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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 −34.5 mV 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 1.3 μg/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. [ABSTRACT FROM AUTHOR]

The present work reports pyridine-based chalones using spectroscopic techniques to use pyridine derivative analysis. The solvatochromic behavior of 3DPP in non-polar, polar protic and aprotic solvents has been investigated experimentally. The photophysical property of the compound in diverse solvents is attributed to the intra-molecular charge transfer interactions. The dipole moment of 3DPP is estimated theoretically and experimentally using various solvatochromic methods. It is observed that there is a bathochromic shift in the emission spectra of 3DPP, which confirms the π → π* transition. Fluorescence quenching of 3DPP is studied. The type of fluorescence quenching mechanism is found to be collisional quenching. A study of FRET theory on 3DPP was carried out with metal ions. There is a considerable energy transfer between 3DPP and metal ions. NLO behaviors of the compound have been revealed with the help of Kurtz–Perry powder technique. Additionally, the title molecule is docked, carried ADMET studies and drug-like activity using in silico tools. It is probed for antifungal activity through bioinformatics kit which showed potential information. [ABSTRACT FROM AUTHOR]

Quinoline derivative, i.e. quinilone yellow with the scientific name [sodium 2‐(2,3‐dihydro‐1,3‐dioxo‐1H‐inden‐2‐yl)quinoline‐6,8‐disulphonate] (SQDS) is analysed for fluorescence resonance energy transfer (FRET). Fluorescence quenching mechanism is studied by employing steady state and transient state spectroscopic measurements. Cobalt chloride is used as quencher in the present study. Linearity was observed in Stern–Volmer plots for transient state as well as steady state. This was further attributed to a mechanism of collisional quenching. Efficiency in fluorescence quenching is observed as there is a correlation between quenching constants of both transient and steady state. A significant energy transfer is reported between metal ions and SQDS molecule, according to FRET theory. Characterization results are studied and analysed. Application in the field of non‐linear optics are predicted for SQDS. With Kurtz and Perry powder technique, SHG (second harmonic generation) efficiency was measured using Q‐switched mode locked Nd:YAG laser emitting 1064 nm the first time with this compound. [ABSTRACT FROM AUTHOR]

Abstract: A study on fluorescence quenching was carried out for the coumarin derivative 2‐acetyl‐3H‐benzo[f]chromen‐3‐one (2AHBC) with aniline at room temperature. Efficient fluorescence quenching was observed and Stern–Volmer (S–V) plots showed upward curves from linearity in all solvents of different polarities. For the solute 2AHBC, ground state complex formation does not hold in our study. The kinetic distance (r) value was found to be greater than the encounter distance (R) and indicated that the quenching reaction was held within the sphere of action. Diffusion‐limited reactions were found to be more prominent in high polarity solvents, namely dimethyl sulfoxide (DMSO), DMF, ACN, methanol, ethanol, propanol and DCM. The relationships between quenching constant (KSV) and dielectric constants (ε) of the different solvents were studied. [ABSTRACT FROM AUTHOR]

We here for the first time demonstrate an analytical approach for the highly selective and sensitive detection of amoxicillin (Amox) in aqueous medium based on the fluorescence quenching of quantum dots (QDs). The change in fluorescence intensity of mercaptopropionic acid-capped cadmium sulphide (MPA-CdS) QDs is attributed to the increasing concentration of Amox. The results show that the fluorescence quenching of QDs by Amox takes place through both static and dynamic types of quenching mechanism. The fluorescence quenching of QDs with increase in concentration of Amox shows the linear range between 5 μg ml−1 and 30 μg ml−1 and the limit of detection (LOD) is 5.19 μg ml−1. There is no interference of excipients, which are commonly present in pharmaceutical formulation and urine samples. For the practical application approach, the developed method has been successfully applied for the determination of Amox in pharmaceutical formulations and urine samples with acceptable results. [ABSTRACT FROM AUTHOR]

A simple and straightforward method for the determination of dolasetron mesylate (DM) in aqueous solution was developed based on the fluorescence quenching of 3-Mercaptopropionic acid (MPA) capped CdS quantum dots (QDs). The structure, morphology, and optical properties of synthesized QDs were characterized by using UV-Vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Under the optimum conditions, the MPA-CdS QDs fluorescence probe offered good sensitivity and selectivity for detecting DM. The probe provided a highly specific selectivity and a linear detection of DM in the range of 2–40 µg/mL with detection limit (LOD) 1.512 µg/mL. The common excipients did not interfere in the proposed method. The fluorescence quenching mechanism of CdS QDs is also discussed. The developed sensor was applied to the quantification of DM in urine and human serum sample with satisfactory results. [ABSTRACT FROM AUTHOR]

We estimated the relative florescence quantum yield (Φ) of 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin [8MDTC] using a single-point method with quinine sulfate in 0.1 M of sulfuric acid used as a standard reference. The fluorescence lifetimes, radiative and non-radiative decay rate constants are calculated. Relative quantum yields were found to be less in the non-polar solvents, indicating that the solute exhibits less fluorescence in a non-polar environment. The fluorescence quenching of [8MDTC] by aniline was studied at room temperature by examining the steady state in five different solvents in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern-Volmer plots in all solvents. Ground state complex and sphere of action static quenching models were used to interpret the results. Many quenching rate parameters were calculated using these models. The values of these parameters suggest that the sphere of action static quenching model agrees well with the experimental results. Further, a finite sink approximation model was used to check whether these bimolecular reactions were diffusion limited or not. The values of the distance parameter R′ and the diffusion coefficient D were determined and are compared with the values of the encounter distance R and diffusion coefficient D calculated using the Stokes-Einstein equation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The molecular interactions between salicylic acid (SA) and proflavin hemisulfate (PF) were investigated using fluorescence and UV-VIS absorption spectroscopy in an aqueous micellar environment. Changes in the absorption spectra of SA in the presence of PF indicate a ground state interaction between salicylate and proflavine hemisulfate ions to form a complex. The excitation bands of SA monitored at its emission wavelength reveal a red spectral shift of 8390.54 and 2037.75 cm-1 when compared with absorption bands. The intensity of both excitation bands decreased in the presence of increasing amounts of PF. The absence of excitation bands of PF rules out the possibility of its direct excitation and suggests energy transfer from excited SA to PF, resulting in quenching of the SA fluorescence. The fluorescence quenching results were found to fit the well-known Stern-Volmer (S-V) relation. S-V plots at different temperatures were used to further evaluate thermodynamic parameters such as ∆G, ∆H and ΔS. The thermodynamic and kinetic data obtained from the quenching results were used to investigate the possible mechanism of binding, the nature of the binding force and the distance between SA and PF molecules. The linear relation between SA fluorescence quenching and PF concentration used to develop an analytical method for the determination of PF from Lorexane (a veterinary cream) using a fluorescence quenching method. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel, simple but highly selective fluorescent probe is developed for the direct detection of sulfide ions [S2−] based on the fluorescence quenching of the functionalized CdS QDs in aqueous solution at trace levels and successfully applied for quantitation of S2− from water samples in a complex matrix exclusive of pretreatment by standard addition method. [ABSTRACT FROM AUTHOR]

Fluorescence quenching mechanism of tryptophan (Trp) by norfloxacin (NORF) was investigated by spectrofluorometric method at physiological pH. Stern−Volmer quenching constant is positively related with temperature shows the dynamic type of quenching. Life time of Trp decreases by the addition of NORF supports dynamic type of quenching. Fluorescence quenching method was successfully applied for direct determination of NORF from pharmaceutical sample. [ABSTRACT FROM AUTHOR]

The steady state studies of fluorescence quenching of excitation energy of heterocyclic compound namely 2‐bromophenyl boronic acid (2BPBA) by aniline was carried out in 1, 4 dioxane (DX), toluene (TL), methanol (ML), heptane (HP), nonane (NN), butanol (BL), and propanol (PL) solvents with a view to understand the role of quenching mechanism. The quenching process is studied in the selected solvents using steady state method by Stern–Volmer (S–V) plots having upward curvature. [ABSTRACT FROM AUTHOR]

The steady state studies of fluorescence quenching of excitation energy of heterocyclic compound namely 2‐isopropylphenyl boronic acid (2IPBA) by aniline quencher was carried out in 1,4‐dioxane (DX), toluene (TL), methanol (ML), heptane (HP), nonane (NN), butanol (BL), and propanol (PL) solvents with a view to understand the role of diffusion in the quenching mechanism. The quenching process is studied in the selected solvents using steady state method by linear S‐V plots. [ABSTRACT FROM AUTHOR]

Surfactant‐capped nanoparticles of 9, 10‐diphenyl anthracene prepared by reprecipitation method found highly fluorescent due to aggregation‐induced enhanced emission (AIEE). Cetyltrimethyl ammonium bromide (CTAB) surfactant not only generated positive zeta potential on the surface of nanoparticles to attract anions of interest but also stabilized nanoparticles into brick‐shape morphology. The fluorescence of nanoparticles is quenched by Cr2O72‐ ion very significantly in comparison with other diverse ions, namely, MnO4‐, S2O82‐, HCO3‐, and Cr2O42‐. Though S2‐ and IO3‐ showed increase in the fluorescence of nanoparticles, the interference found is negligible in the Cr (VI) analysis. The selectivity and sensitivity of nanoparticles for recognition of Cr2O72− were explored by systematic fluorescence titration. The fluorescence quenching data fits into the usual Stern‐Volmer equation. A calibration curve constructed by plotting quenching of fluorescence (∆F) against concentration of Cr (VI) exhibiting a linear fit in the equation, ∆F = 3070x, is used for the estimation of chromium concentration (x). The correlation coefficient value R2 = 0.998 obtained from curve is nearly equal to 1 indicates linear fit between quenching data and concentration of Cr (VI). The estimated values of limit of detection (LOD) in the method 0.01392 μg.mL−1 is far below the permissible value of Cr (VI) 0.05 μg.mL−1 in drinking water approved by world health organization (WHO) and United State Environmental Protection Agency (USEPA). The proposed method of Cr (VI) detection is applied for real sample collected from hard chrome deposition industry from nearby region. The amount of Cr (VI) estimated by present method is comparable with AAS determination for the same samples. Schematic presentation of formation of DPANPs and adsorption of Cr2O72‐ ion on the surface of CTAB‐capped DPANPs by fluorescence quenching. [ABSTRACT FROM AUTHOR]

This investigation relates FRET, photocatalytic and a biological study of AgQDs which found to be dependent on particle size and capping agent used. Surface of AgQDs was one of the most important factors that govern its activity. AgQDs with BSA binding was systematically studied by fluorescence quenching and electrostatic interaction. AgQDs mainly interacted to site II of BSA, binding distance r evaluated according to the FRET theory and was 4.6 nm for AgQDs, which suggested transfer of energy (non-radioactive) between surface modified AgQDs and biological molecule BSA. The photocatalytic activity of AgQDs for the appreciable degradation of erythrosine dye using Ultraviolet-B light was investigated. AgQDs showed specific antibacterial activity against E. coli bacterial stain. Quantum dots displayed a pronounced and specific activity causing >50% growth of COLO-205 and MCF-7 human cancer Cells at concentrations <10−7 M. Hence, present black box synthetic protocol of AgQDs could be life science application. Image 1 [ABSTRACT FROM AUTHOR]

Nowadays scientist over the world are engaging to put forth improved methods to detect metal ion in an aqueous medium based on fluorescence studies. A simple, selective and sensitive method was proposed for detection of Co 2+ ion using fluorescent organic nanoparticles. We synthesized a fluorescent small molecule viz. 4,4′-{benzene-1,4-diylbis-[(Z)methylylidenenitrilo]}dibenzoic acid (BMBA) to explore its suitability as sensor for Co 2+ ion and biocompatibility in form of nanoparticles. Fluorescence nanoparticles (BMBANPs) prepared by simple reprecipitation method. Aggregation induced enhanced emission of BMBANPs exhibits the narrower particle size of 68 nm and sphere shape morphology. The selective fluorescence quenching was observed by addition of Co 2+ and does not affected by presence of other coexisting ion solutions. The photo-physical properties, viz. UV-absorption, fluorescence emission, and lifetime measurements are in support of ligand-metal interaction followed by static fluorescence quenching phenomenon in emission of BMBANPs. Finally, we develop a simple analytical method for selective and sensitive determination of Co 2+ ion in environmental samples. The cell culture E . coli , Bacillus sps., and M . tuberculosis H 37 RV strain in the vicinity of BMBANPs indicates virtuous anti-bacterial and anti-tuberculosis activity which is of additional novel application shown by prepared nanoparticles. [ABSTRACT FROM AUTHOR]

A simple carbazole based nanoprobe prepared by reprecipitation method shows selective sensing behavior for Fe 3 + ion in aqueous medium. The prepared SDS capped 9-phenyl carbazole nanoparticles (9-PCzNPs) has narrower particle size distribution with an average diameter 35 nm and zeta potential of − 34.3 mV predicted a good stability with negative surface charge over the nanoparticles. The Field Emission Scanning Electron Microscopy (FE-SEM) image showed cubic shape morphology of nanoparticles. The aqueous suspension of SDS capped 9-phenyl carbazole nanoparticles exhibited aggregation induced enhanced red shifted intense emission in comparison with the emission arising from dilute solution of 9-phenyl carbazole in DCM. The cation recognition test based on fluorescence change shows Fe 3 + ion induce significant fluorescence quenching, however remaining cations responds negligibly. The obtained quenching data fit into Stern–Volmer relation in the concentration range of 0.0–1.0 μg·mL − 1 of Fe 3 + ion solution and the detection limit is 0.0811 μg·mL − 1 . The probable mechanism of fluorescence quenching of SDS capped 9-PCzNPs is because of adsorption of Fe 3 + ion over the negatively charged surface of NPs through electrostatic interaction. Thus the proposed method was successfully applied for the detection of Fe 3 + ion in environmental water sample. [ABSTRACT FROM AUTHOR]

Highlights: [•] An efficient fluorescent chemosensor was reported in aqueous media. [•] The probe showed high selectivity for Al3+ over other coexisting ions. [•] The system exhibits turn-off fluorescence via ICT and PET process. [•] Probe was fruitfully applied for the direct detection of Al3+ in environmental samples. [ABSTRACT FROM AUTHOR]

Abstract: Steady state fluorescence and UV–vis absorption spectroscopic techniques have been exploited to explore the binding interaction of a antibacterial pyrimidine derivative 2-amino-6-hydroxy-4-(4-hydroxyphenyl)-pyrimidine-5-carbonitrile (AHHPPC) with the model transporter protein, human serum albumin (HSA) under the physiological conditions. It exhibits antibacterial activity against Escherichia coli and Staphylococcus aureus. Analysis of fluorescence quenching data of HSA at different temperatures using Stern–Volmer methods revealed the formation of AHHPPC–HSA complex with binding affinities of the order 104 M−1. The binding site number (n ≈1) and corresponding thermodynamic parameters (ΔG), (ΔH) and (ΔS) were calculated, indicated that binding reaction was endothermic and the hydrophobic interactions plays a major role in stabilizing the complex. The binding distance (r =3.13nm) between donor (HSA) and acceptor (AHHPPC) was obtained according to FRET. Changes in the albumin secondary structure imparted by the compound was confirmed using synchronous fluorescence, electronic absorption, circular dichroism (CD) and three-dimensional (3D) fluorescence spectroscopy. All these experimental results clarified that AHHPPC could bind to HSA and be effectively transported and eliminated in body, which could be a useful guideline for further drug design. [Copyright &y& Elsevier]

Abstract: Current study employs fluorescence spectroscopy, UV–Vis absorbance spectroscopy, dynamic light scattering (DLS) and cyclic voltammetry (CV) to investigate the interaction of safranine dye with spherical shaped silver nanoparticles (AgNPs) coated with trisodium citrate. In fluorescence spectroscopic study we used the AgNPs and safranine dye as component molecules for the construction of FRET, whereas AgNPs serve as donor fluorophore and safranine as acceptor. The fluorescence quenching of AgNPs followed by sensitization of safranine occurs almost simultaneously by addition of safranine dye with different concentrations, indicating fluorescence energy transfer observed between them. Interaction between safranine and AgNPs is also confirmed by using UV–Vis absorption spectroscopy. Addition of safranine results in the significant decrease in the absorbance of AgNPs at 423nm and simultaneous increase in the absorbance of safranine at 518, 276 and 248nm which is indication of rapid binding of safranine molecules with AgNPs. However CV measurements reveals that the safranine molecule does not alter the redox properties of the AgNPs but the safranine molecule lose their redox properties upon getting bonded with AgNPs. This clearly confirms that the safranine molecules get attached on the surface of AgNPs which was also supported by the DLS as well as zeta potential measurement. [Copyright &y& Elsevier]