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

Iron-induced self-assembly of beta-cyclodextrin, beta-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 beta-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 well-dispersed state in the beta-CD nanospheres. In the (1)H NMR spectrum of the beta-CD/Fe(OAc)(2), beta/Fe, solution before adding acetone, the peaks corresponding to beta-CD were broadened and their spin-spin splitting had disappeared. In particular, the beta/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 beta-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 beta-CD nanospheres were generated by the formation of iron-embedded beta-CD primary particles with disordered cage type structure and simultaneous spherical assembly of the primary particles during the addition of acetone to the beta/Fe solution with appropriate mole ratio between beta-CD and Fe(OAc)(2). Interestingly, the size of the beta-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.