Measurements and Measurement lists

About

A “Measurement” is a value that is derived from NMR data and connects to one or more resonances (which may be assigned to atoms). There are several different kinds of measurements that may be included within a CCPN project, for example J-coupling, hydrogen exchange rate, chemical shift anisotropy, T1 relaxation and chemical shift. Of the different types of measurements, the chemical shift is the most important and most used, and is derived from recording the positions of peaks in spectra. A "Measurement list" is simply a collection of measurements.

Shift Lists

Being the most important type of measurement, the chemical shifts have a special place in Analysis. Chemical shifts lists, or Shift Lists, are important attributes of Experiments. Each Experiment has an associated Shift List, which is used to store chemical shifts derived from peaks in the NMR spectra. The same shift list can be associated with multiple experiments, which is typically done for experiments recorded on the same or similar samples and under the same conditions (where the chemical shifts remain constant). It is important to understand that the average chemical shifts are calculated over all the associated experiments, their spectra, peak lists and peaks (Figure 1).

Figure 1. The hierarchy between experiments, spectra, peak lists and peaks.

A convenient feature of Analysis is that one can use multiple shift lists, while using a single set of resonances. So a resonance may have a several chemical shift measurements, which is a very useful feature when studying different experimental conditions (Figure 2).

Figure 2. A resonance can have different chemical shifts, if the peaks to which it is assigned originate from spectra (Experiments) that have different chemical shift lists associated. The purple peaks originate from experiments connected to Shift List 1, the light red peaks originate from experiments connected to Shift List 2.

To separate chemical shifts measurements for experiments where the chemical shifts change, typically for different experimental conditions, one should thus use different shift lists for these experiments.