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The dynamic isotope effects (IE) on the translational and rotational motion in liquid ammonia and water are reassessed by NMR measurements. For H2O/D2O the translational and rotational IE are clearly distinct. At 298 K, 23% and 30% are obtained, respectively. Both effects as well as the slopes of the temperature dependencies increase with decreasing temperature. For NH3/ND3 a rotational IE of 37% was observed at 298 K. A small increase to 40% at 222 K could be ascertained. The translational IE is about 15% at room temperature and exhibits a stronger temperature dependence. It is suggested that the observed deviations of the IE’s from the square root of mass and square root of moments of inertia laws are caused by translation-rotation coupling as well as quantum effects. The experimental data obtained in the present paper are also of importance for the correct interpretation of all kinds of experiments on water and ammonia, where isotopic substitutions are involved.

Small angle neutron scattering of direct micelles in binary and ternary surfactantÈalcoholÈ surfactantÈD 2 O systems has been measured. The nonionic surfactant was poly(oxyethylene-23) lauryl ether D 2 O (C 12 E 23, commercial name : Brij 35) which was used at concentrations far beyond its critical micellar concentration : between 0.1 and 15 mass% (about 1.0 ] 10~3È1.5 ] 10~1 mol l~1). The alcohols were butan-1-ol, pentan-1-ol, hexan-1-ol, and heptan-1-ol at concentrations of about 0.25 mol l~1. The spectra could quantitatively be modelled by the PercusÈYevick integral equation method in combination with a core/shell model yielding detailed information about the size, the (ellipsoidal) shape, the aggregation number, the internal structure and the distribution of the micelles. The ternary systems were modelled with an additional parameter, the partition of the alcohol between the outer aqueous bulk and the inner micellar pseudo-phase. In the case of the pentanol system the partition coefficient inferred from NMR self-di †usion measurements was used to describe the scattering result.

The application of adiabatic polarization-transfer experiments to resonance assignment in solid, uniformly 13C-15N-labelled polypeptides is demonstrated for the cyclic decapeptide antamanide. A homonuclear correlation experiment employing the DREAM sequence for adiabatic dipolar transfer yields a complete assignment of the C(alpha) and aliphatic side-chain 13C resonances to amino acid types. The same information can be obtained from a TOBSY experiment using the recently introduced P9(12)1 TOBSY sequence, which employs the J couplings as a transfer mechanism. A comparison of the two methods is presented. Except for some aromatic phenylalanine resonances, a complete sequence-specific assignment of the 13C and 15N resonances in antamanide is achieved by a series of selective or broadband adiabatic triple-resonance experiments. Heteronuclear transfer by adiabatic-passage Hartmann-Hahn cross polarization is combined with adiabatic homonuclear transfer by the DREAM and rotational-resonance tickling sequences into two- and three-dimensional experiments. The performance of these experiments is evaluated quantitatively.

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Articles you may be interested inCollective rotational dynamics in ionic liquids: A computational and experimental study of 1-butyl-3-methylimidazolium tetrafluoroborate J. Chem. Phys. 126, 084511 (2007) Model calculations to investigate the deuteron quadrupolar relaxation in liquid water are performed.Techniques not amenable to experiment, such as switching on and off the intermolecular or intramolecular electric field gradients and simulating rigid liquid water, give insight into the microscopic effects leading to relaxation. In experimental studies it is usually assumed that the deuteron quadrupolar relaxation is governed largely by the reorientational motion of an average electric field gradient, and the error in this assumption is readily extracted from the model calculations. As expected, this error is significant for deuterons in hydrogen bonds. These model calculations should provide a guide to better understanding of quadrupolar relaxation and experimental evaluation of relaxation.

manyMultiple emulsions of W 1 /O/W 2 type are of major interest in life sciences, offering possibilities for the encapsulation of water-soluble active agents. In food science, they are also applied for fat reduction. The droplet size distributions of the inner and outer emulsions are of main importance as they influence the rheological and sensorial properties, the release kinetics, as well as the structural and microbial stability. However, the determination of the inner and outer droplet size distributions is a major challenge, as conventional measurement techniques cannot be applied. Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) is well known as a non-destructive tool for droplet size determination, especially in simple emulsions. In this work, double emulsions of the W 1 /O/W 2 type were prepared with polyglycerol-polyricinoleate (PGPR) and polyoxyethylen-20-sorbitan monolaurate (Tween 20) as emulsifiers by means of rotor-stator emulsification machines. PFG-NMR was applied for measurements of the inner phase (W 1 ) droplet size distribution as well as for the characterization of the O phase. The W 1 values were compared with results from laser light diffraction of simple emulsions (W 1 /O type) and were found to be consistent within the experimental errors, if restricted diffusion in the outer water phase (W 2 ) and additional effects are considered.