TR-ESR Investigation On The Reaction Between Vitamin C And Excited Triplet State Of Several Quinone Molecules

The excited triplet state of quinone molecules is harmful for biological tissues such as cells, proteins and so on. Vitamin C (VC) is an effective biological antioxidant. Based on a brief introduction to the principle of CIDEP and TR-ESR spectrometer, the reaction mechanism and dynamics of the excited triplet state of environment-related polycyclic acenaphthenequinone (ACQ) and the biological quinone molecules such as duroquinone (DQ) and anthraquinone (AQ) quenched by VC have been investigated in this dissertation. The main work is shown as following(1) The photochemical reaction mechanism on photolysis of ACQ has been investigated in ethylene glycol (EG) homogenous solution. ACQ neutral radical ACQH^·and EG ketyl radical EG[-H]^·were generated by a hydrogen abstraction of ³ACQ^* from EG. The radical pair triplet mechanism is the main CIDEP mechanism. When TEMPO was added into ACQ/EG solution, ³ACQ^* is quenched by TEMPO effectively and spin polarization transfers from ³ACQ^* to TEMPO. In ACQ/VC/EG system, ³ACQ^* abstract hydrogen atoms not only from EG, but also from VC. The much stronger CIDEP signal of As^·- indicates that VC is an effective quencher to ³ACQ^*. (2) The reaction mechanism and dynamics of the excited triplet states ³DQ^* in EG homogeneous solution have been also studied. In DQ/EG/H₂O system, the CIDEP spectrum indicates that DQH^·and EG[-H]^·can be generated through hydrogen atom transfer from VC to ³DQ^*. The quenching rate constant of ³DQ^* quenched by VC is 4. 90×10⁷ L·mol^-1·s^-1. The quenching reaction is close to be diffusion-controlled.(3) The quenching mechanism and dynamics investigation on the excited triplet states ³AQ^* quenched by VC in EG homogeneous and micelle systems have been carried out. The reversed micelles are used as a simulation to the physiological environment of biological cells. In AQ/EG/H₂O homogeneous solution, both the time-resolved ESR spectrum and transient absorption spectrum show that AQH^·and EG[-H]^·are formed by a hydrogen abstraction of ³AQ^* from EG. In AQ/VC/EG/H₂O solution, ³AQ^* abstracts hydrogen atoms not only from VC but from EG. The quenching reaction of VC to ³AQ^* is closed to diffusion-controlled and the quenching rate constant is 0 .639×107 L?mol?1. For EG/H₂O/AOT and SDS micelle system, the coulomb repulsion between anion surfactant and As^·- decreases the quenching rate constant. For EG/H₂O/CTAB system, the coulomb attraction between cation surfactant and As^·- increases the quenching rate constant remarkably. As for EG/H₂O/TX-100 system, the quenching rate constant of ³AQ^* quenched by VC is larger than that in EG/H₂O homogeneous solution because AQ and VC are solubilized in the same polyethylene glycol core.