Deciphering the complexation process of a fluoroquinolone antibiotic, levofloxacin, with bovine serum albumin in the presence of additives.

The current work aims to explore the thermodynamic and conformational aspects for the binding of fluoroquinolone antibacterial drug, levofloxacin (LFC), with bovine serum albumin (BSA) using calorimetric, spectroscopic (UV-visible, fluorescence, circular dichroism, and 1H NMR), dynamic light scattering (DLS) and computational methods (molecular docking). The binding of LFC with BSA at two sequential sites with higher affinity (~103M-1) at the first site has been explored by calorimetry whereas the binding at a single site with affinity of the order of ~104M-1 has been observed from fluorescence spectroscopy. The calorimetric study in the presence of additives along with docking analysis reveals the significant role of electrostatic, hydrogen bonding, and hydrophobic interactions in the association process. The slight conformational changes in protein as well as the changes in the water network structure around the binding cavity of protein have been observed from spectroscopic and DLS measurements. The LFC induced quenching of BSA fluorescence was observed to be initiated mainly through the static quenching process and this suggests the formation of ground state LFC-BSA association complex. The stronger interactions of LFC in the cavity of Sudlow site I (subdomain IIA) of protein have been explored from site marker calorimetric and molecular docking study.

Nanoparticle Surface Specific Adsorption of Zein and Its Self-assembled Behavior of Nanocubes Formation in Relation to On-Off SERS: Understanding Morphology Control of Protein Aggregates.

Zein, an industrially important protein, is characterized in terms of its food and pharmaceutical coating applications by using surface enhanced Raman spectroscopy (SERS) on Au, Ag, and PbS nanoparticles (NPs). Its specific surface adsorption behavior on Ag NPs produced self-assembled zein nanocubes which demonstrated on and off SERS activity. Both SERS characterization as well as nanocube formation of zein helped us to understand the complex protein aggregation behavior in shape controlled morphologies, a process with significant ramifications in protein crystallization to achieve ordered morphologies. Interestingly, nanocube formation was promoted in the presence of Ag rather than Au or PbS NPs under in situ synthesis and discussed in terms of specific adsorption. Zein fingerprinting was much more clear and enhanced on Au surface in comparison to Ag while PbS did not demonstrate SERS due to its semiconducting nature.

Biomineralization of gold nanoparticles by lysozyme and cytochrome C and their applications in protein film formation.

Lysozyme (Lys) and cytochrome c (Cyc,c) proteins were used as mild reducing and stabilizing agents to synthesize gold nanoparticles (NPs) at precisely 40 and 80 degrees C. All reactions were monitored simultaneously by UV-visible measurements to determine changes in the nature of the protein during the course of reaction. The synthesis of Au NPs caused the simultaneous denaturation of protein due to the formation of bioconjugate NPs, and the denaturation temperature decreased with the number of NPs. Lys entrapped NPs in a typical gel state, and Cyc,c carried them on well-defined micelles at 80 degrees C or in the form of long fibrils or strands at 40 degrees C. The shape, size, and arrangement of bioconjugate NPs were characterized by atomic force microscopy and transmission electron microscopy measurements. Purified bioconjugate NPs were further used in zein protein film formation. The resulting films were characterized by photophysical and mechanical measurements. The induction of bioconjugate NPs made protein films isotropic and relatively more brittle (with a greater effect for Cyc,c than for Lys conjugate NPs) than in their absence and was considered to be well suited for biomedical applications.

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.

Lamellar phase supported synthesis of colloidal gold nanoparticles, nanoclusters, and nanowires.

Gold nanoparticles (Au NP) have been synthesized in aqueous phase under ambient conditions in the presence of a series of various cationic double chain as well as dimeric (gemini) surfactants. The spacer chain and twin tail length of these surfactants has been systematically varied to see the effect of hydrophobicity on their capping ability. It has been observed that the increase in the length of spacer chain (from 12-2-12 to 12-6-12) and twin tails (from 10-2-10 to 14-2-14) significantly increases the lamellar phase formation and which in return acts as a wonderful template to accommodate the NP in the form of nanoclusters and nanowires. The lamellar phase practically facilitates the nucleation of Au degrees and produces large NP (15 +/- 2 nm). All reactions have also been carried out in the presence of beta-cyclodextrin (CYC) which has strong ability to complex with surfactant tail. The presence of CYC induces a tendency to form nanowire and it is more prominent in the case of surfactants with longer spacer group.