Determination of Intermolecular Interactions Using Polarization Compensated Heteronuclear Overhauser Effect of Hyperpolarized Spins

Abstract

The nuclear Overhauser effect (NOE) has long been used as a selective indicator for intermolecular interactions. Due to relatively small changes of signal intensity, often on the order of several percent, quantitative NOE measurements can be challenging. Hyperpolarization of nuclear spins can dramatically increase the NOE intensity by increasing population differences, but poses its own challenge in quantifying the original polarization level. Here, we demonstrate a method for the accurate measurement of intermolecular heteronuclear cross-relaxation rates by simultaneous acquisition of signals from both nuclei. Using this method, we measure cross-relaxation rates between water protons and (19)F of trifluoroacetic acid at concentrations ranging from 23 to 72 mM. A concentration-independent value of 2.46 × 10(-4) ± 1.02 × 10(-5) s(-1) M(-1) is obtained at a temperature of 301 K and validated using a nonhyperpolarized measurement. In a broader context, accurate measurement of heteronuclear cross-relaxation rates may enable the study of intermolecular interactions including those involving macromolecules where (19)F atoms can be introduced as site-selective labels.

Modeling of Polarization Transfer Kinetics in Protein Hydration Using Hyperpolarized Water

“…The hyperpolarization technique dissolution dynamic nuclear polarization (D-DNP) is capable of producing spin systems showing a population difference that exceeds Boltzmann polarization by orders of magnitude and can also be used to directly hyperpolarize water. Although the D-DNP experiment contains a dissolution step that causes dilution of the spin magnetization, even accounting for dilution, the water signal is enhanced tens or hundreds fold compared to the already strong solvent signal in conventional NMR spectroscopy. − Because hyperpolarization creates a highly nonequilibrium spin state, the transfer of polarization by exchange or cross-relaxation processes is also strongly enhanced. Use of water hyperpolarization transferred to labile protons on amino acids, foremost in amide groups, has been proposed as a means to enhance the signal in biomolecular NMR spectroscopy, such as for the measurement of hyperpolarized 2D NMR .…”

“…Qualitatively, the hyperpolarized water can be used for detecting protein–ligand interactions, relying on the difference in the sign of the NOE between water and bound or unbound ligand . Authors of the present paper have recently developed a method involving dual acquisition of signals from source and target molecules to quantify intermolecular NOE using samples hyperpolarized by D-DNP …”

“…17 Authors of the present paper have recently developed a method involving dual acquisition of signals from source and target molecules to quantify intermolecular NOE using samples hyperpolarized by D-DNP. 15 The ability to record highly sensitive NMR data in a single scan lends itself ideally to the quantification of transient phenomena. Here, we propose the use of D-DNP hyperpolarized water in combination with flow-NMR for quantification of exchange and cross-relaxation rates between water and protein or within the protein.…”

Milli-tesla NMR and spectrophotometry of liquids hyperpolarized by dissolution dynamic nuclear polarization

“…The large spin polarization produced by hyperpolarization can significantly enhance otherwise weak signals by means of the nuclear Overhauser effect [32,33]. In high-field NMR, in particular for the determination of heteronuclear cross-relaxation, this measurement however requires specialized multi-channel detectors [34]. An interesting feature of LF NMR in this regard is the dramatically reduced frequency bandwidth, resulting in the ability to obtain signals from distinct nuclei in the same spectrum.…”

Detection of Protein–Ligand Interactions by 19F Nuclear Magnetic Resonance Using Hyperpolarized Water

“…The transferred signal intensity can be increased by creating a highly enhanced, non-equilibrium source spin polarization. Dissolution dynamic nuclear polarization (D-DNP) is capable of hyperpolarizing water spins, − achieving a 1 H polarization in excess of ≥5% for 2–6% H 2 O in D 2 O and resulting in a water signal that is ∼30 times stronger than that of pure water in a conventional 400 MHz NMR spectrometer. Thus, a DNP-enhanced water LOSGY experiment has enabled the detection of ligand binding with increased sensitivity .…”