Plant–soil negative feedback (NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on ...root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant–soil NF. The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance (NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments. Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon (AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted¹³C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species‐specific toxicity. Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self‐DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant–soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms.
This work is focused on the characterization of the composition of a COsub.2 supercritical fluid extract of Aquilaria sinensis (Chinese agarwood) collected in the Dongguan area (China) and infected ...by mechanical methods. The constituents of this extract were analyzed by gas chromatography–mass spectrometry (GC-MS) and quantified accurately by gas chromatography with a flame ionization detector (GC-FID), using an internal reference and predicted response factors. Since a significant number of components of this extract remained non-identified after the initial GC-MS analysis of the whole extract, its fractionation by chromatography on silica gel helped to characterize several additional constituents by isolation and structural analysis by NMR spectroscopy. The main components are the classical agarwood chromones (Flindersia chromone and its mono-, di-, and trimethoxylated analogues (respectively, 11.01% and 0.11–4.02%) along with sesquiterpenic constituents typically found in agarwood essential oils, like baimuxinal (1.90%) and kusunol (1.24%), as well as less common selinane dialdehydes (1.58–2.27%) recently described in the literature. Moreover, the structure and stereochemistry of a new sesquiterpenic alcohol, 14β,15β-dimethyl-7αH-eremophila-9,11-dien-8β-ol (0.67%), was determined unambiguously by the combination of structural analysis (NMR, MS), hemisynthesis, and total synthesis, leading to dihydrokaranone and a neopetasane epimer.
The intrinsic permeability of porous medium is theoretically independent of percolating fluids. While concerning cementitious material, its water permeability is anomalously lower than that to many ...other fluids. To discover the responsible physical background, the permeability coefficients of two mature white cement mortars are measured using water, isopropanol and nitrogen gas. Their pore structures are also tested on specimens at various states through low-field NMR and MIP methods. It is found that the pore structures of water-saturated mortars are remarkably coarsen due to the contraction of C-S-H gel enforced by water removal through drying or isopropanol exchange. The coarsening of pore structure fundamentally increases the intrinsic permeability by 2–4 orders of magnitudes, which can be approximately quantified through the Katz-Thompson equation. The anomalous low water permeability is physically rooted in the swelling of C-S-H gel specific to water, which is intimately linked to the disjoining pressure of aqueous pore solution.
A general approach towards the synthesis of tetrahydro-4H-pyrazolo1,5-a1,4diazepin-4-one, tetrahydro1,4diazepino1,2-aindol-1-one and tetrahydro-1H-benzo4,5imidazo1,2-a1,4diazepin-1-one derivatives ...was introduced. A regioselective strategy was developed for synthesizing ethyl 1-(oxiran-2-ylmethyl)-1H-pyrazole-5-carboxylates from easily accessible 3(5)-aryl- or methyl-1H-pyrazole-5(3)-carboxylates. Obtained intermediates were further treated with amines resulting in oxirane ring-opening and direct cyclisation-yielding target pyrazolo1,5-a1,4diazepin-4-ones. A straightforward two-step synthetic approach was applied to expand the current study and successfully functionalize ethyl 1H-indole- and ethyl 1H-benzodimidazole-2-carboxylates. The structures of fused heterocyclic compounds were confirmed by sup.1H, sup.13C, and sup.15N-NMR spectroscopy and HRMS investigation.
Keywords: antimony; density functional calculations; main group elements; pnictogens; polycations; structure elucidation The hexacoordinated antimony(V) dication (ppy).sub.3Sb.sup.2+ (1.sup.2+; ...ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor-acceptor interactions, has been isolated as its hexachloroantimonate salt 1SbCl.sub.6.sub.2, prepared by the oxidative addition of chlorine to the neutral stibine (ppy).sub.3Sb (1), followed by the abstraction of chloride. Air-stable 1SbCl.sub.6.sub.2 exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the .sup.1H and .sup.13C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for 1SbCl.sub.6.sub.2 by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature .sup.1H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication 1.sup.2+ is the first 12-Sb-6.sup.2+ chemical species to have been structurally determined. Article Note: This paper is dedicated to the memory of our great mentor, Professor Emeritus Naomichi Furukawa (University of Tsukuba), who recently passed away Supporting information: Additional Supporting Information may be found in the online version of this article As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. CAPTION(S): Supplementary Byline: Masato Sakabe, Soichi Sato
► NMR spectroscopy is the major de novo structure elucidation method in liquid state. ► LC–NMR combines high resolution separation with unequivocal structure elucidation. ► The most advanced ...technical LC–NMR instrumentation is LC–SPE–NMR. ► Application fields range from pharmaceutical industry to phytochemistry.
Combining the most powerful separation techniques, i.e. liquid chromatography (LC) or capillary electrophoresis (CE) with a information rich detection system – the mass spectrometer or the nuclear magnetic resonance (NMR) spectrometer – has been pursued for more than three decades. This compilation shall provide an overview of the advantages and limitations of the LC–NMR hyphenation in the light of its most valued application–the unequivocal analyte identification. Especially the post LC trapping of analytes with an in-line solid phase extraction (SPE) device prior to transferring the analyte of interest to the NMR spectrometer (LC–SPE–NMR) proved to be a robust installation allowing a significant cut-down of the amount of analyte needed for the generation of high quality heteronuclear NMR shift correlation data. Different available technical realizations will be discussed and typical application examples from natural product research and from industrial settings will be given.
We report linewidth and proton
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1
,
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1
ρ
and
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′ relaxation data of the model protein ubiquitin acquired at MAS frequencies up to 126 kHz. We find a predominantly linear improvement in linewidths ...and coherence decay times of protons with increasing spinning frequency in the range from 93 to 126 kHz. We further attempt to gain insight into the different contributions to the linewidth at fast MAS using site-specific analysis of proton relaxation parameters and present bulk relaxation times as a function of the MAS frequency. For microcrystalline fully-protonated ubiquitin, inhomogeneous contributions are only a minor part of the proton linewidth, and at 126 kHz MAS coherent effects are still dominating. We furthermore present site-specific proton relaxation rate constants during a spinlock at 126 kHz MAS, as well as MAS-dependent bulk
T
1ρ
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1
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N
).
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