Efficient synthesis of a porphyrin-N-tripod conjugate with covalently linked proximal ligand: toward new-generation active-site models of cytochrome c oxidase

Functionalization of 1-methyl-1H-imidazole-5-carboxylic acid at the C-2 position: Efficient syntheses of 2-substituted t-butyl 1-methyl-1H-imidazole-5-carboxylates

A number of 2-substituted t-butyl 1-methyl-1H-imidazole-5-carboxylates, which can be readily converted to the corresponding acids, were efficiently prepared from t-butyl 2-bromo-1-methyl-1H-imidazole-5-carboxylate via brominelithium exchange or palladium-catalysed coupling.

Synthesis of chiral porphyrins and their use in photochemical oxidation of carbonyl compounds

A series of chiral A4, A2B2, and AB3 porphyrins bearing proline moieties at the meso-phenyl group has been synthesized. Photostability studies revealed that the number of L-proline units and their position on meso-phenyl rings strongly influence the decomposition rate of the catalyst. 5,10,15-Tris(mesityl)-20-(3-prolinanilidylphenyl)-21,23H-porphyrin is the most stable while porphyrin bearing four 3-prolinanilidylphenyl substituents completely decomposes in CHCl 3 within 3 h. Singlet oxygen quantum yields of the conjugates were determined by measuring the peak areas of the NIR emission of 1 O 2 (1280 nm) generated by these compounds and compared to that generated by the reference standard TPP. Selected porphyrins were tested as catalysts in the photooxidation of carbonyl compounds at the α-position.

Recent applications of a synthetic model of cytochrome c oxidase: beyond functional modeling

This account reports recent developments of a functional model for the active site of cytochrome c oxidase (CcO). This CcO mimic not only performs the selective four-electron reduction of oxygen to water but also catalytically reduces oxygen using the biological one-electron reductant, cytochrome c. This functional model has been used to understand other biological reactions of CcO, for example, the interaction between the gaseous hormone, NO, and CcO. A mechanism for inactivating NO-CcO complexes is found to involve a reaction between oxygen and Cu(B). Moreover, NO is shown to be capable of protecting CcO from toxic inhibitors such as CN(-) and CO. Finally, this functional CcO model has been used to show how H(2)S could induce hibernation by reversibly inhibiting the oxygen binding step involved in respiration.

Iron-porphyrin NO complexes with covalently attached N-donor ligands: formation of a stable six-coordinate species in solution

A series of substituted tetraphenylporphyrin type macrocycles (TMP or To-F(2)PP) with covalently attached N-donor ligands (pyridine or imidazole linker) have been synthesized. Linkers with varying chain lengths and designs have been applied to systematically investigate the effect of chain length and rigidity on the binding affinity of the linker to the corresponding Fe(II)-NO heme complexes. The binding of the linker is monitored in solution using a variety of spectroscopic methods including UV-vis absorption, EPR, and IR spectroscopy. Both the N-O stretching frequency and the imidazole (14)N hyperfine coupling constants show a good correlation with the Fe-(N-donor) bond strength in these systems. The complexes with covalently attached pyridyl and alkyl imidazole ligands only exhibit weak interactions of the linker with iron(II). However, the stable six-coordinate complex [Fe(To-F(2)PP-BzIM)(NO)] (4) is obtained when a rigid benzyl linker is applied. This complex exhibits typical properties of six-coordinate ferrous heme-nitrosyls in which an N-donor ligand is bound trans to NO, including the Soret band at 427 nm and the typical nine line (14)N hyperfine splitting in the EPR spectrum. A crystal structure has been obtained for the corresponding zinc complex. Here, we report the first systematic study on the requirements for the formation of stable six-coordinate ferrous heme nitrosyl complexes in solution at room temperature in the absence of excess axial N-donor ligand.

Appending a tris-imidazole ligand with a Tyr 244 mimic on the distal face of bromoacetamidoporphyrin

[structure: see text] Bromoacetamidoporphyrin is a convenient synthon for the attachment of distal superstructures at room temperature in good yields. New models are presented that contain a tris-imidazole distal ligand set bound to the porphyrin in either a binary or trinary fashion. More importantly, one distal imidazole is cross-linked to a phenol mimicking Tyr(244), making this model the closest structural analogue yet reported of the metal free cytochrome c oxidase (CcO) active site.

New advances in ligand design for synthetic modeling of metalloprotein active sites

Judicious control of ligand steric bulk and auxiliary structural elements enables the construction of novel synthetic complexes that model the properties of metalloprotein active sites, thus providing insight into their structure and function. Major recent developments include the synthesis of a number of unusual and biologically relevant complexes of copper and iron using elaborate N-donor and O-donor ligands.