Refine
Has Fulltext
- no (146) (remove)
Year of publication
- 2011 (146) (remove)
Document Type
- Article (129)
- Doctoral Thesis (8)
- Conference Proceeding (4)
- Review (3)
- Other (2)
Language
- English (146) (remove)
Is part of the Bibliography
- yes (146)
Keywords
- NMR (4)
- Carbohydrates (3)
- Lactones (3)
- Oxygen heterocycles (3)
- conformational analysis (3)
- Base pairing (2)
- Conformational analysis (2)
- DR-UV-Vis (2)
- Fluorescence spectroscopy (2)
- Metathesis (2)
Institute
- Institut für Chemie (146) (remove)
The title compound was prepared by the reaction of 1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane with 4-chloro-2-methyl-phenoxyacetic acid in a ratio of 1:2. The structure has been proved by the data of elemental analysis, IR spectroscopy, NMR ((1)H, (13)C) technique and by X-ray diffraction analysis. Intermolecular hydrogen bonds between the azonium protons and oxygen atoms of the carboxylate groups were found. Immunoactive properties of the title compound have been screened. The compound has the ability to suppress spontaneous and Con A-stimulated cell proliferation in vitro and therefore can be considered as immunodepressant.
We investigate concentrated solutions of poly(styrene-b-N-isopropyl acrylamide) (P(S-b-NIPAM)) diblock copolymers in deuterated water (D2O). Both structural changes and the changes of the segmental dynamics occurring upon heating through the lower critical solution temperature (LCST) of PNIPAM are studied using small-angle neutron scattering and neutron spin-echo spectroscopy. The collapse of the micellar shell and the cluster formation of collapsed micelles at the LCST as well as an increase of the segmental diffusion coefficient after crossing the LCST are detected. Comparing to our recent results on a triblock copolymer P(S-b-NIPAM-b-S) [25], we observe that the collapse transition of P(S-b-NIPAM) is more complex and that the PNIPAM segmental dynamics are faster than in P(S-b-NIPAM-b-S).
Wave energy harvesting could be a substantial renewable energy source without impact on the global climate and ecology, yet practical attempts have struggled with the problems of wear and catastrophic failure. An innovative technology for ocean wave energy harvesting was recently proposed, based on the use of soft capacitors. This study presents a realistic theoretical and numerical model for the quantitative characterization of this harvesting method. Parameter regions with optimal behavior are found, and novel material descriptors are determined, which dramatically simplify analysis. The characteristics of currently available materials are evaluated, and found to merit a very conservative estimate of 10 years for raw material cost recovery.
The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.
The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.
4,4 '-Bis(tert-butyl)-2,2 '-bipyridinedichlorometal(II) - Synthesis, structure and EPR spectroscopy
(2011)
Due to the better solubility of the 4,4'-substituted bipyridine ligand a series of 4,4'0-bis(tert-butyl)-2,2'-bipyridinedichlorometal(II) complexes, [M(tbbpy)Cl(2)], with M = Cu, Ni, Zn, Pd, Pt was synthesised and characterised. The blue copper complex 4,4'-bis(tert-butyl)-2,2'-bipyridinedichlorocopper(II) was isolated in two different polymorphic forms, as prisms 1 with a solvent inclusion and solvent-free as needles 2. Both structures were determined by X-ray structure analysis. They crystallise in the monoclinic space group P2(1)/c with four molecules in the unit cell, but with different unit cells and packing motifs. Whereas in the prisms 1, with the unit cell parameters a = 12.1613(12), b = 10.6363(7), c = 16.3074(15) angstrom, eta = 94.446(8)degrees, the packing is dominated by intra-and intermolecular hydrogen bonds, in the needles 2, with a = 7.738(1), b = 18. 333(2), c = 13.291(3) angstrom, beta = 97.512(15)degrees, only intramolecular hydrogen bonds appear and the complex molecules are arranged in columns which are stabilised by p-p-stacking interactions. In both complexes the copper has a tetrahedrally distorted coordination sphere. These copper complexes were also studied by EPR spectroscopy in solution, as frozen glass and diamagnetically diluted powder with the analogue [Pd(tbbpy)Cl(2)] as host lattice.
Through-space NMR shieldings (TSNMRSs) of a series of 2-alkylidenethiazolines subjected to push-pull activity have been calculated by the GIAO method employing the nucleus-independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs). The ICSSs were applied to quantify and visualize the degree of aromaticity of the studied compounds, which has been shown to be in excellent correlation with the push-pull behavior, quantified by the quotient (pi*/pi) method. Dissection of the absolute magnetic shielding values into individual contributions of bonds and lone pairs by the natural chemical shielding-natural bond orbital (NCS-NBO) analysis has revealed unexpected details.
We have measured differential cross sections (DCSs) for the reaction H + D-2 -> HD- (v' = 2, j' = 0,3,6,9) + D at center-of-mass collision energies E-coll of 1.25, 1.61, and 1.97 eV using the photoloc technique. The DCSs show a strong dependence on the product rotational quantum number. For the HD(v' = 2, j' = 0) product, the DCS is bimodal but becomes oscillatory as the collision energy is increased. For the other product states, they are dominated by a single peak, which shifts from back to sideward scattering as j' increases, and they are in general less sensitive to changes in the collision energy. The experimental results are compared to quantum mechanical calculations and show good, but not fully quantitative agreement.
Highly functionalized dimeric triglycerides, such as compound 2, are obtained as minor products besides branched macromolecules from the acyclic triene metathesis (ATMET) polymerization of unsaturated triglycerides such as glyceryl triundec-10-enoate 1 and methyl acrylate (MA) in the presence of the second generation Hoveyda-Grubbs catalyst. The formed amount of interesting products of lower molecular weight during the ATMET reaction depends on the ratio of MA and triglyceride, reaction time, and temperature. We isolated the dimeric metathesis product 2 and synthesized the respective partially hydrogenated dimer 3 regioselectivly in a seven step reaction sequence starting from 10-undecenoic acid 7 and glycerol. Product 3 was unambiguously characterized by (13)C and (1)H NMR and MS as well as the further intermediate products of the seven step reaction including 10,11 bromo-undecanoic acid 8, the respective brominated 1,3-diglyceride 9, the brominated 1,3-triglyceride 6, and the self-metathesis products 4 and 5 which were isolated and purified.