429.html