br The FT IR spectra of L Dopa
The FT-IR spectra of L-Dopa, Fe3O4, Fe3O4@CaAl-LDH and Fe3O4@CaAl-LDH@L-Dopa are depicted in Fig. 6. In Fig. 6a, the ab-sorption peaks at 1601, 1474, and 862 cm−1 are related to the amine group and 1594, 1419 cm−1 associated with carboxylate, confirm the presence of L-Dopa on the surface of the Fe3O4@CaAl-LDH. The FT-IR spectrum of Fe3O4 nanoparticles (curve b) indicates the stretching vi-bration band of -OH at 1635 cm−1 which are attributed to the existence of surface hydroxyl groups and H2O. In the FT-IR spectra of Fe3O4, Fe3O4@CaAl-LDH and Fe3O4@CaAl-LDH@L-Dopa, the FeeO vibrations
of magnetite phase 7681-49-4 bands at about 575 cm−1 were observed . Also, the FT-IR spectrum of Fe3O4@CaAl-LDH, in addition to Fe3O4 absorption bands, shows the bands at 496 and 521 cm−1 that are related to the M-O vibration modes of CaAl-LDH structure (curve c). It is notable that, the characteristic absorption band around 1388 cm−1 is related to the presence of CO32– in the LDH structure. The intensity reduction of this band in Fe3O4@CaAl-LDH@L-Dopa spectrum clearly indicates the replacement of CO32– anions by L-Dopa molecules. Finally, the FT-IR spectrum of Fe3O4@CaAl-LDH@L-Dopa shows the char-acteristic peaks of Fe3O4 nanoparticles, CaAl-LDH and L-Dopa which is in agreement with the formation of Fe3O4@CaAl-LDH@L-Dopa struc-ture (curve d).
One of the advantages of using magnetic structures as drug carriers is the ability of these systems to delivering the drug through an external magnetic field. Therefore, the evaluation of the magnetic properties of the carriers seems to be necessary. In order to investigate the magnetic features of Fe3O4@CaAl-LDH@L-Dopa, the VSM measurement was carried out at 298 K. As illustrated in Fig. 7, the magnetization of Fe3O4 nanoparticles saturated up to 55 emu/g at an applied field of 9500 Oe and indicates the superparamagnetic behaviours at room temperature. The presence of CaAl-LDH shell and L-Dopa molecules around Fe3O4 cores reduces the magnetic strength of the Fe3O4 nanoparticles by about 20 emu/g (Fig. 7).
One of the most important features of carriers in the drug delivery systems is having an appropriate surface for interaction with drugs. The surface physical properties of Fe3O4@CaAl-LDH and Fe3O4@CaAl-LDH@L-Dopa were studied using N2 adsorption-desorption isotherm and pore distribution diagram (Fig. 8). Both of Fe3O4@CaAl-LDH and
Fe3O4@CaAl-LDH@L-Dopa show isotherm type IV which exhibits the mesoporous structure and presence of nano-voids in these systems. Fe3O4@CaAl-LDH represents the high BET surface area (136.4 m2 g−1),
narrow pore size distribution (centered at 14.2 nm) with the great pore volume (0.236 cm3 g−1), which makes Fe3O4@CaAl-LDH a suitable option for the drug delivery system. The high surface area of this structure improves the interaction of the drug with the carrier (Fig. 8a). Also, the BET analysis of Fe3O4@CaAl-LDH@L-Dopa demonstrates the specific surface area is about 112.3 m2 g−1. Moreover, BJH pore size distribution of the drug-carrier structure shows a narrow mesopore size distribution centered at 19.5 nm. The pore volume of Fe3O4@CaAl-LDH@L-Dopa was estimated as 0.202 cm3 g−1 by BJH analysis (Fig. 8b). Low surface area of Fe3O4@CaAl-LDH@L-Dopa indicates that a large portion of nanovoids are occupied by L-Dopa.
The surface chemical features of Fe3O4@CaAl-LDH@L-Dopa were studied using XPS analysis with a typical wide energy scan (Fig. 9). The obtained results from XPS spectra clearly indicate that the Fe3O4, CaAl-LDH and L-Dopa are presented in the Fe3O4@CaAl-LDH@L-Dopa structure (Fig. 9a). The integral peak area of the drug delivery system estimated the Ca:Al ratio as 2.57, which is in accordance with the ob-tained results from ICP-AES elemental analysis. The ICP-AES results confirm the presence of 27.1 wt% of Ca and 6.25 wt% of Al. According to the obtained results from XPS and ICP-AES data and with respect to the stoichiometric amount of Ca and Al precursors in synthesis process, the chemical formula of CaAl-LDH was evaluated as
It is notable that, the existence of the peaks at 711.4 and 724.7 eV show the presence of Fe3O4 nano particles in the Fe3O4@CaAl-LDH@L-Dopa structure. In high resolution XPS spectrum of 2p region of Fe, the absence of the satellite in the Fe2p3/2 peak confirms the presence of Fe3O4 (Fig. 9d) [30,31].
The TGA analysis clearly shows the presence of L-Dopa in the Fe3O4@CaAl-LDH@L-Dopa structure. Also, TGA analysis confirms that L-Dopa was successfully loaded into/on the Layers of LDHs.
Another factor which makes the carriers an ideal option for use in drug delivery systems is their stability in the body environment. In order to study on the structural persistence of Fe3O4@CaAl-LDH@L-Dopa, TGA analysis has been investigated (Fig. 10). Four mass loss steps were happened with an increase in the temperature.