To account for the conformational space of the PPCPs, conformational sampling was performed using the 4.9 version of the BOSS program package and the implemented OPLS-AA forcefield . Afterwards the molecular axes of the generated conformers were determined by principal component analysis of the cartesian coordinates. From geometrical considerations, a conformer can only be adsorbed in a pore if two of the three molecular axes are smaller than the diameter of the pore. Therefore, the two smallest molecular axes of each generated conformer were compared to the largest diffusing sphere diameters listed in the IZA database . Only the conformers that could geometrically fit into the pores and that were also relatively low energy conformers were subjected to insertion into the zeolite frameworks.