Effects of Self-Assembled Monolayers on Selective Crystallization of Tolbutamide

Selective crystallization of tolbutamide on SAMs with the similar molecule structure of tolbutamide and the functional groups of methyl, trifluoromethyl, and phenyl respectively was studied through characterizations of XRD and crystal morphologies. It is indicated that at low supersaturation tolbutamide (TB) crystallized into form II on the methyl-terminated SAMs and trifluoromethyl-terminated SAMs, whereas the highest bioavailable TB crystals of form IV were obtained on phenyl-terminated SAMs, differing from the precipitated crystals from the solution including TB forms I, II, and III together. The preferential growth orders of the crystallographically important faces of TB forms I–IV were assessed on different functionalized SAMs through molecular modeling based on the prediction of equilibrium morphologies of crystals, which is in accordance with the experimental results. Further time-resolved Raman spectra of TB crystals grown on phenyl-terminated SAMs illustrate that the surface functional groups are paramount to adjust the heterogeneous nucleation of tolbutamide polymorphs at low supersaturation. This work provides a feasible approach combining the experimental with molecular modeling methods to understand deeply the relationship between interfacial functional groups of SAMs and molecular packing of crystals, which is fundamental to the rational design of experimental work on selective crystallization of organic crystals.