Karplus relationship

The diagram of a typical Karplus relationship

The Karplus relationship is an equation named after its discoverer Martin Karplus and describes a correlation between the ³ J coupling constant and the dihedral angle in NMR spectroscopy . ${\displaystyle \!\,\phi }$

Accordingly, the following equation applies:

${\displaystyle J(\phi )=A\cos 2\phi +B\cos \,\phi +C}$

Here, the ³ J coupling constant, the dihedral angle and , and are empirical parameters which are determined by the substitution and functional groups of the constituent atoms. The relationship is used to estimate the magnitude of the ³ J _{H, H} coupling (also called vicinal coupling ). The coupling constant is very low at torsion angles close to 90 ° and significantly greater than usual at angles of 0 ° and 180 °. The relationship between geometry and coupling constant is valuable for determining conformations and calculating the backbones of proteins . ${\displaystyle \!\,J}$ ${\displaystyle \!\,\phi }$ ${\displaystyle \!\,A}$ ${\displaystyle \!\,B}$ ${\displaystyle \!\,C}$

Individual evidence

1. ↑ M. Karplus: In Contact Electron-Spin Coupling of Nuclear Magnetic Moments . In: Journal of Chemical Physics . Volume 30, 1959, pp. 11-15.
2. ↑ M. Karplus: In Vicinal Proton Coupling in Nuclear Magnetic Resonance . In: Journal of the American Chemical Society . Volume 85, 1963, pp. 2870-2871.
3. ↑ Lexikon der Chemie , Spektrum Akademischer Verlag, Heidelberg, Berlin 1999, Volume 2, p. 139, ISBN 978-3-8274-0380-3 .

Web links

• Chemical & Engineering News, Karplus Equation (English)
• ³ J _{H, H} calculators at www.stenutz.eu (English)