Hydrophobic molecules are those who have a tendency to repel water or any polar molecule. Let us discuss more about the hydrophobic molecules.
The examples of hydrophobic molecules are listed below-
Alkane molecules are made of generally carbon and hydrogen molecules. They are nonpolar and cannot be dissolved in water. As water is a polar molecule, thus it does not let alkanes to interact with it. Therefore, alkane shows hydrophobicity. For example, butane, pentane, ethane.
Oils are hydrophobic because it is repelled by water molecule and cannot mix with water due to its nonpolar nature. For this reason, when oil is added into water, the oil floats above the water and form two distinguishable layer of oil and water. Thus, oil cannot be dissolved in water and show hydrophobic nature.
Fatty acid molecules contain long chain, made of carbon and hydrogen covalently bonded with each other. They are also nonpolar molecule and have a tendency to repel water molecule because water is a polar molecule and nonpolar substance will not be dissolved in water (polar solvent).
Therefore, fatty acid is an example of hydrophobic molecule.
Grease is one type of thick and oily lubricant that is formed by inedible lard, fat of waste animal parts or from any synthetic oil. It is also a hydrophobic molecule like oil. Nonpolar character of grease makes does not let it soluble in water and thus it becomes hydrophobic in nature.
Wax is mainly made of the esters of long-chain fatty alcohols, acids and long chain alkanes. Thus, it is one of the most hydrophobic substances in nature. For their strong hydrophobic nature, they function as water repellent on the leaves of many plants, on bird feathers or the cuticles of different insects.
Steroids are biologically active manmade organic compounds (hormones) in which four rings are arranged in a specific molecular arrangement. Due to these four fused carbon rings, they are nonpolar in nature and nonpolar solvent cannot be soluble in polar water solvent. Therefore, steroids are also hydrophobic molecules for their tetracyclic hydrocarbon core.
Some specific vitamins (vitamin A, D, E, K) are hydrophobic in nature. They are lipophilic and not soluble in water. These vitamins are hydrocarbon with one OH group at the end of the structure. This OH group cannot interact with water molecule.
Thus, it is not water soluble. But it can interact with lipid molecules. These four vitamins are nonpolar.
Cholesterol is a sterol type organic molecule, biosynthesized by all animals and an important structural component of animal cell membranes. It contains a polar head, a fused ring structure and a long hydrocarbon chain.
The polar part of cholesterol is hydrophobic as it attracts water but the hydrocarbon part is hydrophilic because it is nonpolar part. Thus, it can be regarded as amphipathic in nature.
Lipid molecules contains two parts, hydrophilic head and hydrophobic tail part. The tail part is made of two fatty acids which are repelled by water molecules. Therefore, water molecules cannot enter into the interior part of lipid molecules and this hydrophobic end does not dissolve in water.
Phospholipid is one type of lipid molecule which has two hydrocarbon tails and one of the most hydrophobic molecules.
Some Amino Acids
There are some amino acids (phenylalanine, leucine, isoleucine, tyrosine, tryptophan, methionine, valine, proline) which are hydrophobic in nature. Phenylalanine is most hydrophobic among all the amino acids.
The hydrophobicity arises because the side chain of these amino acids does not react with water or aqueous environment. These amino acids are also nonpolar.
Some Plant Leaves
Plant leaves are hydrophobic in most of the cases because their outer surface is covered with waxy cuticle (made of many layers of different biological substances). Due to presence of this cuticle, plant leaves are hydrophobic in nature.
There are some ultra-hydrophobic leaves with a special surface having extremely small bumps, known as papillae. For example, lotus leaf.
Hydrophobic interactions (repulsion from water or any polar molecule) have some important sides like folding of proteins, stabilize protein molecules and keeping it biologically active and many more. It is observed that all of the hydrophobic molecules are not soluble in water because of their nonpolar nature.