Systematische Studie zu den Koordinationseigenschaften des Guanidin‐Liganden N1,N2‐Bis(1,3‐dimethylimidazolidin‐2‐yliden)‐ethan‐1,2‐diamin mit den Metallen Mn,Co, Ni,Ag und Cu

A Systematic Study on the Coordination Properties of the Guanidine Ligand N¹,N²‐Bis(1,3‐dimethylimidazolidin‐2‐ylidene)‐ethane‐1,2‐diamine with the Metals Mn, Co, Ni, Ag and Cu The syntheses and characterization of the compounds [Mn(DMEG₂e)Cl₂] ( 1 ), [Co(DMEG₂e)Cl₂] ( 2 ), [Ni(DMEG₂e)₂]I₂ ( 3 ), [Cu(DMEG₂e)I] ( 4 ) and {[Ag(DMEG₂e)]BF₄}_n ( 5 ) with the bisguanidine ligand N¹,N²‐bis(1,3‐dimethylimidazolidin‐2‐ylidene)ethane‐1,2‐diamine (DMEG₂e) are described. All complexes are synthesized by the reaction of the corresponding metal salt with the DMEG₂e ligand in MeCN or THF. The coordination of the metal atoms vary from a distorted tetrahedron in 1 and 2 , a distorted trigonal planar coordination in 4 to linear coordination in 5 . Contrasting to the compounds 1 , 2 , 4 and 5 which exhibit a 1:1 ratio of metal to ligand, two DMEG₂e ligands are bound to the Ni atom in the case of 3 resulting in a coordination polyhedron which represents the stage exactly in the middle between the square‐planar and the tetrahedral geometry. Whereas crystals of 1 , 2 , 3 and 4 contain discrete molecules, in 5 the Ag atoms are alternately linked by two different DMEG₂e ligands to form a chain structure. The comparative discussion of several DMEG₂e containing complexes with the compounds reported herein supplements this systematic study.     

Synthetic Matching of Complex Monoterpene Indole Alkaloid Chemical Space

Monoterpene indole alkaloids (MIAs) are endowed with high structural and spatial complexity and characterized by diverse biological activities. Given this complexity-activity combination in MIAs, rapid and efficient access to chemical matter related to and with complexity similar to these alkaloids would be highly desirable, since such compound classes might display novel bioactivity. We describe the design and synthesis of a pseudo-natural product (pseudo-NP) collection obtained by the unprecedented combination of MIA fragments through complexity-generating transformations, resulting in arrangements not currently accessible by biosynthetic pathways. Cheminformatic analyses revealed that both the pseudo-NPs and the MIAs reside in a unique and common area of chemical space with high spatial complexity-density that is only sparsely populated by other natural products and drugs. Investigation of bioactivity guided by morphological profiling identified pseudo-NPs that inhibit DNA synthesis and modulate tubulin. These results demonstrate that the pseudo-NP collection occupies similar biologically relevant chemical space that Nature has endowed MIAs with.     

Synthesis and light gas separations in cross-linked gemini room temperature ionic liquid polymer membranes

Cross-linkable gemini room temperature ionic liquids (GRTILs) were synthesized and photo-cross-linked into thin films. The resultant polymer membranes were tested for their permeabilities to CO₂, N₂, CH₄ and H₂. Permeabilities for each gas were found to be much lower when compared to previously reported poly(RTIL) membranes, mainly as a result of highly restricted diffusion. Separation factors were similar to previously studied poly(RTIL) membranes. CH₄ and N₂ fluxes were small enough to consider these membranes as “barrier” films to the transport of those gases. Poly(GRTILs) may have use in applications where flow of those gases is not desirable.     

Metabolic Tumor Imaging with Rapidly Signal-Enhanced 1-13C-Pyruvate-d3

The metabolism of malignant cells differs significantly from that of healthy cells and thus, it is possible to perform metabolic imaging to reveal not only the exact location of a tumor, but also intratumoral areas of high metabolic activity. Herein, we demonstrate the feasibility of metabolic tumor imaging using signal-enhanced 1-¹³C-pyruvate-d₃, which is rapidly enhanced via para-hydrogen, and thus, the signal is amplified by several orders of magnitudes in less than a minute. Using as a model, human melanoma xenografts injected with signal-enhanced 1-¹³C-pyruvate-d3, we show that the conversion of pyruvate into lactate can be monitored along with its kinetics, which could pave the way for rapidly detecting and monitoring changes in tumor metabolism.     

Optical response of the Cu2S2 diamond core in (NGuaS)2Cl2

Density functional theory (DFT) and time‐dependent DFT calculations are presented for the dicopper thiolate complex Cu₂(NGuaS)₂Cl₂ [NGuaS=2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu₂S₂Cl₂ core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the Cu_A center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural Cu_A models. The spectrum can be roughly divided in the known regions of metal d‐d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu₂S₂ diamond core mediated between Cu and S‐S π and π* orbitals forming Cu‐S σ bonds. Measured resonant Raman spectra are shown for 360‐ and 720‐nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.     

Synthese und Struktur der basischen Erdalkalinitrate Sr2(OH)3NO3 und Ba2(OH)3NO3

Synthesis and Structure of the Basic Alkaline Earth Nitrates Sr₂(OH)₃NO₃ and Ba₂(OH)₃NO₃ Sr₂(OH)₃NO₃ and Ba₂(OH)₃NO₃ were synthesized from mixtures of freshly prepared strontium or barium hydroxides and their corresponding nitrates in evacuated quartz glass ampoules at 420 °C and 360 °C, respectively. Single crystals of Sr₂(OH)₃NO₃ were obtained in a solidified Sr(NO₃)₂ melt after subsequent heating and cooling cycles in air up to 600 °C. The crystal structure of the strontium compound was refined from single crystal and powder X‐ray data. Sr₂(OH)₃NO₃ crystallizes hexagonally in the space group (No. 189) with Z = 1 and the lattice parameters a = 6.624(2) Å and c = 3.560(1) Å (single crystal data). The powder pattern of Ba₂(OH)₃NO₃ was indexed isotypically to Sr₂(OH)₃NO₃ with the lattice parameters a = 6.9260(1) Å and c = 3.8086(1) Å, and the crystal structure was refined from powder X‐ray data. Alkaline earth ions in the structures are surrounded trigonal‐prismatically by six hydroxide ions. These prisms are sharing their trigonal faces along [001] building up columns. These columns are connected in the ab‐plane by shared edges, and form hexagonal tunnels with the nitrate groups stacked inside. Infrared and thermoanalytical data of Sr₂(OH)₃NO₃ are presented.     

Ultrafast and ultraslow oxygen atom transfer reactions between late metal centers

Oxotrimesityliridium(V), (mes)3Ir=O (mes = 2,4,6-trimethylphenyl), and trimesityliridium(III), (mes)3Ir, undergo extremely rapid degenerate intermetal oxygen atom transfer at room temperature. At low temperatures, the two complexes conproportionate to form (mes)3Ir-O-Ir(mes)3, the 2,6-dimethylphenyl analogue of which has been characterized crystallographically. Variable-temperature NMR measurements of the rate of dissociation of the mu-oxo dimer combined with measurements of the conproportionation equilibrium by low-temperature optical spectroscopy indicate that oxygen atom exchange between iridium(V) and iridium(III) occurs with a rate constant, extrapolated to 20 degrees C, of 5 x 107 M-1 s-1. The oxotris(imido)osmium(VIII) complex (ArN)3Os=O (Ar = 2,6-diisopropylphenyl) also undergoes degenerate intermetal atom transfer to its deoxy partner, (ArN)3Os. However, despite the fact that its metal-oxygen bond strength and reactivity toward triphenylphosphine are nearly identical to those of (mes)3Ir=O, the osmium complex (ArN)3Os=O transfers its oxygen atom 12 orders of magnitude more slowly to (ArN)3Os than (mes)3Ir=O does to (mes)3Ir (kOsOs = 1.8 x 10-5 M-1 s-1 at 20 degrees C). Iridium-osmium cross-exchange takes place at an intermediate rate, in quantitative agreement with a Marcus-type cross relation. The enormous difference between the iridium-iridium and osmium-osmium exchange rates can be rationalized by an analogue of the inner-sphere reorganization energy. Both Ir(III) and Ir(V) are pyramidal and can form pyramidal iridium(IV) with little energetic cost in an orbitally allowed linear approach. Conversely, pyramidalization of the planar tris(imido)osmium(VI) fragment requires placing a pair of electrons in an antibonding orbital. The unique propensity of (mes)3Ir=O to undergo intermetal oxygen atom transfer allows it to serve as an activator of dioxygen in cocatalyzed oxidations, for example, acting with osmium tetroxide to catalyze the aerobic dihydroxylation of monosubstituted olefins and selective oxidation of allyl and benzyl alcohols.