Effects of alcohols on fluorescence intensity and color of a discharged-obelin-based biomarker

Photoproteins are responsible for bioluminescence of marine coelenterates; bioluminescent and fluorescent biomarkers based on photoproteins are useful for monitoring of calcium-dependent processes in medical investigations. Here, we present the analysis of intensity and color of light-induced fluorescence of Ca²⁺-discharged photoprotein obelin in the presence of alcohols (ethanol and glycerol). Complex obelin spectra obtained at different concentrations of the alcohols at 350- and 280-nm excitation (corresponding to polypeptide-bound coelenteramide and tryptophan absorption regions) were deconvoluted into Gaussian components; fluorescent intensity and contributions of the components to experimental spectra were analyzed. Five Gaussian components were found in different spectral regions—ultraviolet (tryptophan emission), blue-green (coelenteramide emission), and red (hypothetical indole-coelenteramide exciplex emission). Inhibition coefficients and contributions of the components to experimental fluorescent spectra showed that presence of alcohols increased contributions of ultraviolet, violet, and red components, but decreased contributions of components in the blue-green region. The effects were related to (1) changes of proton transfer efficiency in fluorescent S*₁ state of coelenteramide in the obelin active center and (2) formation of indole-coelenteramide exciplex at 280-nm photoexcitation. The data show that variation of fluorescence color and intensity in the presence of alcohols and dependence of emission spectra on excitation wavelength should be considered while applying the discharged obelin as a fluorescence biomarker.     

The dependence of DNA luminescence on excitation wavelength in the UV/VUV region

Luminescence emission and excitation spectra have been obtained for DNA films at 77 K under vacuum ultraviolet excitation (150–280 nm). The emission spectra, which cover the wavelength range 310 to 490 nm, consists of two components, a short-lived component around 350 nm which is attributed to fluorescence and a longer-lived component around 410 nm believed to be phosphorescence. The excitation spectra, as functions of emission wavelength, are similar in profile with a fairly broad peak around 9240–260 nm) with a shoulder around 200 nm followed by a gradual but constant decrease into the vacuum ultraviolet region of the spectrum. No evidence of autoionization was seen in the region investigated.     

β-Cyclodextrin derived full-spectrum fluorescent carbon dots: The formation process investigation and biological applications

Carbon dots (CDs), a new building unit, have been revolutionizing the fields of biomedicine, bioimaging, and optoelectronics with their excellent physical, chemical, and biological properties. However, the difficulty of preparing excitation-dependent full-spectrum fluorescent CDs has seriously hindered their further research in fluorescence emission mechanisms and biomedicine. Here, we report full-spectrum fluorescent CDs that exhibit controlled emission changes from purple (380 nm) to red (613 nm) at room temperature by changing the excitation wavelength, and the excitation dependence was closely related to the regulation of sp² and sp³ hybrid carbon structures by β-cyclodextrin-related groups. In addition, by regulating the content of β-cyclodextrin, the optimal quantum yields of full-spectrum fluorescent CDs were 8.97%, 8.35%, 7.90%, 9.69% and 17.4% at the excitation wavelengths of 340, 350, 390, 410 and 540 nm, respectively. Due to their excellent biocompatibility and color tunability, full-spectrum fluorescent CDs emitted bright and steady purple, blue, green, yellow, and red fluorescence in MCF-7 cells. Moreover, we optimized the imaging conditions of CDs and mitochondrial-specific dyes; and realized the mitochondrial-targeted co-localization imaging of purple, blue and green fluorescence. After that, we also explored the effect of full-spectrum fluorescent CDs in vivo fluorescence imaging through the intratumorally, subcutaneously, and caudal vein, and found that full-spectrum fluorescent CDs had good fluorescence imaging ability in vivo.     

Specificity of Glucose Oxidase from Penicillium funiculosum 46.1 Towards Some Redox Mediators

Glucose oxidase (GOx) from Penicillium funiculosum 46.1 was purified using step-by-step ultrafiltration and it was characterized by spectrophotometric and spectrofluorometric methods. It was shown that spectra of GOx produced by P. funiculosum are typical for flavoproteins. Absorption spectrum has distinct peaks at 380 and 457 nm, excitation spectrum at 373 and 447 nm, and emission spectrum at 530 and 562 nm. The pH correlation of enzyme activity and catalytic characteristics in various buffer systems (phosphate (pH 5.0–9.0), citrate (pH 3.0–5.0), citrate-phosphate (pH 3.0–9.0), and universal (pH 3.0–9.0)) were registered. It was determined that the GOx is the most efficiently interacting with substrate (glucose) in phosphate buffer at pH 7.0 with k _cat/K _m?=?21,825 M^?1 s^?1. Interaction of several different redox mediators (9,10-phenantroline-5,6-dione, 9,10-phenanthrenequinone, N-methylphenazonium methyl sulfate, ferrocene, ferrocenecarboxylic acid, α-methylferrocenemethanol, ferrocenecarboxaldehyde) with GOx from P. funiculosum was investigated by evaluation of the difference in fluorescence emission intensity of FAD_(oxidized) and FADH_2(reduced) forms. It was found that 9,10-phenantroline-5,6-dione and 9,10-phenanthrenequinone are the best redox mediators for this type of GOx.

γ-Fe2O3 Nanoparticles Covered with Glutathione-Modified Quantum Dots as a Fluorescent Nanotransporter

The present paper describes the synthesis, characterization, and utilization of multi-functional magnetic conjugates that integrate optical and magnetic properties in a single structure for use in many biomedical applications. Spontaneous interaction with eukaryotic cell membrane (HEK-239 cell culture) was determined using fluorescence microscopy, and fluorescence analyses. Both, differences in excitation, and emission wavelength were observed, caused by glutathione intake by cells, resulting in disintegration of core–shell structure of quantum dots, as well as adhesion of conjugate onto cell surface. When compared with quantum dots fluorescent properties, HEK-239 cells with incorporated nanoconjugate exhibited two excitation maxima (λ _ex = 430 and 390 nm). Simultaneously, application of ideal λ _ex for quantum dots (λ _ex = 430 nm), resulted in two emission maxima (λ = 740 and 750 nm). This nanoconjugate fulfills the requirements of term theranostics, because it can be further functionalized with biomolecules as DNA, proteins, peptides or antibodies, and thus serves as a tool for therapy in combination with simultaneous treatment.     

SPECTROSCOPIC AND MICROSCOPIC CHARACTERISTICS OF HUMAN SKIN AUTOFLUORESCENCE EMISSION

To improve the understanding of human skin autofluorescence emission, the spectroscopic and microscopic characteristics of skin autofluorescence were studied using a combined fluorescence and reflectance spectroanalyzer and a fiber optic microspectrophotometer. The autofluorescence spectra of in vivo human skin were measured over a wide excitation wavelength range (350–470 nm). The excitation–emission matrices of in vivo skin were obtained. An excitation–emission maximum pair (380 nm, 470 nm) was identified. It was revealed that the most probable energy of skin autofluorescence emission photons increases monotonically and near linearly with increasing excitation photon energy. It was demonstrated that the diffuse reflectance, R, can be used as a first order approximation of the fluorescence distortion factor f to correct the measured in vivo autofluorescence spectra for the effect of tissue reabsorption and scattering. The microscopic in vitro autofluorescence properties of excised skin tissue sections were examined using 442 nm He–Cd laser light excitation as an example. It was demonstrated that the fluorophore distribution inside the skin tissue is not uniform and the shapes of the autofluorescence spectra of different anatomical skin layers vary. The result of this study confirms that the major skin fluorophores are located in the dermis and provides an excellent foundation for Monte Carlo modeling of in vivo autofluorescence measurements.     

Effect of pH and α-, β- and γ-cyclodextrin on the spectral properties of etoricoxib: spectroscopic and molecular dynamics study

The spectral properties of etoricoxib (ETR) at pH 2.0, 6.0 and 10.0 in the presence of cyclodextrins (CDs) were investigated. The absorption spectrum of ETR in acidic medium exhibited two bands centered at 236 and 273 nm, while in basic medium it exhibited two bands centered at 236 and 285 nm. No change in the spectrum was observed in the presence of CDs. The fluorescence emission spectra of ETR in acidic and basic media exhibited one band at 380 nm and another one at 484 nm. The emission band at 484 nm was enhanced when ETR was complexed with β-CD and γ-CD at pH 2.0, 6.0 and 10.0, while the band at 380 nm was enhanced selectively when ETR was complexed with α-CD at pH 2.0. Molecular dynamics simulations computations revealed that at pH 2.0, the sulfonyl moiety of H₂ETR²⁺ is preferentially included within the α-CD cavity, which is believed to cause the enhancement of the band at 380 nm. Moreover, at pH 6.0 and 10.0, the enhancement of the band at 484 nm was related to the inclusion of the chloropyridinyl and methylpyridinyl groups of the bipyridine moiety of HETR⁺ and ETR within β-CD and γ-CD cavities. Benesi–Hildebrand analysis showed that the ETR/β-CD complex adopts a 1:1 stoichiometry with association constant of K ₁₁?=?64.8 at pH 2.0, K ₁₁?=?105.4 at pH 6.0 and K ₁₁?=?520.5 at pH 10.0.     

Constant-wavelength synchronous spectrofluorimetry for determination of riboflavin in anchovies

Constant-wavelength synchronous spectrofluorimetry was used for the analysis of riboflavin in anchovies. Synchronous fluorescence spectra were recorded between 300 and 600 nm at a scan rate of 240 nm min^–1 and with excitation and emission slit-widths both set to 5 nm. The excitation-emission wavelength difference was 65 nm. The fluorescence was measured by peak-area base between 430–509 nm. Recovery was higher than 90.8%.     

Enhancement of Fluorescence Intensity of Tramadol and Its Main Metabolites in LC Using Pre-Column Derivatization with 9-Fluorenylmethyl Chloroformate

Tramadol was found to exhibit weak fluorescence with a maximum emission at 300 nm when excited at 200 nm. Also, fluorescence spectra of the drug and its two main metabolites, O-desmethyltramadol and N-desmethyltramadol are not practically identical. Thus low and different sensitivities have been reported for the drug and its metabolites in previously published work. In the present method using 9-fluorenylmethyl chloroformate (FMOC-Cl) as labeling agent, equal and magnified fluorescence intensity were obtained for the analytes. The drug, its metabolites and an internal standard (oseltamivir phosphate) were extracted from serum by dichloromethane. Pre-column derivatization of the analytes was achieved using FMOC-Cl in the presence of borate buffer (0.1 M, pH 7.5). Liquid chromatography with a mobile phase consisting of a mixture of 0.05 M phosphate buffer containing triethylamine (2 ml L^?1; pH = 3.0) and methanol (54:46; v/v) and a Shimpack CLC-ODS column were used for analytical separation of the analytes. The fluorescence of the column effluent was monitored at an excitation and emission wavelengths of 265 and 315 nm, respectively. The analytical method was linear over the concentration range of 1.0–1,280 ng mL^?1 of the parent drug and its metabolites and limit of quantification of 1.0 ng mL^?1 was obtained for the analytes using 10 μL injection. The method validation was studied and the validated method applied in a bioequivalence study of 2 different tramadol preparations in 24 healthy volunteers.     

LC with Fluorescence Detection for the Tissue Pharmacokinetics of 2-Methoxyestradiol Solution and Liposome After Intravenous Administrations to Rats

2-Methoxyestradiol is currently in phase II clinical trials as a chemotherapeutic agent. An LC method with fluorescence detection was developed for determination of methoxyestradiol in rat lung. Sample was extracted with ethyl acetate and separated on a C₁₈ column (150 mm × 4.6 mm, 5 μm) with a mobile phase consisting of potassium dihydrogen phosphate-acetonitrile-triethylamine (55:45:0.3, v/v/v, pH 3.0). The excitation and emission wavelength were set at 285 and 325 nm, respectively. Standard curves were linear over the concentration range of 0.25–64 μg g^?1. The method was found to be precise, accurate and specific and can be applied to tissue pharmacokinetics of methoxyestradiol in rats.     

On <Emphasis Type="Italic">Trans</Emphasis>-Resveratrol in Aqueous Solutions

A thermodynamic study on aqueous solutions of trans-Resveratrol (3,5,4′-trihydroxy-trans-stilbene) at 25.00 ± 0.02 °C, in 0.5 mol·dm^?3 NaCl, has been conducted. The protolysis equilibria and the complex formation between trans-Resveratrol and a metal(II), namely Mn²⁺ and Cu²⁺, have been investigated. The experimental method consists of potentiometric, spectrophotometric (absorption and emission) acid–base titrations. The pH range investigated is 2.5 ≤ pH ≤ 13 for the binary system, while for the ternary system it is 2.5 ≤ pH ≤ 6. The results of the graphical and numerical methods adopted indicate, for all the systems investigated, the formation of a predominant Me(II)–trans-Resveratrol mononuclear complex. UV–Vis absorption spectra and desorption/ionization time of flight mass spectra show the occurrence of hydrolytic species exhibiting a higher molecular weight than the Resveratrol molecule, becoming more evident as the pH and the time increased. Moreover, high performance liquid chromatography analysis and infrared spectroscopy of aqueous cis/trans-Resveratrol solutions upon excitation at 300 nm have highlighted a highly fluorescent compound, with absorption maximum at 250 nm, and a blue shift in the fluorescence emission that have not previously been reported.     

Investigation on the Luminescence Performance of Four Quinolones

Abstract

In this paper we report on the low temperature phosphorescence (LTP), the low temperature fluorescence (LTF), the paper substrate room temperature phosphorescence (PS‐RTP), and the room fluorescence (RTF) properties of ciprofloxacin (CPFX), lomefloxacin (LMX), fleroxacin (FLX), and ofloxacin (OFLX), which were investigated and compared. Some rules were discovered: their maximal excitation wavelength and emission wavelength are in the range of 280–295 nm and 428–500 nm, respectively, except OFLX, and the difference in molecular structure may be responsible for it. The pH experiments show that all their emissions are strongest in acid, followed by neutral, and weakest in alkali medium. The PS‐RTP characters of lifetime and polarization were also investigated and compared. It was found that the lifetimes of PS‐RTP were all in the level of 0.1 s. These quinolones belong to long‐life phosphorescence and their PS‐RTP spectra are incompletely polarized.     

LC Determination of Nosiheptide in Swine Kidney and Liver

A liquid chromatographic method was developed for determination of nosiheptide in swine kidney and liver. The tissue samples were extracted with acetonitrile and defatted with hexane. The analytes were determined at a fluorescence excitation/emission wavelength of 357/515 nm and with gradient elution program. The limits of detection and limits of quantification were 5 and 20 ng g^?1, respectively, for swine kidney and liver. The mean recoveries for nosiheptide in swine kidney and liver ranged from 70.3 to 97.4% with coefficients of variation below 11.3% at 20–100 ng g^?1 fortification levels.     

Photoluminescence of Eu-doped triple phosphate Ca8MgR(PO4)7 (R=La, Gd, Y)

Eu³⁺-doped triple phosphate Ca₈MgR(PO₄)₇ (R=La, Gd, Y) was synthesized by the general high-temperature solid-state reaction. Excitation and emission spectra as well as luminescence decay were used to characterize the phosphors. Photoluminescence excitation and emission spectra showed that the phosphor could be efficiently excited by UV-vis light from 260 to 450 nm to give bright red emission assigned to the transition (⁵D₀→⁷F₂) at 612 nm. The richness of the red color has been verified by determining their color coordinates (X, Y) from the CIE standard.     

Determination of Free Fatty Acids in Tibet Folk Medicine Potentilla anserina L. Using a New Labeling Reagent by LC with Fluorescence Detection and Identification with Online Atmospheric Chemical Ionization-MS Identification

A sensitive method for the determination of free fatty acids using 1,2-benzo-carbazole-9-ethyl-p-toluenesulfonate (BCETS) as tagging reagent with fluorescence detection has been developed. BCETS could easily and quickly label fatty acids in the presence of the K₂CO₃ catalyst at 80 °C for 30 min in N,N-dimethylformamide solvent. In this study, fatty acids from the extracted Potentilla anserina L. plant sample were sensitively determined. The corresponding derivatives were separated on a reversed-phase Eclipse XDB-C₈ column by LC in conjunction with gradient elution. The identification was carried out by post-column APCI-MS in positive-ion detection mode. BCETS-fatty acid derivatives gave an intense molecular ion peak at m/z [M+H]⁺, the collision-induced dissociation spectra of m/z [M+H]⁺ produced the specific fragment ions at m/z [M′+CH₂CH₂]⁺, m/z 216.6 and m/z [MH?H₂O]⁺ (here, M′: corresponding molecular mass of the fatty acids). The fluorescence excitation and emission wavelengths of the derivatives were at λ _ex 279 nm and λ _em 380 nm, respectively. Linear correlation coefficients for all fatty acid derivatives are more than 0.9994. Detection limits, at a signal-to-noise ratio of 3:1, are 10.79–34.19 fmol for the labeled fatty acids.     

Ochratoxin A in Some French Wines: Application of a Direct Competitive ELISA Based on an OTA–HRP Conjugate

Abstract

In the direct-competitive enzyme-linked immunosorbent assay (dc-ELISA) approach, an ochratoxin A–horseradish peroxidase (OTA–HRP) synthesized conjugate was utilized. Fluorescence studies revealed that when excited at 333 nm, the OTA–HRP conjugate shifted in fluorescence from 438 nm to 444 nm. At the 295-nm excitation wavelength, the tryptophan emission peak blue-shifted from 326 nm to 318 nm. Western blot analysis revealed that anti-OTA antibodies specifically binds and recognize the OTA–HRP conjugate. The dc-ELISA showed an IC₅₀ value of 400 ng/L and a linear working range (LWR) value between 100 and 1500 ng/L. The ELISA results were confirmed with high-performance liquid-chromatography (HPLC) analysis to assess the potential of the OTA–HRP conjugate.     

Synthesis and characterization of novel blue emitting Na2CaSiO4:Ce3+ phosphor

The blue phosphors Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ were synthesized by the sol–gel method and their luminescence characteristics were investigated for the first time. Structural information about prepared samples is obtained by analyzing the XRD patterns and SEM micrographs. The photoluminescence (PL) excitation spectra indicate that the Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors can be effectively excited by ultraviolet (360 nm) light. The PL emission spectra exhibit tunable blue broadband emission with the dominant wavelength of 427–447 nm under excitation of 360 nm by controlling the doping concentration of Ce³⁺. The concentration quenching effect for Ce³⁺ was found at the optimum doping concentration of 4 mol%. The Commission Internationale de l’Eclairage 1931 chromaticity coordinates of Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ are (0.1447, 0.0787), which are better color purity compared to the commercial Eu²⁺-doped BaMgAl₁₀O₁₇ phosphor. Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ composition shows intense blue emission (peak wavelength, 439 nm) with relative intensity versus commercial BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor (Nichia) 65 and 158 % under 254 and 365 nm excitation, respectively. All the results indicate that Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors are potential candidate as a blue emitting phosphor for UV-converting white light-emitting diodes.     

Inclusion as a driving force for the intramolecular charge transfer (ICT) fluorescence of p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) in α-cyclodextrin (α-CD) aqueous solution

A 1:1 inclusion complex between p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) molecule and α-cyclodextrin (α-CD) in aqueous solution is formed with a stabilization constant of ca. 45.65 ± 3.59 M^?1 at 25 °C. The formation of the complex is accompanied by enhancement of the long wavelength fluorescence at 510 nm (attributed to intramolecular charge transfer (ICT) due to twisting) relative to the normal fluorescence at 420 nm. In water, the long-wavelength fluorescence is hidden under the red tail of the normal fluorescence band due to quenching by non-radiative transition. Inclusion by CD reduces quenching and thus constitutes a driving force for DPABME to emit at longer wavelength via ICT process.     

Sensitive pH probe developed with water-soluble fluorescent carbon dots from chocolate by one-step hydrothermal method

In present work, fluorescent carbon dots (CDs) with an average diameter of 2.5 nm were firstly synthesised by a simple, convenient and low-cost hydrothermal method from chocolate. The obtained CDs possessed fine monodispersity and bright blue fluorescence that was strongest at an excitation wavelength of 360 nm and had a comparable quantum yield of 12% (in case of dots prepared in presence of nitric acid). The emission peak depended on the excitation wavelength in the range from 320 to 440 nm. Ionic strength had a weak effect up to 1.0 M and then no significant change was found in the range of 1.0–4.5 M. The fluorescence intensity of CDs displayed good pH adaptability and a linear dependence on the pH change in the range of pH 1.0–3.0 and pH 9.0–12.5, which have promising potentials for pH sensor.     

Synthesis of poly(phenylgermanosilanes) and poly(phenylgermanocarbosilanes)

Phenyl-substituted poly(germanosilanes) and poly(germanocarbosilanes) have been synthesized through the Wurtz-Kipping reaction via dechlorination of mixtures of dichlorophenylsilanes (PhSi(R)Cl₂, where R = H, Ph, or vinyl) with diphenyldichlorogermane in the presence of an ultradisperse sodium suspension. The polymers thus synthesized have been investigated by X-ray fluorescence analysis; FTIR and UV spectroscopy; and ¹H, ¹³C, and ²⁹Si NMR spectroscopy. The peak maxima in the UV spectra of the polymers dissolved in THF are in the wavelength range of 300–375 nm. Under the effect of UV irradiation with a wavelength of 320–380 nm, photoluminescence emission peaking in the range of 380–470 nm is observed. Size exclusion chromatography indicates that all the (co)polymers under examination are characterized by a narrow GPC curve and their polydispersity indexes are no larger than 1.5. According to dynamic TGA data, the weight loss of the polymers reaches 80% even at 500°C. Owing to formation of branched structures in vinyl-substituted copolymers, the GPC curves widen (the polydispersity index is ～6), while the yield of an inorganic residue at 900°C amounts to 40%.