Spin-pattern recognition in high-resolution proton NMR spectroscopy

Techniques are introduced for the recognition of specific spin patterns in complex overlapping proton NMR spectra. They are based on the efficient and selective excitation of high-order multiple quantum coherence in systems of specified coupling network topology, and allow the suppression of undesired spin patterns.     

Fluorescence lifetime imaging of molecular rotors to map microviscosity in cells

Fluorescence liftime imaging （FLIM） of modified hydrophobic bodipy dyes that act as fluorescent molecular rotors shows that the fluorescence lifetime of these probes is a function of the microviscosity of their environment. Incubating cells with these dyes, we find a punctate and continuous distribution of the dye in cells. The viscosity value obtained in what appears to be endocytotic vesicles in living cells is around 100 times higher than that of water and of cellular cytoplasm.Time-resolved fluorescence anisotropy measurements also yield rotational correlation times consistent with large microviscosity values. In this way, we successfully develop a practical and versatile approach to map the microviscosity in cells based on imaging fluorescent molecular rotors.     

Anomalous Rotational Resonance Spectra in Magic-Angle Spinning NMR

Magic-angle spinning NMR spectra of samples containing dilute spin-1/2 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13C2-labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13C nuclei and the neighboring 1H nuclei. These couplings strongly influence the rotational resonance 13C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.     

High-order spin diffusion mechanisms in (19)F 2-D NMR of oxyfluorides.

Negative cross-peaks have been observed in the (19)F 2-D magnetization-exchange MAS NMR spectra of Ba(2)MoO(3)F(4) under fast-spinning conditions. The polarization transfer dynamics are studied as a function of the spinning frequency and the frequency separation of the resonances. The results are consistent with a novel mechanism, in which four spins simultaneously exchange Zeeman magnetization with each other, in an energy-conserving process.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

An Interaction Value Perspective on Firms of Differing Size

We present a general model of a network of interacting individuals, each of whom derives a known, real-valued benefit from each possible dyadic interaction. The model views interactions as knowledge-transfer exchanges that add value to the organization. We use this model to derive interaction patterns within an organization. We assume that the value of dyadic interaction benefits is distributed as a randomly permuted geometric series. Moreover, interactions only add value when a large enough waiting period is observed between interaction attempts. We show that an organization optimized for knowledge transfer has a distribution of interaction frequencies which correlates well with observations. Organizations of differing sizes can have similar optimal structures as long they have similar normalized levels of interdependence between interactions, and distribution of interaction benefit values. This research has implications for the design of communication infrastructure in a growing organization, as well as for the predictive value of modeling organizations at different scales.     

Conformation of the glycosidic linkage in a disaccharide investigated by double-quantum solid-state NMR.

Double-quantum heteronuclear local field NMR is performed on a sample of a 13C2-labeled disaccharide, in which the two 13C spins are located on opposite sides of the glycosidic linkage. The evolution of the double-quantum coherences is found to be consistent with the solid-state conformation of the molecule, as previously determined by X-ray diffraction. The dependence of the double-quantum evolution on the glycosidic torsional angles is examined by using a graphical molecular manipulation program interfaced to a numerical spin simulation module.