Layer-by-layer electrostatic entrapment of protein molecules on superparamagnetic nanoparticle: new strategy to enhance adsorption capacity and maintain biological activity

There is a recent interest to use inorganic-based magnetic nanoparticles as a vehicle to carry biomolecules for various biophysical applications, but direct attachment of the molecules is known to alter their conformation leading to attenuation in activity. In addition, surface immobilization has been limited to monolayer coverage. It is shown that alternate depositions of negatively charged protein molecules, typically bovine serum albumin (BSA) with a positively charged aminocarbohydrate template such as glycol chitosan (GC) on magnetic iron oxide nanoparticle surface as a colloid, are carried out under pH 7.4. Circular dichroism (CD) clearly reveals that the secondary structure of the entrapped BSA sequential depositions in this manner remains totally unaltered which is in sharp contrast to previous attempts. Probing the binding properties of the entrapped BSA using small molecules (Site I and Site II drug compounds) confirms for the first time the full retention of its biological activity as compared with native BSA, which also implies the ready accessibility of the entrapped protein molecules through the porous overlayers. This work clearly suggests a new method to immobilize and store protein molecules beyond monolayer adsorption on a magnetic nanoparticle surface without much structural alteration. This may find applications in magnetic recoverable enzymes or protein delivery.

Polymer-mediated disruption of drug crystallinity

Ibuprofen (IB), a BCS Class II compound, is a highly crystalline substance with poor solubility properties. Here we report on the disruption of this crystalline structure upon intimate contact with the polymeric carrier cross-linked polyvinylpyrrolidone (PVP-CL) facilitated by low energy simple mixing. Whilst strong molecular interactions between APIs and carriers within delivery systems would be expected on melting or through solvent depositions, this is not the case with less energetic mixing. Simple mixing of the two compounds resulted in a significant decrease in the differential scanning calorimetry (DSC) melting enthalpy for IB, indicating that approximately 30% of the crystalline content was disordered. This structural change was confirmed by broadening and intensity diminution of characteristic IB X-ray powder diffractometry (PXRD) peaks. Unexpectedly, the crystalline content of the drug continued to decrease upon storage under ambient conditions. The molecular environment of the mixture was further investigated using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopy. These data suggest that the primary interaction between these components of the physical mix is hydrogen bonding, with a secondary mechanism involving electrostatic/hydrophobic interactions through the IB benzene ring. Such interactions and subsequent loss of crystallinity could confer a dissolution rate advantage for IB. (C) 2006 Elsevier B.V. All rights reserved.