1,1'-Bis(diphenylphosphino)ferrocene Platinum(II) Complexes as a Route to Functionalized Multiporphyrin Systems

In this study, the cationic complex [PtMe(Me₂SO)(dppf)]CF₃SO₃ (PtFc) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) was exploited as a precursor to functionalize the multi-chromophoric system hexakis(pyridyl-porphyrinato)benzene (1). The final adduct [PtFc]₁₈-1, containing eighteen platinum(II) organometallic [PtMe(dppf)] fragments, was prepared and characterized through UV/Vis absorption, ³¹P{¹H}-NMR spectroscopy, and fluorescence emission. UV/vis and fluorescence titrations confirmed the coordination between the platinum(II) center and all the pyridyl moieties of the peripheral substituent groups of the porphyrin. The drop casting of diluted dichloromethane solution of [PtFc]₁₈-1 onto a glass surface afford micrometer-sized emissive porphyrin rings.

Peripherally Metalated Porphyrins with Applications in Catalysis, Molecular Electronics and Biomedicine

Porphyrins are conjugated, stable chromophores with a central core that binds a variety of metal ions and an easily functionalized peripheral framework. By combining the catalytic, electronic or cytotoxic properties of selected transition metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. This review article focuses on porphyrins bearing one or more peripheral transition metal complexes and discusses their potential applications in catalysis or biomedicine. Modulation of the electronic properties and intramolecular communication through coordination bond linkages in bis-porphyrin scaffolds is also presented.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Targeted and multifunctional arene ruthenium chemotherapeutics

The introduction of multifunctionalities for tumour targeting is becoming a popular strategy toward the development of new therapeutic agents. In particular, the multifaceted potential of ruthenium(II)-arene complexes show great promise as chemotherapeutics. An ever-increasing number of papers dealing with the integration of ruthenium complexes with biologically active molecules to derive bioorganometallic molecules of chemotherapeutic significance have been published in recent years. This perspective review presents a short overview of multifunctional ruthenium-based drugs, especially those containing arene ruthenium complexes, with the emphasis on the combination of photosensitizers with ruthenium complexes for the preparation of novel multifunctional photodynamic therapy agents.

Synthetic strategies towards ruthenium-porphyrin conjugates for anticancer activity

The conjugation of porphyrins to metal fragments is a strategy for making new compounds that are expected to combine the phototoxicity and the tumour-localization properties of the porphyrin chromophore with the cytotoxicity of the metal fragment for additive antitumour effect. We report here the preparation of new classes of porphyrin-ruthenium conjugates with potential bio-medical applications. Ruthenium was chosen because several Ru compounds have shown promising anticancer activity. The conjugation with the porphyrin moiety was accomplished either through peripheral pyridyl rings (e.g.meso-4'-tetrapyridylporphyrin, 4'TPyP) or through bpy units (e.g.meso-(p-bpy-phenyl)porphyrins, bpy(n)-PPs, n = 1-4). The number of Ru fragments attached to the porphyrins ranges from 1 to 4 and the total charge of the conjugates from -4 to +8. Different types of peripheral fragments, both Ru(III) and Ru(II), have been used: in some cases they are structurally similar to established anticancer compounds. Examples are [Na](4)[4'TPyP{trans-RuCl(4)(dmso-S)}(4)] (2), that bears four NAMI-type Ru(III) fragments, or [4'TPyP{Ru([9]aneS3)(en)}(4)][CF(3)SO(3)](8) (3) and [bpy(4)-PP{Ru([9]aneS3)(dmso-S)}(4)][CF(3)SO(3)](8) (9) (en = ethane-1,2-diamine, [9]aneS3 = 1,4,7-trithiacyclononane) that have four half-sandwich Ru(II) compounds. The Ru fragments may either contain one or more labile ligands, such as in 2 or in 9, or be coordinatively saturated and substitutionally inert, such as in 3 or in [bpy(4)-PP{Ru([12]aneS4)}(4)][CF(3)SO(3)](8) (11) ([12]aneS4 = 1,4,7,10-tetrathiacyclododecane). Most of the ruthenium-porphyrin conjugates described in this work are soluble--at least moderately--in aqueous solution and are thus suitable for biological investigations, in particular for cytotoxicity and photo-cytotoxicity tests.

A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent: synthesis, characterization, DNA binding, and melanoma cell studies

When the new porphyrin 5,10-(4-pyridyl)-15,20-(pentafluorophenyl)porphyrin is reacted with 2 equiv of Ru(bipy)(2)Cl(2) (where bipy = 2,2'-bipyridine) formation of the target ruthenated porphyrin is achieved with 40% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrin Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dpi) to bipy(pi*) metal to ligand charge transfer (MLCT) band. The bipyridyl pi to pi* transition occurs at 295 nm. Cyclic voltammetry experiments reveal two single-electron redox couples in the cathodic region at E(1/2) = -0.80 and -1.18 V vs Ag/AgCl associated with the porphyrin. Two overlapping redox couples at E(1/2) = 0.83 V vs Ag/AgCl due to the Ru(III/II) centers is also observed. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give a K(b) = 7.6 x 10(5) M(-1) indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 400 nm), complete nicking of the DNA is observed. Cell studies show that the ruthenated porphyrin is more toxic to melanoma skin cells than to normal fibroblast cells. When irradiated with a 60 W tungsten lamp, the ruthenium porphyrin preferentially leads to apoptosis of the melanoma cells over the normal skin cells.

Ruthenium porphyrin compounds for photodynamic therapy of cancer

Five 5,10,15,20-tetra(4-pyridyl)porphyrin (TPP) areneruthenium(II) derivatives and a p-cymeneosmium and two pentamethylcyclopentadienyliridium and -rhodium analogues were prepared and characterized as potential photosensitizing chemotherapeutic agents. The biological effects of all these derivatives were assessed on human melanoma tumor cells, and their cellular uptake and intracellular localization were determined. All molecules, except the rhodium complex which was not cytotoxic, demonstrated comparable cytotoxicity in the absence of laser irradiation. The ruthenium complexes exhibited excellent phototoxicities toward melanoma cells when exposed to laser light at 652 nm. Cellular uptake and localization microscopy studies of [Ru 4(eta (6)-C 6H 5CH 3) 4(TPP)Cl 8] and [Rh 4(eta (5)-C 5Me 5) 4(TPP)Cl 8] revealed that they accumulated in the melanoma cell cytoplasm in granular structures different from lysosomes. The fluorescent porphyrin moiety and the metal component were localized in similar structures within the cells. Thus, the porphyrin areneruthenium(II) derivatives represent a promising new class of organometallic photosensitizers able to combine chemotherapeutic activity with photodynamic therapeutic treatment of cancer.

Synthetic strategies and structural aspects of metal-mediated multiporphyrin assemblies

Porphyrins play a major role as active chromophores in artificial systems mimicking the natural photoinduced processes. The formation of coordination bonds between peripheral donor sites on the porphyrins and external metal fragments has proven to be an efficient alternative to covalent synthesis for the construction of multiporphyrin assemblies, whose complexity and beauty gradually approach those of the multichromophore systems found in nature. In a modular approach, relatively simple metal-mediated porphyrin adducts, owing to their thermodynamic and kinetic stability, can be exploited as building blocks in the construction of higher order architectures. Thus, multichromophore systems become accessible on demand, with a limited synthetic effort. The collection of solid-state structures reported here demonstrates that the flexibility of the porphyrins and the metal junctions, combined with the conformational freedom of the coordination bonds, may lead to assemblies with hardly predictable architectures. Examples in which X-ray structural determination was essential for establishing the real composition and geometry of the multiporphyrin assemblies are highlighted.

fac-[Re(CO)3(dmso-O)3](CF3SO3): a new versatile and efficient Re(i) precursor for the preparation of mono and polynuclear compounds containing fac-[Re(CO)3]+ fragments

We show here that the new complex fac-[Re(CO)3(dmso-O)3](CF3SO3) (1), efficiently prepared in one step from [ReBr(CO)5] and featuring a broad range of solubility, is, in general, a better precursor for the one-step synthesis of mono- and polynuclear inorganic compounds containing fac-[Re(CO)3]+ fragments compared to the commonly used (NEt4)2fac-[ReBr3(CO)3] and fac-[Re(CO)3(CH3CN)3](Y) (Y = PF6, BF4, ClO4) species. Compound 1 is the first example of a Re(I)-dmso complex structurally characterized and confirms the rule that dmso is always O-bonded when trans to CO. The reactivity of 1 was tested in the one-step preparation of several new and known complexes. The O-bonded sulfoxides of 1 are replaced under mild conditions by tri- (L3) and bidentate ligands (L2) to produce fac-[Re(CO)3(L3)]+ and fac-[Re(CO)3(L2)(dmso-O)]+ compounds, respectively. An excess of monodentate ligands (L) and more forcing conditions are needed to prepare fac-[Re(CO)3(L)3]+ compounds. The new compounds include fac-[Re(CO)3(bipy)(dmso-O)](CF3SO3) (4), that turned out to be an excellent precursor for binding the luminescent fac-[Re(CO)3(bipy)]+ fragment to polytopic ligands for the construction of more elaborate assemblies. One example reported here is the two-step preparation of fac-[{Re(CO)3(bipy)}(mu-4,4'-bipy){Ru(TPP)(CO)}](CF3SO3) (8) (TPP = tetraphenylporphyrin). The X-ray structures of the new compounds 1, 4, of the bis-porphyrin complex fac-[Re(CO)3Cl(4'MPyP)2] (13) (4'MPyP = 5-(4'pyridyl)-10,15,20-triphenylporphyrin), and of the rhenium-cyclophane [{(CO)3Re(mu-OH)2Re(CO)3}2(micro-4,4'-bipy)2] (15), among others, are described. Compound 1 might find useful applications in supramolecular chemistry (metal-mediated assembly of large architectures), in the in situ preparation of stable Re compounds to be used in nuclear medicine, and for the labeling of biomolecules.