pH Effect on the binding of chlorin derivatives with Cremophor EL, a potential drug delivery vehicle

The binding of chlorin p6 with Cremophor EL (CrEL) at pH 5 and pH 7 has been monitored by fluorescence techniques. Upon binding with the drug delivery agent, the fluorescent species are found to be one and the same at both pH values. This is explained by a hindrance to protonation of chlorin p6 trianions by Cremophor EL. Surprisingly, it is the more hydrophilic species between the two possible chlorin p6 ions that is found to get bound preferentially with the hydrophobic delivery medium.