Interpretation of the differences in the surface energetics of two opticalforms of mannitol by inverse gas chromatography and molecular modelling

Inverse gas chromatography (IGC) has been successfully used to characterise the nature of the surface of two optical forms of mannitol, DL and PD. Thi s has shown that the surface energetics of the two forms are significantly different with the DL form having higher values for the interactions with t he dispersive and basic probes. Molecular modelling was used to predict the slip planes by utilising attachment energy calculations and so the dominan t faces exposed upon milling could be predicted. Imaging these faces showed that the orientation of the molecules at these surfaces differed between t he two forms. A visual comparison of the faces indicated that the DL form h ad a higher density of acidic and dispersive sites exposed at the surfaces than the PD form. The results from the modelling agreed with the trends see n in the changes in surface energetics as measured by IGC. This suggests th at the components of the surface energetic terms reflect the density of exp osed groups at the particle surfaces. (C) 1999 Elsevier Science B.V. All ri ghts reserved.