Fabio Zobi

Reactivity of 17 e− Complex [ReIIBr4(CO)2]2− with Bridging Aromatic Ligands. Characterization and CO-Releasing Properties

Carbon monoxide releasing molecules (CO-RMs) are a newly emerging class of compounds of pharmacological interest. Among the transition metal-based CO-RMs, 17-electron complexes of general formula cis-trans-[Re(II)(CO)(2)Br(2)L(2)] are promising candidates but their poor hydrophilicity hampers future applications. In an effort to increase water solubility of d(5) dicarbonyl rhenium CO-RMs, the reaction of the cis-[Re(II)(CO)(2)Br(4)](2-) anion with bridging aromatic ligands of the pyridine and diazine type was investigated. Mononuclear and binuclear complexes are presented and it is shown that the nature of the bridging ligand critically dictates the formation of either species. Most complexes retained their fundamental CO-releasing properties. The synthesis of the molecules together with structural, spectroscopic and theoretical details are discussed.

Guanine and Plasmid DNA binding of Mono- and Trinuclear fac-[Re(CO)3]+ Complexes with Amino Acid Ligands

We have synthesized and fully characterized four new complexes comprising the fac‐[Re(CO)3]+ moiety and the ligands NH3, L‐proline (Pro), or N,N‐dimethylglycine (dmGly). The reaction of [Re(H2O)3(CO)3]+ with the two amino acids gives trinuclear complexes of general formula [Re(L)(CO)3]3 (where L=amino acid). We have studied the in vitro behavior of these compounds with guanine and DNA in order to understand whether the cytotoxicity exhibited by certain rhenium complexes based on the fac‐[Re(CO)3]+ core is due to the formation of nucleobase complexes and inter‐ or intrastrand links between DNA bases. We have performed model studies with guanine and studied the structural effects induced by different rhenium(I) tricarbonyl complexes on ΦX174 plasmid DNA by electrophoretic methods. Our results show that rhenium complexes with two available coordination sites interact with plasmid DNA to form a stable adduct that is likely to involve two bases.

Synthesis and reactivity of the 17 e- complex [Re(II)Br4(CO)2]2-: a convenient entry into rhenium(II) chemistry.

The reduction of (Et(4)N)[Re(III)Br(4)(CO)(2)] (1) by 0.5 equiv of tetrakis-dimethylaminoethylene in acetonitrile yields directly the air-stable, 17-electron Re(II) synthon (Et(4)N)(2)[Re(II)Br(4)(CO)(2)] (2) in nearly quantitative yield. The versatility of 2 as a synthon for Re(II) chemistry was demonstrated by substitution reactions of [Re(II)Br(4)(CO)(2)](2-) with different mono-, bi-, and tridentate ligands. The resulting Re(II) complexes form highly crystalline compounds, and the solid state structures of the neutral trans-cis-[Re(II)Br(2)(CO)(2)(X)(n)] species (where X = imidazole, pyridine, or phenanthroline) could be determined. All complexes are stable under aerobic conditions, both as solids and in solution, and showed fully reversible one-electron Re(II) --> Re(I) reductions between ca. -70 and -120 mV. Carbonyl stretching frequencies (nu(CO)) of this new family of Re(II) complexes are observed in the 1990 cm(-1) (A(1)) and 1830 (E(g)) cm(-1) regions. With complex 2, a wide variety of fundamental but so far unknown Re(II) complexes become accessible via facile substitution reactions.

Three-dimensional mid-infrared tomographic imaging of endogenous and exogenous molecules in a single intact cell with subcellular resolution.

Microscopy in the mid-infrared spectral range provides detailed chemical information on a sample at moderate spatial resolution and is being used increasingly in the characterization of biological entities as challenging as single cells. However, a conventional cellular 2D imaging measurement is limited in its ability to associate specific compositional information to subcellular structures because of the interference from the complex topography of the sample. Herein we provide a method and protocols that overcome this challenge in which tilt-series infrared tomography is used with a standard benchtop infrared microscope. This approach gives access to the quantitative 3D distribution of molecular components based on the intrinsic contrast provided by the sample. We demonstrate the method by quantifying the distribution of an exogenous metal carbonyl complex throughout the cell and by reporting changes in its coordination sphere in different locations in the cell.

Ligand Electronic Parameters as a Measure of the Polarization of the C≡O Bond in [M(CO)xLy]n Complexes and of the Relative Stabilization of [M(CO)xLy]n/n+1 Species

The electronic description of octahedral (fac-[M(CO)(3)L(3)](n), with M = Re, Ru, and Mn, and [Cr(CO)(5)L](n)), square-planar (cis-[Pt(CO)(2)L(2)](n)), and tetrahedral ([Ni(CO)(3)L](n)) carbonyl complexes (where L = monodentate ligand) was obtained via density functional theory and natural population analyses in order to understand what effects are probed in these species by vibrational spectroscopy and electrochemistry as a function of the ligand electronic parameter of the associated L. The analysis indicates that while ligand electronic parameters may be considered as a measure of the net donor power of the ligand, the net transfer of the electron density (or charge) does not occur from the ligand to the metal ion. In [M(CO)(x)L(y)](n) carbonyl species, the charge transfer occurs from the ligand L to the oxygen atom of the bound carbon monoxides. This charge transfer translates into changes of the polarization (or permanent dipole) and the covalency of the C≡O bonds, and it is this effect that is probed in IR spectroscopy. As the analysis shifts from IR radiations to electrochemical potentials, the parameters best describe the relative thermodynamic stability of the oxidized and reduced [M(CO)(x)L(y)](n/n+1) species. No relationship is found between the metal natural charge of the [M(CO)(x)L(y)](n) fragments analyzed and the parameters. Brief considerations are given on the possible design of CO-releasing molecules.

Heme Oxygenase-1/Carbon Monoxide System and Embryonic Stem Cell Differentiation and Maturation into Cardiomyocytes

AIMS The differentiation of embryonic stem (ES) cells into energetically efficient cardiomyocytes contributes to functional cardiac repair and is envisioned to ameliorate progressive degenerative cardiac diseases. Advanced cell maturation strategies are therefore needed to create abundant mature cardiomyocytes. In this study, we tested whether the redox-sensitive heme oxygenase-1/carbon monoxide (HO-1/CO) system, operating through mitochondrial biogenesis, acts as a mechanism for ES cell differentiation and cardiomyocyte maturation. RESULTS Manipulation of HO-1/CO to enhance mitochondrial biogenesis demonstrates a direct pathway to ES cell differentiation and maturation into beating cardiomyocytes that express adult structural markers. Targeted HO-1/CO interventions up- and downregulate specific cardiogenic transcription factors, transcription factor Gata4, homeobox protein Nkx-2.5, heart- and neural crest derivatives-expressed protein 1, and MEF2C. HO-1/CO overexpression increases cardiac gene expression for myosin regulatory light chain 2, atrial isoform, MLC2v, ANP, MHC-β, and sarcomere α-actinin and the major mitochondrial fusion regulators, mitofusin 2 and MICOS complex subunit Mic60. This promotes structural mitochondrial network expansion and maturation, thereby supporting energy provision for beating embryoid bodies. These effects are prevented by silencing HO-1 and by mitochondrial reactive oxygen species scavenging, while disruption of mitochondrial biogenesis and mitochondrial DNA depletion by loss of mitochondrial transcription factor A compromise infrastructure. This leads to failure of cardiomyocyte differentiation and maturation and contractile dysfunction. INNOVATION The capacity to augment cardiomyogenesis via a defined mitochondrial pathway has unique therapeutic potential for targeting ES cell maturation in cardiac disease. CONCLUSION Our findings establish the HO-1/CO system and redox regulation of mitochondrial biogenesis as essential factors in ES cell differentiation as well as in the subsequent maturation of these cells into functional cardiac cells.

Interaction of mono- and dinuclear metal complexes with mono- and oligonucleotides for analytical, radio- and chemotoxic purposes

In this article we briefly describe our recent results concerning the interaction of mononuclear [M(CO) 3 ] + (M = Re, 9 9 Tc and 9 9 m Tc) based complexes with guanine and plasmid DNA for chemo- and/or radiotherapeutic purposes. Furthermore, studies with mono- and dinuclear, coordinatively unsaturated Ni(II) and Cu(II) complexes inducing B- to Z-DNA transitions are outlined. The strong interaction of [M(CO) 3 ] + with one guanine allows the direct introduction of this core into oligodeoxynucleotides (ODN), without their previous derivatization, for further elucidation of their biological behavior. Vectors labeled in this way can later be used in radioimaging or -therapy studies. The [M(CO) 3 ] + core can also mediate the introduction of further biologically active or, for analytical purposes, fluorescent molecules. Alternatively, ODNs can be derivatized with amino acid based chelators such as histidine. We describe the induction of structural changes in plasmid DNA observed after reaction with the [M(CO) 3 ] + moiety. This indicates a cisplatin-like behavior useful for future chemotherapy. Finally, studies of the interaction of mono- and dinuclear complexes with ODN inducing B- to Z-DNA transitions are described and compared to the effect of common electrolytes alone. A clear correlation between salt type and salt concentration was found. These complexes have a strong potential to be used for analytical or biological purposes as well.

Formation and Reactivity of ((tacn)-N-CO-Re III Br(CO) 2 ) + in Water: a Theoretical and Experimental Study

The chemistry of [(tacn)-N-CO-Re(III)(CO)(2)Br]X (X = Cl or Br), obtained in good yield from the reaction of fac-[(tacn)Re(I)(CO)(3)]Br (1, tacn = 1,4,7-triazacyclononane) with X(2) in water, is described. The [(tacn)-N-CO-Re(III)(CO)(2)Br]X complex (2 with X = Br(-); 2a with X = BrCl(2)(-)), which we have previously communicated, is characterized by an unusual three-membered ring acyl amide bond. Complex 2 is stable as a solid but is reactive in aqueous solution. Under basic conditions (1 M NaOH), reductive decarbonylation was observed, and the bis-carbonyl complex [(tacn)Re(I)(CO)(2)Br] (3) was obtained in quantitative yield. The Br(-) ligand in 3 could be replaced by CN(-), giving the neutral complex [(tacn)Re(I)(CO)(2)(CN)] (4). In acidic media (1 M HBr), complex 2 partially converted to the monocarbonyl mu-oxo bridged dinuclear complex {[(tacn)Re(III)(CO)Br](2)O}(2+) (5 as [PF(6)](-) salt). Under mild oxidative conditions the trioxo [(tacn)Re(VII)O(3)](ReO(4)(-)) (6) was formed almost quantitatively, and small amounts of the uncommon Re(VI) complex [(tacn)Re(VI)O(2)Br](ReO(4)(-)) (7) were identified. Mechanistic investigations at the density functional level of theory (DFT) showed that the elementary steps in the formation of 2 from 1 and 3 from 2 involved reactions of the complexes with hydroxide. The calculated pathway is strongly exothermic (ca. -137 kcal/mol), confirming the energetically and kinetically highly favored formation of 3. The X-ray structures of 2a and 3-5 are reported and discussed.

Ligand-mediated decarbonylation as an efficient synthetic method to Re(I) and Re(II) dicarbonyl complexes

A novel synthetic method based on a ligand-mediated decarbonylation reaction of complexes of the common fac-[Re(CO)3]+ core efficiently yields Re(I) and Re(II) dicarbonyl species.

Post-protein binding metal-mediated coupling of an acridine orange-based fluorophore

The HEW lysozyme (Lys) and the fac-[Re(CO)(3)(H(2)O)(3)](+) complex (1) are used as a simple model system for the description of a new approach to the labelling polypeptides with fluorescent tags. The strategy takes advantage of the reaction of an acridine orange-based fluorophore (AO) with the non-native metal fragment 1 hybridized on the enzyme. A synthetic methodology for the quantitative metallation of the protein is first described and it is then shown that the exogenous metal complex can be exploited for the coupling of the fluorescent probe. All Lys-derived species were characterized by various spectroscopic techniques. It is shown that the approach does not significantly alter the activity of the final fluorescent metallo-protein conjugate (Lys2). The accumulation of Lys2 on Micrococcus lysodeikticus bacteria was observed via confocal laser scanning microscopy.