Stern-Volmer Research Articles

Mango Leaves (Mangifera indica)-Derived Highly Florescent Green Graphene Quantum Dot Nanoprobes for Enhanced On-Off Dual Detection of Cholesterol and Fe2+ Ions Based on Molecular Logic Operation.

In the present study, we have engineered a molecular logic gate system employing both Fe2+ ions and cholesterol as bioanalytes for innovative detection strategies. We utilized a green-synthesis method employing the mango leaves extract to create fluorescent graphene quantum dots termed "mGQDs". Through techniques like HR-TEM, i.e., high-resolution transmission electron microscopy, Raman spectroscopy, and XPS, i.e., X-ray photoelectron spectroscopy, the successful formation of mGQDs was confirmed. The photoluminescence (PL) characteristics of mGQDs were investigated for potential applications in metal ion detection, specifically Fe2+ traces in water, by using fluorescence techniques. Under 425 nm excitation, mGQDs exhibited emission bands at 495 and 677 nm in their PL spectrum. Fe2+-induced notable quenching of mGQDs' PL intensity decreased by 97% with 2.5 μM Fe2+ ions; however, adding 20 mM cholesterol resulted in a 92% recovery. Detection limits were established through a linear Stern-Volmer (S-V) plot at room temperature, yielding values of 4.07 μM for Fe2+ ions and 1.8 mM for cholesterol. Moreover, mGQDs demonstrated biocompatibility, aqueous solubility, and nontoxicity, facilitating the creation of a rapid nonenzymatic cholesterol detection method. Selectivity and detection studies underscored mGQDs' reliability in cholesterol level monitoring. Additionally, a molecular logic gate system employing Fe2+ metal ions and cholesterol as a bioanalyte was established for detection purposes. Overall, this research introduces an ecofriendly approach to craft mGQDs and highlights their effectiveness in detecting metal ions and cholesterol, suggesting their potential as versatile nanomaterials for diverse analytical and biomedical applications.

Sensitive detection of bilirubin using highly luminescent benzylamine capped CH3NH3PbBr3 perovskite quantum dots

Luminescent organic–inorganic metal halide hybrid perovskite quantum dots (PQDs) as a new class of fluorophores are finding increasing attention towards chemical and biological sensing due to their exceptional photophysical properties. Herein, we synthesized highly fluorescent CH3NH3PbBr3 perovskite quantum dots (B-PQDs) through the ligand assisted reprecipitation method (LARP), using benzylamine as the surface capping ligand. Morphological and opto-structural properties of the as-synthesized B-PQDs were thoroughly investigated using high resolution transmission electron microscopy (HR-TEM), X-Ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), UV–Vis absorption, and fluorescence spectroscopy. The as-synthesized electron-rich amine-capped B-PQDs were employed to study their sensing response towards bilirubin (BL). The aromatic amine capped B-PQDs enhance the sensory response towards BL due to the π-π interaction with BL’s conjugated system. The B-PQDs were found to be highly sensitive towards BL with a stern–volmer constant value ≈ 4.3 × 104 M−1 and limit of detection of 0.42 μM. A panel of characterizations were carried out to investigate the detailed sensing mechanism where resonance energy transfer was found to be the dominant quenching mechanism for BL detection. Our results demonstrated the potential for utilizing organic–inorganic halide perovskite quantum dots for sensing applications, through surface ligand modification tailored for detecting specific analytes.

Exploring the Fluorescence Quenching of Sodium Dodecyl Sulfate Doped Polyaniline by Energetic Nitrocompounds

AbstractThe fluorescence quenching studies using conducting polymers (CPs) have greatly contributed in the trace detection of high energy materials (HEMs) with nitro functional groups. Polyaniline doped with the anion surfactant sodium dodecyl sulfate (SDS) acts as a fluorophore and is used in fluorescence quenching studies to detect HEMs at trace levels. A mechanistic approach to understanding electron transfer during the interaction of fluorophore with HEMs were studied by using spectroscopic and electrochemical techniques. The presence of conjugation in conducting polymer shows a molecular wire effect during fluorescence quenching by trace level of HEMs by quenching several emissions in polymer chains. The Stern‐Volmer(S‐V) and limit of detection(LOD) plots give quenching mechanism and the efficiency of quenching. These values indicate that TNT had good sensitivity compared to other HEMs such as RDX, PETN, CL‐20 and CRCC. The FTIR and Raman studies were used to understand the interaction between nitro groups of HEMs with the benzenoid, polaronic and semi‐quinoid units of doped polyaniline. The cyclic voltammetry studies revealed shift in potential and current during the interaction of the fluorophore with HEMs, and these results were combined with fluorescence studies for better understanding of the possible mechanism of quenching.

Fluorescence Quenching Study Of 5-Sulphosalicylic Acid Doped Polyaniline-Γ-Fe2o3 Composite For High Energy Material Sensing (Fe-Spani)

Background: Polymeric nanocomposites containing metal oxides are of interest to researchers because these materials show hybrid properties that are generated from both components. Due to the control and design of structural properties at the nanoscale scale, they have specialized properties for a range of applications. Researchers have tried to improve the desirable characteristics and thus increase their application by reinforcing them with nanoscale materials to provide them with better properties than conventional micro composites. Objective: In our present work we have used 5-sulphosalicylic acid doped polyaniline-γ-Fe2O3 composite (Fe-SPAni) to detect explosives using fluorescence quenching method. Along with ease of synthesis and low cost, Fe-SPAni possesses a variable oxidation state which is important for trace detection of the analytes. Methods: We used the fluorophore Fe-SPAni to detect High Energy Materials (HEMs) using the fluorescence quenching approach, which is still difficult to achieve. UV-Vis spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM/EDAX) were used to determine the molecular structure of the Fe-SPAni composite produced by oxidative chemical polymerization; CV studies were performed to investigate the electrochemical properties. HEMs such as dinitrobenzene (DNB), pentaerythritol tetranitrate (PETN), trinitrotoulene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and hexanitrohexaazaisowurtzitane(CL-20) were used as quenchers.The fluorescence quenching process was determined using the Stern-Volmer graph. Results: The Stern-Volmer(S-V) plot and limit of detection (LOD) data showed that PETN had the greatest results for the quenching constant value (Ksv) (Ksv =1.33 x 106 M-1 and 1.4x 10-6M, respectively). Conclusion: The research points to Fe-SPAni as a promising contender for sensing explosives.

Molecular analysis of NlugCSP3 with behaviorally active ligands of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The insect olfactory system is sensitive to the complicated chemical environment. Insect’s chemosensory proteins (CSPs) supposedly act as transport of plant volatiles across the sensillar lymph and competitive fluorescent binding assay was commonly used to test the binding affinities with various plant volatiles. However, extensive research to determine the physiological role of CSPs is necessary and helpful through binding interaction of a protein with the plant volatiles. In this comparative study, we employed phylogenetic analysis, fluorescence spectra, quenching mode, and thermodynamic force to characterize Nilaparvata lugens CSP3 (NlugCSP3). The phylogenetic tree revealed that amino acid sequence of NlugCSP3 showed extremely close similarities with Laodelphax striatella (LstrCSP10 & LstrCSP11) and Sogatella furcifera (SurCSP3). The Stern-Volmer (SV) curve of NlugCSP3 fluorescence quenching indicated that nonadecane and 2-tridecanone clearly quenched NlugCSP3 fluorescence as a stable static quenching mode. Meanwhile, α-terpinene and farnesene collided with NlugCSP3, instead of forming stable complexes. The thermodynamic analysis of NlugCSP3 revealed that spontaneous binding interaction occurred in nonadecane and 2-tridecanone and is driven primarily by hydrophobic interactions. This study not only provides the information about the binding interaction of protein with the volatiles, but also improves the efficient recognition of behaviorally elicited volatiles that could be used in the management of brown planthopper.

Protein interactions and drug displacement studies of novel copper(II) and zinc(II) complexes of a dipyrazinylpyridine ligand

A one-pot method was employed for the preparation of zinc and copper complexes of 4-methoxyphenyl-2,6-di(pyrazine-2-yl)pyridine ligand (L). The complexes were designed to acknowledge their potential as selective binders with serum albumins. The reaction of the metal chlorides with an excess of ligand L yielded mononuclear [CuL2]Cl2 (1) and [ZnL2]Cl2 (2) complexes. 1H NMR, UV–Vis spectroscopy, ESR, HRMS, XRD, and elemental analysis were carried out to characterize the complexes. The interactions of the synthesized complexes with Human Serum Albumin (HSA) and their drug displacement properties using ibuprofen and warfarin were investigated with the help of spectroscopic as well as molecular modeling techniques. Complex 1 exhibited better binding capability, indicated by its binding constant value (31.2 × 104 M−1) towards HSA, than complex 2 (5.6 × 104 M−1), as depicted from UV–Visible and fluorescence spectroscopic studies. Moreover, the complexes showed better binding affinity towards HSA than the corresponding free ligand (0.2 × 104 M−1). The mechanism through which fluorescence quenching of HSA takes place (when metal complexes 1–2 were added to it) is static in nature. The Stern-Volmer (SV) equation was utilized to deduce the binding constants (Kb) through a fluorescence titration method. Moreover, structure optimization of the synthesized complexes and theoretical studies using density functional theory (DFT) has been carried out to determine the nature of the interaction of the complexes with the biomolecules.

The mechanism of fluorescence quenching of naphthalimide A/C leak detector by copper (II)

BackgroundFluorescence quenching is an interesting phenomenon with the potential to be applied across various fields. The mechanism is commonly used across analytical applications for monitoring the concentration of trace substances. Naphthalimide and its family of compounds are commonly used as fluorescent detectors. This work investigated an analytical technique through which naphthalimide-based dyes could be quantified. A commercial A/C leak detector was used as the dye and Cu2+ ions as the quencher. Experiments were also conducted to investigate the effect of temperature on quenching. To study the mechanism of quenching further, density functional theory (DFT) was used.ResultsThe method detection limit obtained in this work is 1.7 × 10–6 mol/L. The results from the quenching experiments demonstrated a pattern which fit a modified Stern–Volmer (SV) model, with an R2 value of 0.9886. From the experiments on the effect of temperature, a dynamic quenching behavior was observed given the emission spectra demonstrated an inverse relationship with temperature.ConclusionsThe quenching of the commercial A/C dye by Cu2+ ions can be used to develop a rapid and sensitive detection method for metal ions such as Cu2+, and for future fabrication of chemosensors for Cu2+.

Innovative utilization of silver nanoparticles localized surface plasmon resonance for green and sensitive spectrofluorimetric analysis of sildenafil and xipamide in pure forms and pharmaceutical preparations

A green, novel, simple and sensitive spectrofluorimetric approach was investigated and validated for the analysis of two important cardiovascular drugs namely; sildenafil citrate and xipamide using silver nanoparticles as a fluorescence probe (Ag-NPs).Silver nanoparticles were prepared through chemical reduction of silver nitrate using sodium borohydride in distilled water without using non-green organic stabilizer. These nanoparticles were stable, water soluble and had high fluorescence. After addition of the studied drugs, noticeable quenching of Ag-NPs fluorescence occurred. The intensity of Ag-NPs fluorescence was measured at 484 nm (λex 242 nm) before and after complex formation with these studied drugs. The difference between these values (ΔF) were linear with the concentrations in the following ranges (1.0–10.0 μg/mL), (0.5–5.0 μg/mL) for sildenafil and xipamide, respectively. The formed complexes did not need to be separated by solvent extraction before measurement. For proving the complex formation between the two studied drugs and silver nanoparticles, stern volmer method was applied. The suggested method was perfectly validated in compliance with the international conference on harmonization (ICH) Guidelines and the outcomes were acceptable. Furthermore, suggested technique was perfectly applied for the assay of each drug in its pharmaceutical dosage form. Eventually assessment of method greenness was performed using different tools and found that the suggested method was safe and eco-friendly.

Solvent-induced switching between static and dynamic fluorescence quenching of N, S Co-doped carbon dots in sensing of Crotonaldehyde: A detailed systematic study

Blue emissive N, S co-doped carbon dots (NSCDs) (quantum yield = 12%) have been synthesized via one-pot microwave-assisted pyrolysis of optimal mole ratios of tartaric acid and thioacetamide and they are devised as a novel fluorescent probe for assessing the sensitive and selective detection of Crotonaldehyde (CH3CH=CHCHO, CT) in aqueous and ethanol solution. In the presence of CT, the fluorescence of NSCDs was observed to switch between static and dynamic quenching in the two solvents – water and ethanol, although both exhibited a positive deviation from the linearity in the Stern-Volmer (SV) plots. The positive deviation in the SV plots in the aqueous medium has been attributed to a combination of static and dynamic quenching mechanisms, while the deviation in the ethanol medium followed the static quenching model. The LOD values in water and ethanol medium are estimated to be 50 μM and 30.8 μM in the CT concentration range of 0–6 mM and 0–8 mM respectively. The fluorescence quenching mechanism in the two solvents have been differentiated and validated through fluorescence lifetime measurement using time-resolved fluorescence spectroscopy, shifting in absorption maxima using UV–Vis spectroscopy and energy level calculations. The energy level calculations of NSCDs have been carried out using cyclic voltammetry (CV) measurement and that of CT from density functional theory (DFT) calculations.

Spectrofluorimetric methods for the determination of mirabegron by quenching tyrosine and L-tryptophan fluorophores: Recognition of quenching mechanism by stern volmer relationship, evaluation of binding constants and binding sites

Green spectrofluorimetric methods have been adopted for the determination of Mirabegron (MG) in pure drug and pharmaceutical dosage form. The developed methods based on fluorescence quenching of tyrosine and L-tryptophan amino acids fluorophores by the effect of Mirabegron as a quencher. Experimental conditions of the reaction were studied and optimized. The Fluorescence quenching (ΔF) values were proportional to the concentration range of MG 2–20 μg/ml for the tyrosine-MG system in buffered media pH 2 and 1–30 μg/ml for L-tryptophan-MG system pH 6. Good correlation coefficients with low detection limits of 0.163 and 0.234 μg/ml for the two systems respectively. Method validation was applied according to ICH guidelines. The cited methods were successively applied for MG determination in tablet formulation. No statistically significant difference between the results of the cited and the reference methods regarding t and F tests. The proposed spectrofluorimetric methods are simple, rapid, eco-friendly and can contribute to MG’s methodologies in quality control labs. Stern-Volmer relationship, the effect of temperature, quenching constant (Kq), and UV spectra were studied to identify the mechanism by which the quenching might occur. The results demonstrated that fluorescence quenching of tyrosine was a dynamic quenching process and L-tryptophan was static. The double log plots were constructed to determine the binding constants and binding sites. The greenness profile of the developed methods has been assessed by Green Analytical procedure index (GAPI) and Analytical Greenness Metric Approach (AGREE).

Effects of black cumin-based antimalarial drug loaded with nano-emulsion of bovine and human serum albumins by spectroscopic and molecular docking studies

The growing understanding of nanoemulsion biomedical applications necessitates a basic understanding of protein–drug-loaded nanoemulsion interaction. In our present study, we investigated the binding interactions of Mefloquine (MEF)-loaded black cumin seed oil (Thymoquinone) nanoemulsion of different concentrations towards human and bovine serum albumin (HSA&BSA).Fluorescenceemission,three-dimensionalspectra,UV–visible spectroscopy, and FTIR-spectroscopy, techniques were used together with molecular docking studies to identify the binding effects. The ground state complex formation between Mefloquine-loaded black cumin seed oil nanoemulsion and protein fluorophores was confirmed by a decrease in fluorescence intensity and disputed hyper-chronicity found in the UV–visible spectra of albumins. According to three-dimensional fluorescence spectral analysis, the addition of MEF in thymoquinone impacted the microenvironment around aromatic amino acid (tryptophan and tyrosine) residues in HSA. The quenching mechanism is determined to be static contact by stern–volmer analysis, resulting in the formation of a stable bioconjugate. Significant modifications in the amide FTIR frequencies at around 1600 cm−1 correlate to variations in the secondary alpha-helical structures of biomolecules at the MEF-loaded nanoemulsion interface. Molecular dynamic studies have shown the binding affinity scores of the proteins BSA and HSA with the drug, MEF-loaded black cumin seed oil nanoemulsion. The determined thermodynamic parameters were found to agree with molecular docking data, indicating that vander-waals and hydrogen bonding forces were important in the interaction process. MEF prefers a highly polar binding site at the exterior area of domains in HSA than BSA, as shown in the molecular model, and the hydrogen bonds are highlighted. From our results, we have observed that drug delivery has a detrimental effect on protein frame confirmation by altering its physiological function.

Luminescent Porphyrinic Metal–Organic Frameworks for Oxygen Sensing: Correlation of Nanostructure and Sensitivity

Oxygen sensing capabilities of a series of luminescent zirconium-based porphyrinic metal–organic frameworks (MOFs) (PCN-222, PCN-223, and PCN-224) have been investigated. Design of experiments allowed identification of the most sensitive material, a PCN-224 MOF. In this material, luminescence in air is quenched by up to 7.3-fold with a bimolecular quenching constant kq of 56,000 Pa–1 s–1, which is significantly above the previously reported benchmark material of the same MOF type (kq of 34,000 Pa–1 s–1). The oxygen sensitivity increases in the order PCN-222 < PCN-223 < PCN-224 with effective Stern–Volmer (SV) constants in the range of 0.13 kPa–1 for PCN-222, 0.18 kPa–1 for PCN-223 and up to 0.45 kPa–1 for PCN-224-type materials. This effect is attributed to the increase in the porphyrin–porphyrin separation in these nanostructured materials that results in the increase in the fluorescence decay time and thus the probability of the quenching event. Defects in the nanostructure also are important and explain variations in the sensitivity within the MOFs of the same type. Among the investigated materials, those belonging to the PCN-223 type were found to be the most robust in terms of oxygen sensing capabilities with only little variation in the SV constants. The analogues of the PCN MOFs that utilize a Pt(II) porphyrin as a building block were also prepared. It is shown that the same synthetic protocols established for the metal-free systems can be used for the metal complex. Analogous to the MOFs based on the metal-free porphyrin, the oxygen sensitivity increases from Pt(II)PCN-222 (KSV 30 kPa–1) via Pt(II)PCN-223 (KSV 40 kPa–1) to Pt(II)PCN-224 (KSV up to 87 kPa–1).

Selective Low-Level Detection of a Perilous Nitroaromatic Compound Using Tailor-Made Cd(II)-Based Coordination Polymers: Study of Photophysical Properties and Effect of Functional Groups.

Three coordination polymers (CPs 1-3) are prepared based on diverse electron-donating properties and coordination arrangements of conjugated ligands. Interestingly, this is also reflected in their photophysical properties. The distinguishable high emissive nature of the luminescent coordination polymer shows its potentiality toward the detection of the perilous substance 2,4,6-trinitrophenol (TNP) or picric acid (PA). TNP has a higher propensity among explosive nitroaromatic compounds (epNACs) due to its significant π···π interaction with the free benzene moieties present in the CPs. Among CPs 1-3, 2 exhibits the highest sensitivity and selectivity toward TNP because of the most favorable π-π stacking with the conjugated organic linker. The calculated limit of detection (LOD) and corresponding quenching constant (KSV) from the Stern-Volmer (SV) plot for 1, 2, and 3 are found to be 0.68 μM and 7.49 × 104 M-1, 0.41 μM and 8.01 × 104 M-1, and 1.18 μM and 8.1 × 104 M-1, respectively. The fluorescence quenching mechanism is also highly influenced by their structure and coordination arrangement.

Modulation of drug binding ability and augmented enzymatic activity of lysozyme stabilized in presence of surface-active ionic liquids

Binding of polyphenolic compounds like genistein (GTN) and ellagic acid (EGA) with lysozyme (LYZ) shows strong modulation in presence of surface-active ionic liquids (SAILs), N-dodecylpyridinium bromide(PYD),N-dodecyl-N-methylmorpholinium bromide (MOR), 1-dodecyl-3-methylimidazolium bromide(IMD). Fluorescence of both the native LYZ and LYZ-SAIL complex quenched in presence of the drugs. Both GTN (15.62 × 104 M−1) and EGA (53.70 × 104 M−1) show strong binding to LYZ in presence of IMD in comparison with native LYZ (8.18 × 104 M−1 and 31.28 × 104 M−1, respectively). Stern-Volmer (SV) quenching constant (KSV) of GTN binding to LYZ-PYD complex is almost fourfold (35.79 × 104 M−1) higher than the corresponding values in native LYZ. Spectral response of amide I and amide II bands of LYZ remains same even in presence of SAILs, advocating the intactness of the secondary structure of LYZ. MD simulation studies indicate that the drug molecules preferentially bind near some key tryptophan residues through pi-stacking and hydrophobic interactions. Non-specific interactions of SAILs with the protein seem to modulate the conformational flexibility of the protein, which affects the protein-drug binding affinity. Considerably higher activity of LYZ against Gram positive bacteria Micrococcus lysodeikticus was also observed in presence of IMD. Significant modulation in binding behavior in presence of SAIL indicates that the drug transportation capacity of LYZ can be controlled even in the pre-micellar concentration and could further be exploited in advanced drug delivery techniques.

Plasmonic Surface of Metallic Gold and Silver Nanoparticles Induced Fluorescence Quenching of Meso-Terakis (4-Sulfonatophenyl) Porphyrin (TPPS) and Theoretical–Experimental Comparable

Colloidal metallic nanoparticles have attracted a lot of interest in the last two decades owing to their simple synthesis and fascinating optical properties. In this manuscript, a study of the effect of both gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs) on the fluorescence emission (FE) of TPPS has been investigated utilizing steady-state fluorescence spectroscopy and UV–Vis spectrophotometry. From the observed electronic absorption spectra, there is no evidence of the ground state interaction between metallic Au NPs or Ag NPs with TPPS. On the other side, the FE spectra of TPPS have been quenched by both Ag and Au NPs. Via applying quenching calculations, Ag NPs showed only traditional static fluorescence quenching of TPPS with linear Stern–Volmer (SV) plots. On the contrary, quenching of TPPS emission by Au NPs shows composed models. One model is the sphere of action static quenching model that prevails at high quencher concentrations leading to non-linear SV plots with positive deviation. However, at low Au NPs concentrations, traditional dynamic quenching occurs with linear SV plots. The quantum calculations for TPPS structure have been obtained using Gaussian 09 software: in which the TPPS optimized molecular structure was achieved using DFT/B3LYP/6-311G (d) in a gaseous state. Also, the calculated electronic absorption spectra for the same molecule in water as a solvent are obtained using TD/M06/6-311G + + (2d, 2p). Furthermore, the theoretical and experimental results comparable to UV–Vis spectra have been investigated.

Amino benzene dicarboxylic acid-derived luminescent nitrogen-doped Carbon- quantum Dots/anti-TNT antibodies conjugate for detection of nitroaromatic contaminant in water: A comparative analysis of chemo-Bio-sensing affinity

Water contaminants are posing deadly impacts on living beings' survival. Nitroaromatic compounds e.g. Trinitrotoluene (TNT), are one among these lethal contaminants and require to be early detected before their consumption. The nitrogen-doped carbon quantum dots (NCQDs) are synthesized from the precursor 2-aminobenzene-1,4-dicarboxylic acid via the hydrothermal route. The as-synthesized NCQDs are conjugated with anti-TNT antibodies and characterized using various analytical techniques. The spherical NCQDs are having a size of 5.69 nm. At excitation wavelength 347 nm, the emission wavelength of NCQDs is shifted from 445 nm to 443 nm after their conjugation with anti-TNT Ab. The decrease in photoluminescence emission intensity of NCQDs and NCQDs/Ab with the increased concentration of TNT is regulated by the formation of Jackson-Meisenheimer and antigen–antibody complex, respectively. The detection limit of NCQDs and NCQDs/Ab is observed to be 1.39 X 10-5 M and 1.07 X 10-9 M respectively. The stern–volmer quenching constant of NCQDs is increased from 1.5 X 103 M−1 to 8.5 X 105 M−1 after their conjugation with anti-TNT Ab depicting the elevated affinity of NCQDS/Ab for TNT. The biosensing NCQDs/Ab are found to be more selective towards TNT than the chemosensing NCQDs probe. In spiked real water samples, the RSD of NCQDs/Ab is found to be ± 1.5%.

CTV Based Sensor for the Rapid Detection of Nitro Toluene With Computational Studies and Molecular Modelling.

A new tri-naphthoylated Cyclotriveratrylene molecule has been synthesized for the rapid and sensitive detection of 4-nitrotoluene (4-NT) among various nitro aromatic compounds (NACs) by using a spectrofluorimetric method. The newly derrivatized cyclotriveratrylene compound is successfully confirmed by using the available techniques of 1H-NMR, 13CNMR,and ESI-MS. This synthesised molecule is 1NC-CTV (1-Naptholy Chloride-Cyclotriveratrylene). Strong quenching inthe fluorescence intensity of 1NC-CTV was observed upon the addition of 4-NT. Further quantum yield studies were carried outand by using the stern volmer it was concluded that the fluorescence quenching mechanism is dynamic or static. The molecule1NC-CTV was further studied with the help of computational methods such as molecular docking to study the bindinginteractions and properties of the molecule.

A Europium MOF-based turn-off fluorescent sensor for tryptophan detection in human serum, urine and lake water

This work presents a turn-off fluorescence sensor [Eu(SIP)(H2O)4] (Eu-MOF, H3SIP ​= ​5-sulfoisophthalic acid) which features a (3,6) topological network. Eu-MOF exhibits high structure stability in water, organic solvents and at pH ​= ​1–12. The sensitivity test indicates a linear equation of I0/I ​= ​0.04597∙Ctrp + 0.39164 with limit of detection (LOD) calculated as 0.80 ​μM. The fluorescence quenching mechanism is analyzed based on Stern-Volmer (SV) equation, giving the SV quenching rate constant (KSV) of 4.307 ​× ​104 ​M−1 and the quenching rate constant (Kq) of 2.51 ​× ​108 ​M−1 ​s−1, demonstrating tryptophan (trp) quenching Eu-MOF is a dynamic quenching process. In the selectivity test, trp shows the fluorescence quenching compared to twelve control compounds, and the interferents don't affect trp quenching Eu-MOF. Eu-MOF also exhibits a high durability that the characteristic emission remains stable in five-fluorescence quenching-recovery cycles. Eu-MOF returns very close calculated trp concentrations to the theoretic values and high recoveries in the application tests of human serum, urine and lake water based on the linear equation. The paper-based Eu-MOF sensor displays obvious emission color changes, whose red values (R) reveal a linear equation of R ​= ​−0.54857∙Ctrp ​+ ​188.33, indicating the possibility of the on-site trp detection. Totally, Eu-MOF is a rapid turn-off fluorescence sensor to trp with high sensitivity, selectivity, and durability.

Piano-stool type (η6-p-cymene)ruthenium(II) thiazole-derived motifs complexes: Synthesis, crystal structures, DFT studies, molecular docking and in-vitro binding studies with HSA and cytotoxicity

Herein, two new p-cymene ruthenium(II) complexes [(η6-p-cymene)Ru (L1-OH) Cl] 1 and [(η6-p-cymene)Ru(L2-OH)Cl] 2 of thiazolyl-derived ligands i.e., (E)-2-(((5-methylthiazol-2-yl) imino) methyl) phenol (L1) and (E)-4-methyl-2-((5-methylthiazol-2-yl)imino) methyl)phenol (L2) have been designed and synthesized. The FT-IR, 1HNMR, 13C NMR spectroscopy and elemental analysis characterized both the ligands and the complexes. The representative molecular structures of the ligand L2 and complex 1 were determined by single X-ray crystallography. Moreover, the DFT studies were carried out to optimize the geometries and calculate the energies of the molecules by frontier molecular orbitals. Using multi-spectroscopic techniques and computational studies, these ruthenium arenes complexes 1 and 2 were investigated for the binding affinity towards human serum albumin (HSA). The results revealed the significantly good binding propensity of these complexes 1 and 2 towards HSA. The intrinsic binding studies exhibited the decerase in stern–volmer constant (Ksv) with increase in temperature. The mode of binding was also found to be static. The results obtained from extrinsic flouresence using ANS dye, ascertained the competitive binding inducing conformational alterations of HSA. Furrthermore, The cytotoxicity results displayed good IC50 values against HeLa cells compared to cisplatin, which is suggestive of the anti-cancer chemotherapeutic potential of complexes.

Stern-Volmer analysis of photocatalyst fluorescence quenching within hollow-core photonic crystal fibre microreactors.

We report the use of optofluidic hollow-core photonic crystal fibres as microreactors for Stern-Volmer (SV) luminescence quenching analysis of visible-light photocatalytic reactions. This technology enables measurements on nanolitre volumes and paves the way for automated SV analyses in continuous flow that minimise catalyst and reagent usage. The method is showcased using a recently developed photoredox-catalysed α-C-H alkylation reaction of unprotected primary alkylamines.