Let's get right into it! Today we'll be talking about betaines, carbohydrates, carboxylic acids, ethers, ethylene oxide, esters, fatty acids, fatty alcohols, and glycols. These chemical structures are some of the most prevalent molecular structures you'll encounter in cosmetics, so I suggest getting familiar with them. These are especially important if you get into skin care formulations.
Again, let's go over a new word that is imperative for understanding these terms:
- Zwitterion - a neutral ion with positive and negative charge
Ok, let's begin round 2!
1. BETAINES
A type of zwitterion where the positively charged section is either a quaternary ammonium or phosphonium cation and the negatively charged section is usually a carboxylate group (see carboxylic acids below).
Betaines are pretty common surfactants and foam boosters in cleansers. You may have seen cocoamidopropyl betaine on a bottle of skin cleanser before. Betaines can also act as emulsifiers, viscosity increasing agents, and skin and hair conditioners.
Figure 1. Cocoamidopropyl betaine
2. CARBOHYDRATES (SACCHARIDES)
A biological molecule with multiple C-OH bonds and a ketone/aldehyde group; all sugars, starches and cellulose are considered carbohydrates. In cosmetics, sugars like glucose, fructose and maltose are used to adjust the osmolality of a formula. Starches and cellulose are used to increase the viscosity of water. Hydroxyethylcellulose is one of the most common water thickener used in cosmetics.
Figure 2. Glucose
Figure 3. Hydroxyethylcellulose (HEC)
3. CARBOXYLIC ACIDS
A basic functional group in chemistry--contains a C double-bonded to an O and single-bonded to an OH group. Carboxylic acids can be a part of many molecular structures of cosmetic ingredients. On their own, the most common carboxylic acids are the AHA's and BHA's (alpha-hydroxy acids and beta-hydroxy acids) like glycolic acid and salicylic acid respectively. These ingredients are used for their exfoliating properties of the skin.
Figure 4. General structure of carboxylic acid
Figure 5. Glycolic acid
4. ETHERS
An O single-bonded to a C and some functional group (R). Similar to carboxylic acid, this is a very basic functional group and thus prevalent in many molecular structures of cosmetic ingredients. Thus, ethers can have a wide variety of functions.
Figure 6. General structure of ether
5. ETHYLENE OXIDE
A cyclic ether used as a reagent for forming many types of cosmetic ingredients. The more ethylene oxide monomers on a molecule, the more water soluble that molecule is. Ethylene oxides are common reagents in forming ethoxylated molecules, which are used as surfactants in cosmetics. Polysorbate 20 (Tween 20) is a prime example of an ethoxylated surfactant.
Figure 7. Ethylene oxide
Figure 8. Polysorbate 20
6. ESTER
An O single-bonded to a C and H. The difference between this and ether is the R-group or H linkage to the O. Again, esters are another basic functional group that is prevalent in cosmetics. Thus, they also have a wide variety of functions.
Figure 9. General structure of esters
7. FATTY ACIDS
A fatty acid is a molecule with long, saturated or unsaturated aliphatic chains and carboxylic acid end. They are common viscosity boosters in emulsions and cleansing systems. One example is stearic acid--this fatty acid can be neutralized to thicken an emulsion using saponification.
Figure 10. Stearic acid
8. FATTY ALCOHOLS
Alcohols with long, saturated or unsaturated aliphatic chains. Similar to fatty acids, they are common viscosity boosters in emulsions and cleansing systems.
Figure 11. Stearyl alcohol
9. GLYCOLS
A hydrocarbon containing two OH groups. Glycols are commonly used as solvents and hygroscopic agents. Propylene glycol is quite prevalent in cosmetics. It's used as a solvent, hygroscopic agent, and has been shown to have skin penetration properties.
Figure 12. Propylene glycol
Ok, until next time! Stay tuned for the batch of our next couple of structures!