Amazing water and its chemistry
Water has a fundamental role in life processes. Let us begin analysing its properties and roles.
The water molecule in its three-dimensional form is an irregular tetrahedron with oxygen at its core. The electrical charge is not uniformly distributed and thus it form dipoles. Hydrogen nuclei form a region of local positive charge while the free electrons form a negative charge as depicted by the lone pairs below. Other examples of dipoles are ammonia, and other groups of biochemicals like alcohols, phospholipids, amino acids, and nucleic acids.
Tetrahedral Structure of Water
Water dipoles allow its ability to self-associate through hydrogen bonds with an association-dissociation half-life of about 1 microsecond.
About the Bonds Family
The hydrogen bond is a weaker bond compared to its big brother covalent bond. To break hydrogen bonds it requires 5% of 110 kcal/mol of which it takes to break the covalent bonds of O-H. Biological molecules are stabilised by several intramolecular bonds which can range from as little as 0.1 to 10 kcal/mol. These include
- Electrostatic Interactions – charge-charge interactions sometimes known as salt bridges in proteins and its affected inversely proportionate to the dielectric constant of surrounding medium.
- Hydrophobic Interactions – self-associations of nonpolar compounds in aqueous environment.
- Van der Waals Forces – individually weak but contribute much to structure and stability of macromolecules.
Other factors which can affect the structure of macromolecules is the behaviour of the molecule to water itself. Apolars like hydrocarbons, e.g. coconut oil affect the structure of water. Naturally, minimization of the apolar surface area(SA) takes place and this is an entropically driven process. To illustrate further, consider
More apolars SA -> lesser oriented water molecule = higher entropy;
Minimization of apolars SA -> better freedom for water molecule orientation =lesser entropy.
Thus, it can be observed that hydrocarbons in water form a rigid clathrate (cage-like) structure. In living cells this is observed as apolar molecules hiding within the macromolecular structure itself, ideally to minimize contact with water.
Take Home Message
- Water is the fountain of activity for life.
- Dipole property of water gives its own temporal structure and moulds shape of other molecules in it.
- The chemical bonds and other molecular forces contribute to the structure of the molecule.
- There is always a balance for push and pull and water sets the canvas for the game in living cells.
