Photosensitizer-free singlet oxygen generation a charge transfer transition involving molecular O toward highly efficient oxidative coupling of arylamines to azoaromatics.

Photosensitizer (PS)-mediated generation of singlet oxygen, O (aΔ) is a well-explored phenomenon in chemistry and biology. However, the requirement of appropriate PSs with optimum excited state properties is a prerequisite for this approach which limits its widespread application. Herein, we report the generation of O (aΔ) direct charge-transfer (CT) excitation of the solvent-O (XΣ ) collision complex without any PS and utilize it for the catalyst-free oxidative coupling of arylamines to azoaromatics under ambient conditions in aqueous medium.

Biomolecular Condensation of Trypsin Prevents Autolysis and Promotes Ca-Mediated Activation of Esterase Activity.

The presence of Ca ions is known to facilitate the activity of trypsin-like serine proteases via structural stabilization against thermal denaturation and autolysis. Herein, we report a new and hidden regulatory role of Ca in the catalytic pathways of trypsin and α-chymotrypsin under physiological conditions. We discovered that macromolecular crowding promotes spontaneous homotypic condensation of trypsin via liquid-liquid phase separation to yield membraneless condensates over a broad range of concentrations, pH, and temperature, which are stabilized by multivalent hydrophobic interactions.

Macromolecular Crowding Promotes Re-entrant Liquid-Liquid Phase Separation of Human Serum Transferrin and Prevents Surface-Induced Fibrillation.

Protein aggregation and inactivation upon surface immobilization are major limiting factors for analytical applications in biotechnology-related fields. Protein immobilization on solid surfaces often requires multi-step surface passivation, which is time-consuming and inefficient. Herein, we have discovered that biomolecular condensates of biologically active human serum transferrin (Tf) can effectively prevent surface-induced fibrillation and preserve the native-like conformation of phase-separated Tf over a period of 30 days.

Coacervate-Based Plexcitonic Assembly toward Peroxidase-like Activity and Ultrasensitive Glucose Sensing.

Inbuilt catalytic centers anchored inside the confined architecture of artificial nanoreactors have gained tremendous attention owing to their vast applicability in various catalytic transformations. However, designing homogeneously distributed catalytic units with exposed surfaces in confined environment is a challenging task. Here, we have utilized quantum dot (QD)-embedded coacervate droplets (QD-Ds) as a confined compartment for the in situ synthesis of gold nanoparticles (Au NPs) without any additional reducing agent.

Biomolecular Condensates Regulate Enzymatic Activity under a Crowded Milieu: Synchronization of Liquid-Liquid Phase Separation and Enzymatic Transformation.

Cellular crowding plays a key role in regulating the enzymatic reactivity in physiological conditions, which is challenging to realize in the dilute phase. Enzymes drive a wide range of complex metabolic reactions with high efficiency and selectivity under extremely heterogeneous and crowded cellular environments. However, the molecular interpretation behind the enhanced enzymatic reactivity under a crowded milieu is poorly understood.

Synthetic Protocell as Efficient Bioreactor: Enzymatic Superactivity and Ultrasensitive Glucose Sensing in Urine.

It is believed that membraneless cellular condensates play a critical role in accelerating various slow and thermodynamically unfavorable biochemical processes. However, the exact mechanisms behind the enhanced activity within biocondensates remain poorly understood. Here, we report the fabrication of a high-performance integrated cascade bioplatform based on synthetic droplets for ultrasensitive glucose sensing.

Macromolecular Crowding-Induced Unusual Liquid-Liquid Phase Separation of Human Serum Albumin via Soft Protein-Protein Interactions.

Macromolecular crowding has a profound impact on the conformational dynamics and intermolecular interactions of biological macromolecules. In this context, the role of inert synthetic crowders in the protein-protein interactions of globular proteins is poorly understood. Here, using native human serum albumin (HSA) under physiological conditions, we show that macromolecular crowding induces liquid-liquid phase separation (LLPS) via liquid-like membrane-less droplet formation in a concentration- and time-dependent manner.

Kinetic and Mechanistic Insight into the Surfactant-Induced Aggregation of Gold Nanoparticles and Their Catalytic Efficacy: Importance of Surface Restructuring.

Understanding the fundamental interactions between plasmonic metal nanoparticles (MNPs) and small molecules is of utmost importance in various applications such as catalysis, sensing, drug delivery, optoelectronics, and surface-enhanced Raman spectroscopy. Herein, we have investigated the early stage of the aggregation pathway of citrate-stabilized Au NPs with surfactants and explored their catalytic efficacy. Our findings reveal that (17 ± 2)-nm-sized citrate-stabilized Au NPs undergo concentration and time-dependent aggregation with positively charged cetyltrimethylammonium bromide (CTAB).

Nanocatalysis under Nanoconfinement: A Metal-Free Hybrid Coacervate Nanodroplet as a Catalytic Nanoreactor for Efficient Redox and Photocatalytic Reactions.

Nature utilizes cellular and subcellular compartmentalization to efficiently drive various complex enzymatic transformations via spatiotemporal control. In this context, designing of artificial nanoreactors for efficient catalytic transformations finds tremendous importance in recent times. One key challenge remains the design of multiple catalytic centers within the confined space of a nanoreactor without unwanted agglomeration and accessibility barrier for reactants.

Highly Photostable and Two-Photon Active Quantum Dot-Polymer Multicolor Hybrid Coacervate Droplets.

Fabrication and precise control of the physicochemical properties of multifunctional organic-inorganic hybrid nanocomposites find great importance in various research fields. Herein, we report the fabrication of a new class of luminescent hybrid coacervate droplets from CdTe quantum dots (QDs) and a poly(diallyldimethylammonium chloride) (PDADMAC) aqueous mixture. The colloidal stability of these droplets has been explored over wide ranges of composition, pH, and ionic strength.

Insights into the Aggregation Behaviour of a Benzoselenadiazole-Based Compound and Generation of White Light Emission.

We have designed and synthesized the benzoselenadiazole (BDS) based donor-acceptor-donor (D-A-D) π-conjugated compound 4,7-di((E)styryl)benzo[2,1,3]selenadiazole (1). A single-crystal study of 1 shows J-type molecular aggregation in the solid state. The crystal packing of 1 shows head-to-head dimeric intermolecular assembly via Se⋅⋅⋅N interactions while staircase-type interlock molecular packing has occurred via Se⋅⋅⋅π interaction.

Surfactant-Induced Self-Assembly of CdTe Quantum Dots into Multicolor Luminescent Hybrid Vesicles.

Here, we report the interaction of mercaptosuccinic acid (MSA)-capped CdTe quantum dots (QDs) with hexadecyltrimethylammonium bromide (CTAB) surfactant and subsequent formation of self-assembled multicolor luminescent vesicles in aqueous medium. A continuous phase sequence from clear (C1) to turbid (T1), precipitate (P), turbid (T2), and clear (C2) has been observed for QD solution upon increasing the concentration of positively charged CTAB, indicating dynamic equilibrium between various self-assembled supramolecular structures. In contrast, no such changes have been observed in the presence of negatively charged sodium dodecyl sulfate and neutral Triton X-100 surfactants, indicating specific electrostatic interactions behind the observed phase separation behavior.

Synergistic Enhancement of Electron-Accepting and -Donating Ability of Nonconjugated Polymer Nanodot in Micellar Environment.

Understanding the fundamental electron-transfer dynamics in photoactive carbon nanoparticles (CNPs) is vitally important for their fruitful application in photovoltaics and photocatalysis. Herein, photoinduced electron transfer (PET) to and from the nonconjugated polymer nanodot (PND), a new class of luminescent CNP, has been investigated in the presence of N,N-dimethylaniline (DMA) and methyl viologen (MV) in homogeneous methanol and sodium dodecyl sulfate (SDS) micelles. It has been observed that both DMA and MV interact with the photoexcited PND and quench the PL intensity as well as excited-state lifetime in bulk methanol.

Tuning of resonance energy transfer from 4',6-diamidino-2-phenylindole to an ultrasmall silver nanocluster across the lipid bilayer.

Herein we have developed a simple liposome-based donor-acceptor system across the lipid bilayer using 4',6-diamidino-2-phenylindole (DAPI) as the donor and an ultrasmall ligand-capped silver nanocluster (Ag NC) as the acceptor. The process of Förster resonance energy transfer (FRET) between DAPI and the Ag NC across the liposome bilayer has been demonstrated using steady-state and time-resolved fluorescence spectroscopy. The synthesized Ag NCs with a majority of Ag and Ag cores have been characterized using FTIR, mass spectrometry, HRTEM, UV-Vis and PL spectroscopy.

Direct Evidence of Intrinsic Blue Fluorescence from Oligomeric Interfaces of Human Serum Albumin.

The molecular origin behind the concentration-dependent intrinsic blue fluorescence of human serum albumin (HSA) is not known yet. This unusual blue fluorescence is believed to be a characteristic feature of amyloid-like fibrils of protein/peptide and originates due to the delocalization of peptide bond electrons through the extended hydrogen bond networks of cross-β-sheet structure. Herein, by combining the results of spectroscopy, size exclusion chromatography, native gel electrophoresis, and confocal microscopy, we have shown that the intrinsic blue fluorescence of HSA exclusively originates from oligomeric interfaces devoid of any amyloid-like fibrillar structure.

Insights into the Thermodynamics of Polymer Nanodot-Human Serum Albumin Association: A Spectroscopic and Calorimetric Approach.

With the advent of newer luminescent nanoparticles for bioimaging applications, their complex interactions with individual biomolecules need to be understood in great detail, before their direct application into cellular environments. Here, we have presented a systematic and detailed study on the interaction between luminescent polymer nanodots (PNDs) and human serum albumin (HSA) in its free and ligand-bound state with the help of spectrophotometric and calorimetric techniques. At physiological pH (pH = 7.

Resonant excitation energy transfer from carbon dots to different sized silver nanoparticles.

The influence of size on the efficiency of the nanometal surface energy transfer (NSET) process between excited donors and different sized metal nanoparticles (NPs) is poorly explored in the literature. Here we present a systematic study by correlating the size of silver nanoparticles (Ag NPs) with the efficiency of excitation energy transfer (EET) from carbon dots (CDs) to Ag NPs. Three different sized citrate-capped Ag NPs with a mean hydrodynamic diameter of 39.

Effect of compartmentalization of donor and acceptor on the ultrafast resonance energy transfer from DAPI to silver nanoclusters.

The mechanism and dynamics of excitation energy transfer (EET) from photo-excited 4',6-diamidino-2-phenylindole (DAPI) to silver nanoclusters (Ag NCs) and its subsequent modulation in the presence of cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and Calf Thymus DNA (CT-DNA) have been demonstrated using steady-state fluorescence and femtosecond fluorescence upconversion techniques. The synthesized Ag NCs were characterized using FTIR, mass spectrometry, XPS, HRTEM, DLS, UV-Vis and PL spectroscopy. Mass spectrometric analysis reveals the formation of ultrasmall Ag4 NCs with a small amount of Ag5 NCs.

Insights into the morphology of human serum albumin and sodium dodecyl sulfate complex: A spectroscopic and microscopic approach.

Exploring and understanding the fundamental interaction between protein and surfactant is utmost important for various pharmaceutical and biomedical applications. However, very less is known about the arrangement of individual negatively charged sodium dodecyl sulfate (SDS) molecules on the human serum albumin (HSA). Here, we have investigated the morphology and mechanistic insights of complexation between HSA and SDS by means of photoluminescence (PL) spectroscopy, circular dichroism (CD) and PL microscopy using amine-functionalized silicon quantum dot (Si QD) as an external luminescent marker.

Luminescence turn-on/off sensing of biological iron by carbon dots in transferrin.

Iron is a key nutrient as well as a potential toxin for almost all living organisms. In mammalian cells, serum transferrin (Tf) is responsible for iron transport and its iron overload/deficiency causes various diseases. Therefore, closely regulated iron homeostasis is extremely essential for cellular metabolism.

Thermal luminescence quenching of amine-functionalized silicon quantum dots: a pH and wavelength-dependent study.

Understanding and resolving the mechanisms that affect the photoluminescence (PL) of Si QDs are of great importance because of their strong potential for optoelectronic and solar cell materials. In this article, the intrinsic exciton dynamics of water-dispersed allylamine-functionalized silicon quantum dots (Si QDs) have been explored as a function of temperature by means of steady-state and time-resolved PL spectroscopy. Significant PL quenching of Si QDs has been observed with increase in temperature from 278 K to 348 K.

Size-dependent penetration of carbon dots inside the ferritin nanocages: evidence for the quantum confinement effect in carbon dots.

The origin of the excitation wavelength (λex)-dependent photoluminescence (PL) of carbon dots (CDs) is poorly understood and still remains obscured. This phenomenon is often explained on the basis of surface trap/defect states, while the effect of quantum confinement is highly neglected in the literature. Here, we have shown that the λex-dependent PL of CDs is mainly due to the inhomogeneous size distribution.

Concentration-dependent reversible self-oligomerization of serum albumins through intermolecular β-sheet formation.

Proteins inside a cell remain in highly crowded environments, and this often affects their structure and activity. However, most of the earlier studies involving serum albumins were performed under dilute conditions, which lack biological relevance. The effect of protein-protein interactions on the structure and properties of serum albumins at physiological conditions have not yet been explored.

Microscopic evidence of "necklace and bead"-like morphology of polymer-surfactant complexes: a comparative study on poly(vinylpyrrolidone)-sodium dodecyl sulfate and poly(diallyldimethylammonium chloride)-sodium dodecyl sulfate systems.

Here, we report the microscopic evidence of "necklace and bead"-like morphology, which has long been the most widely accepted model for polymer-surfactant complexes. The lack of microscopic evidence of the initial complexation between surfactant and polymer has resulted in many contradictory reports in the literature. In this paper, we visualized these initial complexes formed between negatively charged surfactant sodium dodecyl sulfate (SDS) with neutral poly(vinylpyrrolidone) (PVP) and cationic poly(diallyldimethylammonium chloride) (PDADMAC) polymer through photoluminescence (PL) microscopy and atomic force microscopy (AFM) using silicon quantum dot (Si QD) as an external PL marker.

Spectroscopic investigation of interaction between bovine serum albumin and amine-functionalized silicon quantum dots.

We have investigated the dynamics and mechanistic details of the interaction between bovine serum albumin (BSA) and allylamine-capped silicon quantum dots (Si QDs) by means of fluorescence spectroscopy, circular dichroism (CD), and FTIR spectroscopy. The intrinsic fluorescence of BSA gets quenched in the presence of Si QDs due to ground-state complex formation. The binding stoichiometry and various thermodynamic parameters have been evaluated by using the van't Hoff equation.