1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetra­fluoridoborate

The asymmetric unit of the title compound, C17H13N4 +·BF4 −, contains one half of the benzimidazolium cation and one half of the tetra­fluoridoborate anion, with crystallographic mirror planes bis­ecting the mol­ecules. One F atom of the tetra­fluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C—H⋯F inter­actions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F⋯π contacts involving the tetra­fluoridoborate anions and the five-membered rings [F⋯centroid = 2.811 (2) Å]

Metal Dipyrrin Complexes as Potential Photosensitizers for Photodynamic Therapy

International audienceOver the last decades, the use of photodynamic therapy (PDT) for the treatment of various types of cancer as well fungal, viral and bacterial infections has received increasing attention. Despite its clinical success, the currently approved photosensitizers (PSs) are associated with poor water solubility, aggregation, low photostability and a long excretion time. To overcome these limitations, much research is devoted towards the development of PSs based on transition metal complexes. However, the majority of metals used for this purpose are rare and expensive. Therefore, it would be of high interest to develop effective PDT PSs based on cheap and abundant metals. In this article, the use of Cu(II) and Ni(II) dipyrrin complexes as potential PDT PSs against cancer is presented. As required for PDT applications, these complexes were found to have a strong absorption in the green spectrum and to be stable in an aqueous solution in the dark as well as upon light irradiation. Biological studies revealed that the complexes have a very low cytotoxic effect in the dark with a slight effect upon irradiation at 510 nm in human cervical carcinoma (HeLa) cells

Dinitrosyl rhenium complexes for ring-opening metathesis polymerization (ROMP)

The treatment of benzene solutions of the cations [Re(NO)2(PR3)2][BArF4] (R = Cy and R = iPr; [BArF4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) with phenyldiazomethane afforded the moderately stable cationic rhenium(I) benzylidene dinitrosyl bis(trialkyl) phosphine complexes as [BArF4]- salts in good yields. The cationic rhenium dinitrosyl bisphosphine complexes catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights, and Z configurations of the double bonds in the polymer chain backbones of over 80 %. The benzylidene derivatives are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave first hints for the initial formation of carbene complexes when [Re(NO)2(PR3)2][BArF4] was treated with norbornene. The carbene formation is initiated by an unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylid carbene complex. The [2+2] addition of a norbornene molecule to the Re=C bond leads to the rhenacyclobutane complex, which is expected to be converted into an iminate complex by attack of the ylid function onto one of the NNO atoms followed by Wittig-type phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. This species is thought to drive the ROMP metathesis with alternating rhenacyclobutane formations and cycloreversions. The proposed mechanism is supported by density functional theory (DFT) calculation

Crystal structures of B-DNA dodecamer containing the epigenetic modifications 5-hydroxymethylcytosine or 5-methylcytosine

5-Hydroxymethylcytosine (5-hmC) was recently identified as a relatively frequent base in eukaryotic genomes. Its physiological function is still unclear, but it is supposed to serve as an intermediate in DNA de novo demethylation. Using X-ray diffraction, we solved five structures of four variants of the d(CGCGAATTCGCG) dodecamer, containing either 5-hmC or 5-methylcytosine (5-mC) at position 3 or at position 9. The observed resolutions were between 1.42 and 1.99 Å. Cytosine modification in all cases influences neither the whole B-DNA double helix structure nor the modified base pair geometry. The additional hydroxyl group of 5-hmC with rotational freedom along the C5-C5A bond is preferentially oriented in the 3′ direction. A comparison of thermodynamic properties of the dodecamers shows no effect of 5-mC modification and a sequence-dependent only slight destabilizing effect of 5-hmC modification. Also taking into account the results of a previous functional study [Münzel et al. (2011) (Improved synthesis and mutagenicity of oligonucleotides containing 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine. Chem. Eur. J., 17, 13782−13788)], we conclude that the 5 position of cytosine is an ideal place to encode epigenetic information. Like this, neither the helical structure nor the thermodynamics are changed, and polymerases cannot distinguish 5-hmC and 5-mC from unmodified cytosine, all these effects are making the former ones non-mutageni

One Electron Changes Everything: Synthesis, Characterization, and Reactivity Studies of [Re(NCCH3)6]3+

Oxidation of [Re(NCCH3)6]2+ with the thianthrene radical cation results in the formation of [Re(NCCH3)6]3+, one of the very rare cases of a fully solvated +3 complex. It was fully characterized by spectroscopy and X-ray structure analysis. In contrast to its reduced analogue, [Re(NCCH3)6]3+ exhibits a much faster CH3CN exchange. Hence, substitution reactions proceed at 20 °C within minutes. Its potential as a versatile precursor for ReIII chemistry was examined with a series of substitution reactions. The more lipophilic analogue [Re(NCPh)6]3+ was synthesized by nitrile exchange in benzonitrile (NCPh). The Re(II) analogue of [Re(NCPh)6]3+, [Re(NCPh)6]2+, forms by AgI-mediated oxidation of in situ formed [Re(η6-C6H6)(NCPh3)3]+ in NCPh. The same synthetic strategy is feasible for the synthesis of [Re(NCCH3)6]2+ as well. [Re(NCCH3)6]3+ reacts with 1,4,7-trithiacyclononane (C6H12S3) to yield sevenfold-coordinated [Re(κ3-C6H12S3)2(NCCH3)]3+. The reaction of [Re(NCCH3)6]3+ with 1 equiv of (NBu4)X produces the ReIII monohalide complexes [ReX(NCCH3)5]2+ (X = Cl, Br, I). Mixed ReIII dihalides (trans-[ReXY(NCCH3)4]+) were obtained by treating [ReX(NCCH3)5]2+ with a second equivalent of (NBu4)Y (if X = Cl, Y = Br, I; if X = Br, Y = I). Because of this fast CH3CN exchange, [Re(NCCH3)6]3+ is a very suitable precursor for new ReIII complexes

Reactivities of [Re(η6-C6H6)(η6-C10H8)]+ and [Re(η6-C10H8)2]+ with Cyclic, Nonaromatic Polyenes

The synthesis of sandwich complexes of rhenium is essentially limited to compounds of the type [Re(η6-arene)2]+ via the Fischer–Hafner approach. This strategy is not compatible with arenes carrying functional groups or nonaromatic polyenes in particular. As reported, naphthalene in [Re(η6-C6H6)(η6-C10H8)]+ and in [Re(η6-C10H8)2]+ are exchanged by functionalized arenes in low to medium yields. In contrast, cyclic nonaromatic polyenes exchange naphthalene straight and in good to very good yields. We report herein on the syntheses of rhenium sandwich complexes with seven- and eight-membered rings bearing multiple double bonds such as cyclohepta-1,3,5-triene, tropone, or cycloocta-1,3,5-triene. Starting from [Re(η6-C6H6)(η6-C10H8)]+ and [Re(η6-C10H8)2]+, sandwich complexes such as [Re(η7-C7H7)(η5-C7H9)]+ and others are obtained and fully characterized in high yields (70–86%). These nonaromatic sandwich complexes form highly stable compounds

Naphthalene Exchange in [Re(η6-napht)2]+ with Pharmaceuticals Leads to Highly Functionalized Sandwich Complexes [M(η6-pharm)2]+ (M=Re/99mTc)

Bis-arene sandwich complexes are generally prepared by the Fischer-Hafner reaction, which conditions are incompatible with most O- and N- functional groups. We report a new way for the synthesis of sandwich type complexes [Re(η6-arene)2]+ and [Re(η6-arene)(η6-benzene)]+ from [Re(η6-napht)2]+ and [Re(η6-napht)(η6-benzene)]+, with functionalized arenes and pharmaceuticals. N-methylpyrrolidine (NMP) facilitates the substitution of naphthalene with the incoming arene. A series of fully characterized rhenium sandwich complexes with simple arenes, such as aniline, as well as with active compounds like lidocaine and melatonin are presented. With these rhenium compounds in hand, the radioactive sandwich complexes [99mTc(η6-pharm)2]+ (pharm=pharmaceutical) can be unambiguously confirmed. The direct labelling of pharmaceuticals with 99mTc through η6-coordination to phenyl rings and the confirmation of the structures with the rhenium homologues opens a path into molecular theranostics

Crystal structure of tris­(4,7-diphenyl-1,10-phenanthroline-κ2N,N′)cobalt(III) tris­(hexa­fluoro­phosphate) monohydrate

The title compound, [Co(C72H48N6)](PF6)3·H2O, crystallizes with one tripositive complex mol­ecule, three hexa­fluoro­phosphate anions and one solvent mol­ecule of water in the asymmetric unit. The N6 coordination set around the central CoIII atom defines a distorted octa­hedral environment. Four fluorine atoms of one hexa­fluoro­phosphate anion are disordered over two sets of positions with site-occupancy factors of 0.697 (5) and 0.303 (5). In the crystal, inter­molecular π–π stacking inter­actions, C—H...π, C—H...F and O—H...F and inter­actions are present

Nonacethrene Unchained: A Cascade to Chiral Contorted Conjugated Hydrocarbon with Two sp³-Defects

We demonstrate that structurally complex carbon nanostructures can be achieved via a synthetic approach that capitalizes on a π-radical reaction cascade. The cascade is triggered by oxidation of a dihydro precursor of helical diradicaloid nonacethrene to give a chiral contorted polycyclic aromatic hydrocarbon named hypercethrene. In this ten-electron oxidation process, four σ-bonds, one π-bond, and three six-membered rings are formed in a sequence of up to nine steps to yield a 72-carbon-atom warped framework, comprising two configurationally locked [7]helicene units, a fluorescent peropyrene unit, and two precisely installed sp; 3; -defects. The key intermediate in this cascade is a closed nonacethrene derivative with one quaternary sp; 3; -center, presumably formed via an electrocyclic ring closure of nonacethrene, which, when activated by oxidation, undergoes a reaction cascade analogous to the oxidative dimerization of phenalenyl to peropyrene. By controlling the amount of oxidant used, two intermediates and one side product could be isolated and fully characterized, including single-crystal X-ray diffraction analysis, and two intermediates were detected by electron paramagnetic resonance spectroscopy. In concert with density functional theory calculations, these intermediates support the proposed reaction mechanism. Compared to peropyrene, the absorption and emission of hypercethrene are slightly red-shifted on account of extended π-conjugation and the fluorescence quantum yield of 0.45 is decreased by a factor of ∼2. Enantiomerically enriched hypercethrene displays circularly polarized luminescence with a brightness value of 8.3 M; -1; cm; -1; . Our results show that reactions of graphene-based π-radicals-typically considered an "undefined decomposition" of non-zero-spin materials-can be well-defined and selective, and have potential to be transformed into a step-economic synthetic method toward complex carbon nanostructures

Towards Long Wavelength Absorbing Photodynamic Therapy Photosensitizers via the Extension of a [Ru(bipy) 3 ] 2+ Core

International audienceComplementary to classical treatment methods used against cancer, photodynamic therapy (PDT) has received increased attention over the last years. PDT relies on the generation of reactive oxygen species (ROS) upon light irradiation to trigger cell death. As the wavelength employed during such treatments directly influences the light penetration depth and therefore the possibility to treat deep seated tumours or large tumours, research efforts have been made towards the development of photosensitizers (PS) with an absorption in the phototherapeutic window (600-900 nm). To tackle this drawback, we report herein the preparation and characterisation of new Ru(II)-containing PDT PSs, that are based on a [Ru(bipy) 3 ] 2+ core (1; bipy: 2,2'-bipyridine) and that are extended with methyl groups (2) or vinyl dimethylamino groups (3). As anticipated with our design, we found a red-shift of 65 nm of the maximum absorption of complex 3 in comparison to complex 1. In addition, we report on the in-depth photophysical properties as well as (photo-)cytotoxicity against cervical cancerous HeLa cells of the investigated compounds