Resonance Raman Spectra of Manganese-Porphyrins on Ion-Exchange Resins Exhibiting Uricase-Like Catalytic Activity

Abstract

Ion-exchange resins modified with some manganese(III)-porphyrins (Mn3+-Pr) show a uricase-like catalytic activity, which is applicable to the determination of uric acid. The resonance Raman spectra of Mn3+-Pr indicate that Mn3+-porphyrins on modified resins are reduced to Mn2+-porphyrins with oxidizing uric acid; Mn2+-porphyrins then return to Mn3+-porphyrins by oxidation with 02 in the reaction system. It was concluded on the basis of these results that the modified resins show an uricase-like activity by repeating this redox cycle of manganese-porphyrins on the modified resins. Mn3+-Pr exhibited no oxidative catalytic activity for 7-methylated derivatives of uric acid, indicating that the nitrogen atom at the 7-position of uric acid plays an important role in the activity of Mn3+-Pr. In clinical assays, enzyme reactions catalyzed by uricase, peroxidase and catalase are frequently used as important analytical reactions. However, these enzymes have some disadvantages regarding stability, handling, purity and storage. As a study of improvement of these disadvantages, it was previously indicated that some resins modified with metallo-porphyrins exhibit such enzyme-like activities as peroxidase, catalase and uricase, and are available for clinical analyses as good mimics of these enzymes.2-5In the present study resins modified with Mn3+-tetrakis(4-sulfophenyl)porphine and Mn3+-tetrakis(1-methylpyridinium-4-yl)porphine, exhibiting a uricaselike catalytic activity, were dealt with by means of resonance Raman spectroscopy. In order to know how these modified resins act as a catalyst, the resonance Raman spectra were measured in the course of oxidizing uric acid. As the result, the uricase-like activity of the modified resins was found to be caused by a redox cycle of manganese ion. Experimental CompoundsTetrakis(4-sulfophenyl)porphine (TPPS) and tetrakis(1-methylpyridinium-4-yl)porphine (TMPyP) were purchased from Tokyo Kasei Kogyo Co. Ltd. and used without further purification. Their manganese(III)-complexes, Mn3+-TPPS and Mn3+-TMPyP (Fig. 1), were prepared by methods similar to those given in the literature.6 Anion-exchange (Amberlite IRA 900) and a cation-exchange (Dowex MSC-1) resins were regenerated in their chloride and sodium forms, respectively. The resins modified with manganese-porphyrins (25 µmol/ g), Mn3+-TPPSr and Mn3+-TMPyPr, were prepared as described before.6 All other chemicals were of reagent grade and used without further purification. Stock solutions of the samples were prepared by dissolving uric acid (UA) or its derivatives (0.1 g, Sigma Chemical Co.) with lithium carbonate (0.1 g) in 100 ml water. A buffer solution (pH 11.0) was prepared by mixing a 0.2 M sodium carbonate solution with a 0.2 M boric acid-0.2 M potassium chloride solution.t Present address:

A Spectroelectrochemical Investigation of the Reduction of the Water-Soluble MnTSPP: SERS Spectra of MnIITSPP

“…Resonance Raman spectra were also obtained of MnTPP embedded in the ionic pockets of polymeric Nafion. 45 As was observed for MnTPP, a band was observed at 1453 cm -1 in the RR spectra of Mn III TPP embedded in Nafion. This band was absent in our solution Raman spectra; however, excellent agreement was observed between our solution Raman spectrum of MnTSPP and the RR spectra of MnTPP embedded in polymeric Nafion, except that the 1570 cm -1 solution Raman band is shifted up to 1579 cm -1 in the latter and an upshift of 8 cm -1 is observed for the 1589 cm -1 band in the former.…”

“…Resonance Raman spectra were also obtained of MnTPP embedded in the ionic pockets of polymeric Nafion . As was observed for MnTPP, a band was observed at 1453 cm -1 in the RR spectra of Mn III TPP embedded in Nafion.…”