The role of gold nanoclusters on N-isopropylacrylamide (NIPAM) for drug delivery: A density functional theory study

• Main Author: Bacuyag, Dhonny P.
• Format: text
• Language: English
• Published: Animo Repository 2013
• Subjects: Drug delivery systems; Physics
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/7178
• Institution: De La Salle University

The nature of binding of gold nanoclusters (AuNC) with N-isopropylacrylamide (NIPAM) was investigated using the first principles calculations and by implementing the density functional theory (DFT). Geometrical structures of the NIPAM and the NIPAM-AuNC complexes were fully optimized using the Gaussian 09 programs with the B3LYP level of calculation and the LANL2DZ basis set. Significant structural changes on NIPAM, in terms of the bond lengths, are observed upon complexation with AuNC. This is due to the redistribution of charges upon complexation as shown by the detailed population analysis on the Mulliken charges. Generally, transfer of charges from the NIPAM unit to the AuNC was observed. Losing negative electronic charges led to the shortening of bonds while gaining thereof brought about the lengthening of these bonds. The vibrational analysis proved these structural changes as a consequence when AuNC is attached to NIPAM. Red shifting of frequency resulted from the increase in bond distance. Moreover, significant changes in the bond angles and dihedral angles upon complexation were observed. These changes directly affect the phase transition behavior of NIPAM as well as its lower critical solution temperature (LCST). NIPAM is known to swell below the LCST while it collapses above this LCST. This behavior is dependent on the electronic and geometrical structure of NIPAM. The endothermic solvation of the structure of NIPAM-AuNC showed higher binding energies, giving a higher LCST for the NIPAM. This higher LCST for NIPAM upon gold complexation is important for its purpose as a drug vehicle. This groundwork study provides significant findings that can be used as design guidelines for the implementation of NIPAM-AuNC for drug delivery.