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The interfacial behavior of the hypoglycemia lectin BmoLL purified from the leaves of Bauhinia monandra , and its ability to interact with lipid monolayers has been studied by surface tension ( γ ) measurements. The results of these experiments revealed that in the solution concentration range comprised between 0.2 and 1.0 mg/ml, there was an extremely pronounced increase in the BmoLL adsorption at the interface with the air phase. This adsorption at the higher studied BmoLL concentrations gave rise to a more gradual increase in the surface pressure ( π = γ 0 − γ ). The results showed also that the surface pressure of adsorbed films was pH dependent and it substantially increased at low pHs (between pH 4.0 and pH 2.5). Independently carried out ξ potential measurements demonstrated that BmoLL was negatively charged at all pHs and borne the highest charge at the pH around 5.5. The penetrant ability of BmoLL into the two different in chemical nature monolayers: (dioleoylphosphatidylcholine and octadecylamine) have been assessed measuring Δ π increments at constant area. It was observed that, whereas the monolayers of either pure dioleoylphosphatidylcholine (DOPC) or pure octadecylamine (ODA) stimulated BmoLL adsorption, the lectin adsorption within their mixtures strongly depended on both the content of positively charged octadecylamine in a mixture and on the monolayer compressibility. These findings are discussed in terms of both the electrostatic interaction involved in adsorption of BmoLL and of changes in monolayer compressibilities brought up by the addition of ODA molecules to the phospholipid. The relevance of this work to liposome preparations is indicated in the concluding remarks.

The extent of surfactant penetration into monolayers is often evaluated by thermodynamic approaches. The most formal treatment of the penetration phenomenon is due to Motomura et al. [K. Motomura, Y. Hayami, M. Aratono and R. Matuura, J. Colloid Interface Sci., 87 (1982) 333–338]. However, this model seems to be inadequate to determine adsorption into films in the condensed state. It is also in contradiction with Hall's [O.G. Hall, Langmuir, 2 (1986) 809] work which demonstrated that it is impossible to calculate penetration quantities without extra thermodynamic assumptions. We present here a modified equation for determination of thermodynamic quantities of penetration and calculate the adsorption of poly(oxyethylene)-poly(oxypropylene) block copolymers into soya phospholipid films using our previously obtained experimental data. The proposed modified Motomura equation may yield penetration quantities more reasonable than those obtained with the use of the Alexander-Barnes or classical Motomura equations. It also indicates why the known penetration models give such different adsorption values. Moreover, these contributions allow one to clarify the relationship between different approaches aimed at quantifying surfactant penetration into insoluble films.