Tetrapyrrolic Glycosylated Macrocycles for an Application in PDT.

The synthesis and characterization of amphiphilic glycoconjugated porphyrins, benzochlorin, and azaporphyrins were reported. Among these molecules, several were found to be efficient photosensitizers in an in vitro assay using the human tumoral cell line HT29. Moreover, glycosylated benzochlorin and azaporphyrins, whose absorption bands in the red region of the visible spectrum are substantially increased as compared to porphyrins, display a good photocytotoxicity on tumor cells after irradiation with wavelength above 590 nm. © 1999 Society of Photo-Optical Instrumentation Engineers.

13C CP/MAS NMR Studies of Hemoprotein Models with and without an Axial Hindered Base: (13)C Shielding Tensors and Comparison with Hemoproteins and X-ray Structural Data.

13C cross-polarization magic-angle-spinning (CP/MAS) NMR spectra of several carbonmonoxide (93-99% (13)C enriched) hemoprotein models with 1,2-dimethylimidazole (1,2-diMeIm) and 1-methylimidazole (1-MeIm) as axial ligands are reported. This enables the (13)CO spinning sideband manifold to be measured and hence the principal components of the (13)CO chemical shift tensor to be obtained. Negative polar interactions in the binding pocket of the cap porphyrin model and inhibition of Fe-->CO back-donation result in a reduction in shielding anisotropy; on the contrary, positive distal polar interactions result in an increase in the shielding anisotropy and asymmetry parameter in some models. It appears that the axial hindered base 1,2-dimethylimidazole has little direct effect on the local geometry at the CO site, despite higher rates of CO desorption being observed for such complexes. This suggests that the mechanism by which steric interactions are released for the 1,2-diMeIm complexes compared to 1-MeIm complexes does not involve a significant increase in bending of the Fe-C-O unit. The asymmetry of the shielding tensor of all the heme model compounds studied is smaller than that found for horse myoglobin and rabbit hemoglobin.

X-ray absorption spectroscopy of carbonyl basket handle Fe(II) porphyrins: the distortion of the tetrapyrrolic macrocycle.

The distortion of the tetrapyrrolic macrocycle, the Fe-C-O bond angle and the Fe local electronic structure of carbonyl basket-handle Fe2+ porphyrins as a function of the basket-handle chain length have been studied by X-ray absorption near edge structure (XANES) spectroscopy, both in the solid state and in toluene solution. The Fe-C-O bond angle has been found to be linear in all compounds while the increasing distortion of the macrocycle with shortening of the chain length is indicated by the multiple scattering resonance in the heme plane appearing at 22 eV in the XANES spectrum.

Photoinitiated vectorial transmembrane electron transfer in bilayers sensitized by a face to face triporphyrin acting as a molecular electronic device. Amplification due to ionic coupling.

Under light excitation transmembrane electron transfer is observed when a stacked Zn-Cu-Zn triporphyrin is incorporated in a bilayer between aqueous redox phases. The electric polarization of the membrane due to the photoinduced transmembrane charge flux drives ion transport. This effect increases the net charge transfer across the system, giving rise to an amplification similar to a field effect transistor. Thus this system can be considered an organic phototransistor.

Synthesis, cellular uptake of, and cell photosensitization by a porphyrin bearing a quinoline group.

A tetraphenyl porphine linked to a 7-chloroquinoline (5,10,15,20-tetraphenyl-1-3-[4-(4-aminobutyl)7-chloroquinoline] propioamidoporphine, TPPQ) was synthesized and examined as a potential photosensitizer for photodynamic therapy (PDT) of proliferative diseases. With respect to haematoporphyrin, TPPQ is a good in vitro photodynamic sensitizer producing singlet oxygen in 1% Triton X100 solutions. As with other hydrophobic porphyrins used in PDT, blood lipoproteins strongly bind TPPQ. Thus one low density lipoprotein (LDL) can incorporate 25 TPPQ molecules and 17 TPPQ molecules are taken up by one high density lipoprotein (HDL). Cell delivery of TPPQ using HDL or human serum albumin (HSA) as carrier is rather weak. However, an efficient TPPQ delivery to human skin fibroblasts is observed, partly aided by receptor-mediated endocytosis of LDL. Fluorescence spectroscopy shows that the cellular localization of TPPQ is both carrier and time dependent. During its delivery with LDL, TPPQ does not significantly impair the endocytosis of LDL-receptor complexes. After delivery with LDL, TPPQ is as efficient as other haematoporphyrin derivatives used in the PDT of cancers in photosensitizing human skin fibroblasts.

Linear Fe-C-O configuration in carbonyl 1-methylimidazole iron(II) porphyrin detected by XANES in dispersive mode.

The linear Fe-C-O configuration has been determined in the carbonyl 1-methylimidazole hindered iron(II) porphyrin derived from 'basket handle' complexes in which there are no constraints on the proximal imidazole. The structure at the iron site has been determined in toluene solution by fast measurements of XANES spectra, using the dispersive X-ray absorption method.

Energy barriers in binding of carbon monoxide and oxygen to heme model compounds.

Binding of carbon monoxide and oxygen to sterically protected heme model compounds (basket-handle porphyrins) was investigated in liquid toluene at temperatures from 180 to 300 K by laser flash photolysis. Only a single exponential rebinding process from the solvent could be seen in the time range of 20 nsec to milliseconds. The fraction of ligands that initially escaped into the solvent decreased when the temperature was lowered, and the Arrhenius plots for the rebinding rate coefficients were found to deviate significantly from linearity. These findings suggest that protected heme model compounds might react according to a double energy-barrier scheme. In contrast, the reaction of an unprotected porphyrin can be described by a single energy barrier.

Linear free-energy relationships in binding of oxygen and carbon monoxide with heme model compounds and heme proteins.

For almost a decade heme model compounds have been designed to test the influence of proximal base restraint or of distal steric hindrance upon the ligand affinity of hemoglobins. Despite the variety of molecular structures which have been successively proposed, the evaluation of the reported data is rendered difficult because of the small number of examples available within each series. In this paper we report on the kinetics of binding of oxygen and carbon monoxide with a series of nine closely related heme models. The 'basket-handle porphyrins' allow one to modify the constraints exerted upon a chelated proximal base as well as the chemical environment of the distal side of the heme. One salient feature of these models is the possibility of introducing a hydrogen-bond stabilization of the oxygen by incorporating an amide group in the vicinity of the iron centre. The structural changes among models are sufficiently 'soft' to cause an almost continuous variation of the binding constants and rate parameters. The latter are found to obey a definite linear free energy relationship which proves that the series is homogenous from a thermodynamic viewpoint. This suggests an alternative way for comparing the trends in ligand binding in different heme model families with those of heme proteins, which is developed in the discussion using literature data.

Oxidation of monosubstituted olefins by cytochromes P-450 and heme models: evidence for the formation of aldehydes in addition to epoxides and allylic alcohols.

Aldehydes RCH2CHO are formed in addition to epoxides and allylic alcohols upon oxidation of the monosubstituted olefins RCH=CH2, styrene and 6-phenoxy-hex-1-ene, either by liver microsomal systems in the presence of NADPH and O2 or C6H5IO, or by iron-porphyrin- C6H5IO model systems. These aldehydes do not derive from rearrangement of the corresponding epoxides suggesting that they are formed by an hydrogen migration within an interdiate formed by reaction of the olefin with the active oxygen-iron complex. Heme model studies show that the competition between the three possible routes of oxidation of these olefins is greatly dependent upon the environment of the iron.

NMR investigation of the electric properties and magnetic states of hemes and hemoproteins : the S = 2 state in ferrous porphyrins.

The proton NMR data of a synthetic model of deoxy-myoglobin and hemoglobin show one that:(i) the ground state of the high spin iron (II) complex must be described by at least two electronic levels separated by ca.200 cm-1 and resulting from the removal of the degeneracy of the 5E level; (ii) this in-plane rhombic distorsion is directed towards the methine bridges of the porphyrin ring. It is proposed that the rhombicity results from specific interactions of the lambda orbitals of the axial base with the iron d lambda orbitals.

Five-coordinate iron-porphyrin as a model for the active site of hemoproteins. Characterization and coordination properties.

Preparation of iron(III)-deuteroporphyrin 6(7)-methyl ester, 7(6)-(histidine methyl ester) by coupling histidine methyl ester to deuterohemin has been performed using the mixed carboxylic/carbonic-acid-anhydride method. This compound, which is very soluble in various organic solvents, can be considered as a prosthetic group model for the active site of five-coordinate hemoproteins. In the oxidized state a basic, a neutral or an acid form can be isolated. The basic and acid forms are monomeric at all concentrations. The neutral form is found dimeric in concentrated solutions while it is monomeric at low concentration. The coordination state of iron in these various species is investigated. The neutral form reacts with ligands, such as nitrogenous organic bases, leading to six-coordinate well-known hemichromes which exhibit low-spin electron spin resonance (ESR) spectra. The reaction of anionic ligands, such as F-, CN-, NO-2 and N-3, with the neutral form model leads to unsymmetrical six-coordinate complexes whose optical and ESR spectra are similar to those of synthetic deuteromyoglobin. In benzene, toluene or dichloromethane solutions iron (II)-deuteroporphyrin 6(7)-methyl ester, 7(6)-histidine methyl ester), obtained from ferric forms by heterogeneous reduction with aqueous dithionite, exhibits an optical spectrum characteristic of a five-coordinate high-spin ferrous complex. At low temperature important spectral modifications are observed indicating a dimeric association. At room temperature it binds one nitrogenous base molecule leading to the well-known hemochrome. It reacts also with carbon monoxide with a very high affinity constant (4.5 X 10(8) M-1), comparable to that of the isolated human hemoglobin alpha and beta chains, but much higher than the values reported for other various models, suggesting that the side-chain length bearing the fifth ligand may have an important influence upon the reactivity of the sixth position of the iron ion. At low temperature in toluene or dichloromethane, this compound reversibly binds oxygen without oxidation of the iron ion while oxidation occurs at room temperature. The significance of these results is discussed in relation with the local environment, the electronic nature of the base and the immobilization of the heme group in hemoproteins.