Enantiomeric assay of escitalopram S(+)‐enantiomer and its “in‐process impurities” using two different techniques

The enantiomeric purity of escitalopram oxalate ESC and its “in‐process impurities,” namely, ESC‐N‐oxide, ESC‐citadiol, and R(?)‐enantiomer were studied in drug substance and products using high‐performance liquid chromatography (HPLC)‐UV (Method I), synchronous fluorescence spectroscopy (SFS) (Method IIA), and first derivative SFS (Method IIB). Method I describes as an isocratic HPLC‐UV for the direct resolution and determination of enantiomeric purity of ESC and its “in‐process impurities.” The proposed method involved the use of α_l‐acid glycoprotein (AGP) chiral stationary phase. The regression plots revealed good linear relationships of concentration range of 0.25 to 100 and 0.25 to 10 μg mL^?1 for ESC and its impurities. The limits of detection and quantifications for ESC were 0.075 and 0.235 μg mL^?1, respectively. Method II involves the significant enhancement of the fluorescence intensities of ESC and its impurities through inclusion complexes formation with hydroxyl propyl‐β‐cyclodextrin as a chiral selector in Micliavain buffer. Method IIA describes SFS technique for assay of ESC at 225 nm in presence of its impurities: R(?)‐enantiomer, citadiol, and N‐oxide at ?λ of 100 nm. This method was extended to (Method IIB) to apply first derivative SFS for the simultaneous determination of ESC at 236 nm and its impurities: the R(?)‐enantiomer, citadiol, and N‐oxide at 308, 275, and 280 nm, respectively. Linearity ranges were found to be 0.01 to 1.0 μg mL^?1 for ESC and its impurities with lower detection and quantification limits of 0.033/0.011 and 0.038/0.013 μg mL^?1 for SFS and first derivative synchronous fluorescence spectra (FDSFS), respectively. The methods were used to investigate the enantiomeric purity of escitalopram.     

Synthesis,crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine

Two complexes of Tb³⁺, Gd³⁺/Tb³⁺ and one heteronuclear crystal Gd³⁺/Tb³⁺ with phenoxyacetic acid (HPOA) and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis‐differential scanning calorimetry (TG‐DSC) analysis show that the two complexes are Tb₂(POA)₆(TPTZ)₂·6H₂O and TbGd(POA)₆(TPTZ)₂·6H₂O, respectively. The crystal structure of TbGd(POA)₆(TPTZ)₂·2CH₃OH was determined using single‐crystal X‐ray diffraction. The monocrystal belongs to the triclinic system with the P‐1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C₆H₅OCH₂COO^– and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd³⁺/Tb³⁺ complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb³⁺ ions, and intramolecular energy transfer from the ligands coordinated with Gd³⁺ ions to Tb³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy transfer induced white‐light‐emitting phosphor by co‐doping Ce3+, Tb3+ and Mn2+ into the single Ba9Lu2Si6O24 host

In the Ba₉Lu₂Si₆O₂₄ (BLS) host, Ce³⁺ shows cyan emissions peaking at 490 nm under 400 nm excitations. BLS:Tb³⁺ only can be effectively excited by 254 nm light and gives rise to green emissions at 553 nm. However, both the cyan and green emissions can be obtained in BLS:Ce³⁺,Tb³⁺ under 400 nm excitations due to effective energy transfers from Ce³⁺ to Tb³⁺. BLS:Mn²⁺ shows red emissions peaking at 610 nm under 414 nm excitations. By co‐doping Ce³⁺, Tb³⁺ and Mn²⁺, tunable full‐color emissions were obtained. The BLS:0.3Ce³⁺,0.6Tb³⁺,0.15Mn²⁺ single phosphor exhibits a white light with a high color rendering index of 85 and a correlated color temperature of 5480 K under 400 nm excitation.     

Thermoluminescence and photoluminescence studies on γ‐ray‐irradiated Ce3+,Tb3+‐doped potassium chloride single crystals

Single crystals of KCl doped with Ce³⁺,Tb³⁺ were grown using the Bridgeman–Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo‐stimulated luminescence (PSL), and thermal‐stimulated luminescence (TSL) properties were studied after γ‐ray irradiation at room temperature. The glow curve of the γ‐ray‐irradiated crystal exhibits three peaks at 420, 470 and 525 K. F‐Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F‐ and V‐centres are formed in the crystal during γ‐ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co‐doped KCl:Tb crystals showed broad band emission due to the d–f transition of cerium and a reduction in the intensity of the emission peak due to ⁵D₃–⁷F_j (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co‐doping Ce³⁺ ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb³⁺. The emission due to Tb³⁺ ions was confirmed by PSL and TSL spectra. Copyright © 2015 John Wiley & Sons, Ltd.     

Resonant and non‐resonant energy transfer from Ce3+ → X (X = Tb3+, Eu3+ or Dy3+) in NaMgSO4F material

An inorganic NaMgSO₄F fluoride material was prepared by the wet chemical method and studied for its photoluminescence (PL) and resonant–non‐resonant energy transfer (RET and NORET) capabilities between Ce³⁺ → Tb³⁺, Ce³⁺ → Eu³⁺ and Ce³⁺ → Dy³⁺ rare earth ions. The Tb³⁺ emission for Ce³⁺ → Tb³⁺ transfers under ultraviolet (UV) wavelengths peaked at 491, 547, and 586 nm, for excitation at 308 nm due to ⁵D₄ → ⁷F_J (J = 4, 5, 6) transitions. Eu emission spectra were observed at 440 nm (Eu²⁺), 593 nm and 616 nm (Eu³⁺) recorded for different concentrations of materials, whereas Dy³⁺ emission from Ce³⁺ → Dy³⁺ transfer under UV wavelengths peaked at 485 nm and 577 nm due to ⁴F_9/2 → ⁶H_15/2 and ⁶H_13/2 transitions. The purpose of the present study is to understand the RET and NORET effects of Tb³⁺, Eu³⁺ and Dy³⁺ co‐doping in a NaMgSO₄F:Ce³⁺ luminescent material, which could be used as a green‐emitting material for lamp phosphors.     

Spectrofluorimetric determination of folic acid in tablets and urine samples using 1,10‐phenanthroline‐terbium probe

A new spectrofluorimetric method was reported for the determination of folic acid (FA), based on its quenching effect on the fluorescence intensity of Tb³⁺–1,10‐phenanthroline complex as a fluorescent probe. The quenched fluorescence intensity at an emission wavelength of 545 nm was proportional to the concentration of FA in Tris–HCl buffer solution of pH 6.2. The effects of pH, time, order of addition of reagents, temperature and concentrations of Tb³⁺, buffer and 1,10‐phenanthroline were investigated and optimized. The linear range for the determination of FA was 0.01–1.1 mg/L. The detection limit was 0.003 mg/L and the relative standard deviation for replicated determination of 1 mg/L of folic acid was 1.2%. This method was simple, practical and relatively free from interference effects. It was successfully applied to assess FA in pharmaceutical tablets and urine samples. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and fluorescence properties of 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazol derivatives and their terbium complexes

Eight novel 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazol derivatives have been designed and synthesized, and their corresponding Tb³⁺ complexes were also prepared successfully. The fluorescence properties and fluorescence quantum yields of the target complexes were investigated, the results showed that the ligands were an efficient sensitizer for Tb³⁺ luminescence, and the target complexes exhibited characteristic fluorescence emissions of Tb³⁺ ion. The fluorescence intensity of the complex substituted by chlorine was stronger than that of other complexes. The substituents' nature has a great effect upon the electrochemical properties of the target complexes. The results showed that the introduction of the electron‐withdrawing groups tended to decrease the oxidation potential and highest occupied molecular orbital energy levels of the target Tb³⁺ complexes; however, introduction of the electron‐donating groups can increase the corresponding complexes' oxidation potential and highest occupied molecular orbital energy levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of nucleic acid by [tetra‐(3‐methoxy‐4‐hydroxyphenyl)]–Tb3+ porphyrin as the fluorescence spectral probe in bis(2‐ethylhexyl)sulfosuccinate sodium salt micelle system

A new system for the determination of nucleic acid by rare earth metallic porphyrin of [tetra‐(3‐methoxy‐4‐hydroxyphenyl)]–Tb³⁺ [T(3‐MO‐4HP)–Tb³⁺] porphyrin as fluorescence spectral probe has been developed in this paper. Nucleic acid can enhance the fluorescence intensity of the T(3‐MO‐4HP)–Tb³⁺ porphyrin in the presence of bis(2‐ethylhexyl)sulfosuccinate sodium salt(AOT) micelle. In pH 8.00 Tris–HCl buffer solution, under optimum conditions, the enhanced fluorescence intensity is in proportion to the concentration of nucleic acids in the range of 0.05–3.00 µg mL^?1 for calf thymus DNA (ct DNA) and 0.03–4.80 µg mL^?1 for fish sperm DNA(fs DNA). Their detection limits are 0.03 and 0.01 µg mL^?1, respectively. In addition, the binding interaction mechanism between T(3‐MO‐4HP)–Tb³⁺ porphyrin and ct DNA is also investigated by resonance scattering and fluorescence spectra. The maximum binding number is calculated by molar ratio method. The new system can be used for the determination of nucleic acid in pig liver, yielding satisfactory results. Copyright © 2009 John Wiley & Sons, Ltd.     

BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

A terbium‐sensitized spectrofluorimetric method for determination of catecholamines in a serum sample with micelle medium

A terbium‐sensitized spectrofluorimetric method has been developed for determination of catecholamines such as norepinephrine (NE), epinephrine (EP) and dopamine (DA), using sodium dodecyl benzene sulphonate (SDBS). Fluorescence sensitization of terbium ions (Tb³⁺) by complexation with catecholamines in the presence of SDBS was observed. The fluorescence intensities of the Tb³⁺–catecholamine complexes were highly enhanced by introducing SDBS with an emission maximum at 545 nm after excitation at 290 nm. The conditions for the complex formation of Tb³⁺–catecholamine were investigated systematically and optimized to determine catecholamines in a serum sample. Under the optimum conditions, the fluorescence intensities of the Tb³⁺–catecholamine complexes were increased linearly with the concentration of NE, EP and DA over the ranges 2.5 × 10^–10–1.0 × 10^–8, 2.5 × 10^–10–1.0 × 10^–8 and 2.5 × 10^–9–1.0 × 10^–7 g/mL with correlation coefficients of 0.999, 0.999 and 0.9996, respectively. The limits of detection (3δ) of NE, EP and DA were found to be 4.6 × 10^–11, 7.8 × 10^–11 and 8.38 × 10^–10 g/mL, respectively. Precision of the method was tested at the concentration level of 1.2 × 10^?7 g/mL for five replicate measurements of NE, EP and DA, giving relative standard deviations (RSDs) of 1.41%, 1.23% and 1.89%, respectively. The interaction mechanism of the Tb³⁺–catecholamine complexes system was investigated and presented with ultraviolet absorption spectra. The proposed method has been applied for the quantitative determination of NE, EP and DA in a spiked serum sample and a pharmaceutical preparation sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Emission analysis of Tb3+‐and Sm3+‐ion‐doped (Li2O/Na2O/K2O) and (Li2O + Na2O/Li2O + K2O/K2O + Na2O)‐modified borosilicate glasses

Four series of borosilicate glasses modified by alkali oxides and doped with Tb³⁺ and Sm³⁺ ions were prepared using the conventional melt quenching technique, with the chemical composition 74.5B₂O₃ + 10SiO₂ + 5MgO + R + 0.5(Tb₂O₃/Sm₂O₃) [where R = 10(Li₂O /Na₂O/K₂O) for series A and C, and R = 5(Li₂O + Na₂O/Li₂O + K₂O/K₂O + Na₂O) for series B and D]. The X‐ray diffraction (XRD) patterns of all the prepared glasses indicate their amorphous nature. The spectroscopic properties of the prepared glasses were studied by optical absorption analysis, photoluminescence excitation (PLE) and photoluminescence (PL) analysis. A green emission corresponding to the ⁵D₄ → ⁷F₅ (543 nm) transition of the Tb³⁺ ions was registered under excitation at 379 nm for series A and B glasses. The emission spectra of the Sm³⁺ ions with the series C and D glasses showed strong reddish‐orange emission at 600 nm (⁴G_5/2 →⁶H_7/2) with an excitation wavelength λ_exci = 404 nm (⁶H_5/2→⁴F_7/2). Furthermore, the change in the luminescence intensity with the addition of an alkali oxide and combinations of these alkali oxides to borosilicate glasses doped with Tb³⁺ and Sm³⁺ ions was studied to optimize the potential alkali‐oxide‐modified borosilicate glass.     

Enhanced photoluminescence properties of electrospun Dy3+‐doped ZnO nanofibres for white lighting devices

Dy³⁺‐doped ZnO nanofibres with diameters from 200 to 500 nm were made using an electrospinning technique. The as‐fabricated amorphous nanofibres resulted in good crystalline continuous nanofibres through calcination. Dy³⁺‐doped ZnO nanofibres were characterized using scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) light spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL). XRD showed the well defined peaks of ZnO. UV–vis spectra showed a good absorption band at 360 nm. FTIR spectra showed a Zn–O stretching vibration confirming the presence of ZnO. Photoluminescence spectra of Dy³⁺‐doped ZnO nanofibres showed an emission peak in the visible region that was free from any ZnO defect emission. Emissions at 480 nm and 575 nm in the Dy³⁺‐doped ZnO nanofibres were the characteristic peaks of dopant Dy³⁺ and implied efficient energy transfer from host to dopant. Luminescence intensity was found to be increased with increasing doping concentration and reduction in nanofibre diameter. Colour coordinates were calculated from photometric characterizations, which resembled the properties for warm white lighting devices.     

Magnesium methoxide‐induced chemiluminescent decomposition of bicyclic dioxetanes bearing a 2′‐alkoxy‐2‐hydroxy‐1,1′‐binaphthyl‐7‐yl moiety

Bicyclic dioxetanes 2a–c bearing a 2′‐alkoxy‐2‐hydroxy‐1,1′‐binaphthyl‐7‐yl moiety were effectively synthesized and their base‐induced chemiluminescent decomposition was investigated by the use of alkaline metal (Na⁺ and K⁺) or Mg²⁺ alkoxide in MeOH. When 2a–c were treated with tetrabutylammonium fluoride (TBAF) in dimethyl sulfoxide (DMSO) as a reference system, they showed chemiluminescence as a flash of orange light (maximum wavelength λ_max^CL = 573–577 nm) with efficiency Φ^CL = 6–8 × 10^–2. On the other hand, for an alkaline metal (Na⁺ or K⁺) alkoxide/MeOH system, 2a–c decomposed slowly to emit a glow of chemiluminescence, the spectra of which were shifted slightly toward red from the TBAF/DMSO system, and Φ^CL (= 1.4–2.3 × 10^–3) was considerably decreased. In addition, Mg(OMe)₂ was found to play a characteristic role as a base for the chemiluminescent decomposition of 2a–c through coordination to the intermediary oxidoaryl‐substituted dioxetanes 13. Thus, Mg²⁺ increased Φ^CL to more than twice those with Na⁺ or K⁺, while it shifted λ_max^CL considerably toward blue (λ_max^CL = 550–566 nm). Copyright © 2012 John Wiley & Sons, Ltd.     

Eu3+‐tetrakis β‐diketonate complexes for solid‐state lighting application

Eu³⁺–β‐diketonate complexes are used, for example, in solid‐state lighting (SSL) or light‐converting molecular devices. However, their low emission quantum efficiency due to water molecules coordinated to Eu³⁺ and low photostability are still problems to be addressed. To overcome such challenges, we synthesized Eu³⁺ tetrakis complexes based on [Q][Eu(tfaa)₄] and [Q][Eu(dbm)₄] (Q1 = C₂₆H₅₆N⁺, Q2 = C₁₉H₄₂N⁺, and Q3 = C₁₇H₃₈N⁺), replacing the water molecules in the tris stoichiometry. The tetrakis β‐diketonates showed desirable thermal stability for SSL and, under excitation at 390 nm, they displayed the characteristic Eu³⁺ emission in the red spectral region. The quantum efficiencies of the dbm complexes achieved values as high as 51%, while the tfaa complexes exhibited lower quantum efficiencies (28–33%), but which were superior to those reported for the tris complexes. The structures were evaluated using the Sparkle/PM7 model and comparing the theoretical and the experimental Judd–Ofelt parameters. [Q1][Eu(dbm)₄] was used to coat a near‐UV light‐emitting diode (LED), producing a red‐emitting LED prototype that featured the characteristic emission spectrum of [Q1][Eu(dbm)₄]. The emission intensity of this prototype decreased only 7% after 30 h, confirming its high photostability, which is a notable result considering Eu³⁺ complexes, making it a potential candidate for SSL.     

Luminescence and energy‐transfer properties of color‐tunable Ca2Mg0.25Al1.5Si1.25O7:Ce3+/Eu2+/Tb3+ phosphors for ultraviolet light‐emitting diodes

A series of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺/Eu²⁺/Tb³⁺ phosphors was been prepared via a conventional high temperature solid‐state reaction and their luminescence properties were studied. The emission spectra of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺ and Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Tb³⁺ phosphors show not only a band due to Ce³⁺ ions (409 nm) but also as a band due to Eu²⁺ (520 nm) and Tb³⁺ (542 nm) ions. More importantly, the effective energy transfer from Ce³⁺ to Eu²⁺ and Tb³⁺ ions was confirmed and investigated by emission/excitation spectra and luminescent decay behaviors. Furthermore, the energy level scheme and energy transfer mechanism were investigated and were demonstrated to be of resonant type via dipole–dipole (Ce³⁺ to Eu²⁺) and dipole–quadrupole (Ce³⁺ to Tb³⁺) reactions, respectively. Under excitation at 350 nm, the emitting color could be changed from blue to green by adjusting the relative doping concentration of Ce³⁺ and Eu²⁺ ions as well as Ce³⁺ and Tb³⁺ ions. The above results indicate that Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺/Tb³⁺ are promising single‐phase blue‐to‐green phosphors for application in phosphor conversion white‐light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel europium β‐diketonate organic complexes for solid‐state lighting

Volatile Eu complexes, namely Eu(TTA)₃Phen, Eu_(x)Y_(1‐x)(TTA)₃ Phen; Eu_(x)Tb_(1‐x)(TTA)₃Phen; Eu, europium; Y, yttrium; Tb, Terbium; TTA, thenoyltrifluoroacetone; and Phen, 1,10 phenanthroline were synthesized by maintaining stichiometric ratio. Various characterization techniques such as X‐ray diffraction (XRD), photoluminescence (PL) and thermo gravimetric analysis/differential thermal analysis (TGA/DTA) were carried out for the synthesized complexes. Diffractograms of all the synthesized complexes showed well‐resolved peaks, which revealed that pure and doped organic Eu³⁺ complexes were crystalline in nature. Of all the synthesized complexes, Eu_0.5 Tb_0.5(TTA)₃Phen showed maximum peak intensity, while the angle of maximum peak intensity for all complexes was almost the same with slightly different d‐values. A prominent sharp red emission line was observed at 611 nm when excited with light at 370 nm. It was observed that the intensity of red emissions increased for doped europium complexes Eu_(x)Y_(1‐x)(TTA)₃Phen and Eu_(x)Tb_(1‐x)(TTA)₃ Phen, when compared with Eu complexes. Emission intensity increased in the following order: Eu(TTA)₃Phen > Eu_0.5 Tb_0.5(TTA)₃Phen > Eu_0.4 Tb_0.6(TTA)₃Phen > Eu_0.5Y_0.5(TTA)₃Phen > Eu_0.4Y_0.6(TTA)₃Phen, proving their potential application in organic light‐emitting diodes (OLEDs). TGA showed that Eu complexes doped in Y³⁺ and Tb³⁺ have better thermal stability than pure Eu complex. DTA analysis showed that the melting temperature of Eu(TTA)₃ Phen was lower than doped Eu complexes. These measurements infer that all complexes were highly stable and could be used as emissive materials for the fabrication of OLEDs. Copyright © 2012 John Wiley & Sons, Ltd.     

Terbium (III) coordination polymer–copper (II) compound as fluorescent probe for time‐resolved fluorescence ‘turn‐on’ detection of hydrogen sulfide

With recognition of the biological importance of hydrogen sulfide (H₂S), we present a simple and effective fluorescent probe for H₂S using a Tb³⁺ coordination polymer–Cu²⁺ compound (DPA/Tb/G–Cu²⁺). Dipicolinic acid (DPA) and guanosine (G) can coordinate with Tb³⁺ to form a macromolecular coordination polymer (DPA/Tb/G). DPA/Tb/G specifically binds to Cu²⁺ in the presence of coexisting cations, and obvious fluorescence quenching is observed. The quenched fluorescence can be exclusively recovered upon the addition of sulfide, which is measured in the mode of time‐resolved fluorescence. The fluorescence intensities of the DPA/Tb/G–Cu²⁺ compound enhance linearly with increasing sulfide concentrations from 1 to 30 μM. The detection limit for sulfide in aqueous solution is estimated to be 0.3 μM (at 3σ). The DPA/Tb/G–Cu²⁺ compound was successfully applied to sense H₂S in human serum samples and exhibited a satisfactory result. It displays some desirable properties, such as fast detection procedure, high selectivity and excellent sensitivity. This method is very promising to be utilized for practical detection of H₂S in biological and environmental samples.     

Determination of amlodipine using terbium‐sensitized luminescence in the presence of europium(III) as a co‐luminescence reagent

A sensitive time‐resolved luminescence method for the determination of amlodipine (AM) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of terbium (Tb³⁺) by formation of a ternary complex with AM in the presence of tri‐n‐octylphosphine oxide (TOPO) as co‐ligand, dodecylbenzenesulfate as surfactant and europium ion as a co‐luminescence reagent. The signal for Tb–AM–TOPO is monitored at λ_ex = 242 nm and λ_em = 550 nm. Optimum conditions for the formation of the complex in aqueous system were 0.015 m Tris (hydroxylmethyl) amino methane buffer, pH 9.0, TOPO (1.0 × 10^–4 m ), Eu³⁺ (2.0 × 10^–7 m ), dodecylbenzenesulfate (0.14%) and 6.0 × 10^–5 m of Tb³⁺, which allows the determination of 10–50 ppb of AM with a limit of detection of 1.2 ppb. The relative standard deviations of the method range between 0.1 and 0.2% indicated excellent reproducibility of the method. The proposed method was successfully applied for the assay of AM in pharmaceutical formulations and in plasma samples. Average recoveries of 98.5 ± 0.2% and 95.2 ± 0.2% were obtained for AM in tablet and plasma samples respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Nucleosomal arrays self‐assemble into supramolecular globular structures lacking 30‐nm fibers

The existence of a 30‐nm fiber as a basic folding unit for DNA packaging has remained a topic of active discussion. Here, we characterize the supramolecular structures formed by reversible Mg²⁺‐dependent self‐association of linear 12‐mer nucleosomal arrays using microscopy and physicochemical approaches. These reconstituted chromatin structures, which we call “oligomers”, are globular throughout all stages of cooperative assembly and range in size from ~50 nm to a maximum diameter of ~1,000 nm. The nucleosomal arrays were packaged within the oligomers as interdigitated 10‐nm fibers, rather than folded 30‐nm structures. Linker DNA was freely accessible to micrococcal nuclease, although the oligomers remained partially intact after linker DNA digestion. The organization of chromosomal fibers in human nuclei in situ was stabilized by 1 mM MgCl₂, but became disrupted in the absence of MgCl₂, conditions that also dissociated the oligomers in vitro. These results indicate that a 10‐nm array of nucleosomes has the intrinsic ability to self‐assemble into large chromatin globules stabilized by nucleosome–nucleosome interactions, and suggest that the oligomers are a good in vitro model for investigating the structure and organization of interphase chromosomes.     

Luminescent properties of single‐phase Ba2‐x‐1.5y‐1.5zP2O7:xEu2+,yCe3+, zTb3+ phosphors for white light‐emitting diode

A series of Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors was synthesized via a co‐precipitation method, then their crystal structure, quantum efficiency and luminescent properties were analyzed by XRD and FL, respectively. The results showed that these phosphors not only presented the excitation characteristics of Ba₂P₂O₇:xEu²⁺,zTb³⁺, but also exhibited that of the Ba₂P₂O₇:yCe³⁺,zTb³⁺ phosphor. Meanwhile, the tri‐doped phosphor showed a stronger absorption around 320 nm in contrast with the Eu²⁺/Ce³⁺:Tb³⁺ co‐doped phosphor. Not only can energy transfer from Ce³⁺→Eu²⁺ be observed; the energy transfer mechanism from Eu²⁺ to Tb³⁺ is discussed in the tri‐doped system. Ce³⁺ affects the luminescence properties of Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors just as the sensitizer whereas Eu²⁺ is considered both as the sensitizer and the activator. The chromaticity coordinates of tri‐doped phosphors excited at 320 nm stayed steadily in the bluish‐white light region,and the emitted color and color temperature (CCT) of these phosphors could be tuned by adjusting the relative contents of Eu²⁺, Ce³⁺ and Tb³⁺. Hence, the single phase Ba₂P₂O₇:xEu²⁺,yCe³⁺,zTb³⁺ phosphors may be considered as potential candidates for white light‐emitting diodes.