Compound-compound interaction analysis of baicalin and berberine derivatives in aqueous solution.

Baicalin and berberine are biologically active constituents of the crude drugs Scutellaria root and Coptis rhizome/Phellodendron bark, respectively. Baicalin and berberine are reported to combine together as a 1:1 complex that forms yellow precipitates by electrostatic interaction in decoctions of Kampo formulae containing these crude drugs. However, the structural basis and mechanism for the precipitate formation of this compound-compound interaction in aqueous solution remains unclarified.