Liquid Chemicals: Alcohols, Aldehydes, & Biguanides: Study with Video Lessons, Practice Problems & Examples

Alcohols, aldehydes, and biguanides are key liquid chemicals for controlling microbial growth. Alcohols, like ethanol, act as disinfectants and antiseptics by denaturing proteins and damaging lipid membranes, particularly effective at 60-80% concentrations. Aldehydes, such as glutaraldehyde, sterilize by forming amide cross-links with proteins, requiring long treatment times for endospores. Biguanides, exemplified by chlorohexidine, disrupt cell membranes, leaking cellular contents. Understanding these mechanisms is crucial for effective microbial control in healthcare settings.

Alcohols

In this video, we're going to begin our lesson on liquid chemicals that are used for controlling microbial growth, specifically alcohols, aldehydes, and biguanides. Now in this video, we're going to focus primarily on the alcohols, but later in our course and other videos, we'll talk about the aldehydes and biguanides. And so alcohols can be defined as organic compounds that have at least one hydroxyl group, which is a functional group consisting of an oxygen and hydrogen atom, and the hydroxyl group is going to be bound to a hydrogen saturated carbon atom to create the alcohol. Alcohols are commonly used as disinfectants to treat inanimate surfaces or nonliving surfaces, and alcohols are also commonly used as antiseptics, which recall are a specific type of disinfectant that is safe to be used on tissues, such as human skin. Alcohols are commonly used as antiseptics for cleaning human skin just before a surgery takes place. Alcohols function primarily by denaturing proteins, making those proteins inactive and nonfunctional, and they can also damage cytoplasmic lipid membranes of microorganisms as well to help kill those microorganisms. Now interestingly enough, alcohols are actually more effective when they are diluted to a specific concentration somewhere around 60 to 80%, alcohol diluted in water. Alcohols are also very effective as tinctures as well. And tinctures are really just a medicine or a chemical disinfectant, such as iodine, dissolved in an alcohol-based solution. And so if we take a look at our image down below, we can get a better understanding of these alcohols, which again are going to consist of molecules with these -OH functional groups on them. And so notice over here we're showing you a carbon-based molecule here that has this -OH functional group here. And so this is a hydroxyl group, and that makes this molecule an alcohol. Specifically, this is the alcohol known as ethanol. And ethanol is a specific type of alcohol that is commonly used throughout scientific labs and also commonly used in hospital settings, again, to disinfect, surfaces and to help disinfect or clean the skin before surgeries. Now over here, what we're showing you is these bottles that are commonly used to make tinctures of iodine. And so iodine is usually dissolved in alcohol-based solutions, and that's what we're seeing here. And over here, what we're showing you is just a reminder of how alcohols can be used as antiseptics right before a surgery to help disinfect the skin before a surgery. And so this here concludes our brief introduction to alcohols as liquid chemicals used for controlling microbial growth. Moving forward in our course, we'll be able to get some practice, and then we'll talk about aldehydes and biguanides. So I'll see you all in our next video.

Alcohols are not reliably effective at destroying:

• A. Vegetative bacteria.
• B. Enveloped viruses.
• C. Endospores.
• D. Non-enveloped viruses.
• E. C & D.
• F. A & B.

Aldehydes

In this video, we're going to begin our lesson on the use of aldehydes as chemicals for controlling microbial growth. Aldehydes are any organic compound that has at least one aldehyde functional group, which is a chemical group consisting of a carbon, hydrogen, and oxygen atom. These aldehydes can be used in many different ways. However, they're commonly used as sterilants to sterilize objects and destroy all of the microbes on that object, of course, except for the prions. Aldehydes that are used as sterilants have the ability to diffuse across the cell's plasma membrane and form what are known as amide cross links with amino acids on proteins. When they form these amide cross links with amino acids, they can inactivate the proteins and make those proteins nonfunctional. This inactivation of the proteins is ultimately what destroys the microbes and allows aldehydes to be used to control microbial growth.

The use of aldehydes requires really long treatment times, up to 12 hours, in order to destroy endospores, which, recall from our previous lesson videos, are very resistant. It makes sense that it takes longer treatment times to destroy them. However, it only takes a really short amount of time, such as 10 minutes, to destroy vegetative cells. There are many different types of aldehydes including glutaraldehyde and formaldehyde, which is a gas that we'll get to talk more about later in our course. These must be diluted before their use.

If we take a look at our image down below, we can get a better understanding of these aldehydes. Of course, aldehydes have the functional group, the aldehyde, at the very end of the molecule. Over here on the left-hand side, we're showing you a specific aldehyde called glutaraldehyde. Glutaraldehyde has two aldehyde functional groups, one on this end and one on the other end. These aldehyde functional groups consist of a carbon, oxygen, and hydrogen. The carbon atom is represented by this little corner. Each of these corners represents a carbon atom. So there's a carbon atom, here's the oxygen, and here's the hydrogen atom, and that is what makes the aldehyde group. Glutaraldehyde is an aldehyde that can be used as a sterilant. Once again, glutaraldehyde can diffuse across a cell's plasma membrane to get inside the cell, and then it can react with amino acids on proteins. Notice over here we have an active protein which is going to have, of course, an amino group, on one of its amino acids. The aldehyde that's being added, which could be glutaraldehyde or some other aldehyde, can form a cross link with the protein. Notice that this is an amide cross link right here. This amide cross link that connects the aldehyde to the protein is ultimately going to inactivate the protein. We've gone from having an active protein on the left-hand side to having an inactive protein on the right-hand side. The inactivation of these proteins ultimately leads to the destruction of the microbe. That's how aldehydes can be used to control microbial growth.

This concludes our brief lesson on the use of aldehydes as chemicals for controlling microbial growth. We'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

Glutaraldehyde:

• A. Is, if given enough time, able to destroy all forms of microbial life.
• B. Forms cross-links with active proteins rendering them inactive.
• C. Disrupts lipid membranes.
• D. Is able to destroy one of the hardest types of microbes to kill, endospores.
• E. All of the above.

Biguanides

In this video, we're going to begin our lesson on the use of biguanides as chemicals for controlling microbial growth. Biguanides refer to a group of chemicals that are all derived from the molecule known as biguanide, which has the chemical formula of C₂H₇N₅. Biguanides primarily affect the membranes of vegetative cells, causing these cells to leak small molecules and proteins from their membranes. The most common chemical in this biguanide group is used as an antiseptic. This molecule is known as chlorhexidine.

Chlorhexidine is an example of a biguanide that is commonly used as an antiseptic to treat infections either on the skin or the mucous membranes. Biguanides are also used in prescription mouthwashes, toothpastes, and antiseptic creams. If we take a look at our image down below, we can get a better understanding of these biguanides. These biguanides are a group of chemicals derived from the molecule called biguanide. Here is the molecule biguanide, which has that chemical formula of C₂H₇N₅. Chlorhexidine is a molecule derived from biguanide, and you can see the complex chemical structure of chlorhexidine.

These biguanides disrupt or affect the membranes of vegetative cells, causing those cells to leak molecules and proteins. Notice here that we're showing you a vegetative cell that is leaking these molecules and proteins due to its disrupted membrane. Biguanides such as chlorhexidine are found in prescription mouthwashes and toothpastes and in antiseptic creams, such as face cream, for example. This concludes our brief lesson on biguanides as a chemical for controlling microbial growth. I'll see you all in our next video.

Chlorhexidine:

• A. Is a member of the biguanides group.
• B. Is extensively used as an antiseptic.
• C. Is ineffective against vegetative cells.
• D. Is limited in use due to its high toxicity.
• E. A and B.
• F. C and D.

Here’s what students ask on this topic:

What are the primary uses of alcohols in controlling microbial growth?

Alcohols, such as ethanol, are primarily used as disinfectants and antiseptics in controlling microbial growth. As disinfectants, they are applied to inanimate surfaces to eliminate microorganisms. As antiseptics, they are safe for use on living tissues, such as human skin, to clean and disinfect before surgeries. Alcohols function by denaturing proteins, rendering them inactive and nonfunctional, and by damaging the cytoplasmic lipid membranes of microorganisms. They are most effective at concentrations between 60-80% and can also be used in tinctures, where they dissolve other disinfectants like iodine.

How do aldehydes function as sterilants in microbial control?

Aldehydes, such as glutaraldehyde, function as sterilants by forming amide cross-links with amino acids on proteins, which inactivates the proteins and makes them nonfunctional. This inactivation ultimately destroys the microorganisms. Aldehydes can diffuse across the cell's plasma membrane to reach the proteins inside. They require long treatment times, up to 12 hours, to destroy resistant endospores, but can destroy vegetative cells in as little as 10 minutes. Aldehydes are effective in sterilizing objects and are commonly used in healthcare settings for this purpose.

What is the role of biguanides in microbial control, and how do they work?

Biguanides, such as chlorohexidine, play a significant role in microbial control by disrupting the membranes of vegetative cells. This disruption causes the cells to leak small molecules and proteins, leading to cell death. Chlorohexidine is commonly used as an antiseptic to treat infections on the skin and mucous membranes. It is also found in prescription mouthwashes, toothpastes, and antiseptic creams. By affecting the cell membranes, biguanides effectively control microbial growth and are widely used in healthcare and personal care products.

Why are alcohols more effective at 60-80% concentrations for microbial control?

Alcohols are more effective at 60-80% concentrations for microbial control because this concentration range allows for optimal protein denaturation and membrane damage. At higher concentrations, alcohols can coagulate proteins too quickly, forming a protective layer that prevents further penetration into the cell. At lower concentrations, there is insufficient alcohol to effectively denature proteins and disrupt membranes. The presence of water in the 60-80% range facilitates the penetration of alcohol into cells and enhances its antimicrobial activity.

What are tinctures, and how are they used in microbial control?

Tinctures are solutions where a chemical disinfectant, such as iodine, is dissolved in an alcohol-based solution. They are used in microbial control to enhance the effectiveness of the disinfectant. The alcohol in the tincture helps to dissolve the disinfectant and facilitates its penetration into microbial cells. Tinctures are commonly used for disinfecting skin before surgeries and for treating minor cuts and abrasions. The combination of alcohol and another disinfectant in tinctures provides a broad-spectrum antimicrobial effect, making them highly effective in controlling microbial growth.