Various substituting groups of porphyrin derivatives have great influence on the molecular intercalation and aggregation in DNA helix. In order to investigate the effects of meso-pyridyls on the structure of N-protonated porphyrin, the geometries of tetrapyridylporphine and its diacid were calculated by using AM1 MO method an symmetry restriction. The results show that the method and the symmetry restriction are reasonable and the molecular shape is favorable to the aggregation after the protonation. Meanwhile, the reasons of the configurational change and the selectivity of the aggregation were discussed by means of structure analysis, population analysis and frontier orbital analysis.

Key words: PYRIDYL, PORPHYRIN, CONFIGURATION, PROTONATION, SEMIEMPIRICAL EQUATIONS