2D-NMR spectroscopy
The 1D-NMR clearly demonstrated the resonance overlap in one-dimensional spectra. Due to the number of residues in macromolecules, the repeated use of the same building blocks/aa, and the number of protons per amino acid 1D-spectra contain many lines, most of the significantly overlapped. An identification of individual lines/protons, their assignment, or the observation of individual properties are nearly impossible in this data. However, the signal overlap can be significantly reduced , or the resolution increased by introducing a second time/frequency dimension. The second or indirect dimension frequency domain (or even further) can be obtained by the insertion of a time delay, which is systematically incremented in repeated acquisitions. A Fourier transformation of these FIDS yields a series of 1D-spectra, in which the signals are amplitude-modulated according to the their precession-frequency in the incremented time delay. This is called a half transformed spectrum (interferogram), as the direct dimension is in the frequency domain (transformed), but the indirect dimension given by the stacked spectra is still in the time domain. A second Fourier transform (in direction of t1, of each data point in the spectra(F2), gives a fully transformed, 2D spectrum.