Synthesis, characterization and kinetic studies of porphyrins with thiolated side chains for functionalization of paramagnetic iron-oxide- gold, core- shell nanoparticles

Abstract

5,1 0, ,15,20-Tetrakis[3-(3-thioacetoxypropoxy)phenyl]porphyrin a photosensitizer for photodynamic therapy (PDT) was synthesized from 3-hydroxybenzaldehyde. Acid and alkaline hydrolysis of the thioacetoxypropoxyphenyl porphyrin was attempted to afford a free base porphyrin, 5,10, 15,20-tetrakis[3-(3-thiolpropoxy)phenyl]porphyrin but not achieved. Spectroscopic data indicates that partial hydrolysis occurred. 1HNMR, 13CNMR, UV-Visible and Infra-red spectrometers were used to characterize all the compounds. The synthesized porphyrin was immobilized on gold coated superparamagnetic iron oxide (Fe304@Au) nanoparticles for possible use as a carrier or drug delivery system for the porphyrin to cancer sites.

The use of magnetic nanoparticles for biomedical applications have been proposed to a large extent for several years. In recent years nanotechnology has developed to a stage that makes it possible to produce, characterize and specifically tailor the functional properties of nanoparticles for clinical applications. This has led to various opportunities such as improving the quality of magnetic resonance imaging, hyperthermia treatment for malignant cells, site-specific drug delivery and the manipulation of cell membranes. To this end a variety of iron oxide nanoparticles have been synthesized.

Using co-precipitation method, nanoparticles comprised of gold shell and magnetite/maghemite were synthesized by overgrowing the gold shell onto the magnetic seeds using sodium citrates as a reducing agent. Oxidized magnetites (Fe304) fabricated by co-precipitation of Fe2+ and Fe3+ in strong alkaline solution were used as magnetic cores. These magnetic nanoparticles were characterized by Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray diffraction spectroscopy (XRD). The transmission electron microscopy (TEM) image indicated that the particles were well dispersed nd spherical in shape with an average size of 34 - 58 nm with the mean particle diameter of 42.41 nm :!: 12.03 nm and standard deviation of (a) 0.27 nm indicating broad size distribution for the superparamagnetic iron oxide nanoparticles (SPION), the particle diameters for the gold coated SPION are in the range 34-54 nm while the average particle size as determined from the TEM image for the selected fraction is 44.26 nm :t 6.93 nm. The relative standard deviation of the sizes of the nanoparticles is 0.16 nm and the TEM for the functionalized gold coated SPION shows monodispersed particles which appear in spherical, cubic, irregular hexagon and oblong shapes with an average diameter of 44.65 nm. The HRTEM image, shows the existence of lattice planes which confirms the crystallinity of the material. The spacing between adjacent lattice planes is about 0.23 nm which corresponds to the (311) interplanar distance of Fe304 nanocrystals. Atomic force microscopy (ATM) was used to confirm the transmission electron microscopy (TEM) and HRTEM findings.

The UV-Visible absorption spectra of the deionised water used in the procedure of preparation of the as-synthesized nanoparticles showed no absorption peak in a wavelength range of 350-750 nm, but after introducing the suspension of the Au-coated magnetic nanoparticles, an absorption peak located at 526 nm appeared which is ascribed to the surface plasmon of nanosized Fe304@Au nanoparticles.

The kinetic studies using UV-visible spectrometer and the HRTEM images confirmed the adsorption of the porphyrin macromolecules as a coat on the magnetites particles. At a 5000 revolution per second (rps), aliquot sample of the aqueous phase of the suspension of 0.002 mM Fe304@Au in contact with the organic phase solution of the porphyrin taken for absorbance measurement at every 600 s showed a decrease in the concentration of the suspension while a noticeable and appreciable increase was also noted in the concentration of the porphyrin macromolecules measured at a A max of 420 nm representing the functionalized sample. A new absorption peak of 535 nm was recorded for the nanoparticle/porphyrin phase.

A clear magnetic behaviour was established from the two different samples (coated and functionalised samples) using superconducting quantum interference device (SQUID) magnetometer. No long-range cooperative behaviour is evident anywhere from room temperature down to 2 K, which attests to a characteristic length of the scale of the Fe-magnetic agglomeratios on the nano-scale. Being especially prone to intrinsic ferromagnetic ordering, any impurity form of Fe or macro-scale Fe aggregates would impart a very large and easily identifiable magnetic signal. Such a reponse was completely absent from these stud ies and hence testifies to the homogeneity quality of the materials under investigation.

KEY WORDS: photodynamic therapy, photosensitizer, porphyrins, magnetites, maghemite, crystalinity, magnetic seeds, nanoparticles,