.• For Curcumin, the proton (1H spectrum) shifts are as follows. 2 similar protons on the aromatic groups give rise to shifts at 5.55ppm (aromatic C-OH). The benzene CH of which there are 3, give rise to 7.16 ppm, 6.99 ppm and 6.79 ppm. On the hexadienone bridge, between the two benzene rings (aromatic rings) are 2 pairs of equvalent protons
.• 2 protons are found at 7.60 ppm, that are attached to the aromatic Hydorgen and Carbons. The 2 protons attached to the carbonyl groups can be shown at 6.91 ppm. Lastly, there are two protons in between 2 carbonyl groups at 4.69 ppm
2D 1H-13C HSQCUsing information from 1H NMR data alone is not a new concept. However, applications that also use the 2D 1H-13C HSQC experiment are gaining more interest as a result of the growing feasibility of acquiring these spectra routinely. The 2D HSQC experiment contains additional information (i.e. 13C chemical shift) as well as easier identification of labile and diastereotopic protons.
Positive Reduction in Automated NMR Structure Verification• Sergey S. Golotvin1, Rostislav Pol1, Ryan R. Sasaki2, Asya Nikitina2, and Phil Keyes3• 1Advanced Chemistry Development, Moscow, Russia;• 2Advanced, Chemistry Development, Inc., Toronto, Canada;• 3Lexicon Pharmaceuticals, Princeton, NJ, USA
1H-Proton nmr carboxylated curcumin• For carboxylated curcumin, the proton spectrum differs from curcumin as follows.• First, the carboxyllic chain gives rise to protons at 11.0 (C-O-O-H) group, and 3 carbons at 2.02 ppm and 2 chemically equivalent at 2.30 ppm• (CHa2 –CHb2-CHa2)
• As for the ring structure, it is primarily similar to curcumin of course.• It shows an C-O-H proton at 5.35 ppm , and 3 aromatic ring protons at 7.16 ppm, 6.99 ppm and 6.79 ppm.• The aromatic protons next to the carboxyllic acid chain are now shifted to 7.30 ppm and 7.26 ppm
.• The are also 2 peaks at 3.83 ppm due to C-OH proton on both aromatic rings.
COSY• COSY is one of the simplest and most useful experiment. It is also one of the shortest 2D experiment. It needs a minimum of 4 transients on conventional spectrometer (see phase cycling - vector model or coherence pathway). With the addition of gradients, only one transient is needed which means that on a modern spectrometer, the very precious COSY information can be obtained in 5 min!!!
COSY• This 2D experiment is composed of a 90 degree pulse that creates magnetization in the transverse plane. During the evolution time, the variable delay t1 is incremented systematically in order to sample the spectral width indirectly. Following this variable time period, a second pulse mixes the spin states, transferring magnetization between coupled spins
COSY• The spectra is then acquired during t2 (detection time). After double Fourier Transformation, a spectra like the one below is obtained showing a diagonal component (for magnetization that did not exchange magnetization) and cross peaks (off-diagonal) for nuclei exchanging magnetization through scalar coupling.
COSY• The data is usually symmetrical respect to the diagonal and therefore the data can be symmetrized as part of the processing to improve the quality (care must be taken here to make sure that by getting rid of the non-symmetrical artefacts we are not also getting rid of precious information that might not be totally symmetrical). The data is usually acquired in a phase insensitive (magnitude mode) manner, avoiding the difficulty to phase a 2D data set