Synthesis, characterization and structural aspects of new haptens for PAHs

Two new haptens for PAHs, 4-(naphthalen-2-yl)-4-oxobutanoic acid (I) and 4-(anthracen-1-yl)-4-oxobutanoic acid (II), were synthesized and confirmed by elemental analysis, IR, and 1H NMR. Single crystal X-ray structure showed that compound I crystallizes in the triclinic crystal system (space group = P-1). A classic hydrogen bonded dimer is formed by the carboxylic acid group from two molecules. The R22 (8) graph-set motif links the molecules into pairs around inversion centers in the unit cell. The O-H⋯O hydrogen-bonded interactions involving these pairs are very strong and stabilize molecular packing of these dimers into a unique assembly. Compound II crystallizes in the Monoclinic crystal system (space group = P21/c). Similarly to compound I, a classic hydrogen bonded dimer is formed by the carboxylic acid group from two molecules. The R22 (8) graph-set motif links the molecules into pairs around inversion centers in the unit cell. Besides, an intramolecular hydrogen bonding causes the formation of a planar six-membered ring, which is also coplanar with the adjacent anthracene ring. The geometries of the corresponding parts of the haptens are almost the same as those of naphthalene and anthracene. Ab initio Hartree-Fock computational calculation provided the supports that the size, shape (geometry) and electronic properties at the corresponding parts of the haptens did not change significantly, compared to those of naphthalene and anthracene. The haptens were coupled with bovine serum albumin (BSA) to make antigents. The coupling ratio of I-BSA was 1:20, and II-BSA 1:37, respectively. These results showed that the new haptens could be used to induce specific antibodies for PAHs.