The nature of olefins and carboxyl groups in an Australian brown coal resin

The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (¹³C CP MAS NMR). Some additional solution ¹H and ¹³C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C₁₅ carbon atoms in the diterpenoids without cyclization of the methylene units at C₈.     

Detection of tannins in modern and fossil barks and in plant residues by high-resolution solid-state C nuclear magnetic resonance

Bark samples isolated from brown coal deposits in Victoria, Australia, and buried wood from Rhizophora mangle have been studies by high-resolution solid-state nuclear magnetic resonance (NMR) techniques. Dipolar dephasing ¹³C NMR appears to be a useful method of detecting the presence of tannins in geochemical samples including barks, buried woods, peats and leaf litter. It is shown that tannins are selectively preserved in bark during coalification to the brown coal stage.     

两个三能级原子纠缠的可提纯性猝死

研究了两个全同V 型三能级原子在独立库中纠缠的可提纯性问题.在退相位通道中利用超算符求解出系统的时间演化密度矩阵,在特定的初态条件下得到了系统的负本征值.用负度和重排密度矩阵的迹范数量度了系统可提纯性的演化规律.结果表明：可提纯性保持的时间受参数α 的影响,α 越大,可提纯性保持的时间就越长,但纠缠的可提纯性还是会衰减并最终消失;对于负度不可量度的情况,使用重排密度矩阵的迹范数进一步加以研究,分析了整个范围内的时间演化规律,绘出了其演化曲线,并作了相应的物理解释;得到了在退相位通道中可提纯性会出现猝死的结论.     

Characterization of humic substances by advanced solid state NMR spectroscopy: Demonstration of a systematic approach

Characterization of humic substances is challenging due to their structural complexity and heterogeneity. Solid state nuclear magnetic resonance (NMR) is regarded as one of the best tools for elucidating structures of humic substances. The primary solid state NMR technique that has been used so far is the routine ¹³C cross polarization-magic angle spinning (CP-MAS) technique. Although this technique has markedly advanced our understanding of humic substances, the full potential of NMR for characterizing humic substances has yet to be realized. Recent technical developments and applications of advanced solid state NMR have revealed the promise to provide deeper insights into structures of humic substances. In this paper, we summarized and demonstrated the systematic solid state NMR protocol for characterization of humic substances using a humic acid as an example. This protocol included (1) identification of specific functional groups using spectral editing techniques, occasionally assisted by ¹H¹³C two-dimensional heteronuclear correlation (2D HETCOR) NMR, (2) quantification of specific functional groups based on direct polarization-magic angle spinning (DP-MAS) and DP-MAS with recoupled dipolar dephasing, combined with spectral editing techniques, (3) determination of connectivities and proximities of specific functional groups by ¹H¹³C 2D HETCOR or 2D HETCOR combined with spectral editing techniques, and (4) examination of domains and heterogeneities by ¹H¹³C 2D HETCOR with ¹H spin diffusion. We used a soil humic acid as an example to demonstrate how this protocol was applied to the characterization of humic substances step by step. Afterwards, based on typical ¹³C NMR spectra of humic substances we described how we could combine different NMR techniques to identify specific functional groups band by band from downfield to upfield. Finally, we briefly mentioned the potential new NMR techniques that could be developed to enrich the current systematic protocol. This systematic protocol is not only applicable to humic substances but also to other natural organic matter samples.