M. S. Nieuwenhuizen

Analysis of multinuclear lanthanide-induced shifts. 1. Investigations of some approximations in the procedure for separation of diamagnetic, contact, and pseudocontact shifts

For the 1:1 adducts of La(fod)3, Pr(fod)3, Eu(fod)3, Gd(fod)3, Dy(fod)3, and Yb(fod)3 and adamantanone the 17O, 133C, and 1H bound shifts were determined. With the data set obtained it is demonstrated that a separation of diamagnetic, contact, and pseudocontact shifts gives reliable values for all shift contributions only when a modified procedure is used in the separation. Our data show that diamagnetic and contact shifts are very large for the carbonyl 17O and 13C nuclei. Diamagnetic and contact shifts are also substantial for the remaining 13C nuclei and for 1Hα in the Eu(fod)3 adduct. For all other nuclei the pseudocontact shift is dominant, and a direct comparison of experimental bound shifts with calculated pseudocontact shifts is possible.

Polycarboxylic acids containing acetal functions: calcium sequestering compounds based on oxidized carbohydrates

A number of polycarboxylic acids containing acetal functions have been prepared by a two-step oxidation of carbohydrates. Their calcium sequestering behavior is compared with that of a series of model polycarboxylic acids. It is found that calcium sequestration by oxidized carbohydrates is less than that by corresponding ether polycarboxylates, since (a) acetal oxygens have a lower coordinating power than ether oxygens, and (b) there is extra steric repulsion upon calcium complexation by both the additional CH2 OH groups and the unfavorable natural configuration of the oxidized carbohydrates investigated. Some of the oxidized carbohydrates show greater calcium sequestering capacities than corresponds to the stability constant. This is probably caused by crystal growth inhibition or precipitation-inhibition phenomena. Two model compounds illustrate that the acetal moiety is sufficiently stable under washing conditions, whilst it hydrolyses under acidic waste water conditions into small (hydr)oxycarboxylates.

Oriented coatings of silicalite-1 for gas sensor applications

Summary Silicalite-1 is grown in an oriented way, on a silicon wafer to study the nucleation and growth mechanisms and also on a quartz substrate to form a well-defined SAW-sensor chemical interface for CO 2 detection. The growth mechanism of the crystals seems to involve a silica-gel layer on the silicon surface which is consumed during crystal growth. Afterwards attachment of the crystals to the surface takes place. The SAW-sensor device employing silicalite-1 as a chemical interface responds well to CO 2 while the sensitivity to water seems not to be severe.

Analysis of multinuclear lanthanide-induced shifts. Part 2. The geometry of ketone binding to lanthanides

Multinuclear lanthanide-induced shifts for a variety of Ln(fod)3 shift reagents have been combined with Gd(fod)3-induced longitudinal relaxation-rate enhancements in geometry calculations for lanthanide adducts of adamantanone. The experimental results are most consistent with an Ln–O–C angle of about 180° and an Ln–O distance of approximately 2.5 A. The fit between calculated and experimental data is very soft, and simulated data indicate that this is characteristic of the linear Ln–O–C array. When induced shifts and relaxation rate enhancements are simulated for nonlinear co-ordination geometries, the results are inconsistent with the experimental data.

Analysis of multinuclear lanthanide induced shifts. Part 5. The co-ordination polyhedron of 1 : 3 lanthanide(III)–glycolate complexes in aqueous solution

Experimental 17O, 13C, and 1H bound shifts have been determined for the complexes of lanthanide(III) cations with glycolate (L) in D2O at pD 4.5. These shifts were separated into diamagnetic, contact, and pseudocontact contributions. The contact shifts show that the stoicheiometry of these complexes is LnL3(D2O)3. Glycolate is co-ordinated in a bidentate fashion via one of the carboxylate oxygens and the hydroxylic oxygen. From the pseudocontact shifts it is concluded that lanthanide(III) cations are surrounded by nine oxygens constituting a distorted tricapped trigonal prism, in which the three capping positions are occupied by carboxylate oxygens.