Thin Layers of Metalloporphyrins
Gas Sensing, Catalytica and Heme-Modeling Properties of Metalloporphyrins Sublimed Layers
Tech Area / Field
- CHE-THE/Physical and Theoretical Chemistry/Chemistry
- ENV-APC/Air Pollution and Control/Environment
8 Project completed
Senior Project Manager
Tyurin I A
Scientific Technological Centre of Organic and Pharmaceutical Chemistry SNPO / Molecular Structure Research Center, Armenia, Yerevan
- Crystal Logic Inc., USA, CA, Los-Angeles\nUniversity of California / Department of Chemistry and Biochemistry, USA, CA, Santa Barbara\nCoastal Carolina University, USA, SC, Conway
Project summarySublimed layers of the metalloporphyrins (MP) similar to the other semiconducting organic materials exhibit the high sensitivity of their electrical resistivity to the ambient atmosphere  and can serve as a sensor of the various gases including the toxic ones. Depending on MPs (the nature of metal ion and character of the ring’s substitutes) and supramolecular structure of the layers dictated by the conditions of their formation  they can offer the different functional characteristics in terms of selectivity, reversibility and selectivity to the distinct type of detected gases. Unlike to closely related phthalocyanines  the sensor properties of MP are much less investigated. The influence of electron donor (NH3, CO) and acceptor (Cl2, NO2) toxic gases on the chemiresistant and optical properties of the MPs will be investigated in this part of the project. A large number of MPs with electron-rich and electron-seeking macrocycles and diffe-rent type of metals (transition and non-transition) will be synthesized with this goal. Our research group accumulates experience of the combined application of the electrical and spectral methods (IR, RRS, UV-Vis) for such type of investigations over a number of years [1,4]. The issue of recommendations on the high sensitive and selective gas sensors based on MPs is the main objective of this part of the project.
Metallocomplexes of meso-tetraarylporphyrins (MTAP) can form “porphyrin sponges”, which allows incorporating guest molecule . It was shown that the structure of sublimed layers of MTAP is also sponge-like . The microporosity of samples increases if the sublimed layers are formed during deposition on a low-temperature (T=77 K) surface. In these layers potential reagents can easily diffuse across the thickness, and the adduct that formed can be studied by spectral methods without interference by a solvent. Previously we have found that low tempera-ture sublimed films of meso-tetraphenylporphyrinatocobalt(II) (CoTPP) oxidize CO with O2 . In this part of the project we intend to study catalytic oxidation of different substrates (olefins, phosphins etc.) by the sublimed layers of MTAP which are able to bind dioxygen at low tempe-ratures [2, 8]. Oxidation processes catalyzed by the solutions of MP in the conditions of homoge-neous catalysis are now in the focus of attention . The technique developed in our laboratory  makes it possible to study very air-sensitive compounds like Fe(II)- and Mn(II)- porphyrins and perform spectral measurements without hindering influence of the solvent. By means of spectral methods (IR, RRS, UV-Vis, ESR) and low temperature application the efforts will be mounted to detect the intermediates which will throw light on the mechanism of catalytic process. The chromatographic and mass-spectrometric analysis of gaseous mixtures formed during the catalytic transformation will also be performed. The results obtained will amplify our knowledge on the nature of catalytic processes performed by the MP.
Processes connecting to interactions of MP with the nitrogen oxides and their derivatives cause the large number of functions performed by the heme-containing enzymes in vivo. Among them are the biologically important molecules as nitrogen oxide , nitrite-ion , peroxynitrite radical , etc. It was established by us that interaction of NO2 with the sublimated layer of Fe(II)TPP leads to the formation of nitrato-complex Fe(III)TPPNO3- , instead of the nitro-comlex which was formed in the case of CoTPP . Preliminary results suggest that the same pattern takes place in the case of Mn(II)TPP. In the project it is proposed to elucidate the mechanism of this transformation. For solving this problem the matrix isolation spectroscopy will be used. The experience in this field is available . With application of the same method it is proposed to obtain and spectrally characterize peroxynitrite radical coordinated with M(TPP) (M=Co, Fe, Mn). Although this complex was postulated in a number of works [13, 17] it was spectrally characterized only for the alcali metals ion pairs . Experimental and computational works will be performed in this case.
Nitrosyl metalloporphyrins remain the focus of attention because nitric oxide (NO) has emerged as an important biological messenger involved in a number of physiological processes and the fact that it has been found to target heme-containing proteins. The reactive nature of NO which rapidly oxidizes to form NO2 makes it necessary to search the NO donor systems. Nitrosyl metallo-porphyrins are among the compounds that undergo efficient photodenitrosylation in solution. It is of interest to investigate the photochemical behavior of nitrosyl metalloporphyrins in solid state and its thin layers can provide the convenient objects for such type of investigations.
In connection with the peculiarities that was observed for the nitrosyl complex MnTPPNO  obtained in the sublimed layer, this system will also be studied by matrix isolation method. In all this studies the technique of isotope-substituted species will be used (15NO, 15NO2, MTPP-d8, MTPP-d20 and MTPP-d28). The data obtained will increase our present view on the biologically important transformations taking place in the coordination sphere of MP.
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