低温NMR探头的应用

在过去10年中研发新核磁共振探头一直是制造者争夺的活跃领域. 最近，因其灵敏度的巨大提高，低温冷却探头得到人们格外的关注. 利用这一技术可大量节省谱仪机时. 对于低γ核可直接测定天然丰度样品而不必标记，这远比节省机时更为重要. 本文评述了针对5～10 Hz优化2 mg天然丰度噁唑烷酮抗菌素eperezolid的 CIGAR-HMBC-¹H-¹⁵N谱的比较，一个是采自美国瓦里安公司的5 mm低温探头，另一个是采自瓦里安公司传统室温3 mm 梯度三共振探头. 利用低温探头大约10 min就可记录到大部份¹H-¹⁵N远 程相关，26 min可观察到几乎所有的远程共振. 而在同样条件下使用3 mm传统梯度反式三共振探头无法得到有用的谱图，要想取得相同的结果须累加约18 h.

APPLICATION OF CRYOGENIC NMR PROBES

In the past decade manufactures of NMR systems have put many efforts into the re search and development of new NMR probe technologies. Recently the development o f cryogenically cooled NMR probe has been the subject of considerable interest i n the light of the large sensitivity gains they may provide, and hence the savin gs in acquisition time by using this technology. For low gamma nuclides, such as¹⁵N, the advantages that cryogenic NMR probes provide in terms of det ection sen sitivity and acquisition time may, in a sense more important than the enhancemen t of sensitivity per se, provide the opportunity of direct detection of NMR sign als in their natural abundances, while isotope enriched samples often have to b e used when conventional NMR probes are employed. In this study, 5～10 Hz optimi ze d CIGAR-HMBC ¹H-¹⁵N experiments were performed on a 2 mg natural a bundance sampl e of the oxazolidinone antibiotic eperezolid in a 3 mm NMR tube using a 5 mm Varian ¹H-¹⁵N Cryo-QNMR probe and a 3 mm gradient inverse triple res onance probe, and the results from the two probes were compared. With the cryogenic NMR probe,a ¹H-¹⁵N CIGAR-HMBC spectrum, in which most previously reportedlong -range coup lings were observed, was recorded in ～10 min. Almost all of the expected long-r ange responses were observed when the acquisition time was increased to 26 min. The same experiment using the conventional probe gave data that were of substant ially lower quality. About four hours were required for the conventional probe t o acquire a spectrum that displayed all the coupling responses as those shown by the 26 min cryogenic probe spectrum. Eighteen hours of acquisition time were re quired for the conventional probe to obtain a spectrum that was comparable in terms of signal-to-noise ratio to that obtained by the cryogenic probe in 26 min.