Selectivity enhancement of diastereomer separation in RPLC using crystalline-organic phase-bonded silica

Summary Poly(octadecyl acrylate) exists in a crystalline state at room temperature. This crystalline state was formed even after being grafted onto silica through the terminal group of the polymer. When this polymer-grafted silica (Sil-ODA_n) was used as a reversed phase liquid chromatography packing material, better selectivity for diastereomerized phenylethylamines derivatized by (S)-(−)-(2,3-naphthalenedicarboximidyl)propionyl fluoride was observed at room temperature than was observed for simple octadecylated silica (ODS). On the other hand, increasing temperature reduced the selectivity to be close to that of ODS. Additional experiments showed the better selectivity derived from Sil-ODA_n was due to both the highly-oriented structure of the polymer and the carbonyl-π interaction with the diastereomer. A theoretical investigation of this carbonyl-π interaction is also described briefly.