Zn(II) Robson macrocycles as templates for chelating diphosphines

Chelating diphosphines were constructed using dinuclear Zn(II) complexes of Robson macrocycles (Zn-RMCs) as templates. The assembly process is driven by the interaction between the metal centers (Lewis acids) with anionic and neutral Lewis base-functionalized monophosphines. The stability of the final structure depends on the geometry and the affinity of the functional groups of the ditopic phosphines and on the structure of the RMC. In the free ligand the ditopic phosphines coordinate at opposite faces of the pseudo-planar macrocycle as is shown in the molecular structure of several of the assemblies, according to X-ray diffraction. Pre-organization of the system by coordinating the phosphorus atoms to a transition metal center enforced coordination of the functional groups at the same face of the RMC. For several templated diphosphines cis-PtCl(2) complexes were identified by NMR. The in situ assembled diphosphines showed a chelating effect in the rhodium catalyzed hydroformylation of 1-octene. Combination of Zn-RMC 3 and phosphine A gave the highest l/b ratio (13) in acetonitrile.     

LC-MS/MS profiling for detection of endogenous steroids and prostaglandins in tissue samples

Roles of steroid hormones, and compounds that can influence their levels in cells, are of increasing interest in e.g. cancer research, partly because resistance to hormone therapies often complicates treatment. To elucidate the processes involved, the hormones and related compounds need to be accurately measured. Reversed-phase liquid chromatography with dynamic multiple reaction monitoring mass spectrometric detection in electrospray mode is capable of providing such measurements. Therefore, LC-MS/MS was developed for sensitive, selective analysis of 11 steroid hormones, cholesterol and two prostaglandins. The effects of the tissue matrix, and solid-phase extraction (SPE) sample clean-up, on the LC-MS/MS signals of the hormones were also investigated. The results show that the developed LC-MS/MS method, following SPE clean-up to reduce matrix interference, can detect selected steroids in extracts of mouse tissues. The method provides linear measurements of the steroids at concentrations up to few ng/μL, and limits of detection in the range 0.03-0.2 pg/μL (for some compounds lower than those of previously reported methods).     

Complexation of tauro- and glyco-conjugated bile salts with α-cyclodextrin and hydroxypropyl-α-cyclodextrin studied by affinity capillary electrophoresis and molecular modelling

The interaction of the bile salts taurocholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate, and glycochenodeoxycholate present in man, dog, and rat with α-cyclodextrin and 2-hydroxypropyl-α-cyclodextrin was investigated by mobility shift affinity capillary electrophoresis. The cyclodextrins are applied as excipients for solubilisation of drug substances with poor aqueous solubility. Accurate determination of stability constants is challenging for weak analyte-ligand interactions such as the conjugated bile salt α-cyclodextrin interactions. A new approach for correction of medium effects due to the high additive concentrations in the background electrolyte was introduced. The use of prostaglandin A(1) as an interacting marker molecule offered a more satisfactory approach for correction than the commonly employed methods based on viscosity or current ratios. The interacting marker was chosen over a non-interacting marker to avoid the difficult validation of the non-interacting properties. The investigated bile salts all interacted with α-cyclodextrin and 2-hydroxypropyl-α-cyclodextrin. Stability constants ranging from 14 to 95 M(-1) were obtained with slightly higher affinities toward the substituted cyclodextrin. Molecular modelling demonstrated that the interaction between the two species involves the side chain of the bile salt. All together, these results indicate minor bile salt-mediated displacement of substances from α-cyclodextrin complexes in the small intestine.     

Surface-dependent chemical equilibrium constants and capacitances for bare and 3-cyanopropyldimethylchlorosilane coated silica nanochannels

We present a combined theoretical and experimental analysis of the solid-liquid interface of fused-silica nanofabricated channels with and without a hydrophilic 3-cyanopropyldimethylchlorosilane (cyanosilane) coating. We develop a model that relaxes the assumption that the surface parameters C(1), C(2), and pK(+) are constant and independent of surface composition. Our theoretical model consists of three parts: (i) a chemical equilibrium model of the bare or coated wall, (ii) a chemical equilibrium model of the buffered bulk electrolyte, and (iii) a self-consistent Gouy-Chapman-Stern triple-layer model of the electrochemical double layer coupling these two equilibrium models. To validate our model, we used both pH-sensitive dye-based capillary filling experiments as well as electro-osmotic current-monitoring measurements. Using our model we predict the dependence of ζ potential, surface charge density, and capillary filling length ratio on ionic strength for different surface compositions, which can be difficult to achieve otherwise.     

Temperature-dependent crystal structure of the isopropanol clathrate of Dianin's compound

The title compound undergoes two order-disorder transitions between 15 and 299 K, dictated by ordering of the guest molecules in the host cages, and resulting in three related crystal structures. We anticipate behaviour of this kind to be widespread, and speculate that the concept of "the crystal structure" for individual Dianin's clathrates may be elusive.     

Nature-inspired cascade catalysis: reaction control through substrate concentration--double vs. quadruple domino reactions

The design of biologically inspired, multi-component cascade reactions enables the targeted synthesis of assorted structurally complex products. Similar to regulation in cells the reaction path is controlled by the substrate concentration and complex enantiopure products with high structural diversity are provided.     

Influence of excited state aromaticity in the lowest excited singlet states of fulvene derivatives

The absorption spectra and excited state dipole moments of four differently substituted fulvenes have been investigated both experimentally and computationally. The results reveal that the excited state dipole moment of fulvenes reverses in the first excited singlet state when compared to the ground state. The oppositely polarized electron density distributions, which dominate the ground state and the first excited singlet state of fulvenes, respectively, reflect the reversed π-electron counting rules for aromaticity in the two states (4n + 2 vs. 4n, respectively). The results show that substituents indeed influence the polarity of fulvenes in the two states, however, cooperative interactions between the substituents and the fulvene moiety are most pronounced in the ground state.     

Structure and dynamics of the fast lithium ion conductor "Li7La3Zr2O12"

The solid lithium-ion electrolyte "Li(7)La(3)Zr(2)O(12)" (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, (6)Li and (7)Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E(a) characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10(-4) Scm(-1) to 4 × 10(-4) Scm(-1) depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10(-6) Scm(-1), E(a) = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t(e-) is of the order of 10(-7). Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.