The Mn oxidation state of two water soluble Mn porphyrins, MnTMPyP and MnTPPS 4 , was studied as a function of the aqua or hydroxo ligands of the Mn atom. In NaOH solutions, longlived O=Mn(IV) species were detected in the presence of O 2 . Conversely, the dihydroxo Mn(III) porphyrin reduces spontaneously to the Mn(II) species in the absence of O 2 . In alkaline solutions, these Mn porphyrins were able to electrocatalyze the 4-electron reduction of O 2 to H 2 O on a vitreous carbon electrode. 933397878 ∏ SPP full member in good standing Journal of Porphyrins and Phthalocyanines Published at http://www.u-bourgogne.fr/jpp/ J. Porphyrins Phthalocyanines 2005; 9: 436-443 Published on web 07/21/2005 J. Porphyrins Phthalocyanines 2005.09:436-443. Downloaded from www.worldscientific.com by EMORY UNIVERSITY on 08/05/15. For personal use only.

No abstract

The addition of cyclodextrins (α-CD, β-CD, 2-hydroxopropyl-β-CD and γ-CD) to aqueous solutions of representative cationic (MnTMPyP) and anionic (MnTPPS 4 ) water-soluble Mn porphyrins only substantially affect the behavior of the Mn(III)/Mn(II) couple when inclusion complexes (i.e. for MnTPPS 4 ) are formed. The voltammetric responses were interpreted under the assumption that the inclusion complexes are electroactive, which occurs after their adsorption on the electrode surface. In addition, the results point to a higher affinity of the cyclodextrins for Mn II TPPS 4 than for Mn III TPPS 4 .

ABSTRACT:The effect of the addition of b-and g-cyclodextrin (b-CD, g-CD) to water solutions (D 2 O) of the 4'-sulfonato derivatives of meso-tetraphenylporphyrin (TPPS 4 , TPPS 3 , TPPS 2o and TPPS 2a ) was studied by 1 H NMR at several temperatures. In all cases the disaggregation of the porphyrin homoassociates was detected, although in most cases it was only partial. Nuclear Overhauser signals (ROESY) show that cyclodextrin inclusion complexes were formed with TPPS 4 , TPPS 3 , and TPPS 2o , but not with TPPS 2a . These complexes include the sulfonatophenyl groups as guest, but not the hydrophobic phenyl substituents. The geometry of the complexes corresponds to that in which the sulfonatophenyl substituent is introduced through the secondary face of b-CD and through the primary face of g-CD.In the inclusion complexes the polar sulfonato group is inside the cyclodextrin cavity but near to the hydrophilic interface with the bulk water. This explains the absence of complexation in the case of cationic porphyrins such as 5,10,15,20-tetrakis(N-methylpyridin-4-yl)porphyrin (TMPyP), and the decrease in the solubility when the b-CD complex of 5,15-bis(4-sulfonatophenyl)porphyrin (DPPS 2o ) forms. Complexes of the cyclodextrins with porphyrin homoassociates were also detected. This indicates that the heteroassociation avoids the formation of staggered stacks of porphyrin homoassociates, but has less effect on the association through the hydrophobic region of the phenyl substituents. This last type of aggregation, which is not significantly affected by the addition of a-CD, explains why the hydrophobic phenyl substituents are not complexed by the cyclodextrins.