Róbert Huszánk chemist

Transcription

1 Theses of PhD Dissertation PREPARATION OF WATER-SOLUBLE, HEME-LIKE IRON(II) AND IRON(III) PORPHYRIN COMPLEXES, STUDY OF THEIR FORMATION KINETICS, PHOTOCHEMISTRY AND PHOTOPHYSICS Written by: Róbert Huszánk chemist Supervisor: Dr. Ottó Horváth professor University of Pannonia, Institute of Chemistry Chemistry Doctorate School Department of General and Inorganic Chemistry Veszprém 2007

2

3 1. INTRODUCTION Heme proteins (containing iron porphyrin derivatives in their active sites) play an essential role in living organisms in oxygen transport and storage (hemoglobin, myoglobin) and in electron transfer processes (cytochrome c, cytochrome oxidase). Hemoglobin contained within the red blood cells holds four ferrous porphyrin type groups which provide the active site for oxygen binding and are responsible for the red color of blood. Simple compounds that would bind oxygen reversibly for many cycles could also be of value as emergency blood substitutes or for fractionation of oxygen from air. Besides the significant biological function of ferrous porphyrin derivatives, the description of thermal and photoinduced properties of water-soluble complexes would also be important in bioinorganic chemistry. Nowadays, interest in metalloporphyrins keeps increasing, owing to their importance in many fields, such as biochemistry, medical research and catalysis. The photophysical and photochemical properties of excited metalloporphyrins have been utilized, e.g., in optical sensors, artificial photosynthetic systems (light-harvesting dendrimers) and photodynamic therapy. For realization of biological mimicking systems with iron porphyrins, first of all investigation of these complexes is indispensable in the aspect of inorganic chemistry because the understanding and synthesis of biological systems without exact and detailed coordination chemical, photochemical, photophysical and reaction kinetic knowledges of these molecules is hardly possible. 2. AIMS There have been many attempts to model the function of hemoglobin and myoglobin (the oxygen carbon dioxide cycle) by use of some kind of oxygen carriers as blood substitutes. In the last few decades, considerable efforts were made to find compounds that are able to mimic the hemoglobin function. The synthetic preparation of the heme group (hydrophobic or hydrophilic iron(ii) porphyrin) as a possible blood substitute has been investigated intensively. These studies were focused almost exclusively on nonaqueous environments (probably because of the hydrophobic nature of the heme group), while the desired simple oxygen carrier should be able to function in aqueous media under physiological conditions. Hence, in the frame of my PhD work our investigation was focused 1

4 mainly on the preparation of Fe(II)TPPS 4 (H 2 TPPS 4 =5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin) in aqueous media, then on the formation kinetics, equilibrium, photophysical and photochemical properties of this complex, which, on the basis of its peculiarities, can be classified as a sitting-atop metalloporphyrin. Finally, our goal also was, furthermore, to discover whether this complex can serve as a simple heme model with respect to the reaction with dissolved molecular oxygen. 3. INSTRUMENTS AND METHODS The porphyrin complexes (Fe(II)TPPS 4-, Fe(III)TPPS 3- ) were prepared by in situ, equilibrium reaction in all cases using excess of the iron(ii) ions. Absorption and emission spectra were recorded with a Specord S100 UV vis one-way spectrophotometer and with a PerkinElmer LS50 spectrofluorimeter, respectively. Nanosecond emission lifetimes were measured using PicoQuant time-correlated single photon counting apparatus and Quantel Brilliant Nd-YAG solid-state laser apparatus with a Tektronix TDS 684A digital oscilloscope. For the assessments and data fitting, a deconvolution software was used (FluoFit from PicoQuant). For continuous photolysis at different wavelengths an AMKO LTI system (consisting of a 150-W high pressure Xe Hg arc lamp and a monochromator) was utilized. The light intensity was determined with a thermopile calibrated by ferrioxalate actinometry. Density functional theory (DFT) was applied for the theoretical determination of the structures and energies of iron(ii) porphyrin and its derivatives containing other ligands in the singlet, triplet and quintet states. We used the B3LYP combination of functionals as coded in Gaussian98, in conjunction with the LANL2DZ basis set. 2

5 4. THESES 1. Preparation of the iron(ii)-porphyrin Preparation of the water-soluble, kinetically labile, high-spin iron(ii)-porphyrin (Fe(II)TPPS 4- ) has been realized in neutral or weakly acidic solutions containing acetate buffer, and then, in the presence of different type reductive and nitrogen donor ligand as well Formation of the iron(iii) porphyrin in the presence of iron(ii) ions It has been proved, that in the reaction of free-base porphyrin and iron(ii) ions, the cause of the formation of ferric porphyrin was not an oxidation, but from the temporarily formed, kinetically labile iron(ii) porphyrins the Fe(II) centers have been excluded by Fe(III) ions existing in trace amounts in these systems Formation of the iron(ii) porphyrin in the presence of acetate ions The synthesis of the Fe(II)TPPS 4- complex could be realized in the presence of acetate buffer. The buffer played a double role in these systems: it was used for both adjusting ph, and, via formation of acetato complex, trapping trace amounts of iron(iii) ions, which would convert the iron(ii) porphyrins to the corresponding iron(iii) species. The formed Fe(II)TPPS 4- proved to be stable in these solutions even after saturation with air or oxygen uniquely, on the basis of the literature Equilibrium constant of the iron(ii) porphyrin complex The equilibrium constant of the iron(ii)-porphyrin complex forming in not clearly equilibrial reaction was measured with spectrophotometric method Formation of the iron(ii) -porphyrin in the presence of other ligands The effects of the presence of different ligands (ascorbic acid (C 6 H 8 O 6 ), formaldehyde (H 2 CO), D-glucose (C 6 H 12 O 6 ), nitrogen monoxide (NO), sulfocyanide (SCN - ), and fluoride (F - ) ligandumok) on the formation of iron(ii)- porphyrin were also investigated. 2. Mechanism and kinetics of the formation of the iron(ii) an d iron(iii) porphyrins The reaction kinetics of the formation of iron(ii) and iron(iii) porphyrins were studied with spectrophotometric method Mechanism of formation of the iron(ii) and iron(iii) porphyrin A mechanism was suggested for the reaction between iron(ii) ions and free-base 3

6 porphyrin, where iron(iii) porphyrin was the final product, and the iron(ii) ions plays a catalytic role in the formation of iron(iii) porphyrins Rate constants of the formation of the iron(ii) and iron(iii) porphyrins On the basis of the determined rate constants, the formation rate of the iron(iii) porphyrin has been found to be more than two orders of magnitude larger than the appropriate rate constant of the iron(ii) porphyrin. With the fitting of the model to the spectras measured in the systems with and without acetate buffer, the suggested mechanism has been confirmed Temporarily formed bi-nuclear porphyrin derivative On the basis of the fitting of Lorentz functions to the spectra recorded at a certain time during the formation of iron(iii)-porphyrin, at least one new porphyrin type intermediate complex was suggested in the solution, assigned as [Fe(II)-TPPS-Fe(III)]. 3. Photophysical and photochemical properties of iron(ii)- and iron(iii)-porphyrin The ground and excited state absorption and luminescence of Fe(II)TPPS 4- and Fe(III)TPPS 3- were studied and compared SAT behavior of the iron(ii) porphyrin Because of the correspondence between the absorption and emission spectra of the unambiguously SAT type porphyrins and the iron(ii) porphyrin, the complex was found to be SAT type, and, because of this, high-spin state Photophysical constants of the iron(ii) porphyrin The important photophysical constants of the iron(ii)-porphyrin were determined such as the molar absorption coefficient (from 350 nm to 800 nm), the Stokes shifts, the fluorescence lifetime with time-resolved spectroscopic method and the fluorescence quantum yields excited at the Soret and Q bands as well. The quantum yield determined with the excitation at the Q band was found to be the higher. The Jablonski type energy level diagram of the iron(ii) porphyrin was also constructed S 2 emission of the iron(ii)-porphyrin It was revealed that the iron(ii) porphyrin shows emission from the second excited state as well, which is very rare. The quantum yields of this emission was determined. 4

7 3.4. Photophysical properties of the iron(iii) porphyrin In accordance with the earlier studies, the iron(iii) porphyrin doesn't show any luminescence, furthermore, transient absorption about the characteristic wavelengths neither could be detected Photochemical properties of the iron(ii) porphyrin It has been revealed that in the photolysis of Fe(II)TPPS 4- photoinduced porphyrin ligand-to-metal charge transfer (LMCT ) process took place, which was followed by detachment of the reduced metal center and an irreversible ringopening of the porphyrin ligand, resulting in the degradation of the complex. A mechanism for this photochemical reaction was proposed, furthermore the overall quantum yields were determined at both the Soret and the Q bands. 4. Fe(II)TPPS 4- as a possible heme model Attempts were made in order to clear up whether Fe(II)TPPS 4- can be used as a water-soluble, synthetic, heme analog oxygen carrier The solution containing Fe(II)TPPS 4- and dissolved molecular oxygen It was found that the dissolved molecular oxygen did not cause any change in the spectra of the iron(ii) porphyrin. DFT calculations revealed that in solutions with large acetate concentration there is very little chance for iron(ii) porphyrin to bind and release O 2, deviating from heme. In the presence of an iron(iii)- trapping additive which is much less strongly coordinated to the iron(ii) center than the acetate ion Fe(II)TPPS 4- may function as a heme model. 5. SCIENTIFIC PUBLICATIONS AND PRESENTATIONS Publications closely related to the dissertation 1. Róbert Huszánk and Ottó Horváth A heme-like, water-soluble iron(ii) porphyrin: thermal and photoinduced properties, evidences for sitting-atop structure Chem. Commun. 2005, Ottó Horváth, Róbert Huszánk, Zsolt Valicsek and György Lendvay Photophysics and photochemsitry of kinetically labile, water-soluble porphyrin complexes Coord. Chem. Rev., 2006, 250,

8 3. Róbert Huszánk, György Lendvay, Ottó Horváth Air-stable, heme-like water-soluble iron(ii)-porphyrin: in situ preparation and characterization J. Biol. Inorg. Chem., 2007, 12, Publication related to the dissertation 1. Ottó Horváth and R. Huszánk Degradation of surfactants by hydroxyl radicals photogenerated from hydroxoiron(iii) complexes Photochem. Photobiol. Sci., 2003, 2, Presentations and posters on international conferences 1. R. Huszánk, O. Horváth Oxidative degradation of organic pollutants by photocatalytically generated hydroxyl radicals microcad 2002 International Scientific Conference, Miskolc, Hungary, 2002, March R. Huszánk, O. Horváth Formation, thermal and photoinduced reactions of a water-soluble iron(ii)-porphyrin Tetranational Conference Perspectives of Photochemistry in the New Millennium Badgastein, Austria 2004, March O. Horváth, R. Huszánk, Z. Valicsek Photophysics and Photochemistry of Kinetically Labile, Water-Soluble Porphyrin Complexes 16th International Symposium on Photochemistry and Photophysics of Coordination Compounds (ISPPCC), Asilomar, USA, 2005, July 2-6, (Abst. O-44). 4. O. Horváth, Z. Valicsek, G. Lendvay, R. Huszánk Photophysics and photochemistry of water-soluble sitting-atop metalloporphyrins Central European Conference on Photochemistry 2006 Bad Hofgastein, Austria, 2006, March O. Horváth,, Z. Valicsek, G. Lendvay, R. Huszánk The Role of Sitting-Atop Coordination in the Photoinduced Properties of Water-Soluble Metalloporphyrins 17th International Symposium on Photochemistry and Photophysics of Coordination Compounds (ISPPCC), Dublin, Ireland, 2007, June 24-28, (Abst. O 29, p. 100). 6

9 Presentations on national conferences 1. Huszánk R., Horváth O. Felületaktív anyagok oxidatív lebontása fotokatalitikusan előállított hidroxilgyökökkel MTA Reakciókinetikai és Fotokémiai MB ülése, Balatonalmádi, április Horváth O., Huszánk R., Valicsek Zs. A központi fémion oxidációs állapotának hatása metalloporfirinek fotofizikai és fotokémiai tulajdonságaira XXXVIII. Komplexkémiai Kollokvium, Gyula, május Horváth O., Huszánk R., Valicsek Zs. Vízoldható metalloporfirinek egyensúlyi, fotofizikai és fotokémiai tulajdonságai MTA Reakciókinetikai és Fotokémiai MB ülése, Balatonalmádi, április Horváth O., Huszánk R., Lendvay Gy., Valicsek Zs. "Különböző összetételű vízoldható porfirin-komplexek szerkezetének és fotoindukált viselkedésének vizsgálata", XL. Komplexkémiai Kollokvium, Dobogókő, május Huszánk R., Horváth O. Hem típusú vas(ii)- és vas(iii)-porfirinek előállítása, termikus, fotofizikai és fotokémiai tulajdonságainak vizsgálata MTA Reakciókinetikai és Fotokémiai MB ülése, Balatonalmádi, április The dissertation is available electronically on the following website: 7