Crystal and molecular structure of augustamine

The crystal and molecular structure of augustamine (1), C₁₇H₁₉NO₄ an amaryllidaceae alkaloid of the tazettine group has been determined by direct methods from single crystal x-ray diffractometer data and refined by full-matrix least squares. The alkaloid (1) crystallizes in the space group P2₁2₁2₁, with cell parameters: a = 7.833(8) b = 11.08(2) å, c = 16.69(6) Å, Z = 4, D_c = 1.381 g/cm^–3, R = 7.6% for 1115 observed reflections. The molecule, having a hexacyclic ring system, is very rigid with the ring B in a chair conformation. Molecular mechanics calculations have been made using MM3(2000) force field.     

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Ohne Zusammenfassung     

Near-Infrared Fluorescence Lifetime Imaging of Biomolecules with Carbon Nanotubes**

Single-walled carbon nanotubes (SWCNTs) are versatile near infrared (NIR) fluorescent building blocks for biosensors. Their surface is chemically tailored to respond to analytes by a change in fluorescence. However, intensity-based signals are easily affected by external factors such as sample movements. Here, we demonstrate fluorescence lifetime imaging microscopy (FLIM) of SWCNT-based sensors in the NIR. We tailor a confocal laser scanning microscope (CLSM) for NIR signals (>800 nm) and employ time correlated single photon counting of (GT)₁₀-DNA functionalized SWCNTs. They act as sensors for the important neurotransmitter dopamine. Their fluorescence lifetime (>900 nm) decays biexponentially and the longer lifetime component (370 ps) increases by up to 25 % with dopamine concentration. These sensors serve as paint to cover cells and report extracellular dopamine in 3D via FLIM. Therefore, we demonstrate the potential of fluorescence lifetime as a readout of SWCNT-based NIR sensors.     

Synthesis, characterization, and multielectron reduction chemistry of uranium supported by redox-active α-diimine ligands

Uranium compounds supported by redox-active α-diimine ligands, which have methyl groups on the ligand backbone and bulky mesityl substituents on the nitrogen atoms {(Mes)DAB(Me) = [ArN═C(Me)C(Me)═NAr], where Ar = 2,4,6-trimethylphenyl (Mes)}, are reported. The addition of 2 equiv of (Mes)DAB(Me), 3 equiv of KC(8), and 1 equiv of UI(3)(THF)(4) produced the bis(ligand) species ((Mes)DAB(Me))(2)U(THF) (1). The metallocene derivative, Cp(2)U((Mes)DAB(Me)) (2), was generated by the addition of an equimolar ratio of (Mes)DAB(Me) and KC(8) to Cp(3)U. The bond lengths in the molecular structure of both species confirm that the α-diimine ligands have been doubly reduced to form ene-diamide ligands. Characterization by electronic absorption spectroscopy shows weak, sharp transitions in the near-IR region of the spectrum and, in combination with the crystallographic data, is consistent with the formulation that tetravalent uranium ions are present and supported by ene-diamide ligands. This interpretation was verified by U L(III)-edge X-ray absorption near-edge structure (XANES) spectroscopy and by variable-temperature magnetic measurements. The magnetic data are consistent with singlet ground states at low temperature and variable-temperature dependencies that would be expected for uranium(IV) species. However, both complexes exhibit low magnetic moments at room temperature, with values of 1.91 and 1.79 μ(B) for 1 and 2, respectively. Iodomethane was used to test the reactivity of 1 and 2 for multielectron transfer. While 2 showed no reactivity with CH(3)I, the addition of 2 equiv of iodomethane to 1 resulted in the formation of a uranium(IV) monoiodide species, ((Mes)DAB(Me))((Mes)DAB(Me2))UI {3; (Mes)DAB(Me2) = [ArN═C(Me)C(Me(2))NAr]}, which was characterized by single-crystal X-ray diffraction and U M(4)- and M(5)-edge XANES. Confirmation of the structure was also attained by deuterium labeling studies, which showed that a methyl group was added to the ene-diamide ligand carbon backbone.     

Platelet adhesion to photodynamic therapy-treated extracellular matrix proteins

Photodynamic therapy (PDT) produces reactive species that alter vascular wall biology and vessel wall proteins. In this study, we examined platelet adhesion to PDT-treated (photosensitizer = Photofrin; fluence 100 J/cm2; lambda = 630 nm) extracellular matrix (ECM), fibrinogen, von Willebrand factor (vWF) and collagen Types I and III, under flow conditions in a recirculating perfusion chamber. Platelet adhesion was quantified by image analysis. The effect of PDT on vWF was assessed by measuring the binding of domain-specific antibodies to treated vWF. PDT significantly decreased platelet adhesion to the ECM, fibrinogen and vWF. However, PDT of collagen resulted in significantly increased platelet adhesion, with large aggregate formation. PDT affected mostly the A1 (glycoprotein [GP]-Ib-binding site), A2 and A3 (collagen-binding site) domains of vWF but not the D'-D3 (factor VIII-binding site) and B-C1 (GP-IIb/IIIa-binding site) domains. In conclusion, PDT can alter the ECM, resulting in decreased platelet adhesion. However, vessels with high collagen content, such as veins and small arteries, may become increasingly prone to thrombosis. The results of this study may thus play a role in understanding the thrombogenic properties and mechanisms of vascular PDT.     

Diruthenium(III,III) bis(alkynyl) compounds with donor/acceptor-substituted geminal-diethynylethene ligands

Reported in this contribution are the preparation and characterization of a series of Ru(2)(DMBA)(4) (DMBA = N,N'-dimethylbenzamidinate) bis(alkynyl) compounds, trans-Ru(2)(DMBA)(4)(X-gem-DEE)(2) [gem-DEE = σ-geminal-diethynylethene; X = H (1), Si(i)Pr(3) (2), Fc (3); 4-C(6)H(4)NO(2) (4), and 4-C(6)H(4)NMe(2) (5)]. Compounds 1-5 were characterized by spectroscopic and voltammetric techniques as well as the single-crystal X-ray diffraction studies of 2 and 3. Both the single-crystal structural data of compounds 2 and 3 and the spectroscopic/voltammetric data indicate that the gem-DEE ligands are similar to simple acetylides in their impact on the molecular and electronic structures of the Ru(2)(DMBA)(4) core. Furthermore, density functional theory calculations revealed more extensive π delocalization in aryl-donor-substituted gem-DEEs and that the hole-transfer mechanism will likely dominate the charge delocalization in Ru(2)-gem-DEE-based wires.     

Concurrent Stabilization of π‐Donor and π‐Acceptor Ligands in Aromatized and Dearomatized Pincer [(PNN)Re(CO)(O)2] Complexes

Aromatized cationic [(PNN)Re(π acid)(O)₂]⁺ ( 1 ) and dearomatized neutral [(PNN*)Re(π acid)(O)₂] ( 2 ) complexes (where π acid=CO ( a ), tBuNC ( b ), or (2,6‐Me₂)PhNC ( c )), possessing both π‐donor and π‐acceptor ligands, have been synthesized and fully characterized. Reaction of [(PNN)Re(O)₂]⁺ ( 4 ) with lithiumhexamethyldisilazide (LiHMDS) yield the dearomatized [(PNN*)Re(O)₂] ( 3 ). Complexes 1 and 2 are prepared from the reaction of 4 and 3 , respectively, with CO or isocyanides. Single‐crystal X‐ray structures of 1 a and 1 b show the expected trans‐dioxo structure, in which the oxo ligands occupy the axial positions and the π‐acidic ligand occupies the equatorial plane in an overall octahedral geometry about the rhenium(V) center. DFT studies revealed the stability of complexes 1 and 2 arises from a π‐backbonding interaction between the d_xy orbital of rhenium, the π orbital of the oxo ligands, and the π* orbital of CO/isocyanide.