The effects of pulse stimulation on biota - Research in relation to ICES advice - Effects on dogfish

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13C and 23Na Solid-state NMR study on zeolite Y loaded with Mo(CO)6

The Na-23 MAS and double rotation (DOR) NMR spectra of dehydrated zeolite NaY loaded with two molecules of Mo(CO)(6) per supercage show three components distinguished by the corresponding quadrupole coupling constants (QCC). Sodium cations in the hexagonal prisms (SI sites) are characterized by a narrow Gaussian line with a QCC value close to zero. A second component with quadrupole coupling constants between 4.4 and 4.8 MHz is assigned to Na+ cations located in the sodalite cages, and the third component with QCC ranging between 2.2 and 2.8 MHz is due to sodium cations in the supercages interacting with Mo(CO)(6). These sites are characterized by structural and/or dynamical disorder as observed by typical line shape properties. Adsorption of Mo(CO)(6) in Y zeolites, where all Na+ cations in the supercages of NaY have been exchanged with NH4+ Or H+, causes the sodium cations in the sodalite cages to migrate into the supercages in order to interact with the adsorbent. For the NH4+-exchanged sample, the anisotropic chemical shift parameters for C-13 in Mo(CO)(6) have been analyzed at ambient temperature. From the results a fast anisotropic local reorientation of Mo(CO)(6) follows. The rotation is about a 3-fold axis of the octahedral complex. The octahedron is slightly elongated along the rotation axis by about 4 degrees when it is located close to the sodium cation

An 27Al NMR study of the interaction of water with AlPO4-11

Exptl. and spectral simulations of 27Al MAS and double rotation NMR spectra measured at 7.0 T proved the preferential hydration of 1 tetrahedral Al site in AlPO-11, transforming this site reversibly into octahedral Al. [on SciFinder (R)

29Si N.M.R longitudinal relaxation times in ZSM-5 zeolites

The presence of Pr4N+ templates causes an increase of Tl for 29Si nuclei in ZSM-5 zeolites of more than one order of magnitude, and relatively small changes in zeolite structure are important; due care is required in extracting quantitative data from 29Si magic angle spinning n.m.r. spectra of zeolites

Conformational equilibria of (E)-6-bromo-7-hydroxy-3,7-dimethyl-2-octene

The 1H NMR spectral parameters of the title compound have been determined in cyclohexane-d12 and p-dioxane-d8 solutions by means of high-frequency NMR. The results are interpreted in terms of conformational equilibria. Linear Electric Field (LEF) effects may play a major role in explaining the differences between the 13C NMR chemical shifts of the title compound and those of the model (E)2,6-dimethyl-2,6-octadiene. Some preliminary calculations of the LEF-induced shifts are presented, as well as the problems involved in the recognition of the LEF contributions to the experimental shift differences

29Si NMR Model Dissolution Study of the Degradation of Reversed Phases for High-Performance Liquid Chromatography

To simulate aging under chromatog. conditions, mono-, di-, and trifunctional octyl and octadecyl derivatized reversed-phase high-performance liq. chromatog. silicas were exposed to very aggressive mobile phases like the medium of 6 M NaOH in MeOH/H2O (50/50 vol./vol.). 29Si NMR was used to study the dissoln. characteristics of these phases by monitoring the concns. of the dissolving silane and silica structures. Dissoln. products of alkylchlorosilanes were used as model compds. for assignment purposes. Octadecyl phases appeared to degrade by dissoln. of the silica substrate; octadecylsilane structures were insol. under the exptl. conditions. Monofunctional octyl phases were shown to deteriorate through initial dissoln. of monomeric ligand silane particles, wheres for difunctional octyl phases, the silica backbone appeared to dissolve with the silane ligands still attached. The latter mechanism was also obsd. for the trifunctional octyl phases, but these phases resemble octadecyl phases, probably because the free ligand silane particles are almost insol. and the major cause of phase degrdn. is dissoln. of the silica substrat