A sandwich anion receptor by a BODIPY dye bearing two calix[4]pyrrole units

A novel dicalix[4]pyrrolyl-substituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye I with an absorption peak at approximately 670 nm and an emission peak at about 690 nm was prepared. As an anion receptor, I displayed a red shift in absorption spectra and fluorescence quenching in varying degrees in the presence of F⁻, AcO⁻, H₂PO₄⁻, or Cl⁻. Compared with the parent calix[4]pyrrole, a representative anion receptor, I exhibited a stronger affinity to these anions due to the formation of a sandwich complex through multiple hydrogen-bonding interactions.     

Photochemistry of the IrCl<Subscript>6</Subscript><Superscript>2−</Superscript> complex in aqueous solutions in the presence of the bromide anions

Laser flash photolysis (308 nm) was applied to study photochemistry of the IrCl₆ ²⁻ complex in aqueous solutions in the presence of the Br⁻ anions. The formation of the Br₂ ^·− radical anions in the reaction between the Br⁻ ion and secondary radical pair formed after the photon absorption by the initial complex was observed. The Br₂ ^·− radical anions decay both in recombination and in the reaction with the initial IrCl₆ ²⁻ complex.     

Special characteristics of fluorescence and resonance Rayleigh scattering for cadmium telluride nanocrystal aqueous solution and its interactions with aminoglycoside antibiotics

CdTe nanocrystals (CdTe NCs) were achieved by reaction of CdCl₂ with KHTe solution and were capped with sodium mercaptoacetate. The product was detected by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), fluorescence spectra, ultraviolet-visible spectra and X-ray diffraction (XRD). The CdTe NCs are of cubic structure and the average size is about 5 nm. The fluorescence quantum yield of CdTe NCs aqueous solution increased from 37% to 97% after 20 d under room light. The maximum λ _em of fluorescence changed from 543 nm to 510 nm and the blue shift was 33 nm. CdTe NCs aqueous solution can be steady for at least 10 months at 4 in° a refrigerator. The resonance Rayleigh scattering (RRS) of CdTe NCs in the aqueous solution was investigated. The maximum scattering peak was located at about 554 nm. The interactions of CdTe NCs with amikacin sulfate (AS) and micronomicin sulfate (MS) were investigated respectively. The effects of AS and MS on fluorescence and RRS of CdTe NCs were analyzed. It was found that AS and MS quenched the photoluminescence of CdTe NCs and enhanced RRS of CdTe NCs. Under optimum conditions, there are linear relationships between quenching intensity (F ₀-F), intensity of RRS (I-I ₀) and concentration of AS and MS. The detection limits (3б) of AS and MS are respectively 3.4 ng·mL⁻¹ and 2.6 ng·mL⁻¹ by the fluorescence quenching method, and 15.2 ng·mL⁻¹ and 14.0 ng·mL⁻¹ by the RRS method. The methods have high sensitivity, thus CdTe NCs may be used as fluorescence probes and RRS probes for the detection of aminoglycoside antibiotics. Supported by the National Natural Science Foundation of China (Grant No. 20475045)     

A Spectroscopic Study of the Effects of Various Solvents and Sol-Gel Hosts on the Chemical and Photochemical Properties of Thionin and Nile Blue A

Tetraethyl orthosilicate (TEOS)-based gels were doped with two optically active organic indicators, thionin and nile blue A. Before trapping in a sol-gel host, thionin and nile blue A were both evaluated for solvent and protonation effects on their spectral properties. Only extreme pH values provided by HCl, NaOH, and NH₄OH produced new absorption and/or fluorescence bands. Introduction of nile blue A into alkaline environments (0.1N NaOH, NH₄OH) results in the appearance of a broad absorption band centered near 520 nm whereas highly acidic environments (1N HCl) show a reduction of the 635 nm absorption peak accompanied by an absorption band located near 460 nm. A marked decrease is observed in the optical density of thionin in 1N HCl solution which results in a reduction in the fluorescence intensity. The absorption and fluorescence spectra also reveal a decrease in a pH 11 solution of NH₄OH as compared to neutral conditions. Both dyes formed dimers when the sol-gel host, initially synthesized with TEOS, was organically modified with methyltrimethoxysilane (MTMS). However, thionin dimers were present in all silica-based sol-gel compositions, as evidenced by the absorption and fluorescence spectra. Substitution of MTMS for some of the TEOS in the gel matrix resulted in blue shifts in the absorption and fluorescence spectra of nile blue A. The absorption peak shifted 50 nm to 596 nm whereas the fluorescence shifted around 40 nm to 635 nm. These blue shifts resulted from the reduced polarity of the silica-based xerogel. Thionin also exhibited shifts in its absorption and fluorescence spectra with organic modification by MTMS. The absorption shifted approximately 3 nm to 595 nm while the fluorescence maximum decreased 7 nm to 630 nm. The blue shifts in the spectra of thionin with additions of MTMS were attributed to surface sites that altered the molecular structure of the adsorbed thionin molecules.     

Studies on bismuth(III) complexes of ligands containing nitrogen/sulfur and extractive procedure for determination of Bi(III)

The coordination behavior of thiosemicarbazide and its thiosemicarbazones towards Bi(III) is the main goal of this investigation. The structure of the isolated complexes has been proved by microanalysis, thermal, spectra (electronic, IR and ms) and voltammetric measurements. The ligands act as neutral or mononegative molecules and the coordination donors were found to be S for HTS; NN for HBTS; NS for HATS and H₂STS and NNS or NSO for H₂DMTS in the complexes. The complexes show thermal decomposition steps ending at 800 °C with a stable fragment. The redox properties of the complexes toward oxidation waves are strongly dependent on = N_thio substituents. At pH 1.5 and excess of iodide, Bi³⁺ forms an orange–yellow [BiI₄]⁻ complex which associated with tricaprylylmethylammonium chloride (TCMAC) forming [TCMA]⁺[BiI₄]⁻ easily extracted into the CHCl₃ layer. The colored organic layer containing the ion pair is determined spectrophotometrically at 490 nm and represents the second goal.     

A CIDEP study of photolysis of duroquinone/hydrogen-donor homogeneous and triton micelle solutions

The CIDEP spectra of transient radicals during photolysis of the duroquinone (DQ)/ethylene glycol (EG) system in acid, basic, and micellar environments were measured with a home-made highly time-resolved ESR spectrometer. In the DQ/EG homogeneous solution, the enhanced emissive CIDEP signal of the neutral durosemiquinone radical DQH^• was observed. When the DQ/EG solution at pH 9 or the DQ/EG/TX-100/H₂O micelle system was photolyzed, the CIDEP signal of the duroquinone anion radical (DQ^•−) was obtained. When the DQ/EG solution at pH 2.5 was irradiated, the CIDEP signal of DQH^• appeared. These experimental results indicate that the neutral radical DQH^• was formed by proton transfer from EG to ³DQ*, and that DQ^•− was formed by dissociation of DQH^• accompanying polarization transfer.     

Infrared spectroscopic study of the structure of the tetrabutyl S-dithiopyrophosphate complex of silver

The structure of the complex Ag·TBDTPP (tetrabutyl S-dithiopyrophosphate) formed in HNO₃ medium was studied by IR and NMR methods. The complex is involved in the isomerization of TBDTPP in the presence of Ag⁺ and NO ₃ ⁻ ions. In the IR spectra, we observe the disappearance of P−O−P band and the occurrence of new absorption bands associated with P−S−P and P=O bonds. The silver ion is coordinated to the thiophosphoryl group of the isomer molecule. The influence of HNO₃ concentration on complex formation is discussed.     

Fluorescence properties of nanosized sulfides

The absorption spectra of nanosized sulfides and selenides (ZnS, CdS, CuS, Cu₂S, AgS, In₂S₃, SnS, PbS, Sb₂S₃, FeS, CoS, NiS, CdSe, and Ag₂Se) showed one absorption band with a maximum at wave-lengths shorter than 300 nm. The UV fluorescence spectra of all of these nanosized sulfides in a polyvinyl alcohol film contained maxima at 380–440 nm. Nanosized sulfides are thus characterized by a very large (up to 15000 cm⁻¹) Stokes shift of fluorescence. In a polyvinyl alcohol film, a decrease in the concentration of cadmium sulfide from 0.05 to 0.002 M led to a threefold increase in the fluorescence intensity. The dependence of the degree of fluorescence buildup on the sulfide concentration is nearly linear. An increase in sulfide concentration to more than 5 × 10⁻³ M in solution led to a complete coagulation of particles.     

Photochemical study of the zinc cis-3-(4-imidazolylphenyl)-1-(pyridin-2-yl)[60]fullereno[1,2-c]pyrrolidine-meso-tetraphenylporphyrinate dyad

Axial coordination of fullerenopyrrolidine bearing the donor imidazolyl group, cis-3-(4-imidazolylphenyl)-1-(pyridin-2-yl)[60]fullereno[1,2-c]pyrrolidine (C₆₀∼Im), with zinc meso-tetraphenylporphyrinate (ZnTPP) in an o-dichlorobenzene solution affords a non-covalently bonded donor-acceptor dyad ZnTPP-C₆₀∼Im. The photochemical behavior of the ZnTPP-C₆₀∼Im complex was studied by fluorescence (excitation at λ = 420 nm) and laser kinetic spectroscopy (excitation at λ = 532 nm, 12 ns). The formation constant of the 1: 1 porphyrin-fullerenopyrrolidine complex determined from quenching of ZnTPP fluorescence assuming static intracomplex quenching is 1.6·104 L mol⁻¹. Absorption spectra of the excited states in the system consisting of ZnTPP and Im∼C₆₀ (ZnTPP/C₆₀∼Im) were measured in solution from 380 to 1000 nm. The quenching constant of the triplet-excited ZnTPP with fullerenopyrrolidine C₆₀∼Im was determined. The results obtained indicate the formation of the triplet exciplex {PL}^* ⇌ {P^δ+…L^δ−} in the ZnTPP/C₆₀∼Im system upon laser photolysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1541–1547, September, 2006.     

Formation and Extraction of Niobium(V) Complex with Xylenol Orange in the Presence of a 4-Pyridone Derivative

Xylenol orange (XO) is a suitable reagent for the spectrophotometric determination of niobium in a weakly acidic medium. The present study shows that the addition of 3-hydroxy-2-methyl-1-phenyl-4-pyridone (HX) influences the complex formation as well as the spectroscopic properties of this colored system. To prevent formation of niobium(V) hydrolyzed species in water, tartaric acid was used when preparing the niobium stock solution. The red-violet colored complex formed by heating niobium(V) with xylenol orange (XO) in the presence of HX at pH=3 has a maximum absorption wavelength at 565 nm. The complex can be extracted by a chloroform solution of tetraphenylphosphonium (TPP) chloride. The optimum reaction conditions and other parameters for complex formation have been evaluated. The mechanism of extraction is probably based on the formation of the associated ion pair between the tetraphenylphosphonium cation and the mixed Nb(V)-XO-HX anion. The extracted complex in chloroform showed a maximum absorbance at 585 nm with the corresponding molar absorption coefficient being 3.72×10⁴ L⋅mol⁻¹⋅cm⁻¹, and obeys Beer’s law in the range 3×10⁻⁶ to 3×10⁻⁵ mol⋅L⁻¹.     

Enhanced fluorescence of 3-tryptimino-1-phenyl-butan-1-one–Tb with 1,10-phenanthroline ternary system, and its analytical application

A new Schiff base ligand, 3-tryptimino-1-phenyl-butan-1-one (TPB), was synthesized. The fluorescence intensity of its terbium(III) complex was greatly enhanced by addition of 1,10-phenanthroline to an acetonitrile solution. Spectrofluorimetric determination of trace amounts of Tb³⁺ was performed based on this effect. The excitation and emission wavelengths are 293 and 546 nm, respectively. Under optimal conditions, the fluorescence intensities varied linearly with the concentration of Tb³⁺ in the range of 2.0 × 10⁻⁶ to 7.0 × 10⁻⁶ M with a detection limit of 2.4 × 10⁻⁹ M. Interference by some rare earth ions is described. This method was applied to the determination of trace amounts of terbium(III) in a high purity Y₂O₃ matrix. The mechanism of fluorescence enhancement was also studied.     

Characteristic changes in the fluorescence spectra of 1-naphthol at the gelation point during the sol-gel-xerogel transitions

The fluorescence spectra of 1-naphthol were observed during the sol-gel-xerogel transitions of two different systems as a function of time; one is in the silicon and titanium (Si:Ti = 4500:1) binary systems involving no catalysts and the silicon and lithium (Si:Li = 99:1) binary systems involving HC1 as the catalyst. During the first stage of the sol-gel reaction of the 1-naphthol system, the fluorescence spectra mainly originated from the broad ’L₂ state. The fluorescence spectrum originating from the anionic species at around 470 nm increased as the reaction proceeded. It was found that the fluorescence spectra originating from the anionic species of 1-naphthol drastically decreased in both systems just after gelation. These findings indicate that it becomes difficult for the dissociation of the excited state of 1-naphthol to give a dissociative proton to the surrounding matrix. The fluorescence-excitation spectra for the Si/Ti system indicated that the main route for the excited state of 1-naphthol to form a dissociative proton is through the excited state of the contact ion pair, while the main route in the Si/Li system is via the direct excitation of the neutral 1-naphthol and its dissociation. The observed changes in the fluorescence spectra of 1-naphthol in these sol-gel systems provide a sensitive means to monitor changes during the sol-gel transition process.     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Polar and Hydrogen-Bonding Effects of Alcohols on the Emission Spectrum of Styrene–Triethylamine System

The emission spectra of styrene (ST)–triethylamine (TEA) systems were measured under steady-state illumination conditions in some tetrahydrofuran (THF)–protic solvent mixtures. The fluorescence spectrum of the ST–TEA system in THF consists of two bands (band A at 304 nm (fluorescence of ST) and band B at 460 nm (emission from an exciplex)). The intensity of band A increased and that of band B decreased with increasing amounts of protic solvents in THF–protic solvent mixtures. The increase in the intensity of band A was explained by the decrease in the concentration of free amine owing to the hydrogen-bonding interaction (or protonation) between TEA and protic solvents. The decrease in the intensity of band B was considered to be caused by the decrease in the concentration of free amine upon the addition of protic solvents and the enhanced conversion of the exciplex to an ion pair with increasing solvent polarity. The polar effect was expressed as a function of the relative permittivity of the solution.     

Spectrofluorimetric determination of trace amounts of coenzyme A using a terbium ion–ciprofloxacin complex probe in the presence of periodic acid

A new spectrofluorimetric method was developed for the determination of trace amounts of coenzyme A (CoA). In the presence of periodic acid (H₅IO₆), CoA can remarkably enhance the fluorescence intensity of the Tb³⁺–ciprofloxacin (CIP) complex at 545 nm in a buffer solution at pH 5.4; the enhanced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of CoA. The optimal conditions for the determination of CoA were also investigated. The linear range and the detection limit for the determination of CoA were 6.08 × 10⁻⁶–1.64 × 10⁻⁵ and 2.1 × 10⁻⁸ mol L⁻¹, respectively. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess CoA in injection and biological samples. Moreover, the enhancement mechanism of the fluorescence intensity of the CoA–Tb³⁺–CIP system in the presence of H₅IO₆ is also discussed.     

Pulse radiolysis study of dithio-oxamide in aqueous solutions

The reactions of e⁻ _aq, H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions using pulse radiolysis technique. The transient species formed by the reaction of e⁻ _aq with DTO at pH 6.8 has an absorption band with λ _max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species produced by H-atom reaction had a different spectrum with λ _max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO₂ ⁻ radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e⁻ _aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1–9.2 also has two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1. This means that all these radicals viz. OH, H-atom and (CH₃)₂COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to the presence of oxygen. One-electron oxidizing radicals such as Br₂ ^−· and SO₄ ^−· radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima at 360 to 520 nm. At acidic pHs, only Br₂ ^−· and Cl₂ ^−· radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is a resonance stabilized species with the electron delocalized over the-N-C-S bond. This species was found to be neutral and non-oxidizing in nature.     

Synthesis, electrochemistry, thin-layer UV-vis and fluorescence spectroelectrochemistry of a new salicylaldimine ligand and its copper complex

The new asymmetric, fluorescent Schiff-base ligand, N-(pyrene)-salicylaldimine (L), and its copper complex having an ONNO donor set, [Cu(L) ₂ ], were synthesized and characterized using elemental analysis, IR, UV-vis, ¹H and ¹³C-NMR spectroscopies. Their electrochemical and spectroelectrochemical behaviors were investigated in a detail by using cyclic voltammetry (CV), square wave voltammetry (SWV), in-situ UV-vis, and fluorescence spectroelectrochemistry. The formation of the complex was monitored by the in-situ fluorescence technique based on the quenching of the fluorescence-probe ligand. Electrochemical studies showed that L exhibits a single irreversible reduction process. However, the SWV indicated that this process was not totally irreversible in the time scale of the measurement. The cathodic peak potential of the reduction process occurred at E _pc = −1.35 V vs Ag/AgCl (scan rate: 0.025 Vs⁻¹). On the other hand, [Cu(L) ₂ ] showed one quasi-reversible one-electron reduction process in the scan rates of 0.025–0.50 Vs⁻¹, which was assigned to metal-based one-electron process; [Cu(2+)(L)₂] + e⁻ → [Cu(+)(L)₂]⁻. The value of half-wave potential (E _1/2) of the reduction process was −0.54 V vs Ag/AgCl (scan rate: 0.025 Vs⁻¹). The time-resolved spectra showed, when the potential (E _app = −1.60 V) was applied in a thin-layer cell, that the main and shoulder bands of (L) at 385, 336, and 407 nm almost disappeared and a new band at 443 nm with a shoulder formed during the reduction process. No change was observed on the final spectrum of the totally reduced ligand for long period under nitrogen atmosphere, which indicated that the singly reduced species remained stable and was not accompanied by a chemical reaction in the time scale of the spectroelectrochemical measurement. The spectral changes during the reduction process of [Cu(L) ₂ ] confirmed the metal-centered reduction process. The fluorescence intensity of L decreased during the reduction process in the thin-layer cell, as result of the perturbation of the conjugated system of the reduced species.     

Effect of electron-withdrawing power of the substituted group on?OH radical reaction with substituted aryl sulphides: A pulse radiolysis study

In neutral aqueous solution of (phenylthio)acetic acid, hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 × 10^-1 dm³ mol⁻s⁻ and the transient absorption bands are assigned to^•OH radical addition to benzene and sulphur with a rough estimated values of 50 and 40% respectively. The reaction of the^•OH radical with diphenyl sulphide (k = 4.3 × 10⁸ dm³ mol⁻¹ s⁻¹) is observed to take place with formation of solute radical cation, OH-adduct at sulphur and benzene with estimated values of about 12, 28 and 60% respectively. The transient absorption bands observed on reaction of^•OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λ_max = 550 and 730 nm), OH-adduct at sulphur (λ_max = 360 nm) and addition at benzene ring (λ_max = 320 nm). The fraction of^•OH radical reacting to form solute radical cation is observed to depend on the electron-withdrawing power of substituted group. In acidic solutions, depending on the concentration of acid and electron-withdrawing power, solute radical cation is the only transient species formed on reaction of^•OH radical with the sulphides studied.     

Vibrationally Resolved Absorption and Fluorescence Spectra of Firefly Luciferin: A Theoretical Simulation in the Gas Phase and in Solution

Firefly bioluminescence has been applied in several fields. However, the absorption and fluorescence spectra of the substrate, luciferin, have not been observed at the vibrational level. In this study, the vibrationally resolved absorption and fluorescence spectra of firefly luciferin (neutral form LH₂, phenolate ion form LH^? and dianion form L^2?) are simulated using the density functional method and convoluted by a Gaussian function, with displacement, distortion and Duschinsky effects in the framework of the Franck–Condon approximation. Both neutral and anionic forms of the luciferin are considered in the gas phase and in solution. The simulated spectra have desired band maxima with the experimental ones. The vibronic structure analysis reveals that the features of the most contributive vibrational modes coincide with the key geometry‐changing region during transition between the ground state and the first singlet excited state.     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.