Synthesis,Characterization And Metallization Of A New Kind Of Amino Acid-Linked Porphyrin

Porphyrins and metalloporphyrins are a kind of macro-cyclic conjugated organicmolecules. They have an extensive system of delocalizedπelectrons and they havegood properties in light, electricity and magnetism. So many scholars have researchedin many aspects of porphyrins. Porphyrins and metalloporphyrins have been appliedin many fields, such as Iatrology, Material Science, Analysis Chemistry, BioChemistry,Energy Sources Chemistry, et al.Chiral recognition is an attractive subject in the area of the Host-GuestChemistry which is a fundamental process of chemistry's and bio-chemistry'sphenomena. Porphyrins exist in nature widely which play a very important role in theprocess of life sciences. Several host molecules for the chiral recognition studies havebeen reported because of their biological and chemical importance. Porhpyrins arerelatively accessible molecules which have been used in the recognition studies inresent years.In this paper, a new histidine-linked porphyrin and 9 different transition metallo-porphyrins and lanthanon metalloporphyrins were prepared by using meso-5-o-aminophenyl -10,15,20- triphenylporphyrin as original material, purified andcharacterized by means of element analysis, IR, UV-Vis, MS and1H NMR. Theirsurface photovoltage, fluorescence characters and electricity chemistry characterswere studied and the lowest energy conformations of them were chosen with 100 ps MD simulation. We used the UV-Vis titration measured the Fe-porphyrin and theZn-porphyrin recognized the imidazoles systems. Our work includes the followingaspects:(1) According to Adler-Longo method, we synthesized the porphyrin monomers. First,we nitrified the meso-tetraphenylporphyrin, and used SnCl2deoxidized it intomeso-NH2-TPP. Then, using EDC as catalyzer, we made the L-Fmoc-His(Trt) andNH2-TPP react to the new chiral tailed histidine-linked porphyrin, by removing theFmoc-protect of the histidine we got the porphyrin 1 at last. We purified theporphyrin by silica gel(ZCX-Ⅱ,100~200) column chromatography with differentratios of chloroform and ethanol as the eluant. By different solvents and differentreaction temperatures, we got 9 different metalloporphyrins, including fourtransition metalloporphyrins and five lanthanon metalloporphyrins. Everycompound has been characterized by means of element analysis, IR, UV-Vis, MSand1H NMR. The reaction process can be represented by the following equation:(2)The initial model of Porphyrin is improved by energy minimization using CVFFforfied with Discovery 3 module. After conjugate gradient (CG) minimizationsteepest descent and Newton - Laplace method performed, the lowest energy of the3D structure of Porphyrin is got through MD simulation. Porphyrin has a hydrophobic structure, which has a positive charge in the histidine. In the 3Dstructure of Porphyrin, ubstituted phenyl and porphin ring is almostperpendicular.The porphyrin 2~5 is optimized at B3LYP/LANL2DZ level. Thetransition metal coordination ability of porphyrin is analyzed. The four porphyrinsare all twisted chair structure. Nitrogen atoms in the porphyrin ring is negativelycharged center which coordinated with Zn,Co,Fe,Mn. The more metal porphyrin4 in this order and the porphyrin a coordinated moleculesthe number is increased,the larger folding of the tail is increased.(3)For investigating the difference of porphyrins, we studied the fluorescenceproperties, surface photovoltage properties and electrochemical properties of thenew histidine-linked porphyrins and the metalloporphyrins. Firstly, we introducedthe fluorescence properties of the histidine-linked porphyrin and metalloporphyrinsand calculated the quantum yield of compounds 1~10 at room temperature.According to TPP, because of the withdraw group which is connected by theporphyrin ring, the fluorescence intensity and the quantum yield were all lower. Thetransitional metals on center of porphyrin ring quench the fluorescence ofporphyrins except Zn porphyrin. The result is the same with references. We testedthe 10 compounds with the surface photovoltage spectroscope (SPS) and theelectric-field-induced SPS. Most porphyrin compounds showed good photovoltageresponse except the porphyrin 4. The porphyrin 6 showed the strongest positiveelectric-field-induced photovoltage response when the electric-field was +1.0 Vwhile the porphyrin 8 showed the strongest response when the electric-field was-1.0 V. We researched the redox properties of all the porphyrins by the cyclicvoltammetry and obtained their redox potentials. The redox potentials of porphyrinring shifted to negative potential which indicated that metalloporphyrins were easierto oxidation compared with porphyrin 1 because of the increase of symmetry andstabilization in metalloporphyrin molecules.(4)The molecular recognitions of imidazoles by the new histidine-linked Fe-porphyrinand Zn-porphyrin were studied and the association constants of the system weremeasured by of UV-Vis titration. The results showed that the coordination numbers of Fe-porphyrin and imidazole systems were close to 1, while the coordinationnumbers of Zn-porphyrin and imidazole systems were close to 0.5 at differenttemperatures. We also investigated the affecting factors of association constantsincluding the steric configuration of host, guest molecules and the reactiontemperature. The thermodynamic properties and enthalpy-entropy compensationwere calculated, and the results are all bellow zero which means the recognitionsystems are all exothermic systems.