Stern-Volmer Method Research Articles

Depopulation mechanisms of atomic hydrogen in the n = 3 level following two-photon excitation by a picosecond laser

One of the major constraints of measurements of atomic hydrogen densities using two-photon absorption laser induced fluorescence in most plasma and combustion environments is the determination of fluorescence decay times ( τfluo H ), especially when using nanosecond-lasers or slow acquisition systems. Therefore, it is necessary to identify the depopulation processes of the laser excited level in order to correctly estimate τfluo H . In this study, depopulation mechanisms of atomic hydrogen excited by two-photon absorption to the n = 3 level (H(n = 3)) have been investigated using a picosecond-laser excitation and acquisition of fluorescence by a streak camera, which allowed for direct measurement of τfluo H and hence, the atomic hydrogen densities, in an H2 microwave plasma operating in the pressure range 20–300 Pa. By combining these measurements with a detailed H(n = 3) collisional radiative depopulation model, it was found that full mixing amongst the H(n = 3) sub-levels occurs in our discharge conditions, even at a pressure as low as 20 Pa. Moreover, it is also seen that the Lyman β line is only partially trapped, as its escape factor Λ31 decreases from 0.94–0.98 down to 0.58–0.86 while the measured atomic hydrogen density rises from 8±5×1019m−3 to 9±6×1020m−3 . This means that the radiative decay rate of H(n = 3) atoms varies with pressure and the classical Stern–Volmer method used to determine the quenching cross-section of excited H(n = 3) in collisions with H2 molecules, σQHn=3/H2 , is not valid for our measurements. We used two different physics-based approaches, and show that the quenching cross-section σQHn=3/H2 lies in the range 90– 106×10−20m2 , which can be averaged as 98±8×10−20m2 . This substantially improved estimation of σQHn=3/H2 obtained in this work will be useful for the accurate estimation of H(n = 3) fluorescence decay times and therefore the atomic hydrogen densities.

Insight into the effect of Ca2+, Mg2+ and Zn2+ on serum albumin interaction of benzimidazole-type new isopropyl substituted N-heterocyclic carbene molecules

N-heterocyclic carbenes are not only revolutionary catalysts in organic synthesis but also well-known anthelmintics, fungicides, antacids, and antibiotics. Serum albumin transports various substances in the body such as hormones, fatty acids, bilirubin, certain drugs, and is also crucial in the maintenance of health and bodily functions. For that reason, in this study five novel benzimidazole-type N-heterocyclic carbenes, 1- Isopropyl-3-benzyl-5,6-dimethylbenzimidazolium chloride (2a), 1- Isopropyl-3-(2-chlorobenzyl)-5,6-dimethylbenzimidazolium chloride (2b), 1- Isopropyl-3-(2-methylbenzyl)-5,6-dimethylbenzimidazolium chloride (2c), 1- Isopropyl-3-(2,3,4,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazolium chloride (2d), 1- Isopropyl-3-naphthyl-5,6-dimethylbenzimidazolium chloride (2e) were gained in 74–85 % yields. The molecules were fully characterized 1H and 13C NMR, elemental analysis, UV–Vis spectroscopy, FT-IR, and DFT- and TDDFT-based in-silico methods. Additionally, Stern-Volmer methods with fluorescence spectroscopy were performed in order to analyze the BSA-binding properties of these molecules. BSA interactions of molecules were evaluated with specific concentrations of Ca2+, Mg2+ and Zn2+. The detailed interaction analyses were also surveyed by molecular docking methods against the BSA and DNA.

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.

Coupling of cationic porphyrins on manganese ferrite nanoparticles: A potential multifunctional nanostructure for theranostics applications

We present here the coupling of cationic meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (TMPyP) and their zinc complex (ZnTMPyP) with magnetic nanoparticles (MNPs) of manganese ferrite (MnFe2O4) covered with citric acid (CA), dimercaptosuccinic acid (DMSA), and tripolyphosphate (TPP). In the presence of MNPs, the fluorescence emission of porphyrins was suppressed through static fluorescence quenching. Stern-Volmer method was employed to determine the binding constants (Kb) between porphyrins and MNPs. These interactions were described based on the coating layer properties and the unfunctionalized metallic sites on the surface of MNPs. The higher binding constants (Kb) were observed for TPP and CA MNPs (KbTPP < KbCA), which possess a poor recovery coefficient. In this case, the residuals unfunctionalized Fe3+/Mn2+ atomic sites on the MNPs surface can interact with nitrogen atoms of macrocyclic ring of free base porphyrin and the free oxygens from carboxylate and phosphate groups interact with amino hydrogens of porphyrin ring through hydrogen bonds. For ZnTMPyP, can occur a coordination of zinc atoms by the carboxylate or phosphate groups that are able to form strong and stable interactions. Furthermore, it was observed that while porphyrins are bound to MNPs, fluorescence emission and singlet oxygen production are reduced. However, such properties were recovered after the release of porphyrins from MNPs. To investigate the molecules release, a proof-of-concept photothermal experiment was designed and performed, where temperatures higher than 50 °C were reached. These results show that this system combines properties which can be employed for development of drug delivery system, magnetic tracers for alternating current biosusceptometry (ACB), as well as application of photodynamic (PDT), photothermal therapy (PTT) and magnetic hyperthermia (MHT) therapies.

Albumin-induced large fluorescence turn ON in 4-(diphenylamino)benzothiazolium dyes for clinical applications in protein detection

A series of [4-(diphenylamino)]styrylbenzothiazolium-based fluorescent probes 1a -1f have been synthesized to investigate their albumin binding properties. The probe 1 was found to be nearly non-fluorescent in both aqueous and organic solvents and exhibited a very large fluorescence turn ON at λem ≈ 630–650 nm (фfl ≈0.38–0.40) upon addition of serum albumin in aqueous solution. Probes exhibited high sensitivity towards detecting albumin in aqueous solution with a limit of detection (LOD) below 7–14 ng/mL. The stability constants for the probe-albumin interactions were calculated by Stern-Volmer method. The stability of the probe-albumin complexes was further investigated during this study to understand the role of the substituents of the probe’s structure towards the observed selectivity. Spectrometric fluorescence titrations were conducted to investigate selectivity, sensitivity, and stability of the probe-albumin complex. Probe’s binding specificity was further studies in the presence of known site-specific drug molecules via competitive displacement method. The large fluorescence response exhibited towards HSA and BSA found to be highly useful for visualizing albumin content in SDS-PAGE up to nanogram scale. The probe 1 was successfully utilized for analysing albumin content in urine samples, showing good linear correlation and indicating the probe’s suitability in clinical diagnostics.

Waste capacitor: A fresh approach to detect and remove Cr(VI) from water and making it an energy harvesting material

The large scale amplification of industrial discharge in the modern era is resulting in widespread water pollution, especially from various industrial effluents and wastewater containing heavy metals, posing a severe threat to our environment. In order to combat such problems, this work aims on Multifunctional Fluorescent Nano-Sensor (MFNS) mediated simultaneous detection and removal of hexavalent chromium from real life wastewater which further converts it into an energy harvesting material, namely, “Waste capacitor”. This smart material can detect the presence of the targeted heavy metal (Cr(VI)) in the wastewater and can entrap it by using a facile adsorption process. Thereafter, it will change its microstructure which further enhances its dielectric properties. Morphology, microstructure and optical properties of the synthesized material have been studied thoroughly and a turn-off based fluorescence sensing has been reported herein. Photoinduced electron transfer (PET) based fluorescence quenching is mainly responsible for this sensing mechanism. The selectivity and sensitivity of the material during fluorescence sensing have also been studied by using standard Stern-Volmer method showing that the synthesized material is tremendously selective and sensitive towards the specific target ion. High surface area with slit-like porous structure enhances the adsorption based removal of the contaminant. Nearly 76% of contaminants have been removed by using this smart material. After adsorbing specified target, this MFNS changes its microstructure and results in superior dielectric constant with a minimal tangent loss. Tremendous sensitivity (in nM range), selectivity towards the specific contaminant and adsorption of toxic heavy metal and converting it into a green energy harvesting material (waste capacitor) makes this smart multifunctional material a real waste to wealth converter.

Recognition of Fe3+ by a new azine-based fluorescent “turn-off” chemosensor and its binding mode analysis using DFT

A highly responsible Fe3+, azine chemosensor (EBHMM) was successfully designed and synthesized. The structure of the synthesized azine was confirmed by FT-IR, UV–Vis, 1H and 13C{1H} NMR spectroscopic techniques and high resolution mass spectrometry. The azine shows sensitive and selective fluorescence “turn-off” towards Fe3+ ion over other metal ions in 1:1 DMF-H2O (5 μM, pH = 7.4) solution. The fluorescence quenching on the addition of Fe3+ ion at various pH clearly indicate that the azine can be used for the quantitative determination of Fe3+. The binding of Fe3+ with chemosensor was analyzed by confirming the formation of metal-ligand complex using HRMS-ESI spectrometry. The binding stoichiometry (1:1) was calculated using Stern-Volmer method and the binding constant 1.0034 M-1 was calculated using Benesi-Hildebrand plot. The exact binding sites of the chemosensor with Fe3+ ion is theoretically explained with Fukui Function using DFT study in B3LYP function with B3LYP/6-311++G (d,p) level of basis set. The “turn-off” fluorescence through photo induced electron transfer (PET) process is discussed and confirmed with the results of Fukui Function and Frontier molecular orbital analysis.

Binding interaction of sodium benzoate food additive with bovine serum albumin: multi-spectroscopy and molecular docking studies

Sodium benzoate (SB) is widely used as a preservative in food industry, and bovine serum albumin (BSA) is a major carrier protein similar to human serum albumin (HSA), the study of the binding between the two has great significance on human health. In this paper, we systematically investigated the binding of SB and BSA under the simulated physiological conditions combining with various common analytical methods, e.g., fluorescence, UV–vis absorption, synchronous fluorescence and circular dichroism (CD) spectra, as well as molecular docking method. The fluorescence quenching measurements were respectively carried out at 298 K, 303 K and 308 K using the Stern–Volmer method. The results reveal that ground state SB–BSA complex was formed within the binding constants from 2.02 × 104 to 7.9 × 103 M−1. Meanwhile, the negative values of ΔH0 (− 43.92 kJ mol−1) and ΔS0 (− 111.6 J mol−1 K−1) demonstrated that both the hydrogen binding interaction and van der Waals forces contributed to stabilizing the SB–BSA complex. The site marker competitive experiments show that the SB and BSA bound at site I. Furthermore, the experimental results of UV–vis absorption, synchronous fluorescence and CD spectra indicate that the binding of SB and BSA may change the conformation of BSA. In addition, the molecular docking experiment suggests that hydrogen bond was formed in the interaction between SB and BSA.

Probing the in vitro binding mechanism between human serum albumin and La 2 O 2 CO 3 nanoparticles

The interaction of La2O2CO3 nanoparticles (La NPs) with human serum albumin (HSA) has been studied. Analysis of the fluorescence quenching data of HSA using Stern–Volmer method showed that La NPs quenched HSA fluorescence in static quenching mode. Thermodynamic analysis indicated that hydrogen bonds and Van der Waals interactions play a major role for HSA–La NPs associations. Fluorescent displacement measurements confirmed that the primary binding site of La NPs was mainly located within site I (subdomain IIA) of HSA. The binding distance was calculated by using Forster resonance energy transfer theory. Also, the results of Fourier-transform infrared spectroscopy, circular dichroism, three-dimensional fluorescence and UV–visible measurements indicated that the binding of above La NPs to HSA may induce conformational and micro-environmental changes of protein. This study suggested that the conformational change of HSA was at secondary structure of it and the biological activity of this protein was changed in the present of La NPs.

The sequential structure of tripyridiniumylporphyrin pendants in water-soluble copolymers and their association behaviour with tetrasulfonatophenylporphyrin guests: UV-vis absorption and fluorescence emission spectra study.

A novel cationic tripyridiniumylporphyrin monomer, 5-[4-[2-(acryloyloxy)ethoxy]phenyl]-l0,l5,20-tris(N-methyl-4-pyridiniumyl)porphyrinate zinc(ii) (ZnTrMPyP), was synthesized, and its self-aggregation in water was studied by UV-vis absorption. The monomer was copolymerized with acrylamide in water and DMSO, respectively, to prepare the water-soluble polymers P-W and P-D. The aggregation behaviour of the copolymers in aqueous solution was investigated by UV-vis absorption and fluorescence emission spectra. The polymer P-D displayed very similar absorption and emission spectra to those of ZnTrMPyP in water, indicating that the polymer chains in P-D have no significant effect on the aggregate structure of ZnTrMPyP in aqueous media. In comparison, two new absorption bands appeared in the Q band range of polymer P-W and its fluorescence spectra red shifted and the fluorescence quantum yield decreased obviously. These characteristics remained unchanged even in a good solvent for the monomer, suggesting that a new aggregation structure for the porphyrin pendants fixed by the covalent bond was formed. According to the different dispersed states of the porphyrin monomer in water and DMSO, the porphyrin pendants should distribute randomly in the P-D polymer chains while having micro-blocky sequences in polymer P-W. The association behaviour between the copolymers and tetra(p-sulfonatophenyl)porphyrin, TSPP, bearing opposite charged substituents were studied by absorption and emission Spectra and further analyzed by the Benesi–Hildebrand and the Stern–Volmer methods. The results showed that relatively discrete porphyrin pendants in P-D formed a 1 : 1 stoichiometric complex with TSPP and both static and dynamic mechanisms were active in this quenching process, while the tightly associated porphyrin pendants in P-W interacted with TSPP as an entirety and static quenching was dominant in this process. This observation was in accordance with their sequential structure. The polymer P-W has a wider absorption range and higher absorption intensity in the long wavelength region than the porphyrin monomer, which can more efficiently absorb light to accomplish light harvesting in water.

Photon Upconversion Using Baird-Type (Anti)Aromatic Quinoidal Naphthalene Derivative as a Sensitizer

A naphtho-p-quinodimethane (QDM) exhibiting Baird’s 4n – π antiaromaticity was used as green photons-harvesting chromophore to sensitize perylene (Per) leading to upconverted blue photoluminescence. The solution phase QDM → Per triplet energy transfer (TET) could not be unraveled via the Stern–Volmer method, but transient absorption measurements revealed that the kinetics of T1 → Tn for QDM (τ = 1.4 μs) was 1 order of magnitude reduced (τ = 0.17 μs) as a result of 3(Per)* formation. Furthermore, we demonstrated that incident light with power densities in the microwatt regime is sufficient to perform photon upconversion using the present set of molecular systems.

In vitro binding comparison of cephalosporins to human serum albumin by spectroscopy and molecular docking approaches: A novel structural pursuing

Contamination of antibiotic residues in food and water is an understudied safety concern and is increasingly gaining importance worldwide due to the rising rates of drug resistant organisms. As a class of antibiotics targeting β-lactam, cephalosporin is frequently used in treatment of bacterial infections. In this study, molecular modeling approaches in combination with absorbance, fluorescence and circular dichroism spectroscopy was employed to investigate the interactions of four cephalosporins (cefalexin, cefaclor, cefixime and cefepime) with human serum albumin (HSA). In the mechanism discussion, it was proved that the fluorescence quenching of HSA by cephalosporin is a result of the formation of cephalosporin-HSA complex. Binding parameters calculating from Stern-Volmer method and Scatchard method showed that cephalosporin bind to HSA with the binding affinities of the order 103–104L·mol−1. The thermodynamic parameters studies revealed that the binding was characterized by negative enthalpy and negative entropy changes and the hydrogen bonds and van der Waals interactions may play major role in complex formation. Furthermore, the investigated result indicates that azyl served as a hydrophilic group to change the chemical property for drug, the chlorine atom on the R1-group of cefaclor weakened the overall molecular polarity or hydrophilicity, while the binding site on HSA was determined by the carboxylate of cefepime. Some other structural characteristics for four kind of cephalosporins were also exhibited in this paper.

Synthesis of triangular silver nanoprisms and spectroscopic analysis on the interaction with bovine serum albumin.

The interactions of triangular silver nanoprisms (TAgNPrs) with bovine serum albumin (BSA) were investigated using multiple spectroscopic techniques. A noticeable absorbance increase was noted in the peak ranges of 250 to 300nm for BSA, and the intensity increased with the increasing concentration of TAgNPrs. Furthermore, a slight blue shift of the surface plasmon resonance band of TAgNPrs occurred, indicating that the protein absorbed on the TAgNPrs surface to form a bio-nano interface. Analysis of fluorescence quenching data using the Stern-Volmer method revealed that static quenching takes place with complex formation. Evaluation of thermodynamic parameter ΔG θ for the binding processes indicated that the binding reaction was exothermic. Furthermore, the values of binding constant K revealed that the size of nanoparticles can affect the binding degree. The order of binding affinity is 43.7nm>36.2nm>25.1nm. The competitive experiments of site markers (flufenamic acid and phenylbutazone) suggested that the binding site of TAgNPrs on BSA was located in the region of subdomain IIIA (Sudlow site II). In addition, the conformational changes of BSA by TAgNPrs were analyzed by using synchronous fluorescence spectra, circular dichroism, and three-dimensional fluorescence spectra. Graphical abstract The protein absorbed on the TAgNPrs surface to form a nanoparticle-protein corona.

Spectroscopic and thermodynamic studies on ferulic acid – Alpha-2-macroglobulin interaction

Ferulic acid is a major phenolic acid found in numerous plant species in conjugated form. It binds to enzymes and oligomeric proteins and modifies their structure and function. This study was designed to examine the interaction of ferulic acid, an active ingredient of some important medicines, with α2M, a key serum proteinase, under physiological conditions. The mechanism of interaction was studied by spectroscopic techniques such as, UV–visible absorption, fluorescence spectroscopy, circular dichroism along with isothermal titration calorimetry. Fluorescence quenching of α2M by ferulic acid demonstrated the formation of α2M-ferulic acid complex by static quenching mechanism. Binding parameters calculated by Stern-Volmer method showed that ferulic acid binds to α2M with moderate affinity of the order of ∼104 M−1. The thermodynamic signatures reveal that binding was enthalpy driven and hydrogen bonding played a major role in ferulic acid-α2M binding. CD spectra analysis suggests very little conformational changes in α2M on ferulic acid binding.

Insights into the interaction of methotrexate and human serum albumin: A spectroscopic and molecular modeling approach.

In this study, fluorescence spectroscopy and molecular modeling approaches were employed to investigate the binding of methotrexate to human serum albumin (HSA) under physiological conditions. From the mechanism, it was demonstrated that fluorescence quenching of HSA by methotrexate results from the formation of a methotrexate/HSA complex. Binding parameters calculated using the Stern-Volmer method and the Scatchard method showed that methotrexate binds to HSA with binding affinities in the order 104 L·mol-1 . Thermodynamic parameter studies revealed that the binding reaction is spontaneous, and that hydrogen bonds and van der Waals interactions play a major role in the reaction. Site marker competitive displacement experiments and a molecular modeling approach demonstrated that methotrexate binds with appropriate affinity to site I (subdomain IIA) of HSA. Furthermore, we discuss some factors that influence methotrexate binding to HSA.

Towards a Unified Macroscopic Description of Exciton Diffusion in Organic Semiconductors

AbstractWe study the exciton diffusion in organic semiconductors from a macroscopic viewpoint. In a unified way, we conduct the equivalence analysis between Monte-Carlo method and diffusion equation model for photoluminescence quenching and photocurrent spectrum measurements, in both the presence and the absence of Förster energy transfer effect. Connections of these two models to Stern-Volmer method and exciton-exciton annihilation method are also specified for the photoluminescence quenching measurement.

Biophysical influence of coumarin 35 on bovine serum albumin: Spectroscopic study

The binding mechanism and protein–fluorescence probe interactions between bovine serum albumin (BSA) and coumarin 35 (C35) was investigated by using UV–Vis absorption and fluorescence spectroscopies since they remain major research topics in biophysics. The spectroscopic data indicated that a fluorescence quenching process for BSA–C35 system was occurred. The fluorescence quenching processes were analyzed using Stern-Volmer method. In this regard, Stern-Volmer quenching constants (KSV) and binding constants were calculated at different temperatures. The distance r between BSA (donor) and C35 (acceptor) was determined by exploiting fluorescence resonance energy transfer (FRET) method. Synchronous fluorescence spectra were also studied to observe information about conformational changes. Moreover, thermodynamics parameters were calculated for better understanding of interactions and conformational changes of the system.

Cu (II) Chemosensor Based on a Fluorogenic Bodipy-Salophen Combination: Sensitivity and Selectivity Studies.

A new fluorescent chemosensor (Bodipy-S) derived from Bodipy and Salophen was developed. After the characterization of all compounds, the behavior of the chemosensor Bodipy-S toward p, d and f block-metal ions was investigated by UV-vis and fluorescence spectroscopy. This chemosensor can selectively detect to Cu (II) in methanol-aqueous solution based on chelation enhanced fluorescence (CHEF) and it almost exhibit to a fluorescence quenching effect with 20-fold. The binding constant of the fluorophore was interpreted by using of the Stern-Volmer method and the complex stoichiometry was defined by using Job's plot. Moreover, the effect of pH was performed by the fluorescence intensities of Bodipy-S in presence of Cu(II) ions. The chemosensor can be successfully used to the detection of Cu(II) in most areas.

Investigation on the Interaction of Hydroxyethyl Starch 130/0.4 (Voluven) and Serum Albumin for Pharmacokinetic and Toxicological Implications.

The interaction of hydroxyethyl starch 130/0.4 (Voluven) with human serum albumin (HSA) has been investigated by fluorescence (steady state and synchronous), Fourier transforms infrared (FT-IR), and circular dichroism (CD) spectroscopies. Analysis of the fluorescence quenching data of HSA by Voluven using the Stern-Volmer method revealed the formation of 1:1 ground-state complex. Evaluation of binding parameters and binding energy indicated that the binding reaction was exothermic. On the basis of fluorescence measurements, it was concluded that electrostatic forces play a crucial role in stabilizing the complex. The binding distance was calculated by using Förster resonance energy transfer (FRET) theory. The conformational changes of HSA were obtained qualitatively as well as quantitatively using synchronous fluorescence, FT-IR, and CD. The HSA underwent partial unfolding in the presence of Voluven.

Copper(II)-Specific Fluorogenic Task-Specific Ionic Liquids as Selective Fluorescence Probes and Recyclable Extractants.

The designed synthesis of a series of copper(II) specific fluorogenic hydrophobic task-specific ionic liquids (TSILs) from a new naphthalene-based tetradentate ligand is reported. Absorption and fluorescence spectral studies reveal both the ligand and its derivative TSILs show exclusive selectivity towards copper(II) ions. The Stern-Volmer method for calculation of the detection limit for ligand and TSIL1-3 shows values of 0.12, 20, 17, and 15 μM, respectively. Extraction and striping studies by doping these TSILs in [bmim][NTf2] demonstrated that these TSILs are recyclable extractants for the selective recovery of Cu(II) ions from a mixture of 14 relevant metal chloride aqueous solutions in biphasic liquid-liquid extraction with approximately 95% recovery.