Heat-initiated detection for reduced glutathione with ¹⁹F NMR probes based on modified gold nanoparticles

For detecting reduced glutathione (GSH) with a (19)F NMR spectroscopy with time-specificity, we developed the probes based on gold nanoparticles modified with the fluorinated groups via the thermally-cleavable linkers. Before the heating treatment with the probe, the maleimide moiety as a binding site with GSH in the probe is inactivated by cycloaddition of furan. At this silent state, the magnitude of (19)F NMR signals from the fluorinated groups was suppressed. By heating for the activation of the probe, the maleimide moiety was produced via retro Diels-Alder reaction, and (19)F NMR signals were observed. From this moment, GSH started the reaction with the probe via Michael addition to the maleimide moiety, leading to the observation of the new peak in (19)F NMR spectra. Finally, the amounts of GSH were determined from the increase of the magnitude of (19)F NMR signals.

Paramagnetic 19F chemical shift probes that respond selectively to calcium or citrate levels and signal ester hydrolysis

Paramagnetic magnetic resonance chemical shift probes containing a proximal CF(3) group have been characterised. Different systems have been created that report reversible changes in calcium ion concentrations in the millimolar regime, signal the presence of citrate selectively in competitive aqueous media and allow the monitoring of remote ester/amide hydrolysis in relayed, irreversible transformations. Chemical shift non-equivalence is amplified by the presence of the proximate lanthanide ion, with a mean separation between the CF(3) group and the metal ion of 6.4 Å found for a thulium complex, in an X-ray structure of the metal complex aqua adduct. The enhanced rate of longitudinal relaxation of the (19)F nucleus allows faster data acquisition.

Fluorinated paramagnetic chelates as potential multi-chromic 19F tracer agents

A class of potential multi-chromic (19)F imaging tracers is made by pairing metal ions with a fluorinated chelator. All fluorinated metal chelates emit a single (19)F signal. Paramagnetic metal ions shifted the (19)F signal frequency and made the (19)F relaxation rates insensitive toward local chemical environment.

Gadolinium-doped LipoCEST agents: a potential novel class of dual 1H-MRI probes

A novel class of paramagnetic liposome-based systems acting as dual T(1) and CEST (1)H-MRI contrast agents is described. The vesicles contain a shift reagent in the aqueous core and a Gd-complex on the external surface conjugated through a biodegradable linker. As such, the probe can generate T(1) contrast only, but after the cleavage and removal of the Gd-coating, the CEST contrast is switched on.

19F-lanthanide complexes with increased sensitivity for 19F-MRI: optimization of the MR acquisition

Fluorine-19 magnetic resonance methods offer advantages for molecular or cellular imaging in vivo due to the absence of radioactivity, lack of naturally occurring background signal, and the ability to easily combine measurements with anatomical MRI. Previous studies have shown that (19) F-MRI sensitivity is limited to millimolar concentrations by slow longitudinal relaxation. In this study, a new class of macrocyclic fluorinated lanthanide complexes is investigated where relaxation rates are significantly shortened by proximity of the fluorine group to a paramagnetic lanthanide ion located within the same molecule. Longitudinal and transverse relaxation rates are field dependent and in the range 50-150 s(-1) and 70-200 s(-1), respectively, at 7 T. Relaxation rates in these complexes are a function of the molecular structure and are independent of concentration at biologically relevant levels, so can be used as criteria to optimize imaging acquisition. Phantom experiments at 7 T indicate a lower limit for detection by imaging of 20 μM.

Measurement of pH by NMR Spectroscopy in Concentrated Aqueous Fluoride Buffers

An NMR spectroscopic technique has been developed to give rapid, accurate pH measurements on tenth-milliliter samples of concentrated acidic aqueous solutions buffered by fluoride ion in the pH 1.5 - 4.5 range. The fluoride (19)F chemical shift has been calibrated as a function of pH at 0.1 and 1.0 M concentration by reference to an internal 3-fluoropyridine standard. Subsequent measurements of fluoride buffer pH required no additives and only two NMR spectra in the presence of an external reference standard.