Achievement of 1 H-19 F heteronuclear experiments using the conventional spectrometer with a shared single high band amplifier

NMR screening method based on 19F spin-spin relaxation time for analyses of fluorinated compound bound to proteins

NMR screening methods based on 19F spin-spin relaxation time (19F-T2) were applied to fluorinated compounds bound to human serum albumin. Diflunisal and fleroxacin (the fluorinated compounds) contain two and three fluorine atoms per molecule, respectively, and are suitable as the model system for 19F NMR analysis. It was shown that 19F-T2 was more sensitive in monitoring the binding affinity to the target protein than 19F spin-lattice relaxation time (19F-T1). The comparisons of 19F signal intensities acquired at different echo times using 19F-T2 pulse sequence were also shown to be an effective means of assessing complex formation for fluorinated compounds.

Development of 1H{19F} saturation transfer difference experiments for detection of a fluorinated compound bound to proteins

The ¹H{¹⁹F} saturation transfer difference (STD) experiment presented here incorporates the WATERGATE W5 sequence to observe protein-ligand interactions in a human serum albumin (HSA)-fleroxacin complex. In conventional STD experiments, ¹H of proteins are first saturated, and the ligands bound to these proteins are then observed. The method proposed here reverses this process: fluorine atoms in fleroxacin are selectively saturated, and saturation transfer then occurs to protons of fleroxacin as well as to those of HSA. The combined use of the present ¹H{¹⁹F} STD and conventional STD methods is expected to provide better insight in the analysis of the role of fluorine atoms in a fluorinated compound.

On-cell nuclear magnetic resonance spectroscopy to probe cell surface interactions

Nuclear magnetic resonance (NMR) spectroscopy allows determination of atomic-level information about intermolecular interactions, molecular structure, and molecular dynamics in the cellular environment. This may be broadly divided into studies focused on obtaining detailed molecular information in the intracellular context ("in-cell") or those focused on characterizing molecules or events at the cell surface ("on-cell"). In this review, we outline some key NMR techniques applied for on-cell NMR studies through both solution-state and solid-state NMR and survey studies that have used these techniques to uncover key information. We particularly focus on application of on-cell NMR spectroscopy to characterize ligand interactions with cell surface membrane proteins such as G-protein coupled receptors (GPCRs), receptor tyrosine kinases, etc. These techniques allow for quantification of binding affinities, competitive binding assays, delineation of portions of ligands involved in binding, ligand bound-state conformational determination, evaluation of receptor structuring and dynamics, and inference of distance constraints characteristic of the ligand-receptor bound state. Excitingly, it is possible to avoid the barriers of production and purification of membrane proteins while obtaining directly physiologically-relevant information through on-cell NMR. We also provide a briefer survey of the applicability of on-cell NMR approaches to other classes of cell surface molecule.

Identification of Binding Epitopes of a Fluorinated Compound Bound to Proteins Using 1H and 19F NMR Spectroscopy

¹H/¹⁹F NMR-based screening methods were applied to a human serum albumin-fleroxacin complex. Fleroxacin contains three fluorine atoms in a molecule, which is suitable as a model fluorinated compound for NMR analysis with ¹H and ¹⁹F detection. The ¹⁹F{¹H} and ¹H{¹H} saturation transfer difference spectra were acquired and the ¹H/¹⁹F spin-lattice relaxation rates were measured with and without any selective irradiation of protein resonance to identify the binding epitopes of fleroxacin. Because several ¹H signals of fleroxacin resonated close to water, its precise signal intensities were unavailable. The ¹⁹F NMR-based screening methods successfully provide complementary information, indicating its importance in the analysis of fluorinated compounds.

Recent developments in the use of fluorine NMR in synthesis and characterisation

A review of developments in fluorine NMR of relevance to synthesis, characterisation and industrial applications of small organic molecules. Developments considered include those in spectrometer technology, computational methods and pulse sequences. The review of 80 references outlines applications in areas of identification, quantitation, mixture analysis, reaction monitoring, environmental studies and fragment-based drug design.

Sensitive Water Ligand Observed via Gradient Spectroscopy with 19F Detection for Analysis of Fluorinated Compounds Bound to Proteins

The water ligand observed via a gradient spectroscopy type experiment with 19F detection was applied to selectively detect fluorinated compounds with affinity to the target proteins. The 19F signals of bound and unbound compounds were observed as opposite phases, which was advantageous to distinguish the binding state. The proposed NMR method was optimized based on the 19F{1H} saturation transfer difference pulse sequence, and various inversion pulses for the water resonance were evaluated with the aim of high sensitivity.

Improved 19F{1H} Saturation Transfer Difference Experiments for Sensitive Detection to Fluorinated Compound Bound to Proteins

The 19F{1H} saturation transfer difference (STD) method was improved for sensitive 19F detection using a human serum albumin-diflunisal complex. Because NMR (nuclear magnetic resonance) experiments with 19F detection are feasible for the selective detection of fluorinated compounds, more sensitive NMR methods are required to be developed for purposes of practicality. The present research focused on the investigations of 19F{1H} STD pulse techniques and experimental parameters, leading to the development of detection methods with higher sensitivity.