Amorphous drug nanosuspensions. 2. Experimental determination of bulk monomer concentrations

A simple turbidimetric method was developed to measure the bulk concentration of drug in nanosuspensions. The bulk concentrations measured were in the range from 1 microM to 1 mM. The accuracy of the method was checked by determination of the bulk concentration of crystalline nanosuspensions, i.e., the crystalline solubility, which compared favorably to solubilities measured by a conventional method. Results obtained for amorphous nanosuspensions agreed with predictions using a theory describing the relative solubility between a supercooled liquid and a crystal. Further, it was found that the bulk concentration in Ostwald ripening inhibited amorphous nanosuspensions and could be lowered by incorporation of higher amounts of the inhibitor, in agreement with predictions using the Bragg-Williams theory of nonideal solutions.     

Isolation of a Diylide‐Stabilized Stannylene and Germylene: Enhanced Donor Strength through Coplanar Lone Pair Alignment

The preparation of the first stable diylide‐substituted stannylene and germylene ( Y₂E, with E=Ge, Sn and Y=[PPh₃‐C‐SO₂Tol]^?) is reported. The synthesis is easily accomplished in one step from the sulfonyl‐substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂Ge and Y₂Sn exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C‐E‐C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π‐donation from the ligands into the empty p‐orbital at the metal due to the strong anion‐stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, Y₂Ge and Y₂Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂Ge and Y₂Sn , which for example undergo an intramolecular C?H activation reaction via metal–ligand cooperation.     

Magnetic Carbon Composite Particles for Dye Adsorption from Water and their Electrochemical Regeneration

Herein, the development of a novel composite particle system prepared from superparamagnetic Fe₃O₄@SiO₂ microparticles as core and coated with a carbon shell is presented. The coating with carbon is done by pyrolyzing furan resin, which was previously deposited on the particle surface by poly‐merization of furfuryl alcohol. The novel composite material thus combines magnetic and sorptive properties. Upon pyrolysis the magnetic material is converted from magnetite to α‐iron and fayalite, changing its behavior from superparamagnetic to ferromagnetic with nearly zero remanence. The magnetic properties can be utilized to magnetically collect the particles dispersed in fluids, whereas the sorptive properties of the carbon shell can be used to remove organic contaminants from these fluids. The adsorption behavior of the composite particles and a potential electrochemical regeneration route are investigated, using the model dye methylene blue.     

Mössbauer and magnetization studies of iron oxide nanocrystals

Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.     

Electrical conductivity of a strongly coupled hydrogen plasma

A kinetic theoretic calculation of the dc conductivity of a strongly coupled, semi-classical hydrogen plasma yields results in reasonable agreement with recent simulations. A closed formula is derived which extends the standard Spitzer result into the strong coupling regime.     

Regioselective lithiation and functionalization of 3-(benzyloxy)isothiazole: application to the synthesis of thioibotenic acid

Direct functionalization of the 3-oxygenated isothiazole heteroaromatic parental system has not yet been reported in the literature. Here, we report the first regioselective lithiation of the 5-position of 3-(benzyloxy)isothiazole (4) using LDA in diethyl ether. The versatility of the methodology was explored by quenching with a variety of electrophiles to give the desired products 7a,b,d-g in 54-68% yield. Only benzoylation aiming at the synthesis of 7c was unsuccessful. Furthermore, a highly convergent synthesis of thioibotenic acid (1), the sulfur analogue of the neurotoxic natural product ibotenic acid, was carried out.     

Fast numerical solution of fredholm integral equations with stationary kernels

A fast recursive matrix method for the numerical solution of Fredholm integral equations with stationary kernels is derived. IfN denotes the number of nodal points, the complexity of the algorithm isO(N ²), which should be compared toO(N ³) for conventional algorithms for solving such problems. The method is related to fast algorithms for inverting Toeplitz matrices.Applications to equations of the first and second kind as well as miscellaneous problems are discussed and illustrated with numerical examples. These show that the theoretical improvement in efficiency is indeed obtained, and that no problems with numerical stability or accuracy are encountered.     

Über die Jeanssche Zahl und die Wärmestrahlung in anisotropen und absorbierenden Körpern

Jeans' number gives the number of vibration modes of electromagnetic equilibrium radiation. By application ofJeans' original method, a formula for this quantity is derived, valid for an anisotropic and dispersive medium. This derivation is followed by a discussion of different points of view of equilibrium radiation as built up by elementary beams. Finally, for an absorbing uniaxial crystal in thermal equilibrium, a relationship is derived, giving the number of quantum transitions related to emission and absorption of light.     

Carbodiimide-Driven Dimerization and Self-Assembly of Artificial,Ribose-Based Amphiphiles

The aqueous self-assembly of amphiphiles into aggregates such as micelles and vesicles has been widely investigated over the past decades with applications ranging from materials science to drug delivery. The combination of characteristic properties of nucleic acids and amphiphiles is of substantial interest to mimic biological self-organization and compartmentalization. Herein, we present ribose- and ribonucleotide-based amphiphiles and investigate their self-assembly as well as their fundamental reactivity. We found that various types of aggregates are formed, ranging in size from nanometers to micrometers and all amphiphiles exhibit aggregation-induced emission (AIE) in solution as well as in the solid state. We also observed that the addition of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) leads to rapid and selective dimerization of the amphiphiles into pyrophosphates, which decreases the critical aggregation concentration (CAC) by a factor of 25 when compared to the monomers. Since the propensity for amphiphile dimerization is correlated with their tendency to self-assemble, our results may be relevant for the formation of rudimentary compartments under prebiotic conditions.