Multinuclear absolute magnetic resonance thermometry

Organic Fluorine Compounds and Their Uses as Molecular MR-Based Temperature Sensors

The interest in fluorinated substances has increased significantly in recent decades due to their diverse properties and possible uses. An important analytical method in this context is NMR spectroscopy, which provides information on the structure as well as on intermolecular interactions or generally on changes in the environment of the nucleus under consideration. A physical quantity that is of great importance in most studies is temperature. However, this is not always easy, e. g. in shielded systems or within an organism. However, the application potential in chemical reactors or in medical diagnosis and therapy is very high and for this reason 13 fluorinated organic compound were chosen for a first 19 F NMR signal temperature sensitivity examination for determination of local temperatures in solution. Polyfluorinated molecules with separate 19 F MR signals are particularly suitable for temperature determination. Those can be serve as internal error-correcting thermometers without the need of a reference substance. Under these conditions, a 19 F MR signal shift of up to 0.03 ppm/K was detectable. Fluorine position and chemical environment were very important for the temperature sensitivity.

19 F VT NMR: Novel Tm3+ and Ce3+ Complexes Provide New Insight into Temperature Measurement Using Molecular Sensors

In the past few decades, magnetic resonance spectroscopy (MRS) and MR imaging (MRI) have developed into a powerful non-invasive tool for medical diagnostic and therapy. Especially 19 F MR shows promising potential because of the properties of the fluorine atom and the negligible background signals in the MR spectra. The detection of temperature in a living organism is quite difficult, and usually external thermometers or fibers are used. Temperature determination via MRS needs temperature-sensitive contrast agents. This article reports first results of solvent and structural influences on the temperature sensitivity of 19 F NMR signals of chosen molecules. By using this chemical shift sensitivity, a local temperature can be determined with a high precision. Based on this preliminary study, we synthesized five metal complexes and compared the results of all variable temperature measurements. It is shown that the highest 19 F MR signal temperature dependence is detectable for a fluorine nucleus in a Tm3+ -complex.

Fluorous Liquids for Magnetic Resonance-Based Thermometry with Enhanced Responsiveness and Environmental Degradation

Accurate temperature measurement via magnetic resonance is valuable for both in vitro and in vivo analysis of local tissue for evaluating disease pathology and medical interventions. ¹H MRI-based thermometry is used clinically but is susceptible to error from magnetic field drift and low sensitivity in fatty tissue and requires a reference for absolute temperature determination. As an alternative, perfluorotributylamine (PFTBA), a perfluorocarbon liquid for ¹⁹F MRI thermometry, is based on chemical shift responsiveness and approaches the sensitivity of ¹H MRI thermometry agents; however, environmental persistence, greenhouse gas concerns, and multiple resonances which can lead to MRI artifacts indicate a need for alternative sensors. Using a ¹⁹F NMR-based structure-property study of synthetic organofluorine molecules, this research develops new organofluorine liquids with improved temperature responsiveness, high signal, and reduced nonmagnetically equivalent fluorine resonances. Environmental degradation analysis using reverse-phase HPLC and quantitative ¹⁹F NMR demonstrates a rapid degradation profile mediated via the aryl fluorine core of temperature sensors. Our findings show that our lead liquid temperature sensor, DD-1, can be made in high yield in a single step and possesses an improved responsiveness over our prior work and an 83% increase in aqueous thermal responsiveness over PFTBA. Degradation studies indicate robust degradation with half-lives of less than two hours under photolysis conditions for the parent compound and formation of other fluorinated products. The improved performance of DD-1 and its susceptibility to environmental degradation highlight a new lead fluorous liquid for thermometry applications.

Quadrupolar 23Na+ NMR relaxation as a probe of subpicosecond collective dynamics in aqueous electrolyte solutions

Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and temperature ranges. We demonstrate that quadrupolar nuclear relaxation is sensitive to subpicosecond dynamics not captured by previous models based on water reorientation or cluster rotation. While ions affect the overall water retardation, experimental trends are mainly explained by dynamics in the first two solvation shells of sodium, which contain mostly water. This work thus paves the way to the quantitative understanding of quadrupolar relaxation in electrolyte and bioelectrolyte systems.

Towards Photoswitchable Contrast Agents for Absolute 3D Temperature MR Imaging

Temperature can be used as clinical marker for tissue metabolism and the detection of inflammations or tumors. The use of magnetic resonance imaging (MRI) for monitoring physiological parameters like the temperature noninvasively is steadily increasing. In this study, we present a proof-of-principle study of MRI contrast agents (CA) for absolute and concentration independent temperature imaging. These CAs are based on azoimidazole substituted NiII porphyrins, which can undergo Light-Driven Coordination-Induced Spin State Switching (LD-CISSS) in solution. Monitoring the fast first order kinetic of back isomerisation (cis to trans) with standard clinical MR imaging sequences allows the determination of half-lives, that can be directly translated into absolute temperatures. Different temperature responsive CAs were successfully tested as prototypes in methanol-based gels and created temperature maps of gradient phantoms with high spatial resolution (0.13×0.13×1.1 mm) and low temperature errors (<0.22 °C). The method is sufficiently fast to record the temperature flow from a heat source as a film.