Fluorescence Spectral Properties Research Articles

An in situ approach for validation of canopy chlorophyll fluorescence radiative transfer models using the full emission spectrum

The intensity and spectral properties of solar-induced chlorophyll fluorescence (SIF) carry valuable information on plant photosynthesis and productivity, but are also influenced by leaf and canopy structure. Physically based models provide a quantitative means to investigate how SIF intensity and spectra propagate and scale from the photosystem to the leaf and to the canopy levels. However, the validation of canopy SIF models is limited by the lack of methods that combine direct, independent, and complementary measurements of the full fluorescence spectrum at the leaf and canopy levels. Here, we propose a novel validation approach that combines in situ measurements of leaf and canopy fluorescence spectra. The approach is demonstrated with measurements in a rice crop at two contrasting stages of canopy development. We measured leaf reflectance, transmittance, and fluorescence spectra in situ, and subsequently inverted leaf structural and biochemical parameters and determined the leaf fluorescence quantum efficiency (FQE) using the Fluspect-Cx model. Two FQE inversion methods (Inversion-IIA and Inversion-IIB) were tested for the forward simulation of leaf fluorescence spectra. Leaf fluorescence spectra were then scaled up to the canopy level using 1D, 2D, and 3D radiative transfer schemes (SCOPE, mSCOPE, and DART), and compared with the direct canopy fluorescence spectral observations measured under red, green, blue, and white illumination. The validation results demonstrate that accounting for 3D canopy structure, as in the DART model, is critical to successfully scale the fluorescence spectrum from the leaf to the canopy level, whereas 1D SCOPE or even 2D mSCOPE were unable to fully reproduce the canopy fluorescence spectra. The results also demonstrate that the Inversion-IIB method matches relatively well the measurements with mean relative absolute errors (MRAE) of 20 %, 37 %, and 43 % versus Inversion-IIA with mean relative absolute errors (MRAE) of 62 %, 100 %, and 108 % for DART, mSCOPE, and SCOPE, respectively. We suggest that our validation approach is transferable to other plant species and canopy geometries, providing a means to standardize and evaluate the performance of canopy SIF models and improve our understanding of canopy SIF observations.

Synthesis, spectral-fluorescence properties and TD-DFT calculations of 4-canotryptophan and its derivatives

Synthesis, spectral-fluorescence properties and TD-DFT calculations of 4-canotryptophan and its derivatives

Effects of Surfactants on the Aggregation of 6,6'-Disubstituted Thiacarbocyanine Dyes in Aqueous Solutions

The aggregation properties of a number of 6,6'-substituted thiacarbocyanine dyes were studied by spectral-fluorescent methods: T-304, T-306, T-307, T-336 and, for comparison, thiacarbocyanine Cyan 2, which has no substituents in the 6,6'-positions, in aqueous buffer solutions and in the presence of various types of surfactants. The method of moments was used to characterize the absorption spectra (band positions, width, shape). Substituents in the 6,6'-positions significantly increase the ability of dyes T-304, T-306, T-307, T-336 to aggregation (dimerization, as well as to the formation of disordered aggregates with broad low-intensity absorption spectra). The introduction of surfactants leads to rearrangement of the spectra associated with the complex nature of the equilibria between monomers and aggregates of various structures (including surfactant molecules, if present), in particular, with a decrease in the contribution of disordered aggregates. However, the decomposition of dimeric aggregates of 6,6'-substituted cyanines is observed only at very high surfactant concentrations (~20 CMC and higher, where CMC is the critical micelle concentration). At the same time, the passing of surfactant concentrations through CMC does not significantly affect the spectral-fluorescent properties of the dyes, which is probably due to rather strong interactions of the dyes with individual surfactant molecules and premicellar associates of surfactants.

Cyclodextrin-enhanced photo-induced fluorescence of tau-fluvalinate, molecular modelling of inclusion complexes and determination in natural waters.

The effect of adding organized supramolecular systems such as β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) on the photochemically-induced fluorescence (PIF) spectral properties of tau-fluvalinate (TFV) in aqueous solutions was examined. The influence of pH, UV irradiation time and photoproduct stability on the cyclodextrin-enhanced photochemically-induced fluorescence intensity was also investigated. The spectral changes associated with the inclusion process yielded values for the formation constants of TFV inclusion complexes between 450 and 640 M-1, which were calculated using the nonlinear iterative regression approach least squares. In addition, host-guest interaction was clearly determined by PIF enhancement and a 1 : 1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with TFV. The negative free energy (ΔG°) value indicated that the reaction of TFV with cyclodextrins was thermodynamically favorable. Furthermore, the structures of inclusion complexes of TFV with cyclodextrins were elucidated by 3-21G ab initio calculations. The limits of detection and quantification obtained ranged between 1.3 and 4.0 ng mL-1 and from 4.4 to 13.0 ng mL-1 in β-CD and HP-β-CD media, respectively. The analytical application in tap and river water samples yielded satisfactory mean recoveries ranging from 98.12 to 102.97%. Due to its sensitivity and ease of use, this method can be reliably applied to routine analysis.

Crystals of 4,7-Di-2-thienyl-2,1,3-benzothiadiazole and Its Derivative with Terminal Trimethylsilyl Substituents: Synthesis, Growth, Structure, and Optical-Fluorescent Properties

Among short donor–acceptor molecules with a central benzothiadiazole fragment, 4,7-di-2-thienyl-2,1,3-benzothiadiazole (T-BTD) is one of the most well-known compounds, valued for its photophysical and semiconductor properties. We have synthesized a derivative of 4,7-di-2-thienyl-2,1,3-benzothiadiazole with trimethylsilyl end-substituents, 4,7-bis(5-(trimethylsilyl)thiophen-2-yl)benzothiadiazole (TMS-T-BTD). The phase transition parameters and thermal stability of T-BTD and TMS-T-BTD were investigated using DSC and TGA methods. The presence of the trimethylsilyl end-groups in TMS-T-BTD significantly enhances solubility, increases the melting temperature, and improves the resistance of TMS-T-BTD to evaporation in the liquid state. Single crystals of T-BTD and TMS-T-BTD were grown from solutions, with the largest sizes being 7 × 2 × 0.5 mm3 and 8 × 1 × 0.45 mm3, respectively. Using single-crystal X-ray diffraction at 293 K, the crystal structure of T-BTD was refined in the rhombic system (sp.gr. Pcab, Z = 8), while for TMS-T-BTD, it was determined for the first time in the monoclinic system (sp.gr. P21/c, Z = 4). The relationship between observed growth anisotropy and molecular packing in the crystals was analyzed. The results of investigations into the spectral-fluorescent properties of solutions in hexane and THF are presented. The solvatochromic effect was studied in a series of solvents, including hexane, THF, dichloromethane, and acetonitrile. The photostability of the compounds in hexane solutions was examined. It was found that the quantum yield of photodestruction for T-BTD is 13 times higher than that of TMS-T-BTD. The fluorescent properties of T-BTD and TMS-T-BTD crystals were investigated.

Preparation and fluorescence properties of SiO2-coated CsPbBrI2 perovskite nanocrystals

All-inorganic perovskite nanocrystals CsPbX3 (X=Cl, Br, I) have garnered significant interest due to their promising applications and have become a leading research subject in the field of optoelectronics. The weak stability of CsPbBrI2 perovskite nanocrystals has hindered their development, however, silica coating can effectively solve this problem. The (3-aminopropyl) triethoxysilane was used as a raw material for silica synthesis to form core-shell structured CsPbBrI2@SiO2 perovskite nanocrystals to obtain enhanced optoelectronic properties. This article reveals the narrow absorption and emission peaks, small half-height widths, 14.6 ns fluorescence lifetimes, and 106.2 meV exciton binding energies of CsPbBrI2@SiO2 perovskite nanocrystals. The results show that the core-shell structured CsPbBrI2@SiO2 perovskite nanocrystals prepared by this method have excellent fluorescence spectral properties and hold significant promise for future applications in optoelectronic devices.

Synthesis and spectroscopic characterization of multifunctional D-π-A benzimidazole derivatives as potential pH sensors

We report multifunctional D-π-A molecular systems having the N,N-diethylamino group as a pH sensitive donor unit connected to the electron accepting substituents such as the cyano moiety and the pH responsive benzimidazole fragment. For that purpose we have synthesized three types of derivatives, namely acrylonitrile, Schiff base and iminocoumarin derived benzimidazoles, whose photophysical characterization has been carried out in several polar and non-polar organic solvents as well as aqueous solution buffers with different pH. Computationally supported determination of species involved in prototrophic equilibria, including their respective pKa values, has been performed to aid in understanding structural and substituent effects on their UV–Vis and fluorescence spectral properties and pH sensing potentials. Both sets of results jointly indicate that all molecules are predominantly unionized under neutral conditions, while their transition towards monocationic forms, responsible for spectroscopic response changes, occurs at pH ≈ 1–4 for acrylonitriles 4–5, pH ≈ 4–5 for Schiff bases 11–12, and pH ≈ 4.5–6.5 for iminocoumarins 7–8, thus increasing their practical attractiveness for a broad range of applications in the same order.

Spectrofluorimetric determination of beta-blockers atenolol and bisoprolol fumarate residues in Senegal natural waters

A spectrofluorimetric method was developed to determine residues of two β-blockers, atenolol (AT) and bisoprolol fumarate (BF), in Senegal's natural waters. The electronic absorption and fluorescence spectral properties of both β-blockers were investigated in several organic solvent mixtures [e.g., MeOH/H2O (60/40 v/v), cyclodextrins (β-cyclodextrin, HP-β-CD], and in the presence of surfactants (SDS, Triton X, Tween 80). After optimization, satisfactory analytical figures of merit were obtained for the determination of both β-blockers: concentration linear dynamic range of over one to two orders of magnitude, limits of detection (LODs) from 1.3 to 5.4 ng/ml for BF and from 1.2 to 3.7 ng/ml for AT, limits of quantification (LOQs) from 4.5 to 18.1 ng/ml for BF and from 4.0 to 12.5 ng/ml for AT. Relative standard deviations (RSDs) were between 2.1 and 5.3 %, according to the β-blockers. The spectrofluorimetric method was applied to the analysis of fortified river water and wastewater (effluent) collected in Senegal and France and spiked with both β-blockers. It yielded good recovery values, from 93.3 to 107.8 % for AT and from 97.4 to 108.9 % for BF. Our results demonstrated the simplicity, rapidity, and sensitivity of the spectrofluorimetric method to quantify residues of β-blockers in environmental waters.

Abstract 3629: Calcium signalling and the breast cancer microenvironment

Abstract Calcium is a key regulator of a variety of pathways important in breast cancer progression, including those involved in cell proliferation and invasiveness. Calcium signaling is implicated in processes relevant to the breast cancer tumor microenvironment and altered calcium influx is a feature of cancer associated fibroblasts. In these studies, simultaneous use of genetically encoded calcium indicators with distinct fluorescence spectral properties (GCaMP6m or JRCaMP1b), were used to explore the cross-talk between breast cancer cells and fibroblasts via calcium signaling and changes in different cellular compartments. HMF3S human fibroblast cells co-cultured with breast cancer cells expressing GCaMP6m or JRCaMP1b were assessed in 2D and 3D co-culture using automated epi-fluorescence or confocal microscopy. Mitochondrial calcium levels were assessed using targeted GCaMP6m (2mtGCaMP6m) in HMF3S cells expressing JRCaMP1b. Results showed distinct spatial and temporal changes in free calcium levels between both fibroblasts and breast cancer cells and the mitochondria and cytosol during activation. These methodological advances provide an opportunity to better understand calcium signaling in cancer associated fibroblasts. These techniques will also help identify the calcium channels and pumps that could be targeted to manipulate the breast cancer tumor microenvironment to inhibit pathways important in breast cancer progression. Citation Format: Alice H. Bong, Krystyna A. Gieniec, Francisco Sadras, Mélanie Robitaille, Sarah J. Roberts-Thomson, Felicity M. Davis, Gregory R. Monteith. Calcium signalling and the breast cancer microenvironment. [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 3629.

Characterization of Spontaneous Melanization by Fluorescence Spectroscopy: A Basis for Analytical Application to Biological Substrates

Melanin is present in various biological substrates where it may participate in several processes, from innate immunity to the still-unsolved opposite roles in antioxidant protection, including photoprotection and the related ability to interact with light. Melanin-light interaction has also been an important source of inspiration for the development of innovative bioengineering applications. These are based on melanin's light-energy-absorption ability of its chemically and structurally complex components and precursors, and on the improvement in analytical and diagnostic procedures in biomedicine. In this regard, here, we characterized the fluorescence spectral properties of melanin and of its precursor L-tyrosine in an aqueous solution during spontaneous melanization. Besides the confirmation of the typical fluorescence-emission signature of melanin and L-tyrosine, we provide additional insights on both emission and excitation spectra recorded during melanization. On these bases, we performed a subsequent characterization on the aqueous extracts from two different melanin-containing biological substrates, namely hairs from a domestic black cat and eggs from the Asian tiger mosquito. The results from the mild extraction procedure, purposely applied to obtain only the soluble components, combined with fluorescence spectral analysis are expected to promote further investigation of the melanization processes, particularly in insects.

Development of Spectral Nano-Flow Cytometry for High-Throughput Multiparameter Analysis of Individual Biological Nanoparticles

Correlated analysis of multiple biochemical parameters at the single-particle level and in a high-throughput manner is essential for insights into the diversity and functions of biological nanoparticles (BNPs), such as bacteria and subcellular organelles. To meet this challenge, we developed a highly sensitive spectral nano-flow cytometer (S-nFCM) by integrating a spectral recording module to a laboratory-built nFCM that is 4-6 orders of magnitude more sensitive in side scattering detection and 1-2 orders of magnitude more sensitive in fluorescence detection than conventional flow cytometers. An electron-multiplying charge-coupled device (EMCCD) was used to acquire the full fluorescence spectra of single BNPs upon holographic grating dispersion. Up to 10,000 spectra can be collected in 1 min with 2.1 nm resolution. The precision, linearity, and sensitivity were examined. Complete discernment of single influenza viruses against the background signal, discrimination of different strains of marine cyanobacteria in a mixed sample based on their spectral properties of natural fluorescence, classification of bacterial categories exhibiting different patterns of antigen expression, and multiparameter analysis of single mitochondria for drug discovery were successfully demonstrated.

Spectral-fluorescent and photochemical study of 6,6′-di(benzoylamino)trimethine cyanine dyes in solutions as possible probes for DNA

Spectral-fluorescent and photochemical properties of trimethine cyanine dyes T-304, T-306, and T-307, having substituents in 6,6′-positions, in various organic solvents, in aqueous buffer solutions, in the presence of surfactants and ethanol additives, and the effect on these properties of addition of DNA have been studied. Strong aggregation of the dyes in aqueous and aqueous buffer solutions has been shown. This is due to increased hydrophobicity of the dyes, which makes it difficult to use them as spectral-fluorescent probes for DNA. In the presence of DNA, trimethine cyanines partially form highly fluorescent complexes of dye monomers with the biomolecule, with slight decomposition of the initial aggregates and the formation of aggregates on DNA molecules. The formation of different types of dye–DNA complexes, i.e., intercalation and binding in the DNA grooves, was modeled by molecular docking. Dye–DNA complexes were also studied by circular dichroism spectroscopy and by thermal dissociation of DNA. To reveal selectivity of the dyes, their interaction with human serum albumin was briefly studied. The presence of moderate concentrations of nonionic surfactants does not lead to a significant decomposition of aggregates, but leads to a biphasic dependence of the fluorescence intensity on the DNA concentration. At the same time, ethanol additives (15%) lead to a more or less linear concentration dependence of the fluorescence intensity, which makes it possible to use these dyes as fluorescent probes for DNA. The effective binding constants of the dyes to DNA and the limits of DNA detection using the dyes in the presence of 15% ethanol were estimated. Photoisomerization and generation of the triplet states of T-304, T-306, and T-307 have been also studied. Along with the fluorescence growth, complexation with DNA leads to an increase in the yield of the triplet states of the dyes. This creates a prerequisite for using the dyes in targeted PDT. In the presence of DNA, the decay kinetics of the triplet states are biexponential, which indicates different types of dye complexes with DNA. The rate constants of oxygen quenching of the triplet states of the dyes bound to DNA are significantly lower than the diffusion-controlled values (taking into account the spin-statistical factor), which is explained by the shielding effect on the triplet molecules in complexes with DNA. The data obtained show that dyes T-304, T-306 and T-307, with addition of 15% ethanol, can be used as possible fluorescent probes for DNA.

Discrimination of normal and cancerous human skin tissues based on laser-induced spectral shift fluorescence microscopy

A homemade spectral shift fluorescence microscope (SSFM) is coupled with a spectrometer to record the spectral images of specimens based on the emission wavelength. Here a reliable diagnosis of neoplasia is achieved according to the spectral fluorescence properties of ex-vivo skin tissues after rhodamine6G (Rd6G) staining. It is shown that certain spectral shifts occur for nonmelanoma/melanoma lesions against normal/benign nevus, leading to spectral micrographs. In fact, there is a strong correlation between the emission wavelength and the sort of skin lesions, mainly due to the Rd6G interaction with the mitochondria of cancerous cells. The normal tissues generally enjoy a significant red shift regarding the laser line (37 nm). Conversely, plenty of fluorophores are conjugated to unhealthy cells giving rise to a relative blue shift i.e., typically SCC (6 nm), BCC (14 nm), and melanoma (19 nm) against healthy tissues. In other words, the redshift takes place with respect to the excitation wavelength i.e., melanoma (18 nm), BCC (23 nm), and SCC (31 nm) with respect to the laser line. Consequently, three data sets are available in the form of micrographs, addressing pixel-by-pixel signal intensity, emission wavelength, and fluorophore concentration of specimens for prompt diagnosis.

Dual-State Emission of 2-(Butylamino)Cinchomeronic Dinitrile Derivatives.

New representatives of 2-(butylamino)cinchomeronic dinitrile derivatives were synthesized as promising fluorophores showing dual-state emission. To characterize the influence of the length (from methyl to butyl) and the structure (both linear and branched) of the alkyl substituent at the amino nitrogen atom, the spectral fluorescence properties of all synthesized compounds were carefully studied both in solution and in solid state. The highest photoluminescence quantum yield values of 63% were noted for solutions of 2-(butylamino)-6-phenylpyridine-3,4-dicarbonitrile in DCM and 2-(butylamino)-5-methyl-6-phenylpyridine-3,4-dicarbonitrile in toluene.

New 2-thiazol-5-yl-benzimidazoles: synthesis and determining of their potential as chemosensor reagents for polyvalent metal ions

Thiabendazole and its analogues are widely used and reasonably well studied in terms of their biological activity, while their potential as chemosensory compounds with optical detection and sensitivity to metal ions remains unexplored. On the other hand, the introduction of a thiazole ring into the heteroaromatic system of benzimidazole significantly expands the directions of practical application of benzimidazole derivatives. Thus, one of the important structural features of the benzimidazole-thiazole system is the presence of a chelate cavity. It is a potential center of complexation with metal ions, which, with their bright fluorescence, create additional opportunities for their use as luminescent probes and chemosensors. Considering the affinity of the sulfur atom for polyvalent heavy metals, sensors based on these compounds can be used in medically and environmentally oriented analysis of toxic metal compounds. In this publication, we focus on the synthesis of various 2- and 4-substituted 2-thiazol-5-yl-benzimidazoles, as well as the determination of their spectral-fluorescence properties. Therefore, we started from 2,4-dihalogen 5-formyl thiazoles, the methods of synthesis of which are well known. Their modification in 2nd position we have described in previous works. To obtain the target products, the Weidenhagen method was chosen, which consists in the reaction of o-phenylenediamine with an aromatic or aliphatic aldehyde under oxidation conditions. For creating such conditions copper acetate was used. The possibility of coordination of metal ions by the obtained compounds was established using electronic absorption and fluorescence spectroscopy. It was found that these compounds selectively form complexes with Cd2+ and Mg2+ ions. Our qualitative studies allow us to make conclusion that the benzimidazole-thiazole fragment is a promising coordination site for metal ions, which can be used in the design of fluorescent probes for the determination of Cd2+ and Mg2+ ions.

Preparation of magnetic fluorescent nanoparticles with quaternary ammonium chitosan derivatives and its properties

To explore a novel solution to the challenges in constructing polymer coated magnetic fluorescent nanoparticles, HTCC/Fe3O4/CdTe magnetic fluorescent nanoparticles (MFCNPs) that can be well dispersed in water were prepared via the electrostatic interaction of the cationic N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) and the anion precoated water-soluble cadmium telluride (CdTe) quantum dots (QDs) and the sodium citrate-coated Fe3O4 (SC-Fe3O4) magnetic nanoparticles (MNPs), which overcame the performance defects of hydrophobic polymer for surface coating and the possible toxicity of cross-linking agent induced by the hydrophilic polymer coating materials. The structural characterizations by FTIR, XRD and XPS reveal that the surfaces of SC-Fe3O4 MNPs and CdTe QDs are coated with HTCC. TEM imaging suggests that the MFCNPs are spherical particles with the diameters of ∼15–20 nm. The MFCNPs exhibit good biocompatibility. Further investigation suggests that the UV-Vis and fluorescence spectral properties and surface electrical properties of HTCC/Fe3O4/CdTe MFCNPs are mainly affected by the relative ratios of SC-Fe3O4 MNPs, CdTe QDs and HTCC. The adsorption and release properties of the MFCNPs were studied using bovine serum albumin (BSA) as the model. The results indicate that the chitosan-based magnetic fluorescent composite is a promising delivery carrier candidate with excellent comprehensive properties for both magnetic response and fluorescence imaging.

Photonics of Trimethine Cyanine Dyes as Probes for Biomolecules

Cyanine dyes are widely used as fluorescent probes in biophysics and medical biochemistry due to their unique photophysical and photochemical properties (their photonics). This review is focused on a subclass of the most widespread and studied cyanine dyes—trimethine cyanines, which can serve as potential probes for biomolecules. The works devoted to the study of the noncovalent interaction of trimethine cyanine dyes with biomolecules and changing the properties of these dyes upon the interaction are reviewed. In addition to the spectral-fluorescent properties, elementary photochemical properties of trimethine cyanines are considered, including: photoisomerization and back isomerization of the photoisomer, generation and decay of the triplet state, and its quenching by oxygen and other quenchers. The influence of DNA and other nucleic acids, proteins, and other biomolecules on these properties is covered. The interaction of a monomer dye molecule with a biomolecule usually leads to a fluorescence growth, damping of photoisomerization (if any), and an increase in intersystem crossing to the triplet state. Sometimes aggregation of dye molecules on biomolecules is observed. Quenching of the dye triplet state in a complex with biomolecules by molecular oxygen usually occurs with a rate constant much lower than the diffusion limit with allowance for the spin-statistical factor 1/9. The practical application of trimethine cyanines in biophysics and (medical) biochemistry is also considered. In conclusion, the prospects for further studies on the cyanine dye–biomolecule system and the development of new effective dye probes (including probes of a new type) for biomolecules are discussed.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5–6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of −0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

Interaction of Novel Monomethine Cyanine Dyes with Proteins in Native and Amyloid States

Molecular interactions between novel monomethine cyanine dyes and non-fibrilar and fibrilar proteins were assessed using fluorescence spectroscopy and molecular docking techniques. To this end, the fluorescence spectral properties of dyes have been explored in the buffer solution and in the presence of insulin and lysozyme in the native and amyloid states. It was observed that association of monomethines with the native and fibrillar proteins was accompanied with a significant enhancement of the fluorophore fluorescence, being more pronounced in the presence of aggregated insulin and lysozyme. The quantitative information about the dye-protein binding was obtained through approximating the experimental dependencies of the fluorescence intensity increase vs protein concentration by the Langmuir model. Analysis of the spectral properties and the binding characteristics of monomethines in the presence of the fibrillar insulin and lysozyme showed that the introduction of chloro- and fluorine-substitutients to the oxazole yellow derivatives, as well as the long aliphatic substitution on the nitrogen atom of the benzazole chromophore of YO-dyes had a negative impact on the dye amyloid specificity. Molecular docking studies showed that monomethines tend to form the most stable complexes with the B-chain residues Val 17, Leu17, Ala 14, Phe1, Gln 4 and Leu 6 and the A-chain residue Leu 13, Tyr 14, Glu 17 of non-fibrilar insulin and interact with the deep cleft of native lysozyme lined with both hydrophobic (Ile98, Ile 58, Thr108, Thr 62 and Thr 63 residues) and negatively (Asp101, Asp 107) charged residues. The wet surface groove Gln15_Glu17 and groove G2-L4/S8-W10 were found as the most energetically favorable binding sites for examined monomethine dyes in the presence of the insulin and lysozyme fibrils, respectively.

Fluorescent sensitized irradiation sensing and recording hybrid quantum dot embedded polymer nanocomposites

This paper presents the preparation and characterisation studies of UV sensing films with a simple mathematical model for quantifying the lower UV irradiation duration/doses. To observe any appreciable changes in any properties of Poly-vinyl alcohol (PVA) films with UV irradiation, it has to be treated for few hours/days together. However, the technique presented here is an ultrasensitive method in which, the quantum dots (QDs) reinforced PVA film has become sensitive to UV radiations even for few seconds of exposure. To achieve this, Mercaptopropionic acid (MPA) capped CdTe QDs with superior fluorescence spectral properties grown in water medium were dispersed in PVA matrix to prepare QD-Polymer nanocomposites. Such fluorescence enriched films were stored in room temperature in ordinary environmental conditions for four years to check the degradability and viability. The stability of fluorescence and electrical properties of QDs inside PVA matrix was remarkable in this test period and were retained by the films even after such long duration. After that they were treated with UV radiation with the interval of few seconds to check the exposure recording ability of such films. The results are very promising in terms of sensitivity and the recording ability. Using the least square linear fit method a mathematical model was developed which would be useful in UV exposure sensing for smaller duration. This study also helps the concerned industries who would prepare film sensors for UV exposure quantification (like Litmus paper for pH sensing).