A comparative study on the effect of Curcumin and Chlorin-p6 on the diffusion of two organic cations across a negatively charged lipid bilayer probed by second harmonic spectroscopy

• Effect of pH on drug induced membrane permeability investigated by SH spectroscopy.
• Real time diffusion kinetics of two SH probes (LDS and MG) were monitored.
• Curcumin showed substantial pH effect; Chlorin-p6 showed modest pH effect.
• This was attributed to pH dependent interaction between the drug and the polar head group of the lipid.

The influence of Curcumin and Chlorin-p6 (Cp6) on the real time diffusion kinetics of two organic cations, LDS (LDS-698) and Malachite Green (MG) across a negatively charged phospholipid bilayer is investigated by Second Harmonic (SH) spectroscopy. The diffusion time constant of LDS at neutral pH in liposomes containing either Curcumin or Cp6 is significantly reduced, the effect being more pronounced with Curcumin. At acidic pH, the quantum of reduction in the diffusion time constant of MG by both the drugs was observed to be similar. The relative changes in the average diffusion time constants of the cations with increasing drug concentration at pH 5.0 and 7.4 shows a substantial pH effect for Curcumin induced membrane permeability, while a modest pH effect was observed for Cp6 induced membrane permeability. Based on available evidence this can be attributed to the increased interaction between the drug and the polar head groups of the lipid at pH 7.4 where the drug resides closer to the lipid–water interface.

Effect of pH on drug (Curcumin and Chlorin-p6) induced membrane permeability probed by second harmonic spectroscopy: relative changes in the diffusion time constants of two organic cations (LDS & MG) with increasing drug concentration at pH 5.0 (hollow) and at pH 7.4 (solid).Figure optionsDownload as PowerPoint slide