Resonance Line Shape Analysis Research Articles

Effect of the pH on the microstructure and magnetic properties of electrodeposited cobalt nanowires

The effect of the electrolyte acidity, or pH, on the structural and magnetic properties of electrodeposited cobalt nanowires has been studied. The main result is that as the pH is lowered from 3.8 down to 2.0, a microstructural change is induced. Ferromagnetic resonance measurements show that at high pH, Co presents an hcp phase with the c-axis aligned perpendicular to the wires, whereas at low pH, a more disordered hcp structure is observed. From the resonance line shape analysis, it is shown that for low-pH Co, no grains oriented with the c-axis perpendicular to the wire are present. The resulting magnetic properties show that for high-pH samples, the effective anisotropy field is weaker than that of the low-pH samples due to the competition between shape anisotropy and the cobalt c-axis magnetocrystalline anisotropy.

Magnetic resonance of zinc- and copper-ferrite ionic magnetic fluids: temperature effects

Magnetic resonance was used to investigate ionic magnetic fluids based on ZnFe 2O 4 and CuFe 2O 4 nanoparticles. Temperature and angular variation measurements were performed with field-frozen samples, using an X-band spectrometer. The resonance line shape analysis indicates the presence of four components, irrespective of the temperature and sample orientation. Intermediate values of the anisotropy field were associated to dimers, while low and high values of the anisotropy field were associated to large- and small-sized monomers, respectively. The temperature dependence of the resonance field associated to each resonance line allowed quantitative investigation of the surface anisotropy component. Positive as well as negative surface anisotropy components, as obtained from the temperature dependence of the resonance field, are reported.

Coherence Transfer Signals in the Rotational Resonance NMR of a Spinning Single Crystal

A recent analysis of rotational resonance lineshapes (M. Helmle et al., J. Magn. Reson. 140, 379-403, 1999) predicted the existence of coherence transfer signals, which are generated by mechanically induced coherence transfer during the detection process. These signals correspond to the generation of observable coherences at spin sites that have no magnetization at the beginning of the observation interval but which acquire coherence while the detection is underway. The coherence transfer signals disappear for powder samples in conventional magic-angle-spinning solid-state NMR experiments. In this Communication, we report the successful detection of coherence transfer signals in rotor-synchronized experiments performed on a single crystal of [1,2-(13)C(2)]glycine. Copyright 2000 Academic Press.

Investigation of the rotational motion of self-assembled fatty acid films: An electron paramagnetic resonance line shape analysis

We have investigated the electron paramagnetic resonance (EPR) of self-assembled stearic acid films adsorbed on an Al2O3-film. Doping the film with spin labels at different positions of the alkyl chain in order to make the films accessible for EPR spectroscopy provides an opportunity to investigate the rotational motion of the molecule along the alkyl chain. The temperature dependent EPR spectra show a strong dependence of the rotational motion of the molecules with variation of the location of the spin label along the chain. We study the rotational motion by means of the EPR line shape analysis.

Doped ionic magnetic fluids: A resonance characterization

Electron paramagnetic resonance is used to investigate ionic cobalt ferrite-based magnetic fluids. Two magnetic fluid samples having particles with different average radius of 6.8 nm and 7.8 nm were doped with Cu2+ at different concentrations. Changes on the resonance line shape of the Cu2+-ion in the aqueous phase was analyzed taking into account the particle polydispersity, the contribution of the dipolar field due to the surrounding magnetic nanoparticles, and the electrostatic interaction between the surface charged magnetic nanoparticles and the Cu2+-probe. The particle polydispersity parameters we found from the resonance line shape analysis are in excellent agreement with the parameters obtained from electron microscopy. The Cu2+ spatial distribution function around the magnetic nanoparticles gives very reasonable values for both, the particle–particle distance and the ionic layer thickness at the particle surface.

Electron paramagnetic resonance lineshape analysis of the photoexcited triplet state of C60 in frozen solution. Exchange narrowing and dynamic Jahn–Teller effect

The EPR lineshape of the photoinduced triplet state of C60 in frozen toluene solution was studied by pulsed EPR spectroscopy. Lineshape calculations of the triplet spectra were performed including dynamical exchange effects. The observed spectra in a glassy matrix are compatible with zero field splitting parameters ‖D1‖ = 0.0114 cm−1 (12.2 mT) and ‖E1‖ = 0.0005 cm−1 (0.5 mT). The temperature dependence of the powder lineshape was simulated using a dynamical exchange model, where the triplet principal axis jumps between all equivalent sites allowed by the D5d symmetry for the lowest excited triplet state. The determined exchange rate turned out to be only weakly temperature dependent and suggests that the dynamic process is due to tunneling between Jahn–Teller distorted states rather than to real molecular jumps. In addition we have observed a different triplet state with zero field splitting parameters ‖D2‖ = 0.0100 cm−1 (10.6 mT), ‖E2‖ = 0.0015 cm−1 (1.6 mT) after annealing of the matrix. We attribute this to a C60 dimer or, alternatively, to crystal field effects.

1H NMR and Calorimetric Measurements on Rabbit Eye Lenses

The dynamic properties of water molecules in the rabbit lens were studied by proton nuclear magnetic resonance line shape analysis, measurements of relaxation times as a function of temperature and calorimetric measurements. The experiments prove, as already suggested by other authors, that there are two types of water in the lens of rabbit eyes, namely bound unfreezable hydration water and bulk freezable water. Line shape analysis and relaxometry showed, that this two types of water exist in two different environments, which may be identified as the nucleus and the cortex of the lens. The line shape analysis showed furthermore that water molecules in the rabbit lens has a common spin lattice relaxation time (T1), but two different transverse relaxation times (T2A and T2B). The tentative model of fast water exchange on the T1 time scale and slow water exchange on the T2 time scale, was used to explain experimental proton relaxation data of the rabbit lens. An estimation for this exchange rate kex by comparing it to the relaxation times is given (T1(-1) << kex << T1(-1)). It has also been shown by a calorimetric measurements, that the lenses can be easily under-cooled to temperatures well below the freezing point of water. The achievable maximum undercooling temperature of the lens is a function of the cooling rate KC, therefore it has to be considered as an experimentally adjustable parameter which is not characteristic for the investigated sample. Thus it must be noted that any previous discussions about the specific value of the temperature of water crystallisation in biological systems need to be carefully reconsidered.

19] Characterization of enzyme-complex formation by analysis of nuclear magnetic resonance line shapes

This chapter discusses the characterization of enzyme–complex formation by analysis of nuclear magnetic resonance (NMR) line shapes. A general approach involving the analysis of NMR line shapes for obtaining chemical exchange rates is described here. The analysis requires measuring changes in line widths and peak positions as a function of ligand concentration from a simple one-dimensional spectrum. The chapter illustrates the description of the general approach with a simple kinetic scheme, followed by the description of a specific example using results from 31 P NMR of the enzyme phosphoglucomutase. A cyclic scheme for binding of a substrate analog to the mono- and di-Cd 2+ complexes of the phospho form of the enzyme is readily characterized with this method. In this system, two magnetic nuclei undergo exchange because of binding—namely, the 31 P nucleus of the ligand and that of the phosphoenzyme. Hence, additional constraints are involved; the spectral characteristics of two sets of exchange sites must be consistent with the same association–dissociation rate constants.

Electron spin resonance line-shape analysis of x-doxylstearic acid spin probes in dihexadecyl phosphate vesicles and effects of cholesterol addition

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance line-shape analysis of x-doxylstearic acid spin probes in dihexadecyl phosphate vesicles and effects of cholesterol additionPeter J. Bratt and Larry KevanCite this: J. Phys. Chem. 1993, 97, 28, 7371–7374Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/j100130a041RIGHTS & PERMISSIONSArticle Views83Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (477 KB) Get e-Alerts

Analysis of 31P nuclear magnetic resonance lineshapes and transversal relaxation of bacteriophage M13 and tobacco mosaic virus

The experimentally observed 31P lineshapes and transversal relaxation of 15% (wt/wt) M13, 30% M13, and 30% tobacco mosaic virus (TMV) are compared with lineshapes and relaxation curves that are simulated for various types of rotational diffusion using the models discussed previously (Magusin, P. C. M. M., and M. A. Hemminga. 1993. Biophys. J. 64:1851-1860). It is found that isotropic diffusion cannot explain the observed lineshape effects. A rigid rod diffusion model is only successful in describing the experimental data obtained for 15% M13. For 30% M13 the experimental lineshape and relaxation curve cannot be interpreted consistently and the TMV lineshape cannot even be simulated alone, indicating that the rigid rod diffusion model does not generally apply. A combined diffusion model with fast isolated motions of the encapsulated nucleic acid dominating the lineshape and a slow overall rotation of the virion as a whole, which mainly is reflected in the transversal relaxation, is able to provide a consistent picture for the 15 and 30% M13 samples, but not for TMV. Strongly improved lineshape fits for TMV are obtained assuming that there are three binding sites with different mobilities. The presence of three binding sites is consistent with previous models of TMV. The best lineshapes are simulated for a combination of one mobile and two static sites. Although less markedly, the assumption that two fractions of DNA with different mobilities exist within M13 also improves the simulated lineshapes. The possible existence of two 31P fractions in M13 sheds new light on the nonintegral ratio 2.4:1 between the number of nucleotides and protein coat subunits in the phage: 83% of the viral DNA is less mobile, suggesting that the binding of the DNA molecule to the protein coat actually occurs at the integral ratio of two nucleotides per protein subunit.

Dynamics of triplet fullerene-60 probed by electron paramagnetic resonance. Motional analysis in isotropic and liquid crystalline matrixes

Detailed analysis of time-resolved electron paramagnetic resonance (EPR) line shapes of photocited triplet states of C[sub 60] in isotropic and anisotropic matrices has been carried out. Two main motional models have been tested over a very wide temperature range. For most temperatures, the best fit to the experimental line shapes was obtained with a model of discrete jumps between two configurations, which can be formally defined as an exchange between the longitudinal (Z) dipolar axis and one of the two transverse axes (X,Y). This exchange process is probably related to two distorted Jahn-Teller (JT) configurations of the molecule. For very high temperatures, the best fit was obtained with a recently developed model of Brownian rotational diffusion. In the latter cases, relating to the liquid phase of the solvent, the triplets appear to be in thermal spin equilibrium, and their kinetics can be described by a special form of transient nutations. In the former cases, related to the glass and amorphous phases (toluene) or nematic phase (E-7), the triplets are clearly spin polarized. For very low temperatures the motional (jump) rate is practically temperature independent. This seems to be due to the nature of the motion, i.e., exchange between JT configurations,more » rather than actual molecular motion. 45 refs., 9 figs., 2 tabs.« less

Nuclear magnetic resonance lineshape studies of interpenetrating polymer networks

Abstract In the so-called in situ sequential interpenetrating polymer networks (IPNs), the two networks are formed after each other, and the network formed first is thought to impede gross phase separation in the final material. This is contrary to the other type of IPNs ( in situ simultaneous), in which the formation of both networks is initiated at once and proceeds to completion more or less simultaneously. In order to verify more accurately this assumption, which is not inconsistent with transmission electron microscopy findings, a solid-state nuclear magnetic resonance lineshape analysis technique has been used to investigate the degree of phase dispersion of IPNs of both types composed of an elastomeric polyurethane (PUR) (25 wt%) and a crosslinked poly(methyl methacrylate). The results confirm that such IPNs, when prepared sequentially, have a higher degree of phase dispersion than those obtained by the simultaneous synthesis method. Furthermore, in the corresponding neat PUR networks, built up from aromatic pluriisocyanate and poly(oxypropylene glycol) (POPG), the rigid crosslink points are not composed of isocyanate only, but include some oxypropylene mers; it appears that the amount of the rigidified part is the same, whatever the molecular weight of POPG.

The 9 and 33 GHz EPR Spectra of Mn 2+ impurity ions in polycrystalline calcite—Central transition

The 293 K EPR spectra of Mn 2+ impurity ions in polycrystalline natural and synthetic calcite and in the calcite impurity in various coal samples have been studied at 9.2 and 33.3 GHz. The spectra obtained at these two frequencies were found to differ dramatically. At 9.2 GHz, the lineshapes of the central transition hyperfine resonances are in good agreement with previous measurements. The 33.3 GHz EPR spectrum has some features which have not been reported previously at Mn 2+ concentrations below 1000 ppm. Computer simulation programs for both spin-Hamiltonian perturbation and diagonalization techniques were used to describe the mono- and polycrystalline spectra. It was found that the simulated spectrum using the spin-Hamiltonian diagonalization method agrees with previous 9.3 GHz monocrystal data within an error of 0.1 mT for the central transitions and of 0.13 mT for the noncentral transitions, whereas the simulation using the perturbation method had errors of 0.2 and 0.6 mT, respectively. An analysis of the polycrystalline hyperfine resonance lineshapes observed at 9.2 and 33.3 GHz for 1, 50, and 520 ppm Mn 2+ concentrations has been performed using both simulation methods. The hyperfine resonance lineshapes observed at 9.2 GHz are due to the magnetic field angular variation caused by the axial zero field splitting (ZFS) term C 0 2( S). The hyperfine resonance lineshapes observed at 33.3 GHz are shown to be due to the combined effect of A-tensor and g-tensor anisotropy, the axial ZFS, and the spin-spin interaction. The Mn 2+ impurity ion EPR spectrum observed in an Alberta coal and several Argonne coal samples is shown, using lineshape analysis, to originate from their calcite mineral impurity. The lineshape broadening observed in coal samples is characteristic of a strong spin-spin interaction and may be due to interactions with the free radicals and other impurity ions as well as between Mn 2+ ions.

Electron spin resonance line shape analysis of x-doxylstearic acid spin probes in dioctadecyldimethylammonium chloride vesicles

Electron spin resonance spectra of a serien of x-doxylstearic acids (x=5, 7, 10, 12, and 16) solubilized in cationic dioctadecyldimethylammonium chloride vesicles were recorded over 298-328 K and analyzed by employing spectral line simulation. The spectra from the vesicle phase are well reproduced by using the miaoncopic order-macroncopic disorder model of Freed and co-workers with Brownian rotational diffusion

Electron paramagnetic resonance lineshape analysis of small and large probes introduced into micellar aqueous solutions of ammonium pentadecafluorooctanoate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron paramagnetic resonance lineshape analysis of small and large probes introduced into micellar aqueous solutions of ammonium pentadecafluorooctanoateSandra Ristori and Giacomo MartiniCite this: Langmuir 1992, 8, 8, 1937–1942Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://doi.org/10.1021/la00044a010RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (641 KB) Get e-Alerts Get e-Alerts

Magnetic resonance studies of ammonia adsorption and decomposition on titania-supported vanadia catalysts

In-situ proton and deuterion single-resonance NMR techniques were used to study the adsorption and decomposition of ammonia as a function of temperature on a series of V{sub 2}O{sub 5}/TiO{sub 2} catalysts with the weight loading of vanadia ranging from 0 to 6.1 wt % (approximately one monolayer). After analysis of magnetic resonance line shapes, several different molecular species were found to be present on the catalyst surfaces. At low adsorption temperatures on the low-loading samples, the predominant adsorbed species was intact, coordinated ammonia rotating about its C{sub 3} axis. As the weight loading or adsorption temperature was increased, the adsorbed, intact ammonia exhibited an increased H-N-H angle; the total number of protons associated with intact ammonia per gram of sample decreased. At the point where intact ammonia was no longer observed, a new species was observed and assigned to NH{sub 2} moieties. On all samples, ammonium ions were observed at low adsorption temperatures (100{degrees}C) but were found to be easily removed by heating. Their concentration was greater on the higher weight loading samples. The formation of short-lived VOH groups from the protons of dissociated NH{sub 3} was inferred on the higher weight loading samples. Multiple-quantum spin-counting experiments were done tomore » further investigate the nature of the adsorbed species and their groupings on the surfaces. 45 refs., 12 figs., 2 tabs.« less

Intramolecular rearrangements studied by two-dimensional nuclear magnetic resonance line shape analysis

The usual theory of nuclear magnetic resonance (NMR) line shapes in the presence of molecular rearrangements has been extended to two-dimensional (2D) NMR in liquids using an explicitly superoperator formalism. Advantages of the proposed 2D method include a clearer ‘‘signature’’ for the presence of a chemical reaction (even at a single temperature), peak shapes providing more information about the underlying NMR parameters, and (in favorable cases) the presence of off-diagonal peaks with characteristic shapes which can be analyzed even in cluttered spectra. Detailed calculations are shown for a single spin 1/2 and for a group of two strongly coupled spins 1/2, jumping between two different spin Hamiltonians. The agreement between the predicted peak shapes and the corresponding experimental results on simple molecules is excellent.

14] Nuclear magnetic resonance line-shape analysis and determination of exchange rates

The fact that chemical exchange processes occur at rates that cover a broad range and produce readily detectable effects on the spectrum is one of the attractive features of high-resolution NMR. The description of these line shapes in the presence of spin-spin coupling requires the density matrix theory which is rather complex. Analysis of the line shapes usually needs computer simulations and is capable of providing reliable information on the exchange rates as well as spectral parameters in the absence of exchange. Simplified procedures, ignoring spin-spin coupling, often result in deviations in these exchange and spectral parameters determined. A step-by-step procedure is detailed in this chapter for setting up the matrices required for computing the line shapes of exchanges involving weakly coupled spin systems on the basis of the density matrix theory without the need for a detailed understanding of the theory. A knowledge of the energy level structure and allowed transitions in the NMR spectra of the individual weakly coupled spin systems is all that is required. The procedure is amenable to numerical computation. The group of illustrative examples chosen to demonstrate the development of the computational tools cover some of the commonly encountered cases of exchange from simple systems to rather complex ones. Such exchanges occur frequently in biological molecules, especially those involving enzyme-substrate complexes. In cases where the experimental line shapes are obtained with respectable precision, and the relevant exchange processes are unambiguously identifiable, the computer simulation method of line-shape analysis is capable of providing useful and incisive information. The example of the 31P exchanges in the adenylate kinase is illustrative of this point. Not only has the line-shape analysis clearly indicated the role of the interchange process, but it has also produced evidence that the rates of interchange of the ADP molecules bound to the enzyme become relevant to the kinetics and mechanism of catalysis by this enzyme. It is probably difficult to obtain this information by any other experimental method or by any other method of analysis.

Notes. Exchange kinetics of gold(I) phosphine complexes by nuclear magnetic resonance line shape analysis

The 31P-{1H} n.m.r. spectra of [NEt4][AuBr2] with various amounts of the ligands PPhMe2 or PBun3 were studied at different ratios in CD2Cl2 solutions. The solutions show the presence of species having one, two, and three co-ordinated phosphine ligands (four in the case of PBun3), and these species exchange with one another at elevated temperatures. The entropies of activation (ΔS‡) for these processes are negative and the mechanism of exchange is thus associative in all cases.

Fluorine-19 nuclear magnetic resonance investigation of fluorine-19-labeled phospholipids. 1. A multiple-pulse study.

A multiple-pulse nuclear magnetic resonance technique has been used to measure the order parameter, SFF, at 40 MHz for dimyristoylphosphatidylcholine labeled with a difluoromethylene group at the 4-, 8-, or 12-position of the sn-2-acyl chain dispersed in water in the liquid-crystalline phase. The Carr-Purcell-Meiboom-Gill multiple-pulse sequence can resolve the homonuclear dipolar coupling between the two fluorine nuclei, thus making a direct determination of the order parameter, SFF, for the F-F internuclear vector possible. Other interactions, such as the 19F chemical shift anisotropy, heteronuclear dipolar couplings, and field inhomogeneity, which normally obscure the dipolar splitting, are effectively canceled. The order parameters obtained in this work compare well with those obtained by 19F nuclear magnetic resonance line-shape analysis of the 19F-labeled phospholipids reported in the following paper [Dowd, S. R., Simplaceanu, V., & Ho, C. (1984) Biochemistry (following paper in this issue)] as well as comparable SCD order parameters, determined for the deuterium-carbon internuclear vector of deuterium-labeled phospholipids [Oldfield, E., Meadows, M., Rice, D., & Jacobs, R. (1978) Biochemistry 17, 2727-2740]. The present results clearly show the usefulness of using nuclear magnetic resonance spectroscopy to investigate lipid-lipid and protein-lipid interactions, especially for those systems containing a difluoromethylene group in the acyl chain of a phospholipid molecule.