hydroxyl groups, both ferrocenes may show a tendency to bind reversibly through hydrogen

bonding to the nanocapsule silica shell, and not only to partition in the oil phase, but also to

reside partly in the silica shell. It has been previously shown that the diffusion coefficients of

these two molecules in hydrated Sol-Gel-derived glasses were only slightly decreased from the

ones in solution with values in the range of 10-6 Cm2/S.251 Therefore, in the presence of diffusion-

driven encapsulation, even with the presence of specific interactions with the silica shell, fast

uptake kinetics would be expected to be seen, because the average time for a molecule to diffuse

through a few tens of nanometers (using the simple relationship252 d = (2Dt)' 2, with t = time of

the experiment, D = diffusion coefficient of the probe, and d = average distance travelled by the

probe during t) is on the order of 10-6 S.

 Absorption and fluorescence spectroscopic studies were also undertaken in order to

supplement and confirm the electrochemical study. The two molecules chosen in this case were

iodine and Nile Red (Figure 6-5). Because of their structures, they should have very low affinity

for the silica shell and are therefore expected to partition strictly between the oil core and the

aqueous solution. Because UV-vis and fluorescence measurements show a chemical-

environment-dependent signal maximum, the shift observed after nanocapsule solution addition

to the iodine or Nile Red solution indicates the environment where the probes end up after

encapsulation.



 CCH,0H N O 0



 ferrocene ferrocene Nile
 methanol dimethanol Red

Figure 6-5. Chemical structures of ferrocene methanol, ferrocene dimethanol, and Nile Red.