Fixed partial charge method

The electrostatic embedding of MM partial charges as a perturbational potential in the Hamilton operator is a frequently used method to account for Coulombic interactions between QM atoms and MM point charges. As the respective potential contributions influence the quantum mechanical calculation and by that the molecular orbitals and the associated electron density, this approach is rated superior compared to a Coulombic interaction model utilising fixed partial charges. 

Gel permeation chromatographic (GPC) analysis was not possible directly on the primary-amine-functionalized oligomers because of their tendency to be adsorbed on the GPC columns rather than to elute. A method has been developed in our laboratories (9, 10) for derivatization of the amine end groups with benzophenone to form an imine functionality. This method allows FPC (fixed-partial-charge) analysis of the oligomers. 

Ion-exchange methods are based essentially on a reversible exchange of ions between an external liquid phase and an ionic solid phase. The solid phase consists of a polymeric matrix, insoluble, but permeable, which contains fixed charge groups and mobile counter ions of opposite charge. These counter ions can be exchanged for other ions in the external liquid phase. Enrichment of one or several of the components is obtained if selective exchange forces are operative. The method is limited to substances at least partially in ionized form. 

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