Spectral editing techniques for 31P NMR spectroscopy of blood

Selective filtration of NMR signals arising from weakly- and strongly-coupled spin systems

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analyzing chemical and biological systems. However, in complex solutions with similar molecular components, NMR signals can overlap, making it challenging to distinguish and quantify individual species. In this paper, we introduce new spectral editing sequences that exploit the differences in nuclear spin interactions (J-couplings) between weakly- and strongly-coupled two-spin systems. These sequences selectively attenuate or nullify undesired spin magnetization while they preserve the desired signals, resulting in simplified NMR spectra and potentially facilitating single-species imaging applications. We demonstrate the effectiveness of our approach using a 31P spectral filtration method on a model system of nicotinamide dinucleotide (NAD), which exists in oxidized (NAD+) and reduced (NADH) forms. The presented sequences are robust to field inhomogeneity, do not require additional sub-spectra, and retain a significant portion of the original signal.

NMR of 31P nuclear spin singlet states in organic diphosphates

³¹P NMR and MRI are commonly used to study organophosphates that are central to cellular energy metabolism. In some molecules of interest, such as adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide (NAD), pairs of coupled ³¹P nuclei in the diphosphate moiety should enable the creation of nuclear spin singlet states, which may be long-lived and can be selectively detected via quantum filters. Here, we show that ³¹P singlet states can be created on ADP and NAD, but their lifetimes are shorter than T₁ and are strongly sensitive to pH. Nevertheless, the singlet states were used with a quantum filter to successfully isolate the ³¹P NMR spectra of those molecules from the adenosine triphosphate (ATP) background signal.

Spectral editing of tumor 13C MRS in situ

The editing pulse sequence DEPT (D.T. Pegg, D.M. Doddrell, and M.R. Bendall, J. Chem. Phys. 77, 2745 (1982)) was modified using a scheme of various composite pulses and a 16-step phase cycling to obtain proton-decoupled natural-abundance 13C edited subspectra of solid tumors. A solenoidal probe including a Faraday shield and an orthogonal saddle decoupling coil was built for this purpose.