On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve

In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use of the retention curve to indirectly determine hydraulic conductivities is analyzed as follows. The theoretical derivation of the relationK(h) – (h) is briefly discussed with regards to potential sources of inaccuracy. The sensitivity of the algorithm forK(h) calculation is studied as a response to possible inaccuracies in the retention curve determination. Conclusions about the usability of calculated hydraulic conductivities are drawn.     

Cluster isobars for high-precision mass spectrometry

Doublet mass measurements of the isobars²⁸Si₃ and¹²C₇ are performed by use of a Penning trap mass spectrometer and the Fourier transform ion cyclotron resonance (FT-ICR). The carbon and silicon cluster ions are produced by laser ablation. Results of these preliminary measurements are presented.     

Synthesis and Diels-Alder Reactivity of 5,6,7,8-Tetramethylidene-2-bicyclo[2.2.2]octanol and -octanone. Selective Oxidations of the Corresponding Bis(irontricarbonyl) Complexes

Hydroboration of the syn, anti-[Fe(CO)₃]₂ double complex 24 of the readily available 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octene ( 22 ) gave the corresponding doubly complexed 2-bicyclo[2.2.2]octanol 25. CrO₃-oxidation furnished ketone 27 . The syn-Fe(CO)₃-groups in 25 and 27 were oxidized selectively with trimethyl-amine oxide and yielded the corresponding anti-Fe(CO₃)-monocomplexed tetraenes 26 and 28. The anti-Fe(CO)₃-group in 28 could be removed, and 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone ( 11 ) was obtained. NaBH₄-reduction of 11 afforded tetraenol 10. TCE-cycloadditions to 10 and 11 (k₁) were at least 10 times as fast as those (k₂) to the corresponding monoadducts 35/36 and 34 , respectively. This Diels-Alder reactivity difference vanishes (k₁ ≈ k₂) with methyl propynoate. The latter dienophile added to the anti-Fe(CO)₃-monocomplexed tetraenone 28 with ‘para’-regioselectivity.     

Site-directed molecular assembly on templates structured with electron-beam lithography

We describe a simple method for patterning biomolecular films on surfaces with high resolution. A conventional polymeric resist is structured by electron-beam lithography. The exposed and developed patterns are then used for the directed self-assembly (SA) of a first molecule from solution. Removal of the remaining resist allows the SA of a second species. We illustrate the potential of the approach by assembling on gold (Au) substrates two alkanethiols of contrasting terminal functionality. The patterns have dimensions from the micrometer range down to 40 nm and an edge resolution of 3.5 nm.     

Functionalized organosilica microspheres via a novel emulsion-based route

Thiol-functionalized organosilica microspheres were synthesized via a two-step process: (1) acid-catalyzed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPTMS), followed by (2) base-catalyzed condensation, which led to the rapid formation of emulsion droplets with a narrow size distribution. These droplets continued to condense to form solid microspheres. Solution (29)Si NMR and optical microscopy were applied to study the mechanism of this novel synthetic route. Solid-state (29)Si NMR, SEM, zeta potential titration, and Coulter counter measurements were used to study the bulk and surface properties and to determine the particle size distributions of the final microspheres. Compared to conventional St?ber silica particles, these microspheres were shown to have a lower degree of cross-linking (average degree of condensation, r = 1.25), a larger average size (up to 6 microm), and a higher isoelectric point (pH = 4.4). Confocal microscopy of dye-labeled microspheres showed an even distribution of dye molecules throughout the interior, characteristic of a readily accessible and permeable organosilica network. These findings have implications for the production of functionalized solid supports for use in catalysis and biological applications, such as optically encoded carriers for combinatorial synthesis.