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

Neutral and Cationic [Bis(η1-amidosilyl)-η5-cyclopentadienyl]titanium and -zirconium complexes: synthesis, X-ray molecular structures and DFT calculations

Treatment of LiNHtBu with THF solutions of C5H4(SiMe2Cl)2 gave C5H4(SiMe2NHtBu)2 (1). Deprotonation of 1 with M(NMe2)4 (M = Ti, Zr) under different conditions provided the monocyclopentadienyl complexes [M{η5-C5H3- [SiMe2(NHtBu)]2}(NMe2)3] [M = Ti (2), Zr (3)] and the single (η-amidosilyl)cyclopentadienyl compounds [M{η5-C5H3[SiMe2(NHtBu)][SiMe2(η1-NtBu)]}(NMe2)2] [M = Ti (4), Zr (5)]. The related dibenzyl compounds [M{η5-C5H3[SiMe2- (NHtBu)][SiMe2(η1-NtBu)]}(CH2Ph)2] [M = Ti (6), Zr (7)] resulted from treatment of 1 with M(CH2C6H5)4 (M = Ti, Zr). Further deprotonation of the amido complexes 4 and 5 and the benzyl complexes 6 and 7 by heating in toluene solution gave the bis(η-amidosilyl)cyclopentadienyl complexes [M{η5-C5H3[SiMe2(η1-NtBu)]2}(NMe2)] [M = Ti (8), Zr (9)] and [M{η5-C5H3[SiMe2(η1-NtBu)]2}(CH2Ph)] [M = Ti (10), Zr (11)], respectively. Treatment of the monobenzyl complexes 10 and 11 with B(C6F5)3 yielded the cationic compounds [M{η5-C5H3[SiMe2(η1-NtBu)]2}]+ as [(CH2Ph)B(C6F5)3] − [M = Ti (12), Zr (13)] salts. All new compounds were characterized by NMR spectroscopy, and the crystal structures of 10 and 13 were studied by diffraction methods. DFT calculations for the neutral and cationic species are described and provide an explanation for the unusual η1 coordination of a phenyl ring to a group-4 metal cationThe authors acknowledge the MCyT (project MAT2001-1309) for\ud financial support and the EC (project COST-D12/0016/98). J. C.\ud acknowledges CAM for a fellowship

Development and disease of the photoreceptor cilium

Primary cilia are microtubule-rich hair-like extensions protruding from the surface of most post-mitotic cells. They act as sensory organelles that help interpret various environmental cues. Mutations in genes encoding proteins involved in ciliogenesis or protein transport to the primary cilia lead to a wide variety of diseases commonly referred to as ciliopathies,which include primary ciliary dyskinesia, situs invertus, hydrocephalus, kidney diseases, respiratory diseases, and retinal degenerations. In the retina, the photoreceptor cells have a highly specialized primary cilium called the outer segment (OS), which is essential for photosensation. Development of the photoreceptor OS shares key regulatory mechanisms with ciliogenesis in other cell types. Accumulating evidence indicates that mutations that affect OS development and/or protein transport to the OS generally lead to photoreceptor degeneration, which can be accompanied by a range of other clinical manifestations due to the dysfunction of primary cilia in different cell types. Here, we review the general mechanisms regulating ciliogenesis, and present different examples of mutations affecting OS ciliogenesis and protein transport that lead to photoreceptor degeneration. Overall, we conclude that the genetic and molecular evidence accumulated in recent years suggest a clear link between the development and function of the primary cilium and various clinical conditions. Future studies aimed at uncovering the cellular and molecular mechanisms implicated in ciliogenesis in a wide variety of animal models should greatly increase our understanding of the pathophysiology of many human diseases, including retinal degenerations.V. R. is supported by a studentship from the Foundation Fighting Blindness – Canada (FFB-C). Work in M.C.’s lab is funded by the Canadian Institutes of Health Research (CIHR) and the FFB-C. M.C. is a CIHR New Investigator and a W.K. Stell Scholar of the FFBC

Binding of Extracellular Maspin to 1 Integrins Inhibits Vascular Smooth Muscle Cell Migration

Maspin is a serpin that has multiple effects on cell behavior, including inhibition of migration. How maspin mediates these diverse effects remains unclear, as it is devoid of protease inhibitory activity. We have previously shown that maspin rapidly inhibits the migration of vascular smooth muscle cells (VSMC), suggesting the involvement of direct interactions with cell surface proteins. Here, using immunofluorescence microscopy, we demonstrate that maspin binds specifically to the surface of VSMC in the dedifferentiated, but not the differentiated, phenotype. Ligand blotting of VSMC lysates revealed the presence of several maspin-binding proteins, with a protein of 150 kDa differentially expressed between the two VSMC phenotypes. Western blotting suggested that this protein was the ß1 integrin subunit, and subsequently both a3ß1 and a5ß1, but not avß3, were shown to associate with maspin by coimmunoprecipitation. Specific binding of these integrins was also observed using maspin-affinity chromatography, using HT1080 cell lysates. Direct binding of maspin to a5ß1 was confirmed using a recombinant a5ß1-Fc fusion protein. Using conformation-dependent anti-ß1 antibodies, maspin binding to VSMC was found to lead to a decrease in the activation status of the integrin. The functional involvement of a5ß1 in mediating the effect of maspin was established by the inhibition of migration of CHO cells overexpressing human a5 integrin, but not those lacking a5 expression. Our observations suggest that maspin engages in specific interactions with a limited number of integrins on VSMC, leading to their inactivation, and that these interactions are responsible for the effects of maspin in the pericellular environment

MOLECULAR DYNAMICS SIMULATIONS OF LASER INDUCED SHOCK RESPONSE IN REACTIVE Ni/Al NANOLAMINATES

To characterize the self-propagating, high-temperature exothermic alloying reactions of Ni/Al nanoscaled multilayered films induced by laser pulse shock loading, classical molecular dynamics simulations were performed. In the current work, a novel technique was developed to facilitate the energy input and distribution into nanolaminate thin films. The laser pulse shock loading technique enables the initial shock response of the material to be captured as well as the late-time mass diffusion controlled alloying reaction and Ni3Al formation. Shock compression raises the temperature, pressure, and density of the Ni and Al layers which triggers the Ni to diffuse into the Al and initiate the self-propagating alloying reaction. Thermodynamic states, enthalpy of reaction, and global reaction rates of the laminated films were obtained. It was determined that the series of complex rarefaction and reflection waves play a significant role in altering the thermodynamic state of the laminate. Attributes of the rarefaction and reflection waves are controlled by the geometry and thickness of the alternating layers. The dependence of layer thickness on the temperature, pressure, enthalpy of reaction, and global reaction rate was investigated and characterized

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

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]