Stern-Volmer Constant Research Articles

Preparation of cellulose nano crystals from cinnamon stick, curcumin delivery and interaction with human hemoglobin protein: A novel view of the oxygenation hemoglobin

Curcumin (Cur), a natural phenolic compound, exhibits promising therapeutic properties including anti-cancer and anti-inflammatory effects. However, its limited bioavailability hinders its efficacy when administered alone. To address this challenge, this study explores the use of cellulose nano crystals (CNCs) derived from cinnamon stick via acid hydrolysis as carriers for Cur. The CNCs were thoroughly characterized, and Cur was successfully bound to them. Structural and morphological analyses of the CNCs-Cur complex were investigated applying Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Interaction studies between hemoglobin and the CNCs-Cur complex were carried out using various fluorescence spectroscopic techniques. Fluorescence spectroscopy revealed hemoglobin fluorescence quenching by the CNCs-Cur complex, with Stern-Volmer constants determined at different temperatures indicating static mechanism for the quenching. Synchronous fluorescence spectroscopy provided insights into the molecular micro-environment surrounding chromophores, and the distance between the CNCs-Cur complex and hemoglobin fluorophores was calculated using Forster's non-radioactive energy transfer theory (FRET), yielding a distance of less than 7 nm. Circular dichroism (CD) analysis indicated structural changes in hemoglobin upon the interaction with CNCs-Cur, while oxygenation techniques were employed to investigate oxygen binding, release, and transfer in hemoglobin. This comprehensive investigation sheds light on the potential of CNCs as effective carriers for curcumin, offering valuable insights into their interaction with biological molecules.

A Fluorescence Sensor Based on Biphenolic Backbone for Metal Ion Detection: Synthesis and Crystal Structure

2′-(hexyloxy)-[1,1′-biphenyl]-2-yl 5-(dimethylamino)naphthalene-1-sulfonate (KC1) was synthesized by using biphenol and dansyl chloride as starting materials. The KC1 was characterized via single X-ray diffraction, FTIR, HRMS and 1H and 13C-NMR. The KC1 indicates triclinic as P1 in the space group type. From the KC1, the biphenolic backbone structure is twisted at an angle of 54.48° due to connecting the dansyl unit and hexyl moiety. Upon the addition of the Fe3+ ion to the KC1 solution, the fluorescence emission at 585 nm of KC1 was quenched due to complexation between KC1 and the Fe3+ ion. The complexation ratio of KC1 and Fe3+ was determined to be a 1:1 formation via Job’s analysis. The Stern–Volmer constant (Ksv) calculated was 21,203 M−1 for the KC1 and the Fe3+ ion complex.

Synthesis and characterization of molecularly imprinted polymer nanoparticles against porcine circovirus type 2 viral-like particles.

PCV2 is a significant epidemic agricultural pathogen that causes a variety of swine diseases. PCV2 infections have significant economic impact on the swine industry, making effective strategies for rapid detection of PCV2 in pigs essential. Herein, we report on the synthesis of the so-called nano-MIPs which can be utilized for molecular recognition of PCV2. The morphology and structure of nano-MIPs were characterized using scanning electron microscopy (SEM). Nano-MIPs are spherical with sizes around 120-150nm. Binding experiments demonstrate that the fluorescence intensity of PCV2 samples decreases proportionally to increasing the concentration of nano-MIPs due to quenching, while non-imprinted polymer nanoparticles (nano-NIPs) do not affect the signal. The Stern-Volmer constant of nano-MIPs binding to PCV2 was 1.3 × 10-3mL/µg, whereas nano-NIPs led to 7 × 10-5mL/µg, i.e., 1.8 orders of magnitude lower. The detection limit for binding MIP particles to PCV2 by fluorescence measurements is 47µg/mL. This affinity test allows for designing both direct and competitive quartz crystal microbalance (QCM) assays for PCV2 leading to QCM measurements. The QCM results show nano-MIPs binding to PCV2 immobilized on the sensor surface with appreciable reproducibility. QCM sensor characteristics reveal signal saturation above around 200µg/mL at a response of - 354Hz and an LOD of approximately 35µg/mL. Nano-MIPs also show selectivity factors of 2-5 for CSFV and PRRSV probably because the three viruses have similar diameters around 50nm.

Chiral discrimination during photoinduced electron transfer from L/D-tryptophan to electron-excited uranyl ion as a part of UO22+ ⊂ α–CD inclusion complex

Spectral-luminescent research indicates the formation of inclusion complexes during the interaction of uranyl nitrate and α–cyclodextrin (α–CD) in aqueous solutions. The chiral α–CD matrix imparts optical activity to the electronically excited uranyl ion *UO22+aq in the clathrate, which manifests itself in the chiral discrimination of the quenching of *UO22+aq by tryptophan enantiomers. It was found that the Stern-Volmer constant for D–Trp is 1.8 ± 0.2 times higher than that for L–Trp. A mechanistic explanation for the observed effect is proposed by DFT calculations.

Thienothiophene based AIE-Active bulky materials for sensitive explosive detection

Sensors for selective and sensitive detection of nitroaromatic (NAC) explosives are of current interest for both national security and environmental protection. In this work, three thienothiophene based AIE active materials (TPE2-TT, TPE3-TT and TPE3-TPA-TT), possessing tetraphenylethylene and triphenylamine units, were designed and synthesized as chemosensors for sensitively detecting 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and trinitrophenol (TNP) explosives. Among the AIEgens, TPE3-TT demonstrated a maximum Stern-Volmer constant (Ksv) reaching to 2.9 x 104 M−1 by quenching response toward TNP. They exhibited vivid visual quenching on absorbent papers. Moreover, probe-explosive complex interactions and their mechanisms were investigated using density functional theory (DFT). Their remarkable properties indicated that TT based AIEgens are promising probes for sensitively detecting the explosives, which provided a new source of potential leading to new designs for detection of explosives.

Carbohydrate-Binding Mechanism of the Coagulant Lectin from Moringa oleifera Seeds (cMoL) Is Related to the Dimeric Protein Structure

This study characterized the binding mechanisms of the lectin cMoL (from Moringa oleifera seeds) to carbohydrates using spectroscopy and molecular dynamics (MD). The interaction with carbohydrates was studied by evaluating lectin fluorescence emission after titration with glucose or galactose (2.0–11 mM). The Stern–Volmer constant (Ksv), binding constant (Ka), Gibbs free energy (∆G), and Hill coefficient were calculated. After the urea-induced denaturation of cMoL, evaluations were performed using fluorescence spectroscopy, circular dichroism (CD), and hemagglutinating activity (HA) evaluations. The MD simulations were performed using the Amber 20 package. The decrease in Ksv revealed that cMoL interacts with carbohydrates via a static mechanism. The cMoL bound carbohydrates spontaneously (ΔG < 0) and presented a Ka on the order of 102, with high selectivity for glucose. Protein–ligand complexes were stabilized by hydrogen bonds and hydrophobic interactions. The Hill parameter (h~2) indicated that the binding occurs through the cMoL dimer. The loss of HA at urea concentrations at which the fluorescence and CD spectra indicated protein monomerization confirmed these results. The MD simulations revealed that glucose bound to the large cavity formed between the monomers. In conclusion, the biotechnological application of cMoL lectin requires specific methods or media to improve its dimeric protein structure.

Nucleic acid binding affinity and antioxidant activity of N-m-Tolyl-4-Chlorophenoxyacetohydroxamicacid.

Hydroxamic acids represent a group of weak organic acids, both naturally occurring and synthetically derived, characterized by the general formula RC(= O)N(R'OH). In this study, we investigated the binding behavior of N-m-tolyl-4-chlorophenoxyaceto hydroxamic acid with calf thymus DNA (ct-DNA) and torula yeast RNA (t-RNA) through a combination of techniques including UV-visible spectroscopy, fluorescence emission analysis, viscometry, and computational simulations using AutoDock4 software. Our findings reveal that the mode of binding between the compound and the nucleic acids is consistent with intercalation. Competitive binding experiments demonstrated that the complex competes effectively with ethidium bromide (EB) for binding to ct-DNA/t-RNA, displacing EB from its binding sites. Additionally, the introduction of the compound into the DNA-EB system resulted in a quenching of fluorescence emission peaks. Analysis of absorption spectra indicated a red shift and hypochromic shift when the compound interacted with DNA, further supporting the intercalative binding mode. The calculated binding constant (Kb) value for the compound is 6.62 × 104M-1 and 5.40 × 103M-1 indicating a strong interaction with ct-DNA and t-RNA respectively. We determined the Stern-Volmer constants for ct-DNA and t-RNA as 9.96 × 104M-1 and 8.13 × 105M-1, respectively. The binding free energy values for ct-DNA/t-RNA were calculated to be -3.741 × 107 and -5.425 × 108kcal/mol, respectively. Viscometric studies corroborated the UV results, showing a continuous increase in relative viscosity of ct-DNA/t-RNA solutions with the addition of the optimal hydroxamic acid concentration. Furthermore, we assessed the antioxidant activity of the compound using DPPH-radical scavenging and β-carotene linoleic acid assays. Gel electrophoresis results demonstrated the compound's remarkable efficacy in preventing DNA damage. Collectively, all experimental evidence supports the conclusion that N-m-tolyl-4-chlorophenoxyaceto hydroxamic acid binds to ct-DNA/t-RNA through an intercalative mechanism, which is consistent with our molecular docking simulations.

Unraveling the Potential of Mononuclear Zn(II) and Cu(II) Schiff Base Metal Complexes: Microwave‐Aided Synthesis, Theoretical Analysis and Application in Biomimetic Catalysis, CT‐DNA Interaction, and In Vitro Biological Assays

ABSTRACTGiven the widespread and diverse effects of transition metal ions such as copper and zinc in multiple biological processes, this research endeavor addresses herein the microwave‐aided synthesis of two novel tetradentate ONNO (L1) and tridentate NNO (L2) donor Schiff base ligands derived from 4,5‐dimethyl‐1,2‐phenylenediamine and 4‐bromo‐2‐hydroxybenzaldehyde in a 1:2 ratio and from 4,5‐dimethyl‐1,2‐phenylenediamine and 5‐methoxy‐2‐hydroxybenzaldehyde in a 1:1 ratio, with their respective zinc, ZnL1(1) and ZnL2(3), and copper, CuL1(2) and CuL2(4), Schiff base metal complexes, which are comprehensively characterized utilizing physiochemical and analytical techniques, along with geometry optimization using the DFT approach. Spectrophotometric analyses have been used to assess the biomimetic activity in the conversion of 3,5‐DTBC to 3,5‐DTBQ with turnover numbers 53.4 and 78 h−1 in methanol for 2 and 4, whereas the zinc complexes are found to be ineffective. With CT‐DNA, possible modes of interaction with the synthesized complexes have been explored using absorption spectroscopy, where the associated binding constants ranged between 1.541 × 105 and 2.186 × 105 M−1. EtBr‐bound DNA was used in the fluorescence quenching experiments with Stern–Volmer constant (Ksv) values in the range 4.084 × 104 and 3.402 × 104 M−1, showing a stronger association with CT‐DNA. The compounds' ability to inhibit bacterial strains was also examined in vitro, as well as their ability to reduce inflammation, through the protein denaturation method and the DPPH assay for antioxidant activity have been performed. Furthermore, molecular docking simulations have been carried out to obtain a deeper comprehension of the molecular‐level interactions with CT‐DNA and cyclooxygenase‐2 (COX‐2).

One-Pot, Multi-Component Green Microwave-Assisted Synthesis of Bridgehead Bicyclo[4.4.0]boron Heterocycles and DNA Affinity Studies.

Anthranilic acids, salicylaldehydes and arylboronic acids reacted in EtOH/H2O (1/3) at 150 °C under microwave irradiation for 1 h to give, in excellent yields and purity, twenty-three bridgehead bicyclo[4.4.0]boron heterocycles via one-pot, three-component green synthesis. The scope and the limitations of the reactions are discussed in terms of the substitution of ten different anthranilic acids, three salicylaldehydes and three arylboronic acids. The replacement of salicylaldehyde with o-hydroxyacetophenone demanded a lipophilic solvent for the reaction to occur. Eight novel derivatives were isolated following crystallization in a toluene-containing mixture that included molecular sieves. The above one-pot, three-component reactions were completed under microwave irradiation at 180 °C within 1.5 h, thus avoiding the conventional prolonged heating reaction times and the use of a Dean-Stark apparatus. All derivatives were studied for their affinity to calf thymus DNA using proper techniques like viscosity and UV-vis spectroscopy, where DNA-binding constants were found in the range 2.83 × 104-8.41 × 106 M-1. Ethidium bromide replacement studies using fluorescence spectroscopy indicated Stern-Volmer constants between 1.49 × 104 and 5.36 × 104 M-1, whereas the corresponding quenching constants were calculated to be between 6.46 × 1011 and 2.33 × 1012 M-1 s-1. All the above initial experiments show that these compounds may have possible medical applications for DNA-related diseases.

Inhibition of α-amylase activity by quercetin via multi-spectroscopic and molecular docking approaches

The quercetin-induced inhibition of α-amylase activity was comprehensively studied using various spectroscopic methods, including UV–Visible, fluorescence, and Fourier-transform infrared spectroscopy. Quercetin acted as a mixed-type inhibitor, and its binding altered the kinetic properties of α-amylase. Quercetin exhibited static binding with α-amylase, as evidenced by a higher Stern-Volmer constant (KSV) at 298 K (9.56 ± 0.63 × 103 L/mol) compared to the KSV value at 318 K (5.56 ± 0.48 × 103 L/mol). Additionally, quercetin induced conformational changes in the hydrophobic micro-environment surrounding the tryptophan and tyrosine residues of α-amylase, as indicated by fluorescence spectroscopy. Hydrophobic interactions primarily drove the spontaneous binding between α-amylase and quercetin from thermodynamic data. Molecular docking studies supported the role of hydrogen bonds (Asp197 and Gln63) and hydrophobic interactions (with active site residues Ala198, Leu165, and Trp59) in the complex formation. These findings provide a detailed understanding of how quercetin inhibits α-amylase activity, reinforcing its potential as a glycemic controller in food formulations.

Iridium(III)-Incorporating Self-Healing Polysiloxanes as Materials for Light-Emitting Oxygen Sensors.

Polymer-metal complexes (PMCs) based on poly(2,2'-bipyridine-4,4'-dicarboxamide-co-polydimethylsiloxanes) with cyclometalated di(2-phenylpyridinato-C2,N')iridium(III) fragments and cross-linked by Zn2+ (Zn[Ir]-BipyPDMSs) or Ir3+ (Ir[Ir]-BipyPDMSs) represent flexible, stretchable, phosphorescent, and self-healing molecular oxygen sensors. PMCs provide strong phosphorescence at λem = 595-605nm. Zn[Ir]-BipyPDMS with PDMS chain length of Mn = 5000 has the highest quantum yield of 9.3% and is a molecular oxygen sensor at different O2 concentrations (0-100vol%) compared to Ir[Ir]-BipyPDMSs. A Stern-Volmer constant is determined for Zn[Ir]-BipyPDMS as KSV = 0.014%-1, which is similar to the reported oxygen-sensitive iridium(III) complexes. All synthesized PMCs exhibit high elongation at break (up to 1100%) and self-healing efficiency (up to 99%).

Mechanosynthesis of pentiptycene-based polyesters and polycarbonates

Iptycenes are common building blocks for the small-molecules or polymer-based chemosensors and fluorophores. In addition, iptycene derivatives are widely presented in polymers of intrinsic microporosity (PIMs) as materials for the separation and purification technologies. In this manuscript we wish to report a mechanochemical approach to pentiptycene-based polyesters and polycarbonates as, possibly, new representatives of PIMs. Our approach involves the polycondensation reaction between 5,7,12,14-tetrahydro-5,14:7,12-bis([1,2]benzeno)pentacene-6,13-diol (pentiptycene-6,13-diol) and triphosgene or oxalyl chloride under ball-milling conditions. The obtained polymers were characterized by means of 1H NMR- and IR-spectroscopy. As the last step, the fluorescence “turn-off” response of pentiptycene-6,13-diol and two pentiptycene-based polymers towards nitroanalytes (2,4-dinitrotioluene (DNT) and 2,4,6-trinitrophenole (picric acid, PA)) was investigated, and Stern-Volmer constants as high as 1o4 M–1 were observed.

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.

Interaction between antidepressant drug trazodone with double-stranded DNA: Multi-spectroscopic and computational analysis

Trazodone (TZD) is an antidepressant drug used to treat major depressive and sleeping disorders. Elevated doses of trazodone are associated with central nervous system depression, which manifests as nausea, drowsiness, confusion, vertigo, exhaustion, etc. To develop a clinically viable active pharmaceutical compound with minimal adverse effects, it is imperative to possess a comprehensive knowledge of the drug's action mechanism on DNA. Hence, we investigate the mode of interaction between trazodone and DNA utilizing various spectroscopic and computational techniques. Studies using UV–vis titration showed that the DNA and trazodone have an effective interaction. The magnitude of the Stern-Volmer constant (KSV) has been calculated to be 5.84 × 106 M−1 by the Lehrer equation from a steady-state fluorescence study. UV–vis absorption, DNA melting, dye displacement, and circular dichroism studies suggested that trazodone binds with DNA in minor grooves. Molecular docking and molecular dynamic simulation demonstrated that the TZD-DNA system was stable, and the mode of binding was minor groove. Furthermore, ionic strength investigation demonstrates that DNA and trazodone do not have a substantial electrostatic binding interaction.

A structural and biochemical approach to effect of temperature and pH on the Molten Globule phenomenon in a thermophilic protease: Molecular dynamics simulation, fluorescence spectroscopy and circular dichroism

Proteins in the molten globule (MG) stage have a reasonably stable secondary structure content, but changes in side-chain packing cause a noticeable decrease in the number of tertiary structures. Here, we investigated serine protease as a suitable model to study the folding route and characteristics of a protein in the MG state. Upon induction with IPTG, the protein exhibited a molecular weight of 42 kDa and achieved a final concentration of 1.7 mg/mL after the concentration process. Serine protease's intrinsic and extrinsic fluorescence was examined in the pH range of 1–12 using fluorescence spectroscopy with maximum intrinsic fluorescence in 335 nm and a blue shift in 510 nm for extrinsic fluorescence. It was suggested that the protein transitions probably to an MG state at pH 3. Evidences showed that serine protease's secondary structure using far-UV circular dichroism (CD) showed a little shift in the MG state intermediate, pH 3, relative to the original state, pH 8, which is typical for MG. Maximum decreases was observed in 228 to 300 nm for UV-near CD. Also revealed a notable alteration in the pH 3 of the enzyme compared to pH 8, which is the pH at which the protein takes on its natural structure. By using acrylamide to quench the fluorescence, the Stern-Volmer constant (KSV) was determined at pH values of 8 and 3, yielding values of 20 and 14 M−1, respectively. This is likely correlated with an increase in the enzyme's molecular volume in the MG state. Molecular dynamics (MD) simulation showed that although the thermal stability of this enzyme at 90° was confirmed in the Root-Mean-Square-Deviation (RMSD), Root-Mean-Square-Fluctuation (RMSF), Radius of gyration (Rg) as well as Solvent-Accessible-Surface-Area (SASA) graphs, but pH 3 may significantly disturb the tertiary structure and secondary structure. These in-silico results may also be analyzed in line with the occurrence of MG at pH 3.

Interaction mechanism of oseltamivir phosphate with bovine serum albumin: multispectroscopic and molecular docking study

Oseltamivir phosphate (OP) is an antiviral drug with potential risks to human health due to overuse, leading to serious consequences such as gastrointestinal disturbances, abnormal neuropsychiatric symptoms, and sudden death. Therefore, gaining an in-depth understanding of its interaction with proteins is crucial. We investigated the interaction between OP and bovine serum albumin (BSA) utilizing multispectral methods (i.e., fluorescence, ultraviolet absorption, circular dichroism) combined with molecular docking techniques. Fluorescence spectroscopy indicated that OP quenched BSA fluorescence by forming the OP-BSA complex. The Stern-Volmer constants (KSV) between OP and BSA were determined to be 3.06 × 103 L/mol, 2.36 × 103 L/mol, and 1.86 × 103 L/mol at 293 K, 298 K, and 303 K, respectively. OP occupies exclusively one binding site on BSA, and the fluorescent probe displacement measurements revealed that this is BSA site I. Thermodynamic data (∆H, ∆S, and ∆G) obtained by fitting the van’t Hoff equation were − 77.49 kJ/mol, -176.54 J/(mol∙K), and − 24.88 kJ/mol, respectively, suggesting that hydrogen bonding and van der Waals forces mainly participate in OP-BSA complex stabilization. Moreover, the reaction occurs spontaneously at room temperature. Synchronous fluorescence spectra indicated that OP interacts with tryptophan residue of BSA. The results of ultraviolet (UV) and 3D fluorescence spectroscopy indicated that the OP-BSA complex formation altered the microenvironment around amino acid residues. Circular dichroism spectra revealed that the addition of OP decreased the α-helix content of BSA by 7.13%. Docking analysis confirmed that OP binds to BSA site I through hydrogen bonding with amino acids VAL342, SER453, and ASP450. Finally, ADMET studies were conducted to explore the pharmacokinetics of OP as an antiviral drug.

Synthesis and Characterizations of MoS2 Nanoflowers and Spectroscopic Study of their Interaction with Bovine Serum Albumin.

Molybdenum disulfide nanoflowers (MoS2 NFs) were prepared by hydrothermal method. The prepared MoS2 NFs was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), specific surface areas, Raman and X-ray photoelectron spectroscopy (XPS). The characterization results show that the flower-like spherical MoS2 is composed of many ultra-thin nanosheets with an average diameter of about 300-400 nm. MoS2 NFs also exhibits excellent UV-vis absorption and high fluorescence intensity. In order to explore the biological behavior of MoS2 NFs, the interaction between MoS2 NFs and bovine serum albumin (BSA) was studied by UV-Vis absorption, fluorescence, synchronous fluorescence spectra, and cyclic voltammetry. The results of absorption and fluorescence show that MoS2 NFs and BSA interact strongly through the formation of complexes in the ground state, and the static quenching is the main mechanism. The Stern-Volmer constant and the quenching constant was calculated about 3.79×107 L mol-1 and 3.79×1015 L mol-1 s-1, respectively. The synchronous fluorescence implied that MoS2 in the complex may mainly bind to tryptophan residues of BSA. The cyclic voltammograms indicated that the addition of BSA makes electron reduction of MoS2 NFs more difficult than the corresponding free state. The results show that hydrophobic forces play a major role in the binding interaction between BSA and MoS2 NFs.

Unraveling the binding behavior of the antifouling biocide 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one with human serum albumin: Multi-spectroscopic, atomic force microscope, computational simulation, and esterase activity

As a marine antifouling biocide, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) exhibited high toxicity to marine organisms. This study investigated the interaction between DCOIT and human serum albumin (HSA) using several spectroscopic techniques combined with computer prediction methods. The UV–vis absorption spectra, Stern-Volmer constant (KSV) and fluorescence resonance energy transfer (FRET) results indicated that DCOIT caused static quenching of HSA fluorescence. The ΔG°, ΔH° and ΔS° values were −31.03 ± 0.17 kJ·mol−1, −133.54 ± 0.88 kJ·mol−1 and −348.46 ± 2.86 J.mol−1·K−1, respectively, suggesting that van der Waals forces and hydrogen bonds governed the spontaneous formation of the complex. Synchronous fluorescence and circular dichroism (CD) spectroscopy observed the burial of Trp residues within HSA and the unfolding of HSA secondary structure induced by DCOIT. Three-dimensional (3D) fluorescence and Atomic Force Microscopy (AFM) further detected DCOIT-induced loosening of HSA peptide chain structure. Site displacement experiments indicated that DCOIT binding at site I of HSA. Computational predictions indicated that hydrophobic interactions were also essential in the complex. The increased RMSD, Rg, SASA, and RMSF confirmed that DCOIT weakened the stability and compactness of HSA, rendering residues more flexible. Lastly, esterase activity assays demonstrated that DCOIT inhibited esterase activity and interfered with the human detoxification process.

Homochiral Tetraphenylethene-Based Metal-Organic Frameworks with Circularly Polarized Luminescence for Enantioselective Recognition.

A pair of water-stable and highly porous homochiral fluorescent silver-organic framework enantiomers, namely, R-Ag-BPA-TPyPE (R-1) and S-Ag-BPA-TPyPE (S-1), had been prepared as enantioselective fluorescence sensors. Combining homochiral 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BPA) with an AIE-based ligand tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPyPE) in complexes R-1 and S-1 made them possess favorable circularly polarized luminescence (CPL) properties, and their CPL spectra were almost mirror images of each other. The luminescence dissymmetry factors (glum) are ±2.2 × 10-3 for R-1 and S-1, and the absolute fluorescence quantum yields (ΦFs) are 32.0% for R-1 and S-1, respectively. Complex R-1 could enantioselectively recognize two enantiomers of amino acids in water or DMF with high Stern-Volmer constants of 236-573 M-1 and enantioselectivity ratios of 1.40-1.78.

Tailored coordination chemistry: A novel Zn(II)-fluorescent coordination material for highly selective and sensitive detection of Hg2+ ions in aqueous environments

The pursuit of advanced sensing materials for precisely detecting heavy metal ions remains a critical imperative in environmental science. This manuscript deal with a novel fluorescent material, ZU-1, designed for the selective and sensitive detection of Hg2+ ions in aqueous suspension. Employing the Hard-Soft Acid-Base (HSAB) concept, Zn2+ serves as the d10 metal ion, and ZU-1 is synthesized with a −S donor ligand (NaSCN) and 2-pyridine methanol (Hhmp). The fluorescence sensing elucidates a unique detection mechanism, unveiling the distinctive coordination facilitated by the larger ionic radius and soft acid characteristics of Hg2+ with the −S donor sites in ZU-1. Fluorescence titration experiments validate ZU-1’s outstanding ability to selectively quench fluorescence intensity in the presence of Hg2+, even amidst interference from other metal ions. The quantitative analysis yields a Stern-Volmer constant (Ksv) of 7.5 × 108 M−1 and an exceptional limit of detection for Hg2+ at ∼0.60 ppm. ZU-1 further distinguishes itself through outstanding recyclability over four cycles, underscoring its potential as a sustainable and reusable sensor for real-time Hg2+ detection. Beyond its practical implications, this research contributes fundamental insights into design principles for materials exhibiting heightened selectivity and sensitivity to heavy metal ions.