Bernhard Trusch

The formation of polynuclear Al13 under simulated natural conditions

Abstract Polynuclear aluminum species can be formed in nature by the dissolution of Al-containing minerals, as a consequence of soil and surface water acidification, followed by neutralization processes. Under simulated natural conditions in the laboratory, i.e., by allowing acidic Al(III) solutions to flow over granulated marble at flow velocities of 3–4 mm/min, large fractions of monomeric Al(III) were transformed to the Al13O4(OH)24(H2O)127+ polymer (thereafter referred to as Al13 or Al137+), which was measured by 27Al-NMR spectroscopy. Over two-thirds of the monomeric Al(III) was converted to polynuclear Al13 even when gibbsite particles were mixed with the marble granules. The Al13 polymer was also formed in stirred batch experiments containing marble granules and dissolved phthalate or salicylate. The results suggest that Al13formation is easily possible in nature if the total Al(III) concentration is high enough. In these experiments, Al13 was detected when the total dissolved Al(III) was 1.9 × 10−4 mol/L. The minimum total Al(III) concentration required to produce Al13, which can be predicted from available thermodynamic data, is on the order of 10−5mol/L.

Semi-preparative gas chromatographic separation of all-trans-perhydrotriphenylene enantiomers on a chiral cyclodextrin stationary phase

Enantiomers of all-trans-perhydrotriphenylene (PHTP) were separated by gas chromatography using heptakis(6-O-tert.-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin (TBDMS-beta-CD) as the chiral selector. Conditions for semi-preparative separations were established using a 2 m x 2 mm I.D. packed column and subsequently extended to a 1.8 m x 4 mm I.D. column which enabled separations on a mg scale. The column packing was TBDMS-beta-CD dissolved in SE-54 coated on Chromosorb P AW-DMCS 80-100 mesh. Optimization of the chromatographic conditions (oven temperature, carrier gas flow, and column load) with respect to better efficiency and peak retention resulted in a system capable of separating up to 10 mg of the racemate per day. Purities of separated enantiomers were determined by capillary gas chromatography. Yields and purities of the fractions obtained by single- and double-step separations are compared. Highly enriched enantiomers with purities of up to 99.6% (99.2% ee) were obtained by a single separation step.

Equipment for controlling nucleation and tailoring the size of solution-grown single crystals

An improved version of the known temperature difference (ΔT) technique of crystallization from solution is presented. A Peltier device was used to control the local temperature of nucleation, dissolution and growth in order to reduce typically occurring delay times in the nucleation process within a given sample tube and to tailor the size of the single crystals to be obtained.

High temperature phase segregation of a new host for Er3+ upconversion: Cs3Tl2Cl9

Cs3Tl2Cl9 is one of the few air stable low-phonon host lattices of interest to Er3+ upconversion. Solution growth at ambient temperature demonstrated that water and a number of other molecular liquids do not yield Er3+doped crystals. Optical and differential scanning calorimetry measurements revealed a phase segregation at 310 °C which is reversible in the presence of 1 atm Cl2 . Growth from molten salt solutions or gas phase deposition techniques is hence restricted to a deposition temperature of less than 300 °C. Preliminary results show that molten ZnCl2 may be used as a flux to obtain lanthanidedoped single crystals or epitaxial layers.