A.P.H.J Schenning

Control of aggregation and tuning of the location of porphyrins in synthetic membranes as mimics for cytochrome P450

The aggregation and location of two series of tetraarylporphyrins in positively and negatively charged bilayers have been examined. Aggregation of the porphyrins can be reduced by introducing pyridinium groups on the porphyrin ring. In the positively charged bilayers, the degree of aggregation of the porphyrins increases with the number of charges on it. The opposite behavior is found in the case of negatively charged bilayers. All the charged porphyrins form face to face type aggregates whereas the uncharged ones form edge to edge type aggregates. Reduction of aggregation can also be achieved by using “picket-fence” type porphyrins which form head to tail aggregates. The location of the porphyrins in the bilayer is also investigated. The charged porphyrins are located near the aqueous interface and the uncharged ones in the hydrophobic part of the bilayer. Picket-fence porphyrin 7 was found to be the most promising candidate for being studied as a catalyst in cytochrome P450 mimics.

Development of supramolecular metalloprotein mimics

Supramolecular mimics of metalloproteins, viz. cytochrome P-450 and iron- sulfur proteins are described. The cytochrome P-450 mimic consists of a Mn porphyrin and a Rh complex which are incorporated within a vesicle membrane in water. This system catalyses the reductive activation of molecular oxygen in the epoxidation of alkenes at Mn, with reducing equivalents derived from the simultaneous Rh catalysed oxidation of formate to carbon dioxide. In the mimics for iron-sulfur proteins, iron-sulfur clusters are encapsulated in diphenylglycoluril and cyclotriveratrylene cavitands. The encapsulation by the cavitands modifies the electrochemical parameters, e.g. the redox potential, of the iron-sulfur clusters, in a way that has certain analogies to the effects of encapsulation by the protein in ferredoxins and high-potential iron-sulfur proteins.

Redox behaviour of novel copper(II) crown ether–pyrazole complexes

A novel dinuclear copper(II) diazacrown ether complex reduces in solution to the copper(I) state; the related mononuclear copper(II) monoazacrown ether complex undergoes reduction, when K+-ions are added.

Copper(II) bipyridine and crown ether-bipyridine complexes: X-ray structures, characterization, and properties as histamine receptors

Abstract he synthesis and characterization, including the crystal structure, of the complex (2) of Cu(II) with the crown-ether bipyridine ligand, 1[5–2,2′-bipyridyl)carbonyl]-1-aza-4,7,10,13-tetraoxacyclopentadecane (1), are described. Compound 2, C27H49N3O18Cl2Cu, crystallizes in the triclinic space group P1 with cell constants a = 10.160(1), b = 13.014(1), c = 15.934(2) A, α = 74.18(1)°, β = 84.83(1)°, γ = 71.54(1)°, V = 1923.0(4) A3, Z = 2, dcalc = 1.448 g cm−3. The crystal structure was solved by vector search methods and refined by full-matrix least-squares on F2 to R = 0.086 for 3163 observed reflections (I > 2σ(I)), 83 restraints and 390 parameters. The crystals contain two formula units per cell as a dimer, with each carbonyl oxygen of one monomer complex coordinating to the copper ion of the other. Each copper has elongated octahedral coordination geometry, with two nitrogens of one bipyridyl unit and four oxygens, viz. two water molecules, one perchlorate, and one carbonyl, as ligand donor atoms...

Supramolecular Models of Metallo-Proteins

Models of metallo-enzymes and -proteins e.g. iron-sulfur proteins, dinuclear copper proteins, and monooxygenases are described. In particular, the potential role of these complexes as supramolecular catalysts is explored.

Design and synthesis of model systems for oxygen binding and activation in dinuclear copper proteins.

Following the spectroscopic1,2 and crystallographie3,6 characterization of the dinuclear copper site of hemocyanin, the coordination chemistry of models for such sites was developed7,8. Nature employs the dinuclear copper site for binding of dioxygen, as found in the hemocyanins, the oxygen transport proteins of molluscs and arthropods. It is also employed in enzymes, such as tyrosinase9, and, in combination with copper ions representing other types of biological copper, lacease10 and ascorbate oxidase11, for the activation of dioxygen. Interestingly, protons and chloride ions affect the cooperativity of the oxygen binding by Panulirus interruptus (spiny lobster)12 and Limulus polyphemus (horseshoe crab)13 hemocyanin, respectively, whereas the aggregation of Octopus dofleini (Pacific octopus) hemocyanin subunits to form a functional unit is controlled by magnesium ions14. Recent crystal structures and spectroscopic studies5,6,15 of oxy- and deoxy-hemocyanin under a variety of circumstances have given indications that these effects may operate at the level of control of the Cu-Cu distance.