Parahydrogen hyperpolarized NMR detection of underivatized short oligopeptides

Parahydrogen hyperpolarization has evolved into a versatile tool in NMR, allowing substantial sensitivity enhancements in analysis of biological samples. Herein we show how its application scope can be extended from small metabolites to underivatized oligopeptides in solution. Based on a homologous series of alanine oligomers, we report on an experimental and DFT study on the structure of the oligopeptide and hyperpolarization catalyst complexes formed in the process. We demonstrate that alanine oligomers coordinate to the iridium carbene-based catalyst in three different ways, each giving rise to distinctive hydride signals. Moreover, the exact structures of the transient oligopeptide-catalyst complexes are oligomer-specific. This work gives a first insight into how the organometallic iridium-N-heterocyclic carbene-based parahydrogen hyperpolarization catalyst interacts with biopolymers that have multiple catalyst binding sites. A preliminary application example is demonstrated for oligopeptide detection in urine, a complex biological mixture. Underivatized oligopeptides can be detected by parahydrogen hyperpolarized NMR in a biofluid sample. The method is supported by an experimental and DFT study of the underlying oligopeptide complexes with the iridium-based hyperpolarization catalyst.

Automated summary

This study demonstrates the application of parahydrogen hyperpolarization in NMR analysis of underivatized oligopeptides in solution. The authors investigate the structure of the oligopeptide and hyperpolarization catalyst complexes formed and show that different coordination modes of alanine oligomers with the iridium carbene-based catalyst result in distinctive hydride signals. The study provides insights into the interaction between the organometallic iridium-N-heterocyclic carbene-based catalyst and biopolymers, and demonstrates the detection of underivatized oligopeptides in urine using parahydrogen hyperpolarized NMR.