Molecular orbital study of polarity and hydrogen bonding effects on the g and hyperfine tensors of site directed NO spin labelled bacteriorhodopsin

• Published in: Molecular physics Vol. 100; no. 23; pp. 3711 - 3721
• Main Authors: PLATO, MARTIN, STEINHOFF, HEINZ-JÜRGEN, WEGENER, CHRISTOPH, TÖRRING, JENS T., SAVITSKY, ANTON, MÖBIUS, KLAUS
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 10.12.2002
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268970210166246

Semiempirical molecular orbital methods (PM3, INDO, ZINDO/S) have been used to calculate the effects of local electric fields and of hydrogen bonding on the g and hyperfine tensors of a nitroxide spin label model system. The results yield a linear correlation between the two principal tensor components g xx and A N zz at label sites of varying polarity. Hydrogen bonding with a single water molecule produces a constant shift of Δg xx ≅ −4 × 10 −4 . These theoretical results are used to interpret recent high field (3.4 T, 95 GHz) electron paramagnetic resonance investigations on site-directed spin labelled bacteriorhodopsin. This protein reveals a close correlation between proticity and polarity at the various label sites. The slope of the g xx versus A N zz dependence is affected strongly by polarity induced structural strains of the spin label.