Static quenching upon adduct formation: a treatment without shortcuts and approximations

An Investigation into Substitution-Kinetics, Biomolecular Responses and Multimodal Anticancer Potential of a Dihalide Pd(II) Complex

This study addresses a novel palladium dihalide complex, cis-[Pd(PCAH)Cl₂] (C1), as a promising anticancer agent. XRD analysis reveals a deformed square planar geometry stabilized by hydrogen bonds and π•••π interactions. The M-Cl bonds in C1 demonstrate susceptibility to nucleophilic substitution by 2,2'-bipyridine (Bpy), with kinetic parameters evaluated using spectrophotometry. Fluorometric and spectrophotometric investigations demonstrate that C1 binds to CT DNA and protein with an avidity of around 105 M-1. The interaction with DNA is multifaceted, employing covalent bonding and intercalation, as supported by viscosity measurements. Fluorescence lifetime experiments illustrate that C1 produces static dampening of BSA fluorescence, implying structural adjustments near the tryptophan residue, further corroborated by spectroscopic analyses. The pair's (BSA and C1) FRET distance has also been computed. In vitro cytotoxicity tests suggest that C1 selectively suppresses the growth of breast carcinoma, MDA-MB-231 with IC50=20±2.64 μM, while showing minimal effects on non-cancerous HEK-293 cells. The mechanism of action includes the creation of ROS, leading to mitochondrial apoptosis, as evidenced by various assays, including annexin-V-FITC/PI labeling. Overall, complex C1 exhibits encouraging promise as a selective anticancer drug with a ROS-triggered apoptotic mechanism, particularly effective against breast carcinoma MDA-MB-231 cells.

Coordination bonds as a tool for tuning photoconductance in nanostructured hybrid materials made of molecular antennas and metal nanoparticles

The synthesis of robust, versatile materials in which electrical conduction is enhanced by light irradiation is of prime importance for fields as varied as photodetectors, photodiodes, solar cells and light sensors. Hybrid materials offer the advantage of combining the robustness of an inorganic building block with the adaptability of a molecular subunit. Herein, we demonstrate the importance of properly investigating the nature of the chemical interactions between the constituent elements in order to optimize photoconductance within hybrid materials. To this end, platinum nanoparticle self-assemblies are synthesized in solution, including a series of zinc-porphyrins differentially functionalized with pyridine moieties in the meso position. The presence of coordinating groups on the molecular entities drastically reinforced both the structural cohesion of the system and its photoconductive properties.

A Fluorescent Covalent Organic Cage for Ultrafast Detection of Picric Acid and HCl Vapor Sensing

Covalent organic cages (COCs) have recently gained massive attention owing to their solution processability and structural flexibility. Herein, we report an amine-linked fluorescent COC (COC2) synthesized by adopting dynamic covalent imine chemistry followed by imine bond reduction and characterized with different spectroscopic techniques. The COC2 was utilized for highly sensitive, selective, and ultrafast detection of picric acid at the nanomolar level. The fluorescence quenching efficiency of PA towards the COC2 is 98.6 %, with a detection limit of 2.7 nM. PA sensing with the COC2, coated on a TLC plate and paper strip, exhibited an outstanding fluorescence quenching property. Furthermore, the COC2 unveiled solid-state acidochromism upon exposure to HCl acid fumes and was transferred back to the original form on exposure to NH3 vapors.

Color and fluorescence orthogonal dual-functional visual turn-on sensing for acidic and alkaline glyphosate and additive

In this work, benefitting from the sensitive pH-responsiveness of both meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS4) and calixpyridinium, and their controllable strong noncovalent interactions, the first orthogonal dual-functional visual sensor for simultaneously and separately detecting acidic and alkaline substances without interference by using UV-Vis absorption and fluorescence emission spectra with both "turn on" signal changes was constructed by the supramolecular assembly of calixpyridinium with TPPS4. Color and fluorescence orthogonal dual-functional visual "turn-on" sensing for acidic and alkaline glyphosate and additive by calixpyridinium-TPPS4 sensor was further practically applied. The preparation of this sensor is quite simple in an environmentally friendly water medium. Only 2 μM calixpyridinium and 3 μM TPPS4 are needed to construct this assembly sensor. This sensor has a good biocompatibility, a high selectivity and sensitivity. Moreover, calixpyridinium-TPPS4 sensor can also be applied as a thermal switch and a light controlled anti-counterfeit material.

Can conformational flexibility influence the self-assembly behavior and sensing efficacy of fluorogenic amphiphiles? A case study with bisbenzimidazole-based probes

In this work, we have explored the metal ion sensing properties of two bisbenzimidazole-based fluorescent probes, that differ in their conformational flexibility, in an aqueous medium. The compound with a flexible methyl spacer (1) experienced blue shifts in its absorption and emission maxima (along with a turn-off response) upon the addition of Hg2+ ions. On the contrary, the compound with a relatively rigid structure (2) showed red shifts in both its absorption and emission maxima (along with a turn-off response) when treated with Hg2+ under similar conditions. Detailed mechanistic studies indicated that compound 1 formed a 1 : 2 complex with the Hg2+ ions, where both the pyridine nitrogen ends and benzimidazole units are involved in the coordination. However, for compound 2, the binding stoichiometry changed to 1 : 1 and the Hg2+ ions remained connected only through the pyridine nitrogen ends. Not only did changes in the molecular level interactions alter the optical response, but they also altered the efficacy of the Hg2+ sensing; the degree of response was more prominent with compound 1 than that of compound 2. Also, it was observed that the addition of Hg2+ to compound 1 could dissociate the preformed aggregated structures of 1, while in the case of compound 2, the addition of Hg2+ promotes aggregate formation. The sensor was further utilized for analysis of real-life water samples and the detection of Hg2+ under intracellular conditions (HeLa cells).

Facile preparation of a hydrophilic Eu-based ratiometric fluorescent nanosensor for Cu2+ ion detection and imaging in living cells

In this work, a hydrophilic Eu-based ratiometric fluorescent nanosensor (PAAC-Eu) was developed for Cu2+ ion detection in aqueous solutions and imaging in living cells. The sensor was prepared via a simple one-step reaction at room temperature, leveraging the synergistic coordination of commercially accessible polyacrylic acid (PAA) and coumarin-3-carboxylic acid (CCAH) with Eu3+ ions. PAAC-Eu was easy to disperse in aqueous media and exhibited two characteristic emission bands at 406 nm and 618 nm, respectively, upon excitation at 350 nm. Cu2+ ions could bind with the free carboxyl groups in PAAC-Eu within 10 min, leading to a decrease in fluorescence at 618 nm (I618) and a negligible effect on fluorescence at 406 nm (I406). Accordingly, a rapid, sensitive and selective method for detecting Cu2+ ions was established, which could complete Cu2+ ion assay within 30 min. A good linear relationship was observed between I406/I618 and Cu2+ ion concentration at 0-20.0 μM (0-1.28 mg L-1) with a detection limit as low as 0.175 μM (11.2 μg L-1). The proposed method was successfully applied to quantify Cu2+ ions in real water samples. Moreover, a portable paper-based sensor was developed by loading PAAC-Eu in filter paper, which could enable visual detection of Cu2+ ions without using large instruments. Finally, cell experiments demonstrated the low cytotoxicity and good cell permeability of PAAC-Eu, and ratiometric fluorescence imaging of Cu2+ ions in living cells was successfully performed.

Astragalin Exerted Hypoglycemic Effect by Both Inhibiting α-Glucosidase and Modulating AMPK Signaling Pathway

BACKGROUND

The hypoglycemic activity of mulberry leaf polyphenols has been widely studied, while its mechanism of action needs further elucidation.

METHODS

The inhibitory activity mechanism of astragalin on α-glucosidase was investigated with a combination of multispectroscopic techniques and molecular docking. The hypoglycemic pathway was further revealed with a high-glucose human hepatocellular carcinomas (HepG2) cell model.

RESULTS

The results indicated that astragalin inhibited α-glucosidase with IC50 of 154.5 µM, which was the highest in potency among the main polyphenols from mulberry leaves. Astragalin could bind to α-glucosidase with a single inhibition site and quench its endofluorescence with a static quenching mechanism. Astragalin changed the secondary structure of α-glucosidase, and the decreased α-helix content, representing the un-folding conformation, resulted in the decreased activity. The molecular docking further indicated that two sustainable hydrogen bonds were generated between astragalin and α-glucosidase residue Ser-88 and Tyr-133. The main driving forces to form the astragalin-α-glucosidase complex were the van der Waals force and hydrogen bond. Astragalin at a concentration of 80 µg/mL obtained the best hypoglycemic effect by activating the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway.

CONCLUSIONS

This study provides new insights into the potential utilization of astragalin-rich foods in the improvement of diabetes mellitus.

Multitopic Corannulene-Porphyrin Hosts for Fullerenes: A Three-Layer Scaffold for Precisely Designed Supramolecular Ensembles

A method to synthesize cofacial dimeric porphyrins bearing eight corannulene units has been developed. It relies on the stability of octahedral CO-capped Ru(II) complexes linked by N-donor ligands. This specific arrangement provides an optimal scaffold to accommodate fullerenes by imposing corannulene groups at a precise distance and relative orientation. Their capabilities for C60 recognition have been thoroughly assessed, revealing that each system can encapsulate up to four guests, giving rise to a compact supramolecular van der Waals complex echoing a discrete donor-acceptor-donor trilayer offering significant potential properties for further exploitation.

Sensing features, on-site detection and bio-imaging application of a tripodal tris(hydroxycoumarin) based probe towards Cu2+/His

A new tripodal tris(hydroxycoumarin) based Schiff base, HCTN was synthesized and characterized by FT-IR, 1H NMR, 13C NMR and ESI-HRMS. The probe, HCTN exhibits cyan emission in DMSO/HEPES buffer (9:1, v/v) which selectively detects Cu2+ ion via turn-off fluorescence. The quenching of the fluorescence was due to the binding of the probe, HCTN towards paramagnetic Cu2+ ion resulting in chelation enhanced quenching effect (CHEQ). From the spectroscopic results, the limit of detection of Cu2+ ion was obtained as very low as 0.40 × 10-9 M. The complexation of the metal ion, Cu2+ towards the probe HCTN was confirmed by the ESI-HRMS and Job's plot analysis which supports 1:1 binding stochiometric ratio. In order to validate the affinity of Cu2+ ion towards histidine, the HCTN+Cu2+ system was utilized for the detection of histidine via turn-on mode by the metal displacement approach. The detection limit of His was found to be 7.31 × 10-10 M. In addition to the above, the probe was utilized for various detection applications such as paper strips, cotton swabs, logic gates and thin film applications. The probe, HCTN extends its application to the confocal bioimaging to sense the Cu2+ and Histidine intracellularly.

Post-Functionalization of Fluorinated Dibenzosulfone-Based Conjugated Polymer for Smart 'Turn-off' Sensing of Cu2+ Ions

Post-functionalization of conjugated polymeric backbone with various N-containing heterocycles through nucleophilic aromatic substitution reaction (SNAr) demonstrates crucial tailoring of their photophysical properties. This study explores an approach of post-polymerization modification of a fluorinated dibenzosulfone-based conjugated polymer aiming to incorporate functional groups having coordinating sites to bind metal ions. The resulting polymers, namely BDT-DBTS-IM, BDT-DBTS-TR, and BDT-DBTS-PY revealed successful substitution reactions with imidazole, triazole, and pyridine respectively, and showed significant changes in their absorption and emission properties. Notably, BDT-DBTS-IM demonstrated exceptional performance as a chemosensor, exhibiting a dramatic fluorescence turn-off response specifically to copper ions (Cu2+) with the limit of detection of 26 nM and Stern-Volmer quenching constant (KSV) of 8.2×105 Lmol-1. This high selectivity and sensitivity are attributed to the ability of the imidazole group to form a stable complex with Cu2+, resulting in both static and dynamic quenching efficiently. Our findings underscore the potential of post-polymerization modifications to significantly enhance the functionality of conjugated polymers. The ability of BDT-DBTS-IM to detect trace levels of copper ions with high precision highlights its practical utility in environmental and biological monitoring. This research not only demonstrates an approach for post-polymeric modification through SNAr reaction but also opens new avenues for developing sensors.

Synergistic optical sensing of heavy metal ions using Mesua Ferrea derived carbon dot embedded Alginate based biopolymeric film as a sensor platform

Widespread environmental pollution from heavy metals poses severe health hazards, necessitating advanced detection methods. This study presents an innovative approach utilizing Mesua Ferrea Carbon Dots (MFCDs) incorporated biopolymeric nanocomposite films for optical identification of heavy metal ions (Fe3+, Cd2+, Hg2+, Pb2+, Cu2+). A blend of Na-Alginate and Agarose biopolymer was prepared as a matrix. Hydrothermally synthesized MFCDs possess negative zeta potential with their characteristic photoluminescence property. The MFCDs incorporated Na-Alginate-Agarose biopolymeric nanocomposite (MAA) film displayed enhanced hydrophilicity and UV absorption behaviour, showcasing its potential for optical detection of heavy metal ions. The optical analysis like fluorescence intensity and photoluminescence lifetime studies of the MAA film in response to heavy metal ions were thoroughly studied. The interaction dynamics highlighted specific metal ion quenching capabilities, emphasizing the potential of MFCDs coated film for sensitive heavy metal detection. The quenching mechanism for Fe3+ ions underscored the lowest level of detection in comparison with Cd2+, Hg2+, Pb2+ and Cu2+ ions, contributing to a comprehensive understanding of the optical detection phenomenon. Our research work provides a robust and scientifically validated solid platform for development of economically viable and environmentally benign optical sensor as an alternative of other existing methods for detection of heavy metal ions.

Luminescent Fe(III) Complex Sensitizes Aerobic Photon Upconversion and Initiates Photocatalytic Radical Polymerization

Light energy conversion often relies on photosensitizers with long-lived excited states, which are mostly made of precious metals such as ruthenium or iridium. Photoactive complexes based on highly abundant iron seem attractive for sustainable energy conversion, but this remains very challenging due to the short excited state lifetimes of the current iron complexes. This study shows that a luminescent Fe(III) complex sensitizes triplet-triplet annihilation upconversion with anthracene derivatives via underexplored doublet-triplet energy transfer, which is assisted by preassociation between the photosensitizer and the annihilator. In the presence of an organic mediator, the green-to-blue upconversion efficiency ΦUC with 9,10-diphenylanthracene (DPA) as the annihilator achieves a 6-fold enhancement to ∼0.2% in aerated solution at room temperature. The singlet excited state of DPA, accessed via photon upconversion in the Fe(III)/DPA pair, allows efficient photoredox catalytic radical polymerization of acrylate monomers in a spatially controlled manner, whereas this process is kinetically hindered with the prompt DPA. Our study provides a new strategy of using low-cost iron and low-energy visible light for efficient polymer synthesis, which is a significant step for both fundamental research and future applications.

Melanin and Light

Melanin is responsible, in Nature, for photoprotection, for this reason it is expected to be poorly photoreactive. However, the photo-reactivity of melanin and related materials is well documented. Here we discuss some relevant recent examples to demonstrate that, indeed, the actual mechanism of interaction of melanin with light is complex and still not completely understood. Photochemical and photothermal processes are involved, giving a contribution that strongly depends on light wavelength and intensity. Moreover, some interesting experiments demonstrated that photochemical reactivity of melanin related compounds is likely to be indirect, in the sense that the effect of light is to increase the number of radical species rather than creating photoreactive excited state. These suggestions open-up new perspectives in the interpretation of the role of melanin in photoprotection and in the design of new melanin based photoactive materials for energy conversion, environmental remediation, and nanomedicine. Further complication is given by the role of atmospheric oxygen and humidity in the photoinduced processes. Beside this complexity of behavior makes it difficult a systematic understanding of the interaction of melanin with light, it surely strongly contributes to make the properties of melanin and related materials unique.

Spontaneous interactions between typical antibiotics and soil enzyme: Insights from multi-spectroscopic approaches, XPS technology, molecular modeling, and joint toxic actions

A large amount of antibiotics enters the soil environment and accumulates therein as individuals and mixtures, threatening the soil safety. However, there is little information regarding the influence of single and mixed antibiotics on key soil proteins at molecular level. In this study, setting sulfadiazine (SD) and tetracycline hydrochloride (TC) as the representative antibiotics, the interactions between these agents and α-amylase (an important hydrolase in soil carbon cycle) were investigated through multi-spectroscopic approaches, X-ray photoelectron spectrometry, and molecular modeling. It was found that both SD and TC spontaneously bound to α-amylase with 1:1 stoichiometry mainly via forming stable chemical bonds. The interactions altered the polarity of aromatic amino acids, protein backbone, secondary structure, hydrophobicity and activity of α-amylase. The SD-TC mixtures were designed based on the direct equipartition ray to comprehensively characterize the possible concentration distribution, and interactive effects indicated that the mixtures antagonistically impacted α-amylase. These findings reveal the binding characteristics between α-amylase and typical antibiotics, which probably influence the ecological functions of α-amylase in soil. This study clarifies the potential harm of antibiotics on soil functional enzyme, which is significant for the environmental risk assessment of antibiotics and their mixtures.

Purification, fibrinolytic activity and substrate binding of nattokinase from Bacillus subtilis: A rapid and sensitive detection for fibrinolytic activity of nattokinase

Nattokinase (NK, EC 3.4.21.62) is an alkaline serine protease secreted by B. subtilis, which has a strong fibrinolytic activity in vitro and in vivo. Here, we fermented NK using a B. subtilis strain and purified the protein, designed a peptide segment derived from fibrin as a substrate of NK. Based on fluorescence resonance energy transfer (FRET), we found that NK exhibits a high hydrolytic activity towards the peptide, with Km of 9.33 ± 1.28 μM, kcat of 0.20 ± 0.01 s-1, and kcat/Km of 21,436.23 s-1 M-1, demonstrating that the peptide is a substrate for NK. Furthermore, we investigated the binding of the substrate with NK by tryptophan fluorescence quenching, molecular docking and dynamics simulation. Fluorescence quenching showed that the substrate binds to NK mainly through hydrogen bonding and van der Waals forces, with dissociation constants KD of 13.73 and 21.24 μM at 25 and 35 °C, respectively. Molecular docking and dynamics analysis revealed that the substrate recognizes the active site of NK, and provides new information on the characteristics of the binding of the substrate with NK. Our study demonstrated a rapid and sensitive method for the quantitative measurement of fibrinolytic activity of NK based on the substrate, which is very reproducible and rapid with virtually complete results in approximately 20 min.

The lipase inhibitory effect of mulberry leaf phenolic glycosides: The structure-activity relationship and mechanism of action

The present study found for the first time that phenolic glycosides were an important material basis for mulberry leaves to inhibit lipase. The corresponding IC50 for hyperoside, rutin, astragalin and quercetin were 68, 252, 385 and 815 μg/mL respectively. The inhibitory effect was ranked as monoglycosides > phenolic hydroxyl groups > disaccharides on the benzone ring. Hyperoside bound to lipase in competitive inhibition type with one binding site, while the others bound to lipase in a mixed inhibition type by two similar sites. All four compounds altered the microenvironment and secondary conformation of lipase through static quenching. The docking score, stability, and binding energy were consistent with the compound inhibitory activity. The main binding between compounds and lipase amino acid residues were spontaneously though hydrophobic interactions and hydrogen bonding. The strong hydrogen bonds formed with SER-152 inside the lipase pocket, might be important for the strong inhibitory activity of hyperoside.

Polybrominated diphenyl ethers and polychlorinated biphenyls induced rice "diabetes" by disturbing the transport and decomposition of soluble sugars

Halogenated flame retardants in farmlands were observed to inhibit the growth of exposed crops. This study aimed to elucidate the mechanism of inhibition on rice by employing four representative polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs). The exposure to these contaminants at 200 nM led to a decrease of 0.63-0.95 fold in rice below-ground biomass and 0.49-0.66 fold in yield, and a corresponding 4%-10% increase in soluble sugars in leaves. PBDEs and PCBs were found to significantly disrupt the synthesis, decomposition, and transport of sugars in leaves, the three pivotal determinants of crop growth. Notably, these compounds promoted a 1.41- to 7.60-fold upregulation of the triose phosphate translocator, significantly enhancing soluble sugar synthesis. Conversely, a 0.45-0.97 fold downregulation was observed for sucrose transporters, thus impeding the leaf-to-shoot efflux of soluble sugars. Furthermore, PBDEs and PCBs were favorably bound to fructose-1,6-bisphosphate aldolase (FBA), inducing its substrate-specific dysfunction in fructose-1,6-diphosphate decomposition (3%-14%). Overall, PBDE and PCB exposure promoted a notable intracellular accumulation of soluble sugars in rice leaves, a typical symptom of plant diabetes, since the intensified synthesis of soluble sugars in leaves and the repressed decomposition and transportation of soluble sugars to other storage organs, thus impeding crop growth. This study provided an insightful understanding of the toxic effects and molecular mechanisms of halogenated flame retardants, highlighting their role in abnormal sugar accumulation and growth inhibition in crops and offering vital information for the risk assessment and administration of these compounds to guarantee the safety of agricultural products.

Efficient Energy and Electron Transfer Photocatalysis with a Coulombic Dyad

Photocatalysis holds great promise for changing the way value-added molecules are currently prepared. However, many photocatalytic reactions suffer from quantum yields well below 10%, hampering the transition from lab-scale reactions to large-scale or even industrial applications. Molecular dyads can be designed such that the beneficial properties of inorganic and organic chromophores are combined, resulting in milder reaction conditions and improved reaction quantum yields of photocatalytic reactions. We have developed a novel approach for obtaining the advantages of molecular dyads without the time- and resource-consuming synthesis of these tailored photocatalysts. Simply by mixing a cationic ruthenium complex with an anionic pyrene derivative in water a salt bichromophore is produced owing to electrostatic interactions. The long-lived organic triplet state is obtained by static and quantitative energy transfer from the preorganized ruthenium complex. We exploited this so-called Coulombic dyad for energy transfer catalysis with similar reactivity and even higher photostability compared to a molecular dyad and reference photosensitizers in several photooxygenations. In addition, it was shown that this system can also be used to maximize the quantum yield of photoredox reactions. This is due to an intrinsically higher cage escape quantum yield after photoinduced electron transfer for purely organic compounds compared to heavy atom-containing molecules. The combination of laboratory-scale as well as mechanistic irradiation experiments with detailed spectroscopic investigations provided deep mechanistic insights into this easy-to-use photocatalyst class.

Investigation of antitumor activity and albumin interaction of new sulfosalicylate-based complex by spectroscopic and computational approaches

In the present study, the drug delivery by albumin protein and antiproliferetaive activity of new transition metal complex i.e., [Pd (phen)(SSA)] (where phen and SSA represent 1, 10 phenanthroline and sulfosalicylic acid, respectively) was investigated. DFT (density functional theory) calculations were conducted at B3LYP level with 6-311G(d,p)/aug-ccpVTZ-PP basis set for the purpose of geometry optimization, frontier molecular orbital (FMO) analysis, molecular electrostatic potential (MEP), and natural bond orbital (NBO) analysis. Experimental tests were conducted to preliminarily assess the lipophilicity and antitumor activity of the metal complex, resulting in promising findings. In-silico prediction was accomplished to assess its toxicity and bioavailability. To evaluate the binding of the newly formed complex with DNA (which results in halting the cell cycle) or serum albumin protein (drug transporter to the tissues), in-silico molecular modeling was employed. Experimental results (spectroscopic and non-spectroscopic) showed that the new compound interacts with each biomolecule via hydrogen bond and van der Waals interactions. Molecular docking demonstrated the binding of this complex to the DNA groove and site I of BSA occurs mainly through hydrogen bonds. Molecular dynamics simulation confirmed the interactions between [Pd (phen)(SSA)] with DNA or BSA through stable hydrogen bonds.

A Highly Efficient Fluorescent Turn-Off Nanosensor for Quantitative Detection of Teicoplanin Antibiotic from Humans, Food, and Water Based on the Electron Transfer between Imprinted Quantum Dots and the Five-Membered Cyclic Boronate Esters

Teicoplanin has been banned in the veterinary field due to the drug resistance of antibiotics. However, teicoplanin residue from the antibiotic abuse of humans and animals poses a threat to people's health. Therefore, it is necessary to develop an efficient way for the highly accurate and reliable detection of teicoplanin from humans, food, and water. In this study, novel imprinted quantum dots of teicoplanin were prepared based on boronate affinity-based precisely controlled surface imprinting. The imprinting factor (IF) for teicoplanin was evaluated and reached a high value of 6.51. The results showed excellent sensitivity and selectivity towards teicoplanin. The relative fluorescence intensity was inversely proportional to the concentration of teicoplanin, in the range of 1.0-17 μM. And its limit of detection (LOD) was obtained as 0.714 μM. The fluorescence quenching process was mainly controlled by a static quenching mechanism via the non-radiative electron-transfer process between QDs and the five-membered cyclic boronate esters. The recoveries for the spiked urine, milk, and water samples ranged from 95.33 to 104.17%, 91.83 to 97.33, and 94.22 to 106.67%, respectively.

Study on the interaction mechanism of whey protein isolate with phosphatidylcholine: By multispectral methods and molecular docking

The elucidation of the interaction mechanism between phospholipids and milk proteins within emulsions is pivotal for comprehending the properties of infant formula fat globules. In this study, multispectral methods and molecular docking were employed to explore the relationship between phosphatidylcholine (PC) and whey protein isolate (WPI). Observations indicate that the binding constant, alongside thermodynamic parameters, diminishes as temperature ascends, hinting at a predominantly static quenching mechanism. Predominantly, van der Waals forces and hydrogen bonds constitute the core interactions between WPI and PC. This assertion is further substantiated by Fourier transform infrared spectroscopy, which verifies PC's influence on WPI's secondary structure. A detailed assessment of thermodynamic parameters coupled with molecular docking reveals that PC predominantly adheres to specific sites within α-lactalbumin, β-lactoglobulin, and bovine serum albumin, propelled by a synergy of hydrophobic interactions, hydrogen bonding, and van der Waals forces, with binding energies noted at -5.59, -6.71, and -7.85 kcal/mol, respectively. An increment in PC concentration is observed to amplify the emulsification properties of WPI whilst concurrently diminishing the zeta potential. This study establishes a theoretical foundation for applying the PC-WPI interaction mechanism in food.

Multi-Emission Carbon Dots Combining Turn-On Sensing and Fluorescence Quenching Exhibit Ultrahigh Selectivity for Mercury in Real Water Samples

Mercury is a ubiquitous heavy-metal pollutant and poses serious ecological and human-health risks. There is an ever-growing demand for rapid, sensitive, and selective detection of mercury in natural waters, particularly for regions lacking infrastructure specialized for mercury analysis. Here, we show that a sensor based on multi-emission carbon dots (M-CDs) exhibits ultrahigh sensing selectivity toward Hg(II) in complex environmental matrices, tested in the presence of a range of environmentally relevant metal/metalloid ions as well as natural and artificial ligands, using various real water samples. By incorporating structural features of calcein and folic acid that enable tunable emissions, the M-CDs couple an emission enhancement at 432 nm and a simultaneous reduction at 521 nm, with the intensity ratio linearly related to the Hg(II) concentration up to 1200 μg/L, independent of matrix compositions. The M-CDs have a detection limit of 5.6 μg/L, a response time of 1 min, and a spike recovery of 94 ± 3.7%. The intensified emission is attributed to proton transfer and aggregation-induced emission enhancement, whereas the quenching is due to proton and electron transfer. These findings also have important implications for mercury identification in other complex matrices for routine, screening-level food safety and health management practices.

Selective Hydrolysis of Ovalbumin by Zr-Based Lacunary Polyoxotungstate in Surfactant Solutions

This study aims to design an artificial metalloprotease based on a Zr-containing polyoxometalate Na8[Zr(W5O18)2] [Zr(W5)2] for the hydrolysis of ovalbumin (OVA) in the presence of different surfactants, which can be used in many areas of the biological and medical sciences, particularly for targeted proteolytic drug design. For this reason, parameters, including the free energy of binding, the chemical nature of amino acid residues, secondary structures, and electrostatic potentials, of Zr(W5)2-OVA and Zr(W5)2-OVA-surfactant were analyzed by molecular docking simulations. The investigations showed that the presence of surfactants decreases the binding affinity of Zr(W5)2 for OVA amino acids, and hydrogen bonds and van der Waals interactions are formed between Zr(W5)2 and OVA amino acids. Additionally, GROMACS further illustrated the significance of SDS and CTAB surfactants in influencing the conformational changes of the OVA that lead to selective protein hydrolysis. In agreement with molecular dynamics simulation results, the experimental analysis showed more protein hydrolysis for the Zr(W5)2-OVA-surfactant systems. For instance, circular dichroism spectroscopy indicated that Zr(W5)2-OVA-CTAB and Zr(W5)2-OVA-TX-100 were more hydrolytically efficient due to the increased level of β-structures rather than α-chains, which showed that surfactants can facilitate the accessibility of Zr(W5)2 to the cleavage sites by inducing partial unfolding of the OVA structure.

Ultrafast Electron Transfer from CuInS2 Quantum Dots to a Molecular Catalyst for Hydrogen Production: Challenging Diffusion Limitations

Systems integrating quantum dots with molecular catalysts are attracting ever more attention, primarily owing to their tunability and notable photocatalytic activity in the context of the hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR). CuInS2 (CIS) quantum dots (QDs) are effective photoreductants, having relatively high-energy conduction bands, but their electronic structure and defect states often lead to poor performance, prompting many researchers to employ them with a core-shell structure. Molecular cobalt HER catalysts, on the other hand, often suffer from poor stability. Here, we have combined CIS QDs, surface-passivated with l-cysteine and iodide from a water-based synthesis, with two tetraazamacrocyclic cobalt complexes to realize systems which demonstrate high turnover numbers for the HER (up to >8000 per catalyst), using ascorbate as the sacrificial electron donor at pH = 4.5. Photoluminescence intensity and lifetime quenching data indicated a large degree of binding of the catalysts to the QDs, even with only ca. 1 μM each of QDs and catalysts, linked to an entirely static quenching mechanism. The data was fitted with a Poissonian distribution of catalyst molecules over the QDs, from which the concentration of QDs could be evaluated. No important difference in either quenching or photocatalysis was observed between catalysts with and without the carboxylate as a potential anchoring group. Femtosecond transient absorption spectroscopy confirmed ultrafast interfacial electron transfer from the QDs and the formation of the singly reduced catalyst (CoII state) for both complexes, with an average electron transfer rate constant of ≈ (10 ps)-1. These favorable results confirm that the core tetraazamacrocyclic cobalt complex is remarkably stable under photocatalytic conditions and that CIS QDs without inorganic shell structures for passivation can act as effective photosensitizers, while their smaller size makes them suitable for application in the sensitization of, inter alia, mesoporous electrodes.

Synthesis, Crystal Structure, DFT and Fluorescence Quenching Study of Novel syringe aldehyde-derived hydrazinyl-imidazole Based Schiff base Chemosensor

In this study, we report a new syringe aldehyde-derived hydrazinyl-imidazole based fluorescent sensor (L) for sensitive detection of different inorganic quenchers (halide ions, bicarbonate ion, sulphide ion and transition metal ions). The chromophore (L) was obtained in good yield by the 1:1 condensation reaction of 2-hydrazino-4,5-dihydroimidazole hydrobromide and 4-hydroxy-3,5-dimethoxy benzaldehyde. L exhibited strong fluorescence in the visible region (around 380 nm) and its interaction with different quenchers was studied in details via fluorescence technique. For the halide ions series, its sensitivity is higher for NaF (Climit = 4 × 10- 4 M) than for NaCl while the fluorescence quenching occurred mainly through a dynamic process. Similar considerations were observed for HCO3- and S2- quencher too, when static and dynamic quenching take place simultaneously. Regarding transition metal ions, at a fixed ion concentration (4 × 10- 6 M), best performance was achieved for Cu2+ and Fe2+ (fluorescence intensity was reduced by 79% and 84.9% respectively), while for other metal ions, the sensor performance was evaluated and found to be very less (< 40%). Thus, minimum detection limits (10- 6 - 10- 5 M range) recommended the use of such derivatives as highly sensitive sensors capable to monitor delicate changes in varied environments.

Interactions of ferulic acid and ferulic acid methyl ester with endogenous proteins: Determination using the multi-methods

Ferulic acid (FA) and ferulic acid methyl ester (FAM) are important phenolic compounds in Baijiu. In this study, the interaction of FA and FAM with human serum albumin (HSA) and lysozyme (LZM) was investigated using multispectral methods and molecular dynamics simulation. FA and FAM could interact with HSA and LZM, changing the conformation and hydrophilicity of the protein. The quenching mechanisms of FA-HSA, FA-LZM, FAM-HSA, and FAM-LZM were all static-quenching. In the FA-HSA, FAM-HSA, and FA-LZM systems, the interaction forces were mainly hydrophobic interactions and hydrogen bonding. In the FAM-LZM system, the interaction forces were mainly hydrophobic interactions, hydrogen bonding, and van der Waals force. Common metal ions such as K+, Ca2+, Cu2+, Mg2+, and Mn2+ could affect the binding ability of FA and FAM to HSA and LZM. Moreover, FA and FAM could increase the stability of HSA and LZM, and the protein bound to FA/FAM was more stable than the free protein. FA and FAM had varying degrees of impact on the physiological activities of HSA and LZM. This study provides relevant information on the interactions and metabolic mechanisms of FA and its derivatives with endogenous proteins.

Elucidating binding mechanisms of naringenin by alpha-chymotrypsin: Insights into non-binding interactions and complex formation

As an inevitable parameter in the description of enzyme properties, the investigation of enzyme-ligand interactions has attracted a lot of attention. Alpha-Chymotrypsin (α-Chy) is essential for protein digestion and plays an important role in human health. Naringenin (NAG) as a potent antioxidant has recently been applied in the pharmaceutical industry. Using multispectral methods and computational simulation techniques, the binding strength of NAG to α-Chy was investigated in this research. UV-vis and fluorescence quenching data showed significant spectral changes upon binding of NAG to α-Chy. As demonstrated by fluorescence techniques, NAG could employ a static quenching process to decrease the intrinsic fluorescence of α-Chy. Both circular dichroism (CD) and FTIR spectroscopic analyses revealed that binding of NAG to α-Chy caused more flexible conformation. The slight increases in RMSD (0.06 nm) were observed for the NAG-(α-Chy) compound was supported by the results of thermal stability data. Docking computation confirmed that hydrogen and Van der Waals interactions are the important forces, which is in exact agreement with thermodynamics studies. Kinetic analysis of the enzyme showed an increase in activity, which was consistent, with the MD simulation results. The findings from the in-silico studies were in complete agreement with the experimental results.

Coulomb interactions for mediator-enhanced sensitized triplet-triplet annihilation upconversion in solution

Sensitized triplet-triplet annihilation upconversion offers an attractive possibility to replace a high-energy photon by two photons with lower energy through the combination of a light-harvesting triplet sensitizer and an annihilator for the formation of a fluorescent singlet state. Typically, high annihilator concentrations are required to achieve an efficient initial energy transfer and as a direct consequence the most highly energetic emission is often not detectable due to intrinsic reabsorption by the annihilator itself. Herein, we demonstrate that the addition of a charge-adapted mediator drastically improves the energy transfer efficiency at low annihilator concentrations via an energy transfer cascade. Inspired by molecular dyads and recent developments in nanocrystal-sensitized upconversion, our system exploits a concept to minimize intrinsic filter effects, while boosting the upconversion quantum yield in solution. A sensitizer-annihilator combination consisting of a ruthenium-based complex and 9,10-diphenylanthracene (DPA) is explored as model system and a sulfonated pyrene serves as mediator. The impact of opposite charges between sensitizer and mediator - to induce coulombic attraction and subsequently result in accelerated energy transfer rate constants - is analyzed in detail by different spectroscopic methods. Ion pairing and the resulting static energy transfer in both directions is a minor process, resulting in an improved overall performance. Finally, the more intense upconverted emission in the presence of the mediator is used to drive two catalytic photoreactions in a two-chamber setup, illustrating the advantages of our approach, in particular for photoreactions requiring oxygen that would interfere with the upconversion system.

Insights into the Mechanism of Tryptophan Fluorescence Quenching due to Synthetic Crowding Agents: A Combined Experimental and Computational Study

Intrinsic tryptophan fluorescence spectroscopy is an important tool for examining the effects of molecular crowding and confinement on the structure, dynamics, and function of proteins. Synthetic crowders such as dextran, ficoll, polyethylene glycols, polyvinylpyrrolidone, and their respective monomers are used to mimic crowded intracellular environments. Interactions of these synthetic crowders with tryptophan and the subsequent impact on its fluorescence properties are therefore critically important for understanding the possible interference created by these crowders. In the present study, the effects of polymer and monomer crowders on tryptophan fluorescence were assessed by using experimental and computational approaches. The results of this study demonstrated that both polymer and monomer crowders have an impact on the tryptophan fluorescence intensity; however, the molecular mechanisms of quenching were different. Using Stern-Volmer plots and a temperature variation study, a physical basis for the quenching mechanism of commonly used synthetic crowders was established. The quenching of free tryptophan was found to involve static, dynamic, and sphere-of-action mechanisms. In parallel, computational studies employing Kohn-Sham density functional theory provided a deeper insight into the effects of intermolecular interactions and solvation, resulting in differing quenching modes for these crowders. Taken together, the study offers new physical insights into the quenching mechanisms of some commonly used monomer and polymer synthetic crowders.

Efficient Hole Transfer from CdSe Quantum Dots Enabled by Oxygen-Deficient Polyoxovanadate-Alkoxide Clusters

A limitation of the implementation of cadmium chalcogenide quantum dots (QDs) in charge transfer systems is the efficient removal of photogenerated holes. Rapid hole transfer has typically required the ex situ functionalization of hole acceptors with groups that can coordinate to the surface of the QD. In addition to being synthetically limiting, this strategy also necessitates a competitive binding equilibrium between the hole acceptor and native, solubilizing ligands on the nanocrystal. Here we show that the incorporation of oxygen vacancies into polyoxovanadate-alkoxide clusters improves hole transfer kinetics by promoting surface interactions between the metal oxide assembly and the QD. Investigating the reactivity of oxygen-deficient clusters with phosphonate-capped QDs reveals reversible complexation of the POV-alkoxide with a phosphonate ligand at the nanocrystal surface. These findings reveal a new method of facilitating QD-hole acceptor association that bypasses the restrictions of exchange interactions.

Green one-step synthesis of mushroom-derived carbon dots as fluorescent sensors for Fe3+ detection

Blue photoluminescent carbon dots were synthesized from Lentinus polychrous Lèv. via a simple hydrothermal process without additional chemical reagents or functionalization. The carbon dots (hereafter referred to as LCDs) were quasi-spherical with an average diameter of 6.0 nm. The strong fluorescence emissions of LCDs were utilized as the basis of efficient turn-off probes for Fe3+. The quenching phenomenon could be used to rapidly determine Fe3+ concentrations in the range of 0.0-2.0 mM in aqueous solution, with a limit of detection (LOD) of 16 μM. In the presence of interference, LCDs demonstrated good sensitivity and selectivity towards Fe3+ in both solution-based and paper-based systems. The LCDs also exhibited excellent photostability and an eco-friendly nature, making them an ideal choice for environmental monitoring with significant potential for diagnostic applications.

(1-(4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-Bisfunctionalized 3- and 4-PEG: Synthesis and Photophysical Studies

Two new azaheterocycle-based bolas, such as (1-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-bisfunctionalized PEGs, were prepared via Cu-catalyzed click reaction between 2-(4-azidophenyl)-5-(aryl)-oxadiazole-1,3,4 and terminal ethynyls derived from PEG-3 and PEG-4. Due to the presence of two heteroaromatic cores and a PEG linker, these bola molecules are considered as promising fluorescent chemosensors for electron-deficient species. As a result of a well-pronounced "turn-off" fluorescence response towards common nitro-explosive components, such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), hard-to-detect pentaerythritol tetranitrate (PETN), as well as Hg²⁺ cation was observed.

Fluorescent sensing of non-steroidal anti-inflammatory drugs naproxen and ketoprofen by dansylated squaramide-based receptors

Bis-squaramide receptors L1-L4 bearing a dansyl moiety were synthesised and their potential applications as fluorescent probes towards non steroidal anti-inflammatory drugs naproxen and ketoprofen was investigated. A detailed photophysical characterization in CH₃CN/DMSO solution (9 : 1 v/v) was conducted and demonstrated that the two macrocyclic receptors L1 and L2 show good sensitivity towards ketoprofen with an ON-OFF fluorescent response, while the two open chain receptors L3 and L4 behave similarly with the three guests considered. DFT theoretical calculations carried out on L2 and L4 as model receptors allowed to propose a possible coordination mode towards the guests. Finally, ¹H-NMR spectroscopy in DMSO-d₆/0.5% water solution demonstrated that the four receptors interact with the considered guests via H-bonds.

Structural Insights into the Ligand–LsrK Kinase Binding Mode: A Step Forward in the Discovery of Novel Antimicrobial Agents

LsrK is a bacterial kinase that triggers the quorum sensing, and it represents a druggable target for the identification of new agents for fighting antimicrobial resistance. Herein, we exploited tryptophan fluorescence spectroscopy (TFS) as a suitable technique for the identification of potential LsrK ligands from an in-house library of chemicals comprising synthetic compounds as well as secondary metabolites. Three secondary metabolites (Hib-ester, Hib-carbaldehyde and (R)-ASME) showed effective binding to LsrK, with KD values in the sub-micromolar range. The conformational changes were confirmed via circular dichroism and molecular docking results further validated the findings and displayed the specific mode of interaction. The activity of the identified compounds on the biofilm formation by some Staphylococcus spp. was investigated. Hib-carbaldehyde and (R)-ASME were able to reduce the production of biofilm, with (R)-ASME resulting in the most effective compound with an EC50 of 14 mg/well. The successful application of TFS highlights its usefulness in searching for promising LsrK inhibitor candidates with inhibitor efficacy against biofilm formation.

Effect of positional isomerism on the excited state charge transfer dynamics of anthracene-based D-π-A systems

Understanding the dynamics of the back electron transfer (BET) rate of ion pairs from the electronically excited state of donor-acceptor systems is crucial for developing materials for organic electronics. The structure-property relationships in the organic molecular architectures play a key role in controlling the BET rate and have been utilized as a criterion to design systems with a reduced BET rate. Here, we examine the influence of isomerism on the BET rate in anthracene based systems, viz., (E)-2-(2-(anthracen-9-yl)vinyl)benzonitrile (ortho-CN) and (E)-3-(2-(anthracen-9-yl)vinyl)benzonitrile (meta-CN) with N,N-diethylaniline (DEA) in methylcyclohexane using time-resolved spectroscopy. The radical cation (DEA˙⁺) and the radical anion (ortho-CN˙^- or meta-CN˙^-) generated after photoexcitation show synchronous decay kinetics, and the rate constant of back electron transfer (k_BET) for the DEA/ortho-CN pair was 6.6 × 10⁴ s^-1, which is ca. 2 orders of magnitude lower compared with the DEA/meta-CN pair. The role of isomerism in providing resonance stabilization for the organic radicals is expected to have implications for strategies that retard charge recombination in photovoltaics. The role of the molecular structural features that dictate the kinetics for charge recombination has been further identified using quantum calculations.

Fluorescence Detecting of Paraquat and Diquat Using Host-Guest Chemistry with a Fluorophore-Pendant Calix[6]arene

Paraquat (PQ) and diquat (DQ), some of the most widely used herbicides in the world, both present a high mortality index after intentional exposure. In this paper, a fluorescence sensing method for PQ and DQ, based on host-guest molecular recognition, is proposed. Calix[6]arene derivatives containing anthracene or naphthalene as pendant fluorophore at their lower rim recognize DQ and PQ in hydroalcoholic solution with a broad linear response range at the μg L^-1 level concentration. The linear response ranges were found from 1.0 to 18 μg L^-1 with the detection limit of 31 ng L^-1 for paraquat, and from 1.0 to 44 μg L^-1 with the detection limit of 0.16 μg L^-1 for diquat. The recognition process is detected by following the decrease in the fluorescence emission consequent to complexation. The proposed quenching method has been applied to the determination of paraquat in drinking water samples.

A neutral mononuclear rhenium(I) complex with a rare in situ-generated triazolyl ligand for the luminescence "turn-on" detection of histidine

A rare in situ-generated mononuclear rhenium complex [Re(bpt)(CO)₃(NH₃)] (1, bpt = 3,5-bis(2-pyridyl)-1,2,4-triazolate) can be used as a "turn-on" luminescent probe for selectively sensing L-histidine against other amino acids. Compound 1 was prepared by reacting Re₂(CO)₁₀, 2-cyanopyridine and hydrazine with an in situ formed bpt ligand through cyclization via C-N and N-N couplings with its single-side chelating mode arrayed with respect to the Re center. Compound 1 was highly stable and showed a green light MLCT emission in DMF solution at 507 nm upon excitation at 360 nm. Interestingly, the emission from 1 could be quenched by the addition of metal ions such as Ni²⁺ and Cu²⁺ but the emission efficiently recovered with the introduction of histidine. However, histidine could only be selectively detected when a combination of compound 1 and Ni²⁺ was used. Therefore, the luminescence response of the Ni²⁺-modified compound 1 could be utilized as a "turn-on" probe for the selective detection of histidine. This work provides a simple method for developing new sensing platforms of a discrete metal complex based on rare in situ generation.

Polybrominated diphenyl ethers interact with the key protein involved in carbohydrate metabolism in rice

Rice exposed to organic pollutants such as polybrominated diphenyl ethers (PBDEs) usually experiences reduced biomass and increased soluble sugar content. This study showed that 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) led to increased glucose, fructose, and sucrose in rice leaves, accompanied by decreased photosynthetic rate and biomass. In order to identify the key enzyme that BDE-47 interacted with, a diazirine-alkynyl photoaffinity probe was designed, and photoaffinity labeling based chemoproteomics was conducted. Among all differentially expressed proteins, fructose-1, 6-bisphosphate aldolase (FBA) involved in carbohydrate metabolism was most likely the target protein of BDE-47. Spectral techniques and molecular docking analysis further revealed that the pollutant-protein interaction was driven by hydrophobic force. BDE-47 inhibited FBA catalytic efficiency by competing with its substrate, fructose-1, 6-diphosphate (F-1, 6-P), leading to soluble sugar accumulation, photosynthetic rate decline and biomass reduction. This study unraveled the influencing mechanism of PBDEs on rice by combining the novel photoaffinity labeling-based chemoproteomics with conventional proteomics. The improved knowledge on direct interaction between organic pollutants and proteins will help alleviate the harmful effects of soil pollution on plants.

Lectin-Fortified Cationic Copper Sulfide Nanoparticles Gain Dual Targeting Capabilities to Treat Carbapenem-Resistant Acinetobacter baumannii Infection

Targeted drug delivery maximizes the chance to combat infection caused by drug-resistant pathogens. Herein, lectin-fortified cationic copper sulfide (cCuS) nanoparticles were suggested for targeted adhesion to bacterial membranes and to enforce bacterial death. Jacalin, a lectin from jackfruit seed, was conjugated to fluorescein isothiocyanate (FITC), and its ability to recognize bacterial cell surface glycans was demonstrated. Jacalin formed a noncovalent complex with cCuS, which was investigated by fluorescence quenching measurements. The data revealed that jacalin-cCuS (JcCuS) had a good affinity with an association constant K a of 2.27 (± 0.28) × 104 M-1. The resultant JcCuS complex displayed excellent anti-infective activity against carbapenem-resistant Acinetobacter baumannii (CRAB). The minimum inhibitory concentration (MIC) of cCuS was 62.5 μM, which was 2-fold lower than that of the broad-spectrum antibiotic ciprofloxacin. Interestingly, the MIC of JcCuS was reduced to 15.63 μM, which was attributed to jacalin fortification. The mechanistic study unveiled that JcCuS affected the membrane integrity, depolarized the inner membrane, and produced excess reactive oxygen species to combat CRAB at a lower concentration compared to cCuS. A. baumannii formed a biofilm more readily, which played a critical role in pathogenesis and resistance in clinical settings. JcCuS (3.91 μM) displayed stronger antibiofilm activity without affecting the metabolic viability of CRAB. Microscopy analyses confirmed the inhibition of biofilm formation and disruption of the mature biofilm upon treatment with JcCuS. Furthermore, JcCuS hindered pellicle formation and inhibited the biofilm-associated virulence factor of CRAB such as exopolysaccharide, cell surface hydrophobicity, swarming, and twitching mobility. The anti-infective potential of JcCuS was demonstrated by rescuing CRAB-infected zebrafish. The reduction in pathogen proliferation in muscle tissues was observed in the treated group, and the fish recovered from the infection and was restored to normal life within 12 h. The findings illustrate that lectin fortification offers a unique advantage in enhancing the therapeutic potential of antimicrobials against human pathogens of critical priority worldwide.

A Fluorescent Cage for Supramolecular Sensing of 3-Nitrotyrosine in Human Blood Serum

3-Nitrotyrosine (NT) is generated by the action of peroxynitrite and other reactive nitrogen species (RNS), and as a consequence it is accumulated in inflammation-associated conditions. This is particularly relevant in kidney disease, where NT concentration in blood is considerably high. Therefore, NT is a crucial biomarker of renal damage, although it has been underestimated in clinical diagnosis due to the lack of an appropriate sensing method. Herein we report the first fluorescent supramolecular sensor for such a relevant compound: Fluorescence by rotational restriction of tetraphenylethenes (TPE) in a covalent cage is selectively quenched in human blood serum by 3-nitrotyrosine (NT) that binds to the cage with high affinity, allowing a limit of detection within the reported physiological concentrations of NT in chronic kidney disease.

Nontraditional Redox Active Aliphatic Luminescent Polymer for Ratiometric pH Sensing and Sensing-Removal-Reduction of Cu(II): Strategic Optimization of Composition

Here, redox active aliphatic luminescent polymers (ALPs) are synthesized via polymerization of N,N-dimethyl-2-propenamide (DMPA) and 2-methyl-2-propenoic acid (MPA). The structures and properties of the optimum ALP3, ALP3-aggregate and Cu(I)-ALP3, ratiometric pH sensing, redox activity, aggregation enhanced emission (AEE), Stokes shift, and oxygen-donor selective coordination-reduction of Cu(II) to Cu(I) are explored via spectroscopic, microscopic, density functional theory-reduced density gradient (DFT-RDG), fluorescence quenching, adsorption isotherm-thermodynamics, and electrochemical methods. The intense blue and green fluorescence of ALP3 emerges at pH = 7.0 and 9.0, respectively, due to alteration of fluorophores from -C(═O)N(CH₃ )₂ / -C(═O)OH to -C(O^- )═N⁺ (CH₃ )₂ / -C(═O)O^- , inferred from binding energies at 401.32 eV (-C(O^- )═N⁺ (CH₃ )₂ ) and 533.08 eV (-C(═O)O^- ), significant red shifting in absorption and emission spectra, and peak at 2154 cm^-1 . The n-π* communications in ALP3-aggregate, hydrogen bondings within 2.34-2.93 Å (intramolecular) in ALP3 and within 1.66-2.89 Å (intermolecular) in ALP3-aggregate, respectively, contribute significantly in fluorescence, confirmed from NMR titration, ratiometric pH sensing, AEE, excitation dependent emission, and Stokes shift and DFT-RDG analyses. For ALP3, Stokes shift, excellent limit of detection, adsorption capacity, and redox potentials are 13561 cm^-1 /1.68 eV, 0.137 ppb, 122.93 mg g^-1 , and 0.33/-1.04 V at pH 7.0, respectively.

Near-Infrared Light-Induced Photoresponse in Er3+/Li+-Codoped Y2O3/Poly(methyl methacrylate) Composite Film

We demonstrate Li⁺-doping engineering for improving the near-infrared (NIR) photoresponse in an Er³⁺-activated Y₂O₃ phosphor. We show that the rational incorporation of Li⁺ results in a large enhancement of the upconversion (UC) emission intensity up to 29 times upon excitation of NIR light. The improved UC properties could be associated with the enhanced dipole-dipole transition probability due to Li⁺-induced changes in the local site symmetry for Er³⁺ ions and improvement in the crystallinity of the samples. We further demonstrate the construction of UC phosphor/polymer composite films by attaching the UC phosphor/polymer composite film onto a Si-photoresistor. The device shows a large enhancement of the photovoltage response from 0.16 to 0.4 V in Li-doped samples under NIR light illumination. These results suggest an effective doping strategy for the improvement of the UC performance of the oxide phosphor and its wide applications in solar energy utilization and NIR response devices.

Crystal Packing-Driven Selective Hg(II) Ion Sensing Using Thiazolothiazole-Based Water-Stable Zinc Metal-Organic Framework

A soft acid-soft base interaction is highly predictable. However, we demonstrate how the crystal packing of the newly synthesized zinc framework [Zn₂(5-AIA)₂(DPTTZ)]·DMF (where 5-AIA = 5-aminoisophthalic acid, DPTTZ = N,N'-di(4-pyridyl)thiazolo-[5,4-d]thiazole, DMF = N,N'-dimethylformamide) directs an unexpected interaction between the soft acid Hg(II) and the hard base oxygen instead of having a soft center like nitrogen and sulfur in the system attributed to a strong solvent interaction and a favorable ionic radius of Hg(II) ion for oxygen chelation. This engenders selective Hg(II) ion sensing through a "turn-off" emission quenching in water (limit of detection = (2.174 ± 0.06) × 10^-9 M) along with natural water resources and in a broad pH range. A quantum-chemical calculation elucidates the turn-off quenching mechanism and favorable Hg(II) interaction with encompassed oxygen atoms inside the framework.

Isomerization-Induced Excimer Formation of Pyrene-Based Acylhydrazone Controlled by Light- and Solvent-Sensing Aromatic Analytes

Pyrene is a fluorescent polycyclic aromatic hydrocarbon, and it would be interesting to determine whether its C═N-based conjugate can be used for sensing of aromatic analytes at its supramolecular aggregated state. For this purpose, we have synthesized (E)-3,4,5-tris(dodecyloxy)-N'-(pyren-1-ylmethylene)benzohydrazide (Py@B) by alkylation, substitution, and the Schiff base reaction methodology. The E-isomer of Py@B (E-Py@B) exhibits a bright fluorescence due to excimer formation in nonaromatic solvents. Upon photoirradiation with λ = 254 nm, it exhibits E-Z isomerization across the C═N bond at a low concentration (10^-4 M), resulting in a quenched fluorescence intensity, and interestingly, upon photoirradiation with λ = 365 nm, the Z-isomer of Py@B returns to the E-isomer again, indicating that E-Z isomerization of Py@B is reversible in nature. The thick supramolecular aggregated morphology of E-Py@B changes to a flowery needlelike morphology after photoirradiation with λ = 254 nm. The UV-vis absorption band at 370 nm for 10^-4 M Py@B in methyl cyclohexane (MCH) is due to excimer formation for closer proximity of pyrene moieties present in E-Py@B and changes to the absorption peak at 344 nm for its Z-isomer formation. The fluorescence spectroscopy results also support the fact that the optimum concentration of the E-isomer of Py@B is 2 × 10^-4 M in MCH for excimer formation. From spectral results, it may be concluded that nonaromatic solvents assist in constructing the excimer, but aromatic solvents resist forming an excimer complex of E-Py@B. The fluorescent emission of E-Py@B in MCH is quickly quenched on addition of different aromatic analytes through both static and dynamic pathways. In the solid state, E-Py@B also senses aromatic vapors efficiently via fluorescence quenching. Absorbance spectra of a model molecule obtained using time-dependent density functional theory (TDDFT) calculations on a DFT-optimized structure indicate complex adduct formation between E-Py@B and aromatic analytes from the well-matched theoretical and experimental UV-vis spectra on addition of different analytes with E-Py@B.

A review on fluorescence spectroscopic analysis of water and wastewater

In recent years, the application of fluorescence spectroscopy has been widely recognized in water environment studies. The sensitiveness, simplicity, and efficiency of fluorescence spectroscopy are proved to be a promising tool for effective monitoring of water and wastewater. The fluorescence excitation-emission matrix (EEMs) and synchronous fluorescence spectra have been widely used analysis techniques of fluorescence measurement. The presence of organic matter in water and wastewater defines the degree and type of pollution in water. The application of fluorescence spectroscopy to characterize dissolved organic matter (DOM) has made the water quality assessment simple and easy. With the recent advances in this technology, components of DOM are identified by employing parallel factor analysis (PARAFAC), a mathematical trilinear data modeling with EEMs. The majority of wastewater studies indicated that the fluorescence peak of EX/EM at 275 nm/340 nm is referred to tryptophan region (Peak T1). However, some researchers identified another fluorescence peak in the region of EX/EM at 225-237 nm/340-381 nm, which described the tryptophan region and labeled it as Peak T2. Generally, peak T is a protein-like component in the water sample, where T1 and T2 signals were derived from the <0.20μm fraction of pollution. Therefore, a more advanced approach, such as an online fluorescence spectrofluorometer, can be used for the online monitoring of water. The results of various waters studied by fluorescence spectroscopy indicate that changes in peak T intensity could be used for real-time wastewater quality assessment and process control of wastewater treatment works. Finally, due to its effective use in water quality assessment, the fluorescence technique is proved to be a surrogate online monitoring tool and early warning equipment.

Modulating optical properties and interfacial electron transfer of CsPbBr3 perovskite nanocrystals via indium ion and chlorine ion co-doping

In this work, we demonstrated an in situ approach for doping CsPbBr₃ nanocrystals (NCs) with In³⁺ and Cl^- with a ligand-assisted precipitation method at room temperature. The In³⁺ and Cl^- co-doped NCs are characterized by the powder x-ray diffraction patterns, ultraviolet-visible, photoluminescence (PL) spectroscopy, time-resolved PL (TRPL), ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. Based on PL and TRPL results, the non-radiative nature of In³⁺-doping induced localized impurity states is revealed. Furthermore, the impact of In³⁺ and Cl^- doping on charge transfer (CT) from the NCs to molecular acceptors was investigated and the results indicate that the CT at the interface of NCs can be tuned and promoted by In³⁺ and Cl^- co-doping. This enhanced CT is attributed to the enlarged energy difference between relevant states of the molecular acceptor and the NCs by In³⁺ and Cl^- upon co-doping. This work provides insight into how to control interfacial CT in perovskite NCs, which is important for optoelectronic applications.