Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: molecule_787 on August 16, 2011, 04:23:03 AM
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Hello, I am looking for some help in interpreting the data from an HNMR report to confirm that it is the correct structure of the peptide Aldehyde "Proteasome Inhibitor I" (PSI).
Any help or details regarding the confirmation of the two is greatly appreciated. Please feel free to PM me if preferred.
Thank you very much
Peptide Aldehyde/Chemical Structure (examples)
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HNMR Report
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Hello, I am looking for some help in interpreting the data from an HNMR report to confirm that it is the correct structure of the peptide Aldehyde "Proteasome Inhibitor I" (PSI).
Any help or details regarding the confirmation of the two is greatly appreciated. Please feel free to PM me if preferred.
Thank you very much
Peptide Aldehyde/Chemical Structure (examples)
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OR
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HNMR Report
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Don't see the aldehyde proton! Can't see which solvent was used is it DMSO?
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I'm guessing you bought this and want to make sure its good? Your best bet with a peptide would be LC-MS-MS if you've got access to the instrument. If you don't, regular LC-MS would probably be OK. This proton spectrum looks pretty clean and free of crap, so as long as the mass works out I think its safe to assume they wouldn't spend all that time cleaning up a bad molecule.
The best way to do this by NMR would probably be to look up the spectrum and compare it to the one you've acquired. If you want to do this the hard way, you'll have to do a few more things:
1. Your spectrum cuts off before the region where aldehydes (which you're looking for), and carboxylic acids (which you don't want to see yet because yours is protected) show up
2. Get a 13C spectrum too. While not the largest molecule ever measured by NMR, you've still got 50 protons and 32 carbons in there and things get muddled. More information is better.
3. Consider some 2D experiments. Even the 90 MHz permanent magnet instruments can do those, and they tell you a lot.
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^ Thanks a lot for the information.
Yes you are correct, this is a peptide I have purchased and want to make sure that the compound is good/correct.
So basically, you are saying that by the NMR it looks clean and good but that a Mass Spec would help further due to its ability to determine the Molecular weight of 618.77 which if checks out then should solidify the identity of the peptide?
Or if I am off, please chime in. How would I go about looking up the "spectrum" and comparing it exactly...
I also have an HPLC report I can post but I know that really only relates to its purity, if that helps any please let me know and I can post it as well.
Thanks again.
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/szkd2u.png[/img]
Don't see the aldehyde proton! Can't see which solvent was used is it DMSO?
Hi, Yes the Solvent used was DMSO as indicated in the right hand column, I have highlighted it with a red arrow.
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So you are saying that the Aldehyde proton is missing? Obviously this is not good...?
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Since you've got the CAS#, I'd check scifinder or something similar for when it was first made. Someone had to have done an NMR spec on it, and you can compare. When it comes to the MS, make sure you know whether you're looking for the [m+H]+ or whatever you're set up to measure.
As for the proton spec you've posted. Do you have the spectrum file? You should be able to expand the view. Aldehydes tend to show up around 9 - 10 ppm and the field of view has been cut off right before this critical region.
Again, if you got it from a reputable supplier and the mass is right, there's really no reason to solve the structure for this thing. Unless, that is, you want practice solving structures but there's better molecules to start on.
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Since you've got the CAS#, I'd check scifinder or something similar for when it was first made. Someone had to have done an NMR spec on it, and you can compare. When it comes to the MS, make sure you know whether you're looking for the [m+H]+ or whatever you're set up to measure.
As for the proton spec you've posted. Do you have the spectrum file? You should be able to expand the view. Aldehydes tend to show up around 9 - 10 ppm and the field of view has been cut off right before this critical region.
Again, if you got it from a reputable supplier and the mass is right, there's really no reason to solve the structure for this thing. Unless, that is, you want practice solving structures but there's better molecules to start on.
Thanks, I will request an expanded file. I had the same idea in terms of finding an NMR spec on it and comparing but could not locate/find one anywhere online. I will try scifinder though.
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Number of protons seems to not fit with the structure (too less). Again, as mentioned already, aldehyde signal is missing.
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Number of protons seems to not fit with the structure (too less). Again, as mentioned already, aldehyde signal is missing.
It is sad that a commercial company cannot provide proper data for their products.
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Depends on the company ;D. Our customers always get a specific QoA with spectra, HPLC etc. This is what I call quality.
I would not wonder if that peptide has been delivered from China (or India). I had this problem several times too. After the compound received from China, NMR and LC-MS was performed. When it is crap it goes right back without paying anything.
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Depends on the company ;D. Our customers always get a specific QoA with spectra, HPLC etc. This is what I call quality.
I would not wonder if that peptide has been delivered from China (or India). I had this problem several times too. After the compound received from China, NMR and LC-MS was performed. When it is crap it goes right back without paying anything.
So do you think this peptide is crap? I did receive an HPLC report along with the NMR and they also have promised a Mass Spec.
Honclbrif said "This proton spectrum looks pretty clean and free of crap, so as long as the mass works out I think its safe to assume they wouldn't spend all that time cleaning up a bad molecule."
So now I am a bit confused?
Btw, do you know of any other labs that can offer this peptide at a competitive price? Feel free to PM me.
They should get back to me regarding the expanded view and missing aldehyde issue along with the Mass Spec. I will post their response for some further feedback.
Thanks again for the comments everyone.
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@ molecule_787
Google is your best friend:
http://www.emdchemicals.com/life-science-research/proteasome-inhibitor-i/EMD_BIO-539160/p_w_.b.s1LzxMAAAEW02EfVhTm?WFSimpleSearch_NameOrID=Proteasome&BackButtonText=search+results
5mg @ ~200 USD
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Number of protons seems to not fit with the structure (too less). Again, as mentioned already, aldehyde signal is missing.
By the way are you just referring to the missing Aldehyde Proton as the reason it is not fitting with the structure?
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NA
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Not only the aldehyde signal. Structure and spectrum does not fit somehow.
I would do LC-MS additionally.
I see a Z group and Boc, but the rest is a bit strange.
There are some companies outside which sell crap. Especially when they offer a very cheap price.
The Merck price is realistic. 3k for 1g seems a bit too cheap since these companies will make it (synthesis after request). No one will store large amounts of a (sensitive) peptide. I know what I write, I work for such a CRO company.
They should provide a proper NMR and LC-MS at least. When it fits you can order it. I would only pay after analyzing this stuff soon after receiving it.
I´m sure half of the providers will not answer to your spectra-request. This will separate the boys from the men.
Where are these labs from you ordered situated? China?
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It's the protons around 8ppm which concern me. The rest of the structure looks more or less plausible. The large signal around 7ppm is the 5 protons in the benzyl C-protection... but there's no reason there should be two signals around 8ppm.
The other part that concerns me is the 4-5 region. These should be the alpha protons between the C=O and the N for each amino acid. There are 4 amino acids in this chain, so there should be 4 protons here. Scaling up the integration values between 4-5ppm gives, from left to right, 2H, 1H, 1H, 2H, 1H. The 2H signal on the left is the two protons between the N-terminus and the benzene ring. That leaves 5 protons to account for. But there are only 4 amino acids. IMHO, there is one too many protons in this region.
The aliphatic region (1-3) is too messy to analyze, but a nice COSY spectrum would help.
IMHO, not the right structure... or at least not a clean sample.
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It's the protons around 8ppm which concern me. The rest of the structure looks more or less plausible. The large signal around 7ppm is the 5 protons in the benzyl C-protection... but there's no reason there should be two signals around 8ppm.
IMHO, not the right structure... or at least not a clean sample.
They are probably some of the NH protons, I can't read the intensity on this picture, it's too small for my bad eyes!
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I dunno... I guess. But only 2, not 4? They look too regular and sharp for me. Almost like a plasticizer or some such impurity.
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I have included the NMR from another supplier. These are two separate "PSI" peptides/compounds produced by two separate labs. The structures to the "untrained" eye appear quite similar with the exception of the missing Aldehyde which appears to show up in between the 9 - 10 ppm in the NMR report from Lab B (as several of you stated it should).
Any comments on the similarities or differences would be most appreciated. Is Lab B's compound of any significant difference? If so, does it appear to be the correct structure of the desired Tetrapeptide Aldehyde PSI, posted at the top of the thread? I have also included the Mass Spec from Lab B which appears to be on target with the Mass weight of the peptide which is 618.77 and Lab B's peptide peaks on the Mass Spec report at around 619.5.
Still trying to seek out an NMR that was done on the original PSI peptide for further comparison.
LAB A (CHINA) NMR REPORT
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LAB B (USA) NMR REPORT
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LAB B (USA) MASS SPEC REPORT
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Any insight regarding the above reports and their relation to the correct PSI structure is again appreciated. Thank you.
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Who integrates these spectra!
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Not only the aldehyde signal. Structure and spectrum does not fit somehow.
I would do LC-MS additionally.
I see a Z group and Boc, but the rest is a bit strange.
There are some companies outside which sell crap. Especially when they offer a very cheap price.
The Merck price is realistic. 3k for 1g seems a bit too cheap since these companies will make it (synthesis after request). No one will store large amounts of a (sensitive) peptide. I know what I write, I work for such a CRO company.
They should provide a proper NMR and LC-MS at least. When it fits you can order it. I would only pay after analyzing this stuff soon after receiving it.
I´m sure half of the providers will not answer to your spectra-request. This will separate the boys from the men.
Where are these labs from you ordered situated? China?
Yes, they have only done the synthesis to order but of course we require HPLC, NMR and Mass Spec to confirm correct structure and purity before shipping and payment. Also have a third party lab set up to re-test the delivered product if the HPLC, NMR and Mass Spec check out from the original labs.
LAB A is based in China
LAB B is based in the USA
I know you know your stuff and I respect your insight and opinion very much, hence why I am here. ;D
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I dunno... I guess. But only 2, not 4? They look too regular and sharp for me. Almost like a plasticizer or some such impurity.
I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.
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I dunno... I guess. But only 2, not 4? They look too regular and sharp for me. Almost like a plasticizer or some such impurity.
I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.
What are your thoughts specifically on the two different NMR's from the two different suppliers on two different peptides? Does the US lab appear to be the correct structure in your opinion?
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I dunno... I guess. But only 2, not 4? They look too regular and sharp for me. Almost like a plasticizer or some such impurity.
I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.
What are your thoughts specifically on the two different NMR's from the two different suppliers on two different peptides? Does the US lab appear to be the correct structure in your opinion?
At least you see the aldehyde signal, although the resolution does not seem to be so good. Run a reverse phase HPLC to check out both samples.
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Seems Lab B has done a proper job. NMR does not look nice but correlates with the structure and taking also the mass-spec into account I´m convinced.
Lab B is the winner ;D
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Seems Lab B has done a proper job. NMR does not look nice but correlates with the structure and taking also the mass-spec into account I´m convinced.
Lab B is the winner ;D
I fail to see why the could not get the spectrum in phase and get a better resolution. I would not accept this from my co-workers. It looks as if lab B has the correct structure.
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Yeah I would not send such a crude spectrum too. Seems their Quality Management is not working properly ::)
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Yeah I would not send such a crude spectrum too. Seems their Quality Management is not working properly ::)
^You are referring to the "unpolished" LAB B report/paperwork, correct?
When you say LAB B has done a proper job but the NMR does not look nice I assume you are simply referring to just the quality/resolution of the paperwork/report. I did ask/inquire about this also and was given an apology along the lines of it being substandard and that the issue will be addressed internally et.
So the consensus is that LAB B has done a correct job, the peptide is clean and the structure is correct as per NMR and MS. So LAB B seems to be the better choice and more importantly, a legitimate one.
The USA based lab as oppose to the China...
Just a FYI, the HPLC came back at >98% for LAB B and only around 91% for LAB A but LAB A stated that they could try and bring up the purity to 98% et. We require a minimum 98% purity.
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According to that NMR which lab B sent, this compound is far from being >98% pure. They should really provide a much better NMR. This one is a joke.
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Somehow neither of those spectra manages to convey the message "freshly measured from the stuff we sent/will send you".
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I'm going to preface my statement with the admission that I am neither a NMR spectroscopist or an expert in the specifics of peptides. But... I think a lot of people's assessment of the NMR's has been somewhat 'unfair' it's easy to be critical of someone else's work.
I suspect that the NMR spectra are generally fine (perhaps apart from the missing aldehyde peak). Some factors that I think are worth considering are:
Rotamer effects
Tumbling/averging effects - by which I mean NMR relies on the concept that the molecules tumble freely - as only the N-terminus of the peptide is protected, I suspect that it is likely that there aggregates forming in the tube - in which case these large aggregates would tumble more slowly - meaning that the averaging effect is probably not working properly.
I'll concede that those two statements are somewhat speculative, and I'd be happy to hear the opinions of others if they disagree.
In the end as others have stated I think that a proper assessment should be based on HPLC-MS (if you really doubt the purity, perform your own analysis on their product - if it doesn't match their stated purity levels you would be in your rights to request a replacement of the sample with one of the quality that they promised to supply or a refund)
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According to that NMR which lab B sent, this compound is far from being >98% pure. They should really provide a much better NMR. This one is a joke.
Below you will find the HPLC reports from both LAB A and LAB B. What are your thoughts on it? I read the results/purity as: LAB B (97.87%) and LAB A (91.46%), correct?
@ the.khemist.ds, arit and anyone else who would like to chime in,
please feel free to also further/add your opinion on the HPLC reports and overall purity.
*I have whited out some of the sensitive information regarding lab names, files et. for privacy reasons.
LAB A (CHINA) HPLC REPORT (91.46%)
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LAB B (USA) HPLC REPORT (97.87%)
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My response would be: Looking at the two chromatographs, the approach to peak area measurement is not the same (ie you are not comparing the same data) the main point is that lab A have treated the shoulder at RT 7.887 as a separate peak. Looking at lab B's report, you can see a similar shoulder which is not treated as a separate peak.
Of course any assessment is based on the principle that the chromatographic conditions are suitable to separate impurities from the desired peptide.
In the end, you have to either make the peptide yourself or assume that the supplier can provide the product at the specification they have stated - this isn't saying that you shouldn't perform your own QC when you receive the sample (remember that whatever data they provide is only true about the sample they measured at that time and it is possible that the sample you receive may be of different quality for any number of reasons)
If you are interested in other possible suppliers check out ChemSpider (I think the correct record is: http://www.chemspider.com/Chemical-Structure.8136267.html)
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My response would be: Looking at the two chromatographs, the approach to peak area measurement is not the same (ie you are not comparing the same data) the main point is that lab A have treated the shoulder at RT 7.887 as a separate peak. Looking at lab B's report, you can see a similar shoulder which is not treated as a separate peak.
Of course any assessment is based on the principle that the chromatographic conditions are suitable to separate impurities from the desired peptide.
In the end, you have to either make the peptide yourself or assume that the supplier can provide the product at the specification they have stated - this isn't saying that you shouldn't perform your own QC when you receive the sample (remember that whatever data they provide is only true about the sample they measured at that time and it is possible that the sample you receive may be of different quality for any number of reasons)
If you are interested in other possible suppliers check out ChemSpider (I think the correct record is: http://www.chemspider.com/Chemical-Structure.8136267.html)
Thanks for your response. It is my understanding that the sample reports of the HPLC and results will always be variable meaning it is an average taken at a certain point in time as the structure itself will never be completely uniform or the results consistently exact et. However my own or third party QC to verify structure and purity should be within the stated or same parameters.
Basically, what you are saying is that the HPLC reports do reflect the stated percentages in regards to purity and the separation of impurities (albeit by different methods/means) but what it comes down to is whether or not I can lend credence to the supplier and that they will supply the peptide at the stated purity from these reports, correct?
LAB A has stated that they are going to bring the purity level up to 98%, they just wanted me to verify that the compound/structure (HNMR report) is satisfactory before they proceed in furthering the purification and yield et.
As stated, I have sent them an email stating that the HNMR report is unsatisfactory due to the missing Aldehyde signal and the ppm being cut off on the report at the critical region et. They have responded by forwarding the information onto their engineers and will forward a revised document. So I will likely post that for further feedback once it arrives.
In my humble opinion, I don't think LAB B would go to the trouble of fabricating an HPLC when they have produced (what appears to be) supportive data (HNMR and Mass Spec) that is satisfactory in terms of verifying the compounds identity et. The quality/resolution of the report is an issue in itself but the data, from what others have stated, seems to be accurate with the desired compound. Would you agree with this statement?
I have in fact contacted a 3rd supplier and received an initial quote with a guarantee of purity and identity of the peptide with supportive data of a HPLC and Mass Spec. They will not however, produce and provide tests until I commit to an order, at which point, they will provide a written guarantee in regards to the purity and identity by internal test reports et. Obviously if things were to not mesh, the guarantee would be void and funds reimbursed (as you outlined).
Essentially, it would seem that LAB B has the correct or desired structure and purity, so purchase from this lab and third party verification is an option with this supplier. I will however, perhaps wait on LAB A to correct and forward the HNMR so it includes the missing information. Still, some of the other experts in this thread have stated that LAB A seems to be slightly off not only due to the missing Aldehyde signal but also on the subsequent structure itself.
Thank you again for your time and comments.
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My other question is, can the identity and purity of this peptide be properly verified by HPLC and Mass Spec alone? Is including a HNMR vital in determining the identity of the compound?
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My other question is, can the identity and purity of this peptide be properly verified by HPLC and Mass Spec alone? Is including a HNMR vital in determining the identity of the compound?
If you run the HLPC against a known standard compound you can measure the content in your sample, otherwise it's just area%.
The NMR is not vital but it does give a lot of structural information, for example, it will indicate if the compound has epimerised, i.e. a mixture of diastereoisomers. A 2D spectrum would also be nice to have as well as a 13C.
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Any other thoughts on the HPLC reports and stated purity, specifically LAB B's?
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The LC's look pretty good, but I don't know the method of detection. Probably UV. Could hide something depending on the detection wavelength, but I prefer to believe in the intrinsic goodness of Humanity (feel free to laugh here). Your MS has a big fat 619.5 peak which I'm assuming is your [m+H]+, and a 641.5 which is probably [m+Na]+. I've no idea what the 673.7 peak is, but its about 54 units too heavy. Works out to the mass of 3 H2Os. Might be a coincidence, might not. When I do MS of peptides I don't see H2O bound, but I've got fairly harsh ionization conditions.
My major concern in all this is that, as others have pointed out, the NMRs are a little wacky for a couple of reasons:
A. One lab cut off before the critical aldehyde region. Makes it look like they either don't know what they're doing or they have something to hide. Neither smells good.
B. Both specs' integrations are all over the place. In the first one they picked a random peak to be A = 1, in the second (seriously, who phased that thing?) they picked the aldehyde to be A = 1, but the phenyl group integrates to 12.5. They're both soaking wet so the aldehyde may have hydrated making it look like the aldehyde peak is smaller than it really is. I haven't done many NMRs of aldehydes in wet DMSO, so I don't know if this happens readily under those conditions or not.
Overall: You've got a clean HPLC, and an MS that has the right mass as the major peak and those facts are difficult to ignore. If you can get an MSMS you'll know the sequence and that should eliminate pretty much all doubt. Based on the LC and MS evidence I'm inclined to believe its probably the right compound and there's some weirdness happening in the NMR for what could be many reasons. If you can afford to use it, I'd go ahead and try a positive control. If it fails, you know the stuff is bad, stop using it, make a really angry phone call to the supplier, and try to get your money back and get it from a better supplier. If you can't afford to use it in an experiment skip all that, get your money back, and get it from a better supplier.
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The LC's look pretty good, but I don't know the method of detection. Probably UV. Could hide something depending on the detection wavelength, but I prefer to believe in the intrinsic goodness of Humanity (feel free to laugh here). Your MS has a big fat 619.5 peak which I'm assuming is your [m+H]+, and a 641.5 which is probably [m+Na]+. I've no idea what the 673.7 peak is, but its about 54 units too heavy. Works out to the mass of 3 H2Os. Might be a coincidence, might not. When I do MS of peptides I don't see H2O bound, but I've got fairly harsh ionization conditions.
My major concern in all this is that, as others have pointed out, the NMRs are a little wacky for a couple of reasons:
A. One lab cut off before the critical aldehyde region. Makes it look like they either don't know what they're doing or they have something to hide. Neither smells good.
B. Both specs' integrations are all over the place. In the first one they picked a random peak to be A = 1, in the second (seriously, who phased that thing?) they picked the aldehyde to be A = 1, but the phenyl group integrates to 12.5. They're both soaking wet so the aldehyde may have hydrated making it look like the aldehyde peak is smaller than it really is. I haven't done many NMRs of aldehydes in wet DMSO, so I don't know if this happens readily under those conditions or not.
Overall: You've got a clean HPLC, and an MS that has the right mass as the major peak and those facts are difficult to ignore. If you can get an MSMS you'll know the sequence and that should eliminate pretty much all doubt. Based on the LC and MS evidence I'm inclined to believe its probably the right compound and there's some weirdness happening in the NMR for what could be many reasons. If you can afford to use it, I'd go ahead and try a positive control. If it fails, you know the stuff is bad, stop using it, make a really angry phone call to the supplier, and try to get your money back and get it from a better supplier. If you can't afford to use it in an experiment skip all that, get your money back, and get it from a better supplier.
Ok great, thanks for the insight. I was thinking along the same lines due to the clean HPLC and MS from LAB B. The NMR has some odd points but the general consensus was that overall it correlates with the desired structure.
I will await for LAB A to forward a revised NMR and also include a MS to make a final decision on that supplier. (I will likely post their results again for some feedback).
I have a third supplier lined up should the third party HPLC and MS testing on LAB B's peptide show any discrepancies et.
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The LC's look pretty good, but I don't know the method of detection. Probably UV. Could hide something depending on the detection wavelength, but I prefer to believe in the intrinsic goodness of Humanity (feel free to laugh here). Your MS has a big fat 619.5 peak which I'm assuming is your [m+H]+, and a 641.5 which is probably [m+Na]+. I've no idea what the 673.7 peak is, but its about 54 units too heavy. Works out to the mass of 3 H2Os. Might be a coincidence, might not. When I do MS of peptides I don't see H2O bound, but I've got fairly harsh ionization conditions.
My major concern in all this is that, as others have pointed out, the NMRs are a little wacky for a couple of reasons:
A. One lab cut off before the critical aldehyde region. Makes it look like they either don't know what they're doing or they have something to hide. Neither smells good.
B. Both specs' integrations are all over the place. In the first one they picked a random peak to be A = 1, in the second (seriously, who phased that thing?) they picked the aldehyde to be A = 1, but the phenyl group integrates to 12.5. They're both soaking wet so the aldehyde may have hydrated making it look like the aldehyde peak is smaller than it really is. I haven't done many NMRs of aldehydes in wet DMSO, so I don't know if this happens readily under those conditions or not.
Overall: You've got a clean HPLC, and an MS that has the right mass as the major peak and those facts are difficult to ignore. If you can get an MSMS you'll know the sequence and that should eliminate pretty much all doubt. Based on the LC and MS evidence I'm inclined to believe its probably the right compound and there's some weirdness happening in the NMR for what could be many reasons. If you can afford to use it, I'd go ahead and try a positive control. If it fails, you know the stuff is bad, stop using it, make a really angry phone call to the supplier, and try to get your money back and get it from a better supplier. If you can't afford to use it in an experiment skip all that, get your money back, and get it from a better supplier.
By the way, Have the coupling constants for the multiplets (doublets, triplets, etc.) been picked out in both these NMR's?
Thanks
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Unless they sent them over in a separate document, no. The spectrum from LAB A needs better S/N-ratio to start to estimate couplings and multiplicities.
Spectrum from LAB B on the other hand suffers from horrible shimming and phasing, and I wouldn't even try to calculate the couplings or guess multiplicities.
Both spectra would have gained a lot from a more homogeneous magnetic field, and maybe from a higher field spectrometer.
As to the integrals, LAB A hasn't even bothered to aim for quantitative spectra (D1 1s, NS 120). 1 second isn't probably even the average T1 for the compound,
and ideally you'd want it somewhere around 10*T1 for quantitative purposes. I'd assume spectrum from LAB B suffers from same problems, but can't really tell
since the parameters are cropped out.
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Unless they sent them over in a separate document, no. The spectrum from LAB A needs better S/N-ratio to start to estimate couplings and multiplicities.
Spectrum from LAB B on the other hand suffers from horrible shimming and phasing, and I wouldn't even try to calculate the couplings or guess multiplicities.
Both spectra would have gained a lot from a more homogeneous magnetic field, and maybe from a higher field spectrometer.
As to the integrals, LAB A hasn't even bothered to aim for quantitative spectra (D1 1s, NS 120). 1 second isn't probably even the average T1 for the compound,
and ideally you'd want it somewhere around 10*T1 for quantitative purposes. I'd assume spectrum from LAB B suffers from same problems, but can't really tell
since the parameters are cropped out.
Ok, thanks again for the info arit. By stating that LAB A has not even bothered to aim for quantitative spectra ie. 1 second is probably not even the average T1 for the compound, you are referring to a form of its relaxation rate in the NMR test, correct?
T1 relaxation are generally strongly dependent on the NMR frequency and so vary considerably with magnetic field strength. Small amounts of paramagnetic substances in a sample speed up relaxation very much. By degassing, and thereby removing dissolved Oxygen, the T1/T2 of liquid samples easily go up to an order of 10 seconds. Correct? So in other words, LAB A has not even bothered to attempt to gather this data properly so it appears the average T1 stated (1 sec) could be incorrect because of this?
LAB B you cannot draw any conclusions on in regards to the relaxation rate or T1 for the compound because the parameters are cut off but you are assuming that they have not even bothered to aim for quantitative spectra (ie. T1 et.)?
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Also, is it fair to say that these suppliers have used a simple 1-dimensional proton NMR spectrum? It wouldn't be a 2D spectrum (such as a COSY or NOESY)?
Thanks.
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Yes, I'm making a point about how in quantitative measurements you want the relaxation delay (D1) to be 10*T1. This follows
from the fact that at 10*T1, 99% of the spins have returned back to their equilibrium state, and you get the same amount of signal
when repeating the experiment.
When the relaxation delay is shorter, the spectrum can still be fine, just not reliably quantitative. The length of the delay doesn't of course
matter if the number of scans is 1.
To put it shortly, LAB A hasn't aimed for quantitative spectra. Either knowing what they were doing or not.
LAB B you cannot draw any conclusions on in regards to the relaxation rate or T1 for the compound because the parameters are cut off?
I can't tell whether the relaxation delay LAB B used is in the general vicinity of a "usual" T1 for a smallish organic molecule. The actual relaxation rate is a property of the sample, not experiment setup. Just the fact that the parameters are cut off raises a few questions in my mind, but I tend to worry too much
anyway. Since the parameters aren't there, you can't tell what relaxation delay, window function, line broadening etc. settings they used that might have an
effect on the spectrum. Actually, even calculating the coupling constants would be difficult, since you don't know the operating frequency of the spectrometer.
And yes, both suppliers have sent just plain 1D proton spectra. Which of course doesn't mean that they wouldn't have used an array of 2D experiments
in their internal QA process.
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^Once again, thank you very much for the explanation arit.