title: New pinch-porphyrin complexes with quantum mixed spin ground state S=3/2,5/2 of iron (III) and their catalytic activity as peroxidase.
abstract: New complexes of the pinch-porphyrin family were obtained from the dimethylester of (proto-, meso-, and deutero-porphyrinato)iron(III) with the ligand [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine] 1-3 and with the ligand [N-pyridin-2-ylmethyl-N'-[3-[(pyridin-2-ylmethyl)-amino]-propyl]-propane-1,3-diamine] 4-6. The UV/VIS studies of 1-6 indicate an increase in the distortion of the ligand field excited state. The 1H NMR spectra of 1-6 at RT and over the range 223-328 K show iron(III)-complexes with quantum mixed spin state (qms) S=5/2, S=3/2. The chemical shifts of the meso protons are consistent with qms state S=3/2, S=5/2, where the S=3/2 spin state is lowest in energy. For methyl-heme the chemical shifts are also consistent with a qms state but now the S=5/2 ground state is lowest in energy. ESR spectra of 1-6 show two different species, B and C, of iron(III) with qms, S=5/2, S=3/2 consistent with the 1H NMR results. Species B with 70% of S=5/2 and species C with 72.5% of S=3/2. The catalytic activity as peroxidase of 1-6 was quantified by guaiacol test; their theoretical maximum rate constants were k(cat) approximately 10(2)-10(3) M(-1) s(-1). A quantitative empirical correlation is found: the higher the 32 spin contribution to the qms state and the higher proportion of this species into the samples, the higher the peroxidase activity. Such a correlation was also obtained for pinch-porphyrins already reported.
authors.affiliation: Centro de Química, Instituto de Ciencias, Universidad Autónoma de Puebla. 14 Sur 6301. Col. San Manuel, Puebla, Pue 72570, Mexico.
authors.forename: Amparo
authors.initials: A
authors.lastname: Sánchez-Sandoval
authors.forename: Daniel
authors.initials: D
authors.lastname: Ramírez-Rosales
authors.forename: Rafael
authors.initials: R
authors.lastname: Zamorano-Ulloa
authors.forename: Cecilio
authors.initials: C
authors.lastname: Alvarez-Toledano
authors.forename: Mónica
authors.initials: M
authors.lastname: Moya-Cabrera
authors.forename: Yasmi
authors.initials: Y
authors.lastname: Reyes-Ortega
mesh_terms: D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000737:chemistry* / Q000378:metabolism*; D058085:Iron Compounds / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009195:Peroxidase / Q000737:chemistry / Q000378:metabolism*; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism*; D011522:Protons; D013053:Spectrophotometry; D013816:Thermodynamics
chemical_list: D058085:Iron Compounds; D008024:Ligands; D011166:Porphyrins; D011522:Protons; D007501:Iron; D009195:Peroxidase