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Figure 1
The local multipole frame of the carbonyl O atom of the peptide backbone is shown. The positive z axis is along the C=O bond and the x axis is chosen in the O=C—Cα plane in the direction of the Cα atom. The y axis is directed into the page in order to achieve a right-handed coordinate system. Also shown are the nonzero multipole moments of the O atom and a qualitative representation of their shape. The dz Cartesian Gaussian dipole (in Debye units) places electron density along the C=O bond, while the trace of the Cartesian Gaussian quadrupole (in Buckingham units) positions electron density approximately at lone-pair positions.

Journal logoBIOLOGICAL
CRYSTALLOGRAPHY
ISSN: 1399-0047
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