Analysis of the structure of aqueous ferrofluids by the small-angle neutron scattering method

The structures of several aqueous magnetic fluids stabilized by different combinations of surfactants have been compared using small-angle neutron scattering. The size distribution functions of colloidal particles in water have been determined. The degree of clustering of magnetic nanoparticles has been obtained from comparison with electron microscopy data. The combinations of surfactants that lead to a minimum clustering have been revealed.     

Bildung eines 14-gliedrigen (SiNC4O)2-Heterocyclus – THF-Spaltung und Addition an die Si–N-Bindung

Formation of a 14-Membered (SiNC₄O)₂ Heterocyclus – THF-Cleavage and Addition on the Si–N Bond Lithiated di-tert.-butylmethylsilylaminotrichlorosilane reacts with tetrahydrofurane with formation of the 14-membered heterocyclus 1 [(CMe₃)₂MeSi–N–SiCl₂–O(CH₂)₄]₂ and LiCl. The mechanism of the THF-cleavage is discussed and the results of the crystal structure of 1 are reported.     

Lichenysin

The lipopeptide lichenysin (cyclo-[L-Gln1→D-Leu2→L-Leu3→L-Val4→L-Asp5→D-Leu6→L-Ile7-β-OH fatty acid]) produced by Bacillus licheniformis structurally resembles surfactin from Bacillus subtilis. The main difference is the presence of a glutaminyl residue in position 1 of the peptide sequence in place of glutamic acid in surfactin. This local variation causes significant changes in the properties of the molecule compared to surfactin. Lichenysin has a higher surfactant power, the critical micellar concentration (c.m.c.) being strongly reduced from 220 to 22 μM and a much higher hemolytic activity because 100% hemolysis was observed with only 15 μM instead of 200 μM. Lichenysin is also a better chelating agent because its association constants with Ca²⁺ and Mg²⁺ are increased by a factor of 4 and 16, respectively. This effect is assigned to an increase in the accessibility of the carboxyl group to cations owing to a change in the side chain topology induced by the Glu/Gln exchange. Additionally, the propensity of the lipopeptide for extensive hydrophobic interactions, as illustrated by its low c.m.c., contributes to further stabilization of the cation and an increase in the partitioning of lichenysin into the erythrocyte membrane. Our data support the formation of a lichensyin-Ca²⁺ complex in a molar ratio of 2:1 instead of 1:1 with surfactin, suggesting an intermolecular salt bridge between two lichenysin molecules. Therefore, when Ca²⁺ ions are present in the solution, micellization occurs via a dimer assembly, with a possible long-range effect on the spatial arrangement of the micelles or other supramolecular structures. Finally, among all the surfactin peptidic variants so far known, lichenysin is the one for which the three tested activities are the most substantially improved.     

A Dual-Metal-Catalyzed Sequential Cascade Reaction in an Engineered Protein Cage**

Herein, we describe the creation of an artificial protein cage housing a dual-metal-tagged guest protein that catalyzes a linear, two-step sequential cascade reaction. The guest protein consists of a fusion protein of HaloTag and monomeric rhizavidin. Inside the protein capsid, we established a ruthenium-catalyzed allylcarbamate deprotection reaction followed by a gold-catalyzed ring-closing hydroamination reaction that led to indoles and phenanthridines with an overall yield of up to 66 % in aqueous solutions. Furthermore, we show that the encapsulation stabilizes the metal catalysts against deactivation by air, proteins and cell lysate.