Keto-Enol Tautomerism of Temperature and pH Sensitive Hydrated Curcumin Nanoparticles: Their Role as Nanoreactors and Compatibility with Blood Cells.

In order to provide a solution for the poor aqueous solubility and poor bioavailability of curcumin, we present the synthesis and characteristic features of water-soluble curcumin hydrated nanoparticles (CNPs). They are stable and nearly monodisperse in the aqueous phase where the keto form of curcumin self-assembles into spherical CNPs, which are highly sensitive to temperature and pH variations. The CNPs are quite stable up to 40 °C and at neutral pH. A higher temperature range reduces their hydration and makes them unstable, thereby disintegrating them into smaller aggregates. Similarly, a higher pH converts the keto form of CNPs into the enol form by promoting their interparticle fusions driven by hydrogen bonding with a remarkable color change from yellow to bright orange-red which demonstrates their excellent photophysical behavior. The stable keto form CNPs are highly efficient nonreactors for the in situ synthesis of Au, Ag, and Pd NPs which are simultaneously entrapped in curcumin aggregates, thus promoting the metal NP carrying ability of curcumin aggregates. The CNPs also demonstrate their excellent dose-dependent biocompatibility with blood cells. A concentration range up to 5 mM of CNPs is quite safe for their applications in biological systems.

Applications of rice protein in nanomaterials synthesis, nanocolloids of rice protein, and bioapplicability.

Rice protein conjugated nanomaterials were synthesized and characterized by using anionic and cationic forms of rice protein. Both forms showed unique characteristic features when used in in situ reaction conditions for synthesizing the protein stabilized gold (Au) and silver (Ag) nanoparticles (NPs). Au NPs synthesis was highly facilitated than Ag NPs synthesis while the reverse was true when rice protein was simply used in the basic medium. Photophysical behavior clearly showed the contributions of both electrostatic and non-electrostatic interactions driving the rice protein surface adsorption on nanometallic surfaces. Rice protein conjugated NPs were easily transferred and extracted into the organic phase while the extraction process was related to the amount of protein coating. Under the controlled pH reaction conditions, rice protein - dye colored NPs were synthesized which were further characterized by the DLS and SDS Page analysis. Both rice protein conjugated Au/Ag NPs and rice protein NPs showed remarkable biocompatibility with blood cells. These NPs demonstrated their excellent ability to selectively extract protein fractions from complex biological fluid like serum. The results proposed significant applications of rice protein conjugated NPs in biological systems as well as bio-nanotechnology.

Protein mixtures of environmentally friendly zein to understand protein-protein interactions through biomaterials synthesis, hemolysis, and their antimicrobial activities.

Industrially important zein protein has been employed to understand its interactions with two model proteins bovine serum albumin (BSA) and cytochrome c (Cyc,c) following the in vitro synthesis of Au NPs so as to expand its applicability for biological applications. Interactions were studied under the effect of temperature variation by UV-visible and fluorescence emission studies. Temperature induced unfolding in the protein mixtures indicated their degree of mutual interactions through simultaneous nucleation of gold nanoparticles (Au NPs) and their subsequent shape control effects. Zein + BSA mixtures showed favorable protein-protein interactions over the entire mole fraction range with maximum close to x(BSA) = 0.24, whereas zein + Cyc,c showed such interactions only in the zein rich region with significant demixing in the Cyc,c rich region of the mixtures. Both hydrophobic as well as hydrophilic domains in the unfolded states were driving such interactions in the case of zein + BSA mixtures while demixing was the result of the predominant hydrophilic nature of Cyc,c and its self-aggregation behavior in the Cyc,c rich region in contrast to the predominant hydrophobic nature of zein. Zein + BSA mixtures produced small roughly spherical Au NPs fully coated with protein, whereas the demixing zone of zein + Cyc,c mixtures generated highly anisotropic NPs with little protein coating. To explore their biological applications, protein conjugated NPs of both mixtures were subjected to hemolysis where NPs coated with the former mixture showed little hemolysis and may act as drug delivery vehicles in systemic circulation in comparison to the latter. Both kinds of NPs further demonstrated their extraordinary antimicrobial activities with different kinds of strains and proved to be highly important environmentally friendly biomaterials.

Block copolymer micelles as nanoreactors for self-assembled morphologies of gold nanoparticles.

Self-assembled gold (Au) nanoparticles (NPs) were synthesized in micelle surface cavities of a L121 block polymer in the presence of zwitterionic (viz. DPS, TPS, and HPS) and sugar surfactants (OG and DDM) in aqueous phase at 70 °C by using the surface cavities of L121 as reducing sites for converting Au(III) into Au(0). All reactions were monitored simultaneously by UV-visible spectroscopy to determine the growth kinetics in gold nucleating centers on the basis of surface plasmon resonance that also helped in tracing the structure micelle transitions over a wide temperature range of 10-70 °C. The surfactant/L121 mole ratio was changed systematically from 0.5 to 2.5 by keeping L121 and HAuCl4 concentrations constant at 10 and 0.25 mM, respectively, to determine the shape and size of the micelles and their relation to the self-assembled behavior of Au NPs. TEM studies were used to have a direct insight into the morphology of micelle templates and their shape and size for self-assembled NPs. L121 along with DPS (C12 carbon chain) produced well-defined micelles loaded with tiny NPs of 3-6 nm in the L121-rich region of the mixture, while large flower-like compound micelles with a clear core-shell morphology were produced in the DPS-rich region. TPS and HPS (C14 and C16 hydrocarbon chains, respectively) with stronger hydrophobicity than DPS also produced almost similar micelles loaded with tiny NPs in the L121-rich region, but they disappear in the surfactant-rich region. Replacement of zwitterionic with ionic surfactants did not yield micelle templates for self-assembled NPs. Results conclude that well-defined micelles of L121 are the fine templates for self-assembled NPs that can only be achieved in the presence of a neutral surfactant with low concentration and low hydrophobicity.

How PEO-PPO-PEO triblock polymer micelles control the synthesis of gold nanoparticles: temperature and hydrophobic effects.

Aqueous micellar solutions of F68 (PEO(78)-PPO(30)-PEO(78)) and P103 (PEO(17)-PPO(60)-PEO(17)) triblock polymers were used to synthesize gold (Au) nanoparticles (NPs) at different temperatures. All reactions were monitored with respect to reaction time and temperature by using UV-visible studies to understand the growth kinetics of NPs and the influence of different micellar states on the synthesis of NPs. The shape, size, and locations of NPs in the micellar assemblies were determined with the help of TEM, SEM, and EDS analyses. The results explained that all reactions were carried out with the PEO-PPO-PEO micellar surface cavities present at the micelle-solution interface and were precisely controlled by the micellar assemblies. Marked differences were detected when predominantly hydrophilic F68 and hydrophobic P103 micelles were employed to conduct the reactions. The UV-visible results demonstrated that the reduction of gold ions into nucleating centers was channeled through the ligand-metal charge-transfer complex (LMCT) and carried out by the surface cavities. Excessive hydration of the surface cavities in the case of F68 micelles produced a few small NPs, but their yield and size increased as the micelles were dehydrated under the effect of increasing temperature. The results concluded that the presence of well-defined predominantly hydrophobic micelles with a compact micelle-solution interfacial arrangement of surface cavities ultimately controlled the reaction.