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The effect of hindered axial ligand rotation on the NMR properties of ortho-substituted TPPFEL2+ complexes
268
Abstracts
H()fjl
NEAR IN%ARED ADSDRPTIMU SPECTRA CiF CVANOMETtiEMM;LOBIN AT CRYOGENIC TEMPERATURES. M. Leone, A. Cupane, E. Vitrano and L. Cordons. Istituto di Fisica and UVSM-CISN - 90123 Palermo-Italy. We measured the temperature dependence of nir absorption spectra of cyanomethemoglobin in solutions containing D,O and dsuterated glycerol as samples were horrogenecus and transparent in the whole a cryoprotectant; features were observed at temperature range (290-20 K). Two relevant temperatures near the solvent glass transition (220-180 K): a) besides the four charge transfer bands already reported Cll, a new band at abak all band profiles exhibited a non rnomtonic 5SOO cm-' was resolved, b) thermal evolution. Both features can be ascribed to a readjustment of the CN-Fe3'-porphyrin complex related to the structural change of the external medium following the glass transition. The data reported are tentatively interpreted in terms of vibronic coupling of the Fe-Ml stretching mode with the electronic transitions. Cl1 Eaton, W.A. and Hofrichter J. (1981) Methods Enzymol. 7&, 175-261.
H()SzTHE INTERACTION OF WATER WITH THE ACTIVE SITE OF LACTOPEROXIDASE. G.B. Crull and H.M. Goff, The University of Iowa, Iowa City, IA 52242, U.S.A. To evaluate the accessibility of water to the active site of lactoperoxidase (LPO), the relaxation rate of bulk water protons has been studied. These rates have been measured in the presence of native LPO, as well as the fluoride, thiocyanate and cyanide complexes of LPO. A pair of fast exchanging protons has been shown to come within 3.2 A of the iron atom of native LPO. In the presence of either fluoride ion, a known ligand for the iron, or thiocyanate ion, these rapidly exchanging protons were found at a similar distance of 3.2 A. In the presence of saturating amounts of cyanide ion, a tight binding ion for the heme iron, no rapidly exchanging protons were observed. These data are consistent with proton interaction at an amino acid site near the heme iron.
H()f#3TlWEFFEXT OF HINDWED PROPERTIES
AXIAL LIGAND ROT$T~lXWO OF ORTHO-SUBSTITUTED TPPFEL
NMR
U. Simonis, F. A. Walker, San Francisco State Zlniversity, 'San Francisco, CA 94132. It has been suggested that the orientation of axial ligands may affect the spectroscopic and redox properties of heme proteins. In order to evaluate the importance of the orientation effect we have synthesized ortho-substituted tetraphenylporphinatoiron(II1) complexes ith imidazoles and pyridines as axial ligands. Temperature dependent Y H NMR studies showed a very unique pyrrole splitting pattern: Depending on the nature of the axial ligand, up to eight pyrrole resonances were observed. The splitting pattern can be explained by unsymmetrical substitution and a nonrotating axial ligand. The results and interpretation will be discussed in detail.
Abstracts
H()fjl
NEAR IN%ARED ADSDRPTIMU SPECTRA CiF CVANOMETtiEMM;LOBIN AT CRYOGENIC TEMPERATURES. M. Leone, A. Cupane, E. Vitrano and L. Cordons. Istituto di Fisica and UVSM-CISN - 90123 Palermo-Italy. We measured the temperature dependence of nir absorption spectra of cyanomethemoglobin in solutions containing D,O and dsuterated glycerol as samples were horrogenecus and transparent in the whole a cryoprotectant; features were observed at temperature range (290-20 K). Two relevant temperatures near the solvent glass transition (220-180 K): a) besides the four charge transfer bands already reported Cll, a new band at abak all band profiles exhibited a non rnomtonic 5SOO cm-' was resolved, b) thermal evolution. Both features can be ascribed to a readjustment of the CN-Fe3'-porphyrin complex related to the structural change of the external medium following the glass transition. The data reported are tentatively interpreted in terms of vibronic coupling of the Fe-Ml stretching mode with the electronic transitions. Cl1 Eaton, W.A. and Hofrichter J. (1981) Methods Enzymol. 7&, 175-261.
H()SzTHE INTERACTION OF WATER WITH THE ACTIVE SITE OF LACTOPEROXIDASE. G.B. Crull and H.M. Goff, The University of Iowa, Iowa City, IA 52242, U.S.A. To evaluate the accessibility of water to the active site of lactoperoxidase (LPO), the relaxation rate of bulk water protons has been studied. These rates have been measured in the presence of native LPO, as well as the fluoride, thiocyanate and cyanide complexes of LPO. A pair of fast exchanging protons has been shown to come within 3.2 A of the iron atom of native LPO. In the presence of either fluoride ion, a known ligand for the iron, or thiocyanate ion, these rapidly exchanging protons were found at a similar distance of 3.2 A. In the presence of saturating amounts of cyanide ion, a tight binding ion for the heme iron, no rapidly exchanging protons were observed. These data are consistent with proton interaction at an amino acid site near the heme iron.
H()f#3TlWEFFEXT OF HINDWED PROPERTIES
AXIAL LIGAND ROT$T~lXWO OF ORTHO-SUBSTITUTED TPPFEL
NMR
U. Simonis, F. A. Walker, San Francisco State Zlniversity, 'San Francisco, CA 94132. It has been suggested that the orientation of axial ligands may affect the spectroscopic and redox properties of heme proteins. In order to evaluate the importance of the orientation effect we have synthesized ortho-substituted tetraphenylporphinatoiron(II1) complexes ith imidazoles and pyridines as axial ligands. Temperature dependent Y H NMR studies showed a very unique pyrrole splitting pattern: Depending on the nature of the axial ligand, up to eight pyrrole resonances were observed. The splitting pattern can be explained by unsymmetrical substitution and a nonrotating axial ligand. The results and interpretation will be discussed in detail.