Study of Intermolecular Interaction of Hydroxypropyl-β-cyclodextrin Complexes through Phase Diagrams of the Fusion Entropy: Contrast between Nifedipine and Nicardipine Hydrochloride

In amorphous state, we examined the intermolecular interactions between the guest drugs nifedipine (NIF) and nicardipine hydrochloride (NIC), which are 1,4-dihydropyridine calcium channel blockers, and a host hydroxypropyl-β-cyclodextrin (HP- β-CD). Differential scanning calorimetry and powder X-ray diffraction showed that the interaction of NIC with HP-β-CD was remarkable stronger than that of NIF for both preparation methods. The structure of amorphous state complex of NIF/HP-β- CD presented as inclusion complex, and HP-β-CD in NIC/HP-β-CD complex was more like a surfactant which around NIC with its out-surface in any ratio. Fourier transform-infrared spectroscopy showed that the NIC/HP-β-CD complex contained multiple contact groups, whereas the NIF/HP-β-CD complex contained a single site bound to the HP-β-CD. Further, molecular dynamics simulation exhibited a much more vehemently reaction trend in NIC/HP-β-CD complex than that in NIF/HP-β-CD using compare the reaction constant. From the simulation images of NIF and NIC binding to HP-β-CD, we insure the different including situation in amorphous state of NIF/HP-β-CD and NIC/HP-β-CD. Consequently, we speculated that NIC binding to HP-β-CD with a different mechanism with NIF/ HP-β-CD complex. And this unique binding method may lead NIC has a higher potential energy changing in forming amorphous complexes.