Oppositely charged nanoparticle (NP)−nanoparticle (NP) interactions were studied by titrating sodium dodecyl sulfate (SDS) stabilized NPs with cetyltrimethylammonium bromide (CTAB) stabilized NPs at constant temperature with the help of UV−visible and dynamic light scattering measurements. CTAB stabilized NPs were systematically replaced with a series of cationic gemini surfactants to demonstrate the effect of head group and hydrocarbon tail modifications on the electrostatic interactions with SDS stabilized NPs. Introduction of the dimeric gemini head group (alkylammonium or imidazolium), spacer length, and double tail hydrocarbon length all significantly reduced the NP−NP interactions and delayed their salting-out process. They lead to the formation of stable colloidal aqueous solubilized NP−NP complexes. The results concluded that NP−NP interactions can be overcome if appropriately stabilized NPs are used to maintain their colloidal stability so as to achieve maximum applicability.
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.
Nanoparticle−nanoparticle (NP−NP) interactions between Au and Ag NPs were studied by using sodium dilauraminocystine (SDLC)-and Gemini surfactant-stabilized NPs to demonstrate the unique NP surface adsorption behavior of SDLC in controlling and mimicking such interactions in complex mixtures. They were significantly affected by the spacer as well as the polymeric nature of the head group of Gemini surfactants. A longer spacer impeded while a polymeric head group facilitated the interactions. The Au−Ag NPs interactions in an aqueous phase were also controlled by placing surface-active magnetic NPs at an aqueous−air interface, which interacted with either or both kinds of interacting NPs in an aqueous phase and reduced their ability to interact with each other. On the other hand, water-soluble zwitterionic magnetic NPs proved to be excellent extractants of both Au and Ag NPs from the aqueous phase. Extraction efficiency depended on the strength of interactions between the water-soluble magnetic NPs and aqueous-solubilized Au and/or Ag NPs.
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