Localized in vivo (1) H NMR spectroscopy is playing an increasing role in preclinical studies, because of its ability to quantify the concentrations of up to 20 metabolites in rat brain. To assess the differences between often-used rat strains, the neurochemical profiles of Sprague-Dawley, Wistar and Fischer rats were determined at ultrashort TE at 16.4 T. To ascertain high-qualitative quantification, a first experiment examined the dependence of the measuring time on the quantification results and precision by precisely the number of averages between 16 and 320. It was shown that most metabolites can be quantified accurately within a short scan time, yielding Cramér-Rao lower bounds below 20% and stable concentrations for 16 metabolites with as few as 32 or 64 averages in the thalamus and hippocampus, respectively. Interstrain differences in metabolite concentrations were shown to be moderate, with taurine varying significantly between Sprague-Dawley and Wistar rats, and slightly more distinct differences from Fischer rats, including variations in glutamate and myo-inositol. The high spectral quality and quantification precision of all data again demonstrated the potential of in vivo (1)H NMR spectroscopy at ultrahigh field. 相似文献
(1)H-NMR spectroscopy at 500 MHz was used to confirm that a previously unidentified singlet resonance at 3.14 ppm in the spectra of cerebrospinal fluid and plasma samples corresponds to dimethyl sulfone (DMSO(2)). A triple resonance inverse cryogenic NMR probe, with pre-amplifier and the RF-coils cooled to low temperature, was used to obtain an (1)H-(13)C HSQC spectrum of CSF containing 8 microM (753 ng/ml) DMSO(2). The (1)H-(13)C correlation signal for DMSO(2) was assigned by comparison with the spectrum from an authentic reference sample. In plasma and CSF from healthy controls, the concentration of DMSO(2) ranged between 0 and 25 micromol/l. The concentration of DMSO(2) in plasma from three of four patients with severe methionine adenosyltransferase I/III (MAT I/III) deficiency was about twice the maximum observed for controls. Thus, DMSO(2) occurs as a regular metabolite at low micromolar concentrations in cerebrospinal fluid and plasma. It derives from dietary sources, from intestinal bacterial metabolism and from human endogenous methanethiol metabolism. 相似文献
Owing to the small quantity of tissue available in human biopsy specimens, aqueous and lipid components often have to be determined in the same tissue sample. Perchloric acid (PCA) used for the extraction of aqueous metabolites has a deleterious effect on lipid components; the severity of the damage is not known. In this study, human muscle tissue was first treated with PCA to extract aqueous metabolites, and the residue was then used for lipid extraction by conventional methods, i.e. the methods of Folch and Bligh & Dyer and a standardised one using methanol/chloroform (1:3, v/v) used in our laboratory. A (1)H-NMR spectrum was obtained for each lipid extract. Lipid was quantified by measuring the integral area of N(+)-(CH(3))(3) signals of phospholipids (PLs). Triacylglycerol (TG) and cholesterol (CHOL) were quantified using the -CH(2)- signals of glycerol and the C18 methyl signal, respectively. This study shows that prior use of PCA caused marked attenuation of TG, PL, and CHOL. This was confirmed by recovery experiments and observation of the direct effect of PCA on the standard lipid components. On the basis of the quantity of lipid lost in each case, three novel equations (with respect to TG, PL, and CHOL) were derived. Application of these equations to lipid quantities estimated in different pathological tissues after PCA pre-treatment produced values equivalent to those estimated without PCA use. This study conclusively shows that PCA pre-treatment damages all three lipid moieties, TG, PL, and CHOL. When PCA is used in a fixed ratio to the tissue, the lipid damage is also proportional and correctable by statistically derived equations. These equations will be useful in human biopsy specimens where aqueous and lipid components have to be studied using the same tissue sample because of the small quantity available. 相似文献
Using 1H and 13C NMR spectroscopy, cationic intermediates formed by activation of (Cp‐R)2ZrCl2 (R = nBu, tBu and 1,2,3‐Me3) with MAO in toluene were monitored at Al/Zr ratios from 50 to 1 000. The catalysts (Cp‐R)2ZrCl2/AlMe3/CPh3+B(C6F5)4? (nBu, tBu and 1,2,3‐Me3) were also studied for comparison of spectroscopic and polymerization data with MAO based systems. Complexes of type (Cp‐R)2ZrMe+ ← Me?‐Al?MAO ( IV ) with different Me‐MAO? counter anions have been identified in the (Cp‐R)2ZrCl2/MAO systems at low Al/Zr ratios. At Al/Zr ratios of 200–1 000, the complex [(Cp‐R)2Zr(μ‐Me)2AlMe2]+ Me‐MAO? ( III ) dominates in all MAO‐based reaction systems. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr = 200–1 000) for the systems (Cp‐nBu)2ZrCl2/MAO and (Cp‐tBu)2ZrCl2/MAO, while it is virtually constant in the same range of Al/Zr ratios for the catalytic system (Cp‐1,2,3‐Me3)2ZrCl2/MAO. The data obtained are interpreted on the assumption that complex III is the actual precursor of active centers of polymerization in MAO based systems.
Formation of cationic intermediates by activation with MAO. 相似文献