The Velcro Called Intermolecular Interaction

Participant Profile

Shuichi Osanai

Shuichi Osanai

Most people would use a needle and thread to sew two pieces of fabric together. But if you use Velcro to join them, the two pieces of fabric can be easily attached or separated back into two. The same can be said when bonding molecules together.

For example, carboxylic acids and alcohols are joined by a covalent bond called an ester bond. Breaking this bond is a bit tricky; it is broken through hydrolysis with the help of an acid or a base. This is just like using scissors or a razor to cut the thread when you've sewn something with a needle and thread.

Covalent bonds are not the only way to join molecules. For example, there are various other interactions, such as electrostatic interactions, van der Waals interactions, hydrogen bonding interactions, as well as charge-transfer interactions and hydrophobic interactions. The energy of each individual interaction is about 1/10 to 1/100 smaller than that of a covalent bond.

These small intermolecular forces gather to become a large force that determines the shape of complex molecules such as proteins and DNA. Furthermore, although 70% of the components of living organisms is water, it is thanks to these intermolecular forces that cells can function as cells within that environment. Don't you think it's similar to that Velcro? A single fiber, like one on an insect's leg, can be easily detached, but when hundreds of them come together, they can be firmly fixed.

A compound that has both a hydrophilic group, which is compatible with water, and a hydrophobic group with a long carbon chain, which is compatible with oil, is called an amphiphilic compound. These also take on various aggregate states in a solvent due to the aforementioned intermolecular interactions. Examples include micelles, reverse micelles, lamellae, vesicles, and liposomes. Active research is being conducted to synthesize new amphiphilic compounds and apply their self-assembly capabilities to change their spatial arrangement and stereostructure, thereby enabling artificially controlled molecular recognition, chemical conversion, transport, and information conversion.