A study on the structure and intramolecular proton transfer (IPT) of hypomycin B(HMB), a novel type of perylenequinonoid photosensitizer (PQP), with semiempirical method AM1 and HF ab inito method with 6-31G basis sets has been performed for the first time in this paper. We designed nine model compounds to study the effect of the sidechain and made comparison with perylenequinonoid(PQ). The most important results are: (1) On the ground state, the barrier of HMB's IRT is only 20.0180 kJ/mol (for versa conformer) and 37.9819 kJ/mol(for parallel conformer), so the rate of IPT is fast. (2)The side-chain has a little influence on the barrier of HMB's IPT, and the IPT barrier is mostly determined by the conjugation structrue or the resonance mode. (3)The charge of the proton transferred increases on it's transition tate. The IPT's barrier is linear to the change of the atom's charge for most similar systems. (4)The barrier of HMB's IPT is linear to the change of the H-bond length or hydroxyl O-H bond length. (5) Comparing with PQ, with only one IPT mode, the IPT and the resonance mode of HMB is still similar to PQ, which is the basis of HMB's photosensitization.

Key words: INTERNAL MOLECULAR REACTION, PROTON TRANSFER, PHOTOSENSITIVE DRUG, RESONANCE THEORY, QUANTUM CHEMISTRY, SEMIEMPIRICAL EQUATIONS, AB INITIO CALCULATION, FUNGI