Organic synthesis
Squaramide macrocycles that prefer sulfate in water
Open access · cc by · source: Europe PMC
Meta-linked squaramide macrocycles bind SO42− so tightly in wet DMSO that NMR cannot measure Ka, and they still select sulfate in 50% water.
Study at a glance
- Design
- Other — Synthesis and aqueous NMR titration of squaramide macrocycles for sulfate recognition
- N
- Anion-receptor binding study — no sample N
- Population
- Macrocyclic squaramide receptors in water/DMSO mixtures
- Outcome
- Sulfate binding affinity and selectivity versus competing anions
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Meta receptors 1, 2, 5, and 6 are potent, selective sulfate ligands even in 50% water. 1 and 2 have Ka(SO42−) > 10^4 M−1; 2 is more sulfate-selective versus phosphate and acetate. The crystal shows a bowl/cone geometry with four NH···O hydrogen bonds. Receptor 6 discriminates sulfate from chromate better than the sulfate-binding protein.
Methodology
Authors synthesized [2]- and [3]-squaramide macrocycles, titrated anions by 1H NMR in 0.5–50% water/DMSO, crystallized a 1:1 sulfate complex, and compared selectivity with chromate and with the sulfate-binding protein benchmark.
Limitations
Process-scale nuclear-waste extraction and clinical plasma sulfate assays are suggested applications, not demonstrated; some isomers are too insoluble for full Ka tables.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
This library holds 7 empirical chemistry papers on organic synthesis with isolated findings, rates or spectra rather than reviews.
Evidence for the claim as stated.
Meta-linked squaramide macrocycles bind SO42− so tightly in wet DMSO that NMR cannot measure Ka, and they still select sulfate in 50% water.
Evidence for the claim as stated.
A high yield on one substrate is not a general method, and many 'new reactions' are still one-pot screens rather than mechanism-complete syntheses.
Evidence for the claim as stated.
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.
Evidence for the claim as stated.
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.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
A high yield on one substrate is not a general method, and many 'new reactions' are still one-pot screens rather than mechanism-complete syntheses.
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.
Related papers in this topic
Same topic cluster — not a recommendation engine.