Calorimetric Study of the Interaction of Local Anesthetics [2-(Alkyloxy)phenyl]-2-(1-piperidinyl)ethyl Carbamates with Model Dipalmitoylphosphatidylcholine Membranes
Local anesthetics of the homologous series of monohydrochlorides of [2-(alkoxy)phenyl]-2-(1-piperidinyl)ethyl esters of carbamic acid decrease the temperature of phase transitions L β' → P β (pretransition) and P β → L α (main transition) of 1,2-dipalmitoyl- sn -phosphatidylcholine in aqueous phase at pH 6.2. The efficiency of the anesthetics in decreasing the pretransition temperature increases with the number of carbon atoms n of the alkoxy substituent up to n = 6. For n > 6 no pretransition could be detected. The efficiency in decreasing the temperature of the main transition increases up to n = 8 - 9 while it starts decreasing at n = 10. Computer simulation of the thermograms has shown that the decrease of efficiency at n = 10 is caused by the dependence of the partition coefficients of the anesthetics K P,G and K P,LC between the aqueous phase and the P β and L α phases, respectively, on the length of the alkoxy substituent, thus: log K P,LC = A LC + B LC n and log K P,G = A G + B G n , where B LC B G .