An Understanding of the
Modulation of Photophysical
Properties of Curcumin inside a Micelle Formed by an Ionic Liquid:
A New Possibility of Tunable Drug Delivery System
- Publication date
- Publisher
Abstract
The present study reveals the modulation of photophysical
properties
of curcumin, an important drug for numerous reasons, inside a micellar
environment formed by a surfactant-like ionic liquid (IL-micelle)
in aqueous solution. Higher stability of the drug inside IL-micelle
in the absence and presence of a simple salt (sodium chloride) as
well as considerably large partition coefficient (<i>K</i><sub>p</sub> = 8.59 × 10<sup>3</sup>) to the micellar phase
from water make this system a well behaved drug loading vehicle. Remarkable
change in fluorescence intensity with a strong blue-shift implies
the gradual perturbation of intramolecular hydrogen bond (H-bond)
present within the keto–enol group of curcumin along with considerable
formation of intermolecular H-bond between curcumin and the headgroup
of surfactant-like IL. Very fast nonradiative decay channels in curcumin
mainly caused by the excited state intramolecular proton transfer
(ESIPT) are thus depleted remarkably in the presence of IL-micelle
of reduced polarity and as a result of restricted rotational and vibrational
degrees of freedom when bound to the micelle. Moreover, time-resolved
results confirm that not only the keto–enol group of curcumin
is playing here but also the phenolic hydroxyl groups are also responsible
for such modulation in photophysical properties. From a thermodynamic
point of view, our system shows good correlation with its stability
parameters (higher binding constant with very less hydrolytic degradation
rate ∼1%) and higher negative value of binding enthalpy of
interaction (−Δ<i>H</i>) than total free energy
change (−Δ<i>G</i>) implies that the nature
of binding interaction is enthalpy driven not entropy alone. Summarizing
all the above observations, we have concluded that the modulation
of the intramolecular proton transfer is due to the presence of both
intermolecular proton transfer as well as strong hydrophobic interaction
between curcumin and the IL-micelle
