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1.
High-precision heteronuclear three-bond coupling constants including3J(HN, C′),3J(HN, Cβ),3J(Hα,Cγ), and3J(Hβ, C′) are determined for the nonproline residues in uniformly13C-enrichedantamanide,cyclo-(-Val1-Pro2-Pro3-Ala4-Phe5-Phe6-Pro7-Pro8-Phe9- Phe10-), using quantitative numerical 2D NMR spectrum evaluation based on the product-operator formalism. The experimental basis comprises two-dimensional1H,13C-heteronuclear relayed E.COSY spectra [J. M. Schmidt, R. R. Ernst, S. Aimoto, and M. Kainosho,J. Biomol. NMR6,95 (1995)], the multiplet patterns of which are subjected to iterative least-squares 2D multiplet-simulation procedures. Accuracy and precision of the spectrum fit are assessed byFstatistics and analysis of variances (ANOVA) leading to confidence intervals for the optimized spin-system parameters. The long-range J coupling constants obtained and their standard deviations provide the experimental foundation for a later detailed analysis of φ and χ1dihedral-angle equilibrium conformations contributing to the flexible peptide structure.  相似文献   

2.
The highly hydrophobic fluorophore Laurdan (6-dodecanoyl-2-(dimethylaminonaphthalene)) has been widely used as a fluorescent probe to monitor lipid membranes. Actually, it monitors the structure and polarity of the bilayer surface, where its fluorescent moiety is supposed to reside. The present paper discusses the high sensitivity of Laurdan fluorescence through the decomposition of its emission spectrum into two Gaussian bands, which correspond to emissions from two different excited states, one more solvent relaxed than the other. It will be shown that the analysis of the area fraction of each band is more sensitive to bilayer structural changes than the largely used parameter called Generalized Polarization, possibly because the latter does not completely separate the fluorescence emission from the two different excited states of Laurdan. Moreover, it will be shown that this decomposition should be done with the spectrum as a function of energy, and not wavelength. Due to the presence of the two emission bands in Laurdan spectrum, fluorescence anisotropy should be measured around 480 nm, to be able to monitor the fluorescence emission from one excited state only, the solvent relaxed state. Laurdan will be used to monitor the complex structure of the anionic phospholipid DMPG (dimyristoyl phosphatidylglycerol) at different ionic strengths, and the alterations caused on gel and fluid membranes due to the interaction of cationic peptides and cholesterol. Analyzing both the emission spectrum decomposition and anisotropy it was possible to distinguish between effects on the packing and on the hydration of the lipid membrane surface. It could be clearly detected that a more potent analog of the melanotropic hormone α-MSH (Ac-Ser1-Tyr2-Ser3-Met4-Glu5-His6-Phe7-Arg8-Trp9-Gly10-Lys11-Pro12-Val13-NH2) was more effective in rigidifying the bilayer surface of fluid membranes than the hormone, though the hormone significantly decreases the bilayer surface hydration.  相似文献   

3.
Accurate and efficient grid based techniques for the solution of the time-dependent Schrödinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H2 + with fixed internuclear separation, H2 + with vibrating nuclei and H2 with fixed internuclear separation and illustrative results presented.Received: 19 November 2002, Published online: 24 April 2003PACS: 02.60.Cb Numerical simulation; solution of equations - 02.70.Bf Finite-difference methods - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.80.-b Photon interactions with molecules  相似文献   

4.
A high-accuracy finite-difference beam-propagation method (HAFD-BPM) based on high-accuracy divided-difference formulas is presented. The truncation error in this HAFD-BPM is reduced to o(Δr)4in the transverse direction, whereas the error in a conventional FD-BPM is typically o(Δr)2. Gaussian beam propagation in vacuum and nonlinear medium is simulated by this new method and conventional one. The comparison between them in computing time and accuracy reveals the advantage of this new method. As an example, this method is applied to the simulation of blow-up in self-focusing of a Gaussian beam. PACS 42.65.Hw; 42.25.Bs; 02.70.Bf  相似文献   

5.
A novel dual-emitter vacuum Compton detector (D-VCD) with higher gamma ray detecting efficiency is proposed. The emitters are made of Ta--Al clad metal. The gamma ray sensitivity is studied by Monte Carlo simulation using the MCNP code. A comparison between calculations and results measured by using the 1.25~MeV gamma ray of Co-60 is also performed. Experimental sensitivities for two sample D-VCDs with the same materials and structures are 1.92×10^ - 20 and 2.02×10^ - 20~C.cm2/MeV separately, which are consistent with the simulation result of 1.98×10^ - 20~C.cm2/MeV and are 4 times higher than that of VCD with a single Fe emitter. According to the simulation results, in a gamma energy range from 0.5 to 3~MeV, the maximum sensitivity variance for the D-VCD is less than 15%, and less than 5% in a range from 1 to 2~MeV in particular. The novel D-VCD is applicable to the detection of intense pulse gamma rays.  相似文献   

6.
We observed hyperfine structures of the 4D5/2 state of 85Rb atoms and applied them to the frequency stabilization of a laser diode by using the double resonance optical pumping (DROP). The hyperfine structures of the 4D5/2 states of 85Rb atoms were highly resolved in the Rb vapor cell. We compared the DROP with the optical-optical double resonance (OODR) in the 5S1/2-5P3/2-4D5/2 ladder-type system of 85Rb atoms. When we stabilized the frequency of a laser diode to the hyperfine structure of the 5P3/2(F″ = 4)-4D5/2(F″ = 3) transition by using the DROP spectrum, the frequency stability was approximately 2.3 × 10− 12 after 100 s.  相似文献   

7.
For LiYF4:Ce3+, LiLuF4:Ce3+ and LuF3:Ce3+ crystals UV/visible emission and time-resolved VUV/UV excitation spectra were recorded at liquid helium temperature with spectral resolution of 0.1 nm for excitation spectra and better than 0.3 nm for emission spectra. Well resolved fine structures due to zero-phonon lines were clearly observed in both excitation and emission spectra for LiYF4:Ce3+ and LiLuF4:Ce3+. For LuF3:Ce3+ crystal no fine structure was detected in the spectra even at the highest spectral resolution. Under the host excitation, the fine structure for high-energy emission band of Ce3+ (5d-2F5/2) in LiLuF4:Ce3+ becomes well pronounced because of weaker reabsorption effect, as compared to Ce3+ 4f-5d absorption, due to small penetration depth for exciting radiation. As a result the crystal-field splitting for 2F7/2 and 2F5/2 levels of Ce3+ in LiLuF4 crystal was measured. First observation of zero-phonon lines at ∼81,550 and ∼82,900 cm−1 as well as vibronic side bands due to interconfigurational 4f14-4f135d transitions in Lu3+ is reported for excitation spectrum of LiLuF4:Ce3+.  相似文献   

8.
In this article, we calculate the masses and residues of the heavy baryons Ωc *(css) and Ωb *(bss) with spin–parity with the QCD sum rules. The numerical values are compatible with the experimental data and other theoretical estimations. PACS 14.20.Lq, 14.20.Mr  相似文献   

9.
Quantitative optical spectroscopy measurements of the emission spectra of the N(B2u,)ν′→X2gν″ transition (first negative system) in an Ar-N2 microwave discharge at atmospheric pressure have allowed determination of the rate coefficient of the production of N molecules in the B2u, state with vibrational level ν′ = 0. The N(B2u, ν′) molecules are produced by the reaction in a surface-wave-induced microwave discharge (2450 MHz) sustained in an open-ended dielectric tube. The rate coefficient K (T) has been obtained for ν′ν″ = 0 for different gas temperatures by varying the incident microwave power. The K00(T) values are between 7.10?10 and 4.10?10 cm3 s?1 for the temperature range 2500 to 3450K.  相似文献   

10.
2 /p-Si MOS structures were prepared in 0.1 M K2SO4 electrolyte with a pH of 7 (the 0.1 M KOH solution was buffered with H2SO4) at current densities of 3, 5, and 7 mA/cm2 and with four different pH values of the electrolyte at 3 mA/cm2. It is found that thermal annealing at a relatively low temperature can be used to improve the anodic MOS characteristics. Moreover, of the pH and current density it followed that the pH has a dominant role in the interface electrical properties. The lowest interface state densities at the maximum and the midgap positions are 7.1×1011 and 2.7×1010 eV-1cm-2 for a sample made with pH=7, J=3 mA/cm2. The characteristics of this sample seem satisfactory for device applications of anodized p-Si. Received: 8 July 1996/Accepted: 22 January 1997  相似文献   

11.
We perform a simulation with the aim of checking the existence of a well defined stationary state for a two dimensional system of driven hard disks when energy dissipation takes place at the system boundaries and no bulk impurities are present. PACS: 02.70.Ns, 05.60.-k, 47.27.ek  相似文献   

12.
Rate constants and kinetic isotope effects have been determined for the formation of nitronate anions from the ethers 1‐(2‐methoxyphenyl)‐2‐nitropropane, 7 (X = H, L = H and D) and 1‐(2‐methoxy‐5‐nitrophenyl)‐2‐nitropropane, 7 (X = NO2, L = H and D), and from the corresponding phenols, 1‐(2‐hydroxyphenyl)‐2‐nitropropane, 3 (X = H, L = H and D), and 1‐(2‐hydroxy‐5‐nitrophenyl)‐2‐nitropropane, 3 (X = NO2, L = H and D), in aqueous basic medium. For the ethers 7 , rates of deprotonation by hydroxide are comparable with those found for deprotonations of 2‐nitropropane, with kH/kD (25 °C) = 7.7 and 7.8, respectively. In both the cases, the isotope effects are conventionally temperature dependent. For the corresponding phenols 3 , conditions have been established under which the deprotonations of the nitroalkane are dominated by intramolecular deprotonation by the kinetically first‐formed phenolate anion, with an estimated effective molarity EM ~ 250. For 3 (X = H, L = H or D), kH/kD (25 °C) = 7.8, with E ? E = 6.9 kJ mol?1 and AH/AD = 0.5. For 3 (X = NO2, L = H or D), rates of intramolecular deprotonation are reduced 30‐fold, and an elevated kinetic isotope effect is found (kH/kD (25 °C) = 10.7). Activation parameters (E ? E = 17.8 kJ mol?1 and AH/AD = 0.008) are compatible with an enhanced tunnelling contribution to reactivity in the H‐isotopomer. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
The energies of formation, enthalpies, and entropies of the conformers of 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionic acid and sodium and potassium 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates are calculated by quantum-chemical methods in the PM6 approximation. A doubling of signals in the 1H NMR spectrum of the first conformer is observed, which merge into singlets when the compound is heated. Changes in the structure of the conformers and donor-acceptor complexes (solvates) occur with the preservation of the metal-ligand coordination bond. Calculations of the characteristics of 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionic acid and sodium and potassium 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates in the PM6 approximation make it possible to predict the structure and properties of the solvated structures. The energies of homolysis of the H-O bond D (OH) are calculated, and a linear dependence of the antioxidant activity on D (OH) for the structures of the studied compounds is demonstrated. The results make it possible to predict the properties of antioxidants in the biological environment.  相似文献   

14.
芶清泉  黄树勋 《物理学报》1965,21(6):1293-1303
我们在文献[1]中设计了一套五个参数的变分波函数用来计算了周期表中前面十个原子的能量,所得结果比过去一些作者用四参数波函数所算得的结果为好。我们在过去计算经验的基础上,另外找到了一套特别简单的解析波函数,其形式为1s电子:ψ1(r)=N1e-μar,2s电子:ψ2(r)=N2[(μr)e-μr-Ne-μar],2p电子:ψ3(r)=N3(μr)cosθe-μr4(r)=N4(μr)sinθeiφ-μr5(r)=N5(μr)sinθe-iφ-μr,式中的α与μ为变分参数;N1,N2,N3,N4,N5为归一化因子;N为正交化系数。μ可用解析法来决定,因而只有一个参数α要由数值法来决定。我们用这样的波函数算出了第二周期元素的正常态原子和离子(共有八十几个原子态)的各电子的各种能量积分值及总能量值,并确定了波函数的最佳参数值。其结果与五参数波函数的计算结果相比,一般相差在万分之一至千分之一的范围内,并比最近有些作者用一种三参数波函数所算的结果还好。根据这些结果,我们还讨论了Slater近似计算法的可靠程度和适用范围。  相似文献   

15.
原子的解析波函数   总被引:5,自引:0,他引:5       下载免费PDF全文
我们设计了一套变分波函数,用来计算了周期表中前面十个原子的能量。我们设计的单电子试探波函数具有下列形式:1s:ψ1(r)=N1e-μαr[1+(μbr)2], 2s:ψ2(r)=N2[(μr)e-μr-Ne-μcr], 2p:ψ3(r)=N3(μdr)cosθe-μdr, ψ4(r)=N4(μdr)sinθeiφ-μdr, ψ5(r)=N5(μdr)sinθe-iφ-μdr。式中的a,b,c,d及μ为五个变分参数。N1,N2,N3,N4与N5为归一化因子;N由ψ1与ψ2的正交条件来决定。用这种波函数来计算原子的能量,所得的结果比莫尔斯等人(P.M.Morse,L.A.Young and E.S.Haurwitz)用他们设计的四参数波函数所算得的结果为好,更接近实验值,同时也接近于由自洽场所算出的结果。若我们的波函数中固定c等于1不变,这时就变为只有四个参数的波函数,结果仍比莫尔斯等人的好。  相似文献   

16.
The conductivity and thermal stability of NH+4, H+(H2O)nβ″ and ion-rich β-alumina single crystals have been measured by the complex impedance method in the 25–700°C temperature range. Both structures have similar properties, but ion-rich β-alumina shows a higher stability and a lower activation energy (β: 0.18 eV, β″ 0.24 eV below 400°C and 250°C respectively). The room temperature conductivity is about 3×10-5ω-1cm-1. The conducting properties and mechanisms are discussed and compared to other protonic or ionic conductors.  相似文献   

17.
Emission and absorption spectra of Tm3+ in single crystal K2YF5 with different concentrations are reported and analyzed. The non-exponential feature of the fluorescence decay of 1D2 level for the high concentration sample indicates the existence of a cross-relaxation process. Energy level simulation has been carried out by using a phenomenological model with 16 parameters accounting simultaneously for the free ion and crystal field (CF) effects. A good fit was achieved with a root mean square deviation σ=18 cm−1. The free ion and CF effects were then discussed by comparing the available data of K2YF5:Nd3+, LiYF4:Tm3+ and LiYF4:Nd3+.  相似文献   

18.
用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对(Ca3N2)n(n=1—4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、成键特性、电荷特性和稳定性等进行了理论分析.结果表明,(Ca3N2)n(n=1—4)团簇最稳定构型中N原子为3—5配位,Ca—N键长为0.231—0.251nm,Ca—Ca键长为0.295—0.358nm;N原子的自然电荷在-1.553e—-2.241e之间,Ca原子的自然电荷在1.035e—1.445e之间,Ca和N原子间相互作用呈现较强的离子性,Ca3N2和(Ca3N2)3团簇有相对较高的动力学稳定性. 关键词: 3N2)n(n=1—4)团簇')" href="#">(Ca3N2)n(n=1—4)团簇 密度泛函理论 结构与性质  相似文献   

19.
B.S. Cao  Y.Y. He  M. Song 《Optics Communications》2011,284(13):3311-3314
Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er3+, 10 mol% Yb3+ and 0-20 mol% Li+ codoped TiO2 [1Er10Yb(0-20)Li:TiO2] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO2 were divided into three parts by the addition of Yb3+ and Li+. Both green and red upconversion emissions were observed from the 2H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ in Er3+-Yb3+-Li+ codoped TiO2, respectively. The green and red upconversion emissions of 1Er:TiO2 were enhanced significantly by Yb3+ and Li+ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (Igreen/Ired) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er3+ and Yb3+ as well as the distortion of crystal field symmetry of Er3+ caused by the dissolving of Li+ at lower Li+ codoping concentration and the phase transformation at higher Li+ concentration. It is concluded that codoping with ions of smaller ionic radius like Li+ can efficiently improve the upconversion emissions of Er3+ or other rare-earth ions doped luminsecence materials.  相似文献   

20.
The 1H and 13C NMR spectra of sugar (5-methyl [1, 2, 4]-triazino [5, 6-b] indol-3-yl) hydrazones (1), per-0-acetyl aldehydo sugar 1-acetyl-1-(5-methyl [1, 2, 4] triazino [5, 6-b]-indol-3-yl) hydrazones (2), l- (penta-0-acetyl-pentitol-1-yl)-10-methyl [l, 2, 4] triazolo [3′, 4′:3, 4] [l, 2, 4] triazino [5, 6-b]-indoles (3) have been investigated. The 2 D NMR (H, C COSY) spectrum of 2a has been studied.  相似文献   

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