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Structure and Properties of Gallium-Rich Sodium Germano-Gallate Glasses
摘要： Glass compositions in the gallium-rich region of the ternary GaO3/2-GeO2-NaO1/2 vitreous system are studied as a function of the Na/Ga cationic ratio (ranging from 1.30 to 1.61) for a fixed GeO2 content. Glass structures are investigated by 71Ga MAS-NMR, infrared and Raman spectroscopies, and the thermal, optical and physical properties are characterized. Vibrational spectra are interpreted with the help of density functional theory (DFT) calculations. Gallium oxide generally enters the germania network in four-fold coordination, however for Na/Ga ratio below unity, gallium cations tend to charge balance with the formation of 5- or 6-fold coordination units. When the amount of sodium is greater than gallium, non-bridging oxygens (NBOs) are formed preferably on germanate tetrahedral units. These structural descriptions are used to understand the evolution of glass properties such as glass transition temperature, density and refractive index.
关键词： germano-gallate glasses,infrared,vibrational spectroscopy,glass structure,71Ga NMR spectroscopy
更新于2025-09-04 15:30:14
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Improving the sensitivity of <i>J</i> coupling measurements in solids with application to disordered materials
摘要： It has been shown previously that for magic angle spinning (MAS) solid state NMR the refocused INADEQUATE spin-echo (REINE) experiment can usefully quantify scalar (J) couplings in disordered solids. This paper focuses on the two z filter components in the original REINE pulse sequence, and investigates by means of a product operator analysis and fits to density matrix simulations the effects that their removal has on the sensitivity of the experiment and on the accuracy of the extracted J couplings. The first z filter proves unnecessary in all the cases investigated here and removing it increases the sensitivity of the experiment by a factor ～1.1–2.0. Furthermore, for systems with broad isotropic chemical shift distributions (namely whose full widths at half maximum are greater than 30 times the mean J coupling strength), the second z filter can also be removed, thus allowing whole-echo acquisition and providing an additional √2 gain in sensitivity. Considering both random and systematic errors in the values obtained, J couplings determined by fitting the intensity modulations of REINE experiments carry an uncertainty of 0.2–1.0 Hz (～1?10 %).
关键词： solid state NMR,disordered materials,REINE experiment,J coupling,sensitivity improvement
更新于2025-09-04 15:30:14
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DVD Review
摘要： This DVD course, “Basic Concepts in NMR”, is exactly what the title claims – a very thorough and detailed description of the underlying “concepts” that one needs to know to fully understand one-dimensional NMR experiments. Since I have been an industrial NMR spectroscopist training scientists to do NMR for over 40 years, I have a full appreciation for the amount of time this course would have saved me. The course explores the basic theory behind NMR experiments and even explains the components of the hardware necessary to obtain NMR data. The author’s presentations show the result of decades of teaching this topic. He presents each concept clearly and at a pace that allows the student to think about what the lessons mean. He frequently relates abstract principles to more easily understood physical observations such as his use of a common spring to illustrate the rate of return to equilibrium of excited nuclei during the relaxation process.
关键词： spectroscopy,DVD course,NMR,basic concepts
更新于2025-09-04 15:30:14
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TiO2 Nanoparticles Catalyze Oxidation of Huntingtin Exon 1-Derived Peptides Impeding Aggregation: a Quantitative NMR Study of Binding and Kinetics
摘要： Polyglutamine expansion within the N-terminal region of the huntingtin protein results in the formation of intracellular aggregates responsible for Huntington’s disease, a fatal neurodegenerative condition. The interaction between TiO2 nanoparticles and huntingtin peptides comprising the N-terminal amphiphilic domain without (httNT) or with (httNTQ10) a ten-residue C-terminal polyglutamine tract, is investigated by NMR spectroscopy. TiO2 nanoparticles decrease aggregation of httNTQ10 by catalyzing the oxidation of Met7 to a sulfoxide, resulting in an aggregation-incompetent peptide. The oxidation agent is hydrogen peroxide generated on the surface of the TiO2 nanoparticles either by UV irradiation or at low steady-state levels in the dark. The binding kinetics of non-aggregating httNT to TiO2 nanoparticles is characterized by quantitative analysis of 15N dark state exchange saturation transfer and lifetime line broadening NMR data. Binding involves a sparsely-populated intermediate that experiences hindered rotational diffusion relative to the free state. Catalysis of methionine oxidation within the N-terminal domain of the huntingtin protein may potentially provide a strategy for delaying the onset of Huntington’s disease.
关键词： Huntingtin,TiO2 nanoparticles,aggregation,NMR spectroscopy,oxidation
更新于2025-09-04 15:30:14