Growth and spectroscopic properties of Nd-doped Sr3Y2 (BO3)4 crystal

A new crystal of Nd³⁺:Sr₃Y₂ (BO₃)₄ with a dimension of Φ 15×30 mm³ was grown by the Czochralski method. The grown crystal was characterized using X-ray diffraction. The absorption and emission spectra of Nd³⁺:Sr₃Y₂ (BO₃)₄ were investigated. The absorption transition at 807 nm has an FWHM of 16 nm. The absorption and emission cross sections are 6.32×10⁻²⁰ cm² at 807 nm and 1.07×10⁻¹⁹ cm² at 1065 nm, respectively. The luminescence lifetime τ_f is 51.7 μs at room temperature.     

Chemiluminescence behavior of sodium hydrogen carbonate in the potassium permanganate-hydrogen peroxide reaction

Chemiluminescence (CL) phenomenon of hydrogen peroxide with potassium permanganate in the presence of sodium hydrogen carbonate was reported. Effects of the surfactant on the CL system were investigated. Nonionic surfactants could effectively increase the CL signal. Radical scavengers and organic reagents such as nitro blue tetrazolium chloride (NBT), cytochrome c, sodium azide, ascorbic acid, thiourea, tert-butanol and dimethyl sulphoxide were used to study the emitting species. CL emission spectrum was recorded and the results showed that the maximal emission wavelengths of NaHCO₃-H₂O₂-KMnO₄ system were 440 and 634 nm. The mechanism was discussed based on electron spin resonance (ESR) spectra, fluorescence spectra and UV-vis absorption spectra. The addition of rhodamine B or uranine into this CL system enhanced the CL signal. It was due to part of the energy transfer from singlet oxygen and excited triplet dimers of two CO₂ molecules to rhodamine B or uranine. The CL could be induced by excited rhodamine B or uranine.     

Chemiluminescence from singlet oxygen that was detected at two wavelengths and effects of biomolecules on it

We developed the detection apparatus that equipped with the two-photomultiplier tubes for chemiluminescence from singlet oxygen. Singlet oxygen was generated with reaction between sodium hypochlorite and hydrogen peroxide. The chemiluminescence from singlet oxygen, the dimol light emission (ca. 634 nm) and the monomol light emission (ca. 1270 nm), was observed simultaneously for the same reaction cell. The effects of sodium azide as an antioxidant, human serum albumin, and α-amino acids on the chemiluminescence based on the both emissions were examined; the observed chemiluminescence could provide direct information with regard to the reaction between singlet oxygen and antioxidant/biomolecules. The apparent rate constants for quenching singlet oxygen in the presence of human serum albumin were calculated to be ca. 3.3 × 10⁹ and ca. 8.8 × 10⁸ M⁻¹ s⁻¹ for the dimol and monomol light emissions, respectively, under the present conditions. The chemiluminescence intensities of the dimol emission decreased in the presence of His, Asp, Phe, Ser, and Tyr, and that of the monomol decreased in the presence of Cys and Trp. The chemiluminescence observed in the presence of biomolcules was discussed together with the reactivities of sodium hypochlorite and hydrogen peroxide to biomolecules.     

Carbazole‐based colorimetric and fluorescent probe for Cu2+ and its utility in bio‐imaging and real water samples

A new carbazole functionalized Schiff base CBM was synthesized and characterized. CBM can selectively recognize Cu²⁺ via UV–vis and fluorescence signal among common biologically relevant metal ions. When Cu²⁺ was added to CBM, there was a significant enhancement at the maximum absorption wavelength of 393 nm and with a distinct blue shift. The maximum emission peak was significantly attenuated by a factor of about 15 times at 535 nm and the blue shift of emission wavelength was observed. When other metal ions were added, there was no remarkable change at the maximum absorption and emission peak. Under the illumination of 365 nm ultraviolet lamp, the color of the CBM solution changed from light blue to dark blue after the addition of Cu²⁺. The combination mechanism of CBM with Cu²⁺ was nicely explored by density functional theory studies. The probe CBM has good cell permeability, fluorescence electron microscopy experiments show that CBM can be used as a fluorescent probe to detect the presence or absence of Cu²⁺ in Hela cells. Furthermore, the probe CBM can also be used for the detection of copper ions in actual water samples.     

Synthesis,characterization and photoluminescence of 8-oxyquinolinato organoboron complexes derived from pyrazole

A one-pot protocol was developed for the synthesis of a series of luminescent heteroleptic diaryldiborinic complexes containing the central aryl ring bonded to two boron atoms substituted with pyrazole and complexed with 8-hydroxyquinoline. The luminescent properties of these compounds were measured. In dilute solutions they exhibited an emission at ca. 513 nm with quantum yields of 22–27% which are typical for borinic 8-hydroxyquinoline complexes. The only exception was the complex containing the bithiophene scaffold, for which no fluorescence was observed. The obtained pyrazole-based complexes show improved solubility and thermal stability with respect to their phenyl analogues. The experimental UV–vis absorption and emission data are supported by theoretical calculations of the frontier molecular orbitals, revealing the aromatic linker to quinolinato ligand excitation mechanism.     

Studies of the mechanism of formation of calcium silicate compounds by titration based on emission and atomic absorption spectroscopy

In this paper, the inhibition effect of silicate on emission or absorption of calcium was used for an investigation of the mechanism of formation of calcium silicate compounds. For that purpose, calcium chloride solutions were continuously titrated with a standard solution of sodium silicate (Na₂SiO₃), with simultaneous aspiration of the titrand into an air-hydrogen flame. During the titration, changes in the emission of the CaO-band at 622 nm and the CaOH-band at 554 nm were registered automatically on the recorder. Changes in the absorption of calcium were also registered at 422 nm. Thus curves of the same shape were obtained, with the same number of characteristic points, in which the SiO₂/Ca ratio is constant, when the concentration of silicate in the titrant varies. This fact suggests that calcium reacts with silicate to form compounds with a constant composition.Curves of the same shape were obtained by titration of a standard solution of sodium silicate, with a calcium chloride solution, while monitoring the changes in the absorption of calcium at 422 nm and changes in the emission of the CaO-band at 622 nm. In this case, the mole ratios SiO₂/Ca at the characteristic points of the curves were the same as in the case of the titration of calcium chloride solution with the silicate solution.On the basis of the mole ratios SiO₂/Ca at the characteristic points on the titration curves, which amount to 0.21, 0.33 and 0.50, the mechanism of formation of calcium silicate compounds was represented by chemical equations.It may be concluded that in the process of evaporation of spray droplets a chain of reactions take place, resulting in compounds that can be represented by the general formula xCaO·SiO₂.     

Ratiometry of monomer/excimer emissions of dipyrenyl thiacalix[4]arene for Cu detection: a potential Cu and K switched INHIBIT logic gate with NOT and YES logic functions

A new thiacalix[4]arene derivative 2 of 1,3-alternate conformation possessing two pyrene groups has been synthesized and examined for its cation recognition abilities towards different cations such as lithium, sodium, potassium, nickel, zinc, cadmium, silver, mercury, lead and copper by fluorescence spectroscopy. In CH₃CN/CH₂Cl₂ (1:1), the presence of Cu(II) induces the formation of a 1:2 ligand/metal complex, which exhibits increasing monomer emission at 376 nm at the expense of the fluorescent excimer emission of 2 centered at 476 nm. In the presence of K⁺, the intensity of the excimer emission increases along with the formation of a new blue shifted band at 435 nm which corresponds to a static dimer. The compound behaves as a fluorescent molecular switch upon chemical input of Cu²⁺ and K⁺.     

Single red up-conversion luminescence of Er sensitized layered Y2Ti2O7 phosphor

High color purity red emission with single band successfully achieved in a new Er³⁺, Tm³⁺ co-doped Y₂Ti₂O₇ system under 1550 nm excitation, value of red to green emission ratio of the samples is more than 10³. Efficient up-conversion luminescence can be obtained while the ⁴I_13/2 level of Er³⁺ pumped by 1500 nm directly based on the large absorption section and long luminescence lifetime, and red emission composition will greatly enhanced by co-doping with Tm³⁺ ions, color purity of red emission under 1550 nm excitation is much higher than that of 980 nm. The quenching concentration of Er³⁺ ions is up to 28 mol% in Y₂Ti₂O₇ rely on the layer distribution of cations, which can further improve the red emission color purity.     

Urea mediated 5-substituted-1H-tetrazole via [3 + 2] cycloaddition of nitriles and sodium azide

A simple, new and convenient metal free procedure for the synthesis of 5-substituted 1H-tetrazoles using various nitriles and sodium azide in the presence of urea and acetic acid with good to high yields is developed. The reaction plausibly proceeds through in situ formation of urea azide active complex without toxic and/or expensive metal catalysts.     

Resonance Raman studies of the coupled binuclear copper active site in met azide hemocyanin

Spectroscopic studies were performed on the met azide derivative of hemocyanin in order to probe small molecule binding to the coupled binuclear copper active site. The charge transfer spectrum shows a broad band near 380 nm in the absorption and a negative feature near 450 nm in the CD. Resonance Raman results indicate the presence of two enhanced vibrations, the copper—azide stretch at 397 cm⁻¹ and the asymmetric intraazide stretch at 2042 cm⁻¹. The 397 cm⁻¹ peak is maximally enhanced near 500 nm and the 2042 cm⁻¹ peak shows increasing enhancement into the u.v. At least three separate charge transfer transitions are needed to simultaneously fit the absorption, CD and resonance Raman profile, which requires that the azide bridges the binuclear copper active site. Mixed isotope results, using ¹⁴N¹⁴N¹⁵N, shows that the 2042 cm⁻¹ peak splits into two peaks at 2023 and 2035 cm⁻¹ and the 397 cm⁻¹ peak shifts to 393 cm⁻¹. A normal coordinate analysis was used to determine that the mixed isotopic splitting is not due to a simple mass effect but requires nonequivalence in bonding within the azide molecule. Combined with previous data, the results indicate that the azide is bound in a μ-1,3 geometry and the nonequivalence in bonding within the azide molecule is due to a strong interaction with residue(s) in the protein pocket.     

PHOTOCHEMISTRY OF THE REACTION CENTERS OF SYSTEM II UNDER REPETITIVE FLASH GROUP EXCITATION IN ISOLATED CHLOROPLASTS

Abstract— Absorption changes induced in isolated chloroplasts by excitation with repetitive flash groups have been measured at 690 nm, indicating the photochemical turnover of chlorophyll-a_II (Chl-αn), and at 480 nm and 513 nm respectively, reflecting via electrochromic effect the formation of a transmembrane electric field. The data are compared with measurements of oxygen evolution. In chloroplasts with practically fully intact oxygen evolving capacity it was found: 1. The initial amplitude of the 690 nm absorption change induced by the second flash as a function of the time t_v between the first and second flash of a group increases with a half life of about 35 µs. On the other hand, the average oxygen yield due to the second flash as a function of the time t_v rises with a half life of about 600 µs (and a kinetics in the ms-range of minor extent), confirming the data of Vater et al. (1968). 2. Under far red background illumination, where contributions due to PS I in the µs-range can be excluded, the difference spectrum in the red of the absorption changes induced by the first flash corresponds with that of the absorption changes induced by the second flash fired 200 µ after the first flash. 3. The pattern of the absorption changes at 690 nm induced by repetitive double flash groups at t_v= 200 µs does not markedly change in normal chloroplasts by the presence of DBMIB?. Similar 690 nm absorption changes occur in trypsin treated chloroplasts, independent of the presence of DCMU. 4. The fast regeneration in the µs-range of Chl-a_n is also observed in the third flash of a triple flash group at a time t_v= 200 µs between the flashes of the group. 5. The initial amplitudes of the absorption changes with a decay kinetics slower than 100 µs induced by the second flash at 480 nm and 513 nm, respectively, as a function of the time t, between the first and second flash of a group, are characterized by a recovery half-time of about 600 µs, confirming earlier measurements at 520 nm (Witt and Zickler, 1974). On the basis of these results it is inferred that there does exist a photoreaction of Chl-α_n., with an electron acceptor, referred to as X_a, other than the ‘primary’ plastoquinone acceptor X320, if X320 persists in its reduced state. Under conditions of X320 being in the reduced state, this photochemical reaction was shown to be highly dissipative with respect to charging up the watersplitting enzyme system Y. Furthermore, this Chl-a_n-photoreaction with X_a does not lead to a vectorial transmembrane charge separation, which is stable for more than a few microseconds. Different models for the functional and structural organization of PS II are discussed.     

Synthesis of zigzag- and fjord-edged nanographene with dual amplified spontaneous emission

We report the synthesis of a dibenzodinaphthocoronene (DBDNC) derivative as a novel nanographene with armchair, zigzag, and fjord edges, which was characterized by NMR and X-ray crystallography as well as infrared (IR) and Raman spectroscopies. Ultrafast transient absorption (TA) spectroscopy revealed the presence of stimulated emission signals at 655 nm and 710 nm with a relatively long lifetime, which resulted in dual amplified spontaneous emission (ASE) bands under ns-pulsed excitation, indicating the promise of DBNDC as a near-infrared (NIR) fluorophore for photonics. Our results provide new insight into the design of nanographene with intriguing optical properties by incorporating fjord edges.

Dibenzo[a,m]dinaphtho[ef,hi]coronene with zigzag and fjord edges was synthesized and characterized, demonstrating a nonplanar structure with near-infrared stimulated emission with a relatively long lifetime and dual-amplified spontaneous emission.     

Synthesis,photophysical, and electrochemical properties of wide band gap tetraphenylsilane-carbazole derivatives: Effect of the substitution position and naphthalene side chain

Four tetraphenylsilane-carbazole derivatives with wide bandgaps (3.38–3.55 eV) were synthesized. The effects of the substitution position and of the presence of naphthalene groups on the photophysical, electrochemical and thermal properties were investigated. The derivatives exhibited maximum absorption peaks ranging from 293 to 304 nm and maximum emission peaks ranging from 347 to 386 nm. Changing the carbazole substitution position on the tetraphenylsilane did not significantly change the photophysical and electrochemical properties. However, p-substituted compounds exhibited higher glass transition temperatures than m-substituted compounds. Naphthalene groups with bulky structures had extended the conjugation lengths that red-shifted both the absorption and emission spectra. The LUMO level was decreased, which reduced the optical bandgap and triplet energy level. However, the naphthalene groups significantly improved the thermal stability by increasing the glass transition temperature of the compounds.     

Biosynthesis of zinc oxide nanoparticles using Euphorbia milii leaf constituents: Characterization and improved photocatalytic degradation of methylene blue dye under natural sunlight

A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m²/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm³/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm^?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.     

Spectroscopic and HPLC methods for the determination of alendronate in tablets and urine

Two methods (spectrophotometric and HPLC) have been developed and validated for the analysis of alendronate sodium in tablet dosage form. Both methods depend on the ability of alendronate sodium to react with o-phthalaldehyde (OPA) at basic pH to produce a light-absorbing derivative. The derivative was found to possess absorption maximum at 330 nm where neither the derivatizing agent nor the analyte had any absorption. Thus, spectroscopic method was based on the derivatization-induced absorption of alendronate sodium at 333 nm. The HPLC method was based on separation of the formed derivative from other ingredients in tablets with detection at 333 nm. Both methods were satisfactory with regard to accuracy, prescion and linearity. Moreover, a HPLC method with fluorescence detection (HPLC-FD) was developed for the quantification of alendronate sodium in urine. The method was also based on the derivatization of alendronate with OPA, but fluorescence detection was employed. Linearity, recovery, selectivity, prescision and sensitivity were satisfactory for the proposed HPLC-FD method. Yet a new quantification limit (0.6 ng ml⁻¹) for alendronate in urine was achieved.     

A Golgi Apparatus-Targeting,Naphthalimide-Based Fluorescent Molecular Probe for the Selective Sensing of Formaldehyde

Formaldehyde (FA) is a colorless, flammable, foul-smelling chemical used in building materials and in the production of numerous household chemical goods. Herein, a fluorescent chemosensor for FA is designed and prepared using a selective organ-targeting probe containing naphthalimide as a fluorophore and hydrazine as a FA-binding site. The amine group of the hydrazine reacts with FA to form a double bond and this condensation reaction is accompanied by a shift in the absorption band of the probe from 438 nm to 443 nm upon the addition of FA. Further, the addition of FA is shown to enhance the emission band at 532 nm relative to the very weak fluorescent emission of the probe itself. Moreover, a high specificity is demonstrated towards FA over other competing analytes such as the calcium ion (Ca²⁺), magnesium ion (Mg²⁺), acetaldehyde, benzaldehyde, salicylaldehyde, glucose, glutathione, sodium sulfide (Na₂S), sodium hydrosulfide (NaHS), hydrogen peroxide (H₂O₂), and the tert-butylhydroperoxide radical. A typical two-photon dye incorporated into the probe provides intense fluorescence upon excitation at 800 nm, thus demonstrating potential application as a two-photon fluorescent probe for FA sensing. Furthermore, the probe is shown to exhibit a fast response time for the sensing of FA at room temperature and to facilitate intense fluorescence imaging of breast cancer cells upon exposure to FA, thus demonstrating its potential application for the monitoring of FA in living cells. Moreover, the presence of the phenylsulfonamide group allows the probe to visualize dynamic changes in the targeted Golgi apparatus. Hence, the as-designed probe is expected to open up new possibilities for unique interactions with organ-specific biological molecules with potential application in early cancer cell diagnosis.     

Pesticide analysis in herbal infusions by solid-phase microextraction and gas chromatography with atomic emission detection

A direct immersion solid-phase microextraction (SPME) procedure was used in combination with capillary gas chromatography with atomic emission detection (GC-AED) for the determination of 10 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in herbal and tea infusions. Ionic strength, sample dilution and time and temperature of the absorption and desorption stages were some of the parameters investigated in order to select the optimum conditions for SPME with a 100 μm PDMS fiber-coating. Element-specific detection and quantification was carried out by monitoring the chlorine (479 nm) and bromine (478 nm) emission lines, which provided nearly specific chromatograms. Calibration was carried out by using a spiked sample infusion. The detection limits varied between 11.9 ng ml⁻¹ for deltamethrin and 0.03 ng ml⁻¹ for p,p′-DDE and p,p′-DDD. The recoveries ranged from 73.5% for deltamethrin to 108.3% for p,p′-DDT in a spiked white tea infusion. Two of the eight samples analyzed contained low levels of some the pesticides considered.     

Determination of trace metallothioneins at nanogram levels with Eosin Y by resonance light scattering method

The interactions of metallothioneins with Eosin Y were studied by the absorption spectra and resonance light scattering (RLS) spectra methods. A direct RLS spectra method was applied for the determination of trace metallothioneins. The interaction of Eosin Y and metallothioneins enhanced the RLS intensity of system in Britton-Robinson buffer (pH 3.91), with the help of anionic surfactant (sodium dodecyl benzene sulphate). The mechanism was studied and discussed in terms of the RLS and UV-absorption spectra. Under optimal experimental conditions, at 366 nm, there was a linear relationship between the RLS intensity and the concentration of the metallothioneins in the range of 0.04–14.0 μg mL^?1, with a correlation coefficient of r = 0.9985 and detection limit of 11.9 ng mL^?1. The relative standard deviation was 3.1% (n = 11), and the average recovery was 95.2%. The method proposed was reliable, selective and sensitive in determining trace metallothioneins in human urine samples with the results in good agreement with those obtained by high-performance liquid chromatography.     

UV absorption properties of ceria-modified compositions within the fluorite-type solid solution CeO2-Y6WO12

A new fluorite-type solid solution domain has been evidenced in the system (1−x) CeO₂−x/7 Y₆WO₁₂□₂ using the amorphous citrate route. All the studied phases (0?x?1) crystallize in a cubic-type symmetry. Diffuse reflectance spectra reveal a strong optical absorption between 380 and 400 nm. All substituted compositions spectral selectivities are estimated suitable for application as inorganic UV absorbers. The non linear variation observed in the optical gap values between Y₆WO₁₂ and CeO₂ is attributed to the presence of the cerium 4f-block band. Additionally, Time Resolved Microwave Conductivity (TRMC) experiment and phenol photodegradation analyses carried out on the Ce_0.81Y_0.16W_0.03O_1.95□_0.05 (x=0.19) composition do not indicate any photocalatytic activity for this material.     

Unexpected highly selective fluorescence ‘turn-on’ and ratiometric detection of Hg based on fluorescein platform

Methylated fluorescein 1 was explored for fluorescence ‘turn-on’ and ratiometric detection of Hg²⁺ in THF and CH₂Cl₂/MeOH (v/v=9:1), respectively, with unexpected high selectivity. In the presence of Hg²⁺, characteristic structured absorption band of 1 diminished and a new sharp band appeared at 445 nm. Meanwhile a blue shifted and enhanced emission was observed. The ratio of the fluorescence intensity at 559 and 478 nm increased linearly with [Hg²⁺], and solution color changing from yellow to cyan under irradiation at 365 nm in CH₂Cl₂/MeOH. Job plot indicated a 1:1 stoichiometry for 1-Hg²⁺ complex in solution. ¹H NMR titration and IR spectra suggested the coordination of carbonyl group in xanthene moiety to Hg²⁺, affording its spectral behavior. Compound 2 bearing two triazolyl amino esters in place of methyl group showed quite similar behavior to Hg²⁺, which indicated that substituents did not interfere with the specific binding behavior of fluorescein platform. Our work presents a new way to explore xanthene dyes as new chemosensors by modulating electron density on the xanthene ring through non-covalent interactions with carbonyl group.