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1.
A test based on time-resolved fluorescence experiments ( Anal. Biochem.
245, 28–37, 1997) allows one to assess the interference of the excited-state association with the fluorimetric determination of the ground-state dissociation constant K
d of fluorescent ion:indicator complexes. If an inflection point occurs in the plot of the fluorescence signal vs – log[ion] in the ion concentration range where both decay times are invariant, this inflection point can be associated with the correct K
d. Here we apply this test to the fluorescent ion indicators SBFO (for Na +), Mag-fura-2 (for Mg 2+), and APTRA-BTC (for Ca 2+). In all three cases the decay times are invariant in the concentration ranges of the respective ions where the fluorescence titrations show unique inflection points, indicating that the fluorimetrically determined K
d values are the true K
d values. 相似文献
2.
A new 7-nitrobenz-2-oxa-1,3-diazole (NBD) derived fluorescent probe ( 1) exhibiting high selectivity for Cu 2+ detection, produced significant fluorescence quenching in the presence of Cu 2+ ion, while the metal ions Ca 2+, Cd 2+, Co 2+, Fe 2+, Hg 2+, Mg 2+, Mn 2+, Ni 2+ and Zn 2+ produced only minor changes in fluorescence. The apparent association constant ( K
a) for Cu 2+ binding in chemosensor 1 was found to be 1.22 × 10 3 M −1. The maximum fluorescence quenching activity caused by Cu 2+ binding to 1 was observed over the pH range 6–10. 相似文献
3.
The quenching constants for the UO 2+2 ion fluorescence by the Eu 3+ ion in H 2O, D 2O, potassium formate and acetic acid media were determined by measuring the decrease in intensity of the 5050 Å fluorescence peak and the lifetime of the UO 2+2 ion fluorescence. The energy transferred to the Eu 3+ ion was found to be a small fraction of the energy lost by the UO 2+2 ion by the non-radiative processes. The variations of the quenching constants of the UO 2+2 ion and the fluorescence lifetimes were determined for different concentrations of potassium formate and acetic acid. These results indicate that the UO 2+2 ion forms inner sphere complexes with the two ligands mentioned. 相似文献
4.
ABSTRACT The properties of NAD Glycohydrolase (NADase), purified from Agkistrodon acutus venom, have been studied by fluorescence and CD spectroscopy. The fluorescence intensities of NADase decrease by about 1% or 3% when the concentrations of I ? ion are 0.1 mol/L or 0.2 mol/L in the NADase solutions, respectively. However, the fluorescence intensities of the NADase are quenched by about 25% and 48%, respectively, with further addition of 1 mmol/L EDTA into solutions. CD spectra also suggested that EDTA could remove Cu 2+ ion from NADase molecule and the conformation of NADase changed much. So Cu 2+ ion is very important to maintain the geometrical structure of NADase. 相似文献
5.
The effects of polar and nonpolar solvents on both the ground and the excited-state properties of [1-(4-methoxyphenyl)-3-(amino)-2,4-(dicyano)-9,10-tetrahydrophenanthrene] is examined. Light absorption results in a population of a locally excited (LE) first singlet state (S 1, n*) which shows sensitivity to the polarity of the surrounding solvent and hydrogen-bonding ability to the quencher 4-methylpyridine. Relaxation of this state leads to an intramolecular charge-transfer state (ICT) which leads to a large Stokes shift in polar solvents and an excited-state dipole moment of e= 10D. The quenching of the fluorescence state by 4-methylpyridine studied in n-hexane and acetonitrile at room temperature is found to be efficient and a positive deviation from linearity was observed in the Stern-Volmer plots even at concentrations of 4-methylpyridine below 0.4 M. This is explained as a result of the occurrence of both a dynamic and a static quenching mechanism. The static quenching constants ( K
sv) along with those obtained by visible spectroscopy ( K
GS) indicate that the ground-state complex is weak and relatively solvent dependent. 相似文献
6.
A new pyrene derivative (chemosensor 1) containing a picolinohydrazide moiety exhibits high selectivity for Cu 2+ ion detection in mixed aqueous media (CH 3OH:H 2O = 7:3). Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu 2+. However, the metal ions Ag +, Ca 2+, Cd 2+, Co 2+, Cu 2+, Fe 2+, Fe 3+, Hg 2+, K +, Mg 2+, Mn 2+, Ni 2+, Pb 2+, and Zn 2+ produced only minor changes in fluorescence for the system. The apparent association constant ( K
a) of Cu 2+ binding in chemosensor 1 was found to be 2.75*10 3 M −1. The maximum fluorescence enhancement caused by Cu 2+ binding in chemosensor 1 was observed over the pH range 5–8. Moreover, by means of fluorescence microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for detecting Cu 2+ in living cells. 相似文献
7.
Fluorescence lifetime imaging microscopy (FLIM) is a new methodology for studying the spatial and temporal dynamics of macromolecule, molecules, and ions in living cells. In FLIM image contrast is derived from the mean fluorescence lifetime at each point in a two-dimensional image. In our case the lifetime was measured by the phase-modulation method. We describe our FLIM apparatus, which consists of a fluorescence microscope, high-speed gated proximity focused MCP image intensifier, and slow-scan CCD camera. To accomplish subnanosecond time-resolved imaging, the gain of the image intensifier is modulated with a high-frequency signal, resulting in stationary phase-sensitive intensity images on the image intensifier. These images are recorded using a cooled slow-scan CCD camera and stored in an image processor. The lifetime images are created from a series of phase-sensitive images at various phase shift of the gain-modulation signal. We demonstrate calcium concentration imaging in living COS cells based on Ca 2+-induced lifetime changes of Quin-2. The phase-angle image is mapped to the Ca 2+ concentration image using an in vitro-determined calibration curve. The Ca 2+ concentration was found to be uniform throughout the cell. In contrast, the intensity image shows significant spatial differences, which likely reflect variations in the thickness and distribution of probe within the cell. 相似文献
8.
Electronically excited argon in the 3 P 1 state was generated in a flow system by resonance absorption of the λ=106·7 nm emission line. This photochemical source is particularly convenient for kinetic studies since Ar( 3 P 1) alone is produced in the primary exciting step. Energy transfer from excited argon may lead to Penning ionization: This process has been studied for M=NO and M=O 2( 1Δ g ). Relative concentrations of Ar* were estimated from the Penning ion current, and it is shown that Ar* is probably in the initially excited 3 P 1 state and not in the metastable 3 P 2 state. Kinetic studies showed that Penning ionization of NO occurs for about one in every five gas kinetic collisions with Ar( 3 P 1). The Penning process can only compete effectively with radiative loss of Ar( 3 P 1) as a result of extensive imprisonment of resonance fluorescence. Penning ionization of O 2( 1Δ g ) is shown to proceed at nearly the same rate as ionization of NO. The decrease in Penning ion current on addition of a quenching gas, such as N 2 or O 2, is used to derive rate constants for the quenching process relative to the rate of quenching by NO. Estimated absolute rate constants are presented in a table. 相似文献
9.
ABSTRACTThe spin-Hamiltonian parameters ( g factors gi, hyperfine structure constants Ai ( 95Mo 5+) and Ai ( 97Mo 5+), i?=?// and ⊥) assigned to the tetragonal Mo 5+ (4d 1) tetrahedral center in α-ZnMoO 4 crystal caused by a Mo 6+(1) ion trapping an electron after x-ray irradiation are calculated from the high-order perturbation formulas resting on the two-mechanism model. The model takes account of both the effects of crystal-field (CF) mechanism concerning the CF excited states in the CF theory and that of the charge-transfer (CT) mechanism related to CT excited states. The calculated results are reasonably consistent with the experimental values, confirming this assignment (or defect model). The calculations also indicate that the effect of CT mechanism cannot be neglected. The defect structure (particularly, the angular distortion) and signs of constants Ai ( 95Mo 5+) and Ai ( 97Mo 5+) of this Mo 5+ defect center are also decided from the calculations. The outcomes are discussed. 相似文献
10.
lin-Benzo-adenine nucleotides can act not only as probes for fluorescence studies but also as structural active site probes for enzymes. To understand the basic properties of lin-benzo-ATP and-ADP, protolysis and Mg 2+ and Ca 2+, binding are investigated between pH 6.2 and pH 8.5 by spectrophotometric and spectrofluorometric titrations. Based on a reaction model, a set of equilibrium constants is determined which is consistent with all available experimental results. The p K values of the Mg 2+ and Ca 2+ complex of lin-benzo-ATP in the chosen medium are 4.6 and 4.1, respectively, and those for the corresponding diphosphate are 3.1 and 2.8, respectively. Fluorescence and absorption spectra are reported.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993. 相似文献
11.
The luminescence of Ca 2GeO 4: Cr 4+ single crystals at wavelengths in the range of 1.3 μm upon excitation with a 1-μ m semiconductor laser is investigated in the temperature range up to 573 K. At T<110 K, the Ca 2GeO 4: Cr 4+ crystals are characterized by the electron paramagnetic resonance, which is attributed to the Cr 4+ ions substituted for Ge 4+ ions. The components of the g tensor and its principal axes are determined. It is revealed that the Cr 4+ impurity centers in calcium germanate affect the crystal symmetry to a lesser degree compared to Cr 4+ ions in forsterite. The observed deviation of the temperature dependence of the electron paramagnetic resonance from the Curie law is explained by the transition to the excited state with a low activation energy, as is the case in impurity 3 d ions in diamond-like semiconductors. The inference is made that the giant effective degeneracy multiplicity of the excited state is associated with the initiation of soft phonon modes in the crystal upon excitation of the defect. 相似文献
12.
Ca 2+ concentrations in biological cells are widely studied with fluorescent probes. The probes have a high selectivity for free calcium and exhibit marked changes in their photophysical properties upon binding. The differences in the fluorescent lifetime of the probes can now be used as a contrast mechanism for imaging purposes. This technique can be further exploited for the quantitative determination of ion concentrations within the cells. We describe the use of a fast fluorescence lifetime imaging method in combination with a standard confocal laser scanning microscope for the determination of Ca 2+ concentrations in single rat cardiac myocytes using the intensity probe Calcium Green. 相似文献
13.
Mathematical relations describing the properties of spontaneous steady-state dual fluorescence under conditions of dynamic quenching of excited states by foreign impurities are derived. It is shown that, in the case of a kinetic character of the reaction, the initial form of the dye and its photoproduct are quenched, the intensity ratio of the fluorescence bands of the initial form and the product linearly increasing with the quencher concentration. Analysis performed is applicable to a wide range of photoreactions accompanied by the dual fluorescence (charge transfer, proton transfer, complexation, etc.). The properties of the fluorescence, absorption, and dual fluorescence excitation for 3-hydroxyflavone in acetonitrile under conditions of dynamic quenching by the TEMPO spin quencher with a concentration below 1.25 × 10 ?2 M are studied. 3-Hydroxyflavone is characterized by the excited-state intramolecular proton transfer and by the fluorescence spectrum consisting of two well-spaced bands. The observed dependences of the intensity of both fluorescence bands on the quencher concentration correspond to the theoretical conclusions. The Stern-Volmer constants calculated from the experimental data on the assumption of diffusion quenching of the excited states are 858 and 1141 M ?1 for the normal and tautomeric fluorescence bands, respectively. The experimental results reveal the kinetic character of the excited-state proton transfer in 3-hydroxyflavone in acetonitrile. 相似文献
14.
The X-ray excited optical luminescence spectrum of Pr 3+ in YPO 4 was investigated. In addition to the sharp line f-f transitions involving the energy levels of the 4f 2 configuration of Pr 3+ ion, the spectrum contains some broad groups of fluorescence lines in the ultraviolet and blue region. These groups of fluorescence are attributed to transitions from the lowest 4f I5d state at 43050 cm -1 to the 4f 2 levels of the Pr 3+ion in YPO 4. 相似文献
15.
We report an investigation of the resonance fluorescence spectrum of NO 2 excited by several laser lines. Sixty transitions, mostly in ν 2 progressions of the ground state, have been assigned. Analysis of the spectra extend the knowledge of the ground state constants, especially of the anharmonic coefficients. It is possible to establish that transitions are occurring to a 2B1 state and to a 2B2 state in the same energy region. 相似文献
16.
Abstract In the present investigation the excitation and fluorescence spectra and lifetimes of Mn 2+ ions in calcium chloride, for various manganese concentrations and sample temperatures have been studied for the first time. The fluorescence spectrum consists of an asymmetric broad band, which upon lowering the sample temperature, shifts its maximum from 580 nm at 300 K to 596 nm at 11 K. This luminescence band was associated with the 4T lg( 4G)→ 6A lg( 6S) spin-forbidden transition in the manganese ions occupying Ca-sites in the lattice of CaCl 2. The excitation spectrum of the Mn 2+ fluorescence revealed the features of manganese ions in octahedral coordination and consisted of nine excitation peaks which were associated with Mn 2+-crystal-field-sensitive transitions. A crystal field analysis of the wavelength positions of these transitions by means of the model developed by Curie et al. allowed us to determine the magnitude of the cubic field splitting 10 Dq, the reduced Racah parameter B', the Koide-Pryce covalency parameter ε and the spin transfer coefficients f [sgrave] and f σ. From the measurement of the temperature dependence of the Mn 2+ fluorescence lifetime, we have also obtained information about the different mechanisms which are involved in the relaxation of excited Mn 2+ ions in this host crystal in the temperature range (11–300 K). 相似文献
17.
采用化学共沉淀法制备了Ca 2-xMgSi 2O 7:xEu 2+绿色荧光粉.用X射线衍射仪、荧光分光光度计及光色综合测试系统对Ca 2-xMgSi 2O 7:xEu 2+绿色荧光粉的相结构、发光性能进行了测试.结果表明:其激发光谱分布在300–480 nm波长范围,谱峰位于389,430 nm处,可以被InGaN管芯产生的360–480 nm辐射有效激发;在波长为430 nm蓝光激发下,其发射光谱谱峰位于531 nm处.Ca 2-xMgSi 2O 7:xEu 2+绿色荧光粉的发光强度随Eu 2+掺杂量的增加而增强,当Eu 2+掺杂量x为0.04时,发光强度达到最大值,而后开始降低,发生浓度猝灭.根据Dexter能量共振理论,浓度猝灭是由电偶极-电偶极相互作用引起的.
关键词:
2MgSi 2O 7∶Eu 2+')" href="#">Ca 2MgSi 2O 7∶Eu 2+
绿色荧光粉
发光特性
白光发光二极管 相似文献
18.
Calixarenes, which have a great place in supramolecular chemistry, have become the most prominent macrocyclic compounds in synthetic organic chemistry due to their easy synthesis and functionalization. In this study, p-tert-butyl calix[4]arene dihydrazide derivative was synthesized and then reacted with 3-oxo-3,4-dihydro-2 H-benzo[b][1,4] thiazin-2-ylideneacetyl chloride to prepare new calixarene based chromophore compound 4. The structure of the synthesized compound was elucidated by spectroscopic methods such as 1H NMR 13C NMR and FT-IR spectroscopy. Chromogenic and fluorescence properties of compound 4 were evaluated. It was observed from both studies that compound 4 was Co2+ selective and shows fluorescence Switched-off behavior. Stoichiometry, binding constant and the detection limit were calculated. The stoichiometry between compound 4 and Co2+ was found to be 1:1. The binding constant value (K) was calculated as 666.67 M??1 using Benesi–Hildebrand equation, while the detection limit for Co2+ ion was calculated as 0.0465 µM. 相似文献
19.
In this work, density functional theory, Møller–Plesset second-order perturbation theory, and ab initio molecular dynamics (AIMD) were used to investigate hydrated characteristics of Mg 2+ and Ca 2+ as a function of coordination number in the first hydration shell ( CN) and cluster size. It is generally accepted that the CNs of Mg 2+ and Ca 2+ are both six. Calculations show that the hydration of Mg 2+ generally prefers six-coordinated structures, whereas the CN value of Ca 2+ varies from 6 to 8 as the hydration proceeds. Moreover, the first hydration of Ca 2+ is found to be more flexible than that of Mg 2+, as indicated by the results of transition state calculations and AIMD simulations. In addition, the constraint of Mg 2+ on the first hydration shell is obviously stronger than that of Ca 2+, while the constraint on the inner hydration shells fades slightly faster for Mg 2+ than Ca 2+. It is also found that the charge transfer from central cation to water molecules is affected only by the first hydration shell for Mg 2+, whereas by the first and second hydration shells for Ca 2+. Based on hydration characteristics, approximatively saturated ion hydration shells for the hydration of Mg 2+ and Ca 2+ were proposed. 相似文献
20.
ABSTRACT The concern of this work is to study molecular structure, electronic absorption and emission spectra of several N-quaternary salts of the well-known diaryloxazole scintillating compounds: 2,5-diphenyloxazole, para-, meta- and ortho- isomers of bis-2-(5-phenyl-oxazolyl)-benzene (POPOP). All of them were obtained from the initial aryloxazoles by their methylation with dimethylsulfate. We found, that N-methylation manifests itself in arising of sterical hindrance in the molecules of diaryloxazolium salts, which results in distortion of their planarity. On the contrary to the ground state, the investigated molecules become more planar in their lowest singlet excited state. As a result of such an excited state flattening, fluorescence Stokes shifts values of the diaryloxazolium salts exceed 9000–10,000 cm ?1. The excited state flattening rate constants, estimated for the studied oxazolium compounds, are of the 10 10 s ?1 range. No considerable increase of radiationless losses, induced by the excited state structural relaxation, was found. Owing to these facts, N-quaternary diaryloxazolium salts may be considered as effective abnormally high Stokes shift organic luminophores. 相似文献
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