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5 Ways to Make Nuclear Magnetic Resonance (NMR) Easier for Students

Nabiha Khalid
Higher Education
Teaching with Labster

The traditional structural analysis method of nuclear magnetic resonance technology can be used to identify the structure and kinetics of biological macromolecules and their aggregates in solution. This can be accomplished through the use of nuclear magnetic resonance technology. In addition to this, it can be utilized to a large extent as a standard testing procedure for the purpose of researching the interactions of biomacromolecules with other biomacromolecules as well as biomacromolecules with chemically synthesized ligands.

In order to accomplish time-sensitive target discovery, nuclear magnetic resonance can be combined with mass spectrometry technology in order to gather information on the structure of the molecule as well as its molecular weight. NMR technique is used to screen lead compound fragments while the target protein serves as the observation object. Structural modification, optimization, and chemical connection are also carried out during this process. Structure-activity relationship by nuclear magnetic resonance (SAR-by-NMR) and water-ligand seen by gradient spectroscopy are examples of the technical methods that we are able to supply.

The Nuclear Magnetic Resonance (NMR) technique is based on the idea that many nuclei possess spin and that all nuclei have an associated electrical charge. When an external magnetic field is introduced, there is the potential for an energy transfer from the lower energy level of the base to a higher energy level. In NMR, unlike other spectroscopies, sample quality affects the resultant spectrum. Follow a few easy criteria to ensure that your sample produces a meaningful spectrum.

1) Correctly measure material: 5 to 25mg is needed for 1H spectra of organic compounds. Smaller volumes can obtain spectra, but water and grease peaks dominate at low concentrations. 13C is 6,000 times less sensitive than 1H; it provides enough material for a saturated solution. 0.2 to 0.3 millimoles dissolved in 0.7ml will take 30 minutes to record. If material is halved, data collection time quadruples. If you make a high-concentration 13C sample and record a 1H spectrum from it, the higher solution viscosity may result in a spectrum with broader lines than a more dilute solution.

2) Eliminate solids: Solid particles disrupt magnetic field homogeneity because their magnetic susceptibility differs from solution's. Every suspended particle in a sample distorts the field homogeneity. This generates broad lines and uncorrectable spectra. Filter ALL samples into the NMR tube to remove solids. Filter samples using a Pasteur pipette with glass wool. If the plug is too big, some of your samples will be caught in it. Most NMR solvents dissolve cotton wool particles, as seen in 1H spectra. The filtered sample should be clear as water but not colorless.

3) Make deep samples: The magnet's principal field runs vertically along the sample. Each sample end distorts field homogeneity, which is adjusted by the spectrometer's shim settings. A thorough correction takes hours. So that this tedious task is done as little as possible, your samples must be made to the same depth after filtration. Bruker spectrometers need 4 cm (0.55 mL) of height. Varian spectrometers are 5 cm (0.7 mL) tall. Shorter samples are hard to shim and slow spectrum recording. Too-long samples are hard to shim and waste solvent. Ruler-check sample depth. After preparation, press the cap fully onto the tube to reduce solvent evaporation.

4) Deuterated solvents: Preparing samples requires deuterium-containing solvents. The spectrometer uses the deuterium NMR signal to stabilize. The stockroom has deuterated solvents. NMR doesn't provide solvents.

5) Clean tubes and caps: After usage, NMR tubes should be cleaned with acetone and dried with dry air or nitrogen. Drying tubes in a hot oven will leave solvent peaks in your spectrum. Caps must be used with tubes. Chipped or cracked NMR tubes can splinter longitudinally and are harmful.

6) Label samples: Mark the tube or cap with a permanent marker. Your tube label must stick smoothly with a sticker or adhesive. The magnetized tube must spin at 20Hz (1200rpm).

7) Refer internally: The provider adds a reference to the solvent. The amount of TMS or other reference material needed for a 1H spectrum is far less than what can be added to the sample. One drop of TMS generates an altered baseline and surpasses the dynamic range. Standard TMS in CDCl3 is too much. I put 2-3 mL of CDCl3 containing TMS into a container without TMS to prepare samples. This reduces the TMS signal, which should never be higher than the solvent signal. Alternately, leftover protons in the deuterated solvent can be employed. Internal reference for D2O samples is DSS or TSP. 

8) Degassing samples: Some samples must be degassed. Only three cycles of Freeze-Pump-Thaw are effective. Sometimes nitrogen above the sample surface is enough. NMR tubes should not have nitrogen bubbles. This wastes solvent and is ineffective in removing oxygen.

NMR interpretation helps identify molecules. Chemical shift, spin multiple, coupling constants, and integration can be used to analyze NMR spectra and determine the structure of unknown and recognized compounds. This module focuses on 1H and 13C NMR spectra to determine structure, although 14N, 19F, and 31P are also relevant. NMR x-axis is a chemical shift in ppm. Integral regions, splitting patterns, and coupling constants are included. Some NMR signals overlap and cannot be assigned to specific nuclei. Signal assignment combines data from multiple NMR tests. 1H-NMR is proton NMR. Deuterated solvents, such as D2O, are utilized to record only the target molecules. D2O is a lock signal. In 1D spectra, the X-axis shows chemical changes, and the Y-axis signal intensity. The signal's intensity relies on its nuclei count. Due to overlapping signals, 1D spectra are only relevant for tiny molecules/proteins (figure).

Stable magnetic field required for high-resolution NMR spectra. The solvent's deuterium resonance (lock signal) is measured to monitor and modify the magnetic field strength during the experiment to counteract field drift. Shimming adjusts magnetic field homogeneity. The sample is surrounded by electromagnets (shims). Shimming improves peak sharpness.

After shimming, calibrate RF pulses. Because 1H pulse length is sensitive to sample composition, 1D-1H pulses are recorded. 13C and 15N pulses are rarely calibrated. Find the optimal pulse length to rotate magnetization 90 degrees from the z- to the y-axis. The strongest signal is a 90-degree pulse. Because it's difficult to establish the signal's maximum, a 360-degree pulse is used to rotate the magnetization. Optimal pulse length means no signal. From the 360-degree pulse, the 90-degree pulse is calculated.

Why does Nuclear Magnetic Resonance (NMR): Analyze small protein samples a difficult topic for students?

1. Weak fundamental basis

Students cannot understand how light can be employed to gauge a sample's concentration. The main causes of this recurrent problem include ignorance of spectrometry, photometry, the Beer-Lambert equation, and the choice of the best wavelength. Additionally, they are forced to speculate where the light source, digital display,  collimator, monochromator, wavelength sector, photoelectric detector,  and cuvette section are inside the spectrophotometer when used with NMR. The dilemma is made worse by how challenging it is to comprehend and calculate transmittance and absorption.

2. It has a lot of content

It is important to understand the electromagnetic wave types, definitions, applications, and graphs to understand the difficult issue of nuclear magnetic resonance. Because of how much substance there is in this subject, many students dislike it. They find this subject time-consuming and dull. Plus, analyzing small protein or drug samples and their individual properties can overwhelm them.

3. Unaware of Applications 

Students are ignorant of the NMR's uses outside standard lab experiments. Their desire to find out more about the capabilities of the approach and equipment is dampened by this. Rarely are they informed of the actual applications in clinical labs, FMCG industry R&D, forensics, and genetic testing facilities. 

Five ways to make  Nuclear Magnetic Resonance (NMR); an easy topic for students

1. Basic knowledge of the instruments

Students need instrument knowledge. It's an antenna. It comprises RF coils to transmit console RF pulses to the sample. Observer coils read NMR signals. The magnet's magnetic field affects atomic nuclei. The field aligns the spins and provides a measured energy difference. It can harm a credit card's magnetic strip. Console and NMR probe communicate. It creates RF pulses and processes NMR signals.

2. Application in real world

Protein structure, amino acid profile, carotenoids, organic acids, lipid fractions, and the mobility of water in foods are all determined using NMR spectroscopy. The metabolites in food are also identified and measured using NMR spectroscopy. This will attract students to learn.

3. Integration into the lab

Our students shouldn't only learn protocols for exams and assessments. Teachers can help students include spectrophotometry in research projects.

4. Seeing is believing

Color diagrams are useful in learning how to prepare cancer samples for NMR. The variety of hues may increase pupils' interest in the subject. Students that study through color visuals will retain the information. It simplifies complex concepts like how to prepare cancer samples for NMR.

Nuclear Magnetic Resonance (NMR)

Image from Labster's Nuclear Magnetic Resonance (NMR): Analyze small protein samples Virtual Lab.

5. Utilizing the Virtual lab simulation

An electromagnetic spectrum virtual lab simulation is advanced. Labster's 3D laboratory simulations include gamification and a scoring system. Labster's Nuclear Magnetic Resonance (NMR): Analyze small protein samples Virtual Lab shows how a popular antibiotic might induce adverse effects. After learning about NMR, you'll learn how this antibiotic interacts with a kidney protein, causing kidney dysfunction. Identifying critical interaction locations is crucial for drug improvement.

Nuclear Magnetic Resonance (NMR): Analyze small protein samples Virtual Lab GIF

References

https://nmr.chem.umn.edu/samprep.html

Breitmaier, E., Structure elucidation by NMR in organic chemistry : a practical guide. 3rd rev. ed.; Wiley: Chichester, West Sussex, England, 2002; p xii, 258.

NMR database from John Crerar Library : http://crerar.typepad.com/crerar_lib...h_ir_nmr_.html

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