The dynamics of solvent relaxation in ionic liquid (IL)-water, IL-methanol, and IL-acetonitrile mixtures have been investigated using steady state and picosecond time-resolved fluorescence spectroscopy. We have used Coumarin 153 (C-153) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF(6)]) as fluorescence probe and IL, respectively. The steady-state emission spectra showed that the gradual addition of cosolvents increases the polarity of the mixtures. In neat [hmim][PF(6)] and all IL-cosolvent mixtures, solvation occurs in two well-separated time regimes within the time resolution of our instrument. A substantial portion of the solvation has been missed due to the limited time resolution of our instrument. The gradual addition of cosolvents decreases the viscosity of the medium and consequently solvation time also decreases. The decrease in solvation time is more pronounced on addition of acetonitrile compared to water and methanol. The rotational relaxation time of the probe is also decreasing with gradual addition of the cosolvents. The decrease in viscosity of the solution is responsible for the decrease in the rotational relaxation time of the probe molecule.
The conventional drug delivery systems made from organic- or inorganic-based materials suffer from some problems associated with uncontrolled drug release, biocompatibility, cytotoxicity, and so forth. To overcome these problems, zeolitic imidazole framework (ZIF) hybrid materials can be one of the solutions. Here, we report a very easy and successful encapsulation of an anticancer drug doxorubicin inside two ZIFs, namely, ZIF-7 and ZIF-8, which are little explored as drug delivery systems, and we studied the controlled release of the drug from these two ZIFs under external stimuli such as change in pH and upon contact with biomimetic systems. Experimental results demonstrate that ZIF-7 remains intact when the pH changes from physiological condition to acidic condition, whereas ZIF-8 successfully releases drug under acidic condition. Interestingly, both the ZIFs are excellent for drug release when they come in contact with micelles or liposomes. In the case of ZIF-8, the drug delivery can be controlled for 3 h, whereas its analogue ZIF-7 delivers the drug for a time span of 10 h. We explained the reluctance of ZIF-7 toward drug release in terms of rigidity. This study highlights that by using different ZIFs and liposomes, the drug release rate can be easily modulated, which implies ample possibility for ZIFs as a good drug delivery system. The study shows a novel strategy for easy drug encapsulation and its release in a controlled manner, which will help future development of the drug delivery system.
The interaction of ionic liquid with water in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/Triton X-100 (TX-100)/H2O ternary microemulsions, i.e., "[bmim][PF6]-in-water" microregions of the microemulsions, has been studied by the dynamics of solvent and rotational relaxation of coumarin 153 (C-153) and coumarin 151 (C-151). The variation of the time constants of solvent relaxation of C-153 is very small with an increase in the [bmim][PF6]/TX-100 ratio (R). The rotational relaxation time of C-153 also remains unchanged in all micremulsions of different R values. The invariance of solvation and rotational relaxation times of C-153 indicates that the position of C-153 remains unaltered with an increase in R and probably the probe is located at the interfacial region of [bmim][PF6] and TX-100 in the microemulsions. On the other hand, in the case of C-151, with an increase in R the fast component of the solvation time gradually increases and the slow component gradually decreases, although the change in solvation time is small in comparison to that of microemulsions containing common polar solvents such as water, methanol, acetonitrile, etc. The rotational relaxation time of C-151 increases with an increase in R. This indicates that with an increase in the [bmim][PF6] content the number of C-151 molecules in the core of the microemulsions gradually increases. In general, the solvent relaxation time is retarded in this room temperature ionic liquid/water-containing microemulsion compared to that of a neat solvent, although retardation is very small compared to that of the solvent relaxation time of the conventional solvent in the core of the microemulsions.
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