Abstract
Traditional 31P NMR or MRI measurements suffer from low sensitivity relative to 1H detection and consequently require longer scan times. We show here that hyperpolarization of 31P nuclei through reversible interactions with parahydrogen can deliver substantial signal enhancements in a range of regioisomeric phosphonate esters containing a heteroaromatic motif which were synthesized in order to identify the optimum molecular scaffold for polarization transfer. A 3588-fold 31P signal enhancement (2.34% polarization) was returned for a partially deuterated pyridyl substituted phosphonate ester. This hyperpolarization level is sufficient to allow single scan 31P MR images of a phantom to be recorded at a 9.4 T observation field in seconds that have signal-to-noise ratios of up to 94.4 when the analyte concentration is 10 mM. In contrast, a 12 h 2048 scan measurement under standard conditions yields a signal-to-noise ratio of just 11.4. 31P-hyperpolarized images are also reported from a 7 T preclinical scanner.
Highlights
Phosphorus containing molecules are essential to the human body.[1−5] In addition, a number of widely prescribed pharmaceutical products contain one or more phosphorus atoms.[6−8] Due to 31P′s high natural abundance, coupled with a wide chemical shift range that is indicative of molecular environment, 31P signal detection represents an exciting probe for magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) studies in both inorganic chemistry and biochemistry
Signal Amplification by Reversible Exchange (SABRE) has been shown to be successful for a growing range of biologically relevant molecules; this has established the potential of the method to produce 1H and 13C hyperpolarized agents for subsequent MRI measurement.[29,32,35,39,40]
We address the potential of these substrates to act as MRI agents for which in-phase 31P signals are desirable
Summary
Phosphorus containing molecules are essential to the human body.[1−5] In addition, a number of widely prescribed pharmaceutical products contain one or more phosphorus atoms.[6−8] Due to 31P′s high natural abundance, coupled with a wide chemical shift range that is indicative of molecular environment, 31P signal detection represents an exciting probe for magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) studies in both inorganic chemistry and biochemistry. MT.[24] PHIP has, been widely used to probe reaction mechanisms where it enables the detection of many metal hydride containing complexes.[25−27] In these studies magnetization transfer to 31P has proven to be a very important feature of the characterization of many reaction products.[28]
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