Iron-Induced Cyclodextrin Self-Assembly into Size-Controllable Nanospheres

摘要

Iron-induced self-assembly of β-cyclodextrin, β-CD, into size controllable nanospheres with a well-defined spherical morphology and a relatively narrow size distribution was formed when acetone was added to a solution of β-CD with iron(II) acetate, Fe(OAc)_2, in DMF. Thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy, and high resolution transmission electron microscopy showed that the irons were present as a welldispersed state in the β-CD nanospheres. In the 1~H NMRspectrum of the β-CD/Fe(OAc)_2, β/Fe, solution before adding acetone, the peaks corresponding to β-CD were broadened and their spin-spin splitting had disappeared. In particular, the β/Fe solutions were found to remain in a clean solution state at 1 week after solution preparation. These findings indicate the isolation of individual iron ions caused by the surrounding of each ion with the β-CD molecules in the solution before the addition of acetone. X-ray crystal structure analysis, morphological observations, and N_2 adsorption and desorption experiments showed that the β-CD nanospheres were generated by the formation of iron-embedded β-CD primary particles with disordered cage type structure and simultaneous spherical assembly of the primary particles during the addition of acetone to the β/Fe solution with appropriate mole ratio between β-CD and Fe(OAc)_2. Interestingly, the size of the β-CD nanospheres could be simply controlled by changing the speed at which acetone was added to the solution, with higher acetone addition speeds yielding smaller particles.