M. M. Pintar

Two-dimensional nmr time evolution correlation spectroscopy in wet lysozyme

Abstract A two-dimensional time evolution approach with which the free-induction decay of a heterogeneous system can be resolved partially was applied to natural and deuterated wet hen egg-white lysozyme (HEWL). The study was performed in the laboratory and rotating reference frames. The two-dimensional approach made possible a resolution of the heterogeneous spin distribution into four groups, which are briefly discussed. It is shown that in HEWL the strongly coupled nonexchangeable protein protons and water protons are relaxed either by the intramolecular water relaxation mechanism or by an intermolecular protein-water mechanism.

Nuclear magnetic resonance monitoring of capillary imbibition and diffusion of water into hardened white cement paste

Nuclear magnetic resonance (NMR) experiments monitoring the imbibition (sorption) and diffusion of water into white cement paste are reported. The sample was a 1.3 cm long cylinder (6 mm o.d.) of hardened ordinary white cement paste, with a water/cement ratio of 0.42 containing 0.5% Ca(NO2)2 and 2% NaCl. Water proton magnetization and T2 values were obtained as functions of time. Imbibition of H2O and diffusion of H2O and D2O were monitored with 1H NMR at 26 and 30 MHz. The countercurrent water imbibition experiments revealed a two-stage process. A rapid uptake of water, involving about 85% of the total, took place in about 45 min. Maximum saturation was reached in about 2 days. Both stages of the process were well described by a nonlinear diffusion-like equation. Diffusion of both H2O and D2O was characterized by a single diffusion coefficient. The diffusion coefficient for H2O and D2O, derived by fitting the data to the diffusion equation, is well predicted by D0/(Fφ).

Proton free induction decay evolution during hydration of white synthetic cement

Nuclear magnetic resonance (NMR) of protons in hydratlng cement paste(l) can be employed to differentiate between protons whlch are In llquld phases, such as bulk-llke water or very fluld gel, and those embedded In rlgld structures such as crystalline water or hydroxyl groups in portlandlte, CH. As the hydratlon proceeds (2), progresslvely more of the water Inltlally added to the cllnker becomes crystalllne water and hydroxyls of CH. The total amplltude of the proton Nt4R free induction decay (FID) followlng a 90 ° r.f. excltatlon, whlch Is a measure of the total number of protons In the paste, is expected to remaln Independent of the hydratlon time provided there is no loss of water by evaporatlon. Thus, during the hydration the total proton FID amplitude does not change, as Its solld-llke component grows at the expense of its llquld-llke component. The solld-llke FID can be very easily differentiated from the llquld-llke FID as their respectlve shapes differ drastically. Whlle the solld-llke FID is Gausslan, wlth a characterlstlc decay time T on the order of 20 ~s, the llquld-llke FID Is nearly 2

Self-regulation of iron ion concentration in hydrated porous glasses

The water proton spin‐lattice relaxation rate was measured in Fe contaminated water filled porous glasses with pore diameters of 548 and 2917 A at 0.65T at room temperature as a function of pore hydration. Two distinct regimes could be defined. A ‘‘wet’’ pores regime (0.6<V0/V<1) and a regime with water only within the pores (1<V0/V<4), where V0 is the pore volume and V the water volume. In both regimes, the proton relaxation rate varies linearly with V0/V. A small Fe ion concentration in porous silica glass water remains constant while the hydration of pores is changed by a factor of ≊4, which is a necessary assumption to model the observed proton spin‐lattice relaxation rate. Such a constant small concentration premise agrees with the Langmuir isotherm, which for systems with large surface to volume ratios (S/V0), predicts a constant small volume concentration. In the two studied porous glasses with S/V0 of 9.2×106 and 42×106 m−1, the condition for large S/V0 was satisfied, while the Fe volume concentra...

A ZEEMAN LEVEL CROSSING STUDY OF THE SYMMETRY OF THE POTENTIAL HINDERING THE TORSIONAL OSCILLATOR CH3

Abstract Four proton Zeeman-torsional level matching resonances were observed in the γ phase of tetrahedrally coordinated Si (CH3)4. The resonances were observed by measuring the Larmor frequency dependence of the coupling time between proton Zeeman and CH3 torsional-tunneling energy reservoirs. Two such resonances are known to occur if the potential, which hinders the angular displacements of planar CH3 oscillators, has threefold symmetry. If the hindering potential is a mixture of a strong sixfold and a weaker threefold term, seven such level matching resonances are possible. However, in only four of these cases does the dipolar interaction bring about observable fast (∼ 10 m s) polarization transfer between the saturated spin states and the torsional-tunneling states. Since the sixfold contribution to the hindering potential is caused by inter-CH3 oscillator interactions, the observation of four resonances indicates a strong torsion-torsion interaction. In general, level-matching resonance spectra and the associated magnetization fractions give clues about the ground state manifold, while the resonance linewidth and intensity contain information about CH3 dynamics.

Relaxation of water proton spins by paramagnetic spin-label molecules in porous glass

A water proton spin-lattice relaxation study of the spin-label molecules 2,2,6,6- tetramethyl-4-acetamido-piperidine-1-oxyl (TMAPO) solution in glass pores of 127 nm diam reveals that when the porous glass is hydrated with a 1 mM TMAPO solution, the TMAPO concentration in pore water is maintained constant during dehydration. However, it was observed that if the pore diameter is 49.1 nm or smaller, the Langmuir isotherm is not applicable, although the surface-to-volume ratio is larger. The observed proton relaxation’s dependence on pore volume-to-water volume ratio V0/V, is in excellent accord with the results of the electron paramagnetic resonance experiments and supports a model based on the fast exchange of water between nonequivalent environments.

Rotating-frame NMR relaxation in the dipolar spin glass Rb1-x(NH4)xH2AsO4

Abstract Low-temperature T1ϱ relaxation measurements of a proton pseudo-spin glass system in mixed rubidium-ammonium dihydrogen arsenate crystals are presented. The experimentally observed features of the magnetization decay in the rotating frame are explained with a model which incorporates rotational tunneling of the ammonium ions.

Enhancement of nuclear Zeeman-rotational tunneling polarization transfer by paramagnetic impurities

Abstract It has been observed that the paramagnetic impurities introduced by 60Co γ-irradiation very significantly shorten the coupling time between the nuclear Zeeman and rotational tunneling energy reservoirs in addition to the well-known shortening of the spin lattice relaxation time.

Study of the NH4 tunneling manifold by energy level matching in the proton spin rotating frame

Matching of Zeeman and tunneling levels in the proton spin rotating frame is used to detect splitting of the torsional ground state due to rotational tunneling of the NH4 group in solid NH4I. When highly polarized Zeeman splitting matches tunneling splitting a fast resonant transfer of polarization between Zeeman and tunneling states occurs. This in turn causes a change of the proton magnetization. When the magnetization change is monitored as a function of the magnetic field strength in the rotating frame, peaks are observed whenever two levels match. The model spectrum of the NH4 group with a split F-symmetry state, indicating that the symmetry of the lattice potential at the site of the NH4 group is lower than tetrahedral, reproduces the observed spectrum. The energy differences between the A state and the nondegenerate, lower F state and between this F state and the degenerate, higher F state, as measured by level matching in units kHz, are 82±4 and 41±2, respectively. The magnetization evolution spec...

Four time domains of spin polarization torsional spectroscopy

Abstract There are four basic types of spin polarization torsional spectroscopy (SPOTS) experiments, corresponding to four time domains of observations. It is possible to determine the spectrum, the specific heat, and the relaxation time of the set of energy levels produced by the splitting of the degenerate ground state of torsional oscillators in solids. It is shown that SPOTS resolution is not always good enough to allow the determination of the tunnelling spectrum if the splitting is not much greater than the dipolar splitting.