Minimum cross-sectional diameter: calculating when molecules may not fit through a biological membrane

Area of Science:

• Computational chemistry
• Environmental toxicology
• Molecular modeling

Background:

• Predicted aquatic toxicity of compounds does not always align with observed results.
• Molecular size is a key factor, as large molecules may not permeate biological membranes.
• The minimum effective cross-sectional diameter is a critical parameter for membrane transport.

Purpose of the Study:

• To develop a novel, accessible method for determining the minimum effective cross-sectional diameter of molecules.
• To provide a tool for better prediction of aquatic toxicity by accounting for molecular size limitations.

Main Methods:

• A new method based on vector analysis is presented.
• The method requires only atomic Cartesian coordinates and van der Waals radii as input.
• Calculations are performed on a desktop computer, providing results in minutes.

Main Results:

• The method successfully calculates the minimum effective cross-sectional diameter for molecules.
• The approach is efficient, even for large molecules.
• Gas-phase, energy-minimized structures are used as approximations due to lack of experimental solution data.

Conclusions:

• This computational method offers a practical solution for determining molecular size relevant to membrane transport.
• The findings can improve the accuracy of aquatic toxicity predictions.
• The technique facilitates a deeper understanding of passive transport limitations in toxicology.