Research method
NMR Spectroscopy
28 studies
Nuclear magnetic resonance reports how atomic nuclei in a magnetic field absorb radiofrequency energy. Chemical shift, coupling, and diffusion (DOSY) tell you which environments are present, whether two species are in the same assembly, and — with titration — how tightly they bind. In this library NMR is used in flasks, in crystals’ mother liquor, and inside living oocytes; each setting changes what a missing or shifted peak is allowed to mean.
Chemists reach for NMR when the question is identity, isomer, binding constant, or whether a designed structure actually formed in solution. It answers 'what is in this sample, and how are the spins coupled or exchanging?' Its main limitation is that invisibility is not absence: a complex can broaden, precipitate, or bind extra partners and drop out of the spectrum, and a Ka measured in DMSO/water is not a process-scale extraction result.
Studies
28
Findings
5
7 supporting · 0 challenging · 0 qualifying citations
Open tensions
2
Currently
What we know
- Titration NMR can rank anion affinities in wet DMSO and still not be a waste-treatment plant. Meta-linked squaramide macrocycles were potent sulfate ligands even in 50% water, with Ka(SO4²⁻) > 10⁴ M⁻¹ for receptors 1 and 2; a crystal showed a bowl/cone with four NH···O hydrogen bonds. Process-scale extraction and plasma assays are suggested, not demonstrated, and some isomers were too insoluble for full Ka tables.
- Isotope-edited NMR can watch a G-quadruplex inside a cell rather than only in a buffer. ¹⁵N/¹³C-labelled d(TG4T)₄ micro-injected into Xenopus oocytes kept an all-parallel fold for hours; the same oligonucleotide plus ligand 360A became NMR-invisible in cells, implying extra partners or precipitation that in-vitro ligand studies miss.
- ¹H, DOSY and variable-temperature NMR, with crystallography and DFT, can lock which Pd₂L₄ cage isomer formed. Methyl steric bias and non-coplanar donors favoured a single cis isomer; ligand 1 was trans in MeCN but a cis/trans mix in DMSO. Guest binding and catalysis inside those cages were not shown.
- ³¹P NMR is often the identity test for unusual phosphorus multiple bonds. Arylhalodiphosphene 8 showed ³¹P signals at 433 and 502 ppm with ¹JPP = 574 Hz; the solid was 85% E / 15% Z. Halide abstraction still did not isolate a free diphosphadiazonium salt.
- Mechanism papers use NMR as one reporter among several. ¹³C NMR plus crystallography showed how crotonaldehyde inactivates DERA via K167 and C47; isotope-resolved NMR with ThT and cryo-TEM showed Aβ40 and Aβ42 forming separate homomolecular fibrils after mixed nucleation; ¹H NMR Ka ≈ 75 558 M⁻¹ for DMA binding tracked allosteric opening of a Pt tweezer catalyst.
Largest unresolved question
Solution NMR, in-cell NMR and solid-state/identity NMR are not the same experiment. Titration Kas in wet DMSO, oocyte SOFAST-HMQC of a labelled oligonucleotide, and ³¹P shifts of a diphosphene answer different questions. A student who says 'we ran NMR' without saying which nuclei and which medium cannot compare those papers.
Procedure
How it works
The main stages of the method. Specific protocols and analysis choices vary between studies.
Place the sample in a magnetic field
Nuclei with spin (¹H, ¹³C, ³¹P, and others) align with the field. The spectrometer's frequency is tuned to those nuclei; nuclei that are not NMR-active, or that are too dilute, never appear.
Pulse and record the free induction decay
A radiofrequency pulse tips the magnetisation; the decaying signal is Fourier-transformed into a spectrum of chemical shifts. Pulse sequence, solvent, and temperature decide which environments are resolved.
Read shift, coupling, and diffusion
Chemical shift reports local electronic environment; scalar coupling reports through-bond neighbours; DOSY reports whether species travel as one assembly. Assignment is an interpretation of those patterns, not a crystal structure.
Titrate when the question is binding
Adding ligand or receptor and tracking shift or intensity can yield a binding constant in that solvent. A Ka in DMSO/water is not a process-scale extraction result, and insolubility can simply empty a table.
Treat a missing peak as a limit, not an absence
NMR answers what is visible in this sample: identity, isomer, exchange, or binding under these conditions. Broadening, precipitation, extra partners, or isotopic choices can hide a bound species — invisibility is not proof the ligand did not bind, and the spectrum need not report every mole fraction in the flask.
Common misconceptions
If the ligand-bound DNA is invisible by in-cell NMR, the ligand did not bind.
The unbound parallel G-quadruplex was visible in oocytes; adding 360A made the oligonucleotide NMR-invisible, which the authors interpret as additional partners or precipitation, so in-vitro bound spectra need not transfer.
A large NMR binding constant means the receptor is ready for industrial or clinical use.
Squaramide sulfate Kas above 10⁴ M⁻¹ were measured in DMSO/water mixtures; nuclear-waste extraction and plasma assays are proposed applications, and insolubility blocked some Ka tables.
NMR always sees every species in the mixture at its true mole fraction.
Broadening, precipitation, exchange, and isotopic labelling choices hide populations. The diphosphene ³¹P spectra still showed trace impurities after recrystallisation; Aβ mixed-oligomer atomic structures were not solved by NMR in that paper.
Related
Claim ledger
What the evidence shows
Drawn from 28 studies in this library. Mix labels say which citation roles are present; they are not a strength score. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope.
Titration NMR can rank anion affinities in wet DMSO and still not be a waste-treatment plant. Meta-linked squaramide macrocycles were potent sulfate ligands even in 50% water, with Ka(SO4²⁻) > 10⁴ M⁻¹ for receptors 1 and 2; a crystal showed a bowl/cone with four NH···O hydrogen bonds. Process-scale extraction and plasma assays are suggested, not demonstrated, and some isomers were too insoluble for full Ka tables.
Isotope-edited NMR can watch a G-quadruplex inside a cell rather than only in a buffer. ¹⁵N/¹³C-labelled d(TG4T)₄ micro-injected into Xenopus oocytes kept an all-parallel fold for hours; the same oligonucleotide plus ligand 360A became NMR-invisible in cells, implying extra partners or precipitation that in-vitro ligand studies miss.
¹H, DOSY and variable-temperature NMR, with crystallography and DFT, can lock which Pd₂L₄ cage isomer formed. Methyl steric bias and non-coplanar donors favoured a single cis isomer; ligand 1 was trans in MeCN but a cis/trans mix in DMSO. Guest binding and catalysis inside those cages were not shown.
³¹P NMR is often the identity test for unusual phosphorus multiple bonds. Arylhalodiphosphene 8 showed ³¹P signals at 433 and 502 ppm with ¹JPP = 574 Hz; the solid was 85% E / 15% Z. Halide abstraction still did not isolate a free diphosphadiazonium salt.
Mechanism papers use NMR as one reporter among several. ¹³C NMR plus crystallography showed how crotonaldehyde inactivates DERA via K167 and C47; isotope-resolved NMR with ThT and cryo-TEM showed Aβ40 and Aβ42 forming separate homomolecular fibrils after mixed nucleation; ¹H NMR Ka ≈ 75 558 M⁻¹ for DMA binding tracked allosteric opening of a Pt tweezer catalyst.
- Why acetaldehyde kills the DERA aldolase
- Aβ40 and Aβ42 make separate fibrils after mixed nuclei
- On–off allosteric control of a bifunctional catalyst
Study Role Design N Population Outcome Why acetaldehyde kills the DERA aldolase Supports Animal / in-vitroCrystallography, 13C NMR, and a C47M mutant of E. coli DERA in concentrated acetaldehyde Enzyme kinetics and structures rather than a biological sample N E. coli deoxyribose-phosphate aldolase and orthologues Crotonaldehyde covalently inactivates DERA via K167–C47; C47M retains activity in 300 mM acetaldehyde Aβ40 and Aβ42 make separate fibrils after mixed nuclei Supports Animal / in-vitroThT, CD, isotope-resolved MS/NMR, cryo-TEM, and self- versus cross-seeding of Aβ40/Aβ42 mixtures Kinetic and structural assays on 10^14–10^15 monomers per sample Binary mixtures of synthetic Aβ40 and Aβ42 peptides Aβ40 and Aβ42 form separate homomolecular fibrils; they cross-react mainly during primary nucleation On–off allosteric control of a bifunctional catalyst Supports Animal / in-vitroPt(II) weak-link tweezer with chloride toggling, 1H NMR binding, and timed Michael addition Multiple catalyst states and kinetic runs rather than a single sample N In situ bifunctional squaramide–amine catalysis in organic solvent Fully closed Na+ complex binds DMA and catalyzes nearly quantitative Michael addition; chloride switching turns activity off
Debates
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes.
Solution NMR, in-cell NMR and solid-state/identity NMR are not the same experiment. Titration Kas in wet DMSO, oocyte SOFAST-HMQC of a labelled oligonucleotide, and ³¹P shifts of a diphosphene answer different questions. A student who says 'we ran NMR' without saying which nuclei and which medium cannot compare those papers.
Solution NMR, in-cell NMR and solid-state/identity NMR are not the same experiment. Titration Kas in wet DMSO, oocyte SOFAST-HMQC of a labelled oligonucleotide, and ³¹P shifts of a diphosphene answer different questions. A student who says 'we ran NMR' without saying which nuclei and which medium cannot compare those papers.
- Squaramide macrocycles that prefer sulfate in water
- In-cell NMR of a DNA G-quadruplex and ligand
- Isolating rare arylhalodiphosphene P=P–X bonds
Study Role Design N Population Outcome Squaramide macrocycles that prefer sulfate in water Supports OtherSynthesis and aqueous NMR titration of squaramide macrocycles for sulfate recognition Anion-receptor binding study — no sample N Macrocyclic squaramide receptors in water/DMSO mixtures Sulfate binding affinity and selectivity versus competing anions In-cell NMR of a DNA G-quadruplex and ligand Supports Animal / in-vitroIn-cell NMR of 15N/13C-labeled d(TG4T)4 microinjected into Xenopus oocytes ± 360A ligand Oocyte in-cell NMR — no single reported oocyte analytic N in stored summary Living Xenopus laevis oocytes Intracellular G-quadruplex persistence and ligand-bound NMR visibility Isolating rare arylhalodiphosphene P=P–X bonds Supports OtherSynthesis, SC-XRD, and DFT of thermally robust arylhalodiphosphenes and halide exchanges Main-group synthesis/structure study — no sample N Arylhalodiphosphene compounds and silver coordination complexes P=P bonding metrics and E/Z preferences across halide series
PaperFren reads this as a limit on how far one study travels — different assays, populations, or outcomes — not a forced fight between papers.
A missing peak can mean opposite things. In oocytes the ligand-bound G-quadruplex vanished, which the authors read as extra binding or precipitation — not as 'the complex did not form.' In cage isomer assignment, extra peaks mean a second isomer is present. Treating silence as non-binding is unsafe.
A missing peak can mean opposite things. In oocytes the ligand-bound G-quadruplex vanished, which the authors read as extra binding or precipitation — not as 'the complex did not form.' In cage isomer assignment, extra peaks mean a second isomer is present. Treating silence as non-binding is unsafe.
Study Role Design N Population Outcome In-cell NMR of a DNA G-quadruplex and ligand Supports Animal / in-vitroIn-cell NMR of 15N/13C-labeled d(TG4T)4 microinjected into Xenopus oocytes ± 360A ligand Oocyte in-cell NMR — no single reported oocyte analytic N in stored summary Living Xenopus laevis oocytes Intracellular G-quadruplex persistence and ligand-bound NMR visibility Unsymmetrical ligands still make one Pd2L4 cage isomer Supports OtherUnsymmetrical bis-pyridyl ligands assembled with Pd(II) to control cis/trans Pd2L4 isomers Coordination-cage synthesis/DFT — no sample N Pd2L4 coordination cages in MeCN/DMSO Ligand sterics locking preferred Pd2L4 cage isomers
PaperFren reads this as a limit on how far one study travels — different assays, populations, or outcomes — not a forced fight between papers.
Timeline
How understanding moved
Study years are when the paper was published. Evidence edits are dated changes to this page's claims. Explanations are when PaperFren added a Discovery — not a claim that the science happened that day.
2026
- Isolating rare arylhalodiphosphene P=P–X bonds
Concept page published
NMR Spectroscopy
Change log
What changed
Dated edits to this page's evidence: studies added or removed from a claim, claims added or withdrawn, and new explanations tagged here. Coverage edits are distinct from reviewed research changes and corrections. Dates record PaperFren updates; study publication dates appear in the timeline.
- Coverage updated · Concept page published
Papers
28 studies in this library bear on NMR Spectroscopy, ordered by citations.
- Aβ40 and Aβ42 make separate fibrils after mixed nuclei
In mixtures, Aβ42 fibrillizes first; elongation and secondary nucleation stay homospecific, so each peptide builds its own fibrils.
- Anion–π contacts are common in the PDB
A PDB-wide search finds anion–π interactions in most protein structures, with Asp/Glu carboxylates packing on aromatics and frequent cation–π partners opposite.
- Unsymmetrical ligands still make one Pd2L4 cage isomer
Steric and geometric ligand design plus solvent polarity steer unsymmetrical dipyridyl ligands into a single cis or trans Pd2L4 cage rather than a statistical isomer mix.
- Protecting-group-free peptide CF3 labeling
ZnTFMS/TBHP or Ir photoredox trifluoromethylates tyrosine C–H on unprotected peptides, including insulin, without hitting polar side chains.
- A zinc polymer that lights down for picric acid
A fluorescent Zn(II)–Tröger’s-base coordination polymer senses phenolic nitroaromatics in water, detecting picric acid down to 26.3 ppb.
- PQ and water oxy-trifluoromethylate enynes
Sunlight-excited phenanthrenequinone turns Langlois’ CF3SO2Na into CF3· and uses water as the oxygen atom to build CF3 benzofurans, benzothiophenes and indoles.
- In-cell NMR of a DNA G-quadruplex and ligand
A parallel d(TG4T)4 G-quadruplex remains NMR-visible and long-lived in Xenopus oocytes, but ligand 360A can hide the complex on the NMR timescale.
- DASA photoswitches work in chloroform if N-methyl
First-generation donor–acceptor Stenhouse adducts with a small N-methyl substituent switch well in chloroform; kinetics split photoisomerisation from cyclisation.
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- Ten-gram grinding makes lanthanum coordination polymers
Manual grinding of LaCl3 with 5-sulfosalicylate and 8-hydroxyquinoline yields ternary CPs whose IR/XPS/MS match a chelated nanocomposite.
- Squaramide macrocycles that prefer sulfate in water
Meta-linked squaramide macrocycles bind SO42− so tightly in wet DMSO that NMR cannot measure Ka, and they still select sulfate in 50% water.
- Pyrazine reservoirs that lower cobalt HER overpotential
Moving a redox-active pyrazine on a cobalt polypyridine ligand cuts hydrogen-evolution overpotential by about 200 mV versus pyridine analogues in water.
- H2O2 is not born at the air–water droplet surface
Sensitive assays show microdroplet H2O2 comes from dissolved O2 reacting at solid–water interfaces, not from ultrahigh fields at the air–water surface.
- Gold C–N/C–O coupling without extra oxidants
Cyclometalated gold catalyzes aryl C–N and C–O coupling in air/water by Au(I)/Au(III) oxidative addition, without sacrificial I(III) or F+ oxidants.
- Pt TPE cages harvest light for cyclization
Self-assembled platinum–tetraphenylethene cages transfer energy to rhodamine B (up to 77% ΦET) and photocatalyze maleimide–aniline cyclization in water-rich solvent.
- Calixarene docks dimethyllysine on lysozyme
p-Sulfonatocalix[4]arene selectively encapsulates Lys116-Me2 on dimethylated lysozyme, mimicking an aromatic cage.
- 2D IR indexing maps hIAPP helix-to-sheet kinetics
Paired 13C18O labels report dihedral angles: monomeric hIAPP is partly helical at L12A13, then oligomers lose helix and fibers form β-sheets.
- Catalytic Mitsunobu chemistry with recyclable azo reagents
Ethyl arylazocarboxylates plus iron phthalocyanine and air replace stoichiometric DEAD in Mitsunobu esterifications with high inversion.
- Watching RAFT PISA grow spheres, worms, vesicles
In situ SAXS shows PGMA45-PHPMA200 aqueous RAFT PISA nucleating in 9–10 min and finishing as ~227 nm vesicles.
- CH···anion bonds that template zinc molecular knots
Weak C–H···anion contacts in water/methanol steer a Zn(II) dynamic library toward a trefoil knot that binds two bromides in its cavity.
- Solid Rh crystals isomerize butene without dissolving
A crystalline Rh σ-alkane complex swaps NBA for alkenes in the solid state and the porous ethene polymorph isomerizes 1-butene with high TOF.
- Why acetaldehyde kills the DERA aldolase
Crotonaldehyde, the acetaldehyde aldol product, covalently bridges catalytic K167 to nearby C47; a C47M mutant survives 300 mM acetaldehyde.
- Phen-DC3 probes that reveal G4 ligand localization
A Phen-DC3 handle lets chemists add BODIPY or a cell-penetrating peptide without losing G4 selectivity, showing the parent ligand misses the nucleus.
- Clicking Fe metallohelices tunes cancer-cell selectivity
Copper-click derivatisation of a stable Fe2L3 helix gives Δ-[Fe2L3a3]Cl4, which is more cancer-selective than the parent, hits cancer stem cells, and still has a fully characterised coordination core.
- Frustrated Lewis pairs oxidize H2 without metals
A carbon Lewis acid, BArF18, and lutidine cleave H2 and oxidize it at carbon electrodes about 1 V milder, without CO poisoning.
- Ultrasound microdroplets make H2O2 from dissolved O2
Water-in-hexadecane droplets under 40 kHz ultrasound produce H2O2 at 0.24 mM min−1, almost entirely at the oil–water interface via superoxide from dissolved oxygen.
- On–off allosteric control of a bifunctional catalyst
A Pt(II) weak-link tweezer and a sulfonate regulator switch a squaramide–amine co-catalyst fully on or off in situ.
- A higher-yield route to FP–PEG–biotin ABPP probe
Reworking Cravatt’s FP–PEG–biotin synthesis cuts chromatography and raises overall yield from 1% to 28.5%.
- Isolating rare arylhalodiphosphene P=P–X bonds
A bulky aryl-PPCl diphosphene is isolated as a monomer, swapped to Br and I, and shown to have a P=P double bond unlike diazonium chlorides.
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Questions
What is still open
Solution NMR, in-cell NMR and solid-state/identity NMR are not the same experiment. Titration Kas in wet DMSO, oocyte SOFAST-HMQC of a labelled oligonucleotide, and ³¹P shifts of a diphosphene answer different questions. A student who says 'we ran NMR' without saying which nuclei and which medium cannot compare those papers.
A missing peak can mean opposite things. In oocytes the ligand-bound G-quadruplex vanished, which the authors read as extra binding or precipitation — not as 'the complex did not form.' In cage isomer assignment, extra peaks mean a second isomer is present. Treating silence as non-binding is unsafe.
Ask PaperFren about NMR Spectroscopy
Study this conceptflashcards and short-answer questions
Why can a G-quadruplex be 'NMR-visible' in an oocyte without ligand and 'NMR-invisible' with ligand 360A, without that meaning the DNA unfolded?
The unbound all-parallel fold matched the in-vitro fingerprint and survived for hours. Ligand-bound oligonucleotide disappearing is read as extra cellular partners or precipitation that remove the species from the sharp-spectrum pool, so in-vitro ligand complexes may not be what exists in the cell.
A Pd₂L₄ paper reports one isomer in MeCN and a mix in DMSO. What did NMR contribute that a single crystal structure could not?
Solution ¹H/DOSY and VT NMR report which isomers are populated in each solvent, including a cis/trans mix for ligand 1 in DMSO. A crystal can lock one isomer of what happened to crystallise; it does not by itself give the solution equilibrium in both solvents.
What does ¹JPP = 574 Hz together with shifts at 433 and 502 ppm tell you, and what did halide abstraction still fail to deliver?
Those ³¹P data support a P=P diphosphene. Abstracting chloride with GaCl₃/AlCl₃ decomposed 8 rather than yielding a free diphosphadiazonium salt; only silver coordination gave a defined complex.
How is titration NMR used in the squaramide and Pt-tweezer papers, and what quantity do you walk away with?
Anion or DMA guest is added and ¹H shifts are fit to a binding model, giving Ka (sulfate > 10⁴ M⁻¹; DMA ≈ 75 558 M⁻¹ in the closed tweezer). That is a solution association constant under those solvents, not a demonstration of catalysis scope or waste-stream performance.