Cobalt-Catalyzed Deacylative Ipso-C-C Bond Functionalization: An Approach toward Indole-Acyloins and Its Photophysical Studies.

Selective functionalization of the indole-C3-C bond with aromatic/heteroaromatic 1,2-diketones has been uncovered for the first time. Cobalt catalyst was found to be an effective catalyst for this unusual transformation. This ipso-C-C bond functionalization occurred in the presence of easily available weakly coordinating groups such as ketone and ester. One of the salient features of this methodology is the in situ generation of water from hexafluoro-2-propanol which acts as a reactant for the removal of the pivaloyl/ester group in a deacylative manner. The plausible mechanism has been supported by DFT calculations. Moreover, photophysical studies show the potential utility of indole-C3-acyloin and indolo-fused carbazole, which could be used in photovoltaic and optoelectronic application.

The Importance of Spin-Polarized Charge Reorganization in the Catalytic Activity of D-Glucose Oxidase.

The front cover artwork is provided by Prof. Ron Naaman's group at the Weizmann Institute of Science. The image shows that direct electron transfer through GOx is governed by electron spins, which result from the chiral-induced spin selectivity (CISS) effect. Read the full text of the Research Article at 10.1002/cphc.202400033.

The Importance of Spin-Polarized Charge Reorganization in the Catalytic Activity of D-Glucose Oxidase.

The reaction of D-glucose oxidase (GOx) with D- and L-glucose was investigated using confocal fluorescence microscopy and Hall voltage measurements, after the enzyme was adsorbed as a monolayer. By adsorbing the enzyme on a ferromagnetic substrate, we verified that the reaction is spin dependent. This conclusion was supported by monitoring the reaction when the enzyme is adsorbed on a Hall device that does not contain any magnetic elements. The spin dependence is consistent with the chiral-induced spin selectivity (CISS) effect; it can be explained by the improved fidelity of the electron transfer process through the chiral enzyme due to the coupling of the linear momentum of the electrons and their spin. Since the reaction studied often serve as a model system for enzymatic activity, the results may suggest the general importance of the spin-dependent electron transfer in bio-chemical processes.

Assessing the impact of choline chloride and benzyltrimethylammonium chloride-based deep eutectic solvents on the structure and conformational dynamics of bovine serum albumin: a combined steady-state, time-resolved fluorescence and fluorescence correlation spectroscopic study.

Although deep eutectic solvents (DESs) are regarded as useful substitutes for both ionic liquids and common organic solvents for storage and applications of biomolecules, it is still unclear whether all DESs or only specific types of DESs will be suitable for the said purpose. In view of this, the current study aims to report on the structure and conformational dynamics of BSA in the presence of two DESs, namely ethaline (choline chloride:ethylene glycol) and BMEG (benzyltrimethyl ammonium chloride:ethylene glycol), having the same hydrogen bond donor but with a distinct hydrogen bond acceptor, so that how small changes in one constituent of a DES alter the protein-DES interaction at the molecular level can be understood. The protein-DES interaction is investigated by exploiting both ensemble-averaged measurements like steady-state and time-resolved fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and single-molecule sensitive techniques based on fluorescence correlation spectroscopy (FCS). Interestingly, the results obtained from these studies have demonstrated that while a very small quantity of BMEG completely unfolds the native structure of the protein, it remains in a partially unfolded state even at very high ethaline content. More interestingly, it has been found that at very high concentrations of BMEG, the unfolded protein undergoes enhanced protein-protein interaction resulting in the aggregation of BSA. All of the results obtained from these investigations have essentially suggested that both protein-DES interaction and interspecies interaction among the constituent of DESs play a crucial role in governing the overall stability and conformational dynamics of the protein in DESs.

Understanding the mechanism of the energy transfer process from non-plasmonic fluorescence bimetallic nanoparticles to plasmonic gold nanoparticles.

Understanding the fundamentals behind the photophysical response of a fluorescing species in the vicinity of plasmonic nanoparticles is of great interest due to the importance of this event in various applications. The present work has been carried out to throw light on how plasmonic nanoparticles electronically interact with non-plasmonic nanoparticles. Specifically, in this work, the excitation energy transfer (EET) from fluorescence bimetallic silver capped gold (F-AgAu) to gold nanoparticles (AuNPs) and how this process can be modulated by cetyltrimethylammonium bromide (CTAB) have been investigated at both ensemble average and single particle levels. Steady-state and time-resolved fluorescence studies have revealed that the fluorescence intensity and lifetime of F-AgAu in the presence of AuNPs are significantly quenched. Cyclic voltammetry (CV) and polarity-dependent studies have ruled out the possibility of an electron transfer mechanism. The increased non-radiative decay rate has substantiated that the photoluminescence quenching is due to excitation energy transfer from F-AgAu to AuNPs. Interestingly, investigations have revealed that the energy transfer efficiency is reduced from 87% to 28% in the presence of CTAB due to the formation of a CTAB bilayer over AuNPs. Analysis of the data by conventional EET, nano surface energy transfer (NSET), and stretched exponential models have firmly established that the EET process follows a 1/d4 distance dependence (NSET) rather than conventional 1/d6 distance dependence as predicted with the Förster resonance energy transfer model. Additionally, single particle level measurements through fluorescence lifetime imaging microscopy (FLIM) studies have clearly demonstrated that the surfactant (CTAB) can play an important role in controlling the EET process from non-plasmonic to plasmonic nanoparticles. The outcome of the present EET between two different classes of nanoparticles is expected to be useful in developing nanoscale systems for various optoelectronic applications.

Realization of a Model-Free Pathway for Quantum Dot-Protein Interaction Beyond Classical Protein Corona or Protein Complex.

Although in recent times nanoparticles (NPs) are being used in various biological applications, their mechanism of binding interactions still remains hazy. Usually, the binding mechanism is perceived to be mediated through either the protein corona (PC) or protein complex (PCx). Herein, we report that the nanoparticle (NP)-protein interaction can also proceed via a different pathway without forming the commonly observed PC or PCx. In the present study, the NP-protein interaction between less-toxic zinc-silver-indium-sulfide (ZAIS) quantum dots (QDs) and bovine serum albumin (BSA) was investigated by employing spectroscopic and microscopic techniques. Although the analyses of data obtained from fluorescence and thermodynamic studies do indicate the binding between QDs and BSA, they do not provide clear experimental evidence in favor of PC or PCx. Quite interestingly, high-resolution transmission electron microscopy (HRTEM) studies have shown the formation of a new type of species where BSA protein molecules are adsorbed onto some portion of a QD surface rather than the entire surface. To the best of our knowledge, we believe that this is the first direct experimental evidence in favor of a model-free pathway for NP-protein interaction events. Thus, the outcome of the present study, through experimental evidence, clearly suggests that NP-protein interaction can proceed by following a pathway that is different from classical PC and PCx.

Probing How Various Metal Ions Interact with the Surface of QDs: Implication of the Interaction Event on the Photophysics of QDs.

With an aim to understand the mechanism of interaction between quantum dots (QDs) and various metal ions, fluorescence response of less-toxic and water-soluble glutathione-capped Zn-Ag-In-S (GSH@ZAIS) QDs in the presence of different metal ions has been investigated at both ensemble and single-molecule level. Fourier transform infrared (FT-IR) spectroscopy has also been performed to obtain a molecular level understanding of the interaction event. The steady-state data reveal no significant change in QD emission for alkali and alkaline earth metal ions, while there is a decrease in fluorescence intensity for transition metal (TM) and some heavy transition metal (HTM) ions. Interestingly, a significant fluorescent enhancement (FE) (19-96%) of QDs is found for Cd2+ ions. Time-resolved fluorescence studies reveal that all the three decay components of QDs decrease in the presence of first-row TM ions. However, in the case of Cd2+, the shorter component is found to increase while the longer one decreases. The analysis of data reveals that photoinduced electron transfer is responsible for fluorescence quenching of QDs in the presence of first-row TM ions and destruction/removal of trap/defect states in the case of Cd2+ causes the FE. In FT-IR experiments, a prominent peak at 670 cm-1, corresponding to Cd-S stretching vibrations, indicates strong ground-state interactions between the -SH of GSH and Cd2+ ions. Moreover, a decrease in the diffusion coefficient of QDs in the presence of Cd2+ ions during fluorescence correlation spectroscopy (FCS) studies further substantiates the removal of GSH by Cd2+ from the surface of QDs. The optical output of this study demonstrates that ZAIS can be used for fluorescence signaling of various metal ions and in particular selective detection of Cd2+. More importantly, these results also suggest that Cd2+ can effectively be used for enhancing the fluorescence quantum yield of thiol-capped QDs such as GSH@ZAIS.

Highly efficient energy transfer from a water soluble zinc silver indium sulphide quantum dot to organic J-aggregates.

The present work has been carried out with the aim to design and develop an efficient light harvesting inorganic-organic hybrid nanoscale material by employing a less toxic, environment friendly inorganic substance and also to understand the mechanism of inter-particle electronic interaction between the inorganic and organic components of the nanomaterial. Specifically, the inorganic-organic hybrid associate has been made by integrating water soluble semiconductor (zinc-silver-indium-sulfide (ZAIS)) QDs and organic J-aggregates of a cyanine dye (S2165). The fabrication of the present nano-hybrid system has been achieved via electrostatically driven self-assembly of organic dyes over ZAIS QDs. The interaction between QD and J-aggregates has been investigated by using steady state and time resolved fluorescence measurements. Zeta potential measurements have also been performed to understand the role of electrostatic interaction and thermodynamic feasibility of the association process. The investigations have revealed that the energy transfer (ET) process between QD and J-aggregates was mediated through a dipole-dipole mechanism. Interestingly, data analysis based on Förster theory has further revealed that the ET from QD to J-aggregates is very high, indicating efficient electronic coupling between the inorganic QD and the organic J-aggregates. Zeta potential measurements and thermodynamic calculations have demonstrated that the interaction between QD and organic dye is electrostatically driven and the association of organic dyes over QDs is thermodynamically feasible. The outcome of the present study is expected to be helpful in designing efficient nanoscale light harvesting devices. Additionally, fluorescence microscopy and toxicity studies on the QDs have also shown their suitability for biological applications.

Interaction of Lysozyme with Monocationic and Dicationic Ionic Liquids: Toward Finding a Suitable Medium for Biomacromolecules.

With an objective to understand the differences in the behavior of monocationic and dicationic ionic liquids (ILs) in their interaction with protein, we have investigated the binding interaction of lysozyme enzyme with two monocation ionic liquids (MILs), [C3MIm][Br], [C6MIm][Br], and one dicationic ionic liquid (DIL), [C6(MIm)2][Br]2, by exploiting various experimental methods. These ILs are purposefully chosen so that the effect of both hydrophobicity and structural arrangements of the cationic moiety of ionic liquids (ILs), if any, on the interaction event is understood. Both average ensemble and single molecule pathways have been adopted to obtain a comprehensive picture. For ensemble averaged measurements, the interaction events have been investigated by steady-state and time-resolved fluorescence spectroscopy, whereas for single molecule measurements, fluorescence correlation spectroscopy (FCS) has been utilized. Additionally, the behavior of protein in the absence and presence of ILs has also been investigated through circular dichroism (CD) measurements. The investigations have revealed that MILs and DIL interact differently with the protein. In particular, as compared to MILs, the influence of DIL toward protein is observed to be significantly less in terms of change in the structure and dynamics of protein. The outcome of the present work has demonstrated that imidazolium-based DIL can be a better choice over MILs for retaining native structure of protein in aqueous medium.

Evidence of homo-FRET in quantum dot-dye heterostructured assembly.

With an aim to understand the intermolecular/particle interaction and the optical properties of the inorganic-organic hybrid nanostructured materials, Förster resonance energy transfer (FRET) between negatively charged CdS quantum dots (donor) and positively charged Oxazine 170 perchlorate (acceptor) has been investigated by employing steady-state and time-resolved fluorescence spectroscopy. Investigations revealed that size-dependent changes in the FRET efficiency of different QD-dye FRET pairs occurred mainly due to the electrostatic effects. Interestingly, the present study also reveals that at a higher concentration of dye molecules, aggregation occurs on the QD surface and the quenching of dye fluorescence occurs due to homo-FRET process. The homo-FRET process in this case has been established by exploiting steady-state fluorescence anisotropy measurements. The feasibility of aggregate formation and the homo-FRET interaction between the dye molecules has also been demonstrated through quantum mechanical calculations.