Spectral-luminescence and quantum-chemical study of the anionic forms of 5-fluorouracil

A spectral-luminescence study of neutral (pH 7) and alkaline (pH 11 and 14) aqueous solutions of the anticancer drugs 5-fluorouracil (FU) and tegafur has been performed. The fluorescence spectra of the N3- and N1-centered anions of 5-fluorouracil, its dianion, and the tegafur monoanion with emission maxima at wavelengths (λ_em) of 358, 372, 366, and 358 nm and photoluminescence quantum yields (φ) of 11.2 × 10^–4, 35.1 × 10^–4, 26.5 × 10^–4, and 8.6 × 10^–4, respectively, have been recorded for the first time. The fluorescence characteristics of the FU anionic forms have been related to the magnetic shielding constant as one of the criteria of aromaticity.     

Fluorescence of 5-fluorouracil upon the transition from the second singlet excited state <Emphasis Type="Italic">S</Emphasis><Subscript>2</Subscript> to the ground state

Effect of the wavelength of excitation light (λ_ex) on the fluorescence excitation and emission spectra of 5-fluorouracil in acidic solution (pH 2.5) was studied upon excitation at the S ₂ ← S ₀-transition absorption band. It has been found that direct excitation at the second or the shorter wavelength absorption band results in 5-fluorouracil fluorescence that originates not only from the first excited state S ₁ but is also due the transition from the second excited state S ₂ to the ground state.     

Spectrofluorimetric Determination of Reduced Glutathione Using Organic Nanoparticle Probes

Introduction Reduced glutathione (GSH) is a very important tripeptide.1 GSH widely exists in living tissues. In ani-mal organization, the concentration of free glutathione is in the range 0.5—10.0 mmol/L. Usually over 99% of glutathione is present in the reduced form in all organ-isms.2 Intermediates of GSH biosynthesis such as cys-teine, g-glutamyl-cysteine (g-Glu-Cys) or cysteinyl-gly- cine (Cys-Gly) also occur in the cell but at much lower concentrations.3 GSH plays an important bio…     

Microwave synthesis and characterization of europium complexes with cinnamic acid and phenanthroline

We report here the synthesis and characterization of a host of Eu(Phen)L₃ with cinnamic acid (C₆H₅CH = CHCOOH, HL) and phenanthroline (Phen), and employing microwave radiation, where the microwave radiation is used just for the uniform heating of the reaction mixture. Its IR absorption spectra, scanning electron microscopy (SEM), and fluorescence spectra were studied. The results show that the particles of Eu(Phen)L₃ phosphors are basically spherical in shape, with good dispersing. The mean particle size is 1–2 μm. The excitation spectrum is a broad band and the main peak is at 320.0 nm. Moreover, excitation peak at 396.0 nm was found in the excitation spectrum. The emission spectrum shows that Eu(Phen)L₃ has narrow emission peaks. The emission peaks are ascribed to Eu³⁺ ions transition from ⁵ D _J (J = 0) to ⁷ F _J (J = 1, 2, 4). However, the strongest main emission peak locates at 614.0 nm, which corresponds to the electric dipole transition of Eu³⁺(⁵ D ₀ → ⁷ F ₂) The article is published in the original.     

Synthesis and characterization of a one-dimensional polymeric copper(Ⅱ)-tetrathioporphyrazine

The title polymer PCuS4Pz was synthesized by reaction of 2,3-dicyano-5,6-dihydro-1,4-dithiin,pyromellitic dianhydride and urea with cuprous salt in optimized gentle method.The structure and properties of the PCuS4Pz were characterized by elemental analysis,X-ray powder diffraction,IR,UV-Vis,fluorescence and EPR spectra and variable-temperature magnetic susceptibility.The polymer is black sublimable crystallite and the degree of polymerization has been found to be n>4.The PCuS4Pz in H2SO4 exhibits intensive absorption bands at 236,342,656 and 767 nm and intensive fluorescence band at 410 nm or 464 nm under the excitation of the ultraviolet light of a determined wavelength at room temperature.It has been found that the polymer exhibits a weaker antiferromag-netic interaction (J=-2.cm-1,εff=1.68 B.M.) with an apparent spin S<1/2 in the ground state and its conductivity 298K is 1.01×10-5 S-cm-1 at 13.73 MPa.     

A Novel Fluorescence Probe for the Reversible Detection of Bisulfite and Hydrogen Peroxide Pair in Vitro and in Vivo

The detection of changes in the reactive oxygen species (ROS)/reactive sulfur species (RSS) couple is important for studying the cellular redox state. Herein, we developed a 1,8-naphthalimide-based fluorescence probe ( NI ) for the reversible detection of bisulfite (HSO₃⁻) and hydrogen peroxide (H₂O₂) in vitro and in vivo. NI has been designed with a reactive ethylene unit which specifically reacts with HSO₃⁻ by a Michael addition reaction mechanism, resulting in the quenching of yellow fluorescence at 580 nm and the appearing of green fluorescence at 510 nm upon excitation at 500 nm and 430 nm, respectively. The addition product ( NI−HSO₃ ) could be specifically oxidized to form the original C=C bond of NI , recovering the fluorescence emission and color. The detection limits of NI for HSO₃⁻ and NI−HSO₃ for H₂O₂ were calculated to be 2.05 μM and 4.23 μM, respectively. The reversible fluorescence response of NI towards HSO₃⁻/H₂O₂ couple can be repeated for at least five times. NI is reliable at a broad pH range (pH 3.0–11.5) and features outstanding selectivity, which enabled its practical applications in biological and food samples. Monitoring the reversible and dynamic inter-conversion between HSO₃⁻ and H₂O₂ in vitro and in vivo has been verified by fluorescence imaging in live HeLa cells, adult zebrafish and nude mice. Moreover, NI has been successfully applied to detect of HSO₃⁻ levels in food samples.     

EXCITED-STATE PROPERTIES OF DNA METHYLATED AT THE NV7 POSITION OF GUANINE AND ITS FREE FLUOROPHORE AT ROOM TEMPERATURE

The room-temperature optical properties of calf thymus DNA, with about 75% of its guanine residues methylated at position N-7, are compared with those of 7-methyl GMP which has the same fluorophore. The fluorescence spectrum of the methylated guanine residues depends strongly on the excitation wavelength, shifting to the blue as the wavelength increases. The fluorescence quantum yield, corrected for the contribution to absorption by the other virtually nonfluorescent residues, exhibits a pronounced drop at long excitation wavelengths relative to that for excitation at 265 nm. The degree of fluorescence polarization exhibits a weak dependence on the excitation and emission wavelengths. For 7-methyl GMP, the fluorescence spectrum is very weakly dependent on the excitation wavelength and its fluorescence quantum yield shows a moderate increase at long wavelengths. The degree of fluorescence polarization increases with increasing excitation wavelength particularly when monitoring the emission in the short wavelength region of the fluorescence spectrum. A pronounced drop of unknown origin is observed when exciting at 265 nm, which is not observed for methylated DNA. The methylated DNA data are interpreted in terms of a combination of (i) a heterogeneous environment of the methylated guanine residues, which results from sequence-dependent stacking interactions, and (ii) transfer of excitation energy from the other residues to the fluorescing methylated guanine residues. From the values of the quantum yields and those of the decay times, which we have recently reported (Georghiou et al., 1985), the following values are obtained for the radiative, k_t, and the sum of the nonradiative, σk₁, rate constants for deexcitation of the excited states of methylated DNA and its free fluorophore: 1.6 × 10⁸ s^-1 7 × 10⁷ s^-1 and 5 × 10¹⁰ s^-lvs 6 × 10⁹ s^-1. Because of energy transfer from the other residues. the k_f value for the methylated guanine residues is overestimated but their σk₁, value is not affected significantly and is by about an order of magnitude larger than that for 7-methyl GMP, apparently because of stacking interactions.     

Synthesis,characterization and oxygen‐sensing properties of a novel luminescent Cu(I) complex

A novel luminescent copper(I) complex with formula [Cu(PPh₃)₂(PIP)]BF₄ (PPh₃ = triphenyl phosphine, PIP = 2‐phenyl‐1H‐imidazo[4,5‐f][1,10]phenanthroline) has been synthesized and characterized by ¹H NMR, IR, elemental analysis and X‐ray crystal structure analysis. In solid state, it displays broad band emission upon excitation at λ = 420 nm with the emission maximum locates at 551 nm. Its excited‐state lifetime is in the microsecond time scale (3.02 µs); as a result, its emission intensity is sensitive to oxygen concentration and shows oxygen‐sensing properties after being encapsulated into mesoporous silica MCM‐41. For the system with 60 mg/g loading level, a sensitivity (I₀/I) of 4.35, a fluorescence quenching time (t_Q) of 5 s and a recovery time (t_R) of 36 s were achieved. Even after aging for 5 months, the sensitivities of the three loading level systems can be retained, ignoring the measurement error, which indicates that they possess long‐term stability. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Nonlinear Optical Properties of a New A-π-A Two-Photon Compound Utilizing Dibenzothiophene as Center

A new two‐photon material, 3E,6E‐bis(2‐pyrid‐4′‐ylvinyl)dibenzothiophene (BPVDBT), has been firstly synthesized by an efficient Pd‐catalyzed Heck coupling route. The single‐ and two‐photon fluorescence, quantum yields, lifetimes, solvent effects of the chromophore were studied in detail and the compound exhibited solvent‐sensitivity. The fluorescence intensity (I_out) and input excitation intensity (I_in) can fit in well with the quadratic parabolas, which indicates that the up‐converted fluorescence was induced by the two‐photon absorption (TPA). TPA cross‐section of BPVDBT has been measured using the two‐photon‐induced fluorescence method, whose value is 14.24×10^?50 cm⁴·s·photon^?1·molecule^?1 at 750 nm. The experimental results confirm that BPVDBT is a good two‐photon absorbing chromophore with an A‐π‐A type.     

Singlet exciton interactions in crystalline naphthalene

The decay of prompt fluorescence in crystalline naphthalene at 300 K, excited by a picosecond 266 nm pulse, has been studied as a function of excitation intensity. Experimental decay curves can be fitted only when the exponential distribution in depth of excitation and the radial (gaussian) intensity profile of the excitation are both taken into account. From an analysis of the decay at early time (?5 ns) a best fit value of the singlet—singlet annihilation rate constant is found γ_SS = (4 ± 1) × 10^?10 cm³ s^?1. If the reaction is diffusion-limited, this rate implies an average singlet diffusivity D_S = (2 ± 1) × 10^?4 cm² s^?1.     

Photodissociation of CF3NO: observation of NO (υ=1)

That excitation of CF₃NO with wavelengths between 580 and 660 nm yields CF₃ + NO has been shown by two direct techniques. In the first, the CF₃ and NO radicals have been scavenged by their reaction with Cl₂ to yield CF₃Cl and NOCl. as detected by both infrared and mass spectrometry. In the second technique, NO (υ=1) vibrational fluorescence has been observed following tunable dye laser excitation of CF₃NO. The rate of vibrational relaxation of NO (υ=1) in collisions with CF₃NO has been found to be (2.19 ± 0.19) × 10³ s^?1 torr ^?1.     

PHYCOBILIPROTEINS: COMPARISON OF SOLUTION AND SINGLE CRYSTAL FLUORESCENCE FOR C-PHYCOCYANIN AND B-PHYCOERYTHRIN*

Abstract— Trimeric and hexameric solution forms of C-phycocyanin (CPC) from the cyanophyte Agme-nellum quadruplicatum have been isolated and their spectral properties compared to those obtained from single crystals. Although the absorbance peak of a suspension of small C-phycocyanin crystals is red-shifted only 7 nm relative to the solution forms, the single crystal fluorescence is red-shifted 60 nm relative to the solution forms. The crystal fluorescence spectrum exhibits a single peak at LD_max= 708 nm when excited at 514.5 or 530.9 nm and two peaks (LD_max= 661 and 708 nm) when excitation occurs at 568.2 nm. Fluorescence depolarization measurements indicate that extensive energy transfer could occur for both solution and crystal forms with the latter being dependent upon the relative orientation of the crystal with respect to the excitation dipole. Similar results were obtained with B-phycoerythrin (BPE) from the red alga Porphyridium cruentum where the single crystal fluorescence is red-shifted =50nm relative to the solution spectra with two peaks (LD_max= 583 and 617 nm) observed whose relative intensities are dependent on the excitation wavelength (LD_max– 514.5 and 530.9 nm). Single crystal fluorescent lifetimes exhibited considerable shortening relative to that observed for the solution forms. The implications of these results are discussed with respect to the possible relationships of the crystalline structures to the assembly forms present within phycobilisomes.     

Fluorescence spectroscopy of C60 in toluene solutions at 5 K

We have recorded the dispersed fluorescence and the fluorescence excitation spectra of C₆₀ in toluene matrices at 5 K. Upon excitation with the green Ar⁺ laser line (λ=514 nm) we obtained for the first time in this matrix well resolved visible fluorescence spectra which we have compared with those observed in other low temperature matrices. Our spectra were interpreted and assigned using theoretical assessments of vibronic activities of transitions between the three lowest excited electronic states ¹T_1g, ¹T_2g, ¹G_g and the totally symmetric ground state, and on the basis of a single 0⁰ level which has pseudo-Jahn–Teller (JT) components of the three near-degenerate excited states. The fluorescence spectra exhibit prominent JT induced h_g(1) progressions, Herzberg–Teller-induced h_u and other ungerade mode vibrations, including a very active t_1u(4) mode. Excitation wavelength independent bands are assigned to the fluorescence of C₆₀ molecules in toluene microcrystals embedded in the toluene glass whereas excitation wavelength dependent features are interpreted as originating from C₆₀ molecules isolated in the toluene glass itself. These interpretations are supported by the results of spectrally selective detected fluorescence excitation spectra.     

Protoporphyrin IX‐Functionalized AgSiO2 Core–Shell Nanoparticles: Plasmonic Enhancement of Fluorescence and Singlet Oxygen Production

Metal‐enhanced processes arising from the coupling of a dye with metallic nanoparticles (NPs) have been widely reported. However, few studies have simultaneously investigated these mechanisms from the viewpoint of dye fluorescence and photoactivity. Herein, protoporphyrin IX (PpIX) is grafted onto the surface of silver core silica shell NPs in order to investigate the effect of silver (Ag) localized surface plasmon resonance (LSPR) on PpIX fluorescence and PpIX singlet oxygen (¹O₂) production. Using two Ag core sizes, we report a systematic study of these photophysical processes as a function of silica (SiO₂) spacer thickness, LSPR band position and excitation wavelength. The excitation of Ag NP LSPR, which overlaps the PpIX absorption band, leads to the concomitant enhancement of PpIX fluorescence and ¹O₂ production independently of the Ag core size, but in a more pronounced way for larger Ag cores. These enhancements result from the increase in the PpIX excitation rate through the LSPR excitation and decrease when the distance between PpIX and Ag NPs increases. A maximum fluorescence enhancement of up to 14‐fold, together with an increase in photogenerated ¹O₂ production of up to five times are obtained using 100 nm Ag cores coated with a 5 nm thick silica coating.     

Trace Determination of Germanium by Continuous Flow Hydride Generation Laser-Induced Fluorescence Spectrometry

A continuous flow hydride generation laser-induced fluorescence (HG-LIF) spectrometry technique has been investigated for performing trace determination of germanium (Ge). Hydride generation of Ge is performed using reagent concentrations of 2?M H₃PO₄ and 0.5% NaBH₄ and fluorescence detection is performed using tunable dye laser radiation at 253.323?nm for Ge excitation with fluorescence measured at 303.907?nm. The HG-LIF approach provides a linear response for Ge in the concentration range from 1.0 to 50?ng mL^?1 and a limit of detection of 0.1?ng mL^?1. Replicate measurements at 10?ng mL^?1 have a relative standard deviation of 0.1% (n?=?8). Measurements of Ge in different sample matrices have demonstrated the effectiveness of thiourea and ascorbic acid as masking agents that compensate for samples containing interfering ions. The determinations of the Ge content in reference water samples, fly ash samples, and supplement capsules demonstrate that the HG-LIF approach has feasibility for measuring Ge in different sample matrices at environmentally relevant concentrations.     

Rational Design of Emissive NIR‐Absorbing Chromophores: RhIII Porphyrin‐Aza‐BODIPY Conjugates with Orthogonal Metal–Carbon Bonds

The facile synthesis of Group 9 Rh^III porphyrin‐aza‐BODIPY conjugates that are linked through an orthogonal Rh?C(aryl) bond is reported. The conjugates combine the advantages of the near‐IR (NIR) absorption and intense fluorescence of aza‐BODIPY dyes with the long‐lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads. The generation of a locally excited (LE) state with intramolecular charge‐transfer (ICT) character has been demonstrated by solvatochromic effects in the photophysical properties, singlet oxygen quantum yields in polar solvents, and by the results of density functional theory (DFT) calculations. In nonpolar solvents, the Rh^III conjugates exhibit strong aza‐BODIPY‐centered fluorescence at around 720 nm (Φ_F=17–34 %), and negligible singlet oxygen generation. In polar solvents, enhancements of the singlet‐oxygen quantum yield (Φ_Δ=19–27 %, λ_ex=690 nm) have been observed. Nanosecond pulsed time‐resolved absorption spectroscopy confirms that relatively long‐lived triplet excited states are formed. The synthetic methodology outlined herein provides a useful strategy for the assembly of functional materials that are highly desirable for a wide range of applications in material science and biomedical fields.     

A Phosphole Oxide Based Fluorescent Dye with Exceptional Resistance to Photobleaching: A Practical Tool for Continuous Imaging in STED Microscopy

The development of stimulated emission depletion (STED) microscopy represented a major breakthrough in cellular and molecular biology. However, the intense laser beams required for both excitation and STED usually provoke rapid photobleaching of fluorescent molecular probes, which significantly limits the performance and practical utility of STED microscopy. We herein developed a photoresistant fluorescent dye C‐Naphox as a practical tool for STED imaging. With excitation using either a λ=405 or 488 nm laser in protic solvents, C‐Naphox exhibited an intense red/orange fluorescence (quantum yield Φ_F>0.7) with a large Stokes shift (circa 5900 cm^?1). Even after irradiation with a Xe lamp (300 W, λ_ex=460 nm, full width at half maximum (FWHM)=11 nm) for 12 hours, 99.5 % of C‐Naphox remained intact. The high photoresistance of C‐Naphox allowed repeated STED imaging of HeLa cells. Even after recording 50 STED images, 83 % of the initial fluorescence intensity persisted.     

Synthesis and Properties of a New Two—Photon—absorbed Material DMAEAS

IntroductionSubstitutedstilbeneshavesignificantpotentialapplica tionssuchasfluorescencemicroscopy ,two photonphotody namictherapy ,opticalpowerlimiting ,three dimensionalstorage,andthree dimensionalmicrofabrication .1 4 Thesedyeshavestrongtendencyofintra molecularchargetransferundertheexcitedstate.Asaresult,theyusuallyexhibitlargetwo photonabsorption (TPA) ,inthemeanwhileemitstrongup convertedfluorescence .Ontheotherhand ,theirsolutionsgenerallydisplaylineartransmissionof >90 %atwavelengthof…     

Synthesis and crystal structure of a novel two-dimensional network complex [Mn(O2CCH2Cl)2(phen)] n

A novel two-dimensional network manganese(II) polymer complex [Mn(O₂CCH₂CI)₂-(phen)] _n has been synthesized and characterized by elemental analysis and IR spectrum. The crystal structure of title complex has also been determined, which is in monoclinic of a space group P2₁/c with the following unit cell parameters at 294K:a =1.9738 (4) nm,b=1.1384 (2) nm,c =0.74915(14) nm,V = 1.6795(5) nm³, Z= 2.

     

A π-Extended Pentadecabenzo[9]Helicene

A novel chiral nanographene (i.e. EP9H ) with a pentadecabenzo[9]helicene core fragment has been synthesized and fully characterized. Single-crystal X-ray diffraction unambiguously confirms the helical structure. The fluorescence emission of EP9H is located in the near infrared region (λ_em=684 nm) with a medium quantum yield (0.10) for helicene derivatives. Cyclic voltammetry reveals its seven quasi-reversible redox states from −2 to +5. Furthermore, enantiopure EP9H displays distinct CD signals in a broad spectral range from 300 to 700 nm. Notably, compared to the reported small organic molecules, EP9H displays an outstanding |g_lum| value of 4.50×10⁻² and B_CPL as 304 M⁻¹ cm⁻¹.