Quantum Chemical Calculation Of Biological Macromolecules Chlorophyll-a

As the important factors affecting water quality, both water eutrophication and the consequent bloom has become a serious threatening the environment of all over the world. With the coming of Three Gorges after The Times era, algal bloom in the reservoir area has been frequently outbreaks. It is necessary to study the formation mechanisms of water bloom and the photosynthesis of energy transfer. Chlorophyll-a, which is the important optical pigment of algae cells, plays the key role of the absorption and transition of light in photosynthesis. In order to study the energy transfer mechanism of algae in the course of the outbreak in water bloom, it is of great ecological environment and theory significance to research the molecular structure and the activity of chlorophyll-a.Geometry optimizations of the four simplified models of chlorophyll-a constraints at the HF level using the 6-31G basis set in gas, frequency is calculated for the infrared absorption spectra. In order to verify the reliability of the molecular models of chlorophyll-a, the infrared spectrum of the chlorophyll-a is tested extract from algae, then the theoretical calculations of the infrared spectrum is compared with the measured results. Studies have shown that there is no natural changes in the spectral properties of the main functional groups, the designed simplified model of the chlorophyll-a is reasonable.Moreover, the differences between the different molecular properties of Chlorophyll-a under gas phase and liquid phase were compared according infrared spectroscopy, frontier orbits, excited state and Mulliken atomic charges. The results show that the calculation in liquid phase is more closed to the real situation which the Chlorophyll-a itself, and there are significant differences between the properties under liquid phase and gas phase.The bioactivity and absorption wavelength of the characteristic groups of chlorophyll-a molecule was compared according to the spectral characteristic, contribution rates of characteristic groups to the energy of frontier orbits, excited states, Mulliken atomic charges and other quantization parameters which is calculated using the B3LYP flavor of density functional theory(DFT)with the 6-31G basis set in solvents. The results show that in the five characteristic groups of chlorophyll-a molecule, the activity of the ketone composed of C(33)and O(34)is the strongest, the porphyrin ring take the second place, the ester carbonyl in C(13)and C(36)the conjugated double bond own the weaker activity. After the transition of HOMO to LUMO, the charges transfer total quantity of the porphyrin ring are 0.00012 and the charges transfer total quantity of the ketone are -0.00062.