I have synthesized a poly(glutamine) sample and am currently analyzing it using NMR spectroscopy. I am facing challenges in differentiating the -NH protons from the backbone of the structure and the -NH2 from the side chain. Although I can see the -NH protons from the backbone, it is proving difficult to identify the -NH2 signal from the side chain. I ran a proton spectrum (in DMSO-d6) and observed a slight chemical shift change, confirming the backbone's amide attachment. I also ran a 15N spectrum, but I had no luck. Do you have any ideas about how I can differentiate both? What else I can try to confirm amide presence in my polymer's side chain?
Jamie Singleton Thank you. The product does not dissolve in various solvents. I tried to change the solvent system, but I still got a similar outcome.
Try drop of D2O in DMSO-d6 to do the NMR again to see the H-D exchange? NH2 will exchange much fast than NH of amide.
Maybe cpmapre the H1NMR in D2O and DMSO-d6?
Alternatively, you always can decouple by performing a single frequency irradiation to simplify the spectra.
Dear Nirupama,
- a simple (multiplicity edited) 2D 1H-15N HSQC experiment should do....the 15N shifts are expected to be different (119 (NH), 111 (NH2) ppm 15N shift). With multiplicity editing also the sign of the "blobs" should be different.
- For multiplicity editing the sequence hsqcedgpph in the Bruker library should do.
- Note: Sensitivity depends on the line-width you have....if it is much broader than 90 Hz it will get difficult due to relaxation. In this case I would not use the multiplicity editing and the hsqcgpph sequence should do (not knowing whether you have a Bruker instrument).
- In your 1D 1H you need a Signal/Noise of your relevant signal in the range of 300/1...with 8 scans. If this is the case the 2D experiment (256 increments, 8 scans) should work within about 1 hour ... Note: if you have 10 fold less Signal/Noise the experiment might take 100 fold longer - which is about one long weekend.
- In my experience direct 15N NMR NEVER worked within acceptable time.
I hope this helps - good luck
Alfred
P.S. have you seen this: Article Solubilization and disaggregation of polyglutamine peptides
Simply take a small amount of your polyglutamine and let is react with 2N HCl during a couple of hours which will hydrolyze the glutamine end groups. you will obtain a polyglutaminic acid substance.
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