Optical properties of bis(cyclopentadienyl)magnesium: excimer-type luminescence of the bis(cyclopentadienyl) ligand frame

The electronic spectra of solid MgCp₂ (Cp = cyclopentadienyl) show features which indicate the presence of intramolecular interligand interactions. The fluorescence of MgCp₂ (λ_max = 363 nm) undergoes a considerable Stokes shift which is apparently caused by a bonding attraction between both Cp rings in the excited state. An additional phosphorescence of the (Cp⁻)₂ fragment (λ_max = 535 nm) appears at 77 K.     

Determination of the antidepressant paroxetine and its three main metabolites in human plasma by liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method has been developed for the determination in human plasma of the specific serotonin reuptake inhibitor (SSRI) antidepressant paroxetine and its three main metabolites (M1, M2, M3). Fluorescence detection was used, exciting at λ = 294 nm and monitoring emission at λ = 330 nm for paroxetine (λ_exc = 280 nm, λ_em = 330 nm for M1 and M2; λ_exc = 268 nm, λ_em = 290 nm for M3). Separation was obtained on a reversed-phase C18 column using a mobile phase composed of 66.7% aqueous phosphate at pH 2.5 and 33.3% acetonitrile. Imipramine (λ_exc = 252 nm, λ_em = 390 nm) was used as the internal standard. A careful pre-treatment of plasma samples was developed, using solid-phase extraction with C8 cartridges (50 mg, 1 mL). The calibration curves were linear over a working range of 2.5-100 ng mL⁻¹ for paroxetine and of 5-100 ng mL⁻¹ for all metabolites. The limit of detection (LOD) was 1.2 ng mL⁻¹ for PRX and 2.0 ng mL⁻¹ for the metabolites. The method was applied with success to plasma samples from depressed patients undergoing treatment with paroxetine. Hence, the method seems to be suitable for the therapeutic drug monitoring of paroxetine and its main metabolites in depressed patients’ plasma.     

Facile, sensitive and selective fluorescence turn-on detection of HSA/BSA in aqueous solution utilizing 2,4-dihydroxyl-3-iodo salicylaldehyde azine

A novel fluorescence turn-on detection method of human serum albumin (HSA) and bovine serum albumin (BSA) in aqueous solution is investigated using 2,4-dihydroxyl-3-iodo salicylaldehyde azine (DISA). Upon the addition of DISA to HSA/BSA solution, a fluorescence turn-on effect at 529 nm can be observed with a large stokes shift of ∼129 nm based on hydrophobic binding-mode between protein and dye. Under the optimal condition, the linear ranges of fluorescence intensity for HSA and BSA are 0.1-30 μg mL⁻¹ with the relative correlation coefficient of R² = 0.991 (n = 10) and 0.3-50 μg mL⁻¹ with R² = 0.997 (n = 10); and the detection limits for HSA and BSA based on IUPAC (C_DL = 3S_b/m) are 20 ng mL⁻¹ and 50 ng mL⁻¹, respectively.     

Novel photoluminescent lanthanidomesogens forming bilayer smectic phase derived from blue light emitting liquid crystalline, one ring O-donor Schiff-base ligands

A series of new mononuclear lanthanide(III)-salicylaldimine complexes of the type [Ln(LH)₃(NO₃)₃] (Ln = La, Pr, Sm and Gd; LH = N-(2-hydroxyethyl)-4n-alkoxysalicylaldimine, n = 14, 18) have been synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, UV-Vis, FAB-mass and magnetic susceptibility measurements. The ligand (LH) coordinate to lanthanide ions in zwitterionic form via the phenolic-oxygen with the proton shifted to the imine-nitrogen. The nitrato groups occurring in chelated bidentate fashion complete a nine-coordinate geometry. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) show that the ligands are monotropic and their complexes exhibit enantiotropic highly viscous smectic A (SmA) mesophase in the temperature range 60-185 °C. A bilayer self organized assembly of the molecules in the mesophase are proposed on the basis of the small angle XRD study. The ligands are blue light emitters with a broad emission maxima at ∼447 nm while the lanthanide complexes show intense emission in the visible range (∼465-679 nm) at 350 nm excitation. The samarium(III) complex, [Sm(LH)₃(NO₃)₃] is distinct from the rest in emitting bright orange light (∼660 nm, Φ = 48%). The S_o-S₁ excitation band being stronger than the direct f-f excitation in the samarium complex clearly suggests that the Schiff-base ligands efficiently sensitize the luminescence of Sm³⁺. DFT calculations have been performed using DMol3 program at BLYP/DNP level to obtain the stable electronic structure of the ligand and complex.     

Coumarin–TPA derivative: a reaction-based ratiometric fluorescent probe for Cu(I)

A coumarin-based reactive probe 1 is reported for the highly selective detection of Cu⁺. The benzylic ether (C–O) bond of probe 1 can be cleaved selectively by the reaction with Cu⁺ under a physiological reducing environment, resulting in a fluorescent change. The maximum emission peak exhibited a red shift from 410 nm to 472 nm, and a remarkable enhancement of emission intensity ratios (I₄₇₂/I₄₁₀) from 0.26 to 13.82 was observed.     

Al selective an efficient colorimetric receptor derived from 5-aminouracil

An interference-free naked-eye recognition of Al³⁺ at its micromolar level has been done in 5% aqueous DMSO solution employing a Schiff base 5-[(2-hydroxy-5-nitro-benzylidene)-amino]-1H-pyrimidine-2,4-dione (receptor 1) which is an intramolecular charge transfer (ICT) probe. The pyrimidine and nitrophenyl groups serve as electron rich (donor) and deficient (acceptor) pockets in receptor 1 exhibiting a broad ICT band at 434 nm (olive green). The concomitant additions of Al³⁺ as its chloride salt to the 5 × 10⁻⁵ M aqueous DMSO solution of the receptor 1 lead hypsochromic shifting of its ICT band to 395 nm (colorless). The same ICT band undergoes a marginal bathochromic shifting (6 nm) along with a hyperchromic shift on separate additions of a basic anion like F⁻, CH₃COO⁻ and H₂PO₄⁻ to the receptor 1 and faced almost similar fate on concomitant additions of Al³⁺ as mentioned above.     

Tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence sensor based on carbon nanotube/organically modified silicate films

In this paper, a novel electrochemiluminescence (ECL) sensor was constructed to determine herring sperm (HS) double-stranded (ds) DNA. Tetramethoxysilane and dimethyldimethoxysilane were selected as co-precursors to form an organically modified silicate (ORMOSIL) film for the immobilization of multiwall carbon nanotubes (MWNTs) wrapped by poly(p-styrenesulfonate) (PSS), and then Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) was successfully immobilized on a glassy carbon electrode via ion-association. PSS was employed to increase the conductivity of the ORMOSIL film and disperse the cut MWNTs, which were cut and shortened in a mixture of concentrated sulfuric and nitric acids, in the film. It was found that MWNTs could adsorb Ru(bpy)₃²⁺ and acted as conducting pathways to connect Ru(bpy)₃²⁺ sites to the electrode. MWNTs also played a key role as materials for the mechanical and thermal properties. The ECL performance of this modified electrode was evaluated in a flow injection analysis (FIA) system, and the detection limit (S/N = 3) for HS ds-DNA was 2.0 × 10⁻⁷ g mL⁻¹ with a linear range from 1.34 × 10⁻⁶ to 6.67 × 10⁻⁴ g mL⁻¹ (R² = 0.9876). In addition, the ECL sensor presented excellent characteristics in terms of stability, reproducibility and application life.     

The photochemistry of (η-2-R-C3H4)Fe(CO)(NO)(X) (R = H or Cl; X = CO or PPh3) in room temperature solution or frozen gas matrixes

A photochemical study of allyl iron complexes of the type, (η³-2-R-C₃H₄)Fe(CO)(NO)(X) (R = H or Cl; X = CO or PPh₃) is presented. These compounds were studied in solid matrixes at 20 K, and at room temperature, by a combination of laser flash at 355 nm and steady-state photolysis. The predominant photochemical process for these compounds is loss of a CO ligand. In addition, exhaustive irradiation of (η³-2-R-C₃H₄)Fe(CO)(NO)(PPh₃) with λ_exc > 300 nm provided evidence for a haptotropic shift of the allyl group from η³ to η¹ coordination.     

Synthesis of a new type of dibenzopyrromethene-boron complex with near-infrared absorption property

A new type of π-extended 4-bora-3a,4a-diaza-s-indacene (BODIPY dye), bis(isoindole)-derived benzo[1,3,2]oxazaborinine 1, has been synthesized by seven-step procedure from 2-methoxybenzoic acid methyl ester. The benzannulation of the pyrrole ring and the formation of a structurally strained intramolecular B-O ring enable the dye to absorb near-infrared light at ca. 750 nm with a molecular extinction coefficient (ε) of ca 8.3 × 10⁴ M⁻¹ cm⁻¹ in THF. The absorption properties are discussed on the basis of DFT calculations. Interestingly, a film of 5,5-dihexyloxy derivative 1b, which was fabricated by a spin-coating procedure on a glass plate, exhibited a dramatic bathochromic shift of absorbance as compared to the solution, with λ_max of 922 nm.     

Dioxouranium(VI)-carboxylate complexes: A calorimetric and potentiometric investigation of interaction with oxalate at infinite dilution and in NaCl aqueous solution at I = 1.0 mol L and T = 25 °C

In this paper we investigated the interactions between dioxouranium(VI) and oxalate using (H⁺-glass electrode) potentiometry and titration calorimetry. Potentiometric measurements were carried out in NaCl aqueous solutions and at T = 25 °C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants) at low ionic strength values (I ≤ 0.090 mol L⁻¹, without supporting electrolyte) and at I = 1.0 mol L⁻¹; different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the binary mononuclear species UO₂(ox)⁰, UO₂(ox)₂²⁻, UO₂(ox)₃⁴⁻ widely reported in literature, the ternary hydroxyl mononuclear species UO₂(ox)OH⁻, UO₂(ox)(OH)₂²⁻, UO₂(ox)₂OH³⁻, UO₂(ox)₃OH⁵⁻, the protonated ternary mononuclear species UO₂(ox)₃H³⁻ and the binuclear species (UO₂)₂(ox)₅⁶⁻.Calorimetric measurements were carried out following similar procedures and in the same experimental conditions as employed for the potentiometric measurements at I = 1.0 mol L⁻¹ in NaCl. The stability of UO₂²⁺-oxalate²⁻ complexes is fairly high and their main contribution to stability is entropic in nature. Some linear empirical relationships were found which make it possible to calculate (i) the contribution of a single bond: and ; (ii) chelate stabilisation per ring: and and (iii) the mean stability of negatively charged Na⁺-ion pair complexes: log^TK = (0.46 ± 0.02)·|z| (z = charge of complex species), ΔG° = −(2.60 ± 0.1)·|z| kJ mol⁻¹ and TΔS° = 2.5 ± 0.5 kJ mol⁻¹. Both potentiometric and calorimetric results provide evidence of the penta-coordination of the species UO₂(ox)₃⁴⁻. SIT parameters were calculated from the data at I = 0 and I = 1.02 mol kg⁻¹. Comparisons are made with literature data. An insoluble dioxouranium(VI) ternary complex was synthesised (at I = 1.0 mol L⁻¹ in NaCl) and characterised by thermoanalysis and elemental analysis.     

Spectroscopic and structural characterization of Na2[(VO)2(ttha)]·8H2O (ttha = triethylenetetraamine-N,N,N′,N″,N′″,N′″-hexaacetate): Interpreting the results with density functional theory

Na₂[(V^IVO)₂(ttha)]·8 H₂O (ttha = triethylenetetraamine–N,N,N′,N″,N′″,N′″–hexaacetate ion), prepared by treating [VO(H₂O)₅][(VO)₂(ttha)]·4 H₂O with Na₆(ttha), has been characterized by single crystal X-ray diffraction, infrared spectroscopy, UV–Vis absorption spectroscopy, electron spin resonance spectroscopy, and modeled by density functional theory (DFT). The X-ray structure revealed a distorted octahedral geometry around each vanadium center. The electronic absorption spectrum of [(VO)₂(ttha)]²⁻ (aq) features absorptions at ca. 200 nm (ε > 13900 L mol⁻¹ cm⁻¹), 255 nm (ε = 3480 L mol⁻¹ cm⁻¹), 586 nm (ε = 33 L mol⁻¹ cm⁻¹), and 770 nm (ε = 38 L mol⁻¹ cm⁻¹). The time-dependent density functional theory (TDDFT) calculated electronic absorption spectrum was remarkably similar to the actual spectrum, and TDDFT predicts absorption peaks at 297, 330, 458, 656, and 798 nm. TDDFT assigned the peak at 798 nm to be the α spin HOMO → LUMO transition. Hence, the peak at 770 nm in the actual spectrum is most likely the α spin HOMO → LUMO transition. Moreover, the TDDFT calculations revealed that the α spin HOMO and LUMO are partly comprised of d orbitals on both vanadium centers, and the first derivative electron spin resonance spectrum also suggests that the two unpaired electrons in [(VO)₂(ttha)]²⁻ are localized near the vanadium centers.     

Cation distribution and particle size effect on Raman spectrum of CoFe2O4

Mössbauer and Raman spectroscopic studies were carried out on CoFe₂O₄ particles synthesized with size ranging from 6 to 500 nm (bulk). Cation distribution studies were carried out on the high temperature and room temperature phases of the microcrystalline CoFe₂O₄ by Mössbauer and Raman spectroscopic methods. The high temperature phase of CoFe₂O₄ showed a decreased inversion parameter of 0.69 as compared to the value of the room temperature phase of 0.95, indicating that the structure gradually transforms towards a normal spinel. Corresponding Raman spectra for these two phases of CoFe₂O₄ showed a change in relative peak intensity of the vibrational mode at 695 cm⁻¹(A_1g(1)) to 624 cm⁻¹ (A_1g(2)). The relative peak intensity ratio, I_v between the A_1g(1) and A_1g(2) vibrational mode was decreasing with lowering of inversion parameter of the CoFe₂O₄ spinel system. A variation of laser power on the sample surface was reflected in the cation distribution in ferrite phase. Superparamagnetic, single domain CoFe₂O₄ particles (6 nm) showed a 20 cm⁻¹ red shift and broadening of phonon modes when compared to the macro-crystalline CoFe₂O₄ (500 nm). Variation of Raman shift with particle size was studied by considering the bond polarization model. Raman spectroscopic studies clearly indicate the variation in the cation distribution in nano-sized particles and distribution tending to a normal spinel structural configuration.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

A study of the direct determination of Cd, Cr, Cu, Pb and Zn in certified reference materials of soils by solid sampling electrothermal atomic absorption spectrometry

A simple and rapid method for the direct determination of Cd, Cr, Cu, Pb and Zn in soil was developed. The method was developed using three certified reference materials of soil: Eutric Cambisol, Orthic Luvisols and Rendzina, which differed in their matrix composition. Chemical modifiers were essential to achieve reproducible and interference-free signals for the analytes studied. The best results were obtained with a Pd/Mg(NO₃)₂ admixture for the determination of Cd, Pb and Zn and NH₄F for Cu. The combination of W (as a permanent modifier) and Mg(NO₃)₂ provided well-defined signal profiles for Cr. The following spectral lines were used: Cd 228.8 nm, Cr 520.6 nm, Cu 218.2 nm, Pb 205.3 nm and Zn 307.6 nm. The limit of detection was 4.2 ng g^− 1 for Cd, 1.1 μg g^− 1 for Cr, 0.5 μg g^− 1 for Cu, 1.3 μg g^− 1 for Pb and 8.6 μg g^− 1 for Zn for the maximum sample mass used. Under optimized conditions, the analyte and matrix were separated effectively in situ, and aqueous standards could be used for calibration.     

Study on spectroscopic characterization of Pd porphyrin and its interaction with ctDNA

The fluorescence and solid substrate room temperature phosphorescence (SS-RTP) properties of Pd(II) meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Pd(II)TMPyP) were studied. The factors influencing the SS-RTP emission, such as filter type, inorganic salt sort, drying temperature, pre-drying time and drying time were investigated in detail. Strong SS-RTP signal can be induced on the slow speed filter paper in the presence of the external inorganic salt, Ca(NO₃)₂, with the maximum excitation and emission wavelengths at 421 nm and 675 nm, respectively. The interaction between calf thymus DNA (ctDNA) and Pd(II)TMPyP was investigated at pH 7.2 using SS-RTP, fluorescence and UV-vis spectroscopy. The SS-RTP intensity of Pd(II)TMPyP was enhanced efficiently with the increasing amount of ctDNA. This phenomenon demonstrates that the intercalated porphyrin is shielded by ctDNA to avoid collision quenching. This result was supported by SS-RTP lifetime measurement, SS-RTP anion quenching experiment and fluorescence polarization measurement. Furthermore, with the addition of ctDNA, the UV-vis spectra of Pd(II)TMPyP shows apparent hypochromicity (40%) at the Soret maximum of 417 nm and a red shift of Δλ = 15 nm, also indicating that Pd(II)TMPyP intercalates into ctDNA bases. The binding constant of Pd(II)TMPyP to ctDNA was calculated to be 4.41 × 10⁵ L/mol based on the derivative McGhee-von Hippel plots.     

Composition dependent frequency upconversion of Er/Yb-codoped lead chloride tellurite glasses

The green and red upconversion luminescence of Er³⁺ in lead chloride tellurite glasses excited at 980 nm is investigated. Three intense emission bands centered at 530, 545, and 658 nm corresponding to the transitions ⁴S_3/2→⁴I_15/2, ²H_11/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2, respectively, were simultaneously observed at room temperature. With increasing PbCl₂ content, the intensity of green (530 nm) emissions increase slightly, while the green (545 nm) and red (658 nm) emissions increase significantly. The results indicate that PbCl₂ has more influence on the green (545 nm) and red (658 nm) emissions than the green (530 nm) emission. The dependence of upconversion intensities on excitation power and possible upconversion mechanisms are discussed and evaluated.     

Fluorescence and terbium-sensitised luminescence determination of garenoxacin in human urine and serum

Fluorescence and terbium-sensitised luminescence properties of new quinolone garenoxacin have been studied. The fluorimetric method allows the determination of 0.060-0.600 μg ml⁻¹ of garenoxacin in aqueous solution containing HCl/KCl buffer (pH 1.5) with λ_exc=282 nm and λ_em=421 nm. Micellar-enhanced fluorescence was also studied, leading to a higher than 400% increase in analytical signal in presence of 12 mM sodium dodecyl sulphate (SDS), allowing the determination of 0.020-0.750 μg ml⁻¹ of garenoxacin. The terbium-sensitised luminescence method allows the determination of 0.100-1.500 μg ml⁻¹ of garenoxacin in 12 mM SDS solution containing 0.08 M acetic acid/sodium acetate buffer (pH 4.1) and 7.5 mM Na₂SO₃ (chemical deoxygenation agent), with λ_exc=281 nm and λ_em=546 nm. Relative standard deviation (R.S.D.) values for the three methods were in the range 1.0-2.0%. The proposed procedures have been applied to the determination of garenoxacin in spiked human urine and serum.     

Two different spectrofluorimetric methods for simultaneous determination of gemfibrozil and rosiglitazone in human plasma

Two accurate, reliable, and highly sensitive spectrofluorimetric methods were developed for simultaneous determination of binary mixture gemfibrozil and rosiglitazone in human plasma without prior separation steps. The first method is based on synchronous fluorescence spectrometry using double scans. At Δλ = 27 nm, gemfibrozil yields detectable signal that is independent of the presence of rosiglitazone. Similarly, at Δλ = 120 nm the signal of rosiglitazone is not influenced by the presence of gemfibrozil. Signals at two wavelengths, 301 (Δλ = 27 nm) and 368 nm (Δλ = 120 nm) vary linearly with gemfibrozil and rosiglitazone concentrations over the range 100-700 ng mL⁻¹ (for gemfibrozil) and 20-140 ng mL⁻¹ (for rosiglitazone), respectively. The limits of detection (LOD) were 2.3 and 2.72 ng mL⁻¹ for gemfibrozil and rosiglitazone, respectively. The second method is based on the technique of simultaneous equations (Vierodt's method), in which 258 nm was selected as the excitation wavelength. Two equations are constructed based on the fact that at (λEm₂=302 nm of gemfibrozil) and (λEm₂=369 nm of rosiglitazone) the fluorescence of the mixture is the sum of the individual fluorescence of gemfibrozil and rosiglitazone. The limits of detection (LOD) were 28.1 and 23.63 ng mL⁻¹ for gemfibrozil and rosiglitazone, respectively. The proposed methods were successfully applied for the determination of the two compounds in synthetic mixtures and in human plasma with a good recovery.     

Trifluoroacetyl-chlorin as a new chemosensor for alcohol/amine detection

Chlorophyll derivative possessing a trifluoroacetyl group at the 3-position was synthesized as a new chemosensor for alcohols and amines. Intense Q_y peak of the trifluoroacetyl-chlorin (701 nm in CHCl₃) showed blue shifts to 667 nm in MeOH and 665 nm in n-BuNH₂ due to the formation of the corresponding hemiacetal and hemiaminal with visible color changes. Thermodynamic parameters for the complexation between trifluoroacetyl-chlorin and n-BuNH₂ in CDCl₃ were determined to be ΔH = −48 kJ mol⁻¹ and ΔS = −147 J K⁻¹ mol⁻¹. Ratiometric fluorescence sensing of n-BuNH₂ in THF was also demonstrated.     

An immunoassay for bisphenol A based on direct hapten conjugation to the polystyrene surface of microtiter plates

Based on direct hapten coated format a competitive indirect enzyme-linked immunosorbent assay (ciELISA) for bisphenol A (BPA) was developed. Polystyrene surface was modified by 3-Aminopropyltriethoxysilane (APTES) to produce amino groups after H₂SO₄/HNO₃-pre-treatment. 4,4-bis (4-hydroxyphenyl) valeric acid (BVA) which is analogue of BPA, was successfully immobilized on the surface of microtiter plates by N,N′-dicyclohexylcarbodiimide (DCC) method. The essential steps of the assay were optimized, especially blocking procedure which is key step to prevent unspecific binding of antibody. The results indicated that compared with hapten-protein coated format (IC₅₀ = 176.67 ng ml⁻¹, LOD = 15.90 ng ml⁻¹), the direct hapten coated format (IC₅₀ = 23.50 ng ml⁻¹, LOD = 0.27 ng ml⁻¹) could improve assay sensitivity and the detection ranges were 2.30 ng∼157.60 ng ml⁻¹ with good signal reproducibility (P value > 0.05) after careful optimization of assay conditions. Tap water samples and seawater samples were spiked with a known amount of BPA and measured by ciELISA. The average recoveries were between 70 and 142%. As far as we are aware this is the most sensitive ELISA for BPA yet reported.