Spin-lattice Relaxation Time In Rotating Frame Research Articles

Domain size and thermal stability of amine-cured hybrid films as corrosion resistance treatments for aluminum alloy

Amine-cured Ormosil coatings were prepared from tetraethylenepentamine (TEPA), 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) by sol–gel method. These Ormosil films were deposited by spin coated on aluminum alloy to improve the corrosion protection. The effect of the concentration of curing agent TEPA on the chain dynamic, domain size, thermal stability and corrosion performance of coated samples was investigated. The rotating frame spin–lattice relaxation times (T1ρH) and scale of the spin-diffusion path length (L) indicated that the configuration of the Ormosil films was highly crosslinked and dense and adhered to the aluminum alloy (AA) substrates. The thermal stability and the apparent activation energy (Ea), evaluated by van Krevelen’s method, of the TEPA-cured GPTMS–TEOS Ormosils decreased with increasing TEPA content. Potentiodynamic and salt-spray analysis revealed that the Ormosil films provided exceptional barrier and corrosion protection in comparison with untreated AA substrates.

β-Relaxation of Insulin Molecule in Lyophilized Formulations Containing Trehalose or Dextran as a Determinant of Chemical Reactivity

The purpose of this study was to elucidate whether the degradation rate of insulin in lyophilized formulations is determined by matrix mobility, as reflected in glass transition temperature (Tg), or by beta-relaxation, as reflected in rotating-frame spin-lattice relaxation time (T1rho). The storage stability of insulin lyophilized with dextran was investigated at various relative humidities (RH; 12-60%) and temperatures (40-90 degrees C) and was compared with previously reported data for insulin lyophilized with trehalose. Insulin degradation was monitored by reverse-phase high-performance liquid chromatography. Furthermore, the T1rho of the insulin carbonyl carbon in the lyophilized insulin-dextran and insulin-trehalose systems was measured at 25 degrees C by 13C solid-state NMR, and the effect of trehalose and dextran on T1rho was compared at various humidities. The degradation rate of insulin lyophilized with dextran was not significantly affected by the Tg of the matrix, even at low humidity (12% RH), in contrast to that of insulin lyophilized with trehalose. The insulin-dextran system exhibited a substantially greater degradation rate than the insulin-trehalose system at a given temperature below the Tg. The difference in degradation rate between the insulin-dextran and insulin-trehalose systems observed at 12% RH was eliminated at 43% RH. In addition, the T1rho of the insulin carbonyl carbon at low humidity (12% RH) was prolonged by the addition of trehalose, but not by the addition of dextran. This difference was eliminated at 23% RH, at which point the solid remained in the glassy state. These findings suggest that the beta-relaxation of insulin is inhibited by trehalose at low humidity, presumably as a result of insulin-trehalose interaction, and thus becomes a rate determinant. In contrast, dextran, whose ability to interact with insulin is thought to be less than that of trehalose, did not inhibit the beta-relaxation of insulin, and thus, the chemical activational barrier (activation energy) rather than beta-relaxation becomes the major rate determinant. Beta-relaxation rather than matrix mobility seems to be more important in determining the stability of insulin in the glassy state in lyophilized formulations containing trehalose and dextran.

Dynamics and corrosion resistance of amine-cured organically modified silicate coatings on aluminum alloys

Hybrid coatings based on amine-cured organically modified silicate were synthesized through a sol–gel technique. 3-glycidoxypropyltrimethoxysilane tetraethylenepentamine, and tetraethoxysilane were used as precursors for the hybrid coatings. These Ormosil films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the curing agent content of tetraethylenepentamine (TEPA) on the chain dynamics and corrosion performance of the coated samples were investigated. The Si–H polarization transfer relaxation times and the rotating-frame spin-lattice relaxation times indicated that the configuration of the Ormosil films was highly crosslinked and dense and adhered to the aluminum alloy substrates. Potentiodynamic evaluation revealed that the Ormosil films provided exceptional barrier and corrosion protection in comparison with untreated AA substrates.

Investigation of the dynamics of an elastin-mimetic polypeptide using solid-state NMR.

Elastin is the main structural protein that provides elasticity to various tissues and organs in vertebrates. Molecular motions are believed to play a significant role in its elasticity. We have used solid-state NMR spectroscopy to characterize the dynamics of an elastin-mimetic protein as a function of hydration to better understand the origin of elastin elasticity. Poly(Lys-25), [(VPGVG)(4)(VPGKG)](39), has a repeat sequence common to natural elastin. (13)C cross-polarization and direct polarization spectra at various hydration levels indicate that water enhances the protein motion in a non-uniform manner. Below 20% hydration, the backbone motion increases only slightly whereas above 30% hydration, both the backbone and the side-chains undergo large-amplitude motions. The motional amplitudes are extracted from (13)C-(1)H and (1)H-(1)H dipolar couplings using 2D isotropic-anisotropic correlation experiments. The root mean square fluctuation angles are found to be 11-18 degrees in the dry protein and 16-21 degrees in the 20% hydrated protein. Dramatically, the amplitudes increase to near isotropic at 30% hydration. Field-dependent (1)H rotating-frame spin-lattice relaxation times (T(1rho)) indicate that significant motions occur on the microsecond time-scale (1.2-2.3 micros). The large-amplitude and low-frequency motion of poly(Lys-25) at relatively mild hydration indicates that the conformational entropy of the protein in the relaxed state contributes significantly to the elasticity.

Rotating-frame spin—lattice relaxation measurements (T 1ρ) with weak spin-locking fields in the presence of homonuclear dipolar coupling

The rotating-frame spin-lattice relaxation time T1ρ, for two identical protons in the presence of residual dipole-dipole coupling is examined both theoretically and experimentally. The measured T1ρ, value as well as the amplitude and frequency of the dipolar oscillations are described by a theoretical framework involving three coupled rotating-frame magnetization modes. These modes include the magnetization along the spin-lock field, an antiphase magnetization, and an unobservable form of two-spin order. Inhomogeneity in the spin-locking field decouples the two latter modes resulting in the rapid damping of dipolar oscillations. Both theoretical considerations and experimental observations demonstrate conclusively that whenever the amplitude of the spin-locking field B1 greatly exceeds the dipolar coupling, the measured T1ρ, is independent of B1. Conversely, if B1 is on the order of the dipolar coupling, the measured T1ρ, increases as B1 increases. Dipolar oscillations that are important for times short compared to T1ρ, are rapidly damped for larger magnitudes of B1.

Rotating-frame spin–lattice relaxation time imaging by radio-frequency field gradients: visualization of strained crosslinked natural rubbers

NMR imaging by radio-frequency field gradients ( B 1 gradients) is especially convenient for heterogeneous samples and/or in the case of relatively short transverse relaxation times. The method has been combined with the application of two spin-lock periods of different duration so as to produce rotating-frame spin–lattice relaxation time ( T 1 ρ ) images. In the case of natural rubber samples with different crosslink densities, such images are not only characteristic of the crosslink density but also reveal the way in which the material has been stressed. The strained parts can be visualized either directly or through histograms showing the T 1 ρ distribution over the whole sample.

Molecular mobility of lyophilized poly(vinylpyrrolidone) and methylcellulose as determined by the laboratory and rotating frame spin-lattice relaxation times of 1H and 13C.

Laboratory- and rotating- frame spin-lattice relaxation times (T(1) and T(1rho)) of (1)H and (13)C in lyophilized poly(vinylpyrrolidone) (PVP) and methylcellulose (MC) are determined to examine feasibility of using T(1) and T(1rho) as a measure of molecular motions on large time scales related to the storage stability of lyophilized formulations. The T(1rho) of proton and carbon was found to reflect the mobility of PVP and MC backbones, indicating that it is useful as a measure of large-time-scale molecular motions. In contrast to the T(1rho), the T(1) of proton measured in the same temperature range reflected the mobility of PVP and MC side chains. The T(1) of proton may be useful as a measure of local molecular motions on a smaller-time-scale, although the measurement is interfered by moisture under some conditions. The temperature dependence of T(1) and T(1rho) indicated that methylene in the MC molecule had much higher mobility than that in the dextran molecule, also indicated that methylene in the PVP side chain had a higher mobility than that in the MC side chain.

NMR study of proton beam irradiated TlH2PO4

ABSTRACTWe have investigated proton beam irradiation effects on TlH2PO4 (TDP) showing an antiferroelectric phase transition and a ferroelastic phase transition. The sample was irradiated by 1 MeV proton beams to a dose of 1015 ions/cm2 and studied by means of 1H NMR measurements. The NMR rotating-frame spin-lattice relaxation time was measured as a function of temperature, and analyzed in order to understand the proton motions and the order parameter reflecting the structural changes caused by the proton irradiation.

Determination of distances between aluminum and spin-1/2 nuclei using cross polarization with very weak radio-frequency fields

In this work the possibility of using cross-polarization (CP) experiment for the determination of distances between spin-5/2 and spin-1/2 nuclei in polycrystalline and amorphous materials was investigated. The properties of the method were experimentally studied in an isolated Al2H spin system within the as-synthesized AlPO4-31 and in “infinite” aluminophosphate networks within the calcined AlPO4-31 and the hydrated VPI-5. In all three cases time-dependent oscillations due to coherent polarization transfer between aluminum and spin-1/2 nuclei were detected. The crucial parameters that influenced the visibility of dipolar oscillations were rotating-frame spin-lattice relaxation times of both nuclear species involved in a CP process and the homogeneity of rf fields. For a successful measurement the relaxation times, which varied remarkably with amplitudes of applied rf fields, had to be comparable to or larger than the period of time-domain oscillations. Radio-frequency field inhomogeneity was minimized when amplitudes of rf fields were adjusted to the Hartmann–Hahn sideband matching condition 3ν1I+ν1S=νR, the nutation frequency of spin-5/2 nuclei was limited to νR/2<3ν1I<νR, and the nutation frequency of spin-1/2 nuclei was limited to 0<ν1S<νR/2. Such adjustment assured also an efficient spin locking of quadrupolar spins. Experiments in the as-synthesized and calcined AlPO4-31 showed that in small isolated spin systems the time evolution of CP can elucidate the underlying geometry of the system whereas in “infinite” spin networks the splitting of a Pake-type doublet in the Fourier transform of a CP signal can yield an overall strength of the dipolar coupling. Although the use of weak rf fields reduced the robustness of the experiment it also introduced the selectivity of polarization transfer, which, as indicated by numerical simulation, in some cases allows the extraction of pairwise dipolar couplings in multispin systems. The possibility of a selective polarization transfer and a selective determination of distances between octahedrally coordinated Al1 nuclei and tetrahedrally coordinated P2 and P3 nuclei in the hydrated VPI-5 was demonstrated experimentally.

Solid-state NMR investigation of the dynamics of the soluble and membrane-bound colicin Ia channel-forming domain.

Solid-state NMR spectroscopy was employed to study the molecular dynamics of the colicin Ia channel domain in the soluble and membrane-bound states. In the soluble state, the protein executes small-amplitude librations (with root-mean-square angular fluctuations of 0-10 degrees ) in the backbone and larger-amplitude motions (16-17 degrees ) in the side chains. Upon membrane binding, the motional amplitudes increase significantly for both the backbone (12-16 degrees ) and side chains (23-29 degrees ), as manifested by the reduction in the C-H and H-H dipolar couplings and (15)N chemical shift anisotropy. These motions occur not only on the pico- to nanosecond time scales, but also on the microsecond time scale, as revealed by the (1)H rotating-frame spin-lattice relaxation times. Average motional correlation times of 0.8 and 1.2 micros were extracted for the soluble and membrane-bound states, respectively. In comparison, both forms of the colicin Ia channel domain are completely immobile on the millisecond scale. These results indicate that the colicin Ia channel domain has enhanced conformational mobility in the lipid bilayer compared to the soluble state. This membrane-induced mobility increase is consistent with the loss of tertiary structure of the protein in the membrane, which was previously suggested by the extended helical array model [Zakharov et al. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 4282-4287]. An extended structure would also facilitate protein interactions with the mobile lipids and thus increase the protein internal motions. We speculate that the large mobility of the membrane-bound colicin Ia channel domain is a prerequisite for channel opening in the presence of a voltage gradient.

A solid-state 13C NMR study on phase heterogeneity in the miscible blend of amorphous poly(benzyl methacrylate) with semicrystalline poly(ethylene oxide)

The rotating-frame spin–lattice relaxation time for protons, T 1 ρ ( 1H), was measured indirectly from 13C CP/MAS/DD NMR to probe possible molecular scales of heterogeneity in the miscible poly(benzyl methacrylate) (PBzMA)/poly(ethylene oxide) (PEO) blend over the whole composition range. According to the NMR results, only one phase was observed for the blends in which the PEO component is less than 16% (w/w). This miscible amorphous phase with PBzMA and PEO chains was mixed at the molecular level. Three phases were detected for the blends with PEO component >16%, containing one miscible homogenous PBzMA-rich phase, one constrained PEO phase and one crystalline PEO phase. The PEO component asymptotically increases in the miscible homogenous PBzMA-rich phase as the PEO composition increases. NMR analysis helped resolve the complex phase domains in the PBzMA/PEO blend that is composed of an amorphous mixture of PBzMA/PEO and crystalline PEO spherulite regions. The intra- and inter-lamellar domains in the PEO spherulites are influenced and complicated by the surrounding amorphous PBzMA/PEO mixture with varying composition.

An n.m.r. investigation of the dynamical characteristics of water absorbed in Nafion

Proton and deuterium spin–lattice relaxation times ( T 1), spin–spin relaxation times ( T 2), and rotating frame spin–lattice relaxation times ( T 1ρ) and Fluorine T 1 and T 2 were measured as a function of hydration and temperature in hydrated Nafion. The proton and deuterium data display an apparent dynamical transition which we have attributed to a change in the degree of order within the aqueous phase. The temperature at which this transition occurs, T t, is a function of the level of hydration, increasing for decreasing hydration. Above T t, the relaxation processes are similar to those observed in bulk water.

Proton rotating frame spin-lattice relaxation study of slow motion of pore water

Proton rotating frame spin-lattice relaxation times of water in hydrated porous silica glass, with pore diameters of 7.4, 23.7, 49.1, and 54.8 nm, are reported. Experiments were limited to hydrations corresponding to more than one-third hydrated pore volumes. The frequency dependence of the relaxation rates reveals a slow motion of pore water with a characteristic correlation time of ∼10−5 s. Within the limits given above, this correlation time depends on pore dimension and hydration only slightly. This indicates that the surface water molecules, which reorient with a characteristic time of ∼10−8 s, are changing their orientational axis with the slower correlation time ∼10−5 s. This process, which disrupts the nearby water molecules, depends primarily on the environment in the vicinity of the molecule’s original binding site. The analysis, based on the two-site fast exchange model, indicates that in small pores all the water may be affected by these slow jumps.

High-pressure proton NMR study of lateral self-diffusion of phosphatidylcholines in sonicated unilamellar vesicles

Effects of pressure on the lateral diffusion of phospholipid molecules in sonicated pure 1,2-dipalmitoylphosphatidyl-choline (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) vesicles (15 wt%) in D 2O were examined using the high-pressure proton NMR rotating frame spin-lattice relaxation time ( T 1 π ) method. Proton T 1 ϱ were measured at pressures from 1 bar to 5000 bar and at temperatures of 50°C to 70°C for DPPC and 5°C to 35°C for POPC. The T 1 ϱ −1 values were plotted as a function of the square root of the spin-locking field angular frequency ( ω 1 1 2 ) and the lateral diffusion coefficient ( D) calculated from the slope. Pressure effects on lateral diffusion were observed in the liquid-crystalline (LC) phase. The lateral diffusion coefficient exhibited sharp decreases in response to the various pressure-induced phase transitions encountered. However pressure had little, if any, effect on lateral diffusion in the pressure-induced gel I (GI) phase and pressure-induced interdigitated gel (Gi) phase. The activation volumes for diffusion were calculated from the slopes from plots of ln D versus pressure for both DPPC (37 ml/mol at 50°C, 34 ml/mol at 60°C and 25 ml/mol at 70°C) and POPC (16 ml/mol at 5°C, 9 ml/mol at 20°C and 6 ml/mol at 35°C) sonicated vesicles in the LC phase. The activation energy for diffusion ( E a) was calculated using the slopes from plots of ln D versus the inverse of the temperature ( 1 T ) for both DPPC and POPC in the LC phase (3.5 kcal/mol and 3.9 kcal/mol, respectively) and for both DPPC and POPC in the GI phase (6.0 kcal/mol and 4.4 kcal/mol, respectively). From the lateral diffusion coefficient and line width data pressure-temperature phase diagrams for sonicated pure DPPC and POPC vesicles were constructed. The values of the temperature to pressure equivalence of DPPC (d T m/d P) were estimated to be 22.1°C/kbar for the LC to GI phase transition and 28.6°C/kbar for the GI to Gi phase transition. The value of the temperature to pressure equivalence of POPC for the LC to GI phase transition was estimated to be 19.0°C/kbar.

Structure and interactions in homopolymers and blends as studied by the methods of vibrational and nmr spectroscopy

The combination of IR, Raman and NMR spectroscopy was used in the study of the blends of semicrystalline and amorphous polymers with considerably different strength of intermolecular interactions: poly(ϵ-caprolactam)/polystyrene (PCL/PS), poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) and poly(N-methyllaurolactam)/poly(4-vinylphenol) (PNMLL/PVPh). In the vibrational and NMR spectra of the blends composed of non-interacting polymers (PCL/PS) and weakly interacting polymers (PEO/PMMA), no band changes were observed which would indicate changes of the conformational structures. 1H NMR relaxation of the PCL and PS components in the blends is the same as in the respective homopolymers similarly treated. In the blends of weakly interacting polymers (PEO/PMMA), the crystallinity of PEO is influenced by the presence of PMMA and is negligible in the blends with less than 30 wt.-% of PEO. The rotating-frame spin-lattice relaxation time for protons TH1p of PMMA indicates close contact of the PMMA and PEO chains. In the blends PNMLL/PVPh with strong hydrogen-bonding interactions, both components are intimately mixed on a scale of 3–4 nm and significant shifts of some bands both in vibrational and in NMR spectra reveal changes of structure.

87Rb spin-lattice relaxation in the rotating frame and the phason gap in incommensurate Rb 2ZnCl 4

The temperature dependence of both the phason-induced 87 Rb 1 2 →- 1 2 rotating-frame spin-lattice relaxation time ( T 1ϱ) and the laboratory frame relaxation time ( T 1) was measured in the incommensurate phase of Rb 2ZnCl 4. The observed ratio T 1/ T 1ϱ≅1.6 is much smaller than that predicted for the case of a gapless phason ( T 1/ T 1 ϱ =√ ω L / ω 1≅86), thereby demonstrating the presence of a phason gap in this system. The phason gap was estimated to be 50 GHz, in agreement with other measurements.

Spin dynamics and spin counting in the 13C CP/MAS analysis of Argonne Premium coals

The carbonyl-labelled compound, [3.2.1]bicyclo-4-pyrrolidino- N-methyl-octan-8-one triflate ( 13CO-123), has been used as an intensity standard for quantitative 13C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (n.m.r.) analysis (including spin counting) of Argonne Premium coals. The cross-polarization time constants, T CH , and the rotating-frame proton spin-lattice relaxation times, T 1 ϱ H , have been determined for each major 13C peak of each coal via a combination of variable contact-time and variable spin-lock experiments. Two or three components of rotating-frame 1H relaxation decay and two or three components of T CH behaviour have been observed for each major 13C peak of each coal. These data have been used to determine the number of carbon atoms detected in each coal; these values are in the range 77–87% of the amount of carbon known to be in each coal from elemental analysis data, except for Pocahontas No. 3, for which only 50% of the carbon was detected.

The Main Chain Dynamics of a Peptide Bound to Calmodulin

The main chain dynamics of a peptide corresponding to the smooth muscle myosin light chain kinase calmodulin-binding domain bound to calcium-saturated calmodulin have been studied by 15N relaxation techniques. Laboratory and rotating-frame spin lattice relaxation times and nuclear Overhauser effects have been determined for nine amide 15N sites in the peptide using two-dimensional NMR spectroscopy. The global motion of the 1:1 complex is shown to be isotropic and is characterized by a correlation time of 10 ns rad−1. The generalized order parameters (S2) of the nine backbone amide N-H vectors of the peptide all fall closely about a value of 0.83. The corresponding effective correlation times all tend to zero, indicating that, on the subnanosecond time scale, backbone motion of the bound peptide is highly restricted and dominated by extremely fast motions.

Statistical n-butyl acrylate-sulfopropyl betaine copolymers. 3. Domain size determination by solid-state NMR spectroscopy

The morphology of two statistical copolymers of n-butyl acrylate (A) and dimethyl(3-methacrylamidopropyl)(9-sulfopropyl)ammonium betaine (B) of B molar fraction 0.04 and 0.12 (copolymers AB-4.0 and AB-12) were analyzed through solid-state NMR spectroscopy ( 13 C CP/DD/MAS) over a broad temperature range (160-360 K). In spite of the complexity of molecular motions and carbon line overlapping, the measurement of selective hydrogen rotating frame spin-lattice relaxation time T 1p through 13 C detection clearly shows that spin diffusion actually occurs over rigid microdomains of about 1 and 2.2 nm for the unclustered AB-4 and clustered AB-12 copolymers, respectively

Backbone dynamics of the glucocorticoid receptor DNA-binding domain.

The extent of rapid (picosecond) backbone motions within the glucocorticoid receptor DNA-binding domain (GR DBD) has been investigated using proton-detected heteronuclear NMR spectroscopy on uniformly 15N-labeled protein fragments containing the GR DBD. Sequence-specific 15N resonance assignments, based on two- and three-dimensional heteronuclear NMR spectra, are reported for 65 of 69 backbone amides within the segment C440-A509 of the rat GR in a protein fragment containing a total of 82 residues (MW = 9200). Individual backbone 15N spin-lattice relaxation times (T1), rotating-frame spin-lattice relaxation times (T1 rho), and steady-state (1H)-15N nuclear Overhauser effects (NOEs) have been measured at 11.74 T for a majority of the backbone amide nitrogens within the segment C440-N506. T1 relaxation times and NOEs are interpreted in terms of a generalized order parameter (S2) and an effective correlation time (tau e) characterizing internal motions in each backbone amide using an optimized value for the correlation time for isotropic rotational motions of the protein (tau R = 6.3 ns). Average S2 order parameters are found to be similar (approximately 0.86 +/- 0.07) for various functional domains of the DBD. Qualitative inspection as well as quantitative analysis of the relaxation and NOE data suggests that the picosecond flexibility of the DBD backbone is limited and uniform over the entire protein, with the possible exception of residues S448-H451 of the first zinc domain and a few residues for which relaxation and NOE parameters were not obtained. in particular, we find no evidence for extensive rapid backbone motions within the second zinc domain. Our results therefore suggest that the second zinc domain is not disordered in the uncomplexed state of DBD, although the possibility of slowly exchanging (ordered) conformational states cannot be excluded in the present analysis.