What is the correct order of permeability through the lipid bilayer?
Permeability across pure phospholipid bilayer without proteins follows solubility-diffusion model where permeability coefficient P equals oil-water partition K times diffusion within hydrocarbon D divided by thickness delta. Consequently small hydrophobic molecules lacking hydrogen bonds partition efficiently into acyl core exhibiting highest permeability. Gases O2 and CO2 permeability around ten to fifty cm per second diffusing almost freely enabling instantaneous alveolar capillary equilibration and mitochondrial respiration. Water despite small size eighteen Daltons polar forming bonds permeability three orders lower around 0.001 cm/s still appreciable and augmented hundredfold by aquaporins for kidney reabsorption. Glucose larger one eighty Daltons five hydroxyls poorly partitions permeability about 10^-6 cm/s six orders less than water needing GLUT carriers for physiological uptake. Small monovalent ions Na+ K+ Cl- face enormous Born self-energy around three hundred kilojoules plus electrostatic cost in low dielectric about two permeability below 10^-12 negligible without selective channels. Large polyanions ATP four negative charges and RNA polyphosphate backbone essentially impermeant below 10^-14 relying entirely on specific transporters. This hierarchy explains dependence on selective transport proteins for polar metabolites while gases exchange without assistance.
Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Relative Permeability – O2, CO2, H2O, Glucose, Ions, RNA.