The surface interactions between gold nanoparticles (AuNPs) and lipase from Candida antarctica fraction B (CALB) were investigated at macromolecular and colloidal length-scales. In order to elucidate the reciprocal effect of the interactions on the individual component’s properties, CALB was either added during the synthesis of AuNPs or added to pre-synthesized AuNPs. In both cases, it was observed that the AuNPs are spherical and stable and, by fluorescence and circular dichroism spectroscopies, changes were observed in the secondary and tertiary structure of CALB, that were dependent on the AuNPs concentration. Nevertheless, the catalytic activity of CALB was maintained, although at a lower percentage (≥ 80%), thus new bio-functionalities were inserted into AuNPs upon interaction with CALB. Using simple and straightforward approaches and state-of-the-art techniques important knowledge about CALB/AuNPs bioconjugates was gained, thus contributing to the development of new nano-biomaterials and for the safe use of AuNPs in biomedical applications.

The influence that urea has on the conformation of water-soluble globular protein, bovine serum albumin (BSA), exposed directly to the aqueous solution as compared to the condition where the macromolecule is confined in the Aerosol-OT (AOT - sodium bis-2-ethylhexyl sulfosuccinate)/n-hexane/water reverse micelle (RM) is addressed. Small angle X-ray scattering (SAXS), tryptophan (Trp) fluorescence emission and circular dichroism (CD) spectra of aqueous BSA solution in the absence and in the presence of urea (3M and 5M) confirm the known denaturating effect of urea in proteins. The loss of the globular native structure is observed by the increase in the protein maximum dimension and gyration radius, through the Trp emission increase and maximum red-shift as well as the decrease in alpha-helix content. In RMs, the Trp fluorescence and CD spectra show that BSA is mainly located in its interfacial region independently of the micellar size. Addition of urea in this BSA/RM system also causes changes in the Trp fluorescence (emission decrease and maximum red-shift) and in the BSA CD spectra (decrease in alpha-helix content), which are compatible with the denaturation of the protein and Trp exposition to a more apolar environment in the RM. The fact that urea causes changes in the protein structure when it is located in the interfacial region (evidenced by CD) is interpreted as an indication that the direct interaction of urea with the protein is the major factor to explain its denaturating effect.