Species；valve size；and pretreatment effects on delta O-18 and delta C-13 values of ostracod valves from Lake Qinghai；Qinghai-Tibet Plateau

IEECAS SKLLQG

Contribution of inherent organic carbon to the bulk delta C-13 signal in loess deposits from the arid western Chinese Loess Plateau

IEECAS SKLLQG

delta C-13 variation of C-3 and C-4 plants across an Asian monsoon rainfall gradient in arid northwestern China

IEECAS SKLLQG

Multi-electron processes in C-13(6+) ions with neon collisions in energy region 4.15-11.08 keV/u

The cross-section ratios of double-, triple-, quadruple-, and the total multi-electron processes to the single electron capture process sigma(DE)/sigma(SC), sigma(TE)/sigma(SC), sigma(QE)/sigma(SC) and sigma(ME)/sigma(SC)) as well as the relative ratios among reaction channels in double-electron active, triple-electron active and quadruple- electron active are measured in C-13(6+) -Ne collision in the energy region of 4.15-11.08 keV/u by employing position-sensitive and time-of-flight coincident techniques. It is determined that the cross-section ratios sigma(DE)/sigma(SC), sigma(TE)/sigma(SC), sigma(QE)/sigma(SC) and sigma(ME)/sigma(SC) are approximately the constants of 0.20 +/- 0.03, 0.16 +/- 0.04, 0.06 +/- 0.02 and 0.42 +/- 0.05. These values are obviously smaller than the predictions of the molecular Coulomb over-the-barrier model (MCBM) [J. Phys. B 23 (1990) 4293], the extended classical over-the-barrier model (ECBM) [J. Phys. B 19 (1986) 2925] and the semiempirical scaling laws (SL) [Phys. Rev. A 54 (1996) 4127]. However, the relative ratios among partial processes of DE, TE and QE are found to depend on collision energy, which suggests that the collision dynamics depends on the collision velocity. The limitation of velocity-independent character of ECBM, MCBM and SL is undoubtedly shown.

The first synthesis of a water-soluble alpha-cyclodextrin/C-60 supramolecular complex using anionic C-60 as a building block

A novel supramolecular inclusion complex of alpha-CD/C-60 was synthesized using anionic C-60. The reaction progress was monitored in situ by visible and near-IR spectroscopy. The obtained complex was characterized by UV-vis, C-13 NMR, MALDI-TOF, and cyclic voltammetry. The induction and dispersion forces are considered to be the major driving forces for the formation of a resulting alpha-CD/C-60(.-) inclusion complex.

Carbon-13 nuclear magnetic resonance spectrum simulation of pyridines and quinolines

Artificial neural network (ANN) and multiple linear regression (MLR) were used for the simulation of C-13 NMR chemical shifts of 118 central carbon atoms in 18 pyridines and quinolines. The electronic and geometric features were calculated to describe the environments of the central carbon atom. The results provided by ANN method were better than that achieved by MLR.

Studies on the solution structures of lanthanide(III) complexes of DTPA-BIN by NMR

The solution structures of diamagnetic lanthanide (III) complexes of DTPA-BIN (Ln = La, Y, Lu, Sc) have been investigated by H-1 NMR, C-13 NMR and 2D NMR. For each complex, two or more species of asymmetric conformations with little distinction were identified at room temperature. And their solution structures vary with the radius of the central metals. NMR spectra support the hypothesis that Sc3+ with smaller radius formed an eight-coordinated structure with DTPA-BIN, La3+ with larger radius formed nine- or ten-coordinated structures with DTPA-BIN, and Y (DTPA-BIN) and Lu (DTPA-BIN) had nine-coordinated solution structures. The solution structure of Gd (DTPA-BIN) was obtained from the similarity of radius between Gd3+ and Y3+, which is a nine-coordinated structure formed by three nitrogens, three acetate oxygens, two acetyl oxygens, one water molecule and a gadolinium(III) cation.

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines is performed. The topological, geological and electronic descriptors are generated. To reduce the variables, the best subsets of the descriptors are obtained by using leaps-and-bounds regression analysis. The model is achieved using multiple regression with satisfactory results.

碳-13核磁共振谱图的自动解析研究

为了C-13NMR的自动解析，ESESOC系统从13CNMR本身的特征出发， 提出了不确定层数的子结构模型。即以共振碳原子为中心，以与之相连的完整的官能团为外围环境， 对这样的子结构， 其外围环境根据官能团的不同可以是一层、或二层乃至多层， 即环境层数是可变的。在此子结构模型的基础上， 从CIAC-13CNMR谱图数据库统计出13CNMR知识库。

High resolution solid-state NMR and DSC study of poly(ethylene glycol) silicate hybrid materials via sol-gel process

Hybrid materials incorporating poly(ethylene glycol) (PEG) with tetraethoxysilane (TEOS) via a sol-gel process were studied for a wide range of compositions of PEG by DSC and high resolution solid-state C-13- and Si-29-NMR spectroscopy. The results indicate that the microstructure of the hybrid materials and the crystallization behavior of PEG in hybrids strongly depend on the relative content of PEG. With an increasing content of PEG, the microstructure of hybrid materials changes a lot, from intimate mixing to macrophase separation. It is found that the glass transition temperatures (T-g) (around 373 K) of PEG homogeneously embedded in a silica network are much higher than that (about 223 K) of pure PEG and also much higher in melting temperatures T-m (around 323 K) than PEG crystallites in heterogeneous hybrids. Meanwhile, the lower the PEG content, the more perfect the silica network, and the higher the T-g of PEG embedded in hybrids. An extended-chain structure of PEG was supposed to be responsible for the unusually high T-g of PEG. Homogeneous PEG-TEOS hybrids on a molecular level can be obtained provided that the PEG. content in the hybrids is less than 30% by weight. (C) 1998 John Wiley & Sons, Inc.

The structure analysis and characterization of N-100 by NMR

To improve the mechanics properties of polyurethane materials at a high or low temperature, a hydroxy compound N-100 of HDI was synthesized, The structure analysis and characterization were made by NMR (H-1, C-13, H-1-H-1 COSY, C-13-H-1 COSY), In addition, quantitative description of the network was made on the basis of some ideal assumptions, 1D and 2D NMR can differentiate four sorts of carbonyl groups and establish the connections of all carbon and hydrogen atoms of mixed structures that originated from five different substitutions, Besides, the alkene and isocyanate, urea, biuret and trimerized isocyanuric groups were also detected, Therefore, the structure of N-100 was suggested be a polyisocyanate with complicated network which contained nitrogen atom as cross-linkage, isocyanate and alkene as end groups, The consistence of calculated values with tested values of isocyanate content, mean function degree and mean molecular weight demonstrated the correct of structure characterization and the validity of network description.

W-183 NMR characterization of rare earth heteropolymetalates in aqueous solution

W-183 NMR spectra were obtained for [La(AsW11O39)(2)](11-), [La(As2W17O61)(2)](17-), [La(SiW9Mo2O39)(2)](13-), [LaSb9W21O86](16-), [LaAs4W40O140](25-) and alpha-, beta-[(CeO)(3) . (SiW9O34)(2)](14-) complexes, Tungsten NMR studies showed that the C-s symmetry of the square antiprism for [La(ASW(11)O(39))(2)](11-) and [La(As2W17O61)(2)](17-) anions keep constant in aqueous solution; the lanthanide accupied the central S-1 site in [LnSb(9)W(21)O(86)](16-) and [LnAs(4)W(40)O(140)](25-) complexes, respectively, and lanthanide metal cations gave [(CeO)(3) . (SiW9O34)(3)](14-) type of complexes with SiW9O3410-.