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Adsorption of arsenic by graphene-based adsorbents is widely applied to remove arsenic from water and has become a promising technology. However, most of the reported studies were conducted at a relatively higher concentration of arsenic in As (V) oxidative form, whereas the As (III) is more difficult to remove from water and more toxic, which prompted us to conduct the study at a lower concentration of 1 ppm in As (III). A Facile and controlled synthesis of graphene-based metal/metal oxide nanomaterials and adsorptive removal of aqueous As (III) is reported here. Adsorbents were characterized using spectroscopy (FTIR, XPS and Raman) and microscopy (TEM). The maximum uptake of arsenic obtained was 88.8% from the RGO-Fe3O4composite among all the adsorbents. The pseudo-second-order model and Intra-particle mass transfer diffusion model were applied to determine the adsorption kinetics with varying contact time between the adsorbents and the As (III) in water to interact. Experimental results suggest that the adsorption of As (III) onto the adsorbents was a multi-step process involving external adsorption to the surface followed by diffusion to the interior. A simple spectrophotometric method also was used for the detection and quantification of As (III).

The conformational plasticity of intrinsically disordered proteins (IDPs) allows them to adopt a range of conformational states that can be important for their biological functions. The driving force for the conformational preference of an IDP emanates from an intricate interplay between chain–chain and chain–solvent interactions. Using ultrafast femtosecond and picosecond time-resolved fluorescence measurements, we characterized the conformational and solvation dynamics around the N- and C-terminal segments of a disordered repeat domain of a melanosomal protein Pmel17 that forms functional amyloid responsible for melanin biosynthesis. Our time-resolved fluorescence anisotropy results revealed slight compaction and slower rotational dynamics around the amyloidogenic C-terminal segment when compared to the proline-rich N-terminal segment of the repeat domain. The compaction of the C-terminal region was also associated with the restrained mobility of hydration water as indicated by our solvation dynamics measurements. Our findings indicate that sequence-dependent chain–solvent interactions govern both the conformational and solvation dynamics that are crucial in directing the conversion of a highly dynamic IDP into an ordered amyloid assembly. Such an interplay of amino acid composition-dependent conformational and solvation dynamics might have important physicochemical consequences in specific water–protein, ion–protein, and protein–protein interactions involved in amyloid formation and phase transitions.

Solvents, particularly those having low volatility, are of great interest for the biocatalytic synthesis of utility chemicals and fuels. We show novel and universal solvent-like properties of a neat and water-less polymer surfactant–bovine serum albumin (BSA) conjugated material (WL-PSpBSA). This highly viscous, nonvolatile material behaves as a liquid above its solid–liquid transition temperature (∼25–27 °C) and can be used as a solvent for variety of completely dry solutes of different sizes and surface chemistries. We show using a combination of optical microscopy and steady -state and time-resolved fluorescence spectroscopy that dry and powdered dyes (hydrophobic Coumarin 153 (C153)), enzymes (α-chymotrypsin (α-Chy)), or even 1 μm microparticles (diffusion coefficient ca. three orders slower than C153), can be solubilized and completely dispersed in the WL-PSpBSA solvent above 25 °C. While C153, irrespective of its mode of addition to WL-PSpBSA, binds similarly to BSA, α-Chy can be stabilized and activated to perform its hydrolysis function, even at 100 °C. This work therefore provides insights into the form of universal solvent characteristic property for this new class of nonaqueous, nonvolatile, biodegradable protein–polymer surfactant-based conjugated materials and suggests potential new avenues that can have a huge impact on biocatalysis, bionanotechnology, drug delivery, and other applications.

A comprehensive understanding of exciton dynamics of water-soluble quantum dots (QDs), especially those synthesized directly in aqueous media, is critical for devising their applications. Trapping processes are expected to play a pivotal role here, as surface trap states are abundant in such QDs. The present study, based on ultrafast transient absorption, provides insight into exciton dynamics in PEI-capped CdS QDs synthesized by a one-pot reaction in water. They are robust and strongly photoluminescent (PL), unlike many other aqueous QDs. Excitation energy dependence of PL and the underlying mechanisms have been investigated. Analysis of fluence-dependent transient absorption bleach and photoinduced absorption is performed to deconvolute contributions from multiexciton recombination and carrier trapping. A simple kinetic model is used to quantify the rate constants associated with intraband relaxation of hot excitons and hot carrier trapping. Similar magnitudes observed for the two pathways highlight the competitive kinetics between them, which is responsible for a drastic decrease in PL quantum yields for excitation above the band gap. Such efficient hot carrier trapping in these QDs may possibly foreshadow ultrafast trap-mediated electron transfer and thus render them suitable for redox-sensing and photocatalysis.

Dimethyl-2,5-bis(4-methoxyphenylamino)terephthalate (DBMPT) is a water-insoluble fluorogenic molecule, which has been rendered water-soluble in physiological conditions, by the addition of triblock copolymers (TBPs), P123 (PEO19PPO69PEO19), and F127 (PEO100PPO65PEO100). DBMPT-TBP mixed aggregates, formed in the process, exhibit significant aggregation-induced enhancement of emission, with nanosecond fluorescence lifetimes. Dynamics involved in suppression of nonradiative pathways and consequent enhancement of fluorescence are followed by femtosecond transient absorption and time-resolved fluorescence spectroscopic techniques. Interestingly, shapes of the aggregates formed with the two TBPs are found to be very different, even though they differ only in the length of hydrophilic blocks. DBMPT-P123 aggregates are micrometer-sized and spherical, while DBMPT-F127 aggregates form nanorods. Evolution of their morphologies, as a function of TBP concentration, is monitored using cryo-TEM, FESEM, and fluorescence lifetime imaging microscopy. Fluorescence lifetime distribution provides useful insight into microheterogeneity in these mixed aggregates. Excellent cell permeability is observed for DBMPT-F127 nanorods, in contrast to DBMPT-P123 microspheres. These fluorescent nanorods exhibit the ability to mark lipid droplets within the cell and hence bear the promise for application in intracellular imaging.

Nonionic surfactant modulated aggregation induced emission enhancement (AIEE) of Dimethyl-2,5-bis(4-(methoxyphenyl)amino)terephthalate (DBMPT) has been investigated. DBMPT exhibits unidirectional aggregated growth with nonionic triton X-100 (TX-100) to produce highly luminescent nanorods, the dimensions and emission intensities of which are controlled by concentration of DBMPT. Energy transfer from perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTAD) to these nanorods in aqueous medium produces pure white light emission with the CIE chromaticity coordinates (0.33, 0.36) and a significantly high quantum yield of 35%. Gelation of the system with agarose yields a bright white light emitting gel. Both these factors demonstrate an excellent potential for application of this system in light harvesting and as an advanced material for organic electronic devices.

Dynamics of preferential solvation of 5-aminoquinoline (5AQ) has been studied in hexane–alcohol solvent mixtures. Significant spectral red shift and fluorescence quenching are observed, even for miniscule amounts of alcohols. A nonlinear variation of these parameters, with alcohol mole fraction, indicates dipolar enrichment around 5AQ in its excited state. A nanosecond rise at the red end of emission spectra is ascribed to translational diffusion of alcohol molecules and consequent preferential solvation of 5AQ. Electrostatic stabilization and hydrogen bonding between the dipolar excited state of the fluorophore and polar alcohol molecules are major driving factors here. Time evolution of emission spectra, from those in a predominantly hexane-like environment to those in a predominantly alcohol-like environment, takes place in nanosecond time scale and depends on the alcohol concentration in the mixture. This in agreement with calculations using an existing model. Hence, 5AQ is found to be a suitable fluorescent probe for the study of dynamics in complex systems.

A series of composites were synthesized having graphene oxide (GO)/reduced graphene oxide (RGO), decorated with Ag halide within inert poly(vinyl alcohol) (PVA) matrix. A calculated amount of cuprous iodide was also synthesized with Ag halide. On exposure to light, due to the photochromic effect, Ag halide converts into Ag nanoparticles as a donor, whereas cuprous iodide acts as a hole trapper to introduce a band gap in graphene. With increasing exposure time, the Ag nanoparticles increase in size and number and composites become increasingly dark. The appearance of the plasmonic peak in ultraviolet–visible plots after exposure to light confirms the presence of Ag nanoparticles in these composites. The apparent red shift of the surface plasmon resonance peak, reduction of its intensity, and broadening of the peak are dependent on the dielectric constant of the surrounding matrix and the distance between the GO/RGO sheet and the Ag nanoparticles. The increasing number and size of Ag nanoparticles introduce tunable n-type doping in the GO/RGO–PVA composites, as determined directly by Raman spectroscopy, without the necessity of electrically gated device.

Protein hydration water plays a fundamentally important role in protein folding, binding, assembly, and function. Little is known about the hydration water in intrinsically disordered proteins that challenge the conventional sequence-structure-function paradigm. Here, by combining experiments and simulations, we show the existence of dynamical heterogeneity of hydration water in an intrinsically disordered presynaptic protein, namely α-synuclein, implicated in Parkinson’s disease. We took advantage of nonoccurrence of cysteine in the sequence and incorporated a number of cysteine residues at the N-terminal segment, the central amyloidogenic nonamyloid-βcomponent (NAC) domain, and the C-terminal end of α-synuclein. We then labeled these cysteine variants using environment-sensitive thiol-active fluorophore and monitored the solvation dynamics using femtosecond time-resolved fluorescence. The site-specific femtosecond time-resolved experiments allowed us to construct the hydration map of α-synuclein. Our results show the presence of three dynamically distinct types of water: bulk, hydration, and confined water. The amyloidogenic NAC domain contains dynamically restrained water molecules that are strikingly different from the water molecules present in the other two domains. Atomistic molecular dynamics simulations revealed longer residence times for water molecules near the NAC domain and supported our experimental observations. Additionally, our simulations allowed us to decipher the molecular origin of the dynamical heterogeneity of water in α-synuclein. These simulations captured the quasi-bound water molecules within the NAC domain originating from a complex interplay between the local chain compaction and the sequence composition. Our findings from this synergistic experimental simulation approach suggest longer trapping of interfacial water molecules near the amyloidogenic hotspot that triggers the pathological conversion into amyloids via chain sequestration, chain desolvation, and entropic liberation of ordered water molecules.

Schiff bases and their metal ion complexes have potential biological applications. It is important to study their interactions with biomimemtic assemblies in order to design such applications. To this effect, the nature and interaction between the aggregates of an organic fluorophore (Znsalampy) and surfactants viz. sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) have been monitored using bulk macroscopic techniques like steady state and time resolved fluorescence as well as single molecule techniques like Fluorescence Correlation Spectroscopy (FCS). The presence of more than one kind of aggregates is observed in neat aqueous solutions is confirmed by the complementary techniques. The more rigid aggregates are found to be less prone to disruption by surfactants. SDS is found to be significantly more effective than CTAB in breaking the aggregates of Znsalampy.

Elucidation of host–guest chemistry of 2-(4′-pyridyl)benzimidazole (4PBI) and 2-(2′-pyridyl)benzimidazole (2PBI) with cucurbiturils in aqueous solution is rather challenging. The guest molecules are capable of binding in three different states of protonation: cation C, tautomer T, and normal N. Charge distribution on the species governs the formation of the inclusion complexes. Binding modes of the guest molecules with cucurbiturils have been investigated by proton NMR spectroscopy. 4PBI binds with its benzimidazole ring pointing inward, while the binding mode is opposite for 2PBI. This difference is governed by the position of substitution of the pyridyl ring. Energetics of complexation has been studied by quantum chemical calculations for 4PBI-CB as 2PBI-CB type complexes, for each form (C, T, and N) of both the molecules. Release of high energy water from cucurbituril cavity is the main driving force for complexation. Excited state proton transfer (ESPT) in 2PBI and 4PBI are affected strongly upon complexation, as is manifested in steady state and time-resolved fluorescence experiments.

Salophen is a weakly emissive molecule with a flexible structure. The decrease in the flexibility of the molecule, which can be achieved by chemical or physical means, causes a significant increase in the emissivity and fluorescence lifetime. This phenomenon has been observed upon incorporation of salophen in the solid polymer matrix of poly(methyl methacrylate) (PMMA). The enhancement in emission is even more prominent in the pure solid form of salophen. An enhancement of emission is also observed in the case of the zinc complex of salophen, SalZn, which is inherently more emissive than free salophen in solution. However, the enhancement in emission is greater in the PMMA matrix for the complex than in its solid form. Interestingly, a quenching of fluorescence is observed in the crystals of the aluminum complex of salophen (SalAl+), which is strongly emissive in solution phase. These apparently conflicting trends have been rationalized in the light of the molecular arrangement of salophen and its complexes in a solid matrix and in the pure solid forms. In the case of salophen, torsional motion provides major nonradiative channels of depopulation of its excited state in solution. These channels are blocked in the rigid environment provided of the polymer matrix and of the crystal, giving rise to aggregation induced enhancement of emission (AIEE). In the case of SalAl+, the torsional motion is restricted anyway due to complexation. The X-ray crystal structure indicates the possibility of π–π interaction between the planar ligands of two neighboring complex molecules, which could lead to aggregation-caused quenching (ACQ). This provides a justification for the lower emissivity of SalZn, as compared to SalAl+. SalZn is likely to exist as a dimer, in which intramolecular π–π interaction is possible. Thus, the emissivity of salophen and its complexes is found to be governed by interplay of torsional motion and intermolecular interaction. Experiments have been performed at liquid nitrogen temperature, whereby conformational motion is arrested, but additional intermolecular interactions are not brought in. Maximal fluorescence of each of the three species studied is observed in this condition.

This article dealt with the ruthenium and osmium derivatives of isomeric 1H-indazole-3-carboxylic acid/2H-indazole-3-carboxylic acid (H2L1) and 1H-benzimidazole-2-carboxylic acid (H2L2) along with the π-acidic bpy (bpy = 2,2′-bipyridine) and pap (pap = 2-phenylazopyridine) co-ligands. It thus extended structurally authenticated monomeric ([(bpy)2RuII(HL1–)]ClO4[1]ClO4, (pap)2RuII(L12–) 2, (bpy)2OsII(L12–) 3, (pap)2OsII(L12–) 4, (bpy)2RuII(L22–) 5, (bpy)2OsII(L22–) 8, and (pap)2OsII(L22–) 9) and dimeric ([(bpy)2RuII(μ-L22–)RuII(bpy)2](ClO4)2[6](ClO4)2) complexes. It also described modified L2′2–(L2′2–= 2,2′-bisbenzimidazolate)-bridged [(pap)2RuII(μ-L2′2–)RuII(pap)2](ClO4)2[7](ClO4)2, where L2′2–was developed selectively with the {Ru(pap)2} metal fragment via in situ intermolecular C–C coupling of the two units of decarboxylated benzimidazolate. Moreover, chemical oxidation (OsIIto OsIII) of (bpy)2OsII(L12–) 3(E0= 0.11 V versus SCE) and (bpy)2OsII(L22–) 8(E0= 0.12 V versus SCE) by AgClO4yielded unprecedented OsIII-AgIderived polymeric {[(bpy)2OsIII-L12–-AgI(CH3CN)](ClO4)2}n{[10](ClO4)2}nand dimeric [(bpy)2OsIII-L22–-AgI(CH3CN)](ClO4)2[11](ClO4)2complexes as a function of transand cisorientations of the active N2 donor with special reference to the carboxylate O2 of L2–, respectively. Microscopic (FE-SEM, TEM–EDX, and AFM) and DLS experiments suggested a homogeneously dispersed hollow spherical shaped morphology of {[10](ClO4)2}nwith an average particle size of 200–400 nm as well as its non-dissociative feature in the aprotic medium. Experimental (structure, spectroscopy, and electrochemistry) and theoretical (DFT/TD-DFT) explorations revealed a redox non-innocent feature of L2–in the present coordination situations and the selective anion sensing (X = F–, CN–, and OAc–) event of [1]ClO4involving a free NH group at the backface of HL1–, which proceeded via the NH···X hydrogen bonding interaction.

Optical second-harmonic generation (SHG) is a reliable technique for probing material surface and interface characteristics. Here, we have demonstrated a non-destructive, contactless SHG-based semiconductor/dielectric interface characterization method to measure the conduction band offset and quantitatively evaluate charge densities at the interface in oxide and at the oxide surface. This technique extracts the interface-trapped charge type (donor/acceptor) and qualitatively analyzes the process-induced variation in interface states (Dit), oxide, and oxide surface state density. These qualitative and quantitative analyses provide us with a glimpse into the band bending. The metrology method is validated through a detailed characterization of the Si/HfO2interface. An optical setup has been developed to monitor the time-dependent second-harmonic generation (TDSHG) from the semiconductor/oxide interface. The temporal characteristics of TDSHG are explained with its relationship to the filling of Ditand spatio-temporal trapping of photoexcited charge in oxide and at the oxide surface. A numerical solver, based on plausible carrier dynamics, is used to model the experimental data and to extract the electronic properties at the Si/HfO2interface.

Förster resonance energy transfer (FRET) has been studied between fluorescein (donor, D) and rhodamine B (acceptor, A) bound covalently to the surface of silica nanoparticle (SNP-dye). This is a part of an ongoing effort toward development of light harvesting nanoantennae. The role of the D:A ratio and the total chromophore content on the efficiency of FRET has been investigated. At low number density (ca. 75 ± 15 dye molecules/particle) efficiency is dependent on the D:A ratio. It appears that the distribution of the dyes on the surface is inhomogeneous and that FRET occurs only between D and A molecules in very close proximity. The effect of self-quenching of the donor is not very significant for this number density. At higher number densities (ca. 700–1100 dye molecules/particle), a prominent rise in the acceptor emission is observed, perhaps indicating a more homogeneous distribution of the dye molecules, and D emission is quenched completely. However, D–D quenching is an issue here. So, it appears that the lower number density is a more favorable condition for FRET in these systems.