Advancing Quantitative 31P NMR Spectroscopy for Reliable Thiol Group Analysis

TL;DR

A new 31P NMR method using TMDP enables accurate and reliable thiol group analysis across various substrates.

Contribution

A novel phosphitylation reagent (TMDP) extends 31P NMR for thiol quantification with high specificity and stability.

Findings

The TMDP-based 31P NMR method shows superior selectivity and resolution compared to Ellman’s assay and 1H NMR.

The method is effective for substrates ranging from small molecules to polymers with molecular weights up to 8000 g·mol–1.

It provides simultaneous insights into hydroxy and carboxyl functionalities alongside thiol quantification.

Abstract

Accurate thiol quantification is essential for advancing
thiol–X-ligation
strategies in polymer and materials synthesis. Conventional assays,
most notably Ellman’s test, are limited in scope, particularly
for hydrophobic or multifunctional thiols. Here, we introduce a straightforward
and broadly applicable 31P NMR spectroscopy method for
thiol quantification, using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane
(TMDP) as a phosphitylation reagent. The approach extends established 31P NMR protocols for hydroxyl and carboxyl group analysis
to thiols, offering high specificity and stability in readout. The
method demonstrates applicability across a wide range of substrates,
from small organic molecules to polymeric multi thiols with M
n up to 8000 g·mol–1.
Comparative validation against Ellman’s assay and 1H NMR spectroscopy reveals superior selectivity and resolution of
the TMDP-based 31P NMR protocol, particularly for technical-grade
thiols, where conventional methods fail to distinguish degradation
products. This study establishes the TMDP-enabled 31P NMR
as a reliable, information-rich tool for thiol quantification, giving
simultaneously insights on hydroxy and carboxyl functionality patterns.

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