Disentangling crystallographic inequivalence and crystallographic forms of L-arginine by one- and two-dimensional solid-state NMR spectroscopy

Combinations of arginine and pullulan reveal the selective effect of stabilization mechanisms on different lyophilized proteins

The stability of lactate dehydrogenase (LDH) and β-galactosidase (β-gal), incorporated in arginine/pullulan (A/P) mixtures at various weight ratios by lyophilization, was determined. The physicochemical characteristics of various A/P mixtures were assessed. With decreasing A/P ratios, the glass transition temperature of the formulations increased. Furthermore, arginine crystallization due to high relative humidity (RH) exposure was prevented at an A/P weight ratio of 4/6 or less. When stored at 0 % RH / 60 °C for 4 weeks, arginine was superior to pullulan as stabilizer. During storage at 43 % RH / 30 ℃ for 4 weeks, the enzymatic activity of LDH was best retained at an A/P weight ratio of 2/8, while β-gal activity was relatively well-retained at A/P weight ratios of both 8/2 and 2/8. LDH seemed to be more prone to degradation in the rubbery state. In the glassy state, β-gal degraded faster than LDH. Solid-state nuclear magnetic resonance spectroscopy showed that (labeled) arginine experienced a different interaction in the two protein samples, reflecting a modulation of long-range correlations of the arginine side chain nitrogen atoms (Nε, Nη). In summary, LDH stabilization in the A/P matrix requires vitrification. Further stabilization difference between LDH and β-gal may be dependent on the interaction with arginine.

The “Wine-T1” NMR experiment for novel wine-metabolome fingerprinting with nuclear-spin relaxation

In agreement with the draft resolution OENO-SCMA 17-618 at step 5 “Quantitation of glucose, malic acid, acetic acid, fumaric acid, shikimic acid and sorbic acid in wine using proton nuclear magnetic resonance spectroscopy (1H NMR)” said technique has been recently accepted within the OIV chair as a primary quantitative analytical technique for beverage analysis such as wine. However, poor chemical shift dispersion in 1H NMR spectra severely penalizes quantification within overlapped or crowded regions. To outflank said penalization and quantify metabolites in signal overcrowding situations, the novel “Wine-T1” experiment is proposed. The novel scheme comprises the addition of a second dimension, wherein the proton spin-lattice relaxation times (T1-{1H}) of each metabolite's spin-system is correlated to a chemical-shift dimension. The new experiment includes a water and ethanol signal pre-saturation module, prior to the T1 saturation-inversion recovery dimension in order to maximize signal-to-noise ratio of wine metabolome NMR spectra. “Wine-T1” pulse sequence can be adapted to all commercial spectrometers (Bruker, Varian/Agilent, Jeol) and with acquisition times in the order of minutes, it should be considered as a fast repetition method to produce a robust metabolome fingerprint that has not been described before, to the best of our knowledge.

Probing structural and motional features of organic and inorganic solids through extended family of cross-polarization experiments

Combined use of cross-polarization and magic-angle spinning in the middle of the seventies has opened a new era of high-resolution solid-state NMR spectroscopy. Cross-polarization procedure is commonly used to obtain a shorter measuring time and to investigate or exploit one nucleous by means of the other nucleous involved in the polarization transfer. An extended family of cross-polarization experiments including constant time cross-polarization approach, cross-polarization inversion and indirect observation of proton spin system is reviewed and illustrated with applications to a large range of solids.

Quantitative one- and two-dimensional 13C spectra of microcrystalline proteins with enhanced intensity

We recorded quantitative, uniformly enhanced one- and two-dimensional (13)C spectra of labelled microcrystalline proteins. The approach takes advantage of efficient equilibration of magnetization by low-power proton irradiation using Phase Alternated Recoupling Irradiation Schemes and benefits simultaneously from uniform sensitivity enhancement due to efficient spin exchange that can overcome T1((13)C) constraints and the presence of heteronuclear Overhauser effects.