Relaxation measurements, NMR

Yuan P, Marshall VP, Petzold GL, Poorman RA, Stockman BJ. Dynamics of stromelysin/inhibitor interactions studied by 15N NMR relaxation measurements Comparison of ligand binding to the SrS3 and S -Sy subsites. J Biomol NMR 1999 15 55-64. 

NMR relaxation measurements such as cross-polarization time constants (7ch) can also yield useful information regarding alkyl-chain mobility. Sindorf and Maciel [159] have characterized the relative mobility of low-density Cg and Cig stationary phases ( 2.6 and 1.7 p,mol/m, respectively) as a function of carbon position from the... 

Structural information on aromatic donor molecule binding was obtained initially by using H NMR relaxation measurements to give distances from the heme iron atom to protons of the bound molecule. For example, indole-3-propionic acid, a structural homologue of the plant hormone indole-3-acetic acid, was found to bind approximately 9-10 A from the heme iron atom and at a particular angle to the heme plane (234). The disadvantage of this method is that the orientation with respect to the polypeptide chain cannot be defined. Other donor molecules examined include 4-methylphenol (p-cresol) (235), 3-hydroxyphenol (resorcinol), 2-methoxy-4-methylphenol and benzhydroxamic acid (236), methyl 2-pyridyl sulfide and methylp-tolyl sulfide (237), and L-tyrosine and D-tyrosine (238). Distance constraints of between 8.4 and 12.0 A have been reported (235-238). Aromatic donor proton to heme iron distances of 6 A reported earlier for aminotriazole and 3-hydroxyphenol (resorcinol) are too short because of an inappropriate estimate of the molecular correlation time (239), a parameter required for the calculations. Distance information for a series of aromatic phenols and amines bound to Mn(III)-substituted HRP C has been published (240). 

A NMR probe for very high temperature and high pressure was published by Jonas in 1979 [5]. The probe had a relatively low spectral resolution but allowed NMR relaxation measurements at temperatures up to 700 °C. The pressure vessel was made from the IMI-680 titanium alloy and could withstand pressures up to 200 MPa. Because of the high temperatures attained with the probe, gaseous argon was used as the pressure transmitting medium. A first NMR relaxation study of supercritical water performed with this probe was published in 1981 [25]. 

It is apparent that the dipolar coupling is a short range coupling and rapidly vanishes with the distance. This does not hold for the scalar coupling. It is also apparent that small / values can affect ts under favorable conditions. In other words, small / values can be revealed through the linewidth of the EPR signal or through NMR relaxation measurements. 

Carbon-13 rotating-frame relaxation rate measurements are used to elucidate the mechanism of gas transport in glassy polymers. The nmr relaxation measurements show that antiplasticization-plasticization of a glassy polymer by a low molecular weight additive effects the cooperative main-chain motions of the polymer. The correlation of the diffusion coefficients of gases with the main-chain motions in the polymer-additive blends shows that the diffusion of gases in polymers is controlled by the cooperative motions, thus providing experimental verification of the molecular theory of diffusion. Carbon-13 nmr relaxation... 

Section IA summarizes the molecular model of diffusion of Pace and Datyner (1 2) which proposes that the diffusion of gases in a polymeric matrix is determined by the cooperative main-chain motions of the polymer. In Section IB we report carbon-13 nmr relaxation measurement which show that the diffusion of gases in poly(vinyl chloride) (PVC) - tricresyl phosphate (TCP) systems is controlled by the cooperative motions of the polymer chains. The correlation of the phenomenological diffusion coefficients with the cooperative main-chain motions of the polymer provides an experimental verification for the molecular diffusion model. 

Examples of studies of the molecular dynamics of dissolved dendrimers with the aid of NMR relaxation measurements POPAM dendrimers a) J.F.G.A. Jansen, E.M.M. Brabander-van den Berg, E.W. Meijer, Science 1994, 265, 1226-1229 ... 

Otto,W.H.,Burton,S. D.,Carper,W. R.,and Larive, C.K. (2001a).Examination of Cadmium(II) complexation by the Suwannee River fulvic acid using 113Cd NMR relaxation measurements. Environ. Sci. Technol. 35,4900-4904. 

The characterization of solid polymeric material often includes the need to characterize the variety of molecular motions present as well as the molecular and morphological structure. NMR relaxation measurements have a long history of application to molecular motion studies of polymers where NMR data often complements mechanical and dielectric measurements with a more complete identification of the mobile, or immobile, entities. 

Similar results to these were found by Schwarz and Schonhoff [110] on nanoparticles coated by the PEM composed of poly(allylamine) (PAA) and PSS via XH NMR relaxation measurements. There, an increased water immobilization is reported for all odd polycation (PAA) terminating PEMs in contrast to even polyanion (PSS) terminating PEMs, which was found to be not just a property of the last adsorbed layer but more of the whole multilayer phase. 

Ramanuja et al.13 have carried out proton NMR relaxation measurements in AFE betaine phosphate (BP), FE betaine phosphite (BPI) and the mixed system BPI( X)BPX, at 11.4 and 23.3 MHz from 300 to 80 K for x=0.0, 0.25, 0.45,0.85, and 1.0. The temperature dependence of SLR time l i exhibits two minima as expected from the BPP model in parent compounds BP and BPI. The Larmor frequency dependence of Tj in the mixed system is rather unusual and exhibits different slopes for the low-temperature wings at the two frequencies, which is a clear experimental evidence of the presence of different methyl groups with different activation energies (Ea) indicating disorder. 

Buck, M., Boyd, J., Redfield, C., MacKenzie, D.A., Jeenes, D.J., Archer, D.B., and Dobson, C. M. (1995) Stmctural determination of protein dynamics analysis of 15N NMR relaxation measurements for main-chain and side-chain nuclei of hen egg white lysozyme, Biochemistry 34, 4041-4055. 

Lillemoen, J. and Hoffman, D.W. (1998) An investigation of the dynamics of ribosomal protein L9 using heteronuclear NMR relaxation measurements, J. Mol. Biol, 281, 539-551. 

Some indirect experimental evidence exists for the liquid-liquid critical point hypothesis from the changing slope of the melting curves, which was observed for different ice polymorphs (30, 31). A more direct route to the deeply supercooled region, by confining water in nanopores to avoid crystallization, has been used more recently by experimentalists. These researchers applied neutron-scattering, dielectric, and NMR-relaxation measurements (32-35). These studies focus on the dynamic properties and will be discussed later. They indicate a continuous transition from the high to the low-density liquid at ambient pressure. The absence of a discontinuity in this case could be explained by a shift of the second critical point to positive pressures in the confinement. This finding correlated with simulations, which yield such a shift when water is confined in a hydrophilic nanopore (36). 

Recently, we have observed a similar inapplicability of the SED law to a much larger molecule (benzene) in water in a high pressure NMR relaxation measurement The initial compression does not decrease but increases the rotational correlation time for a benzene molecule in water at 30 C. In other words, the viscosity exponent defined by Eq. (3) is negative at lower pressures. The exponent is turned over to a large positive at higher pressures. 

C-NMR relaxation measurements in solution of pH 8.6 suggested the participation of carboxylate, deprotonated amide and deprotonated alcoholic OH groups in the chelate ring of the copper(ll) complex formed in the physiological pH range. 

The 10 s order rate constants for the thermal-induced (ground state) intramolecular electron transfer rates of the mixed-valence biferrocene monocation were first elucidated in various solvents by the H-NMR relaxation measurements. The obtained solvent dependent frequency factors indicated significant contribution of the solvent dielectric friction on the barrier crossing. An existence of the faster processes compared with the ET rate such as the internal vibration as an escape route of the reaction dynamics along the solvent coordination was also proposed in some extent. 

In an example that illustrates the application of NMR relaxation measurements for studying ligand flexibility, Kessler and colleagues (57) investigated the role of disulfide bonds in the a-amylase inhibitor tendamistat. This small protein contains two disulfide bonds (C11-C27 and C45-C73) and opening cf the latter is known to reduce the melting temperature of the protein (i.e., reduce its stability), but in this case does not affect its a-amylase inhibitor function. The latter observation... 

NMR relaxation methods discussed herein can be applied to obtain kinetic parameters, discriminate regions of flexibility within bound ligands, and determine the structure of bound ligands. As with all NMR relaxation measurements, structure information and dynamic information are interwoven, and the goal is to develop methods to obtain structural and dynamic information separately. Two approaches will be discussed in this paper the first focuses on dynamie information and the second on structural information. These methods... 

Ahmad, M. U., Tashiro, Y., Matsukawa, S., and Ogawa, H. 2004. Comparison of gelation mechanism of surimi between heat and pressure treatment by using rheological and NMR relaxation measurements. J. FoodSci. 69(9) E497-E501. 

This chapter will focus on the specific research area of combining MD simulations and experimental NMR relaxation studies to obtain information about intermolecular interactions and molecular motion in liquids and solutions [4]. To combine MD simulations and NMR relaxation measurements is an ideal tool in many respects. In spite of the fact that it enables studies of the most fundamental molecular properties in liquids, difficult to obtain using other methods, it has re-... 

Since the electrical resistance of the effiuent and parasitic currents are minimal at high level of impurities, specihc interest in electrically assisted membrane processes could increase due to more strict laws and legislation around effluents. The depletion of freshwater resources and the necessity to process brackish or seawater to produce potable water could promote the use of electrically assisted membrane processes in the future. Electrodialysis will have to compete with pressure-driven membrane processes such as reverse osmosis. The growing awareness of the unique cleaning ability of electrically ionized water (EIW) [47], a byproduct of electrodialysis, may be a factor to consider in the choice between ED and RO systems. NMR relaxation measurements were used to determine the water cluster size of electrically ionized water EIW. It is known that the water cluster size of EIW is signihcantly smaller than that of tap water. The smaller water cluster size is believed to enhance the penetration and extractive properties of EIW. Recently, EIW has been produced and used in several cleaning processes [47] in industry. 

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