Phys-chemical parameters (logP and PSA)

Understanding the Significance of LogP and PSA in Physicochemical Parameters

Physicochemical parameters play a crucial role in drug discovery and development. Among these, LogP (partition coefficient) and PSA (polar surface area) are two essential parameters that provide valuable insights into the behavior and characteristics of molecules. In this blog, we will delve deeper into these parameters and understand their significance in drug design.

LogP – The Partition Coefficient

LogP measures the partitioning behavior of a molecule between two immiscible phases, typically octanol and water. It quantifies the lipophilicity or hydrophobicity of a compound, indicating the compound’s ability to permeate biological membranes. LogP values are determined experimentally or predicted using computational models.

A higher LogP value indicates a more lipophilic compound, suggesting that it is more likely to cross biological barriers such as cell membranes. Conversely, a lower LogP value indicates higher water solubility and indicates a less permeable compound.

LogP values are crucial in drug design as they impact various aspects of a molecule’s pharmacokinetics. For example, a high LogP value might lead to poor absorption or excessive accumulation in adipose tissues. Therefore, optimizing the LogP value helps in achieving the right balance between bioavailability and permeability.

PSA – The Polar Surface Area

The Polar Surface Area (PSA) is a measure of the molecular surface area that is occupied by polar atoms or groups. It gives an indication of the compound’s ability to form hydrogen bonds, which is vital for interactions with proteins, enzymes, and receptors in the body. PSA is typically measured in square angstroms (Ų) or alternatively in a count of acceptor and donor atoms.

A higher PSA value implies a larger interaction surface area and stronger potential for hydrogen bonding. This makes it more likely for the molecule to establish favorable interactions with the target protein, leading to higher binding affinity and potentially enhanced drug efficacy.

On the other hand, a lower PSA value suggests a smaller interaction surface area and lesser propensity for hydrogen bonding. In drug design, a lower PSA is desired for drug-like molecules as it reduces the risk of non-specific interactions, improves oral bioavailability, and helps in minimizing off-target effects.

The Interplay between LogP and PSA

The interplay between LogP and PSA is crucial in achieving optimal drug-like properties. Balancing the lipophilic and hydrophilic characteristics of a molecule is critical to ensure proper absorption, distribution, metabolism, and excretion (ADME) profiles.

In general, drug-like molecules should have an appropriate LogP value to enable efficient cellular entry, while also having an appropriate PSA to engage in specific protein interactions. By tuning these properties, medicinal chemists can modulate a molecule’s pharmacokinetics and enhance its chances of success in drug development.


Understanding the physicochemical properties of molecules is essential for rational drug discovery and development. LogP and PSA are two key parameters that provide valuable insights into a compound’s lipophilicity and polar surface area.

Optimizing the LogP value enables molecules to have the correct balance between permeability and bioavailability, while controlling the PSA helps in enhancing target interactions and reducing off-target effects. The interplay between LogP and PSA is crucial in achieving successful drug design and development, contributing to the advancement of pharmaceutical research and the improvement of patient care.