Inhibiting the Fibrillation of Serum Albumin Proteins in the Presence of Surface Active Ionic Liquids (SAILs) at Low pH: Spectroscopic and Microscopic Study

One of the key necessary steps to prevent human neurological disorders is the efficient disruption of protein aggregation or amyloid fibril. In this article, we have explored the effect of three amphiphilic surface active ionic liquids (SAILs), namely 1-methyl-3-octylimidazolium chloride ([C₈mim]­Cl), 1-dodecyl-3-methyllimidazolium chloride ([C₁₂mim]­Cl), and 1-hexadecyl-3-methyllimidazolium chloride ([C₁₆mim]­Cl) having concentrations of 5.8, 0.29, and 0.08 mM, respectively, on bovine serum albumin (BSA) and human serum albumin (HSA) fibril. These SAILs have different alkyl chain length attached to the cationic imidazolium headgroups. Interestingly, it is observed that all of the three SAILs exhibit fibril inhibition at room temperature itself as initially evidenced from thioflavin T (ThT) fluorescence assay study. However, C₁₆mimCl is found as the most efficient quencher having highest quenching constant than the other two analogues. In addition, circular dichroism (CD) data give valuable insights into the conformational changes of BSA fibril as a consequence of interaction with SAILs. The field emission scanning electron microscopy (FESEM) and fluorescence lifetime imaging microscopy (FLIM) confirm the inhibitory effect of SAILs. It is evident from fluorescence correlation spectroscopy (FCS) study that 62% fibril is ruptured in the presence of C₈mimCl while C₁₂mimCl and C₁₆mimCl completely destroy the fibrillar morphology. So the inhibition efficiency is related to the hydrophobicity associated with the long alkyl chain attached with the cationic imidazolium headgroup of SAILs

Comparative Fluorescence Resonance Energy-Transfer Study in Pluronic Triblock Copolymer Micelle and Niosome Composed of Biological Component Cholesterol: An Investigation of Effect of Cholesterol and Sucrose on the FRET Parameters

The formation of pluronic triblock copolymer (F127)–cholesterol-based niosome and its interaction with sugar (sucrose) molecules have been investigated. The morphology of F127–cholesterol -based niosome in the presence of sucrose has been successfully demonstrated using dynamic light scattering (DLS) and transmission electron microscopic (TEM) techniques. The DLS profiles and TEM images clearly suggest that the size of the niosome aggregates increases significantly in the presence of sucrose. In addition to structural characterization, a detailed comparative fluorescence resonance energy transfer (FRET) study has been carried out in these F127-containing aggregates, involving coumarin 153 (C153) as donor (D) and rhodamine 6G (R6G) as an acceptor (A) to monitor the dynamic heterogeneity of the systems. Besides, time-resolved anisotropy and fluorescence correlation spectroscopy measurements have been carried out to monitor the rotational and lateral diffusion motion in these F127–cholesterol-based aggregates using C153 and R6G, respectively. During the course of FRET study, we have observed multiple time constants of FRET inside the F127–cholesterol-based niosomes in contrast with the F127 micelle. This corresponds to the presence of more than one preferential donor–acceptor (D–A) distance in niosomes than in F127 micelle. FRET has also been successfully used to probe the effect of sucrose on the morphology of F127–cholesterol-based niosome. In the presence of sucrose, the time constant of FRET further increases as the D–A distances increase in sucrose-decorated niosome. Finally, the excitation-wavelength-dependent FRET studies have indicated that as the excitation of donor molecules varies from 408 to 440 nm the contribution of the faster rise component of the acceptor enhances considerably, which clearly establishes the dynamics heterogeneity of both systems. Our findings also indicate that FRET is completely intravesicular in nature in these block copolymer-cholesterol-based aggregates

Unveiling the Interaction of Duplex DNA with Graphene Oxide in the Presence of Two Diverse Binders: A Detailed Photophysical Study

Coupling of biomolecules with nanomaterials has drawn immense attraction because of the improved synergistic properties, functions, and biocompatible nature. Thus, this process manifests its important role and fascinating potential in various nanobiotechnogical, biomedical, biosensing, and imaging applications. In this work, fundamental understanding of the interfacial properties and the interaction of double-stranded DNA (dsDNA) with graphene oxide (GO) has been systematically investigated by employing two different DNA-binding probes. Our results suggest that the unusual adsorption of duplex DNA onto the GO surface has been facilitated due to the partial deformation of the helical structure of DNA as evident from circular dichroism (CD) spectroscopy. Depending on the location of the probes inside the DNA helix, the photophysical properties of the dye-bound DNA in the presence of GO have been changed. Interestingly, the translational diffusion and rotational motion of the minor groove-binding probe, 4'-6-diamidino-2-phenylindole (DAPI) bound DNA, have been significantly altered with the addition of GO. In contrast, efficient electron transfer may occur from the DNA-intercalated ethidium bromide (EB) to GO with a time constant of ∼300 fs as evident from the ultrafast time-resolved measurement. Conclusively, a basic understanding of the interaction mechanism and dynamics of two different probes inside DNA and at the DNA-GO interface opens up new windows for the future development of various nano/bio applications

Translational and Rotational Diffusion of Two Differently Charged Solutes in Ethylammonium Nitrate–Methanol Mixture: Does the Nanostructure of the Amphiphiles Influence the Motion of the Solute?

In this Article, we have investigated the translational and rotational diffusion of two structurally similar but differently charged solutes (rhodamine 6G perchlorate and fluorescein sodium salt) in ethylammonium nitrate (EAN)–methanol (CH₃OH) mixture to understand the effect of added ionic liquid on the motion of the solutes. EAN and CH₃OH both are amphiphilic molecules and characterized by an extended hydrogen bonding network. Recently, Russina et al. found that a wide distribution of clusters exist in the CH₃OH rich region (0.10 ≤ χ_EAN ≤ 0.15) and EAN molecules preserve their bulk-sponge-like morphology (Russina, O.; Sferrazza, A.; Caminiti, R.; Triolo, A. <i>J. Phys. Chem. Lett</i>. <b>2014</b>, <i>5</i>, 1738–1742). The effect of this microheterogeneous mixture on the solute’s motion shows some interesting results compared to other PIL (protic ionic liquid)–cosolvent mixtures. Analysis of the time-resolved anisotropy data with the aid of Stokes–Einstein–Debye (SED) hydrodynamic theory predicts that the reorientation time of both of the solutes appears close to the stick hydrodynamic line in the methanol rich region. The hydrogen bond accepting solutes experience specific interaction with CH₃OH, and with increasing concentration of EAN, the specific interaction between the solute and solvent molecules is decreased while the decrease is more prominent in the low mole fraction of EAN due to the large size of cluster formation. The temperature dependent anisotropy measurements show that the hydrogen bonding interaction between EAN and CH₃OH is increased with increasing temperature. Moreover, fluorescence correlation spectroscopy (FCS) shows the dynamic heterogeneity of the mixture which is due to the segregation of the alkyl chain of the PIL. Formation of a large cluster at a low mole fraction of IL (0.10 ≤ χ_EAN ≤ 0.15) can be proved by the insensitivity of the translational diffusion and rotational activation energy of the solutes to the concentration of EAN. Thus, the result of the work suggests that the addition of EAN to the CH₃OH affects the specific interaction between solute and solvent and, as a consequence, the translational motion as well as the rotational motion of the solutes are modulated

Picosecond Solvation and Rotational Dynamics: An Attempt to Reinvestigate the Mystery of Alcohol–Water Binary Mixtures

In this article, we have investigated the anomalous behavior of two alcohol–water (<i>tert</i>-butyl alcohol (TBA)–water and ethanol–water) binary mixtures using femtosecond fluorescence upconversion technique. Recently, Gupta and Patey (Gupta, R.; Patey, G. N. <i>J. Chem. Phys</i>. <b>2012</b>, 137, 034509(1)–034509(12)) have used four force fields to simulate TBA–water binary mixtures. Surprisingly, two of them do not identify any aggregation of TBA molecules. We have calculated average solvation time of Coumarin 480 (C480) using two different methods. Our results indicate slowdown in solvation time in the mole fraction ranges <i>X</i>_T = 0.09–0.15, <i>X</i>_T = 0.40–0.46 and <i>X</i>_E = 0.06–0.08, <i>X</i>_E = 0.20–0.25 for TBA–water and ethanol–water binary mixtures, respectively. Additionally, we have detected another anomalous region at <i>X</i>_T ∼ 0.03. Slow solvation responses in the ranges <i>X</i>_T = 0.40–0.46 and <i>X</i>_E = 0.20–0.25 are probably due to the higher shear viscosity of the medium. However, <i>X</i>_T = 0.09–0.15 and <i>X</i>_E = 0.06–0.08 are the manifestation of aggregation induced structural transition of alcohol molecules. Hindered rotation of C480 in the ranges <i>X</i>_T = 0.04–0.09 and <i>X</i>_E = 0.03–0.07 corroborates our solvation dynamics results. From temperature dependent anisotropy measurements, we have shown that aggregation of alcohol molecules increases with increase in temperature

Modulation of the Excited-State Dynamics of 2,2′-Bipyridine-3,3′-diol in Crown Ethers: A Possible Way To Control the Morphology of a Glycine Fibril through Fluorescence Lifetime Imaging Microscopy

In this article, we have investigated the modulation of excited-state intramolecular double proton transfer (ESIDPT) dynamics of 2,2′-bipyridine-3,3′-diol (BP­(OH)₂) in two crown ethers (CEs), namely, 18-Crown-6 (18C6) and 15-Crown-5 (15C5). From steady-state UV–visible measurements, we have shown that there is no significant interaction between the dienol tautomeric form of BP­(OH)₂ and two CEs. However, in the presence of CEs, an additional emission band (∼415 nm) is generated along with the diketo tautomer band (∼465 nm). In time-resolved analysis, we have observed the generation of ∼260 ps rise component in the presence of 18C6. Therefore, by combining the results of steady-state and time-resolved emissions, we have proposed that the water-assisted ESIDPT route of BP­(OH)₂ generates a hydronium ion (H₃O⁺) in the excited state. 18C6 binds nicely to this H₃O⁺ ion. As a result, retarded ESIDPT dynamics is observed in 18C6. However, as 15C5 cannot bind H₃O⁺ properly, no rise component is found. With the addition of potassium chloride (KCl), the contribution of the rise component decreases due to unavailability of free 18C6 cavity to capture the H₃O⁺ ion generated in the excited state. Addition of calcium chloride (CaCl₂) leads to complete removal of the rise component due to the inhibition of the water-assisted ESIDPT route. From wavelength-dependent behavior, we have observed that the rise component is present only at 465 nm in 18C6. We have also shown that the fibrillar morphology of glycine can be successfully probed through fluorescence lifetime imaging microscopy using BP­(OH)₂ as an imaging agent. Modulation of fibrillar morphology has been found in the presence of two CEs. The interaction of glycine fiber with CEs can be explained by lifetime distribution analysis

Anomalous Dynamics in <i>tert</i>-Butyl Alcohol–Water and Trimethylamine <i>N</i>‑Oxide–Water Binary Mixtures: A Femtosecond Transient Absorption Study

In this article, we have investigated the unusual dynamics of <i>tert</i>-butyl alcohol (TBA)–water and trimethylamine <i>N</i>-oxide (TMAO)–water binary mixtures using solvation dynamics as a tool. For this purpose, femtosecond transient absorption spectroscopy has been employed. Although these two molecules are isosteres to each other, a significant difference in water dynamics has been observed. The solvation times in TBA–water binary mixtures are found to be between 1.5 and 15.5 ps. On the contrary, we have observed very fast dynamics in TMAO–water binary mixtures (between 210 and 600 fs). Interestingly, unusual retardation in dynamics is observed at 0.10 mole fraction of TBA and TMAO in both the binary mixtures

Unveiling the Mode of Interaction of Berberine Alkaloid in Different Supramolecular Confined Environments: Interplay of Surface Charge between Nano-Confined Charged Layer and DNA

In this Article, we demonstrate a detailed characterization of binding interaction of berberine chloride (BBCl) with calf-thymus DNA (CT-DNA) in buffer solution as well as in two differently charged reverse micelles (RMs). The photophyscial properties of this alkaloid have been modulated within these microheterogeneous bioassemblies. The mode of binding of this alkaloid with DNA is of debate to date. However, fluorescence spectroscopic measurements, circular dichroism (CD) measurement, and temperature-dependent study unambiguously establish that BBCl partially intercalates into the DNA base pairs. The nonplanarity imposed by partial saturation in their structure causes the nonclassical types of intercalation into DNA. Besides the intercalation, electrostatic interactions also play a significant role in the binding between BBCl and DNA. DNA structure turns into a condensed form after encapsulation into RMs, which is followed by the CD spectra and microscopy study. The probe location and dynamics in the nanopool of the RMs depended on the electrostatic interaction between the charged surfactants and cationic berberine. The structural alteration of CT-DNA from B form to condensed form and the interplay of surface charge between RMs and DNA determine the interaction between the alkaloid and DNA in RMs. Time-resolved study and fluorescence anisotropy measurements successfully provide the binding interaction of BBCl in the nanopool of the RMs in the absence and in the presence of DNA. This study motivates us to judge further the potential applicability of this alkaloid in other biological systems or other biomimicking organized assemblies

Protein-Guided Formation of Silver Nanoclusters and Their Assembly with Graphene Oxide as an Improved Bioimaging Agent with Reduced Toxicity

As an emerging category of fluorescent metal nanoclusters (NCs), protein-based NCs are considered as one of the promising candidates for the biomedical applications because of their luminescent properties and inherent biocompatibilities. Protein-capped silver NCs impregnated onto graphene oxide (GO) sheets can be internalized into the K562 cell, a human erythroleukemic cell line, and the Ag NCs/GO assembly can act as a synergistic drug carrier for Imatinib, a first-generation tyrosine kinase inhibitor. Further, Ag NCs adsorbed on GO have a great potential to be used as X-ray computer tomography (CT) imaging contrasting agents, and CT images show significant contrast enhancement of bone tissues in mice models. Overall, this assembly can exhibit great potential in the field of biomedical application and therapeutic studies

Unveiling the Self-Assembling Behavior of 5‑Fluorouracil and its <i>N</i>,<i>N</i>′‑Dimethyl Derivative: A Spectroscopic and Microscopic Approach

Under physiological conditions, 5-fluorouracil (5-FU), an anticancer drug, self-assembles into fibrils by strong hydrogen-bonding network, whereas its N,N′-dimethyl derivative, 5-fluoro-1,3-dimethyluracil (5-FDMU), does not make fibrils due to lack of strong hydrogen-bonding motif. In vitro, 5-FU self-assembly is sensitive to physicochemical conditions like the pH and ionic strength of the solution, which tune the strength of the noncovalent driving forces. Here we report a surprising finding that the buffer, which is necessary to control the pH and is typically considered to be inert, also significantly influences 5-FU self-assembly, which indicates an important role of counterions in the fibril formation. We have also monitored concentration- and time-dependent fibrillar growth of 5-FU. Again, fibril growth process is probed under dynamic conditions using microfluidic platform. The self-assembly of 5-FU compared with its N,N′-dimethyl derivative shows lower cytotoxicity to the cultured human erythroleukemic cells (K562 cells), which plausibly states the reason behind the greater effectiveness of 5-FU derivative drugs than 5-FU itself