Analytical Instrument Documents

13C NMR spectra provide wide range chemical shift, and it suggests that can easily distinguish each signals. But carbon resolution of 2D spectra such as HSQC and HMBC is worse than 1D 13C spectra due to small data points. In order to analyze a compound with close 13C chemical shifts, a high resolution 2D spectrum is required frequently. In this document, some improvements to distinguish each signals on 13C axis of 2D hetero nuclear experiments are presented.

The NMR signal of a spin reflects its local magnetic environment. If a spin due to chemical exchange samples two magnetically different states then its NMR signal would reflect both states. Its appearance on a NMR spectrum would be determined by the dynamics of the exchange event. In the case of chemical exchange that is slow on the NMR time scale, it is possible to observe two distinct signals for the same spin, one signal for each state under exchange. Presence of chemical exchange is often demonstrated with the exchange experiment (2D NOESY experiment). A exchange peak (cross peak) of the same sign can be observed between the two autopeaks (diagonal peaks) that represent the two states under exchange. Because the same results can be interpreted in a different way based on NOE, further evidence is desirable.

In 2013, JEOL RESONANCE launched the cryogenic NMR probe systems,”UltraCOOL” and “SuperCOOL”. Delivering sensitivity far exceeding conventional room temperature probes together with ease of use beyond that previously associated with cooled probes, such as probe change whilst cooled, and variable temperature measurement capability, the products received a lot of positive response. However, many dramatic stories lay behind the birth of these products.

Here we present the recent development at RIKEN CLST-JEOL collaboration laboratory to explore the molecular structures of low-molecular weight pharmaceutical compounds in natural abundance (without any isotopic labeling); the recent progress in fast magic angle spinning (MAS) technology in solid-state nuclear magnetic resonance (ssNMR) and in ultra high sensitivity camera in transmission electron microscopy (TEM) paves a new way to answer problems in the pharmaceutical industry and sciences. 1) Crystalline polymorphs and 2) salt/cocrystal are two major concerns in terms of quality control, stability, and intellectual property. To identify the crystalline form, powder X-ray diffraction and 13C cross-polarization MAS ssNMR are widely used methods, however, the former is sometimes not suitable for mixture analysis and latter fails to distinguish crystalline forms with similar molecular conformations. To solve these issues, we use electron diffraction (ED) and 1H fast MAS NMR. The crystalline form can be determined from nano- to micro-meter sized single crystals using ED, since electron interactions are 4 to 5 order stronger than X-ray interactions. 1H NMR also gives suitable information to molecular packing since 1H is located at the surface of the crystals. The salt/cocrystal issue, where hydrogen plays a key role, is a serious problem, since single crystal X-ray diffraction (SCXRD) cannot determine the hydrogen atom position precisely. Here we determine the internuclear distances between 1H and 15N using ssNMR at fast MAS conditions, while the global structure is obtained through SCXRD, answering the salt/cocrystal questions.

Download all eight Delta QuickTime movie tutorials.

How to acquire and process proton spectra: process lists in 1D Processor, using the Pointer Tools to interact with data, peak picking, J-coupling tool, integration, plotting.

How to acquire and process 1D, 2D, nOe spectra: comparing multiple data sets in Data Slate, loading high-resolution projections, Level Tool, plotting, understanding through-bond correlations, common nOe experiments, data interpretation.

A comprehensive description and demonstration of contouring data with Level Tool.

How to acquire and process HMBC spectra: loading high-resolution projections, Level Tool, plotting, understanding HMBC, data interpretation.

How to acquire and process multiplicity-edited HSQC spectra: phasing 2D data, loading high-resolution projections, setting contrast colors in Level Tool, plotting, HMQC versus HSQC, data interpretation.