Thermotropic phase behavior of long-chain alkylammonium-alkylcarbamates

A series of alkylammonium-alkylcarbamates with different chain length including transdermal permeation enhancer Transkarbam 12 have been prepared and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), temperature-dependent Fourier transform infrared spectroscopy (FTIR) and temperature-dependent X-ray powder diffraction. Four transitions have been observed including solid-solid transition (I), melting (II), decomposition of the carbamate salt (III) and boiling of the released amine (IV). The first transition was connected with rearrangement of the hydrocarbon chain packing and unusual shift of symmetric CH₂ stretching vibration in the IR spectra to lower wavenumbers indicated increase of conformational order. The second transition represented melting of the molecule and the third one was attributed to the decomposition of the carbamate salt into two amine molecules and carbon dioxide as evidenced by combination of DSC and TGA curves.     

Interaction of [Mo6Cl14]2− with H2Se: Selective Preparation of [Mo6SeCl13]3−

Reaction of [Mo₆(μ₃-Cl)₈Cl₆]²⁻ with H₂Se, generated in situ from ZnSe and 4 M HCl under hydrothermal conditions lead to the substitution of one or two bridging chlorides, depending on the reagents ratio. With the Mo₆/ZnSe 1:3 molar ratio [Mo₆(μ₃-SeCl₇)Cl₆]³⁻ forms selectively in high yield. Further substitution is more hindered, and even at 1:20 cluster-to-selenide molar ratio a mixture of [Mo₆(μ₃-SeCl₇)Cl₆]³⁻ and [Mo₆(μ₃-Se₂Cl₆)Cl₆]⁴⁻ is formed. The products were characterized by X-ray, Raman spectra and electrospray ionization mass spectrometry.     

Annealing-induced structural transformation of gelatin-capped Se nanoparticles

Selenium nanoparticles were obtained by a new facile synthetic route from gelatin-stabilized aqueous colloidal solutions. The dependence of structural and optical properties of the nanoparticles upon duration of post-synthesis thermal treatment of Se sols was studied by optical absorption, photoluminescence and Raman scattering. We have shown that ageing of colloidal Se solutions at elevated temperatures results in an enlargement and crystallization of selenium nanoparticles, accompanied with noticeable changes in their optical spectra: an enhancement of the photoluminescence of the NPs, incorporated in gelatin films; a “red” shift of both the absorption threshold and emission band maximum; appearance of new peaks in Raman spectra, attributed to the formation of the crystalline phase in the course of the ageing.     

Prediction of coating uniformity in batch fluidized-bed coating process

Coating of particulate materials in fluidized beds is a widely used technique to eliminate particle agglom-eration,provide slow release of an active substance,o...     

Approximation of Periodic Solutions of a System of Periodic Linear Nonhomogeneous Differential Equations

The present paper does not introduce a new approximation but it modifies a certain known method. This method for obtaining a periodic approximation of a periodic solution of a linear nonhomogeneous differential equation with periodic coefficients and periodic right-hand side is used in technical practice. However, the conditions ensuring the existence of a periodic solution may be violated and therefore the purpose of this paper is to modify the method in order that these conditions remain valid.     

Silver Fractal-Like Structures for Metal-Enhanced Fluorescence: Enhanced Fluorescence Intensities and Increased Probe Photostabilities

Substantial increases in fluorescence emission from fluorophore-protein–coated fractal-like silver structures have been observed. We review two methods for silver fractal structure preparation, which have been employed and studied. The first, a roughened silver electrode, typically yielded a 100-fold increase in fluorophore emission, and the second, silver fractal-like structures grown on glass between two silver electrodes, produced a 500-fold increase. In addition, significant increases in probe photostability were observed for probes coated on the silver fractal like structures. These results further serve to compliment our recent work on the effects of nobel metal particles with fluorophores, a relatively new phenomenon in fluorescence we have termed both metal-enhanced fluorescence [1] and radiative decay engineering [2,3]. These results are explained by the metallic surfaces modifying the radiative decay rate () of the fluorescent labels. We believe that this new silver-surface preparation, which results in ultrabright and photostable fluorophores, offers a new generic technology platform for increased fluorescence signal levels, with widespread potential applications to the analytical sciences, imaging, and medical diagnostics.     

Cyclosporins of Symmetry P21 – a Series of Clathrates

A series of isomorphous clathrates(cyclosporin A: solvent = 1 : 1) is reported. Thestructure of the tetrahydrofuran (1) anddibutylether (2) clathrates have been determinedby X-ray single crystal diffraction. The cyclosporinmolecules in both structures are associated via vander Waals interactions forming cavities occupied bysolvent molecules. The structure refinement based onroom-temperature data sets show significant disorderof the side chains of the cyclosporin A molecule withno adequate model of the solvent molecule in bothstructures. In contrast, the position of dibutyletherwas successfully localised using a low-temperaturedata set for 2.     

Crystal structures of mollugin and lucidin

Mollugin was isolated from the extract of Rubia tinctorum roots. Lucidin was obtained by semisynthesis from xanthopurpurin. Mollugin crystallises in space group P-1 (No. 2), a = 8.5857(7), b = 11.473(4), c = 15.024(1) Å, α = 77.64(2)^∘, β = 89.36(1)^∘, γ = 89.71(2)^∘, and V = 1445.5(5) ų, lucidin crystallises in space group P2₁/c (No.14), a = 16.800(6), b = 9.637(2), c = 7.073(7) Å, β = 98.01(5)^∘, and V = 1134(1) ų.     

Fluoro-tagged osmium and iridium nanoparticles in oxidation reactions

Osmium and iridium metal nanoparticles were supported on a fluorous organic-inorganic hybrid material prepared by the sol-gel process. Moreover, we also found that the thermolysis of the Ir₄(CO)₁₂ cluster in simply diphenylether also gave Ir(0) nanoparticles. All the materials were studied as catalysts in oxidation processes. Fluoro-tagged iridium nanoparticles were particularly active in aerobic oxidation processes, whereby the catalytic activity could be greatly enhanced through a simple pre-activation procedure. With this material, benzylic alcohols could be oxidized under O₂ balloon in the absence of a basic additive; the oxidative stopped selectively to the corresponding benzaldehyde. Promisingly, the same reaction conditions were used in a benzylic CH oxidation of xanthene.