No abstract

By using in situ synthesis of gold nanoparticles (Au NPs) in the presence of binary mixtures of cytochrome c (Cyc,c) and bovine serum albumen (BSA) model proteins, we demonstrated a new method of studying protein–protein interactions on the surfaces of nanomaterials. Such interactions were simultaneously evaluated and supported by the molecular dynamics studies in terms of protein docking. Both experimental and theoretical studies collectively indicated a strong complexation among Cyc,c and BSA on the surface of Au NPs with a multipoint anchoring mechanism to Au surface. They also highlighted that the Cyc,c–BSA complex exhibited much stronger surface adsorption rather than Cyc,c or BSA alone. Biofunctional Au NPs thus obtained were tested for hemocompatibility for their possible applications as drug delivery vehicles in systemic circulation by employing the hemolysis. The hemolysis was done for the Au NPs which were coated with entire mixing range of Cyc,c–BSA mixtures to explore the most appropriate mixing compositions of Cyc,c–BSA mixtures for hemocompatibility. In addition, protein coated Au NPs demonstrated strong complexation with DNA which were significantly pronounced for the Cyc,c–BSA complex coated NPs rather than Cyc,c or BSA alone coated NPs. The Cyc,c–BSA docked complex on Au NP surface behaved like a typical helix–turn–helix motif because of the size disparity between a much larger BSA and smaller Cyc,c protein that resulted in stronger complexation with DNA in comparison to surface adsorbed Cyc,c or BSA alone. These finding bear important relevance in biotechnology in terms of gene expression and transcription factors.

We demonstrate the potential use of 1,1′-bis(2-(cyclo­hexyloxy)-2-oxoethyl)-[4,4′-bipyridin]-1,1′-diium bromide (BP) and 1-ethyl-3-methyl­imidazolium chloride (EMI) ionic liquids (ILs) in in situ synthesis of gold nanoparticles (Au NPs) without using any external reducing or stabilizing agents. Both ILs produced nearly monodisperse NPs of 4–8 nm which were present in the form of self-assembled states. BP coated NPs formed self-assembled sheets and easily transferred to the organic phase by employing the water insoluble IL as a phase transfer agent. The efficiency of the phase transfer process was related to the extent of aggregation as well as functional groups. Both IL coated NPs were further used to extract the proteins from the complex biological mixtures. EMI coated NPs extracted proteins of large molar masses whereas BP coated NPs were good for the extraction of low molecular mass proteins. This disparity was controlled by the substituted functional groups of ILs. Bulky cyclohexyloxy functional groups of BP did not allow extraction of large molar mass proteins. Such a wide applicability of ILs in nanomaterials synthesis opens several new applications in the field of nanomedicine and nanobiotechnology where IL coated NPs can be used for diverse protein complexation.

In order to highlight the applications of bioflavonoids in materials chemistry, naringin and its chalcone form were used in the nanomaterial synthesis to produce flavonoid-conjugated nanomaterials in aqueous phase. Chalcone form proved to be excellent reducing as well as stabilizing agent in the synthesis of monodisperse Au, Ag, and Pd nanoparticles (NPs) of ∼5–15 nm, following in situ reaction conditions where no external reducing or stabilizing agents were used. The mechanism of NP surface adsorption of flavonoid was determined with the help of dynamic light scattering and zeta potential measurements. Surface-adsorbed flavonoids also allowed NPs to easily transfer into the organic phase by using aqueous insoluble ionic liquid. Pd NPs attracted the excessive amount of surface adsorption of both naringin as well as its chalcone form that in turn drove Pd NPs in self-assembled state in comparison to Au or Ag NPs. An amount of surface-adsorbed flavonoids selectively determined the extraction of protein fractions from complex zein corn starch protein solution. Self-assembled Pd NPs with a large amount of surface-adsorbed naringin preferentially extracted zein fraction of higher molar mass, whereas Au and Ag NPs almost equally extracted the zein fractions of lower molar masses.

Hard, medium, and soft wheat proteins, based on gluten content, were studied for their important roles in nanometallic surface chemistry. In situ synthesis of Au nanoparticles (NPs) was followed to determine the surface adsorption behavior of wheat protein based on the gluten contents. A greater amount of gluten contents facilitated the nucleation to produce Au NPs. X-ray photoelectron spectroscopy (XPS) surface analysis clearly showed the surface adsorption of protein on nanometallic surfaces which was almost equally prevalent for the hard, medium, and soft wheat proteins. Wheat protein conjugated NPs were highly susceptible to phase transfer from aqueous to organic phase that was entirely related to the amount of gluten contents. The presence of higher gluten content in hard wheat protein readily enabled the hard wheat protein conjugated NPs to move across the aqueous−organic interface followed by medium and soft wheat protein conjugated NPs. Sodium dodecyl sulfate−polyacrylamide gel electrophoresis (SDS page) analysis allowed us to determine molar masses of nanometallic surface adsorbed protein fractions. Only two protein fractions of high molar masses (74 and 85 kDa) from SDS solubilized hard, medium, and soft wheat proteins preferred to adsorb on nanometallic surfaces out of more than 15 protein fractions of pure wheat protein. This made the surface adsorption of wheat protein highly selective and closely related to gluten content. Cetyltrimethylammonium bromide (CTAB) solubilized wheat protein conjugated NPs demonstrated their strong antimicrobial activities against both Gram negative and Gram positive bacteria making them suitable for their applications in food industry.