Secondary Fluorescence Quenching Rate Constants of Eu3+ in D2O by ETOH,CH3COOD and OH-Groups (H2O)

It has been shown recently that the fluorescence efficiency of Eu³⁺ in organic solvents is reduced to a different extent by the solvent molecules located in the primary and in the secondary solvation spheres of the ion^(1,2). The primary solvation sphere was associated with the nonradiative quenching processes of the rare-earth ion, k_h, whereas molecules located in the secondary solvation sphere were associated with a secondary fluorescence quenching effect i.e. k_solv ^sec or K_Q ^sec. The structure of the primary solvation sphere was found to exert a marked effect upon the fluorescence efficiency and lifetimes of Sm³⁺ in POCl₃: SnCl₄ ⁽³⁾. Furthermore, a pronounced effect, due to both the primary and the secondary solvation sphere, was observed upon the intensity and the splitting of absorption and emission bands of Eu³⁺ associated with electric-quadrupole transitions⁽⁴⁾.     

The stretching fundamental bands of 13C2D2

The stretching fundamental bands of the isotopically substituted acetylene ¹³C₂D₂ have been recorded and analysed. The Raman spectra of the Q branch of v ₁ and v ₂, Σ⁺ _g -Σ⁺ _g bands, have been recorded with an instrumental resolution of about 3.0 x 10^?3 cm^?1 using inverse Raman spectroscopy. The infrared spectrum has been recorded in the region between 2350 cm^?1 and 2500 cm^?1 with an instrumental resolution of 4.0 x 10^?3 cm^?1. Transitions belonging to the v ₃, Σ⁺ _u -Σ⁺ _g , fundamental band have been identified and assigned. The vibrational energies and the rotational and centrifugal distortion constants of the excited states of all the observed transitions have been determined. The molecular parameters obtained reproduce the assigned wave-numbers with a standard deviation of the same order of magnitude as the experimental uncertainty.     

In-medium properties of the D13(1520) nucleon resonance

The in-medium properties of the D13(1520) nucleon resonance were studied via photoproduction of pi(0) mesons from nuclei (C, Ca, Nb, Pb) with the TAPS detector at the Mainz Microton accelerator. The inclusive (single and multiple pion production) data disagree with model predictions which explain the disappearance of the second resonance bump in total photoabsorption via a medium modification of the D13-->Nrho decay. The exclusive single pi(0) production data show no broadening of the resonance structure beyond Fermi smearing. Both results together cast doubt on attempts to explain the vanishing of the second resonance bump for nuclei by a broadening of the D13 resonance.     

13C-14N REAPDOR and 13C-2D theta-REDOR NMR on a blend of tri-p-tolylamine and bisphenol-A-polycarbonate

Solid-state NMR experiments are performed on amorphous blends of tri-p-tolylamine (TTA) and polycarbonate. Amines that are similar to TTA are blended with polycarbonates and used as photoconducting components in xerography. Because of its simple molecular structure, TTA is a charge-transporting molecule that is used as a model to understand charge transport in photoconducting materials. Charge transfer between amine molecules must depend on the separation and relative orientation between amine molecules. However, little information is known about the structural relationship between the amine molecules and the polymer host, presumably because of the difficulties associated with characterizing amorphous materials. We report the results of 13C-14N rotational-echo, adiabatic-passage, double-resonance (REAPDOR) and 13C-2D theta-rotational-echo, double-resonance (theta-REDOR) magic-angle spinning NMR experiments on a TTA/polycarbonate blend. The experiments provide information about the organization of TTA relative to polycarbonate.     

环维黄杨星D^13C和^1H化学位移的全归属

环维黄杨星D为自黄杨木中提取精制的有效生物碱,临床上已长期用于心血管疾病的治疗.本文用制备高效液相色谱提取、分离并纯化环维黄杨星D,用1D,2D NMR技术 (COSY,DEPT,HMQC 和 HMBC)对其结构进行研究,并且首次对环维黄杨星D的1H NMR 和 13C NMR 信号进行了全归属,同时通过NMR数据确证了环维黄杨星D的结构.     

Role of the D 13 and S 11 Resonances in Deuteron Photodisintegration

The influence of the N(1520) and N(1535) isobar resonances in deuteron photodisintegration is investigated. The isobar configurations are treated in impulse approximation using one-pion exchange for the transition potentials. Isobar admixtures are included in scattering waves as well as in the deuteron. Their influence on the total and differential cross section and various polarization observables, e.g., nucleon polarization and photon asymmetry is small in the Δ resonance region, but not any longer negligible at higher energies. Received July 14, 1994; accepted for publication November 28, 1994     

3D 1H-13C-14N correlation solid-state NMR spectrum

Nitrogen-14 (spin I = 1) has always been a nucleus difficult to observe in solid-state NMR and until recently its observation was restricted to one-dimensional (1D) spectra. We present here the first 3D ¹H–¹³C–¹⁴N NMR correlation spectrum. This spectrum was acquired on a test sample l-histidine·HCl·H₂O using a recently developed technique, which consists in indirectly observing ¹⁴N nuclei via dipolar recoupling with an HMQC-type experiment.     

二十面体Sc13，Sc13¬+1，Sc13¬-1团簇的稳定性与电子结构研究

采用密度泛函理论框架下的广义梯度近似(DFT/GGA),对Sc13团簇进行了几何结构优化,得到13原子钪团簇的基态结构为正二十面体(Ih),在此基础上对二十面体(Ih)Sc13, Sc13¬+1和Sc13-1团簇的稳定性、电子结构磁矩进行研究.结果发现Sc13,Sc13¬+1和Sc13¬-1团簇都在Ih结构时最稳定,该尺寸团簇的稳定性主要由二十面体密堆积构型决定;带电能使团簇的结构稍稍收缩从而使团簇的稳定性有所增强;团簇的键长和对称性对团簇的磁矩有很明显的影响.     

Development of high resolution 3D hyperpolarized carbon-13 MR molecular imaging techniques

The goal of this project was to develop and apply techniques for T₂ mapping and 3D high resolution (1.5 mm isotropic; 0.003 cm³) ¹³C imaging of hyperpolarized (HP) probes [1-¹³C]lactate, [1-¹³C]pyruvate, [2-¹³C]pyruvate, and [¹³C,¹⁵N₂]urea in vivo. A specialized 2D bSSFP sequence was implemented on a clinical 3T scanner and used to obtain the first high resolution T₂ maps of these different hyperpolarized compounds in both rats and tumor-bearing mice. These maps were first used to optimize timings for highest SNR for single time-point 3D bSSFP acquisitions with a 1.5 mm isotropic spatial resolution of normal rats. This 3D acquisition approach was extended to serial dynamic imaging with 2-fold compressed sensing acceleration without changing spatial resolution. The T₂ mapping experiments yielded measurements of T₂ values of > 1 s for all compounds within rat kidneys/vasculature and TRAMP tumors, except for [2-¹³C]pyruvate which was ~ 730 ms and ~ 320 ms, respectively. The high resolution 3D imaging enabled visualization the biodistribution of [1-¹³C]lactate, [1-¹³C]pyruvate, and [2-¹³C]pyruvate within different kidney compartments as well as in the vasculature. While the mouse anatomy is smaller, the resolution was also sufficient to image the distribution of all compounds within kidney, vasculature, and tumor. The development of the specialized 3D sequence with compressed sensing provided improved structural and functional assessments at a high (0.003 cm³) spatial and 2 s temporal resolution in vivo utilizing HP ¹³C substrates by exploiting their long T₂ values. This 1.5 mm isotropic resolution is comparable to ¹H imaging and application of this approach could be extended to future studies of uptake, metabolism, and perfusion in cancer and other disease models and may ultimately be of value for clinical imaging.     

Anisotropies in carbon-13 chemical shift tensor,H-C-H bond angles and the signs of the coupling constants in 13CH3I, 13CH3Br, 13CH3Cl

A pulsed fast Fourier transform N.M.R. spectrometer is used to investigate the temperature dependence of the ¹³C chemical shifts in the nematic liquid crystal solutions of the following halides: ¹³CH₃I, ¹³CH₃Br, ¹³CH₃Cl. The H-C-H bond angles are accurately measured in this investigation from proton magnetic resonance studies. The signs of the coupling constants D _13CH , D _HH, J _13CH and the ordering parameter have been assigned to be all positive. The ¹³C magnetic shielding anisotropy is found to become more positive with the increasing electronegativity of the halogen substituents. The values of the anisotropies are: Δσ = σ _∥ - σ _⊥ = - 101 ± 15 p.p.m. (¹³CH₃I), - 10 ± 5 p.p.m. (¹³CH₃Br), 22 ± 5 p.p.m. (¹³CH₃Cl). Results for Δσ obtained from the slope of σ_n versus S ₃₃ agree with those obtained from the nematic-isotropic phase subtraction method.     

Analysis of13C(γ,π+)13Bg.s. and13C(e,é)13C* (15.11 MeV)

The DWIA calculation of the differential cross section for photoproduction of π⁺ from¹³C was carried out with the photon multipole expansion. It is shown that the Cohen-Kurath wave function can reproduce the data quite well. We also calculated the ratio of theM1 transition to theE2 transition to be 1.9. The transverse form factor for¹³C(e, é)¹³C* was evaluated consistently with the same wave function as used for^l3C(γ, π⁺)¹³B.     

High resolution 2D 1H-13C correlation of cholesterol in model membrane

High resolution 2D NMR MAS spectra of liposomes, in particular 1H-13C chemical shifts correlations have been obtained on fluid lipid bilayers made of pure phospholipids for several years. We have investigated herein the possibility to obtain high resolution 2D MAS spectra of cholesterol embedded in membranes, i.e. on a rigid molecule whose dynamics is characterized mainly by axial diffusion without internal segmental mobility. The efficiency of various pulse sequences for heteronuclear HETCOR has been compared in terms of resolution, sensitivity and selectivity, using either cross polarization or INEPT for coherence transfer, and with or without MREV-8 homonuclear decoupling during t1. At moderately high spinning speed (9 kHz), a similar resolution is obtained in all cases (0.2 ppm for 1H(3,4), 0.15 ppm for 13C(3,4) cholesterol resonances), while sensitivity increases in the order: INEPT < CP(x4) < CP + MREV. At reduced spinning speed (5 kHz), the homonuclear dipolar coupling between the two geminal protons attached to C(4) gives rise to spinning sidebands from which one can estimate a H-H dipolar coupling of 10 kHz which is in good agreement with the known dynamics of cholesterol in membranes.     

The 2D MAS NMR spin-echo experiment: the determination of 13C-13C J couplings in a solid-state cellulose sample

A simple 13C MAS spin-echo experiment is applied to a partially 13C-labelled cellulose sample extracted from wood. 13C-13C J couplings are determined even though considerable chemical disorder leads to observed linewidths in the normal 1D 13C CP MAS spectrum which far exceed the J couplings. The fitting of the experimental data also allows the quantification of the degree of isotopic enrichment.     

二十面体Sc13,Sc+113,Sc-113团簇的稳定性与电子结构研究

采用密度泛函理论框架下的广义梯度近似(DFT/GGA),对Sc13团簇进行了几何结构优化,得到13原子钪团簇的基态结构为正二十面体(Ih),在此基础上对二十面体Sc13, Sc+113和Sc-113团簇的稳定性、电子结构和磁矩进行研究.结果发现Sc13,Sc+113和Sc-113团簇都在Ih结构时最稳定,该尺寸团簇的稳定性主要由二十面体密堆积构型决定;带电能使团簇的结构稍稍收缩从而使团簇的稳定性有所增强;团簇的键长和对称性对团簇的磁矩有很明显的影响.