The three-dimensional structures of analytes were built in GaussView 5.0 (Gaussian, Wallingford, CT, USA). The analytes were then optimized by density functional theory (DFT) calculations at the TVZP functional level with an M06-2X basis set using the Gaussian 09 program (Wallingford, CT, USA). The epitope distances of the analytes were measured and extracted from the Gaussian formchk file in GaussView 5.0.