A compound of flavonol-based biosurfactant, as C-8-substituted alkylaminomethyl rutin (DAMR) for a potential pharmaceutical or agrochemical use, was prepared experimentally. The surface behavior of DAMR and its mixture with lecithin from soybean (SL) had been studied. DAMR, regarded as a pseudo-amphoteric character, exhibits both liquid-condensed (LC) and liquid-expanded (LE) phases while SL is in the form of the LE phase only. The phase parameters of DAMR (including A(limt) pi(coll)) are observed to strongly depend on both the subphase temperature and the pH, which regulate the degree of ionization. In addition, the observed positive deviation calculated from excess Gibbs free energies of the DAMR-SL system suggests a repulsive interaction between DAMR and SL at all X-DAMR values. Also the interaction parameter is found to increase linearly with surface pressure, regardless of composition. Notably, the relationship of logarithmic activity coefficient vs. X-DAMR(2) reveals that the molecular interaction of DAMR-SL can be adequately simulated using a simple regular mixture model. Importantly, lower C-s(-1) values of this mixture than those with pure DAMR and SL denote weak elasticity of mixed monolayers with values of X-DAMR of 0.2-0.8, indicating that the direct addition of DAMR may exert a somewhat adverse influence on SL membranes. (C) 2010 Elsevier Inc. All rights reserved.