97 research outputs found
Structural, Electrochemical, and Photochemical Properties of Mono- and Digold(I) Complexes Containing Mesoionic Carbenes
Triazolylidenes are a prominent class of mesoionic carbenes (MICs) that are currently widely used in organometallic chemistry. Usually the metal complexes of such ligands are used as homogeneous catalysts even though they have vast potential in other branches of chemistry. We present here three related gold(I) complexes with MIC ligands: a neutral mononuclear chlorido complex [AuCl(MIC)], a cationic mononuclear complex containing two MIC ligands [Au(MIC)2]BF4, and a dicationic digold(I) complex containing two di-MIC ligands [Au2(Îș1,Îș1,”-di-MIC)2](BF4)2. The complexes were characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The gold(I) centers are linearly coordinated through either one MIC-C and chlorido donors or through two MIC-C donors. The triazolylidenes display a delocalized bonding situation within the ring. Additionally, a short AuâAu distance of about 3 Ă
is observed for the digold(I) complex. All complexes display reduction steps in their cyclic voltammograms, and these are assigned to the reduction of the MIC ligands, as opposed to the generation of gold(0). The complexes emit at ca. 500 nm, with lifetimes of several microseconds in deoxygenated solutions; the emission intensity and lifetime are strongly decreased by the presence of oxygen, supporting the triplet origin of the emissive state. The present results display the utility of MIC ligands for generating electro- and photoactive molecules
Use of ring-expanded diamino- and diamidocarbene ligands in copper catalyzed azide-alkyne "click" reactions
The
two-coordinate ring-expanded N-heterocyclic carbene copperÂ(I)
complexes [CuÂ(RE-NHC)<sub>2</sub>]<sup>+</sup> (RE-NHC = 6-Mes, 7-<i>o</i>-Tol, 7-Mes) have been prepared and shown to be effective
catalysts under neat conditions for the 1,3-dipolar cycloaddition
of alkynes and azides. In contrast, the cationic diamidocarbene analogue
[CuÂ(6-MesDAC)<sub>2</sub>]<sup>+</sup> and the neutral species [(6-MesDAC)ÂCuCl]<sub>2</sub> and [(6-MesDAC)<sub>2</sub>(CuCl)<sub>3</sub>] show good
activity when the catalysis is performed on water
Prevention of tumor formation by latent gammaherpesvirus infection.
Recent reports suggested that chronic herpesvirus infection, as a constituent of the so-called virome, may not only exert harmful effects but may also be beneficial to the host, for example mediating increased resistance to secondary infections or to tumors. To further challenge this concept, specifically regarding increased resistance to tumors, we infected chimeric HLA-DR4-H2-E (DR4) mice, a mouse strain which spontaneously develops hematological tumors, with the rodent herpesvirus murine gammaherpesvirus 68 (MHV-68). Using this model, we observed that infection with wildtype MHV-68 completely prevented tumor formation. This happened, however, at the cost of hyposplenism. In contrast to wildtype infection, infection with a latency-deficient mutant of MHV-68 neither prevented tumor formation nor induced hyposplenism. The underlying mechanisms are not known but might be related to an infection-mediated priming of the immune response, resulting in the suppression of a tumor promoting endogenous retrovirus. Thus, under certain circumstances, chronic herpesvirus infection may prevent the development of tumors
Infection of DR4 mice with wt MHV-68 primes T cells for enhanced interferon-Îł production.
<p>Mice were infected at an age of 10â13 weeks. Splenocytes from uninfected and infected DR4 mice were isolated 8â11.75 months after infection, re-stimulated with PMA/ionomycin (stim) or left unstimulated (unstim), and were subsequently analyzed by multicolor FACS analysis for intracellular IFN-Îł production. A) Representative Dot Plots of one mouse per group are shown. B) Summary of three mice per group. Each symbol represents an individual mouse, and the bars represent the mean. n.i.: not-infected (n = 3); wt: infected with wt MHV-68 (n = 3); Î73: infected with latency-deficient MHV-68, carrying a deletion in ORF73 (n = 3).</p
Infection of DR4 mice with wt MHV-68 prevents tumor development but does not improve overall survival.
<p>A) Frequency of tumors. B) Overall survival. Mice were infected at an age of 10â13 weeks and monitored up to an age of 15 months. n.i.: not-infected; wt: infected with wt MHV-68; Î73: infected with latency-deficient MHV-68, carrying a deletion in ORF73; nto: no tumors observed; numbers in brackets (n): number of mice analysed.</p
The Ligand Field of the Azido Ligand: Insights into Bonding Parameters and Magnetic Anisotropy in a Co(II)âAzido Complex
The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)âazido complex (1), which has been characterized experimentally (magnetically and by electronic dâd absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = â10.7 cmâ1, E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying dâd transitions. Calculations were performed on 1 and a related four-coordinate Co(II)âazido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3â ligand is shown to behave as a strong Ï and Ï donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the CoâN bond distances) of the axial ligand on the N3â site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results
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