version date: 1 December 2006 erythrocytes and molecular models of its membrane. The latter consist of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes respectively located in the outer and inner monolayers of erythrocytes and other cell membranes. Erythrocytes were chosen because although less specialized than many other cell membranes, they carry on enough functions in common with them such as active and passive transport, and the production of ionic and electric gradients, to be considered representative of the plasma membrane in general. The capacity of TDs to interact with the erythrocyte membrane can be determined by scanning electron microscopy(SEM), whereas the interaction with the bilayer structures of DMPC and DMPE can be defined by X-ray diffracti These techniques have been used in our laboratories to determine the interaction with and the membrane-perturbing effects of local anesthetics [4-5], antiarrhythmic [6], and anticancer drugs [7-8] MATERIAL AND METHODS X-ray diffraction analysis of phospholipid bilayers The capacity of TDs to perturb the structures of dmPC and dmpe bilayers is to be determined by X-ray diffraction. For this purpose, about 1 mg of each phospholipid (Sigma or Polar Avanti, USA) is introduced into 2-mm-diameter special glass capillaries(Glas-Technik Konstruktion, Berlin, Germany), which are then filled with about 200 HL of(a) distilled water and(b)aqueous solutions of the td in a range of concentrations. The experiments must be performed at 17+ 2C, which is below the main phase transition temperature of both DMPC and DMPE SEM studies on human erythrocytes Blood samples can be taken from clinically healthy adult donors by puncture of the ear lobe disinfected with ethanol and aspiration into a tuberculin syringe without a needle containing 50 units/mL heparin in saline solution (0.9% NaCl). Centrifuge the red blood cells for 10 min at 1000 rpm, wash twice in saline solution, resuspend in salin solutions containing the TD in adequate concentrations, and incubate for 1 h at 37C Control are cells resuspended in saline solution without TD. Fix the specimens overnight at 5C by adding one drop of each sample to plastic tubes containing l mL of 5% glutaraldehyde, wash twice in distilled water, place them on siliconized Al stubs <www.iupac.org/publications/cd/medicinalchemistry/>2 erythrocytes and molecular models of its membrane. The latter consist of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes respectively located in the outer and inner monolayers of erythrocytes and other cell membranes. Erythrocytes were chosen because although less specialized than many other cell membranes, they carry on enough functions in common with them such as active and passive transport, and the production of ionic and electric gradients, to be considered representative of the plasma membrane in general. The capacity of TDs to interact with the erythrocyte membrane can be determined by scanning electron microscopy (SEM), whereas the interaction with the bilayer structures of DMPC and DMPE can be defined by X-ray diffraction. These techniques have been used in our laboratories to determine the interaction with and the membrane-perturbing effects of local anesthetics [4–5], antiarrhythmic [6], and anticancer drugs [7–8]. MATERIAL AND METHODS X-ray diffraction analysis of phospholipid bilayers The capacity of TDs to perturb the structures of DMPC and DMPE bilayers is to be determined by X-ray diffraction. For this purpose, about 1 mg of each phospholipid (Sigma or Polar Avanti, USA) is introduced into 2-mm-diameter special glass capillaries (Glas-Technik & Konstruktion, Berlin, Germany), which are then filled with about 200 µL of (a) distilled water and (b) aqueous solutions of the TD in a range of concentrations. The experiments must be performed at 17 ± 2°C, which is below the main phase transition temperature of both DMPC and DMPE. SEM studies on human erythrocytes Blood samples can be taken from clinically healthy adult donors by puncture of the ear lobe disinfected with ethanol and aspiration into a tuberculin syringe without a needle containing 50 units/mL heparin in saline solution (0.9 % NaCl). Centrifuge the red blood cells for 10 min at 1000 rpm, wash twice in saline solution, resuspend in saline solutions containing the TD in adequate concentrations, and incubate for 1 h at 37 ºC. Control are cells resuspended in saline solution without TD. Fix the specimens overnight at 5 ºC by adding one drop of each sample to plastic tubes containing 1 mL of 2.5 % glutaraldehyde, wash twice in distilled water, place them on siliconized Al stubs <www.iupac.org/publications/cd/medicinal_chemistry/> version date: 1 December 2006