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Author Topic: NMR Help for Compounds Only Dissolving in Water  (Read 751 times)

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michaelduffy39

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NMR Help for Compounds Only Dissolving in Water
« on: July 11, 2018, 01:32:14 PM »

Hello,

I was hoping that someone could help with an NMR problem.

We have several compounds that we need to take an NMR of, however, they are only dissolving in water. We took the NMR using deuterated H20, and the water peak at around 4.7 ppm drowns out the rest of the NMR. We have tried dissolving the compounds in typical organic solvents. However, all the solvents and even DMSO is not dissolving the compounds.

1. Is there anyway I can take an NMR of a compound, that is VERY solluble in water, but not much else, and still get a readable NMR.

2. Does anyone have any suggestions of other solvents we can use to maybe dissolve the compound?

Thanks!
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Babcock_Hall

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #1 on: July 11, 2018, 03:27:16 PM »

Can you dry your compound to remove non-deuterium labeled water that may be associated with it?  Can you dissolve in D2O, remove the solvent in vacuo, then dissolve it again?  If neither of these are realistic options, there are various water suppression NMR experiments, or water non-excitation schemes.  The simplest version of the former is to saturate the water peak with a long, low-power pulse.  The simplest version of the latter is a jump-return experiment, in which the water signal is returned to the z axis.
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wildfyr

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #2 on: July 11, 2018, 03:41:45 PM »

What about some more exotic solvents? Deuterated methanol comes to mind.

Does it melt or exist as an oil? You could do it neat if you have enough.

What about using only 10% D2O in DMSO-d6.
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michaelduffy39

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #3 on: July 11, 2018, 04:58:14 PM »

Thanks for the input. I will try some of these suggestions tomorrow!
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OrganicDan96

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #4 on: July 13, 2018, 02:49:46 AM »

are you sure it has no solubility at all in other solvents? it might have very slight solubility in something like DMSO. if you add some solvent of choice you can filter off the undissolved solid and record an NMR with an increased number of scans to compensate for the very low concentration.
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Irlanur

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #5 on: July 16, 2018, 04:17:00 AM »

Presaturation or something equivalent. Ask your local Protein-NMR guy.
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kriggy

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Re: NMR Help for Compounds Only Dissolving in Water
« Reply #6 on: July 18, 2018, 02:24:47 AM »

maybe use higher concentatio of the sample? or maybe your D2O is contaminated with water. I suggest using new batch of the solvent and dry the sample thoroughly before because you might have residual water in it that makes the spectra bad.
Also, there are many different solvents you might try as well.. Deuterated acetone, alcohols.. or mixture of them with D2O
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