Stern-Volmer Relationship Research Articles

Visible‐Light‐Mediated Activation of Remote C(sp3)−H Bonds by Carbon‐Centered Biradical via Intramolecular 1,5‐ or 1,6‐Hydrogen Atom Transfer

AbstractIn this study, we introduce a novel intramolecular hydrogen atom transfer (HAT) reaction that efficiently yields azetidine, oxetane, and indoline derivatives through a mechanism resembling the carbon analogue of the Norrish‐Yang reaction. This process is facilitated by excited triplet‐state carbon‐centered biradicals, enabling the 1,5‐HAT reaction by suppressing the critical 1,4‐biradical intermediates from undergoing the Norrish Type II cleavage reaction, and pioneering unprecedented 1,6‐HAT reactions initiated by excited triplet‐state alkenes. We demonstrate the synthetic utility and compatibility of this method across various functional groups, validated through scope evaluation, large‐scale synthesis, and derivatization. Our findings are supported by control experiments, deuterium labeling, kinetic studies, cyclic voltammetry, Stern–Volmer experiments, and density functional theory (DFT) calculations.

Visible-Light-Mediated Activation of Remote C(sp3)-H Bonds by Carbon-Centered Biradical via Intramolecular 1,5- or 1,6-Hydrogen Atom Transfer.

In this study, we introduce a novel intramolecular hydrogen atom transfer (HAT) reaction that efficiently yields azetidine, oxetane, and indoline derivatives through a mechanism resembling the carbon analogue of the Norrish-Yang reaction. This process is facilitated by excited triplet-state carbon-centered biradicals, enabling the 1,5-HAT reaction by suppressing the critical 1,4-biradical intermediates from undergoing the Norrish Type II cleavage reaction, and pioneering unprecedented 1,6-HAT reactions initiated by excited triplet-state alkenes. We demonstrate the synthetic utility and compatibility of this method across various functional groups, validated through scope evaluation, large-scale synthesis, and derivatization. Our findings are supported by control experiments, deuterium labeling, kinetic studies, cyclic voltammetry, Stern-Volmer experiments, and density functional theory (DFT) calculations.

Fluorescence immunoassay using triangular carbon dots for detection of the cardiac marker Troponin T in acute myocardial infarction

A cardiac immunosensor was developed to detect heart attacks (myocardial infarctions) at an early stage. This technique, utilizing carboxylic functionalized triangular carbon dots (caf-TCDs) combined with an antibody anti-cardiac Troponin T (anti-cTnT), proved to be a quick and sensitive method for detecting cardiac troponin T (cTnT) in both buffer solutions and biological fluids such as serum. The antibody for cardiac Troponin T (cTnT) was chemically linked to amphiphilic caf-TCDs using a carbodiimide coupling reaction. Exfoliated graphene oxide (GO) sheets effectively bind to anti-cTnT labeled caf-TCDs on their surface, resulting in a non-radiative energy transfer process where the fluorescence is suppressed. This interaction between caf-TCDs and GO follows a nonlinear and increasing Stern-Volmer relationship, indicating a combination of static and dynamic quenching. When antigen (cTnT) is present, the interaction between antibodies (anti-cTnT) and the cTnT molecules hinders the energy transfer process. This interaction also affects the positioning of the nano-couple and causes the detachment of CDs from the GO surface. As a result, the energy transfer process is impeded, leading to the restoration of fluorescence intensity. The sensor exhibits high specificity and low sensitivity to non-specific antigens. It shows a linear reaction to cTnT in the range of 0.05–50 ng mL-1, with a detection limit of 0.046 ng mL-1. Therefore, the anti-cTnT-caf-TCD/GO sensor offers a potential platform for detecting cTnT with increased sensitivity.

Dual Nickel/Photoredox-Catalyzed Arylsulfonylation of Allenes.

The nickel/photoredox dual catalysis system is an efficient conversion platform for the difunctionalization of unsaturated hydrocarbons. Herein, we disclose the first dual nickel/photoredox-catalyzed intramolecular 1,2-arylsulfonylation of allenes, which can accurately construct a C(sp2)-C(sp2) bond and a C(sp3)-S bond. The reaction exhibits excellent chemoselectivity and regioselectivity, allowing modular conformations of a diverse series of 3-sulfonylmethylbenzofuran derivatives. Control experiments showed that the bipyridine ligand is crucial for the formation of a stable σ-alkyl nickel intermediate, providing the possibility for sulfonyl radical insertion. Meanwhile, the electrophilic sulfonyl radical facilitates further oxidative addition of the σ-alkyl nickel intermediate and inhibits addition with allenes. In addition, control experiments, cyclic voltammetry tests, Stern-Volmer experiments, and density functional theory calculations afford evidence for the Ni(0)/Ni(I)/Ni(II)/Ni(III) pathway in this 1,2-arylsulfonylation.

A green reaction-based turn-off fluorescence sensor for determination of copper ions: DFT calculations, quenching mechanism, green chemistry metrics, and application in environmental samples.

When Cu(II) reacts with ascorbic acid (AA) to form Cu(I), Cu(I) can combine with eosin Y (EY) to form ionic associations, resulting in significant fluorescence quenching of the EY. Based on the turn-off of fluorescence in the chemosensor EY, a green reaction is proposed herein for the detection of Cu(II). The novel detection method for Cu(II) demonstrates simplicity, high sensitivity, and excellent selectivity, rendering it suitable for analyzing environmental samples. A static fluorescence quenching mechanism is validated through the Stern-Volmer relationship, and the thermodynamic parameters of the reaction are explored using a van 't Hoff plot. The reaction mechanism is investigated via fluorescence spectra, absorption spectra, and density-functional theory (DFT) calculations. The probe's green nature is confirmed by applying four green analytical chemistry metrics.

High-Sensitivity Creatinine Detection via a Dual-Emission Ratiometric Fluorescence Probe Incorporating Amino-MIL-53@Mo/ZIF-8 and Rhodamine B.

Quantifying creatinine (Cn) in biological fluids is crucial for clinically assessing renal insufficiency, thyroid irregularities, and muscle damage. Therefore, it is crucial for human health to have a simple, quick, and accurate Cn analysis technique. In this study, we have successfully synthesized a 3D ratiometric dual-metal-organic framework, namely, the amino-MIL-53@Mo/ZIF-8 and rhodamie B heterostructure, using an internal strategy for sustained growth. The dual-MOF functions as an adsorbent and preconcentrates Cn. The pH, reaction time, and volume ratio of amino-MIL-53@Mo/ZIF-8/rhodamie B were optimized using the one-variable-at-a-time technique in this study. The quantitative study of the Cn concentration for this RF biosensor was obtained under ideal conditions (R2 = 0.9962, n = 3), encompassing the linear range of 0.35-11.1 μM. The detection and quantitation limits were 0.18 and 0.54 nM, respectively. Both intra- and interday reproducibility showed high repeatability of the RF biosensor, UV-vis, and ZETA potential studies, and the Stern-Volmer relationship was used to clarify the fluorescence quenching process. These superior sensing capabilities and the benefits of simple manufacturing, acceptable stability, and practicality make the RF biosensor intriguing for ultrasensitive Cn detection in practical applications.

Spectroscopic Investigation of the Remote C–H Allylation of Amides via Photoredox and Nickel Dual Catalysis

AbstractThe mechanistic details of a reported allylation reaction are investigated by means of Stern–Volmer experiments and nanosecond transient absorption spectroscopy. Both reference substrates, i.e., an allylic chloride and a trifluoroacetamide, are inefficient quenchers but large quenching rate constants are observed upon the addition of Ni(COD)2 and a bisoxazoline ligand. The large quenching rate constants and absence of observable photoproducts are consistent with a mechanism that operates by energy transfer between the excited-state iridium photosensitizer and the nickel complex.

Visible Light-Promoted β-Functionalization of Carbonyl Compounds in the Presence of Organic Dyes.

Herein, we investigate the use of organic photocatalysts in the visible light-promoted β-functionalization of carbonyl compounds. In particular, we studied the addition of aliphatic aldehydes to α,β-unsaturated compounds (β-Michael addition), and the reaction of cyclic ketones with either ketones (β-aldol condensation) or imines (β-Mannich reaction). Among the dyes tested, donor-acceptor cyanoarenes gave the best results, promoting the transformations of interest in moderate to good yields. The reaction scope was investigated on substrates with different steric and electronic properties. Fluorescence quenching analysis (Stern-Volmer experiments) led us to propose for these reactions a reductive quenching mechanism involving a transient 5πe- activation mode.

Visible-Light Photocatalytic Highly Selective Oxidation of Alcohols into Carbonyl Compounds by CsPbBr3 Perovskite.

Conversion of alcohols into corresponding carbonyl compounds through an oxidation reaction with high conversion and selectivity simultaneously under mild conditions still remains a great challenge. Herein, a cost-effective and highly efficient photocatalytic protocol for selective oxidation of alcohols was developed using CsPbBr3 perovskite as a heterogeneous photocatalyst, which afforded aldehydes/ketones exclusively with a yield of 99% at ambient temperature under an air atmosphere. Moreover, the photocatalyst can be recycled at least 5 times without a significant decrease in catalytic activity. The detailed reaction mechanism was investigated by a series of quenching experiments, including Stern-Volmer experiments and electron paramagnetic resonance spectroscopy analysis as well as DFT calculations.

SDS-capped 1-pyrenecarboxaldehyde nanoprobe for selective detection of Cu2+ ion from water samples: Spectroscopic approach.

Sodium dodecyl sulfate (SDS)-capped 1-pyrenecarboxaldehyde nanoparticles (PyalNPs) were prepared using a reprecipitation method in an aqueous medium and exhibited red-shifted aggregation-induced enhanced emission (AIEE). The dynamic light scattering (DLS) examination showed narrower particle size distribution with an average particle size of 41 nm, whereas -34.5mV zeta potential value indicate the negative surface charge and good stability of nanoparticles (NPs) in an aqueous medium. The AIEE was seen at λmax = 473 nm in a fluorescence spectrum of a PyalNP suspension. In the presence of Cu2+ ions, the fluorescence of PyalNPs quenches very significantly, even in the presence of other metal ions like Ba2+ , Ca2+ , Cd2+ , Co2+ , Al3+ , Fe2+ , Hg2+ , Ni2+ and Mg2+ . The changes in the fluorescence lifetime of PyalNPs in the presence of Cu2+ ions suggested that the type of quenching was dynamic. The fluorescence quenching data for the NPs suspension fitted well into a typical Stern-Volmer relationship in the concentration range 1.0-25 μg/ml of Cu2+ ions. The estimated value of the correlation coefficient R2 = 0.9877 was close to 1 and showed the linear relationship between quenching data and Cu2+ ion concentration. The limit of detection (LOD) was found to be 0.94 ng/ml and is far below the tolerable intake limit value of 1.3μg/ml accepted by the World Health Organization for Cu2+ ions in drinking water. The fluorescence quenching approach for a SDS-capped Pyal nanosuspension for copper ion quantification is of high specificity and coexisting ions were found to interfere very negligibly. The developed method was successfully applied for the estimation of copper ions in river water samples.

Application of aza-BODIPY as a Nitroaromatic Sensor.

Nitroaromatic explosive detection with high sensitivity and selectivity is requisite for civilian and military safety and the ecosystem. In this study, aza boron dipyrromethene (aza-BODIPY) dye was selected as a fluorescent-based chemosensor against nitroaromatic compounds (NACs) including 2,4,6-trinitrophenol (picric acid, TNP), 2,4,6-trinitrotoluene (TNT), and 2,4-dinitrotoluene (DNT). This dye molecule exhibits sharp fluorescent behavior with high quantum yields beyond the near-infrared region (NIR) and is considered as a potential candidate for the detection of NACs. O'Shea's approach was used to synthesize tetraphenyl-conjugated aza-BODIPY molecules. Quenching of fluorescence emission of aza-BODIPY at 668 nm after the exposure to NACs was investigated under acetonitrile-water and acetonitrile-ethanol solvent conditions. The quenching responses and its mechanism were examined by considering the Stern-Volmer relationship Stern-Volmer constants (Ksv) for TNP (in water), TNP (in ethanol), TNT, and DNT, which are predicted to be 1420, 1215, 1364, and 968 M-1, respectively, all of which are sufficiently above the limit of detection (LOD) values. Thus, the present study opens up the possibility of the usage of aza-BODIPY molecules as a low-cost, light-weight sensor for the detection of NAC explosives.

Abstract 4844: Development of an oxygen consumption rate assay for a standard plate reader

Abstract Cells generate ATP by two metabolic pathways, oxidative phosphorylation (OXPHOS) and glycolysis. Together, the amount of ATP generated by both OXPHOS and glycolysis define a cell’s metabolic phenotype and fitness. Researchers are interested in methods to characterize cellular metabolic fitness, which can be a powerful a selection criterion for cell-based therapies such as CAR-T cell therapy. Researchers are also interested in measuring the effects of drug treatment on metabolic fitness, to identify metabolic targets for cancer therapeutics and to determine mitochondrial toxicity of novel therapeutics. Here, we have developed a low-cost strategy for a standard plate reader to monitor the rate change of oxygen concentration, or the oxygen consumption rate (OCR), which is a measure of OXPHOS activity. In our assay, oxygen quenches a phosphorescent porphyrin dye in a concentration dependent manner, allowing one to calculate the oxygen concentration of the culture system with the Stern-Volmer relationship. The porphyrin dye is embedded within nanobeads that are suspended above the cell monolayer and the phosphorescence of the beads is measured from the bottom of the well with a standard plate reader. We found that the OCR increased with cell seeding density in three separate cell lines: HEP-G2, HCT-116, and K-562 suspension cells. We showed that inhibitors of the electron transport chain (ETC) decreased OCR, whereas an uncoupler of the electron transport chain, FCCP, increased OCR in a dose dependent manner. Lastly, mitochondrial fitness (e.g., spare respiratory capacity) was determined by sequentially dosing the mitochondria with poisons specific to the different ETC complexes. Citation Format: Ian Marozas, Zhiyang Zeng, Mike Valley, Jolanta Vidugiriene, James Cali, Wenhui Zhou. Development of an oxygen consumption rate assay for a standard plate reader. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4844.

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).

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

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

Selective Sensing of Darolutamide and Thalidomide in Pharmaceutical Preparations and in Spiked Biofluids.

Selective spectrofluorometric sensing is introduced for the analysis of non-steroidal anti-androgens, darolutamide, and thalidomide in pharmaceutical preparations and biofluids. An organic fluorophore, 2,4,8,10-tetramethylpyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidine 2 was synthesized in our laboratories by new simple methods to act as a fluorescent reagent for the analysis of the studied drugs. Elemental and spectral analyses were performed to approve the fluorophore structure. The fluorophore possesses a fluorescence at λem 422 nm when excited at 328 nm. The interaction between the studied drugs and the fluorophore was found to be quenching. The quenching mechanisms were studied and interpreted through the Stern-Volmer relationship. Moreover, the Stern-Volmer constants were calculated for the quenching interactions of both drugs. The introduced method was validated for the estimation of darolutamide and thalidomide in dosage forms, plasma, and urine, offering good percentage recoveries.

Probing Prolamin-Anthocyanin Interactions for the Rational Design of Plant-Based Encapsulation Systems

Plant proteins are increasingly focused upon as alternatives to animal-derived macromolecules for the encapsulation of bioactives. The rational design of encapsulation carriers should be based on a solid understanding of the interactions between the proteins and bioactives. Encapsulation technology for food applications has focused predominantly on the protection and controlled release of hydrophobic bioactives. For hydrophilic molecules, although not less important from a nutritional and health perspective, significantly fewer encapsulation systems have been explored, designed and described. As hydrophilic molecules tend to partition into the aqueous food matrix, it is even more crucial to understand and to be able to modulate the interactions between the hydrophilic bioactive and the encapsulating matrix material in food relevant conditions. Therefore, examining the nature of the interactions between anthocyanins (ACNs), a hydrophilic bioactive, and prolamin plant proteins (gliadin, hordein, secalin, and avenin) is timely. These interactions were examined using steady-state and time-resolved luminescence spectroscopy techniques. The ACN-induced quenching of the prolamins intrinsic fluorescence emission did not follow a linear Stern-Volmer relationship, but rather displayed an upward curvature for all the prolamins tested. Hence, both static and dynamic quenching likely occurred in the prolamin-ACN systems. The quenching mechanism was further explored based on the changes in fluorescence lifetime as ACN concentration increased. As the independent lifetimes of the prolamin-ACN combinations did not decrease discernibly as a function of ACN concentration, static quenching is presumably the predominant quenching mechanism. The thermodynamic parameters revealed that the interactions between secalin- and avenin-ACN are mainly driven by the hydrophobic effect, while those between gliadin- and hordein-ACN are dominated by ionic interactions. Zeta-potential measurements support the dominant ionic interactions found for gliadin and hordein. The insights gained in this research will serve as a sound basis for further studies focusing on matrix selection with regard to creating performant encapsulation systems for ACNs.

Modulating Role of Co-Solutes in Complexation between Bovine Serum Albumin and Sodium Polystyrene Sulfonate.

The action of three types of co-solutes: (i) salts (NaCl, NaBr, NaI), (ii) polymer (polyethylene glycol; PEG-400, PEG-3000, PEG-20000), and (iii) sugars (sucrose, sucralose) on the complexation between bovine serum albumin (BSA) and sodium polystyrene sulfonate (NaPSS) was studied. Three critical pH parameters were extracted from the pH dependence of the solution’s turbidity: corresponding to the formation of the soluble complexes, corresponding to the formation of the insoluble complexes, and corresponding to the charge neutralization of the complexes. In the presence of salts, the formation of soluble and insoluble complexes as well as the charge neutralization of complexes was hindered, which is a consequence of the electrostatic screening of attractive interactions between BSA and NaPSS. Distinct anion-specific trends were observed in which the stabilizing effect of the salt increased in the order: NaCl < NaBr < NaI. The presence of PEG, regardless of its molecular weight, showed no measurable effect on the formation of soluble complexes. PEG-400 and PEG-3000 showed no effect on the formation of insoluble complexes, but PEG-20000 in high concentrations promoted their formation due to the molecular crowding effect. The presence of sugar molecules had little effect on BSA-NaPSS complexation. Sucralose showed a minor stabilizing effect with respect to the onset of complex formation, which was due to its propensity to the protein surface. This was confirmed by the fluorescence quenching assay (Stern-Volmer relationship) and all-atom MD simulations. This study highlights that when evaluating the modulatory effect of co-solutes on protein-polyelectrolyte interactions, (co-solute)-protein interactions and their subsequent impact on protein aggregation must also be considered.

Recalling the effect of fluorescence anisotropy on the measurement of quantum yields

We present a quantitative analysis of the deviations introduced by the anisotropy of the fluorescence on the measurement of the quantum yield of emission. Errors of up to 40% can be encountered depending on the characteristics of both sample and apparatus. Additionally, we have analyzed the effect of anisotropy on the study of fluorescence quenching in Stern-Volmer experiments, and on the reconstruction of time-resolved emission spectra. We conclude that the use of polarizers is recommended provided they are well characterized.

Capability of novel fluorescence DNA-conjugated CdTe/ZnS quantum dots nanoprobe for COVID-19 sensing

Urgent identification of COVID-19 in infected patients is highly important nowadays. Förster or fluorescence resonance energy transfer (FRET) is a powerful and sensitive method for nanosensing applications, and quantum dots are essential materials in FRET-based nanosensors. The QDs are conjugated to DNA or RNA and used in many applications. Therefore, in the present study, novel fluorescence DNA-conjugated CdTe/ZnS quantum dots nanoprobe designed for detection of Covid-19 after extracting their RNA from saliva of hesitant people. For achieving this purpose, the water-soluble CdTe/ZnS QDs-DNA prepared via replacing the thioglycolic acid (TGA) on the surface of QDs with capture DNA (thiolated DNA) throw a ligand-exchange method. Subsequently, by adding the different concentrations of complementary (target DNA) in a mixture of quencher DNA (BHQ2-labeled DNA) and the QDs-DNA conjugates at different conditions, sandwiched hybrids were formed. The results showed that the fluorescence intensity was decreased with increasing the concentration of target DNA (as a positive control). The linear equation and regression (Y = 40.302 X + 1 and R2 = 0.98) were obtained by using the Stern-Volmer relationship. The Limit of detection (LOD) was determined 0.000823 µM. The achieved results well confirm the outcomes of the RT-PCR method in real samples.

Utilization of waste biomass of Poa pratensis for green synthesis of n-doped carbon dots and its application in detection of Mn2+ and Fe3+

In this study, a novel and sustainable approach was used to synthesize nitrogen-doped carbon dots (NCDs) from the waste biomass of Poa Pratensis (Kentucky bluegrass (KB)) by a facile hydrothermal method. The prepared KBNCDs were subjected to various characterization techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy to verify the formation of carbon dots and their surface functional groups. The KBNCDs exhibited good hydrophilic fluorescence (FLU) properties with an acceptable quantum yield (7%). The synthesized KBNCDs showed excitation wavelength-dependent FLU emission behavior with strong cyan-blue FLU upon irradiation with 365 nm UV-light. The hydrophilic optical properties of the as-synthesized KBNCDs were used to detect Fe3+ and Mn2+ ions in an aqueous medium with good selectivity and sensitivity. It was found that the FLU of the KBNCDs is quenched in the presence of Fe3+ and Mn2+ ions, and the quenching rate was linear with the concentration of Fe3+ and Mn2+ ions. The limit of detection (LOD) of KBNCDs with metal ions was calculated using the Stern–Volmer relationship. The LOD values for Fe3+ or Mn2+ ions were calculated as 1.4 and 1.2 μM, respectively with the detection range from 5.0 to 25 μM. Based on these results, this study provides an underpinning for the development of KBNCD as FLU sensors that can be used in aqueous media.