Modelling hydrophobic interactions

 Dear colleagues;
      I am interested in examining the interactions between biological mem-
 branes and hydrophobic weak acids in order to better understand why some of
 these acids are toxic towards cells and others are not.  The molecular
 modelling software I have at my immediate disposal are Hyperchem 3.0 and
 MOPAC 6.0.  Can anyone suggest how these programmes might be used to examine
 prospective interactions between biomembranes and small molecular weight com-
 pounds?  Would anyone care to recommend _other_ programmes which can be used
 to accomplish this?
      Thanks in advance to all respondents.
                                             S. Shapiro
                                             Internet: toukie (+ at +)
 P.-S.: Of course, references and citations are also useful.