Experiment and theory of low-pressure nitrogen adsorption in organic layers supported or grafted on inorganic adsorbents: toward a tool to characterize surfaces of hybrid organic/inorganic systems

We report experimental nitrogen adsorption isotherms of organics-coated silicas, which exhibit a low-pressure desorption branch that does not meet the adsorption branch upon emptying of the pores. To address the physical origin of such a hysteresis loop, we propose an equilibrium thermodynamic model that enables one to explain this phenomenon. The present model assumes that, upon adsorption, a small amount of nitrogen molecules penetrate within the organic layer and reach adsorption sites that are located on the inorganic surface, between the grafted or adsorbed organic molecules. The number of accessible adsorption sites thus varies with the increasing gas pressure, and then we assume that it stays constant upon desorption. Comparison with experimental data shows that our model captures the features of nitrogen adsorption on such hybrid organic/inorganic materials. In particular, in addition to predicting the shape of the adsorption isotherm, the model is able to estimate, with a reasonable number of adjustable parameters, the height of the low-pressure hysteresis loop and to assess in a qualitative fashion the local density of the organic chains at the surface of the material.     

Ternäre Lithium-Selten-Erd-Nitrate mit einsamen Nitrationen: Li3[M(NO3)5](NO3) (M = Gd?Lu,Y). Die Kristallstruktur von Li3Er(NO3)6

Ternary Lithium Rare Earth Nitrates with Lonesome Nitrate Ions: Li₃[M(NO₃)₅](NO₃) (M = Gd? Lu, Y). The Crystal Structure of Li₃Er(NO₃)₆ Single crystals of the ternary nitrate Li₃Er(NO₃)₆ are obtained from a solution of “Er(NO₃)₃” in the melt of LiNO₃. In Li₃Er(NO₃)₆ (monoclinic, P2₁/n, Z = 4; a = 776.0(1); b = 748.86(8); c = 2 396(1) pm; β = 90.76(3)°; R1 = 0.0490; wR2 = 0.0792), Er³⁺ is surrounded by five bidentate nitrate ligands yielding the anionic units [Er(NO₃)₅]^2?. These are arranged in the direction of the 2₁ screw axis. Two lonesome NO₃^? ions are in the middle of such a “helix” and are connected by Li⁺ with the anions [Er(NO₃)₅]^2?. The helices are moved against each other by about half of the lattice constant a and are connected by further Li⁺ ions.     

[Ga6R8]2– (R = SiPh2Me): Eine metalloide Clusterverbindung mit einem unerwarteten Ga6‐Gerüst

[Ga₆R₈]^2– (R = SiPh₂Me): A Metalloid Cluster Compound with an Unexpected Ga₆‐Frame The reaction of a metastable solution of GaBr with a solution of LiSiPh₂Me in a toluene/THF mixture results in orange coloured crystals of [Ga₆(SiPh₂Me)₈]^2– · 2 [Li(THF)₄]⁺ ( 1 ). The unexpected structure of the planar Ga₆ frame (C_2h) could also be realized with the help of DFT calculation. DFT calculations furthermore show that 1 is energetically favoured against an octahedral Ga₆R₆^2– species and R₂. In contrast calculations for the similar Al and B species show that in these cases the octahedral entities are favoured. These results demonstrate that even for similar compounds of B, Al, and Ga Wade rules are too general and that they cannot predict the correct structure. Moreover the atomic arrangement within 1 shows that a structure is preferred which is also present in allotropic β‐Ga and that therefore clusters of this type should be called metalloid or more general elementoid.     

The hydration of the uranyl dication: Incorporation of solvent effects in parallel density functional calculations with the program PARAGAUSS

The parallel density functional program PARA GAUSS has been extended by a tool for computing solvent effects based on the conductor‐like screening model (COSMO). The molecular cavity in the solvent is constructed as a set of overlapping spheres according to the GEPOL algorithm. The cavity tessellation scheme and the resulting set of point charges on the cavity surface comply with the point group symmetry of the solute. Symmetry is exploited to reduce the computational effort of the solvent model. To allow an automatic geometry optimization including solvent effects, care has been taken to avoid discontinuities due to the discretization (weights of tesserae, number of spheres created by GEPOL). In this context, an alternative definition for the grid points representing the tesserae is introduced. In addition to the COSMO model, short‐range solvent effects are taken into account via a force field. We apply the solvent module to all‐electron scalar‐relativistic density functional calculations on uranyl, UO₂²⁺, and its aquo complexes in aqueous solution. Solvent effects on the geometry are very small. Based on the model [UO₂(H₂O)₅]²⁺, the solvation energy of uranyl is estimated to be about ?400 kcal/mol, in agreement with the range of experimental data. The major part of the solvation energy, about ?250 kcal/mol, is due to a donor–acceptor interaction associated with a coordination shell of five water ligands. One can interpret this large solvation energy also as a compounded effect of an effective reduction of the uranyl moiety plus a solvent polarization. The energetic effect of the structure relaxation in the solution is only about 8 kcal/mol. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Two-dimensional self-assembly of linear molecular rods at the liquid/solid interface

We report on the synthesis and scanning tunneling microscopy (STM) studies of a series of linear molecular rods (1-5) comprising different numbers and/or spatial arrangements of perfluorinated benzene and benzene subunits interlinked with diacetylenes in the para position and decorated with or without terminal dodecyl chains. The molecules organize themselves into well-ordered 2D crystal structures at the liquid/solid interface through intermolecular and molecule-substrate interactions. Whereas the molecules substituted by dodecyl chains form the lamellar structures with alternating rigid core rows and alkyl chain rows, the unsubstituted ones change the orientation of the rigid backbones with respect to the lamellar axis. The molecular arrangement is not influenced by fluoro substituents on any phenyl ring of the backbone, which suggests that the interactions between the π-conjugated backbones are dominated by close packing rather than by the dipole moments of the rods or fluorine-based intermolecular interactions.     

The Ene-Reaction of Phosphaalkynes-Application for the Synthesis of Phosphiranes

Abstract

1,3-Butadienes 1 and 6-Methyl-2H-pyran-2-ones 6 react with two equivalents of phosphaalkynes 2 in a domino-reaction to the diphosphiranes 5 and 9 respectively. Diels-Alder-reaction of 1 with 2 leads to 3 which cannot be isolated. An Ene-reaction of the phosphacyclohexa-1,4-diene 3 with additional 2 gives 4 followed by an intramolecular Diels-Alder-reaction yielding the stable diphosphatricyclooctenes 5.     

Separation of rat pancreatic secretory proteins by cation-exchange fast protein liquid chromatography.

Rat pancreatic secretory proteins were separated by an automated liquid chromatography system utilizing a Mono S cation-exchange column. Optimal resolution was obtained with a multistep salt and pH gradient (0.01-2 M LiCl, pH 5.3-63). A total of fourteen well-separated peaks, as well as several minor peaks, were detected by UV absorption. The main pancreatic enzymes were resolved (two amylases, two chymotrypsinogens, two trypsinogens, proelastase, lipase, prophospholipase A2, procarboxypeptidase A, procarboxypeptidase B, and ribonuclease). In addition, proteins without enzymic activity, such as lithostathine and pancreatitis-associated protein, were identified. Activation of proenzymes did not occur during the separation. At a flow-rate of 0.5 ml/min, ca. 250 micrograms to 5 mg of protein could be applied with equal resolution. The reproducibility of retention volumes and peak areas was high (less than 1% or 5% variation, respectively). When radiolabeled proteins were separated, a comparable pattern of peaks was obtained. The technique described is, therefore, not only useful for analytical and preparative separation of pancreatic proteins but can additionally serve for quantitative determination of the pancreatic isoenzyme pattern.     

Simultaneous determination of ondansetron and tropisetron in human plasma using HPLC with UV detection

A rapid and sensitive HPLC method for the simultaneous quantitation of ondansetron and tropisetron, two serotonin (5-HT) receptor antagonists frequently used in treatment and prevention of nausea and emesis, is described. The procedure involves liquid-liquid extraction of human plasma with dichloromethane coupled with reversed-phase HPLC and UV detection. The lower limits of quantification (LOQ) were 0.62 ng/mL for ondansetron and 1.25 ng/mL or tropisetron. Intra- and inter-assay coefficients of variation ranged from 1.5 to 7.5% and 5.3 to 13.7%, respectively. The sensitivity and precision were sufficient for determination of plasma concentrations after therapeutic administration of both drugs and the method can be used for the estimation of pharmacokinetic parameters.