Colloidal Silica Rods: Material Properties and Fluorescent Labeling

In this paper, the characterization and fluorescent labeling of silica rods are reported. These rods are synthesized following a recently reported method. Material properties of the silica rods measured with NMR, elemental analysis, TGA, and porosimetry are compared with those of well‐established Stöber silica spheres. Additionally, silica rods are made suitable for quantitative real‐space studies by confocal microscopy. Several methods of fluorescent labeling to prepare rods with different fluorescent patterning, ranging from uniform fluorescence levels to gradients from one rod‐end to the other, and even patterns of several colors are presented and discussed.     

Ionic liquid 1-ethyl-3-methylimidazolium acetate: an attractive solvent for native chemical ligation of peptides

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C₂mim][OAc]. In addition to improving the solubility of the peptides in [C₂mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced.     

How to Control the Chemoselectivity of the Catalytic Formation of Chiral γ-Lactams or 2,3-Disubstituted Pyrroles by the Choice of Solvent

Summary. The reaction of the unsaturated imine methyl(3-phenylallylidene)amine with ethylene and carbon monoxide in the presence of catalytical amounts of Ru₃(CO)₁₂ leads to the formation of two heterocyclic products. One of the products is a chiral γ-lactam, the other one a 2,3-disubstituted pyrrole derivative, in which only the carbon atom from carbon monoxide is incorporated. The selectivity in the formation of the products may be controlled by the choice of solvent. In general, in nonpolar solvents the formation of the lactam is preferred whereas the use of more polar solvents enhances the yield of the pyrrole. For most of the solvents used there is a linear dependence of the product ratio on the relative permittivity of the corresponding solvent. Typically, polar aprotic solvents do not follow this rule.     

Steroids and sex hormones. 241. The partial synthesis of 3-methoxy--3-, 9- -oxido-7- hydroxy-11- -acetoxy-5- steroids

The preparation of the title compounds 11 , 37 , and 39 is described. 37 will serve as starting material for a partial synthesis of the steroidal alkaloid batrachotoxinin A ( 1 ).     

Tuning the mechanical properties of silica microcapsules

Heat treatment is a standard method to increase the hardness of silica in various applications. Here, we tested the effect of high temperature annealing on the mechanical properties of silica microcapsules by force spectroscopy under point loads applied to the particle shell. The Young's modulus of the shells moderately increases after annealing at temperatures above 500 °C. Temperatures over 850 °C result in a much stronger increase and the Young's modulus is close to that of fused silica after annealing at 1100 °C. NMR analysis revealed that in untreated microcapsules synthesized by seeded growth using the St?ber method only 55% of the silicon atoms form siloxane bonds with four neighbors, whereas the remaining ones only form three or less siloxane bonds each and, thus, a large number of ethoxy and silanol groups still exist. During annealing at 500 °C, these are successively transformed into siloxane bonds through condensation reactions. This process correlates with only a moderate increase in Young's modulus. The strong increase at temperatures above 850 °C was associated with a densification which was associated by a decrease in capsule size and shell thickness while the shells remained homogenous and of spherical shape. The main strengthening of the shells is thus mainly due to compaction by sintering at length scales significantly larger than that of local siloxane bonds.     

Cyanidverbrückte Koordinationspolymere aus cis‐ oder trans‐[Ru(tBuNC)4(CN)2] und MnCl2: Zum Einfluß unterschiedlicher Topologien auf die magnetischen Eigenschaften von Materialien

Cyanide Bridged Coordination Polymers from cis‐ or trans‐[Ru(^tBuNC)₄(CN)₂] and MnCl₂: About the Influence of Different Topologies on the Magnetic Properties of Materials The reaction of cis‐ or trans‐[Ru(^tBuNC)₄(CN)₂] with MnCl₂ as an additional transition metal fragment yields the one dimensional coordination polymers {cis‐[Ru(CN)₂(^tBuNC)₄] MnCl₂}_n, ( 1 ), and {trans‐[Ru(CN)₂(^tBuNC)₄]MnCl₂}_n, ( 2 ), with a different arrangement of the metal centers caused by the different stereochemistry of the starting compounds. The variation of the Ru‐C‐N‐Mn geometry nevertheless leads to significant differences in the magnetic properties of 1 and 2 . The coordination polymer derived from trans‐[Ru(^tBuNC)₄(CN)₂] shows a more efficient antiferromagnetic intrachain interaction between the manganese centers compared to the cis‐derivative.     

Decontamination of chemical warfare agents using perchloroethylene–Marlowet IHF–H2O-based microemulsions: wetting and extraction properties on realistic surfaces

At the present time, considerable efforts are being made to develop new media for the decontamination of a variety of toxic compounds. In the present contribution, new microemulsions with promising properties are presented. Moreover, the decontamination of surfaces, with an emphasis on varnished metal surfaces of exterior and interior equipment, is investigated using these microemulsions. Studies of the phase behavior of the system water–perchloroethylene–IHF–2-propanol are reported and the microemulsion phases are recognized. The wetting behavior on contaminated surfaces and the extraction capabilities with respect to contaminants are essential for an efficient decontamination. Hence, suitable microemulsions are identified on the basis of these properties. The decontamination efficiency of these microemulsions is first estimated on the basis of the ability to wet typical chemical nonresistant varnished steel sheets, which are authentic model systems for real surfaces. Afterwards, promising microemulsions and, as reference, different solvents are tested with respect to their capability to solubilize sulfur-mustard agent, again using realistic surfaces contaminated with this chemical warfare agent. Several microemulsions are found, which have the desired properties.     

Steroide und Sexualhormone. 248. Mitteilung. Die Partialsynthese von 5α-Dihydrohirundigenin und von 5α-dihydroanhydrohirundigenin

A partial synthesis of dihydroanhydrohirundigenin ( 4 ), a hydrogenation product of naturally occurring anhydrohirundigenin ( 2 ) is described. Furthermore 4 is transformed into the formal dihydroderivative 14 of hirundigenin ( 1 ).