Fluorescence

An Experimental and Theoretical Test of Dielectric Friction Models Using Rotational Diffusion of 7-Diethylamino-2-H-1-Benzopyran-2-One in Non-associative Solvents Abstract The rotational re-orientations times of the 7-DHB dye molecule have been examined in non-associative solvents (DMSO and Octanenitrile) by varying the temperature, by employing the Steady-State Fluorescence Depolarisation and Time-Correlated Single Photon Counting (TCSPC) techniques. Rotational re-orientations time values in DMSO are found larger by a factor of 1.136 than octanenitrile, which indicates that 7-DHB laser dye is experiencing higher friction in DMSO than octanenitrile. To determine mechanical friction Stokes Einstein’s Debye theory (SED) -with a stick, slip boundary conditions parameters are used and found an interesting super slip trend. Point dipole models as Nee-Zwanzig (NZ) and van der Zwan-Hynes (ZH) fail to explain experimental dielectric friction observed trends. Alavi-Waldeck model successfully explains the observed dielectric friction trend in non-associative solvents.

4-Quinolone-Carboxamide and Carbothioamide Compounds as Fluorescent Sensors. New Fluorimetric Methods for Cu 2+ and Fe 3+ Determination in Tap Water and Soil Abstract Ion sensor properties of the carboxamide and carbothioamide compounds carrying 4-quinolone group were investigated by means of emission spectrometry in methanol-water (1:1). The compounds were selectively complexed with Cu2+, Pd2+, and Fe3+ among many metal ions. The complex stoichiometry and the stability constant were determined by fluorimetric measurements. The carboxamide compound having phenyl group (QPO) showed sensitivity for Fe3+ion with a linear range between 0.1 and 0.7 mg/L. The new method was applied in the determination of iron in the spiked tap water samples and the sandy-soil reference material. A modified standard addition method was used to remove the matrix effect. Limit of detection was 0.03 mg/L for the Fe3+ determination method. The carboxamide compound with benzyl group (QBO) showed sensitivity for Cu2+ ion with linear range 0–0.4 mg/L. There was no matrix effect for copper determination in the spiked tap water samples. The detection limit of the method for Cu2+ ion was 0.05 mg/L. The quantification limits of the methods were low enough to determine iron and copper amount in drinking water samples according to EPA.

Effect of Aryl-, Halogen-, and Ms-Aza-Substitution on the Luminescent Properties and Photostability of Difluoroborates of 2,2′-Dipyrrometenes Abstract Boron(III) complexes with alkyl-, phenyl-, and halogen-substituted 2,2′-dipyrromethenes (BODIPY) and meso-aza-dipyrrometenes (ms-aza-BODIPY) were synthesized. The structure relationship of the obtained coordination compounds with their luminescent characteristics is analyzed. Arylated BODIPY, in contrast to alkyl-substituted analogs, is more sensitive to interparticle interactions with a solvent, causing a decrease in the quantum yield by up to 40%. The introduction of phenyl substituents into the BODIPY molecule shifts the first absorption band bathochromic, significantly (32–37 nm) increases the Stokes shift in the emission spectrum, but reduces the probability of the S0 → S1 electronic transition as compared to alkylated complexes. Replacing the methine carbon atom with nitrogen leads to quenching of ms-aza-BODIPY fluorescence compared to BODIPY up to 5–20%. The stability of 2,2′-dipyrromethenes difluoroborates to oxidative destruction under the influence of UV irradiation in cyclohexane solutions was evaluated. It has been shown that symmetric aryl substitution in pyrrole cycles of dipyrromethene significantly increases the photostability of the corresponding compounds as compared to alkyl-substituted analogs and is an effective method of obtaining boron (III) dipyrromethenates with practically useful properties. It has been established that the replacement of the methin ms-spacer of dipyrromethene by a nitrogen atom significantly reduces the photostability of ms-aza-dipyrromethenates of boron. Halogenation of β-positions of pyrrole cycles by a factor of 5–8 reduces the photostability of difluoroborates ms-aza-dipyrromethenes in comparison with a non-halogenated analogue.

Carbon Dots Green Synthesis for Ultra-Trace Determination of Ceftriaxone Using Response Surface Methodology Abstract The present study sought to develop a facile and green synthetic approach for producing fluorescent carbon dots (CDs) from a natural biomass using aqueous extraction of carbonized blue crab shell. Spherical carbon dots (6.00 ± 3.0 nm) exhibited an extended emission range with excellent quantum yield (14.5 ± 3.5%). In order to measure ceftriaxone, we offered a simple and sensitive method, based on fluorescence quenching of carbon dots in plasma and water with recovery values of 94.5–104.1%. Furthermore, with usage of central composite design (CCD) based response surface methodology (RSM); we optimized the effect of different factors. In addition, ANOVA evaluated the accuracy and suitability of quadratic model. Under optimal conditions, fluorescence quenching revealed a sensitive response in the concentration range of 20–1000 nM with the limit of detection 9.0 nM for ceftriaxone. Finally, carbon dots-based fluorescence quenching procedure was able to quantify ceftriaxone in plasma, as well as mineral and tap water. Spiked samples achieved satisfactory efficiencies.

Highly Efficient Colorimetric Sensor for Selective and Sensitive Detection of Arsenite Ion (III) in Aqueous Medium

In-Depth Assessment of the Effect of Sodium Azide on the Optical Properties of Dissolved Organic Matter Abstract Treatment and preservation of samples are critical issues in measuring the optical properties of dissolved organic matter (DOM) due to their high sensitivity to physical and chemical changes upon sample handling. In this study, we rigorously assessed the potential interferences of sodium azide (NaN3) on DOM absorption and fluorescence. A wide range of different samples were poisoned with varying NaN3 concentrations. Several commonly used optical parameters derived from absorbance and fluorescence spectroscopy were compared at different samples and conditions to assess the interfering effect of NaN3. Our results showed that NaN3 altered the original features of absorbance and fluorescence even at the lowest level of the addition. The absorption coefficients of NaN3-treated samples increased up to 2608% at 254 nm and 66% at 280 nm relative to the untreated control. Fluorescence data revealed both a quenching effect and an enhancement in fluorescence. The effect of NaN3 on fluorescence was highly variable and affected by the NaN3 concentrations added, and the sources and the concentrations of DOM samples. None of these factors exhibited a clear linear behavior with NaN3 levels, making it difficult to develop a correction method. It can be recommended from the findings not to use NaN3 in preserving DOM samples for optical measurements.

Probing the Interaction of Newly Synthesized Pt(II) Complex on Human Serum Albumin Using Competitive Binding Site Markers Abstract Considering the importance of pharmacology and the influence of drugs on biological materials, the effects of a newly designed and synthesized platin complex (2,2′-Bipyridine-3,3′-dicarboxylic acid, oxalato Platinum(II), as an antitumor drug was tested on the structure of blood carrier protein of human serum albumin (HSA) using various spectroscopic techniques including UV-visible, fluorescence, and circular dichroism at 25 and 37 °C. Results of the fluorescence measurements revealed that adding the complex caused reduction in intrinsic fluorescence emission of HSA resulted from dynamic quenching of HSA. The number of binding sites and binding constants were calculated at both temperatures of 25 and 37 °C. In addition, in order to identify the complex’s binding site on HSA employing spectroscopy, the competitive studies were followed using warfarin, digitoxin and ibuprofen as site markers of Sudlow sites I, II and III. Competitive binding test results have shown that Pt(II) complex bind on the warfarin binding site (or Sudlow sites I) on HSA. Besides, a reduction in thermal stability for HSA was observed in the presence of the newly designed Pt(II) complex.

Fluorescent Carbon Dots from Nerium oleander : Effects of Physical Conditions and the Extract Types Abstract In this original research, the synthesis of carbon nanodots (CDs) from two different solvent extracts of Nerium oleander by the thermal method was investigated under various physical conditions such as pH, reaction temperature, ionic strength, and surface passivation agent (polyethylene glycol, PEG) presence in the reaction media. The effects of extract types and physical conditions on CDs formation were characterized by UV-Visible spectrophotometry, fluorescence spectrophotometry, Fourier transform infrared spectroscopy and dynamic light scattering analysis. Fluorescent CDs were obtained from PEG included reaction media. Additionally, the enhanced fluorescence intensity correlated with ascending reaction temperature was reported. The hydrodynamic particle size of CDs in aqueous solution was determined between ~1 and 235 nm with negative surface potential in the range of −6 mV and −28 mV. Moreover, CDs synthesized from aqueous extract mostly resulted in smaller size than that of ethanol extract based ones. The impact of surface passivation with PEG on the fluorescence feature of CDs was verified. For the relevant extracts of Oleander, CDs synthesized from PEG included formulations at pH 5 and NaCl free reaction media found as better alternatives than CDs synthesized under other conditions taking account their effect on fluorescence feature, hydrodynamic size and etc. Graphical Abstract

EDC-Induced Self-Assembly of BSA-Au NCs Abstract In this paper, the Au nanoplate with bright red fluorescence was synthesized on the basis of bovine serum albumin stabilized Au nanoclusters (BSA-Au NCs). The small molecule N-ethyl-N′-(dimethylaminopropyl) carbodiimide (EDC) was used as the cross-linking agent to activate the carboxyl group on the surface of BSA, and then the condensation with amino acid in BSA induced the self-assembly of BSA-Au NCs. The particle size of Au nanoplate increased with EDC concentration. In addition, when EDC concentration was 0.0050 M, the Au nanoplate changed from smooth to grainy structure. The Au nanoplate remained the unique fluorescence characteristics of BSA-Au NCs. As EDC concentration reached 0.0025 M, the Au nanoplate even exhibited brighter red emission than that of BSA-Au NCs.

Enhanced Luminescence Based Response towards pH in Highly Acidic Environments by the Silver Nanoparticles and Ionic Liquids Abstract Correct measurement of the pH in highly acidic environments is still a challenge. In such conditions most of the pH indicators suffer from instability in air or leaching from host matrices due to the solubility considerations. In this work, two different fluorescent probes were used along with silver nanoparticles (AgNPs) and ionic liquid (IL) in the polymeric matrices for sensing of the pH in harsh conditions. The pH sensitivities of the probes were tested after exposure to strong acid vapors by steady-state, lifetime based and kinetic mode measurements. The sensing materials were fabricated in form of thin films and electrospun nanofibers. The ionic liquid; 1-butyl-3-methylimidazolium tetrafluoroborate was exploited as additive to enhance the stability as well as response towards pH. Spectral changes were tested in a large scale; between pH 3.00–12.00. Utilization of the dyes in ethyl cellulose and polymethyl methacrylate along with AgNPs in form of electrospun fibers resulted in many advantages such as enhanced long term stability, sensitivity and improvement in all sensor dynamics. Sensing characteristics of the offered designs were tested after exposed to vapors of HCl, H2SO4 and HNO3, respectively.