G. Lasanda

Interfacial water at protein surfaces: Wide-line NMR and DSC characterization of hydration in ubiquitin solutions

Wide-line 1H-NMR and differential scanning calorimetry measurements were done in aqueous solutions and on lyophilized samples of human ubiquitin between -70 degrees C and +45 degrees C. The measured properties (size, thermal evolution, and wide-line NMR spectra) of the protein-water interfacial region are substantially different in the double-distilled and buffered-water solutions of ubiquitin. The characteristic transition in water mobility is identified as the melting of the nonfreezing/hydrate water. The amount of water in the low-temperature mobile fraction is 0.4 g/g protein for the pure water solution. The amount of mobile water is higher and its temperature dependence more pronounced for the buffered solution. The specific heat of the nonfreezing/hydrate water was evaluated using combined differential scanning calorimetry and NMR data. Considering the interfacial region as an independent phase, the values obtained are 5.0-5.8 J x g(-1) x K(-1), and the magnitudes are higher than that of pure/bulk water (4.2 J x g(-1) x K(-1)). This unexpected discrepancy can only be resolved in principle by assuming that hydrate water is in tight H-bond coupling with the protein matrix. The specific heat for the system composed of the protein molecule and its hydration water is 2.3 J x g(-1) x K(-1). It could be concluded that the protein ubiquitin and its hydrate layer behave as a highly interconnected single phase in a thermodynamic sense.

Diffusible and residual hydrogen in amorphous Ni(Cu)-Zr-H alloys

Abstract The partition of hydrogen into diffusible and residual parts was realized by pulse NMR spectroscopy, by gas chromatography and by prompt gamma activation analysis (PGAA). The total hydrogen content was determined by the two non-NMR methods and the diffusible (mobile) component by CPMG NMR pulse sequence. Results on amorphous Ni(Cu)–Zr–H systems of different compositions are shown. Partially crystallized samples were also studied as an extension. A method proposed by us directly gives the fractional population of hydrogen atoms in the free (mobile) state on the spin–spin relaxation time scale. On the other hand the least values of the residual hydrogen content correlate surprisingly well with the numbers of filled four Zr-type H-sites calculated by Batalla et al. [NATO ASI Ser. 136 (1985) 203] for 0.21-nm exclusion distance.

Hydrogen occupancy, 1H NMR spectrum and second moment of ZrxNi1-x-H metallic glasses

Abstract The paper presents the results of an experimental investigation of rigid-lattice proton magnetic resonance (PMR) spectra and second moments in Ni 0.67 Zr 0.33 –H, Ni 0.50 Zr 0.50 –H, Ni 0.33 Zr 0.67 –H binary glassy alloy–hydrogen systems in the range of hydrogen-per-metal ( H / M ) ratio of 0.14≤ H / M ≤1.9. The line shape can be described by the empirical Harper-Barnes function with exponent values ranging from 1.45 to 2.95 in the whole hydrogen concentration range. The generally assumed Gaussian form is valid in a narrow H / M interval only. The second moment as a function of H / M can be fitted by a power function of an exponent 3/4. The exponent is independent of the composition of the alloy. We found that a simple lattice gas model based on a homogeneous hydrogen distribution contradicts the experimental results. Instead, a short-range order model has been proposed in which the hydrogen atoms are located in the centres of distorted tetrahedra of metal atoms, that is in the basic building blocks of the amorphous alloys. The Switendick criterion was also taken into consideration. We have shown that few proton first neighbours (0–2) and a small number of second neighbours (1–8), that is, a cluster of hydrogen is sufficient to account for the measured value of the second moment. Ternary Zr 0.5 Ni 0.5− x Cu x –H alloys have been investigated, too. The addition of Cu nuclei did not lead to the second moment enhancement expected for a homogeneous distribution of components.

High temperature 1H spin–spin relaxation in Zr–Ni–Cu–H amorphous alloys

Abstract 1 H spin–spin relaxation time ( T 2 ) and complementary hydrogen content, PMR spectrum width and spin–lattice relaxation time ( T 1 ) have been measured in Zr y (Ni 1− x Cu x ) 1− y –H ternary amorphous alloys of different hydrogen content at 0≤ x ≤33 at.% Cu and y =33, 50 and 67 at.% Zr concentrations using Carr–Purcell–Meiboom–Gill (CPMG), solid-echo and saturation recovery pulse sequences, respectively. At high hydrogen contents the T 2 measured by the slope of the CPMG echo train depends on both the Zr and Cu content, but is independent of the hydrogen content. The differences in the spin–spin relaxation behaviours can be attributed to the substantial change of correlation time and not to the change of activation energy or local fields. The measurements were made in the “motional narrowing” state, consequently our E a and τ ∞ quantities are averaged to the diffusion motion of protons taking part in this process. At small hydrogen contents T 2 depends on hydrogen content and the T 2 vs. 1/ T curves cannot be fitted by single Arrhenius plots. The hydrogen content measured by echo train has turned out to be systematically smaller than that measured by weight increase, demonstrating that not all the hydrogen takes part in the diffusion process.

PMR measurements on (Ni1 −xCux)0.5Zr0.5-Hy amorphous alloys

Abstract Spin-spin relaxation time ( T 2 ) and complementary hydrogen content (H/M), PMR spectrum width (FWHM) and spin lattice relaxation time ( T 1 ) have been measured in (Ni 1 − x Cu x ) 0.5 Zr 0.5 -H y ternary amorphous alloys at 0 ⩽ x ⩽ 29 at.% concentrations using Carr-Purcell-Meiboom-Gill (CPMG), solid-echo and saturation recovery pulse sequences respectively. The T 2 relaxation time measured by the slope of the CPMG echo train depends on both the hydrogen and Cu content. The dependence can be attributed to the change of correlation time and not to the change of activation energy or local field. The measurements were made in the ‘motional narrowing’ state; consequently our E a and τ ∞ quantities are averaged to the diffusional motion of protons taking part in this process. The extrapolated amplitude of the echo train measured on the alloy-hydrogen system and normalized to the same quantity in water, gives the value of proton magnetization in thermal equilibrium, that is the hydrogen content free from any perturbing effects. The hydrogen content measured by CPMG echo train has turned out to be systematically smaller than that measured by weight increase.

Proton nuclear magnetic resonance and H-site occupancy in Zr0.5Ni0.5-yCuyHx metallic glasses

Abstract The aim of this paper is to reinvestigate the proton magnetic resonance spectra in Zr 0.5 Ni 0.5− y Cu y H x metallic glasses. Solid-echo pulse sequences were used to analyze the line shape. The measurements were made in the temperature range 2.2–300 K and at a frequency of 87.6 MHz. The reinvestigation of the line shape mostly at low temperatures was initiated after having realized that the splitting reported earlier on our samples was a consequence of the relatively long recovery time of our spectrometer. The present solid-echo measurements yielded simple spectra describable by a Harper-Barnes line shape close to gaussian.

1H NMR spectra and h-site occupancy in Zr0.5CuyNi0.5-yH1 metallic glasses

Abstract Proton magnetic resonance spectra of Zr 0.5 Cu y Ni 0.5−y H 1 metallic glass samples with 0 ≤ y ≤ 0.3 were measured in the temperature range 77 K to 400 K and at 8, 28.5, 87.6 and 88.5 MHz frequencies. The data of the free-induction decay (FID) signal were compiled and Fourier transformed by a SMIS NMR spectrometer. The temperature dependence of the line shapes shows three distinctly different features: (i) in the temperature range 400 K to 270 K the spectrum is a motionally narrowed Lorentzian line; (ii) in the temperature range 270 K to 140 K the spectrum consists of a narrow Lorentzian component and a substantially wider Gaussian one; (iii) in the temperature range 140 K to 77 K, the spectrum is a “two-peaked” line. The distance between the two peaks (splitting) was found to be independent of the temperature and the frequency, that means that the low-temperature spectrum is probably the Pake doublet of hydrogen pairs. From the analysis of the splitting of the Pake doublet, a proton-proton distance of 0.167 nm was estimated. This distance corresponds to a transition metal mediated hydrogen pairing.

Temperature dependence of 1H-NMR relaxation in hydrogenated amorphous carbon sample series

Abstract A two-exponential spin-lattice ( T 1 ) relaxation process of hydrogen nuclear magnetization was found in a series of hydrogenated amorphous carbon samples prepared under different self-bias conditions from benzene. The temperature dependence of these relaxation times reveals the different dynamic background of the two sub-systems. Low activation energies (depending on self-bias voltages) were measured for the longer relaxation time components; temperature independence was detected for the shorter relaxation time components.

Susceptibility and proton line shift of Zr0.33Ni0.67Hx alloys

Abstract The proton NMR line shift with respect to water, the bulk susceptibility and in a few cases the Korringa contribution to the spin lattice relaxation time were measured in Zr0.33Ni0.67 Hx amorphous alloys with hydrogen concentration 0.1 ⩽ x ⩽ 0.7and at 343 K. All the parameters, including the hydrogen content and the bulk susceptibility, were measured simultaneously in situ, and in the shift measurements a resolution of ±1 ppm was attained. The residual Knight shift depends on the hydrogen content and is positive relative to water. Preliminary low temperature spin lattice relaxation time measurements indicate that the positive shift is the consequence of the balance of s- and d-contributions.

PMR Spectrum, Proton Spin Relaxation and Diffusion in Zr0.5(CuxNi1−x)0.5H1 Metallic Glasses

Proton magnetic resonance spectrum, laboratory and rotating frame spin-lattice relaxation times were measured on Zr0.5(CuINii.A;)o.5H1 metallic glass samples at x = 0 and 0.3 compositions, at different temperatures and frequencies. The experimental data were compiled by a BRUKER SXP and a SMIS NMR spectrometer. Samples prepared by melt-spinning in vacuum and checked by X-ray diffraction were used, and they were charged with hydrogen from gas. Conclusions concerning the hydrogen sites, the hydrogen diffusion and cross-relaxation were drawn.