Preparative and 1H NMR Investigation on Regioselective Silylation of Starch Dissolved in Dimethyl Sulfoxide

Reaction of starch 1 dissolved in dimethyl sulfoxide (DMSO) with bulky thexyldimethylchlorosilane (TDSCl) in the presence of pyridine leads to regioselectively functionalized silyl ethers with a degree of substitution (DS) up to 1.8. The control of the DS_Si, of the regioselectivity, and of the reaction pathway is described in detail. The reaction proceeds homogeneously up to DS_Si of 0.6. With ongoing silylation the polymers form a separate phase incorporating the silylating agent to form TDS‐starches with DS_Si values higher than 1.0. After peracetylation of the silyl starches, the substitution pattern has been characterized not only in the anhydroglucose repeating units (AGU) but also in the non‐reducing terminal end groups (TEG) by means of two‐dimensional ¹H NMR techniques. Up to DS_Si 1.0, a very high regioselective functionalization of the primary 6‐OH groups in the AGU as well as in the TEG is detectable. With increasing silylation (DS_Si > 1.0), the subsequent silylation takes place at the 2‐OH groups of the AGU and at the 3‐OH groups of the TEG. These results are compared with our own investigations on the silylation of starch in the reaction system N‐methylpyrrolidone (NMP)/ammonia and on the silylation of cellulose in N,N‐dimethylacetamide (DMA)/LiCl/pyridine solution.     

“Living” free radical copolymerization of styrene and N-vinylcarbazole

Poly[styrene-co-(N-vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide-mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene-co-(N-vinylcarbazole)]/polystyrene block copolymers via a controlled chain-extension reaction of the prepared copolymers with styrene.     

Hochdrucksynthese und Kristallstruktur von YbH2, 67

High Pressure Synthesis and Crystal Structure of YbH_2.67 Ytterbiumhydrides can be synthesized by reaction of ytterbium metal in hydrogen atmosphere above 600 K. The experiments were carried out in the pressure range from 200 to 3200 bar. X‐ray investigations on powdered samples and elastic neutron diffraction experiments on deuterated compounds led to a complete structure determination. YbH_2.67 is obtained at reaction pressures of 200, 1400 und 3200 bar. In contrast to reports in literature the deuterides crystallize with trigonal symmetry (P3¯1m, a = 6.344(1)Å, c = 9.002(1)Å, Z = 9) and not in the cubic crystal system. The composition YbD_2.67 was additionally checked by chemical analysis. The crystal structure can be described as a close packing of ytterbium atoms (stacking sequence …ABC…) in which all tetrahedral holes and 2/3 of the octahedral holes are occupied in an ordered manner by hydrogen. Magnetic susceptibility measurements are in agreement with literature data.     

Accurate parametrized variational calculations of the molecular electronic polarizability by NDDO‐based methods

The variational method for the calculation of the electronic polarizability of molecules within the NDDO‐based semiempirical MO methods MNDO, AM1, and PM3 was parametrized to improve its accuracy. A training set of 156 compounds was used to fit 34 parameters simultaneously for 12 elements using a simplex optimization. The resulting parameters were tested for a test set of 83 molecules and the calculated polarizabilities compared with the experimental data. For AM1, the RMS deviation between experimental and calculated polarizabilities was reduced from 2.99 (using the original variational treatment) to 0.70 ų for the test set and from 2.81 to 0.40 ų for the training set. MNDO and PM3 gave similar improvements. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 17–31, 1999     

Production of PHAs from agricultural waste material

Polyhydroxyalkanoates (PHAs) are biodegradable substitutes to fossil fuel plastics that can be produced from renewable raw materials such as saccharides, alcohols and low-molecular-weight fatty acids. They are completely degradable to carbon dioxide and water through natural microbiological mineralization. Consequently, neither their production nor their use or degradation have a negative ecological impact. By keeping closed the cycle of production and re-use, PHAs can enable at least part of the polymer-producing industry to switch from ecologically harmful end-of-the-pipe production methods towards sounder technologies. Up to now such polyesters have been produced biotechnologically from refined raw materials (e.g. glucose and sodium propionate), but they can as well be produced much cheaper from agricultural waste materials (e.g. molasses, maltose, glycerol phase from biodiesel production, whey), as long as these materials have a known composition and are available in appropriate quantities. Yield factors and specific rates for growth and PHA accumulation are shown for 3 strains of Alcaligenes latus for different agricultural waste carbon sources.     

Formation of a Special Intermediate during Phase Transformation of Zeolite NaA to Nepheline

In the process of phase transformation of zeolite NaA to nepheline under hydrothermal conditions a special intermediate occurs. This is due to the high reaction rate of nepheline formation in the presence of water molecules. Consequently, the usually observed amorphous material with high condensed silica does not occur as separate phase. – The intermediate which is formed due to the destruction of the long-range order of zeolite is significantly short-range ordered. The phase transformation process starts at the outer surface of zeolite crystals, thus generating a diffusion barrier for sorption uptake processes.     

Silicate Cross‐Linked Bio‐Nanocomposite Hydrogels from PEO and Chitosan

The compositions and the multi phase structures of bio‐nanocomposite hydrogels made from silicate cross‐linked PEO and chitosan are related to some of their physical and biological properties. The gels are injectable and self‐healing because the cross‐linking is physical and reversible under deformation. The presence of chitosan aggregates affects the viscoelastic properties and reinforces the hydrogel network. The chitosan adds advantageous properties to the hydrogel such as enhanced cell spreading and adhesion. In vitro biocompatibility data indicate that NIH 3T3 fibroblasts grow and proliferate on the bio‐nanocomposite hydrogel as well as on hydrogel films.

     

Ba2[Ni3N2]: a low-valent nitridonickelate-synthesis, crystal structure, and physical properties

The ternary alkaline-earth nitridonickelate Ba2[Ni3N2] (Ba2[NiI2Ni0N2]) was prepared by the reaction of mixtures of Ba2N and Ni in nitrogen gas of ambient back-pressure at 1173 K. The crystal structure determined by X-ray single-crystal and powder diffraction methods as well as from neutron diffraction data at various temperatures between 2 and 298 K is orthorhombic (Cmca (no. 64), 298 K: a=715.27(18) pm, b=1032.99(21) pm, c=740.12(20) pm) and provides the first example of a nitridonickelate with a two-dimensional complex anion. The Ni2 atom is described with a split position and the corresponding superstructure variants are investigated by theoretical full-potential nonorthogonal local-orbital calculations (FPLO). The average oxidation state of Ni in Ba2[Ni3N2] is +0.67, the lowest average value observed in nitridonickelates so far. Investigations of the physical properties demonstrate that Ba2[Ni3N2] acts as a "poor" metal with a large resistivity of approximately 2.7 mOmega cm at 300 K and exhibits low-dimensional magnetism with antiferromagnetic ordering at T approximately 90 K. XAS spectra correspond with low-valent Ni states.