Steady State Fluorescence Studies of Wild Type Recombinant Cinnamoyl CoA Reductase (Ll-CCRH1) and its Active Site Mutants

Fluorescence quenching and time resolved fluorescence studies of wild type recombinant cinnamoyl CoA reductase (Ll-CCRH1), a multitryptophan protein from Leucaena leucocephala and 10 different active site mutants were carried out to investigate tryptophan environment. The enzyme showed highest affinity for feruloyl CoA (K _a ?=?3.72?×?10⁵ M^?1) over other CoA esters and cinnamaldehydes, as determined by fluorescence spectroscopy. Quenching of the fluorescence by acrylamide for wild type and active site mutants was collisional with almost 100 % of the tryptophan fluorescence accessible under native condition and remained same after denaturation of protein with 6 M GdnHCl. In wild type Ll-CCRH1, the extent of quenching achieved with iodide (f _a?=?1.0) was significantly higher than cesium ions (f _a?=?0.33) suggesting more density of positive charge around surface of trp conformers under native conditions. Denaturation of wild type protein with 6 M GdnHCl led to significant increase in the quenching with cesium (f _a?=?0.54), whereas quenching with iodide ion was decreased (f _a?=?0.78), indicating reorientation of charge density around trp from positive to negative and heterogeneity in trp environment. The Stern-Volmer plots for wild type and mutants Ll-CCRH1 under native and denatured conditions, with cesium ion yielded biphasic quenching profiles. The extent of quenching for cesium and iodide ions under native and denatured conditions observed in active site mutants was significantly different from wild type Ll-CCRH1 under the same conditions. Thus, single substitution type mutations of active site residues showed heterogeneity in tryptophan microenvironment and differential degree of conformation of protein under native or denatured conditions.     

Frequency dispersion of dielectric coefficients of layered TlGaS<Subscript>2</Subscript> single crystals

Frequency dependence of the dissipation factor tanδ, the permittivity ɛ, and the ac conductivity σ_ac across the layers in the frequency range f=5×10⁴−3×10⁷ Hz was studied in layered TlGaS₂ single crystals. A significant dispersion in tanδ was observed in the frequency range 10⁶−3×10⁷ Hz. In the range of frequencies studied, the permittivity of TlGaS₂ samples varied from 26 to 30. In the frequency range 5×10⁴−10⁶ Hz, the ac conductivity obeyed the f ^0.8 law, whereas for f>10⁶ Hz σ_ac was proportional to f ². It was established that the mechanism of the ac charge transport across the layers in TlGaS₂ single crystals in the frequency range 5×10⁴−10⁶ Hz is hopping over localized states near the Fermi level. Estimations yielded the following values of the parameters: the density of states at the Fermi level N _F=2.1×10¹⁸ eV⁻¹ cm⁻³, the average time of charge carrier hopping between localized states τ=2 μs, and the average hopping distance R=103 ?. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 6, 2004, pp. 979–981. Original Russian Text Copyright ? 2004 by Mustafaeva.     

Fluorescence lifetimes and radiative rate constants of alkanes at 25°C

Fluorescence lifetimes of 33 alkanes were measured at 25°C using a 0.7 ns pulse radiolysis system and the relationship between molecular structure, fluorescence lifetime (τ), quantum yield (Φ_f) and radiative rate constant (R = $\text{Φ}{}_{\mathrm{f}}\text{τ}$) is discussed. The τ's showed a large dependence on the molecular structure, however, the R-values were approximately constant for groups of alkanes: R = 1.3×10⁶s^?1 for n-alkanes, R ≈ 4×10⁶ s^?1 for aliphatic vicinally substituted dimethyl alkanes, R = 7×10⁶s^-1 for cyclohexane and alkylcyclohexanes, and R = 10×10⁶s^?1 for di- and trimethylcyclohexanes. The excited state lifetimes of some non-fluorescing alkanes were also determined from steady-state photolytic quenching data and found to be very low (? 0.3 ns).     

Selective Fluorescence Sensing of Deoxycytidine 5��-Monophosphate (dCMP) Employing a Bis(diphenylphosphate)diimine Ligand

A new bis(diphenylphosphate)diimine ligand (BP1) was prepared and evaluated for its ability for selective detection of deoxycytidine 5??-monophosphate (dCMP). BP1 exhibited off-type fluorescence in the presence of dCMP. The fluorescence of BP1 was significantly quenched upon the addition of 2.5?×?10^?4 M dCMP and the detection limit was 1.25?×?10^?5 M in MeCN-H₂O (1:1, v/v). The binding ratio between BP1 and dCMP was determined to be 1:1 with the binding constant of 3.98?±?0.60?×?10^?3 M^?1.     

Wavelength-modulation spectroscopy using a frequency-doubled current-modulated diode laser

We have studied atomic absorption in an argon discharge by wavelength-modulation spectroscopy with a frequency-doubled diode laser. The tunable wavelength-modulated radiation at 430 nm was generated by frequency doubling a current-modulated 860-nm diode laser in a KNbO₃ crystal. 2f-, 4f- and 6f-harmonic spectra as a function of diode laser modulation depth were measured on a Doppler-broadened sample of excited argon atoms produced in a capacitively coupled plasma chamber. Characterisation of the harmonic signals was accomplished. Minimum detectable absorbances of 7.7×10^-5 and 1.9×10^-4 based on a 3σ criterion (σ being the standard deviation of the noise) were estimated for 2f- and 4f-harmonic detection of the frequency-doubled radiation with a time constant of 0.1 s. The concentrations of argon in the 1s₄ state were found to be in the range of 3×10⁸ to 1.2×10¹¹ cm^-3 for the experimental conditions studied. Received: 25 February 2002 / Revised version: 4 April 2002 / Published online: 14 May 2002     

Modification of the dielectric properties of copper-doped CdIn2S4 single crystal

The study of the dielectric properties of a CdIn₂S₄〈3 mol % Cu〉 single crystal in alternating-current (ac) electric fields with frequencies f = 5 × 10⁴?3.5 × 10⁷ Hz has revealed the origin of dielectric loss (relaxation loss that is changed by the through current loss at high frequencies). It has been found that CdIn₂S₄〈Cu〉 has permittivity increment Δ?′ = 123, relaxation frequency f _r = 2.3 × 10⁴ Hz, and relaxation time τ = 43 μs. The doping of CdIn₂S₄ single crystal with copper (3 mol %) is established to substantially increase the permittivity (?′), dielectric loss tangent (tanδ), and ac conductivity (σ_ac). In this case, the frequency dispersion of ?′ and tanδ increases and that of σ_ac decreases.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Disordering effects and property changes in fast neutron irradiated YIG

Damage region structure and property changes of YIG irradiated atD=10¹⁸?7.8×10¹⁹ n/cm² were studied. Damage regions at 300 K were found to consist of 1) a core of Fe³⁺ paramagnetic phase (PP) withgΔ=0.8 mm/s; 2) a shell of Fe³⁺ intermediate magnetic phase with heavily distorted bond geometry and <H _eff>≤300 kOe; 3) Fe³⁺ (a, d) surrounded by oxygen vacancies and interstitials. The dose dependence of PP concentration is given byC _PP=1-exp(?βD), yielding PP core radiusr _PP=12,5 Å. Magnetic ordering in PP was found to arise atT _tr=90 K. NGR probabilityf′ under irradiation was found to decrease linearly according to Δf′/f′=?C _PP(D). Net magnetization change was found, using the Gilleo model, to obey an analogous relationship ΔM(T)/M(T)=?C _PP(D).T _c dose dependence is given by ΔT _c/T _c=?0.5×C _PP(D) and can be related to lattice parameter change to yield Δa ₀/a ₀=(1.42±0.04)×10^?4×C _PP(D). External field experiments revealed a complex dependence ofK ₁ on PP concentration, elastic stress field magnitude and a with a minimum atD=10¹⁹ n/cm².     

A frequency-stabilized Yb:KYW femtosecond laser frequency comb and its application to low-phase-noise microwave generation

We present an optically stabilized Yb:KYW fs-laser frequency comb. We use an f–2f nonlinear interferometer to measure the carrier envelope offset frequency (f ₀) and the heterodyne beatnote between the comb and a stable CW laser at 1068 nm to detect fluctuations in the comb repetition rate ( $f_{\mathrm{rep}}$ f rep ). Both of these degrees of freedom of the comb are then controlled using phase-locked loops. As a demonstration of the frequency-stabilized comb, we generate low-phase-noise 10 GHz microwaves through detection of the pulse train on a high bandwidth photodiode. The phase noise of the resulting 10 GHz microwaves was ?99 dBc/Hz at 1 Hz and the corresponding Allen deviation was <2.6 × 10^?15 at 1 s, measured by comparison to an independently stabilized Ti:sapphire frequency comb. This room-temperature, optically based source of microwaves has close-to-carrier phase noise comparable to the very best cryogenic microwave oscillators.     

Laser-induced fluorescence and microwave-optical double-resonance study of the B1Σ+-X1Σ+ system of magnesium monoxide

Doppler-limited, laser-induced fluorescence spectra on the B¹Σ⁺-X¹Σ⁺ (v′ = v″ = 0 and 1) system of MgO have been obtained. The results of the optical analysis were merged with our microwave-optical double-resonance measurements to produce the following set of spectroscopic parameters for the B and X states, where the units are in cm^?1, and the uncertainties represent 95% confidence limits: T′_0.0 = 20003.594(2); B′₀ = 0.58004(3); D′₀ = 1.13(2) × 10^?6; B″₀ = 0.57198(3); D″₀ = 1.20(2) × 10⁶; T′_1.1 = 20043.423(2); B′₁ = 0.57528(4); D′₁ = 1.14(11) × 10⁶; B″₁ = 0.56674(4); D″₁ = 1.22(10) × 10⁶.     

Detecting super-Nyquist-frequency gravitational waves using a pulsar timing array

The maximum frequency of gravitational waves(GWs) detectable with traditional pulsar timing methods is set by the Nyquist frequency( fNy) of the observation. Beyond this frequency, GWs leave no temporal-correlated signals; instead, they appear as white noise in the timing residuals. The variance of the GW-induced white noise is a function of the position of the pulsars relative to the GW source. By observing this unique functional form in the timing data, we propose that we can detect GWs of frequency f_(Ny)(super-Nyquist frequency GWs; SNFGWs). We demonstrate the feasibility of the proposed method with simulated timing data.Using a selected dataset from the Parkes Pulsar Timing Array data release 1 and the North American Nanohertz Observatory for Gravitational Waves publicly available datasets, we try to detect the signals from single SNFGW sources. The result is consistent with no GW detection with 65.5% probability. An all-sky map of the sensitivity of the selected pulsar timing array to single SNFGW sources is generated, and the position of the GW source where the selected pulsar timing array is most sensitive to is λ_s =.0.82,β_s =-1.03(rad); the corresponding minimum GW strain is h = 6.31 × 10~(-11) at f = 1 × 10~(-5) Hz.     

High-resolution laser spectroscopy of ultracold ytterbium atoms using spin-forbidden electric quadrupole transition

We have successfully observed high-resolution spectra of spin-forbidden electric quadrupole transition (¹ S ₀→³ D ₂) in ytterbium (¹⁷⁴Yb) atoms. The differential light shifts between the ¹ S ₀ and the ³ D ₂ states in a far-off resonant trap at 532 nm are also measured. For the spectroscopy, we developed simple, narrow-linewidth, and long-term frequency stabilized violet diode laser systems. Long-term drifts of the excitation laser (404 nm) is suppressed by locking the laser to a length stabilized optical cavity. The optical path length of the cavity is stabilized to another diode laser whose frequency is locked to a strong ¹ S ₀→¹ P ₁ transition (399 nm) of Yb. Both lasers are standard extended-cavity diode lasers (ECDLs) in the Littrow configuration. Since the linewidth of a violet ECDL (～10 MHz) is broader than a typical value of a red or near infra-red ECDL (<1 MHz), we employ optical feedback from a narrow-band Fabry–Perot cavity to reduce the linewidth. The linewidth is expected to be <20 kHz for 1 ms averaging time, and the long-term frequency stability is estimated to be ～200 kHz/h.     

Fluorescence Properties of Twenty Fluorescein Derivatives: Lifetime,Quantum Yield,Absorption and Emission Spectra

The fluorescence lifetime (τ_f), emission quantum yield (Φ_f), absorption and emission spectral data of 20 fluorescein derivatives were measured under the same conditions by using time-correlated single photon counting, steady state fluorescence and absorption methods to get comparable data. Based on the results, the factors and mechanism that control the fluorescence properties of the fluorescein dyes are discussed. Both Φ_f and τ_f are remarkably dependent on the substitution on either xanthene or phenyl rings, but their ratio (Φ_f/τ_f), i.e. rate constant of radiation process, is a constant value (0.20?×?10⁹ s^?1). The rate constant of nonradiation process, on the other hand, is varied with both the structure and the solvent used.     

Simultaneous detection of trace gases using multiplexed tunable diode lasers and a photoacoustic cell containing a cantilever microphone

We report what we believe to be a novel demonstration of simultaneous detection of multiple trace gases by near-IR tunable diode laser photoacoustic spectroscopy using a cell containing a cantilever microphone. Simultaneous detection of carbon monoxide (CO), ethyne (C₂H₂), methane (CH₄) and combined carbon monoxide/carbon dioxide (CO+CO₂) in nitrogen-based gas mixtures was achieved by modulation frequency division multiplexing the outputs of four near-IR tunable diode lasers. Normalized noise-equivalent absorption coefficients of 3.4×10^?9, 3.6×10^?9 and 1.4×10^?9 cm^?1?W?Hz^?1/2 were obtained for the simultaneous detection of CO, C₂H₂ and CH₄ at atmospheric pressure. These corresponded to noise-equivalent detection limits of 249.6 ppmv (CO), 1.5 ppmv (C₂H₂) and 293.7 ppmv (CH₄) respectively over a measurement period of 2.6 s at the relevant laser power. The performance of the system was not influenced by the number of lasers deployed, the main source of noise arising from ambient acoustic effects. The results confirm that small-volume photoacoustic cells can be used with low optical power tunable diode lasers for rapid simultaneous detection of trace gases with high sensitivity and specificity.     

High density excitation effects on fluorescence from the crystals of aromatic hydrocarbons and charge-transfer complexes

High density excitation effects on fluorescence were studied for the crystals of fluoranthene, chrysene, benzo[g, h, i]perylene, pyrene and pyrene-d₁₀ and also for the crystal of 1,2,4,5-tetracyanobenzene (TCNB)-hexamethylbenzene (HMB) complex. Relative fluorescence intensity in the shorter wavelength region decreased with increasing excitation density (for chrysene, fluoranthene, and benzo[g, h, i]perylene), and the vibrational structure became diffuse at high density excitation (for fluoranthene and chrysene). The rate constants of the bimolecular quenching and exciton migration were obtained by analysis of the fluorescence decay curves at high density excitation for chrysene, pyrene, pyrene-d₁₀, and TCNB-HMB. The exciton hopping rates at 295 K were 2.4 × 10¹⁰ s^?1 in chrysene and 7.9 × 10⁸s^?1 in TCNB-HMB. The differences in the rate between chrysene and fluoranthene (2.2 × 10⁹s^?1) and between TCNB-HMB and TCNB-durene (4.2 × 10⁹s^?1) are discussed in terms of the coupling intensity between two neighboring oscillators accompanying the transition between ground and the lowest excited singlet state. The difference in the rate and activation energy of exciton migration between pyrene and pyrene-d₁₀ corresponded to a quasilocalized exciton model.     

Equivalent circuit of silicon diodes subjected to high-fluence electron irradiation

Silicon diodes with a p ⁺-n junction made in a 48-μm-thick phosphorus-doped silicon epilayer (resistivity ρ = 30 Ω cm) grown on antimony-doped Si(111) wafers (ρ = 0.01 Ω cm) are studied. The diodes are irradiated by high-energy (3.5 MeV) electrons with fluences from 5 × 10¹⁵ to 2 × 10¹⁶ cm⁻². It is shown that the conventional equivalent circuit of the diode that consists of a parallel RC network and a series-connected resistor inadequately describes the dependence of the dielectric loss tanδ on variable current frequency f in the range 1 × 10²–3 × 10⁷ Hz. Another equivalent circuit is suggested that includes not only the capacitance and resistance of the n-base (the latter increases because radiation-induced defects are compensated for by shallow donors) but also the f dependence of the capacitance of the space-charge region, which is due to retarded charge exchange between deep-level radiation-induced defects.     

Tunable laser Stark-difference spectra of CD3OH

We present Doppler resolution limited spectra of the P(J) and R(J) multiplets for J ≦ 10 of the 10-μm CO stretch band of ¹²CD₃¹⁶OH using a tunable diode laser. Relative frequencies within the multiplets accurate to ±0.0002–0.0005 cm^?1 are obtained, but no absolute frequencies are given. We are able to assign most of the hindered rotation and K substructure in these multiplets. The assignments are based on analyses of Stark-difference spectra combined with the ground-state microwave data and the intensity variations which are expected theoretically. The ground and excited state A, K = 1 asymmetry splitting parameters are measured to be δ₁″ = (8.5450 ± 0.0080) × 10^?3cm^?1 and δ₁′ = (9.7706 ± 0.0080) × 10^?3cm^?1, respectively. The ground-state value agrees well with the microwave results. A rapid-scan system for recording data and a computer-aided technique for calibrating and plotting the spectra are described.     

Tm3+/Yb3+共掺铋碲酸盐玻璃中的高效蓝色上转换荧光

制备了高折射率Tm³⁺/Yb³⁺共掺杂铋碲酸盐玻璃，利用棱镜耦合法测量出玻璃在632.8和1550nm波长处的折射率分别为2.0365和1.9795. 对玻璃的吸收、荧光和红外透过光谱展开了测试与分析，根据Judd-Ofelt理论对吸收光谱进行拟合，求得Tm³⁺的振子强度参数Ω_t(t=2，4，6)分别为3.90×10^-20, 2.03×10^-20和9.03×10^{-2 关键词： 3+}/Yb³⁺共掺')" href="#">Tm³⁺/Yb³⁺共掺 铋碲酸盐玻璃 光谱参数 上转换荧光     

Resonance absorption and fluorescence in argon

Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10^-18 cm²) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes

The rate constants were estimated relative to k _r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k _r from its natural value and observations of the decay of resonance fluorescence suggest that k _r ～ 1·5 × 10⁵ s^-1 in our system at [Ar] = 2 × 10¹⁷ atom cm^-3. Combining this value with the relative values for the quenching rate constants gives k ₁ < 1·5 × 10^-13, k ₁′(M = N₂) ～ 6 × 10^-12, k ₁′(M = NO) ～ 4 × 10^-10, in units of cm³ s^-1 molecule^-1.     

Selective Fluorimetric Recognition of Cesium Ion by 15-Crown-5-Anthracene

A selective fluorescent cesium optode on a chromoionophore consisting of anthracene covalently linked through an imine bond to a 15-crown-5 derivative has been reported. In the present system, 15-crown-5 derivative including anthracene was used a fluoroionophore. The fluorescence response mechanism is based on the photo-induced electron transfer (PET) from the lone pair of electrons of the nitrogen to the anthracene group and inhibition of PET system by cesium binding while increasing the fluorescence intensity. Emission intensity 15-crown-5 anthracene was measured at 500 nm with absorbance at 400 nm in CH₃CN–H₂O (1:1) media. The method shows a very good selectivity and sensitivity for cesium with respect to other cations such as K⁺, Na⁺ and Li⁺ with linear range and detection limit of 5.0 × 10⁻⁵ to 5.0 × 10⁻¹M and 3.0 × 10⁻⁶M respectively.