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ABSTRACT: The syntheses of H2-phbpz, [Cu2(phbpz)]·2DEF·MeOH () and [Ag2(phbpz)] () (H2-phbpz = 3,3',5,5'-tetraphenyl-1H,1'H-4,4'-bipyrazole) compounds and their crystal structures are described. The Cu(i) containing metal-organic framework crystallizes in the tetragonal crystal system, within space group I41/a (no. 88) and the following unit cell parameters: a = 30.835(14), c = 29.306(7) Å, V = 27 865(19) Å(3). features a flexible 3-D three-connected two-fold interpenetrated porous structure constructed of triangular Cu(i) subunits. Upon exposure to different kinds of liquids (MeOH, EtOH, DMF, DEF) shows pronounced breathing effects. crystallizes in the monoclinic crystal system, within space group P21/c (no. 14) and the following unit cell parameters: a = 16.3399(3), b = 32.7506(4), c = 16.2624(3) Å, β = 107.382(2)°, V = 8305.3(2) Å(3). In contrast to the former compound, features a layered 2-D three-connected structure constructed from triangular Ag(i) subunits. Both compounds are characterized by elemental and thermogravimetric analyses, single crystal structure analysis and X-ray powder diffraction, FTIR- and fluorescence spectroscopy. Preliminary results on oxygen activation in are presented and potential improvements in terms of framework robustness and catalytic efficiency are discussed.
Dalton Transactions 03/2013; · 3.84 Impact Factor
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ABSTRACT: Plasma-enhanced chemical vapor deposited polymers (plasma polymers) are promising candidates for biomaterials applications. In the present study, plasma deposition as a fast and easily scalable method was adapted to deposit coatings from n-heptane and methyl methacrylate monomers onto glass substrates. Linear patterns with line and groove widths between 1.25 and 160 μm were introduced by degrative UV-lithography for cell alignment. Differential interference contrast optical microscopy, profilometry and atomic force microscopy revealed that the patterned surfaces had a smooth, homogeneous appearance and a pattern height of 8 and 45 nm for plasma deposited n-heptane and methyl methacrylate, respectively. UV-lithography increased the oxygen content on the surface drastically as shown by X-ray photoelectron spectroscopy. After immersion in simulated body fluid for 21 days, the pattern was still intact, and the ester groups were also maintained for the most part as shown by infrared spectroscopy. To test the coatings' potential applicability for biomaterial surfaces in a preliminary experiment, we cultured murine preosteoblastic MC3T3-E1 cells on these coatings. Light and electron microscopically, a normal spindle-shaped and aligned cell morphology was observed. At the mRNA level, cells showed no signs of diminished proliferation or elevated expression of apoptosis markers. In conclusion, plasma-enhanced chemical vapor deposited polymers can be patterned with a fast and feasible method and might be suitable materials to guide cell alignment.
ACS Applied Materials & Interfaces 09/2012; 4(10):5196-203. · 4.53 Impact Factor
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ABSTRACT: A 12-connected metal-organic framework based on an unprecedented cyclic Cu(12) cluster with a large internal cavity has been prepared, and its cation exchange property was determined.
Chemical Communications 06/2012; 48(58):7295-7. · 6.17 Impact Factor
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ABSTRACT: Implant medical research and tissue engineering both target the design of novel biomaterials for the improvement of human
health and clinical applications. In order to develop improved surface coatings for hard tissue (bone) replacement materials
and implant devices, we are developing micropatterned coatings consisting of polymer brushes. These are used as organic templates
for the mineralization of calcium phosphate in order to improve adhesion of bone cells. First, we give a short account of
the current state-of-the-art in this particular field of biomaterial development, while in the second part the preliminary
results of cell culture experiments are presented, in which the biocompatibility of polymer brushes are tested on human mesenchymal
stem cells.
Frontiers of Materials Science in China 04/2012; 3(2):132-144.
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ABSTRACT: The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and π-π interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host.
Dalton Transactions 04/2012; 41(19):5995-6002. · 3.84 Impact Factor
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ABSTRACT: The metal-organic framework [Cu(ta)(2)] (Hta = 1H-1,2,3-triazole), containing Jahn-Teller active Cu(II) ions and 1,2,3-triazolate ligands, is prepared under solvothermal reaction conditions. The compound shows a reversible phase transition from the tetragonal crystal system (α-[Cu(ta)(2)]: space group I4(1)/amd (no. 141), a = 11.8447(7) Å, c = 18.9782(13) Å, V = 2662.6(3) Å(3)) to the cubic crystal system (β-[Cu(ta)(2)]: space group Fd3m (no. 227), a = 17.4416(15) Å, V = 5305.9(8) Å(3)) within the temperature range of 120-160 °C. Both [Cu(ta)(2)] polymorphs have identical bonding topologies that might be described as fully condensed Kuratowski-type pentanuclear secondary building units of local T(d) point group symmetry in which four Cu(II) ions occupy the vertices of an imaginary tetrahedron. α-[Cu(ta)(2)], as opposed to the high-temperature β-phase, shows a strong tetragonal Jahn-Teller distortion of CuN(6) coordination octahedra. The compounds are characterized by elemental and thermogravimetric analyses, single crystal and powder X-ray diffraction, FTIR-, UV-vis and fluorescence spectroscopy. Magnetic susceptibility investigations reveal two different Cu(II) sites at a ratio of 1 : 2, in agreement with the solid state structure of [Cu(ta)(2)]. At low temperatures the formation of antiferromagnetically coupled Cu(II) dimers is observed, leading to a spin frustration of roughly 1/3 of all magnetically active Cu(II) sites.
Dalton Transactions 03/2012; 41(14):4239-48. · 3.84 Impact Factor
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ABSTRACT: In the last decades, polymer brush coatings have proven to be excellent anti-fouling materials by preventing protein adhesion. When using this property to restrict cell growth laterally in cell culture, it is crucial to ensure that other cell functions remain unaffected. The present study therefore examines MC3T3-E1 cell growth and morphology on patterned PSBMA brush substrates and probes their proliferation potential at mRNA level. The osteoblastic cells display a more elongated morphology than cells on the control substrates, but show no sign of elevated levels of the apoptosis marker p53 or diminished levels of Ki-67 or H4, which serve as indicators of proliferation. Therefore, patterned polymer brushes do not seem to influence cells in their proliferation state and are suitable cell culture substrates. Nevertheless, the use of polymer brush surfaces in long-term cell culture was found to be limited by their instability in cell culture medium.
Journal of Materials Science Materials in Medicine 12/2011; 23(2):573-9. · 2.32 Impact Factor
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ABSTRACT: Postsynthetic metal ion exchange in a benzotriazolate-based MFU-4l(arge) framework leads to a Co(II)-containing framework with open metal sites showing reversible gas-phase oxidation properties.
Chemical Communications 12/2011; 48(9):1236-8. · 6.17 Impact Factor
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ABSTRACT: The existence region of a polymer-induced liquid precursor (PILP) phase for crystals of an organic compound (DL-glutamic acid, Glu) was determined for the first time in the phase diagram of the Glu-polyethyleneimine-water-ethanol system. The existence region and the amount of PILP phase relative to the thermodynamically stable crystal phase were very small. Other phases detected in the phase diagram were coacervates, homogenous mixtures, and crystals obtained via a clear solution. The PILP phase is rich in the polymeric additive, which helps to explain the long induction period of PILP before crystallization occurs. Volume measurements indicated that its amount is <1 vol%, showing that this precursor phase is only a minor component.
Physical Chemistry Chemical Physics 11/2011; 14(2):914-9. · 3.57 Impact Factor
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Advanced Materials 07/2011; 23(31):3548-52. · 13.88 Impact Factor
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ABSTRACT: Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active Co(II) centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O(2) were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.
Chemistry 06/2011; 17(31):8671-95. · 5.93 Impact Factor
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ABSTRACT: The syntheses of Kuratowski-type pentanuclear clusters featuring {MZn(4)Cl(4)} cores (M(II) = Ru or Zn) that incorporate triazolate ligands are described. The coordination compounds are characterized by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), FTIR- and UV-vis spectroscopy. [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (Me(2)bta(-) = 5,6-dimethyl-1,2,3-benzotriazolate) (1) crystallizes in the cubic system, while [Zn(5)Cl(4)(ta)(6)] (ta(-) = 1,2,3-triazolate) (3) crystallizes in the tetragonal system. Both compounds feature structurally similar cluster topologies in which the central octahedrally coordinated metal ion is coordinated to six triazolate ligands. Each triazolate ligand is coordinated with two zinc ions (μ(3)-bridging mode), leading altogether to a pentanuclear cluster of T(d) point group symmetry. Photophysical investigations reveal that compound [Zn(5)Cl(4)(Me(2)bta)(6)]·2DMF (2) shows a short-lived excited electronic state, which can be populated with high quantum yield. The isostructural compound [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (1), on the other hand, shows a long-lived photoexcited state, owing to an internal singlet to triplet conversion of the electronic states, as revealed by time-resolved fluorescence spectroscopy. Insights gained from these studies open up novel design strategies towards photocatalytically active metal-organic frameworks incorporating photoactive Kuratowski-type secondary building units such as MFU-4 (Metal-Organic Framework Ulm University-4).
Dalton Transactions 06/2011; 40(22):5926-38. · 3.84 Impact Factor
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ABSTRACT: Nanostructured organic crystals have a broad application potential as pharmaceuticals, pigments, or catalysts. The development of facile and reproducible synthetic routes and the upscaling of the process, however, still remain a challenge. Here, we describe the synthesis of macroporous hierarchically structured microspheres with nanoplatelets as building blocks of a model organic molecule—dl-glutamic acid (dl-Glu)—via a polymer-induced liquid precursor (PILP) phase using oppositely charged polyethylene imine (PEI) as a polymeric additive. The impacts of experimental parameters such as [dl-Glu], temperature, solvent composition, and the pH value were systematically investigated for the dl-Glu morphosynthesis process. A mechanism is suggested to explain the precipitation of dl-Glu with PEI as an additive based on a multistep process: (1) the formation, growth, and coalescence of the PILP droplets; (2) the homogeneous nucleation of nanoplatelets within PILP droplets and (3) the reorientation of nanoplatelets into hierarchical microspheres. This model system can be further extended to the precipitation of other amino acids that have a net charge opposite to that of the polyelectrolyte additive.
06/2011;
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ABSTRACT: A highly porous member of isoreticular MFU-4-type frameworks, [Zn(5)Cl(4)(BTDD)(3)] (MFU-4l(arge)) (H(2)-BTDD=bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin), has been synthesized using ZnCl(2) and H(2)-BTDD in N,N-dimethylformamide as a solvent. MFU-4l represents the first example of MFU-4-type frameworks featuring large pore apertures of 9.1 Å. Here, MFU-4l serves as a reference compound to evaluate the origin of unique and specific gas-sorption properties of MFU-4, reported previously. The latter framework features narrow-sized pores of 2.5 Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU-4l has been solved ab initio by direct methods from 3D electron-diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron-beam precession. Independently, it has been solved using powder X-ray diffraction. Thermogravimetric analysis (TGA) and variable-temperature X-ray powder diffraction (XRPD) experiments carried out on MFU-4l indicate that it is stable up to 500 °C (N(2) atmosphere) and up to 350 °C in air. The framework adsorbs 4 wt % hydrogen at 20 bar and 77 K, which is twice the amount compared to MFU-4. The isosteric heat of adsorption starts for low surface coverage at 5 kJ mol(-1) and decreases to 3.5 kJ mol(-1) at higher H(2) uptake. In contrast, MFU-4 possesses a nearly constant isosteric heat of adsorption of ca. 7 kJ mol(-1) over a wide range of surface coverage. Moreover, MFU-4 exhibits a H(2) desorption maximum at 71 K, which is the highest temperature ever measured for hydrogen physisorbed on metal-organic frameworks (MOFs).
Chemistry 02/2011; 17(6):1837-48. · 5.93 Impact Factor
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ABSTRACT: Fusion of pentanuclear Kuratowski-type coordination units leads to homo- and heterononanuclear coordination compounds, two of which are presented, having structural formulae [Zn(9)Cl(6)(OMe(2)bta)(12)]·DMF (1), and [Fe(II)(3)Zn(6)Cl(6)(OMe(2)bta)(12)]·DMF (2), respectively; (OMe(2)btaH = 5,6-dimethoxy-1,2,3-benzotriazole; DMF = N,N'-dimethylformamide). Single crystal X-ray structure analyses reveal the presence of {M(3)Zn(6)L(12)}(6+) cores (M = Zn or Fe(II); L = 5,6-dimethoxy-1,2,3-benzotriazolate) in which the M(II) ions are bridged by μ(3)-OMe(2)bta ligands. In both compounds, the six peripheral Zn ions are tetracoordinated, whereas the remaining three metal ions M are hexacoordinated. The charge of each {M(3)Zn(6)L(12)}(6+) moiety is balanced by six chloride anions that are monodentately bound to the peripheral Zn ions. Based on differences in experimental Fe-N-donor bond lengths (deduced from single crystal data of 2 recorded at 223 K), two out of three Fe(II) ions are found in a high-spin (HS) state, whereas one Fe(II) ion shows a low-spin (LS) state. The assignment of different energetic ground states of Fe(II) ions is corroborated by spectroscopic studies: Both solid-state and solution UV-Vis spectra of 2 (at ambient temperature) display absorption bands owing to the presence of both HS and LS Fe(II) ions. Removal of occluded DMF molecules from the crystal lattices of 1 and 2 in high vacuum leads to fully desolvated powders, termed hereafter 1a and 2a, respectively. Mössbauer studies on 2a show that all three Fe(II) ions are in HS state at 160 K, and upon cooling to 7 K, the central Fe(II) ion undergoes a HS→LS transition while the HS states of the other Fe(II) ions remains unchanged. The cyclic voltammogram of 2 (chloroform solution) exhibits a single reversible oxidation regardless of different Fe(II) spin states in the nonanuclear core of 2.
Dalton Transactions 11/2010; 39(41):9851-9. · 3.84 Impact Factor
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ABSTRACT: Homo- and heteropentanuclear coordination compounds [MZn(4)Cl(4)(L)(6)] (M(II) = Zn, Fe, Co, Ni, or Cu; L = 5,6-dimethyl-1,2,3-benzotriazolate) were prepared containing mu(3)-bridging N-donor ligands (1,2,3-benzotriazolate), which are structurally related to the fundamental secondary building unit of Metal-organic Framework Ulm University-4 (MFU-4). The unique topology of these T(d)-symmetrical compounds is characterized by the nonplanar K(3,3) graph, introduced into graph theory by the mathematician Casimir Kuratowski in 1930. The following "Kuratowski-type" compounds were investigated by single-crystal X-ray structure analysis: [MZn(4)Cl(4)(Me(2)bta)(6)].2DMF (M(II) = Zn, Fe, Co, and Cu; DMF = N,N'-dimethylformamide) and [MZn(4)Cl(4)(Me(2)bta)(6)].2C(6)H(5)Br (M(II) = Co and Ni; C(6)H(5)Br = bromobenzene). The mu(3)-bridging benzotriazolate ligands span the edges of an imaginary tetrahedron, in the center of which a redox-active octahedrally coordinated M(II) ion is placed. Four Zn(II) ions are located at the corners of the coordination units. Each Zn center is bound to a monodentate Cl(-) anion and three N-donor atoms stemming from different benzotriazolate ligands. The fact that open-shell redox-active M(II) ions can be introduced selectively into the central octahedral coordination sites is unambiguously proven by a combination of magnetic measurements, UV-vis spectroscopy, and energy-dispersive X-ray and inductively coupled plasma atomic emission spectrometry analysis. The phase purity of all compounds was checked by powder X-ray diffractometry, IR spectroscopy, and elemental analysis. The electronic spectra and magnetic properties of the compounds are in complete agreement with their structures determined from single-crystal data. Thermogravimetric analysis shows that all compounds possess a high thermal stability up to 673 K. The pentanuclear compounds retain their structural integrity in solution, as evidenced by time-of-flight mass spectrometry analysis and comparative solution and solid-state diffuse-reflectance spectroscopy. High stability paired with the presence of redox-active metal ions and Lewis-acidic Zn centers renders Kuratowski-type compounds structural and functional models for future MFU-4-type bi- and multifunctional heterogeneous catalysts.
Inorganic Chemistry 08/2010; 49(16):7424-34. · 4.60 Impact Factor
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ABSTRACT: The self-assembly of copper(II) ions and 5-(2-(2-hydroxyethoxy)ethoxy)benzene-1,3-dicarboxylic acid (2) leads to hollow nanoballs in which 12 dinuclear copper(II) paddle wheel units are interconnected via 24 ligands, as determined by single crystal X-ray structure analysis. The nanoball dissociates in aqueous solutions, and in the presence of an excess of ligand it transforms into a three-dimensional network, but is stable in organic solvents. The thermodynamic stability of the nanoball against dissociation in aqueous solution is studied and compared to simple copper(II) paddle wheel complexes. The results reveal enhanced thermodynamic stability of the nanoball as compared to discrete copper(II) paddle wheel complexes due to chelate effects and positive cooperativity.
Inorganica Chimica Acta 06/2010; 363(DOI: 10.1016/j.ica.2010.06.022):4220. · 1.85 Impact Factor
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ABSTRACT: Two novel metal coordination polymers, [Zn5Cl4(BBTA)3].3 DMF (1), and [ZnCl(BBTA)(0.5)(DMA)] (2) {H2-BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole}, have been synthesized under solvothermal conditions using ZnCl2 and H2-BBTA in DMF (DMF = N,N'-dimethylformamide) or DMA (DMA = N,N'-dimethylacetamide). Moreover, a highly efficient microwave synthetic route has been developed for 1. The structures of both compounds have been determined by single crystal X-ray diffraction. Compound 1 represents the first example of a novel family of cubic microporous metal-organic frameworks (MFU-4; Metal-Organic Framework Ulm University-4), consisting of dianionic BBTA2- linkers and pentanuclear {Zn5Cl4}6+ secondary building units, whereas compound 2 forms a dense 2D layered framework. Phase purity of both compounds was confirmed by X-ray powder diffraction (XRPD), IR spectroscopy, and elemental analysis. TGA and variable temperature XRPD (VTXRPD) experiments carried out on 1 indicate that solvent molecules occluded in the large cavities of 1 can be removed at a temperature >250 degrees C in high vacuum without significant loss of crystallinity, giving rise to a metal-organic framework with void cavities. Due to the small diameter of the aperture joining the two types of cavities present in 1, the diffusion of guest molecules across the crystal lattice is largely restricted at ambient conditions. Compound 1 therefore exhibits a highly selective adsorption for hydrogen vs. nitrogen at -196 degrees C. The framework is stable against moisture and has a specific pore volume of 0.42 cm3 g(-1) estimated from the water adsorption isotherm.
Dalton Transactions 10/2009; · 3.84 Impact Factor
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Angewandte Chemie International Edition 09/2009; 48(41):7546-50. · 13.45 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 06/2009; 2009(21):3094 - 3101. · 2.94 Impact Factor
