Tin in silicate glasses: structure, thermodynamics and kinetics

In this work Mössbauer spectroscopy is used to investigate the oxidation states and structures of tin in silicate glasses. Thermal treatment of the glasses in atmospheres with varying oxygen partial pressure leads to the simultaneous appearance of reduction and diffusion. Experiments with varying treatment time give the opportunity to study diffusion and reduction processes in detail. Comparison of the hyperfine parameters of reference materials with measured parameter provides information about the local surroundings of the tin atoms. An octahedral surrounding for Sn^4?+? is presumed, while Sn^2?+? and three oxygen atoms form a tetrahedral coordination.     

Practice effects in healthy adults: <Emphasis Type="Italic">A longitudinal study on frequent repetitive cognitive testing</Emphasis>

Background  

Cognitive deterioration is a core symptom of many neuropsychiatric disorders and target of increasing significance for novel treatment strategies. Hence, its reliable capture in long-term follow-up studies is prerequisite for recording the natural course of diseases and for estimating potential benefits of therapeutic interventions. Since repeated neuropsychological testing is required for respective longitudinal study designs, occurrence, time pattern and magnitude of practice effects on cognition have to be understood first under healthy good-performance conditions to enable design optimization and result interpretation in disease trials.     

Enantioselective synthesis of non-natural aromatic alpha-amino acids

We present two complementary methods for the stereoselective synthesis of non-natural alpha-amino acids with aromatic or heteroaromatic side chains. One approach is based on the chemical transformation of methionine, whereas the other applies the stereoselective Myers alkylation of glycine. The resulting product types differ in the linker length between glycine and the aromatic substituent. Since methionine and pseudoephedrine are available in both absolute configurations, R- or S-configured enantiopure amino acids with either C(2) or C(3) linkers can be obtained on gram scales. In each case the key step of the synthesis is hydroboration of the unsaturated building blocks 9 and 17, followed by palladium-catalyzed Suzuki cross-coupling with aryl halides. Attention must in certain cases be paid to the stereochemical integrity when basic Suzuki conditions are applied. Our initial difficulties are reported as well as the final "racemization-proof" procedures. The protecting groups chosen for the alpha-amino acids should be compatible with solid-phase peptide synthesis. This was confirmed by the successful synthesis of a series of tripeptides.     

Intracellular compartmentation in the biosynthesis of caulerpenyne: study on intact macroalgae using stable-isotope-labeled precursors

The biosynthesis of caulerpenyne 1 was studied in the invasive green alga Caulerpa taxifolia. The investigation was performed on intact algae with stable-isotope-labeled precursors administered under mixotrophic growth conditions. According to the labeling pattern, after incorporation of 1-(13)C-acetate and (13)CO(2), respectively, the biosynthesis of the sesquiterpene backbone occurs in the chloroplast and follows the methyl-erythritol-4-phosphate (MEP) pathway. In contrast, the acetyl residues of caulerpenyne 1 are derived from a cytosolic resource. [structure: see text]     

Unprecedented hybrid scorpionate/phosphine ligand able to be anchored to carbosilane dendrimers

The synthesis of a novel hybrid pyrazolate/phosphine anionic ligand [CH2=CHCH2B(CH2PPh2)(pz)2]- is described. Coordination of this ligand to metals in a fac tridentate fashion occurs in the complexes [CH2=CHCH2B(CH2PPh2)(pz)2M(cod)], prepared by reactions of the lithium salt of the ligand with [M(mu-Cl)(cod)]2 (M=Rh, Ir). They are pentacoordinated, with the rhodium complex showing a distorted trigonal-bipyramidal structure in the solid state, as determined by X-ray diffraction methods. Furthermore, the ligand has been linked to the periphery of a carbosilane dendrimer, resulting in the polyanionic dendrimer [Li(TMED)]4[Si{(CH2)3SiMe2(CH2)3B(CH2PPh2)(pz)2}4], which leads further to the corresponding metallodendrimer with four rhodium atoms.     

Oligosaccharide Analogues of Polysaccharides,Part 17, Synthesis and Characterization of a Hexadecamer: Evidence for the Essential Structural Role of the Intramolecular,Interresidue C(3)−OH⋅⋅⋅O−C(5) Hydrogen Bond in Celluloses

The hexadecamer 63 dissolves readily in DMSO and shows no sign of association, in agreement with the essential structural role of the intramolecular, interresidue C(3)−OH⋅⋅⋅O−C(5) H-bond of celluloses. MM3 Calculations predict a rod-like shape for the cello-oligosaccharides. In agreement with this, nanocrystalline domains of parallel chains are observed by high-resolution electron microscopy (HREM) for 54 and 63 on carbon-coated copper grids. For the synthesis of the hexadecamer 54 , we studied the influence of protecting groups on the cross-coupling of acetyleno-oligosaccharides and on their solubility (Scheme 2). The octamer 12 derived from the minimally O-protected monomer 2 is insoluble, while the methoxymethyl- and triisopropylsilyl-protected hexadecamer 54 , prepared in twelve steps from the dimer 41 (Scheme 4), is readily soluble in a variety of solvents. O- and C-deprotection of 54 led in four steps and in 76% yield to the hexadecamer 63 (Schemes 5 and 6). There is only a small difference of spectroscopic properties between the protected octamer 50 and hexadecamer 54 , and, similarly, between the unprotected octamer 64 and hexadecamer 63 (Fig. 3).     

Improvement of the Solubilization and Extraction of Curcumin in an Edible Ternary Solvent Mixture

A water-free, ternary solvent mixture consisting of a natural deep eutectic solvent (NADES), ethanol, and triacetin was investigated concerning its ability to dissolve and extract curcumin from Curcuma longa L. To this purpose, 11 NADES based on choline chloride, acetylcholine, and proline were screened using UV–vis measurements. A ternary phase diagram with a particularly promising NADES, based on choline chloride and levulinic acid was recorded and the solubility domains of the monophasic region were examined and correlated with the system’s structuring via light scattering experiments. At the optimum composition, close to the critical point, the solubility of curcumin could be enhanced by a factor of >1.5 with respect to acetone. In extraction experiments, conducted at the points of highest solubility and evaluated via HPLC, a total yield of ~84% curcuminoids per rhizome could be reached. Through multiple extraction cycles, reusing the extraction solvent, an enrichment of curcuminoids could be achieved while altering the solution. When counteracting the solvent change, even higher concentrated extracts can be obtained.