How Bonding in Manganous Phosphates Affects their Mn(II)-(31)P Hyperfine Interactions

Area of Science:

• Biochemistry
• Biophysical Chemistry
• Spectroscopy

Background:

• Manganous phosphates are implicated in cellular antioxidant functions.
• Current methods for analyzing cellular manganese phosphates rely on indirect comparisons and heuristic models.
• A more rigorous theoretical framework is needed for accurate in situ speciation.

Purpose of the Study:

• To investigate the Mn(II)-(31)P hyperfine interactions in various Mn(II) phosphate complexes.
• To establish a physical and theoretical basis for analyzing cellular manganese phosphate speciation using ENDOR spectroscopy.
• To correlate structural and chemical modifications of phosphates with their electronic properties.

Main Methods:

• Electron-nuclear double resonance (ENDOR) spectroscopy at 95 GHz was used to measure Mn(II)-(31)P hyperfine interactions.
• In vitro model complexes of manganese phosphates were synthesized and analyzed.
• Density functional theory (DFT) calculations were performed on model complexes to interpret experimental findings.

Main Results:

• Dipolar hyperfine interactions were largely insensitive to pH, esterification, and phosphate chain length.
• Isotropic hyperfine interactions significantly varied, increasing with protonation and esterification, indicating higher spin density at phosphorus.
• Extending phosphate chains reduced spin density at phosphorus.
• DFT calculations accurately reproduced experimental hyperfine couplings and elucidated bonding effects on spin polarization.

Conclusions:

• Specific classes of phosphates can be identified by their unique ENDOR spectral signatures.
• The study provides a theoretical framework for interpreting in situ (31)P ENDOR spectra of cellular Mn(II) complexes.
• Understanding these interactions is crucial for elucidating the role of manganous phosphates in cellular processes.