MEASUREMENT OF HOMONUCLEAR COUPLING CONSTANTS USING TWO-DIMENSIONAL MAXIMUM-QUANTUM CORRELATION NMR SPECTROSCOPY (MAXY-NMR)

偶合常数是一个重要的NMR参数,其数值与分子中化学键的二面角有关,可以为分子结构研究提供很重要的信息.多维NMR谱由于具有较大的化学位移分辨率,因此常常被用来测定同核或异核自旋-自旋偶合常数.本文介绍了利用最高量子相关技术（MAXY）测定同核偶合常数的方法.MAXY是最近发展的一种多维NMR谱编辑技术,可以使不同官能团（CH, CH     

同核RELAY相干传递技术在复杂天然有机化合物1H谱解析中的应用

用同核化学位移相关谱和同核RELAY谱等二维NMR方法完全归属了复杂天然有机化合物人参皂甙Rb₁的¹H NMR谱线,并用积算符方法证实一级和二级RELAY实验中观察到的意外交叉峰是通过远程偶合传递的RELAY信号。     

基于纯化学位移的同核二维正交相敏J分解核磁共振波谱

二维J分解(2D J_RES)核磁共振(NMR)波谱是一种简单且用户友好的谱图表达形式,其将J偶合常数和化学位移信息分离到两个正交的频率维度上.自40年前首次被提出以来,2D J_RES技术在脉冲序列和方法的改进,以及实际应用的进展方面一直备受关注.本文回顾了新型2D J_RES脉冲序列,以及用于精确测量同核J偶合常数的2D J编辑谱的最近进展,特别是基于纯化学位移演化机制的正交相敏2D J_RES谱方法及其应用,并阐述其在克服强偶合效应和磁场不均匀性等方面的能力.     

有机磷化合物的NMR研究——Ⅱ0,0-二烷基膦酸酯的1H、13C和31PNMR谱

本文报道了21个0,0一二烷基膦酸酯类化合物的¹H、¹³C和³¹P NMR参数。研究和讨论了不等价的二烷基¹H、¹³C化学位移和磷碳偶合常数与立体化学的关系。测定了(CH₃CH₂O)₂P(O)CH(CH₂NO₂)(p-OCH₃C₆H₄)的¹³C自旋一晶格弛豫时间T₁,二乙基¹³C T₁间的差别,说明在类似化合物中,含有化学位移各向异性对弛豫的贡献。     

中国人参的核磁共振研究Ⅰ.人参皂甙Re的二维核磁共振谱研究

用400MHz和500MHz超导核磁共振谱仪测定了具有生理活性的达玛烷型人参皂甙Re的同核、异核二维化学位移相关谱和相敏双量子滤波二维相关谱,由此归属了人参皂甙Re的氢谱,测定了Re的质子偶合常数。     

改性铑络合催化剂的NMR研究

合成了八种铑的络合催化剂,对它们进行了¹H及¹³C NMR测定、对谱线进行了标识,找出化学位移的一些规律性,测出了一些偶合常数,确定了它们的结构。发现一种反位效应络合产物,并非全是反位化合物而是2:1(反:顺)的位置异构体混合物。当络合配体为β双酮时,在溶液中,该配位化合物结构,特别是CH₃有一定的扭曲,CH₃在¹H及¹³C NMR中都表现出异常的行为。     

中国人参的核磁共振研究Ⅰ．人参皂甙Re的二维核磁共振谱研究

用４００ＭＨｚ和５００ＭＨｚ超导核磁共振谱仪测定了具有生理活性的达玛烷型人参皂甙Ｒｅ的同核、异核二维化学位移相关谱和相敏双量子滤波二维相关谱，由此归属了人参皂甙Ｒｅ的氢谱，测定了Ｒｅ的质子偶合常数。     

19F NMR的特点

¹⁹F的磁旋比和相对灵敏度接近质子;¹⁹F NMR化学位移范围可达 δ 1 000,谱图分辨率高;¹⁹F NMR对环境因素较氢谱远为敏感、复杂,可反映出化合物结构的细微差别. 由于正常生物体内含氟成分很少,干扰小,因此在生物医学研究中引入氟代物进行¹⁹F NMR研究有特殊意义. 对氟化物的¹⁹F NMR化学位移和偶合常数的范围也分类作了总结.     

卤代苯和卤代萘磺化产物的1H NMR研究

研究了卤代苯和卤代萘磺化产物的¹H NMR分析方法.结合各产物有关质子的化学位移,偶合常数,分裂形式,积分高度可得到各种磺化产物的比例.讨论了双共振去偶合实验的具体应用,化学位移理论值的计算及其在质子谱峰归属中所起的作用,磺化产物¹H和¹⁹F的偶合分裂现象.首次报道了卤代芳香化合物多磺酸取代产物的¹H NMR数值.     

使用低磁场NMR谱仪的一维异核化学位移相关实验

本文介绍在FX系列NMR谱仪上完成一维异核化学位移相关实验的方法。使用本文提出的"零强度法",即使在低磁场谱仪上,也能够通过测量几个¹³C谱以较高的精度确定出某些CH₂基团两质子的化学位移之差。     

一种新的三萜化合物的2D NMR研究

本文采用FAB-MS,FTIR和NMR等技术对从沙打旺牧草分离出的一种新的三萜化合物进行结构鉴定,结果表明该化合物为(20R,24S)-3,16-二羰基-6α,25-二羟基-20,24-环氧-9,10环羊毛甾酮.用2D NMR技术,包括¹H-¹³C HETCOR,COLOC,¹H-¹H COSY对,¹H和¹³C NMR进行归属.     

用新近发展的1H NMR技术研究腐殖酸

将一些新近发展起来的¹H NMR技术用于溶在不同溶剂(D₂O,NaOH/D₂O及DMSO-d₆)中的腐殖酸样品的研究,这包括全相关谱方法(TOCSY),扩散谱方法和最大量子谱方法(MAXY).DMSO溶液的TOCSY谱中4与8之间的相关峰表明在腐殖酸中可能包含有不溶于水的多肽,扩散谱指出在碱性条件下,一些小分子脱离了腐殖酸聚合体,而MAXY谱编辑方法则使得一些细致的归属成为可能.     

NOE和二维NMR技术在倍半萜化学位移归属中的应用

本文用NOE和二维核磁共振技术-COSY,C-H化学位移相关,C-H远程化学位移相关(COLOC),DEPT对二个倍半萜分子的立体化学结构进行了研究,并对其¹H和¹³C化学位移进行了归属。     

Two-dimensional high-resolution NMR spectra in matched B(0) and B(1) field gradients

In a recent publication we presented a method to obtain highly resolved NMR spectra in the presence of an inhomogeneous B(0) field with the help of a matched RF gradient. If RF gradient pulses are combined with "ideal" 90 degrees pulses to form inhomogeneous z rotation pulses, the line broadening caused by the B(0) gradient can be refocused, while the full chemical shift information is maintained. This approach is of potential use for NMR spectroscopy in an inhomogeneous magnetic field produced by an "ex-situ" surface spectrometer. In this contribution, we extend this method toward two-dimensional spectroscopy with high resolution in one or both dimensions. Line narrowing in the indirect dimension can be achieved by two types of nutation echoes, thus leading to depth-sensitive NMR spectra with full chemical shift information. If the nutation echo in the indirect dimension is combined with a stroboscopic acquisition using inhomogeneous z-rotation pulses, highly resolved two-dimensional correlation spectra can be obtained in matched field gradients. Finally, we demonstrate that an INEPT coherence transfer from proton to carbon spins is possible in inhomogeneous B(0) fields. Thus, it is possible to obtain one-dimensional (13)C NMR spectra with increased sensitivity and two-dimensional HETCOR spectra in the presence of B(0) gradients of 0.4 mT/cm. These schemes may be of some value for ex-situ NMR analysis of materials and biological systems.     

通过HSQC和1H,13C-COSY叠合增强二维谱分辨率的方法

通常二维谱F₁维分辨率较差,F₂维分辨率较好. 即HSQC实验¹³C维度分辨率较差,¹H维度分辨率较好. 而¹H, ¹³C-COSY实验¹³C维度分辨率较好,¹H维度分辨率较差. 提出一种通过HSQC和¹H, ¹³C-COSY叠合,取较弱的值储存并显示的方法增强分辨率,采用Bruker Topspin软件AU程序实现. 该方法在不明显增加采样时间的情况下,可显著增强分辨率,信噪比也没有降低. 同时抑制了F₁噪声. 处理后,谱图美观清晰.     

Using chemical shift anisotropy to resolve isotropic signals in solid-state NMR

A key problem in solid-state NMR is resolving overlapping isotropic signals. We present here a two-dimensional method which can enable sites with the same isotropic chemical shift to be distinguished according to their chemical shift anisotropy and asymmetry. The method involves correlating sideband spectra at different effective spinning rates using CSA-amplification pulse sequences. The resulting two-dimensional correlation pattern allows very accurate determination of the chemical shift principal values in addition to the recovery of parameters for two overlapping patterns which allows the resolution of overlapping signals.     

<Superscript>1</Superscript>H and<Superscript>13</Superscript>C chemical shift assignments and stereochemistry of matrine and oxymatrine

Matrine and oxymatrine were extracted fromSophora flavescens, and their¹H and¹³C nuclear magnetic resonances (NMR) were unambiguously assigned by a combination of different two-dimensional 2-D¹H-¹³C and¹H-¹H correlation experiments of HMQC, HMQC-TOCSY and MAXY. The technique of using those experiments to make the assignment of the heavily overlapped spectrum is demonstrated. The coupling constants of matrine were measured by 2-DJ-resolved spectrum and 1-D spectra extracted from the slices of 2-D MAXY spectrum. The stereochemistry of the titled compounds was established from the NMR spectroscopy.     

低场核磁共振流体分子结构在线探测技术

流体分子结构的探测是了解其物理、化学性质的基础.目前主要采用的实验室内分子结构探测技术包括光谱法和波谱法等,但这类测量方法具有测量效率低、需添加化学试剂、实验可重复性差等局限.基于低场核磁共振（NMR）技术进行流体组分的探测技术已十分成熟.该文提出进一步将该技术应用于烃类化合物流体分子结构的检测方法,并研发一种快速二维核磁共振驰豫测量脉冲序列和一套低场核磁共振流体在线检测系统.最终实现了一种快速、无损、清洁、有效的流体组分探测技术.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone with Maleic Anhydride: Restricted Motion of Bridgehead Phenyls

¹H NMR studies at 300 MHz have been performed for the Diels-Alder adduct of phencyclone and maleic anhydride in CDCl₃ at ambient temperatures. The 1D spectrum shows four equal (2H) intensity doublets in the aryl region (in addition to other absorptions) which is fully consistent with a slow exchange limit (SEL) spectrum of a system in which the unsubstituted bridgehead phenyls exhibit hindered rotation around the C(sp²)-C (sp³) bond on the NMR timescale. These protons are assigned to H-1,8 and H-4,5 of the phenanthrene moiety and to H-2′ and H-6′ of the phenvls based on the two-dimensional (2D) homonuclear chemical shift correlation spectrum (COSY) together with arguments regarding carbonyl and aromatic ring anisotropy. Full proton assignments are given.