Saptarshi Mukherjee

The development of light-responsive metal nanoclusters (MNCs) for showcasing photoregulated biomimicking catalysis and developing light-mediated potent antibacterial agents remains a central attraction of the present research. However, strategic modulation of the electronic structure in MNCs to impart light-triggered biocatalysis and antibacterial activity is associated with formidable challenges. In this study, the multidimensionally served enzymatic features in tyramine-protected CuNCs (Cu@Tyra NCs) have been comprehensively investigated, which display efficient peroxidase-like activity and a biocatalytic cascade upon coupling with a suitable natural enzyme. Upon visible light activation, photoexcited charge carriers in the Cu@Tyra NCs promote the generation of a hydroxyl radical (•OH) as a reactive oxygen species (ROS), which significantly enhances the catalytic efficiency. The photoinduced ROS also imparts strong antibacterial effects against Gram-negative bacteria (Escherichia coli) by inducing oxidative damage to cell membranes and intracellular components, exclusively in the presence of light.

This work explores the frontier of chirality in copper nanoclusters (CuNCs), which exhibit strong room-temperature phosphorescence along with enhanced circularly polarized luminescence (CPL) at low temperature.

Thermally activated delayed fluorescence (TADF) in metal nanoclusters (MNCs) is an effective strategy to harvest the emission from the excited-triplet states. However, the applications of these TADF-active MNCs are limited by the use of hydrophobic ligands, which generally make these MNCs insoluble. Herein, we report the NIR-TADF emitting CuNCs that are highly water-soluble and display intense-red emission in the solid state. The atomic connectivity of the CuNCs was determined by SC-XRD technique. The delayed fluorescence phenomenon is validated by temperature-dependent photoluminescence studies, and the excited singlet–triplet energy gap (ΔE_ST) was experimentally estimated to be ∼98 meV, thereby substantiating the TADF mechanism. DFT calculations performed on the crystal geometry of the CuNCs further attested to the TADF mechanism along with the associated charge-transfer dynamics. Additionally, the CuNCs demonstrate excellent catalytic activity involving the reduction of ferricyanide and Methylene Blue, highlighting their multifunctional applications in the aqueous phase.

Reversible interconversion in atomically precise metal nanoclusters (MNCs) holds utmost significance in constructing new functional materials for multi-faceted applications and understanding the fundamental mechanism of structural evolution.

Herein, we investigated the molecular interactions of an antimalarial drug, hydroxychloroquine sulfate (HCQS), with liposome nanocarriers. Spectroscopic analyses revealed that in the presence of the anionic liposomes (DMPG), HCQS undergoes significant microenvironmental changes, including a marginal red shift in absorption, a 17 nm blue shift in emission, and a marked reduction in fluorescence lifetime, indicating a partial localization of the drug within the liposomal hydrophobic bilayer. Steady‐state and time‐resolved anisotropy measurements revealed the restricted probe mobility in liposomal environments. However, cholesterol‐dependent studies indicated that increased membrane rigidity reduced the HCQS‐liposome association interactions. Furthermore, solubilization of the anionic liposomes by a cationic surfactant, CTAB led to the complete release of the bound HCQS, with reversibility in spectral signatures. It is suggested that due to mixed micelle formation between CTAB and the lipid molecules, the drug gets released from the liposome environment. These findings highlight the interplay of electrostatic and hydrophobic forces in governing the HCQS–liposome association and provide valuable insights for rational design of liposome‐based drug delivery systems.

The enhanced catalytic activity (superactivity) of iron-depleted apo-human serum transferrin (apo-hTF) in the presence of cationic surfactants with varying chain lengths has been investigated in this work. The progress of ester hydrolysis of two different esterase substrates, para-nitrophenylacetate (PNPA) and 4-methylumbelliferylacetate (4-MUA), was monitored spectroscopically. Catalytic activity of apo-hTF gets enhanced with increasing concentrations of cationic surfactants, up to the micellar concentration, followed by a gradual decrease at postmicellar concentrations. However, the catalytic performance of the protein remained silent in its native form, in the presence of anionic and neutral surfactants, guanidinium hydrochloride-denatured conformation, temperature-induced aggregated form, and liquid-liquid phase-separated (LLPS) form of the protein. This work sheds light on the importance of the location and alignment of amino acids in the catalytic hub and the approachability of the substrate at the active site in micellar catalysis systems. These results provide new insights into enzyme-substrate interactions in the domain of micellar catalysis, potentially aiding the design of surfactant-based catalytic systems.

The study of protein behavior in water-dimethyl sulfoxide (DMSO) solvent mixture is of great interest in biophysical research, as DMSO is a widely used cosolvent in various experimental assays. However, investigating the behavior of intrinsically disordered proteins (IDPs) in a water-DMSO binary solvent mixture is still in its infancy. Herein, we present a comprehensive analysis of the behavior of β-casein (βCN), an IDP, in water-DMSO mixtures using a combination of steady-state fluorescence, time-resolved anisotropy, infrared spectroscopy, and fluorescence correlation spectroscopy (FCS), characterizing the protein stability and conformational dynamics. FCS analysis with Alexa-488-labeled βCN, revealed the variations in hydrodynamic radius with varying content of DMSO, signifying constrained mobility and expanded size of the protein. Further, fluorescence self-quenching of the fluorophore (Alexa-488) was analyzed to probe the conformational dynamics of βCN, with changes in the time constant suggesting protein unfolding followed by an assembly at higher DMSO content. These results were corroborated by infrared spectroscopy, where an increase in the amide-I absorption band indicated the formation of intermolecular antiparallel β-sheet aggregates. At higher DMSO concentrations, additional structural features were observed, which were further examined using optical and field emission scanning electron microscopy (FESEM).

Reported herein are long-lived, red-luminescent silver nanoclusters (AgNCs) protected by the small-molecule ligand thiolactic acid, which exhibit exceptional stability (shelf life exceeding three years, photostability ∼100%), water-solubility, and high biocompatibility, making them suitable for diverse applications such as sensing and live-cell imaging. The AgNCs display extremely sensitive (>2% K^-1) temperature-dependent luminescence, monitored by a dual approach of changes in photoluminescence intensity and excited-state lifetime, enabling precise local thermal environment monitoring with a very high-resolution temperature sensing down to subdegree levels (<0.5 K). MTT assay, confocal fluorescence imaging, and fluorescence lifetime imaging microscopy (FLIM) analysis of mammalian cells suggest that the non-cytotoxic AgNCs specifically stain lysosomes in live cells, functioning as an organelle-specific biomarker and providing critical insights into lysosomal dynamics and intracellular temperature fluctuations. The unique properties of these AgNCs, corroborated by detailed mechanistic studies, open new avenues for studying nanoscale subcellular physiology and developing temperature-sensitive diagnostics and preservation strategies.

Bile salts are highly hydrophobic biosurfactants known for their unconventional structure and abnormal micellization properties, which aid in several biological processes. The intrinsic hydrophobicity of bile salts plays a pivotal role during the binding interactions of these molecules with other biomolecules. The inhibition effects of three bile salts, sodium taurocholate (NaTC), sodium cholate (NaC), and sodium deoxycholate (NaDC), on the temperature‐induced aggregation of BSA are explored. The results acquired from the Thioflavin T (ThT) assay and circular dichroism (CD) experiments demonstrate that all three bile salts can inhibit the BSA aggregation. Additionally, NaDC can have a prominent aggregation inhibition propensity for BSA compared to the other two bile salts. The inhibitory action of three bile salts toward BSA aggregation followed a particular order, complementing their intrinsic hydrophobicity. Further, binding interactions of native BSA with bile salts are characterized by tryptophan fluorescence emission, fluorescence lifetime studies, site marker studies, isothermal titration calorimetry, and thermal melting experiments. The results of these studies substantiate that bile salts bind to the native protein through strong hydrophobic forces and provide significant stabilization to the native conformation of the protein, which subsequently impedes the protein from aggregating.