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

Nemo's Wrath

Courtesy of heavy.com

In honor of Blizzard Nemo, today's post will talk about the science and chemistry of snowflakes! It is said that no two snowflakes are alike, but how could this be possible? How do these intricate ice crystals come to form and what controls the various shapes they make.

Courtesy of blog.needsupply.com

Before we delve deeper, it's important to briefly review the various states of matter and how they interchange. There are four basic types of matter observable in everyday life: solid, liquid, gas, and supercritical fluid. The distinction between these types of matter is mainly based on their qualitative properties. At low temperatures, individual molecules don't have a lot of energy, and as such, they tend to stick together due to intermolcular forces. The molecules pack together in an order arrangement giving the material a high density and rigid shape, making them very difficult to compress. As the molecules warm up, they eventually gain enough energy to break some of the intermolecular bond which hold them in place. The molecules then begin to diffuse into their container, leading to an increase in disorder of the system. This is the liquid state. The particles are still close to one another but now have the ability to move freely. When the temperature gets high enough, the molecules gain enough energy to escape from their intermolecular forces and entirely seperate from one another. In this state, the gaseous state, particles have complete freedom of motion and individual molecules are very spread apart and moving very fast. Because they are mostly space, gases completely fill their containers and can be easily compressed. The fourth state of matter is supercritical fluid, a state with both gas and liquid properties. This state arises at high temperatures and pressures when molecules have too much energy to be compressed into a liquid at any pressure.

Courtesy of chem.ufl.edu

High up in the clouds, when the temperature drops below 32° F (0°C) water droplets (liquid) begin to freeze around dust particles. It is from these small crystals that snowflakes then form! While snowflake formation is a highly dynamic process that depends on temperature, humidity, air currents, etc. there are several general guidelines regarding what types of crystals form at different heights and temperatures. Generally, in high clouds, six-sided hexagonal crystals form, while at mid range heights flat six-sided crystals dominate. At colder temperatures, sharper tipped snowflakes with more intricate branching patterns also tend to form. The short video below gives a great overview of the whole process.

Who knew that fluffy white stuff could be so amazing!

References:

• http://chemistry.about.com/od/moleculescompounds/a/snowflake.htm
• http://www.chem.purdue.edu/gchelp/atoms/states.html

The 99.99%: Part 1

With the flu season in full swing, people are more germ conscious than ever. From Lysol, to Clorox,  to Purell, the shelves are full of consumer products claiming to kill 99.99% of bacteria and/or viruses, but how do they manage to kill germs without hurting our hands or stripping the varnish off our tabletops. 


While many cleaning products accomplish the same goal, most are made up of a unique blend of active ingredients responsible for their potency. These bacteria killing chemicals can be broken down in to a number of more general categories: phenolics, quarternary ammonium centers, alcohols, and halogen based compounds. In this first segment, we'll discuss phenolics.

 Phenolics are molecules which contain a phenol group (an aromatic six carbon ring with a hydroxyl (OH)).  This anti-bacterial, first used as an antiseptic in the 1860s, acts by damaging cell membranes and denaturing enzymes within bacterial cells. On a molecular level, phenolics work by inserting into the phospholipid bilayer of cells, acidifying the cell membrane, and denaturing proteins within the cell. 

The hydrogen atom of the hydroxyl group in phenol is weakly acidic, but can lose it's proton around biological pH (~7). At the surface of the plasma membrane, phenols can exchange protons with molecules and proteins, changing the relative distribution of charge across the cell membrane. While this may seem minor, even small changes in the charge surrounding the cell membrane can cause charge sensitive membranes, responsible for the transport of compounds across the cell membrane to shut down: nothing in and nothing out. 

While phenol compounds contain a polar alcohol (R-OH) group, the phenyl ring make them largely nonpolar. This characteristic allows phenols to insert themselves into the phospholipid bilayer of the cell membrane. As these molecules begin to build up within the cell membrane, they can begin to displace phospholipids, compromising the integrity of the cell membrane. Once within the membrane, phenolics which have lost their hydrogen atom also have the ability to shuttle cations across the cell membrane, leading to further membrane permeability and loss of the cell's content. 

Lastly, once within the cell, phenolics can denature (inactivate) proteins. The cell's cytoplasm is mostly made up of water, a polar substance. Normally, proteins fold in such a way to expose a maximum number of its polar side chains to the surrounding polar environments while hiding its nonpolar side chains internally. When nonpolar phenolic molecules begin to interact with a protein it will change its shape to expose some of its nonpolar portions. This change in conformation leads to inactivation of the protein (denaturation), due to the fact that protein form and function are interdependent.

In terms of disinfectants, phenolics are only one component that makes up the laundry list of ingredients in household cleaners. As you can see, however, the way these molecules interact with bacteria, viruses, and fungi can be quite complicated! Tune in soon for the next antiseptic in the series!

Related Video:

• http://www.youtube.com/watch?v=obDsnyMBZMY

References:

• http://www.madsci.org/posts/archives/mar99/921165350.Mi.r.html
• http://www.cliffsnotes.com/study_guide/Chemical-Methods-of-Control.topicArticleId-8524,articleId-8429.html
• http://books.google.com/books?id=iwiJwnrq6a8C&pg=SA10-PA13&lpg=SA10-PA13&dq=phenolics+inactivate+proteins&source=bl&ots=Agoq5Kp9a4&sig=0WUHpss8Mp2Q6FsWzpQq4Y5oHXU&hl=en&sa=X&ei=BbgOUdD7O_SB0QGq1IHwDw&ved=0CHwQ6AEwCA#v=onepage&q=phenolics%20inactivate%20proteins&f=false
• http://books.google.com/books?id=y5-VzA5CxvsC&pg=PA170&lpg=PA170&dq=mechanism+of+phenolic+membrane+disruption&source=bl&ots=ZY93r4K4X5&sig=OzUFOL1Mvbz5NrW3Oqr9siOiVvY&hl=en&sa=X&ei=HrwOUYjYGMqw0AG1woHYAg&ved=0CEwQ6AEwAw#v=onepage&q=mechanism%20of%20phenolic%20membrane%20disruption&f=false
• http://ecosystems.wcp.muohio.edu/studentresearch/ns1fall02/cummins/morning/resistance/articles/Mechanisms%20of%20Action%20of%20Disinfectants.pdf
• https://facultystaff.richmond.edu/~lrunyenj/bio384/lecturenotes/ch7.pdf