Porous Salts Containing Cationic Al24-Hydroxide-Acetate Clusters from Scalable,Green and Aqueous Synthesis Routes

The solution chemistry of aluminum is highly complex and various polyoxocations are known. Here we report on the facile synthesis of a cationic Al₂₄ cluster that forms porous salts of composition [Al₂₄(OH)₅₆(CH₃COO)₁₂]X₄, denoted CAU-55-X, with X=Cl⁻, Br⁻, I⁻, HSO₄⁻. Three-dimensional electron diffraction was employed to determine the crystal structures. Various robust and mild synthesis routes for the chloride salt [Al₂₄(OH)₅₆(CH₃COO)₁₂]Cl₄ in water were established resulting in high yields (>95 %, 215 g per batch) within minutes. Specific surface areas and H₂O capacities with maximum values of up to 930 m² g⁻¹ and 430 mg g⁻¹ are observed. The particle size of CAU-55-X can be tuned between 140 nm and 1250 nm, permitting its synthesis as stable dispersions or as highly crystalline powders. The positive surface charge of the particles, allow fast and effective adsorption of anionic dye molecules and adsorption of poly- and perfluoroalkyl substances (PFAS).     

Corannulene-based fullerene fragments C20H10-C50H10: when does a buckybowl become a buckytube?

An ab initio study of the structural and physical properties of fullerene fragments based on corannulene shows a distinct defining point between bowl and tube-like character. Received: 14 February 1997 / Accepted: 6 May 1997     

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Enhanced Coulomb and exchange interaction crystal fields in the modified Zener model of magnons in metallic ferromagnets

The Bartel treatment of magnons in metallic ferromagnets within the modified Zener model of itinerant-localized (s-electron or hole) exchange is generalized to include ten-fold d-electron (hole) spin-orbital degeneracy. As such one can ab initio include enhanced intra-cell Coulomb repulsive crystal fields and exchange attractive crystal fields. This treatment includes itinerant-itinerant (d-electron or hole) Coulomb and exchange interactions as well as itinerant-localized (d-electron or hole) interactions; Hund's rule coupling is included automatically. Also, ab initio the ferromagnet specificity is included via the d-bandfilling and d-bandwidth inherent in the degenerate theory; the possibility of finite temperatures is also included. Acoustic and optic ferromagnon branches are recalculated and corrected and the position of the Stoner particle-hole continuum boundary is recalculated at zero and finite temperatures.     

Modifying the BFGS update by a new column scaling technique

LetB be a positive definite symmetric approximation to the second derivative matrix of the objective function of a minimization calculation. We study modifications of the BFGS method that apply a scaling technique to the columns of a conjugate direction matrixZ satisfyingZ ^T BZ = I. For a simple scaling technique similar to the ones considered by Powell (1987) and (1989) we show that, due to a two iteration cycle, linear convergence can occur when the method is applied to a quadratic function and Wolfe's line search is employed, although for exact line searches quadratic termination can be proved. We then suggest a different scaling technique that prevents certain columns thought to contain important curvature information from being scaled. For this algorithm we prove global and superlinear convergence and demonstrate the superiority of our method over the BFGS formula on a range of illconditioned optimization problems. Moreover, we present an implementation of our algorithm that requires only 3n ² +O(n) multiplications per iteration.     

Observations of the use of o-phthalaldehyde condensation for the measurement of histamine

The in vitro study of mast cell degranulation utilises the measurement of histamine as a quantitative marker of this process. Histamine is most commonly assayed, following organic extraction, by condensing it with o-phthalaldehyde (OPT) and thereby obtaining a highly fluorescent adduct. A number of variables that might affect the performance of this assay, including assay conditions, stability and purity, were evaluated during the course of developing this assay for use in our laboratory. We observed the stability of OPT-histamine and found it to be very stable at 0 and 25 degrees C, following acidification. Derivatisation conditions and the purity of the leukocyte histamine extract were also assessed, and indicated that derivatisation at low temperatures slows down decay, providing a greater over-all fluorescence intensity. Extraction procedures are necessary, prior to condensation with OPT, to eliminate both positive and negative interfering substances from leukocyte preparations.