Nuclear Magnetic Resonance - Science method

I saw the 19F NMR of a compound HFPO-DA. I find that the chemical shifts of two fluorines attached on same carbon atom varies by 3.3 ppm. I understand the vicinity of O plays a role. But, can someone explain the mechanism behind such a huge difference? Are there any specific effects other than the inductive effect of oxygen?

Hi, I'm evaluating the biological activity of a plant extract and in the HPLC analysis we found a compound with a peculiar UV spectrum. I still need to do chromatography tests to purify the compound and do an NMR, but does anyone have any idea what compound it could be? It has a peak at 222 and a double peak at 280.

In P NMR, Due to the higher electronegativity of the O atom than the S atom, and higher pi-characteristic of the P=O bond than the P=S bond, it is expected that the signal of P atom in P=O group appear at higher chemical shifts than P=S. But, experimentally this trend is in converse. The P=O signal appears at about 30-50 ppm lower than P=S. For example, for compounds P(=O)(NHBu)₃ and P(=S)(NHBu)₃ the P signals appear at 25 ppm and 60 ppm, respectively. How this trend can be justified?

According to the general theory of electron attraction, I thought the central C in carbonates should have larger chemical shifts than in carboxylic acid esters because it is bonded to one =O and two -O, whereas the latter is bonded to one =O, one -O, and one -C. But the experimental result and software prediction both show that the chemical shift of carboxylic acid esters are higher than carbonates. Can you explain this phenomenon?

I ran an NMR of my compound using CDCL3 but the water peak is tall despite drying for a long time using vacuum pump. How can I eliminate the long water peak

Hi Everyone I got clear NMR spectra for the copper complex? Although it is paramagnetic, copper(II) complexes do not give a clear and usable signal. How do I explain this?

Hello, has anyone had experience with a monomer/vinyl group containing oil (it's pretty thick, like a slime, known to be pure with NMR) for XPS analysis?

Advice appreciated,

thanks

I graduated with a master's degree this year and am currently working as a researcher specializing in ionic liquid synthesis.

I am currently synthesizing EMIM TFSI, and after reviewing 40 papers, I have established a procedure and am conducting the experiment as follows:

(Weighing reagents was performed inside a glove box, and the reaction was carried out in an ambient environment using parafilm)

I uploaded two NMR results: one from the synthesized EMIM TFSI and the other from commercially available EMIM TFSI for comparison.

Upon examining the NMR, I can confirm that the reaction has proceeded, as the EMIM TFSI peak is visible. However, there are still peaks from unreacted EMIM+ cations present

(Looking at the integration, the peaks show that EMIM TFSI cation, an additional EMIM cation, and water are present in a 2:1:1 ratio).

I thought this result is due to the hygroscopic nature of EMIM Br and Li TFSI, which leads to hydration, reducing reactivity and forming a water shell that prevents the reaction. To address this, I performed weighing in a glove box and repeated the experiment.

Nevertheless, the NMR results were similar to those obtained when the glove box was not used.

Therefore, I began to think that I might have been misunderstanding the cause all along, and I’m seeking advice by asking this question.

If there’s anything I might be overlooking, please let me know. I would also be incredibly grateful if you could share any insights or experiences you have regarding NMR results appearing in this form.

Thank you once again for taking the time to read through this lengthy message.

I have Processed tha data.Fit every data with different delay time in a lorentzian function.But on calculating area under the curve to fit it with final equation I am unable to calculate with correct area..could anyareaplease solve my problem...Thank you ..

I need interpretation of following attachments

How can I achieve high precision in differentiating two-bond, three-bond, and four-bond couplings when analyzing HMBC NMR data? Are there any particular experimental or computational approaches that can be employed?

Dear Community,

I am conducting DEPT135 and DEPT90 NMR experiments within the scope of structure elucidation. However, the latter experiments are giving some odd results, I mean not as expected: CH3 and CH having a phase opposite to that of CH2 in DEPT135, and DEPT90 displaying CH groups, only.

What can I do to resolve this problem, knowing that all the performance tests gave good results?

I've got several samples of the same polymer and have reacted them with different plasticisers. On the NMR of all the samples but one, the peaks that I expect to be present in everything are roughly the same width, however for one of the samples, these very same peaks are significantly wider. Is there any reason behind this?

We performed liquid phase NMR with deuterated DMSO as our solvent of a number of treated FAI samples. For all samples we observe a slight shift in the H2O signal (~3.36 ppm instead of the expected ~3.30 ppm), which we assume to be due to interactions between H2O and the FAI. However, one of the samples seems to present an asymmetric H2O peak (attached), which we interpret as a second peak overlapping our first. Our first assumption is that this is evidence of a new material that is interacting with our H2O separately from our main sample. Are there other reasonable assumptions that we could test for?

Our process performs shimming automatically and we have not had issues with shimming on any other measurement. The water signal in our samples should be due to water contamination of our DMSO as our sample should not contain water. We expect the sample to be mildly acidic.

To add additional context, FAI refers to Formamidinium iodide (CH5IN2)

Dear NMR experts,

I am looking for a reference with information on the dependence of the chemical shift of typical NMR solvents if varying amounts of acid (e.g. HCl, TFA, MSA...) are present in solutions? Thanks in advance for any hint.

Alfred

P.S. normally one can't see this pH effect due to locking, but if NMR data are measured without lock it is easily seen.

I have a peptide that i cant express in E. coli cells, so i wanted to try with cell free expression kits.

I want to know what yield can i expect and since the idea is to use my peptide for NMR, is it possible to somehow incorporate labeled C and N (i guess not, since there are not cells to metabolize them, so is there any way to overcome that?)

I am using a Bruker 600M solid-state NMR spectrometer with a Micro 2.5 microimaging system. The test sample is a tube of 1M LiCl aqueous solution, and the nucleus detected is 1H. I am trying to use this sample to debug the UTE pulse. However, in the actual sampling process, the results obtained with UTE often have very strange artifacts. Since the ParaVision manual provides only very limited content, I would like to know the following:

I have attached the NMR data

Hello everyone,

I am facing a consistent issue in my NMR spectra with an unwanted peak appearing at 1.25 ppm. This peak seems to vary with the amount of sample: it becomes more pronounced with smaller sample amounts and diminishes when the sample amount is larger.

Here are some details about my attempts to resolve this issue:

1. Ensured the purity of my solvent.

2. Thoroughly cleaned the NMR tubes.

3. Used fresh samples.

4. Heated the samples in an oven at 100°C.

Despite these efforts, the peak persists. Could anyone provide insights into the potential sources of this peak and suggest effective strategies to eliminate it?

Thank you in advance for your assistance!

Hi folks.

I am looking for alternative ways to study water distribution and mobility in my food sample. Typically time-domain NMR is employed to identify the T2 relaxation time corresponding to free, bound and immobilised water but we dont have the instrument here in my area. I've found a promising (and validated) method using NIR spectroscopy, however it is run on FTIR and requires wavenumber up to 5500 cm-1 to capture the water band. Again, the FTIR I have access to only provide information until 4000 cm-1.

Is there any way I can obtain this information other than the said methods?

Dear Community,

I would like to develop and validate a qualitative NMR method for the analysis of a specific category of chemicals, and my question is the following: What are the criteria that I must assess?

I found a publication that states that the Limit of detection (LOD), the specificity and selectivity (NMR is inherently specific though), and Robustness must be investigated for a qualitative NMR method. But then what would be the experimental protocol to assess those criteria? For example: is there a need to perform the same experiment multiple times (on the same sample) and calculate the standard deviation for the estimation of the LOD, or just one experiment would be enough?

I would be more than grateful if someone experimented with NMR method development could provide more details on the subject.

Thank you.

I isolated a mixture of three compounds from the stem bark of a plant . I have NMR, Mass spec, IR, and UV data. There are a lot of things I can't make meaning out of. Kindly help me with the elucidation of the structures

Solid state NMR study

HI everyone

I'm looking for stander NMR spectra of Decyl gallate (CAS# 19198-75-5) for citation. I tried Wiley spectral Databases and NP-MRD Databases, but there was no result.

Hi, everyone. I am doing CO2 reduction experiments and I wanted to use NMR to detect the liquid products formed. My media is organic (CH3CN). I have seen some similar works by Prof. Kubiak, et al. that use 1H-NMR to detect the liquid products (particularly, formic acid) in CD3CN but the NMR sample requires the addition of Verkade's base. I am not so familiar with this compound. Does anyone know why (1) the peak of formic acid is not visible (supposedly around 8.02 ppm) if you do not add this base, and (2) what happens between the base and formic acid that causes a peak at 8.50 ppm to occur? Thank you so much!

Can I take 13Carbon NMR in quartz NMR tube? Or should it be done in glass (borosilicate) NMR tube?

Reason for the disappearance of O-H peak in NMR

I made an attempt to synthesize an unnatural amino acid containing phenyl group. In the last step of the synthesis I deprotected trityl protected amino group using 1N HCl aq., extracted, collected aq. layer, neutralized it with NaHCO3 aq. till pH roughly 8, evaporated water and used it further in deprotection of methyl ester group using LiOH monohydrate, quenched reaction with water, neutralized the media and purified the residue by reverse column. After purification i can see a strange impurity in the downfield region of the NMR, it looks like a second set of peaks resembling the product (amino acid) peaks but in the upfield region, i did not observe any extra methine and benzylic proton peaks. The amino acid synthesis started from pure enantiomeric starting material. So, I am not sure what could happen during the deprotection step. I would appreciate your help or any suggestions. Thank you. I will attach a proton NMR of the aromatic region where impurity is observed.

I have a macrocyclic complex which is a 1,6-diazacyclodecane which is functionalized with alkyl groups on the amines. I only see one peak on the mass spec so I do not believe there are secondary products or impurities. The NMR looks pretty good except for the fact that some of the signals do not integrate for the correct amount of protons. What could cause these errors in integration if it is not secondary products or impurities?

What would be the best pulse program to obtain a NOESY spectrum with the best peak resolution and shortest acquisition time on a Bruker Avance IIIHD NMR spectrophotometer?

Why is it that in the attached image: H4 is not coupling with C5, C6 if they are separated by two bonds?

Why does H3,5 giving a cross peak with C3,5 if they are pertaining to equivalent centres?

Why are the peaks of C8 not in a cross peak with H8?

I am asking because when I have para substituted systems in my organic molecules I am observing the same phenomenon.

Is there a technological niche in pharmaceutical research that makes NQR or NMR the only measurement methods practically applicable?

If we have an host-guest complex, in water an equilibrium occurs. So you can have

ComplexGuest + H2O <-> ComplexFree + GuestFree.

So I can calculate equilibrium constant, but in the most of papers they used NMR: at 5-6 different temperature you see different signals and with their ratio and different T ( plot linearly together) you can calculate Keq. (using Van't Hoff)

Do you know a method that doesn't use the VT NMR ? any kind of method also other types of techniques.

complex are around 2,000 g/mol and are just well soluble in water/DMF

Thanks

Is there a technological niche in pharmaceutical research that makes NQR or NMR the only measurement methods practically applicable?

how to convert .jdf NMR file to Topspin compatible format?

What are the typical excitation frequency

I heard it has to do with the population ratio, energy difference and Boltzmann factor.

Is it possible to convert a fid file of NMR to any of the following formats - PDB/mmCIF/XML/UCSF

in order to be able to make a characterization NMR?

My protein of interest is an intrinsic disordeed protein. I tried BL21 (DE3) CBV-101, and C43. We have tried 18C overnight, 30C 5h and 37C 3h expression. The BL21 and CBV got killed because the protein leaked and is toxic to these two strains. C43 did not have a great amount of leak and is very healthy at the time of induction They all generate great IPTG inductions. Cells lysis was done by lysis buffer of T4lysozyme incubation with triton 100, protease inhibitor, PMSF 1mM, BME 1mM, 10%glycerol high salt buffer and room temperature shake for 15minutes, followed by sonication 40% amp 15s on 45s off for 5 cycles on ice. The cells were centrifuged at 18000rpm 1H. After His NTA column (by the way I am using the pSMT3 vector which has RBS followed by His-SUMO tag), 50mM,100mM, and 500mM imidazole elution were done. However, I do see my protein came out at 50mM using Western blot, and 100mM had more come out. Surprisingly no protein came out at 500mM imidaozle. While the100mM imidazole elution give me a relatively pure protein, the protein has three bands, a band of its own, a band right below(also same protein after western blot), and a band 10+Kda below. This lower band can also be my protein but because my antibody did not capture it, I wasn’t so sure but my antibody capture the C end so that could still be my protein. All three bands are tightly close and FPLC cannot be possible to purify them.

I am curious that at this situation, if I want to run a NMR do I have to have the pure protein without truncation? Or it is fine to probe the NMR? How do you avoid the truncation after all? Do you have experience on this type of protein and how do you handle them? do you think the truncation was caused by protease or RBS binding?

I want to see the interaction between lipid NPs and proteins by NMR, but I am unsure which solvent is the best.

Sometimes I need to use the NMR tube containing my sample several times. Between experiments, we freeze it at -20C, but the tube broke the last time I did it and lost the sample.

Do you have some recommendations on how to freeze NMR tubes safely?

I want to see the interaction between lipid NPs and proteins, but I am not sure which solvent is the best for both of them.

Hi. I am interested in the following: having a high resolution spectrum by NMR (e.g. a 400 MHz), I want to modify it digitally to see how the same spectrum would look like in low resolution (e.g. in a 60 MHz). I know that the sensitivity of the equipment would be lower, but I would take that into account. I've been thinking about applying some calculation on the FID to reduce the resolution obtained, but I can't find the key. If anyone can help me, I would be very grateful. Best regards. José Raúl.

I am in need to perform variable temperature NMR for my sample. Kindly let me know any universities which makes the services available for externals.

Thanks

How to pronounce 2' when talking about chemical structures or data? for example in NMR structure numbering?

I have prepared some complexes of boron trifluoride with several organic ligands. When we want to analyze the compounds by 11B or 19F nmr we are unable to observe the expected splitting pattern based on 2nI+1 rule, although we clearly see the presence of boron or fluorine. For instance a BF2 unit should show a triplet theoretically in the 11B NMR. Previous literature reports also generally didn't observe the splittings based on 2nI+1 rule. Can anyone provide some explanatin for this? Is it possible to observe the splittings by changing pulse sequence/relaxation time or other NMR parameters?

Efficacy of NMR spectra software

Hi solid-state NMR experts,

What happens to the 1H resonances when a proton exchange starts to take place at the surface of metal oxides? Let's say we have multiple highly resolved 1H resonances in the MAS spectrum of an evacuated metal oxide material. There are basic and acidic hydroxyl functions (terminal, bridging and triply bridging).

If this material is exposed to humidity and rehydroxylation starts to occur, a proton exchange with the acidic OH groups (?) is expected to occur under ambient conditions, isn't it? If yes, what would be the possible effect(s) on the 1H MAS spectrum?

I am coding a solid-state NMR pulse sequence on SIMPON (attached file) but I get this error (error: acq overflow in fid points) that I don't know what it means. Does anyone knows what it means?

Compounds isolated from plant are to be characterized using NMR, FTIR and MS.

It is not possible to quantitatively assess the hole concentration by using the

((Tc)/(Tc_maxc) = {1 − 82.6(p − 0.16)^2 In other words, the argument of determination of holes concentration] is scientifically incorrect by above formula. the correct determination of holes concentration is from nuclear magnetic resonance (NMR) and angle-resolved photo emission spectroscopy (ARPES) experiments that multi-layered cuprate superconductors have non-uniform hole concentrations in each CuO2 plane.

Is the above statement true? Give answer in the light of above comment please.

Hi guys, I am preparing a presentation on diffusion NMR, where I introduce great names on NMR, such as Hahn, Purcell and Stejskal. I can`t seem to find much information on Dr. John E. Turner Jr (from the Stejskal-Tanner equation).

Does anyone know of his fate and birth year?

I have to acquire NMR spectra of marine sediment so I have very high concentrations of salt. I'm using a cryoprobe on a Bruker 600MHz spectrometer and I'm getting very high 90° pulse durations (˜25us) from pulsecal and I'm worried that they could damage the probe.

I have tried diluting the sample to two times the initial volume and the pulse duration goes down a bit (˜18us) but it's still way higher than the suggested 8us.

Dear ResearchGate Community,

I hope this message finds you all well. My name is Michael G. , and I am a Ph.D. student. We are currently synthesizing the lipid NBD-DPPE and are facing some challenges concerning its purification, NMR sample preparation, and in need of NMR data.

Thank you very much for your time and consideration. I look forward to any advice or suggestions the ResearchGate community may have to offer.

Best regards,

Michael G. Ph.D. Student.

4 protons peak may be CH2 near a heteroatom .

How can we employ NMR spectroscopy to determine the molecular weight of polyethylene glycol (PEG)? Is it feasible to use NMR to quantify the number of monomers within the PEG chain?

I checked NMR of commercial PGA NMR and i getting two peaks between 4.9 to 4.8.

It is known that sample conductivity affects pulse durations in 1H NMR experiments. But how does the concentration of NaCl in a sample affects pulse durations in sodium-23 (23Na) NMR experiments? Is it the same effect as with protons?

It would be helpful if some references can be given. Thank you.

Is it possible that the peak intensities of an MTSL-labeled protein+ligand be higher than the peak intensities of the unlabeled protein+ligand in 2D NMR? And what would that mean if it happened?

How can we detect the molecular weight of PEG in NMR? Is it possible to detect the number of monomers in that?

Thanks

I analyzed my polymer sample after polymerization by NMR and GPC. The Mn that I obtained by GPC didn't match with my conversion rate obtained by NMR.

For exemple, for a PEGMA RAFT polymerization I have an average Mn at 20852 and I calculated a conversion rate at 62%. My monomer molecular weight was 500 so, normally I have to have a molecular weight around 31000 for a conversion at 62 (62*500=31000). What is the problem?

Does phosphorus proton coupling exist in solid phosphorus NMR?

Any software for this purpose?

Hello

I wanted a thesis topic in the field of food grade nanostructured lipid carrier (NLC) to work with NMR, XRD and DSC. Can you make suggestions?

To determine the NMR yield of fluorine containing product, I need to calculate %yield from 19F NMR spectra using trifluoromethylbenzene as reference standard.

Dear community,

I am currently running some solvent suppression experiment on water samples. I first run a one scan 1H experiment to get the ''O1P'' and then implement it in the solvent suppression experiment (''zgpurge'' pulse program). However the water signal appears distorted, it is asymmetrical and most likely unphased (other signals appear completly fine), which results in an inefficient solvent suppression experiment. I tried to overcome the problem by performing a 3D shimming, and adjusting the phasing parameters (Autophase during the lock and calibrated the autophase offset) but the problem persisted.

What could be the origin of the problem ?

When I do an NMR of plain DMSO-d6 I have observed a small hump around 1.2-1.3ppm. It looks like a broad signal and am not sure as to what this signal could be assigned to. I have tried with new NMR solvent, NMR tube and also clean dry used NMR tube. All these have shown the same result. However, 13C signals correspond to DMSO-d6 only and nothing else. Was wondering if any one of the experts have any explanation to this observation, can be very helpful to me. TIA

In a ligand-protein binding 2D NMR study, what does it mean when there is no chemical shifts but there's a decrease in peak intensities and an increase in linewidths?

If the intensity of a peak is lower and/or the linewidth is higher, does it mean the specificity/affinity of the ligand is higher for that residue?

I've done 15N hmqc to determine the interaction between ligand-protein.

There was no chemical shifts in amino acids after adding the ligand. However, the peak heights of almost every residue were decreased in a dose dependent manner.

Could someone tell me what it means please?

To start of I am designing an HVAC system where for a laboratory application utilizing Nuclear Magnetic Resonance operating at 300 MHz.

I am well aware of the helium cooling within nitrogen shell and the liquified gases refilling. However, I'd like to know if it emits heat while operation, if there is an extraordinary environment required for operation by the device.

Thank you in advance.

I have synthesized a Schiff base compound but everytime I do NMR I found an aldehyde peak of intensity 0.20 or 0.25 like that. I have tried column, recrystallization, solvent wash but couldn't get the clean NMR of the final product.

I am looking for a good reference for 1-13C NMR peaks for Beta-hmb (beta-hydroxy beta-methylbutyrate), and alpha-HIC (alpha-hydroxyisocaprate). I have not been able to find a single experimental instance of 1 carbon Beta-HMB, or aplha-HIC; however, this experimental data is important for proving a hypothesis in a paper I am working on.

Hello everyone,

for my research project, I am doing synthesis with polymer (PEG) and I confirm the formation of the product via NMR. But for me, I don't really trust NMR and it cannot confirm me the formation of my product based on:

- esterification of PEG-OH with acid compound (step 1)

- imine formation (schiff base reaction-step 2)

So I tried to do FT-IR to see the peaks of COO and C=N in my second product. And it is still unclear for me. My spectrum are really strange.

For the formation of imine (step 2) I see the shift in NMR, characteristic to the formation of CH=N (literature) but for me I need more data to confirm it.

Furthermore, I have some additional peaks (not supposed to be here) with high content of protons. So I think my product is not pure....

So I have 3 questions:

1) in FT-IR, how can I confirm the conjugation of OH and COOH (ester) in my synthesis 1

2) in FT-IR, how can I confirm the C=N bond (synthesis 2)

2) For impurities in NMR, what are the options to remove it ?

Thanks in advance

I am running an MD simulation on a protein-protein complex.

After seeing a similar question on research gate, I checked the amino acids rtp file in my force fields folder, and as expected from this error, the HD1 atom was not present in the HSE entry. The atom HD2 is however present in that entry. So I figured replacing the HD1 atoms in my PDB file with HD2 should solve the error.

And it did. For the time being.

To reaffirm, I made changes in Histidine's hydrogen atoms in the PDB file. When I went ahead with the energy minimization step, I got an error that said there's an Infinite Force on an atom. It turns out that the atom was "HD2" of some Histidine in the PDB file.

I saw online that the reason behind this error was due to atom overlap. Hence, just for seeing if that was the case for me, I changed the coordinates of that atom a little bit (this was just for checking, I can't do this for the actual work). When I ran the EM step again, I got the same error, but for a HD2 of a different Histidine molecule. So yes, overlapping of the atoms is the reason for this particular error. I cannot solve it by changing coordinates of all the HD2 atoms of the Histidines. So it all boils down to the main fatal error that I mentioned.

How do I approach this?

1. Changing the atom name (as in HD1 -> HD2 is not working due to the subsequent error)

2. I do not know if I should add the atom HD1 in the HSE entry in the rtp file (I tried this and got several warnings).

3. I cannot (or should I?) use -ignh because mine is not an NMR structure. I have modelled my proteins on Modeller and refined them online.

Any suggestions/solutions will help me a lot. Thank you in advance!

Hi,

i am starting my master thesis And I am doing polymer synthesis following by precipitation method (dissolution in solvent, non solvent precipitation, centrifugation) repeated 2-3 times. I have some impurities in my NMR analysis.

So I want to know if precipitation method in cold ethyl ether is enough to purify a polymer chain ? if yes, it the best procedure to do a good purification through This method?

Example: addition drop by drop is important ? Stirring fast also ?

Is it better than soxhlet extraction ?

Another suestion regarding the purity of final product. Is GPC can confirm the formation of product ? How can I confirm clearly that the reaction work and the product is formed (in complement with NMR) ?

thanks