配位化学的先驱S.M. Jφrgensen

配位化学的先驱Ｓ．Ｍ．Ｊｒｇｅｎｓｅｎ大学化学化学史张清建（四川师范学院化学系南充６３７００２）今天的化学工作者，大都熟悉配位化学的奠基人ＡｌｆｒｅｄＷｅｒｎｅｒ的名字。然而，很少有人认识到，Ｗｅｒｎｅｒ崭新的具有革命意义的理论，是建立在Ｊｒｇｅ...     

Carbohydrates from Lamiaceae. VIII. α-Glucan from <Emphasis Type="Italic">Scutellaria baicalensis</Emphasis> roots

The homogeneous polysaccharide S _b RP-1″ with MW 110 kDa was isolated during an investigation of water-soluble polysaccharides from Scutellaria baicalensis roots. Its aqueous solution gave a positive reaction with iodine and exhibited high specific rotation ([α]_D +188.0°). Chemical, chromatographic, and spectral methods established that S _b RP-1″ was a slightly branched glucan containing in the main chain α-(1 → 4)-glucopyranose units, 8.3% of which were branched at the C-6 atom with single α-glucopyranose units. Glucan S _b RP-1″ was shown to exhibit immunostimulating activity using an azathioprine model of immunosuppression.     

Hydration of Cl<Superscript>–</Superscript> ion in a planar nanopore with hydrophilic walls. 1. Molecular structure

Computer simulation has been employed to obtain equilibrium molecular configurations, as well as spatial and angular distributions of water molecules, under the action of the field of a single-charged chlorine anion in a model planar nanopore with structureless walls at room temperature. A detailed many-body model of intermolecular interactions calibrated in accordance with experimental data relative to the free energy of hydration in water vapor has been used. The effect of the hydrophilicity of the walls on the ion hydration shell consists in its disintegration into two parts, i.e., molecules retained exclusively due to the interactions with the ion and those adsorbed on the walls. In the regime of strong interactions with the walls, two relatively stable states arise with asymmetric distribution of molecules between opposite walls. The existence of the two metastable states destabilizes the position of ions inside a pore and is expected to accelerate their adsorption on the walls.     

Hydration of Cl<Superscript>–</Superscript> ion in a planar nanopore with hydrophilic walls. 2. Thermodynamic stability

The Monte Carlo bicanonical statistical ensemble method has been employed to calculate the dependences of the Gibbs free energy, formation work, and entropy on the size of a hydration shell grown from water vapor on single-charged chlorine anion in a model planar nanopore with hydrophilic structureless walls at 298 K. A refined model comprising many-particle polarization interactions and calibrated with respect to experimental data on the free energy and enthalpy of the initial reactions of attachment of water molecules to the ion has been used. It has been found that a weak hydrophilicity of pore walls leads to destabilization of the hydration shell, while a strong one, on the contrary, causes its stabilization. The physical reason for the instability in the field of hydrophilic walls qualitatively differs from that under the conditions of hydration in bulk water vapor.     

<Emphasis Type="Italic">In vitro</Emphasis> bioactivity of 70 wt.% SiO<Subscript>2</Subscript> — 30 wt.% CaO sol-gel glass,doped with 1, 3 and 5 wt.% NbF<Subscript>5</Subscript>

The 70SiO₂-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF₅ (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO₃HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time.     

Spin‐Übergänge in supramolekularen Strukturen. Für Speicherbausteine von morgen?

We reported about octahedrally coordinated Fe2+‐complexes, which are able to switch between two stable spin states (LS and HS) with different magnetic properties. This phenomenon is called spin crossover (SCO). The interaction between metal ion and ligand determines the actual spin state and whether an extern stimulus can trigger a spin crossover. Due to this fact it is possible for the chemist through the choice of the ligands to manipulate the character and the temperature region of the SCO. Some metal complexes assemble into highly ordered structures on graphite by molecular self assembly. The substitution of the metal complexes with alkyl chains and the interaction of these chains with the highly ordered graphite is crucial for a periodic arrangement of the complexes on the surface. For the future we are curious to see whether through the cooperative effort of coordination chemistry (SCO phenomenon) and surface science (self assembly of SCO complexes on a surface) the vision of a molecular memory will turn into a reality.