The H(2)(18)O solvent-induced isotope shift in (19)F NMR

Area of Science:

• Analytical Chemistry
• Nuclear Magnetic Resonance Spectroscopy
• Isotope Effects

Background:

• Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for chemical analysis.
• Isotope shifts in NMR can provide detailed information about molecular structure and interactions.
• The influence of solvent on NMR signals, particularly isotope shifts, is an area of ongoing research.

Purpose of the Study:

• To measure and analyze the H(2)(16)O/H(2)(18)O solvent-induced isotope shifts ((18)O SIIS) of fluorine-19 ((19)F) NMR signals.
• To investigate the factors influencing the direction and magnitude of these isotope shifts.
• To assess the utility of (18)O SIIS as a tool in (19)F NMR studies.

Main Methods:

• Measurement of (19)F NMR signals in H(2)(16)O and H(2)(18)O enriched water.
• Analysis of isotope shifts in various fluorinated compounds, including amino acids, 5-fluorouridine, and labeled RNA.
• Correlation of observed shifts with solvent properties and molecular interactions.

Main Results:

• Observed (18)O SIIS for fluorinated amino acids ranged from 0.0014-0.0018 ppm downfield at 25°C with 86% (18)O enrichment.
• 5-Fluorouridine exhibited a wider range of (18)O SIIS values.
• Significant (18)O SIIS were observed in a 5-fluorouridine-labeled RNA molecule, with modified characteristics compared to free 5-fluorouridine.
• Isotope shifts were found to be a combination of upfield and downfield components, influenced by van der Waals, electrical, and hydrogen bonding interactions.

Conclusions:

• The (18)O SIIS are sensitive to the molecular environment and solvent interactions.
• The observed shifts are governed by a balance of attractive and repulsive forces between the fluorine atom and the solvent.
• (18)O SIIS represent a promising and versatile technique for (19)F NMR analysis of diverse chemical systems.