Exploring the mechanism of fluorescence quenching in two biologically active boronic acid derivatives using Stern-Volmer kinetics

Dual Stimulus Responsive GO-Modified Tb-MOF toward a Smart Coating for Corrosion Detection

Smart-sensing coatings that exhibit multistimulus response, rapid indication, and reusability are in urgent need to effectively enhance the practicability of coatings while accurately detecting metal corrosion. In this work, a reusable corrosion self-reporting coating with multiple pH and Fe3+ stimulus responses was first constructed by the integration of a composite fluorescent probe into the resin matrix. This composite sensor was constructed by combining a lanthanide metal-organic framework (Ln-MOF) based on terbium and trimeric acid (H3BTC) with graphene oxide (GO) nanosheets (GO@Tb-BTC). The incorporation of GO formed a sea-urchin-like structure, thereby increasing the specific surface area and active sites of the probe. The coatings were characterized by using electrochemical impedance spectroscopy (EIS), visual observation, and fluorescence spectrophotometry. The surface morphology, wettability, and adhesion of the coating samples were analyzed using SEM, XPS, hydrostatic contact angle test, and an adhesion test. EIS measurements in 3.5 wt % NaCl solution for 72 h demonstrated the superior corrosion protection performance of the 0.3 wt %/GO@Tb-BTC/WEP coating compared to blank coating, with the charge-transfer resistance reaching 4.33 × 107 Ω·cm2, which was 9.5 times higher than that of the pure coating. The bright green fluorescence of GO@Tb-BTC/WEP coating exhibited a turn-off response when there was an excess of OH-/H+, but it demonstrated a reversible turn-on fluorescence when the ambient pH returned to neutral. Furthermore, such Fe3+-triggered fluorescence quenching responded to concentrations as low as 1 × 10-6 M. The fluorescence quenching rate of both intact and damaged coatings surpassed that of visual and EIS detection methods. Significantly, the fluorescence in scratches was effectively quenched within 25 min using 0.3 wt %/GO@Tb-BTC/WPU coating for visual observation. GO@Tb-BTC demonstrated exceptional corrosion self-reporting capabilities in both epoxy and polyurethane systems, making it a versatile option beyond single-coating applications.

Interaction between the antioxidant compound safranal and α-chymotrypsin in spectroscopic fields and molecular modeling approaches

Among various herbal plants, saffron has been the subject of study in various medical and food fields. Among the compounds of saffron, safranal is one of them. Safranal is a monoterpene aldehyde. The precursor of safranal is called picrocrocin, whose hydrolysis leads to the production of safranal. picrocrocin has two sugar components and aglycone. sugar component was separated during the drying process of saffron and safranal is produced. Saffron is the cause of the saffron aroma. Previous studies have shown that safranal offers many benefits such as antioxidants, blood pressure regulation and anti-tumor qualities. On the other hand, α-Chy is an enzyme secreted by the pancreas into the intestine and then acts as an efficient protease. In this study, various methods, such as molecular dynamics (MD) simulation and molecular binding, and different spectroscopic techniques, as well as protein stability techniques, were used to investigate the possible interactions between safranal and α-Chy. UV spectroscopic studies were showing that the existence of safranal decreased α-Chy absorption intensity. safranal caused the intrinsic fluorescence of α-Chy to be quenched too. According to the Stern-Volmer equation, the interaction between safranal and α-Chy was of the static type. In thermodynamic calculations, the interaction between safranal and α-Chy was stabilized by hydrophobic forces. And it was found that this interaction continued spontaneously. These results were, thus, consistent with the Docking data simulation (with the negative ΔG° number and positive changes in enthalpy and entropy). The thermal stability of α-Chy was also measured, showing that its melting point was shifted to a higher threshold as a result of the interaction. also, MD simulation indicated that α-Chy became more stable in the presence of safranal. In this paper, all the results of the laboratory techniques were confirmed by molecular dynamic simulations, so the correctness of the results was confirmed. From this research, we hope to carefully observe the possible changes in the behavior and structure of the enzyme in the presence of safranal.Communicated by Ramaswamy H. Sarma.

The complexation of atmospheric Brown carbon surrogates on the generation of hydroxyl radical from transition metals in simulated lung fluid

Atmospheric particulate matter (PM) poses great adverse effects through the production of reactive oxygen species (ROS). Various components in PM are acknowledged to induce ROS formation, while the interactions among chemicals remain to be elucidated. Here, we systematically investigate the influence of Brown carbon (BrC) surrogates (e.g., imidazoles, nitrocatechols and humic acid) on hydroxyl radical (OH) generation from transition metals (TMs) in simulated lung fluid. Present results show that BrC has an antagonism (interaction factor: 20-90 %) with Cu2+ in OH generation upon the interaction with glutathione, in which the concentrations of BrC and TMs influence the extent of antagonism. Rapid OH generation in glutathione is observed for Fe2+, while OH formation is very little for Fe3+. The compositions of antioxidants (e.g., glutathione, ascorbate, urate), resembling the upper and lower respiratory tract, respond differently to BrC and TMs (Cu2+, Fe2+ and Fe3+) in OH generation and the degree of antagonism. The complexation equilibrium constants and site numbers between Cu2+ and humic acid were further analyzed using fluorescence quenching experiments. Possible complexation products among TMs, 4-nitrocatechol and glutathione were also identified using quadropule-time-of-flight mass spectrometry. The results suggest atmospheric BrC widely participate in complexation with TMs which influence OH formation in the human lung fluid, and complexation should be considered in evaluating ROS formation mediated by ambient PM.

Increasing detection sensitivity of fluorescent polymeric sensors containing fluorescein derivatives by Au NPs

New fluorescent polymeric sensors containing in situ photogenerated gold nanoparticles (Au NPs) and fluorescein-based copolymers are reported. They are tested as efficient fluorescent chemosensors for the sensitive detection of toxic divalent metal ions, such as Co²⁺, Cu²⁺, Cd²⁺, (UO₂)²⁺, Pb²⁺, Zn²⁺and Hg²⁺. Their fluorescence quenching process depends on the concentration of metal cations and is comparatively analyzed for both the starting copolymers and the corresponding hybrid materials. Thus, the best results are recorded for uranyl (4 × 10^-6 M) and copper ions (16 × 10^-6 M), respectively. The detection limits of the investigated hybrid materials are lower by an order of magnitude compared to the starting copolymers, while the fluorescence quenching mechanism mainly occurred by a dynamic process, following a linear Stern-Volmer relationship. Thus, the report fundamentally confirms the influence of small amounts of Au NP (2 wt%) on the improved sensitivity of the final fluorescent sensors.

Effect of halide ions on the fluorescence properties of 3-aminoquinoline in aqueous medium

Fluorescence (FL) quenching of 3-aminoquinoline (3AQ) by halide ions Cl - Br - and I - has been explored in an aqueous acidic medium using the steady-state and time-domain FL measurement techniques. The halide ions showed no significant change in the absorption spectra of 3AQ in an aqueous acidic medium. The FL intensity is strongly quenched by I - ions and the order of FL quenching by halide ions is I - > Br - > Cl - . The decrease in FL lifetime along with a reduction in FL intensity of 3AQ suggested the dynamic nature of quenching. The obtained value of K SV was 328 M - 1 for I - ions and 119 M - 1 for Br - ions and the value k q was around 1.66 × 10 10 M - 1 s - 1 and 6.02 × 10 9 M - 1 s - 1 , respectively. Thus, the observations suggest that the likely governing mechanism for FL quenching should be an electron transfer process and the involvement of the heavy atom effect.

Pyrene-Based Fluorescent Porous Organic Polymers for Recognition and Detection of Pesticides

Eating vegetables with pesticide residues over a long period of time causes serious adverse effects on the human body, such as acute poisoning, chronic poisoning, and endocrine system interference. To achieve the goal of a healthy society, it is an urgent issue to find a simple and effective method to detect organic pesticides. In this work, two fluorescent porous organic polymers, LNU-45 and LNU-47 (abbreviation for Liaoning University), were prepared using π-conjugated dibromopyrene monomer and boronic acid compounds as building units through a Suzuki coupling reaction. Due to the large π-electron delocalization effect, the resulting polymers revealed enhanced fluorescence performance. Significantly, in sharp contrast with the planar π-conjugated polymer framework (LNU-47), the distorted conjugated structure (LNU-45) shows a higher specific surface area and provides a broad interface for analyte interaction, which is helpful to achieve rapid response and detection sensitivity. LNU-45 exhibits strong fluorescence emission at 469 nm after excitation at 365 nm in THF solution, providing strong evidence for its suitability as a luminescent chemosensor for organic pesticides. The fluorescence quenching coefficients of LNU-45 for trifluralin and dicloran were 5710 and 12,000 (LNU-47 sample by ca. 1.98 and 3.38 times), respectively. Therefore, LNU-45 serves as an effective "real-time" sensor for the detection of trifluralin and dicloran with high sensitivity and selectivity.

Insights on the interaction mechanism of exemestane to three digestive enzymes by multi-spectroscopy and molecular docking

Exemestane is an irreversible steroidal aromatase inhibitor, typically used to treat breast cancer. As an anti-tumor drug, exemestane has more obvious side effects on the gastrointestinal tract. The purpose of this work is to investigate the combination of exemestane with three important digestive enzymes including pepsin (Pep), trypsin (Try) and α-Chymotrypsin (α-ChT) so as to analyze the mechanism of the gastrointestinal adverse effects causing by exemestane binding. Enzyme activity experiment showed that the enzyme activity of Pep was decreased in the presence of exemestane. Fluorescence spectra revealed that exemestane formed stable complexes with digestive enzymes, and the quenching mechanism of drug-digestive enzymes interaction were all static quenching. The binding constants of Pep, Try and α-ChT at 298 K were 2.34 × 10⁵, 1.45 × 10⁵, and 2.05 × 10⁵ M^-1, respectively. Synchronous fluorescence and 3D fluorescence spectroscopy showed that the conformation of exemestane was slightly changed after combining with digestive enzymes, and non-radiative energy transfer occurred. Circular dichroism results indicated that exemestane could change the secondary structure of digestive enzymes via increase the α-helix content and decrease in the β-sheet content. Thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) revealed that exemestane interacted with α-ChT through electrostatic force, and the binding force with Pep and Try was van der Waals interactions and hydrogen, which was basically consistent with the molecular docking results.

pH-responsive zwitterionic carbon dots for detection of rituximab antibody

Zwitterionic carbon dots (CDs) have received much attention as a result of good photostability, high biocompatibility, and high quantum yield. In this study, novel zwitterionic CDs were synthesized using a simple hydrothermal method of citric acid (CA) and l-histidine as carbon and nitrogen precursors, respectively. Prepared zwitterionic CDs have an average particle size of 4 nm diameter and showed green fluorescence with a peak at 530 nm when excited at 470 nm; quantum efficiency was 39.34% using rhodamine 6G as a baseline. The fluorescence intensity of zwitterionic CDs was quenched by rituximab in the range 0-400 μmol L^-1 , with a limit of detection of 27 μmol L^-1 . In addition, the synthesized zwitterionic CDs had low toxicity, good stability, and high selectivity and sensitivity sensing for rituximab, therefore zwitterionic CDs are a promising candidate for practical applications.

A novel and cost effective isatin based Schiff base fluorophore: a highly efficient “turn-off” fluorescence sensor for the selective detection of cysteine in an aqueous medium

We designed an efficient, sensitive, and selective chemosensor for the fluorimetric determination of cysteine.

Experimental and theoretical investigations on the interaction of l-methionine molecules with α-chymotrypsin in the aqueous solution using various methods

l-Methionine (l-Met) is one of the necessary amino acids that play unparalleled roles, influencing both the protein structure and metabolism. Understanding the interactions between proteins and small molecules can be realized by various perspectives, and this is significant for the progression of basic sciences and drug development. In this study, the variations in the stability, function, and structure of α-Chymotrypsin (α-Chy) in the presence of l-Met were investigated using spectroscopic and computational approaches. The results of the UV-vis absorption demonstrated that α-Chy had a maximum peak at 280 nm due to the Trp residue. Hyperchromism shift was seen in the presence of l-Met. Ground state system was formed in the presence of l-Met, as confirmed by the fluorescence studies. Fluorescence variations also revealed static quenching. The CD spectra also represented the alteration of the enzyme with an increase in the α-helix and a decrease in the β-sheet. The activity of α-Chy was incremented in the presence of l-Met. Therefore, l-Met served as an activator. Molecular docking results also indicated a negative amount for the Gibbs free energy of the binding of l-Met to the enzyme. α-Chy became more stable in the presence of l-Met, based on the molecular dynamics simulation.

Copolymer based multifunctional conducting polymer film for fluorescence sensing of glucose

A simple, rapid and effective fluorescence sensing platform has been fabricated using a fluorescent conducting polymer surface. For this purpose, a rhodamine based electroactive monomer (RDC) and a functional group containing monomer (SNS) have been copolymerized to develop a conducting polymer based sensor platform having a fluorescence and enzyme-binding surface on ITO electrode. The proposed fluorescence sensing mechanism for detection of glucose is related to the consumption of dissolved oxygen at the double layer of the electrode which is fluorescence quenching agent by glucose-GOx reaction. Concentration of glucose was investigated quantitatively from 0.05 to 1 mM via fluorescence signal measurement. This novel approach could be adapted for the production of various rapid and effective fluorescence sensing platforms for glucose.