Stern-Volmer Equation Research Articles

Examining the inhibitory potency of metal polyphenolic network–coated silver nanoparticles against amyloid fibrillogenesis of lysozyme

There are currently over forty degenerative diseases that are correlated with abnormal accumulation of peptide/protein aggregates in the human body, such as Alzheimer’s disease. Due to their unique physiochemical properties (e.g., small size, large surface-to-volume ratio, and facile surface modification), silver nanoparticles (AgNPs) have been considered potential substrates for designing inhibitors against amyloid fibrillogenesis. Metal polyphenolic network (MPN) that combines the characteristics of organic and inorganic components has been used to suppress amyloid fibril formation. This study is aimed at investigating the effects of MPN–coated AgNPs (MPN–AgNPs) on the in vitro amyloid fibrillogenesis of hen lysozyme (HEWL). The two types of MPN–AgNPs (Zn/MPN–AgNPs and Co/MPN–AgNPs) were synthesized through chemical reduction and metal chelation, and their particle sizes were determined to be in the range of 40–60 nm. The characterization of MPN–AgNPs by ζ–potential and transmission electron microscopy showed that the MPN–AgNPs had negative surface charge and spherical-shaped morphology. Furthermore, the elemental analysis demonstrated that the MPN was uniformly coated on the surface of AgNPs. The thioflavin T fluorescence results revealed that the Co/MPN–AgNPs showed a better percent of inhibition compared to Zn/MPN–AgNPs and TA–AgNPs. The kinetics data of amyloid fibril formation in the presence of MPN–AgNPs were analyzed using the sigmoidal curve, showing that the MPN–AgNPs reduced fibril growth rate and prolonged lag time. Our findings also demonstrated that MPN–AgNPs could effectively suppress HEWL aggregation upon binding to aggregation-prone regions. The quenching of intrinsic fluorescence of HEWL by MPN–AgNPs was found to be a static type. Moreover, the fluorescence quenching data were analyzed using the modified Stern-Volmer equation to determine the number of binding sites. Notably, our findings indicated that the binding between HEWL and MPN–AgNPs was mainly governed by hydrophobic interaction. This work offers an excellent example of utilizing MPN–based materials as anti-aggregating/anti-fibrillogenic nano-drugs for the treatment of amyloidosis.

Preparation of amorphous Nd/Dy-based metal organic framework@MXene for solar driven selective photocatalytic and serving as sensor for fluorescence quenching detection, and biological activity

The development of a new Neodymium/Dysprosium metal–organic framework, referred to as Nd/Dy-BTC MOF, based on benzene-1,2,4-tricarboxylic acid, has been achieved through an in situ growth process on 2D transition metal carbides (MXene) surfaces. This synthesis was conducted via a solvothermal method utilizing a solvent mixture of water, ethanol, and dimethylformamide. The primary objective of this research is to investigate the framework’s efficacy as a photocatalyst for the degradation of anionic dye, as well as its potential for sensing certain explosives. The Nd/Dy-MOF@MXene has been characterized by various analysis techniques. The prepared Nd/Dy-MOF@MXene was utilized as catalyst in selective degradation of methyl orange dye. The study examined the influence of pH and catalyst concentration, revealing that the catalyst achieves peak efficiency of 93.55% when exposed to sunlight in an acidic medium. The reusability of the catalyst shows the highest efficient photocatalyst after four cycles of reusability. The detection of explosives, specifically 2,4,6-trinitrophenol, through photoluminescence techniques has been conducted, utilizing the Stern-Volmer equation to evaluate the quenching efficiency. The findings indicated remarkable efficiency and selectivity of Nd/Dy-MOF@MXene for 2,4,6-trinitrophenol, achieving a quenching efficiency of 91%. Furthermore, the reusability tests demonstrated that Nd/Dy-MOF@MXene exhibits outstanding recyclability, maintaining performance over five cycles. The antibacterial activity of Nd/Dy-MOF@MXene was investigated against Gram-positive and Gram-negative strains due to indication of medicine properties of Nd/Dy-MOF@MXene.

Enhanced Deoxygenation of Solvents via an Improved Inert Gas Bubbling Method with a Ventilation Pathway.

We introduce an improved inert gas bubbling method for solvent deoxygenation, featuring a ventilation path alongside the inert gas inlet to enhance the efficiency and reproducibility. While essential for life, oxygen's reactivity can disrupt scientific and industrial processes by forming unwanted intermediates and deactivating catalysts, necessitating efficient deoxygenation methods. Traditional methods like freeze-pump-thaw (FPT) are effective but time-consuming, require stringent safety measures, and have potential limitations for use with aqueous and biological samples. Our enhanced inert gas bubbling method retains the simplicity and safety of conventional bubbling while achieving FPT-like deoxygenation efficiency, demonstrated by photoluminescence intensity and lifetime measurements in acetonitrile (ACN) and toluene (TOL). Simulations using a simplified kinetic model and the Stern-Volmer equation reveal that the added ventilation pathway reduces oxygen contamination in Ar gas bubbles, improving the deoxygenation efficiency. This method is widely applicable in academic and industrial fields, requiring consistent and efficient solvent deoxygenation.

An Extension of the Stern-Volmer Equation for Thermally Activated Delayed Fluorescence (TADF) Photocatalysts.

Fluorescence quenching experiments are essential mechanistic tools in photoredox catalysis, allowing one to elucidate the first step in the catalytic cycle that occurs after photon absorption. Thermally activated delayed fluorescence (TADF) photocatalysts, however, yield nonlinear Stern-Volmer plots, thus requiring an adjustment to this widely used method to determine the efficiency of excited state quenching. Here, we derive an extension of the Stern-Volmer equation for TADF fluorophores that considers quenching from both the singlet and triplet excited states and experimentally verify it with fluorescence quenching experiments using the commonly employed TADF-photocatalyst 4CzIPN, and multiple-resonance TADF-photocatalyst QAO with three different quenchers in four solvents. The experimental data are perfectly described by this new equation, which in addition to the Stern-Volmer quenching constants allows for the determination of the product of intersystem and reverse intersystem crossing quantum yields, a quantity that is independent of the quencher.

Fluorescence-Based Study of Oligonucleotide Interactions With Recombinant Proteins: Insulin, Interferon α2-β, Somatotropin, and Their Receptors

Background. Oligonucleotides (OLNs) can participate in a wide range of protein-ligand interactions and perform numerous cellular functions by forming structures that enable specific interactions with DNA, RNA, and proteins, what is crucial for many biological processes. Advances in understanding these interactions could lead to the development of new technologies for treating various diseases. However, the mechanism of interaction between proteins and OLNs is complex and still requires detailed study. More research is needed to fully elucidate this process and enhance our understanding of these biomolecular interactions. Objective. The aim of this study was to synthesize, purify, and investigate the interaction of OLNs with recombinant signaling proteins interferon α2-β and insulin with their receptors and somatropin by assessing binding strength using fluorescence spectroscopy. Methods. The interactions were analyzed using the Stern–Volmer equation in both general and modified forms, as well as the Hill equation. OLNs were synthesized via the solid-phase phosphoramidite method, purified through solid-phase extraction, and subsequently verified with a spectrophotometer. Results. Fluorometric titration revealed that OLNs bind to proteins within the medium affinity range, forming non-fluorescent complexes, with the most active interactions observed with shorter OLN. Positive cooperative binding of interferon to G20 and T20, and negative cooperative binding of insulin to C20 and A20, were identified. Additionally, negative cooperative binding of somatropin to C20 was observed. Conclusions. The study demonstrated the interaction between OLNs and recombinant signaling proteins and receptors through various binding mechanisms, which could potentially affect their conformation and biolo­gical activity. These findings have implications for the therapeutic use of OLNs in the context of signaling proteins and receptors.

A new three-dimensional modeling of fluorescence excitation-emission measurements to explore the interaction of hydroxychloroquine and DNA, and to quantify their binding constant

A new three-dimensional chemometric approach was introduced to explore the interaction of hydroxychloroquine (HCQ)-calf thymus deoxyribonucleic acid (DNA) and quantify binding constant using fluorescence excitation and emission measurements. The fluorescence excitation-emission spectra were recorded after gradual titration of HCQ with DNA. Then, the excitation and emission curves and relative concentrations of the drug and drug-DNA complex were quantitatively estimated using a three-dimensional model called Parallel Factor Analysis (PARAFAC) to a cubic fluorescence data array. The interaction of HCQ and DNA was predicted by applying newly modified Stern-Volmer equations to the relationship between the actual DNA concentration, and the HCQ concentration in the relative concentration profile of the PARAFAC model. In the PARAFAC application, the binding constants of the HCQ-DNA complex at 288, 298, and 310 K were found as 6.78 × 103, 5.07 × 103, and 3.74 × 103 L mol−1, respectively. From the temperature studies, the thermodynamic parameters (ΔS0= 3.528 J mol−1 K−1, ΔH0= −20.099 kJ mol−1 and ΔG0=-21.11, −21.12, and −21.19 kJ mol−1 at 288, 298, and 310 K, respectively) were calculated. The drug-DNA interaction is spontaneous due to negative ΔG0 values. The positive ΔS0 and negative ΔH0 values revealed the major role of the electrostatic force on the binding of HCQ to DNA. Assay results obtained from the proposed three-way modeling were compared to those provided by the traditional spectrofluorimetric method.

Exploiting cyanide anion detection in food samples and for constructing logic gates by turn-off fluorescent chemosensor

A high-performance turn-off fluorescent chemosensor MSAP was developed for the selective sensing of cyanide anion without any interferences from other competing anions. MSAP's spectral responses to cyanide anion have been investigated by UV–vis and fluorescence spectroscopy. The limit of detection of cyanide anion was about 2.8 μM, which is much less than the WHO acceptable threshold level. The binding stoichiometry between the MSAP and cyanide anion was about 1:1, which was well augmented by Job`s plot. The quenching constant between MSAP and CN− ion calculated from the Stern-Volmer equation was about 8.7351×104M−1. The proposed detection mechanism of MSAP for the sensing of cyanide anion was further demonstrated by 1H NMR titration, ESI-MS and by density functional theory (DFT) studies. At last, probe MSAP was fruitfully exploited to analyse the presence of cyanide ion in diverse food samples and a XOR molecular logic gate was fabricated.

Impedance Spectroscopy Unveiled the Surfactant-Induced Unfolding and Subsequent Refolding of Human Serum Albumin.

Protein-surfactant interaction is a dynamic interplay of electrostatic and hydrophobic forces that ensues from the folding of a protein. We employ impedance spectroscopy (IS), a label-free method, to investigate the unfolding and refolding of human serum albumin (HSA), a globular plasma protein, in the presence of two surfactants: polysorbate-20 (Tween-20), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. The equivalent electrical analog circuit was predicted from impedance spectra of HSA in an aqueous solution at physiological pH and room temperature, focusing on varying the concentration of codissolved surfactants. A change in the dielectric constant (ε') and ionic conductivity (κ) is observed by comparing the surfactant-treated protein samples to the bare surfactant solutions to assess the conformational changes induced by surfactants in HSA. Far-UV circular dichroism analysis revealed a decrease in α-helices and an increase in β-sheets and random coils upon SDS addition, which were reversed by Tween-20. Dynamic light scattering supported the findings by measuring changes in the hydrodynamic diameter (dh) of HSA. Unfolding and refolding of HSA with surfactants were also observed through photoluminescence spectroscopy by examining the microenvironment surrounding the single tryptophan (W) within the protein, and the thermodynamic parameters were obtained using the modified Stern-Volmer equation. Our research explores the intriguing domain of protein-surfactant interactions, offering insights with promising applications across diverse biological processes and IS as a suitable alternative technique for investigating protein conformational changes by studying the electrical response of the samples.

The interaction between resveratrol and catalase was studied by multispectral method and molecular docking simulation

In this research, we delved into the interaction mechanism between Resveratrol (RES) and Catalase (CAT) utilizing a suite of advanced analytical techniques, including multispectral analysis and molecular docking simulation. A comprehensive assessment of their binding characteristics, modalities, distances, and the subsequent impact on CAT's secondary structure was conducted through fluorescence spectroscopy, ultraviolet spectroscopy, circular dichroism, three-dimensional fluorescence spectroscopy, synchronous fluorescence spectroscopy, and molecular docking simulation. By employing the Stern-Volmer equation to determine KSV and Kq values, Our findings indicate that the RES-CAT interaction results in static fluorescence quenching, By conducting experiments, the binding constant KA and the number of binding sites n for CAT and RES were determined, with the number of binding sites n being close to 1, indicating the presence of a specific binding site between CAT and RES. Parameters at 298 K. The negative values of ΔH and ΔS suggest that van der Waals forces and hydrogen bonding are predominant in mediating the interaction between CAT and RES. The negativity of ΔG indicates the spontaneity of the reaction. The Fӧrster resonance energy transfer theory calculation revealed a binding distance of 4.917 nm, substantiating the occurrence of non-radiative energy transfer between RES and CAT. Furthermore, the UV-VIS absorption spectrum, synchronous fluorescence spectrum, three-dimensional fluorescence spectrum, and circular dichroism analyses collectively demonstrated that RES induces alterations in CAT's secondary structure, augmenting the polarity around tryptophan (Trp) residues, reducing hydrophobic interactions, and bolstering hydrophilicity. This work offers novel insights into the antioxidant mechanisms of resveratrol within biological systems and holds significant theoretical and practical implications for the medical application and development of resveratrol.

Fabrication of Glucose Fluorescent Aptasensor Based on CdTe Quantum Dots.

Diabetes is a chronic metabolic disease characterized by high blood glucose (or blood sugar) levels, which harms the heart, blood vessels, eyes, kidneys, and nerves over time. So, it is crucial to regularly control glucose concentration in biological fluids to check its targets, reduce unpleasant symptoms of high and low blood sugar, and avoid long-term diabetes complications. This study developed a simple, rapid, sensitive, and cost-effective fluorescence system for glucose determination. The fluorescent Aptasensor was fabricated using cadmium telluride quantum dots (CdTe QDs) modified with thioglycolic acid and functionalized with thiol-glucose-aptamer through ligand exchange. The thiol-glucose-aptamer interacted directly with CdTe QDs, increasing fluorescence intensity. However, it decreased when the target molecules of glucose were introduced. The structural and morphological characteristics of the Aptasensor were confirmed by various analytical methods such as UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). According to the typical Stern-Volmer equation, the relationship between fluorescent quenching and target concentration was linear with a detection limit (LOD) of 0.13 ± 1.95 × 10-11 mol L-1 and a relative standard deviation (RSD) of 1.05%. The Aptasensor demonstrated high specificity towards the target and stability over 28 days. Furthermore, it detected glucose in human serum and urine with a recovery rate of up to 99.74%. The results indicate that the fluorescent Aptasensor could be valuable in developing robust sensing technology for low-concentrated analytes.

Investigation of the Sensing Properties of Lanthanoid Metal-Organic Frameworks (Ln-MOFs) with Terephthalic Acid.

The solvothermal synthesis of LnCl3.nH2O with terephthalic acid (benzene-1,4-dicarboxylic acid, H2BDC) produced metal-organic frameworks (LnBDC), [Ln2(BDC)3(H2O)4]∞, where Ln = Sm, Eu, Tb, and Dy. The materials obtained were characterized by a number of physico-chemical techniques. The influence of the ionic radius of the lanthanides on the microstructural characteristics of the Ln-MOFs was evaluated by performing Rietveld refinement. The MOFs obtained were tested as fluorescent sensors for numerous cations and anions in water. The highly luminescent EuBDC and TbBDC demonstrated multi-responsive luminescence sensing functions to detect Ag(I), Fe(III), Cr(III), and Cr(VI), which are essential for their environmental applications. By applying the non-linear Stern-Volmer equation, the fluorescent quenching mechanism was determined. The stability of the obtained materials in water in a wide pH range (acidity pH = 4 and alkalinity pH = 9 solutions) was confirmed.

π-π conjugated PDI supramolecular regulating the photoluminescence of imine-COFs for sensitive smartphone visual detection of levofloxacin

As the contamination and enrichment in food chain of levofloxacin (LV) antibiotics have caused a significant threat to life safety, the instant detection of LV has become an urgent need. Here, a PDI-functionalized imine-based covalent organic framework (PDI-COF300) was prepared by the electrostatic self-assembly method as fluorescent probe for smartphone visual detection of LV, which exhibited excellent fluorescence quantum yield (82.68%), greater stability, high sensitivity with detection limit of 0.303 μM. Based on the results of molecular docking and Stern-Volmer equation, the LV detection by PDI-COF300 was mainly a static quenching process through π-π stacked hydrophobic interactions and fluorescence resonance energy transfer. Besides, PDI-COF300 was applied to LV detection in environmental medium and milk samples with recoveries from 85.56% to 108.34% and relative standard deviations <2.70%. This work also provided a new general strategy for using PDI-COF in smartphone devices and fluorescent papers for LV fluorescence detection and microanalysis.

Investigation on Heterostructured SeO2–TiO2 Nanofluoroprobe for Highly Selective and Sensitive Detection of a Neonicotinoid Insecticide, Imidacloprid in Soil and Water Matrixes

Heterostructured SeO2–TiO2 nanoparticles were used as a highly sensitive and selective fluoroprobe for the detection and determination of neonicotinoid insecticide imidacloprid. The sonication-assisted co-precipitation technique was used to create nanoparticles, which were then characterized using UV–Vis, SEM–EDS, HRTEM, XRD, and TGA. These analyses revealed that the nanoparticles had globular morphology, a crystallite size of 14 nm, a bandgap of 2.45 eV, and stability at high temperatures. Fluorescence emission at 548 nm wavelength exhibits high sensitivity and selectivity for imidacloprid over other pesticides with complete fluorescent quenching at 2 × 10–4 M concentration of imidacloprid. Stern–Volmer equation and thermodynamic parameters applied to the experimental data over a temperature range of 20–50 °C provide the Ksv value in the range of 1.56 × 105 to 2.69 × 105 M−1 and indicate strong interactions, dynamic, spontaneous, and endothermic quenching process. Furthermore, the excellent salient features and notably the unaffected performance even in the presence of various anions, fertilizer, and binary mixture of pesticides often sprayed on plants, will pave the way for the development of rapid, affordable, selective fluoroprobe for onsite monitoring of imidacloprid. The reliability for determination is also examined for spiked soil samples to develop a hybrid SeO2–TiO2 nanoparticles fluoroprobe as a simple alternative to existing techniques for the detection of imidacloprid.Graphical

Pyranine Interaction with Amines in Micelles.

The fluorescence behavior of pyranine in anionic micellar system of sodium dodecyl sulphate was studied in the presence of selected amines. The amines included cyclopropylamine (CPA), ethylenediamine (EDA), benzylamine (BA), dibutylamine (DBA), cyclohexylamine (CHA), and polyethylenediamine (PEDA). All the studied amines quenched the intensity of pyranine. Study was performed in 0.05M and 0.1M SDS. The thermodynamic parameters were determined in order to understand the quenching of pyranine by the studied amines. Change in Gibbs free energy and quenching was found higher in 0.05M SDS concentration and was found lower when SDS concentration was increased to 0.1M SDS. Pyranine quenching by the amines studied were treated with an extended Stern-Volmer equation that produced the Stern-Volmer constant ([Formula: see text]). Binding constant (Kb), number of binding stoichiometry (n) and Gibbs free energy change (ΔGbinding) were found higher for lower surfactant concentration as compare to higher surfactant concentration. More negative (-ve) the Gibbs free energies more will be the quenching, higher will be the sensitivity and vice versa. The Gibbs free energies for all the studied amines were found in the order as cyclopropylamine > ethylenediamine > benzylamine > dibutylamine > cyclohexylamine > polyethylenediamine. Fluorescence quenching of pyranine by amines in aqueous SDS is reproducible and is useful for the determination of amines in environmental samples.

Designing and synthesis of perovskite nanocrystals: a promising wide-spectrum solar light-responsive photocatalyst and lead ion sensor.

Perovskites are an emerging material with a variety of applications, ranging from their solar light conversion capability to their sensing efficiency. In current study, perovskite nanocrystals (PNCs) were designed using theoretical density functional theory (DFT) analysis. Moreover, the theoretically designed PNCs were fabricated and confirmed by various characterization techniques. The calculated optical bandgap from UV-Vis and fluorescence spectra were 2.15 and 2.05eV, respectively. The average crystallite size of PNCs calculated from Scherrer equation was 15.18nm, and point of zero charge (PZC) was obtained at pH 8. The maximum eosin B (EB) removal efficiency by PNCs was 99.56% at optimized conditions following first-order kinetics with 0.98 R2 value. The goodness of the response surface methodology (RSM) model was confirmed from analysis of variance (ANOVA), with the experimental F value (named after Ronald Fisher) of 194.66 being greater than the critical F value F0.05, 14, 14 = 2.48 and a lack of fit value of 0.0587. The Stern-Volmer equation with a larger Ksv value of for Pb2+ suggests its greater sensitivity for Pb2+ among the different metals tested.

Influence of Structural Properties of Oleic Acid-Capped CdSe/ZnS Quantum Dots in the Detection of Hg2+ Ions.

Oleic acid-capped CdSe/ZnS quantum dots (QDs) were used to investigate their photoluminescence (PL) response to Hg2+ ions as a function of the surface properties of QDs. Three distinctly-size CdSe/ZnS QDs were obtained by varying the molar ratio of shell precursors, which were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), Fourier-Transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), absorption spectroscopy, and time-resolved fluorescence spectroscopy. Results revealed the obtention of zinc blende nanocrystals with sizes ranging from 2.7 to 3.2nm (± 0.5) and ZnS thickness between 0.3 and 1.0 monolayer (ML). The variation of the [S]/[Zn] molar ratio introduced chemical species that act as traps, affecting the PL properties differently. Depending on the thickness of the shell and chemical speciation on surface, Hg2+ ions could induce quenching or enhancement of PL. Detection of mercury ions was evaluated in terms of Stern-Volmer equation, where the limit of detection (LOD) for the PL quenching system was 11.2 nM, while for the PL enhancing systems were 8.98 nM and 10.7 nM. Results demonstrate the performance of oleic acid-capped CdSe/ZnS QDs to detect Hg2+ and their capacity to turn the PL on/off depending on surface properties.

Synthesis of P, N-dopped carbon nanosheets for highly sensitive fluorescence analysis of nitrofuran antibiotics in fish

The misuse of antibiotics has caused serious impacts on food safety and human health, making it crucial to develop rapidly and highly sensitive methods for detecting trace nitrofuran antibiotics (NFs). In this study, phosphorus, nitride-doped carbon nanosheets (PN/CNs) were synthesized using a simple hydrothermal method based on graphitic carbon nitride. This prepared material showed excellent water solubility and stable optical properties. A new fluorescence sensing platform based on PN/CNs was constructed for the highly sensitive detection of four NFs. This sensitivity was mainly attributed to the fluorescence resonance energy transfer (FRET) mechanism. The limits of detection for nitrofurazone, nitrofurantoin, furazolidone and furaltadone were determined to be 13.41, 15.24, 16.37 and 19.94 nM, respectively. The high sensitivity and selectivity of PN/CNs for these four NFs were thoroughly evaluated by the Stern-Volmer equation and FRET quenching efficiency. This proposed method exhibited high sensitivity and can be successfully applied to detect NFs in fish.

Unraveling the enigma: Probing the unconventional binding site and binding mechanism of entrectinib with human serum albumin through spectroscopic, molecular docking, and dynamic simulation analyses

Entrectinib (ENB), a novel potent tyrosine kinase inhibitor, has demonstrated promising activity against specific genetic alterations in various solid tumors. Investigating the interaction of ENB with human serum albumin (HSA) provides valuable insights into its binding characteristics and pharmacological behavior. The interaction between ENB and HSA was investigated using various spectroscopic techniques, molecular docking, and simulations approaches. Fluorescence spectroscopy revealed a consistent decrease in the intrinsic fluorescence of HSA upon binding to ENB, indicating a static binding mechanism. The binding constant calculated from Stern Volmer and double-log equations (KSV) and (K) were determined to be 4.11 x104 M−1 and 4.38 x104 M−1, respectively at 298 K, indicating moderate binding affinity. Thermodynamic analysis demonstrated a spontaneous interaction (ΔG < 0) with an enthalpy change (ΔH) of −5.59 kJ mol−1 and an entropy change (ΔS) of + 70.36 J mol−1 K−1, indicating that the interaction is primarily driven by electrostatic forces with potential involvement of hydrogen bonding. Synchronous and 3D fluorescence analysis indicated no significant changes in the microenvironment surrounding Tyr and Trp residues upon ENB binding. Near and far UV spectrophotometric analyses confirmed the formation of the ENB-HSA complex and suggested no conformational changes in the protein structure. Fluorescence measurements and binding competition analysis using site markers revealed that ENB selectively binds to the HSA Sudlow sites I and III, displacing phenylbutazone at both sites. Molecular docking studies confirmed the binding of ENB to Sudlow sites I and III and identified critical residues involved in the interaction. Molecular dynamics simulations further validated the stability of the ENB-HSA complex at both sites, with more favorable binding at site III, and minimal fluctuations observed in the root mean square deviation, root mean square fluctuation, and radius of gyration. Hydrogen bond analysis and solvent accessible surface area calculations supported the strong binding and accessibility of ENB within the HSA structure. Overall, the experimental and computational results provided valuable insights into the ENB-HSA interaction, elucidating the binding mechanism and key residues involved.

Sensing of Co2+ and Cu2+ Ions Using Dimethylamino-functionalized Poly(azomethine-1,3,4-oxadiazole)s.

The ability of OxT and OxFl azomethines to recognize metal ions in THF solutions was investigated using UV-vis absorption techniques. Various metal ions, including Cd2+, Hg2+, Co2+, Sn2+, Cu2+, Ni2+, Zn2+ and Ag+, were tested. The absorption spectra revealed two distinct π-π* transition bands in the 273-278nm and 330-346nm wavelength ranges. Additionally, OxFl displayed an absorption peak at 309nm, attributed to the fluorene group. Spectral titrations were used to study the fluorescence behavior in the presence of these metal ions. The results showed significant quenching with Co2+ and Cu2+ ions, while other metal ions had minimal effects on the fluorescence intensity. The quenching mechanism was further analyzed using the Stern-Volmer and Lehrer equations, and the binding constants ( ) were calculated using the Benesi-Hildebrand relations. The results confirm that Co2+ has a 1:2 stoichiometry and Cu2+ has a 1:1 stoichiometry, indicating the strong affinity of OxFl and OxT for these ions. The negative values of ΔG (Gibbs free energy) suggest that complex formation occurs spontaneously at room temperature.

Azine Based Oligoesteric Chemosensors for Cu2+ Ion Detection: Synthesis, Structural Characterization, and Theoretical Investigations.

Synthesized monomer and its three oligoesters were characterized by techniques such as 1H, 13C{1H}, IR, UV, GPC and applied to chemosensor applications. A series of metal ions was studied with fluorophores to evaluate the sensitivity towards Cu2+ ion. The fluorophores results exhibit the selective and sensitive "Turn off" fluorescence response with Cu2+ ion in DMF/H2O (1:1, pH: 7.4, fluorophore: 5µM) solution. Binding stoichiometry and binding constant of fluorophores were calculated using Stern-Volmer equation and Benesi-Hildebrand plots, respectively. Structure of fluorophores were studied using DFT, B3LYP/6-311 + + G(d,p) level basis set. Quenching mechanisms and electrical properties of fluorophores were explained with theoretical outcomes. Iodine doped and undoped oligoesters electrical conductivity were studied in solid-state and the conductivity was gradually increased with increase the contact time of iodine with oligoesters. At different frequencies and temperatures, the dielectric measurement was calculated using the two-probe method. Among all oligoesters, DMDAP exhibited high electrical conductivity and DMDMP has a higher dielectric constant value than other oligoesters.