Coupling selectivity with sensitivity in an integrated chemosensor framework: design of a Hg(2+)-responsive probe, operating above 500 nm.

For the highly selective and sensitive sensing of Hg2+ in water, a new design concept was realized where the selectivity of the probe's binding site is amplified by electronic properties of the chromophore. The molecular architecture of this phenoxazinone-type sensor molecule combines two potential coordination sites via an amino-keto conjugative backbone. These structural prerequisites allow only the most preferred mercuric ion to bind to the dithia dioxa monoaza crown unit, while other heavy, transition, and main group metal ions as well as protons are trapped at the keto group, inducing opposite spectral effects due to interaction with either the donor (Hg2+) or the acceptor group (other cations) of the probe.

ORSAT and modifications of SEFT and APT.

Up to now, three subspectra are usually needed for the complete assignment of all signals in 13C spectrum: two DEPT spectra (phi = 90 degrees and phi = 135 degrees) and a proton decoupled spectrum. In this paper, we present a method in which a complete assignment becomes possible with merely two spectra. For this purpose, a new pulse sequence (ORSAT) has been elaborated by using off-resonance irradiation.

On reasons of 29Si NMR chemical shift/structure relations for silicon oxides, nitrides, and carbides: an individual-gauge-for-localized-orbitals study.

For alpha-quartz, monoclinic ZSM-5, alpha- and beta-Si3N4 and SiC-6H polytype, the silicon chemical shifts have been calculated using the IGLO (individual gauge for localized orbitals) method and models of different size in real crystal geometry. The result is a theoretical chemical shift scale, which is very similar to the corresponding experimental scale from 29Si MAS NMR experiments. It is shown that the assignment of isotropic silicon chemical shifts of crystallized solids based on theory is a method of practical applicability, also in cases where experimental methods or empirical relations fail.

On the pictorial representation of the magnetic screening tensor: ellipsoid or ovaloid?

The pictorial representation of the magnetic screening tensor as ellipsoid (half axes root 1/sigma ii) is inconvenient. Much more obvious is an ovaloid with half axes sigma ii. The shape of this ovaloid is described in the dependence on the diagonal elements sigma 11, sigma 22 and sigma 33 of the principal axes of the screening tensor.