Difference In Linewidth Research Articles

Conformationally specific misfolding of an integral membrane protein.

Membrane protein misfolding is related to the etiology of many diseases, but is poorly understood, particularly from a structural standpoint. This study focuses upon misfolding of a mutant form of diacylglycerol kinase (s-DAGK), a 40 kDa homotrimeric protein having nine transmembrane segments. Preparations of s-DAGK sometimes contain a kinetically trapped misfolded population, as evidenced by lower-than-expected enzyme activity (with no accompanying change in substrate K(m)) and by the appearance of a second band in electrophoresis gels. Misfolding of s-DAGK may take place during cellular overexpression, but can also be reproduced using the purified enzyme. TROSY NMR spectra of s-DAGK as a 100 kDa complex with detergent micelles exhibit a single additional set of resonances from the misfolded form, indicating a single misfolded conformational state. The relative intensities of these extra resonances correlate with the percent reduction in enzyme activity below the maximum observed for fully folded s-DAGK. Misfolded s-DAGK exhibits a modest difference in its far-UV CD spectrum compared to the folded enzyme, consistent with a small degree of variance in secondary structural content between the two forms. However, differences in NMR chemical shift dispersion and temperature-dependent line widths exhibited by folded and misfolded s-DAGK support the notion that they represent very different structural states. Cross-linking experiments indicate that both the correctly folded enzyme and the kinetically trapped misfolded form are homotrimers. This work appears to represent the first documentation of conformationally specific misfolding of an integral membrane protein.

Morphological Partitioning of Ethylene Defects in Random Propylene−Ethylene Copolymers

A series of four propylene/ethylene, metallocene-catalyzed random copolymer samples, with ethylene mole fractions ranging from 0.8% to 7.5% and melt crystallization histories of cooling at 1 °C/min, were studied by 13C solid-state NMR techniques. The principal objective of the study was to determine the partitioning of the ethylene “defect” residues within the semicrystalline morphology of these isotactic poly(propylene/ethylene) copolymers. Signals from the crystalline (CR) and the noncrystalline (NC) regions were separated on the basis of contrasting T1ρH behaviors. Four new resonances, three distinct and one strongly overlapping, were identified in the spectrum of the CR regions. The assignment of these new defect resonances to specific carbons at or near the ethylene defect site was made principally on the basis of quantum mechanical chemical shift calculations. These calculations were performed on two methyl-terminated oligomers of about 6.5 monomers in length with a 31 helical backbone conformation, characteristic of the iPP backbone conformation in the CR state. One oligomer was the pure iPP chain, and the other contained one centrally located ethylene repeat unit. Good agreement between the experimental shifts associated with the ethylene defect and the computed shifts supported the assumption that the chain conformation in the CR regions in the vicinity of the ethylene defect remained a 31 helix. This good agreement between shifts was obtained when the computed shifts were not used directly, but used in a difference mode. This mode was based on the computed shift differences for corresponding carbons on the two oligomers where these differences were applied to the experimental shifts of the main iPP peaks with the same chemical identity. The assignment of the defect resonances, along with the loss of chemical shift equivalences seen in solution-state spectra, was also rationalized in the context of γ-gauche and vicinal−gauche interactions as applied to the 31 helical structure. Defect line width differences that parallel the line width differences of the main iPP resonances also aid in assigning the defect resonances to particular types of carbons. Over the range of ethylene concentrations studied herein, the partitioning coefficient, PCR(eth), given by the ratio of the concentration of ethylene residues in the CR region to the sample-average concentration of ethylene residues, is found to be constant, taking a value of 0.42 with a standard uncertainty of 0.03. On the basis of measurements of the NMR crystallinities, this partitioning translates to a fraction of the total ethylene residues in CR regions ranging from 0.24 to 0.30 and an average concentration of ethylenes in the NC region about twice the overall concentration. We also looked for evidence that the ethylene residues become highly concentrated at the CR/NC interface. While we cannot say whether this is happening on the NC side of the interface, since we cannot identify any NC defect resonances, we can claim that a high concentration of ethylene residues is not found on the CR side near the interface.

Improved accuracy in composition measurement by atomic fluorescence

Two methods are considered for correcting for scattered light in atomic fluorescence. The first uses the emission line broadening in a single hollow-cathode source together with the absorption in the high-frequency discharge within the quartz envelope. The second uses the differences in emission line width for the hollow-cathode lamp between the start and the end of the exciting current pulse.

Spectroscopic Studies of Liquid Crystals Confined in Sol-gel Matrices

AbstractThermotropic liquid crystals (5CB and 8CB) were confined in silica porous matrices (xerogels and xero-aerogels) with different pore sizes. The structure and dynamics of confined liquid crystals were studied by Raman spectroscopy and Nuclear Magnetic Resonance. In Raman, the frequency of the CN stretching peak is a good probe of the smectic_A-crystal phase transition. The CN peak is observed to split upon quenching. This suggests a coexistence of crystalline and supercooled liquid phases for confined LC which was not observed in the bulk. In NMR, strong differences in both chemical shifts and linewidths are observed in confinement with respect to the bulk. We present a model which analyses the changes in the spectra in terms of changes of the order parameter and molecular dynamics for the confined LC.

Tunable continuous wave DFG-based gas sensor using fibre amplified 1.5 [micro sign]m external cavity diode laser and high power 1 [micro sign]m diode laser

A novel compact, room-temperature mid-infrared difference frequency generation (DFG)-based trace gas sensor based on direct absorption spectroscopy is reported. Tunable, narrow linewidth difference frequency radiation from 3.3 to 3.5 µm is generated in periodically poled lithium niobate at power levels of > 4 µW. The output from an external cavity diode laser, amplified up to 20 dBm by an erbium-doped fibre amplifier is used as the signal source. A 500 mW α-DFB diode laser at 1066 nm serves as the DFG pump source. This sensor has been applied to real time trace gas detection of CH4 and H2CO.

Comparison of dynamics of Eu 3+ in different Y 2O 3 nanostructured materials and with sol–gel produced SiO 2 glass

Transient hole burning due to population redistribution among the hyperfine levels was studied in Y 2O 3 : Eu 3+ nanocrystals produced both by laser evaporation and by sol–gel techniques. The hole line widths in the two samples exhibit a very different temperature dependences. It appears that while the dynamics of the laser–produced nanocrystals is dominated by electron–phonon interactions with the size-restricted normal modes of the nanoparticles, the dynamics of the sol–gel produced nanostructured material is controlled by the some other mechanism, e.g. disorder. Persistent spectral hole burning and fluorescence line narrowing experiments were performed on sol–gel produced SiO 2 glass containing Y 3+ and Eu 3+. While the spectral and temperature dependencies of the hole width are similar to that found in regular glass, the line width is some ∼30 times larger, suggesting that in sol–gel produced glass the dynamical effects of the two-level systems are much stronger than in regular glass. The difference in homogeneous line width measured by hole burning and fluorescence line narrowing suggests the presence of spectral diffusion in this system.

Persistent spectral hole burning and fluorescence line-narrowing studies of theEu3+linewidth in sol-gel producedSiO2glass

Persistent hole burning and fluorescence line narrowing experiments were performed on the ${}^{7}{F}_{0}{\ensuremath{-}}^{5}{D}_{0}$ transition of ${\mathrm{Eu}}^{3+}$ ions in sol-gel produced ${\mathrm{SiO}}_{2}$ glass samples of different composition and annealed at different temperatures. The persistent hole burning is ascribed to a photophysical mechanism. The spectral and temperature dependencies of the hole width are similar to that in regular glass, whereas the linewidth is some \ensuremath{\sim}30 times larger. The difference in linewidth measured by hole-burning and fluorescence line narrowing suggests the presence of spectral diffusion in the system. The experimental results show that in sol-gel produced glass the dynamical effects of the two-level systems are much stronger than in regular melt-produced glasses.

Optically detected magnetic resonance studies of nanostructured PPV-composites

We used the spectroscopic technique of photoluminescence detected magnetic resonance (PLDMR) to monitor the dynamics of singlet excitons as well as polarons of isolated poly(p-phenylenevinylene) (PPV) chains incorporated into a self-assembled matrix, ordered at a nanometer scale, and compare it with the results obtained for bulk PPV. The isolation of the PPV chains in the inorganic matrix which is of hexagonal structure is confirmed by a blue shift of the photoluminescence (PL) spectrum and the increase of the PL quantum yield. The effect on the photo physical properties due to the isolation of the polymer chains is further proved by the difference in the PLDMR linewidth and the observation of a strong difference in the exponent in power-law dependence of ΔPL/PL on the laser power.

Angle dependence of the ferromagnetic resonance linewidth and two magnon losses in pulsed laser deposited films of yttrium iron garnet, MnZn ferrite, and NiZn ferrite

Shorted waveguide ferromagnetic resonance (FMR) measurements were made at 9.5 GHz for pulsed laser deposited yttrium iron garnet (YIG), MnZn ferrite, and NiZn ferrite films with thicknesses of 1.8, 0.5, and 1.5 μm, respectively. The FMR field versus the field angle confirmed the operational assumption of a uniform mode response. For the YIG, the linewidth was 10 Oe when the external field and magnetization vectors were perpendicular to the disk (perpendicular FMR) and increased smoothly to a maximum value of 27 Oe when the field and magnetization were in the film plane (parallel FMR). For the MnZn, the linewidth was 49 Oe at perpendicular FMR, increased with the angle between the film normal and the external field to a broad maximum of 80 Oe at 35°, and then dropped to 65 Oe at parallel FMR. For the NiZn, the linewidth was 310 Oe at perpendicular FMR, increased with the field angle to a broad maximum of 1530 Oe at 45°, and then dropped to 960 Oe at parallel FMR. The linewidths were larger than predicted for reasonable values of the Landau–Lifshitz damping and showed angle dependences which indicated nonintrinsic contributions to the loss. Two magnon scattering was used to model these linewidth differences. The angle dependences of the excess linewidths show qualitative agreement with the two magnon predictions, with inhomogeneity sizes in the submicron range and volume fractions below 1%.

Anisotropic hyperfine field fluctuation in La/sub 0.67/Ca/sub 0.33/Mn/sub 0.99/Fe/sub 0.01/O/sub 3/

Colossal magnetoresistance (CMR), Mossbauer spectra and neutron diffraction of the iron-doped manganite, La/sub 0.67/Ca/sub 0.33/Mn/sub 0.99//sup 57/Fe/sub 0.01/O/sub 3/, have been studied. The crystal structure is found to be cubic perovskite with the lattice parameter a/sub 0/=3.868 /spl Aring/. It is notable that the Curie temperature, T/sub C/=270 K, line broadening and 1,6 and 3,4 linewidth difference appear to suggest anisotropic hyperfine field fluctuation. The temperature dependence of the effective anisotropy energy is also found to decrease rapidly with increasing temperature.

H13CO+and CH3OH Line Observations of Prestellar Dense Cores in the TMC‐1C Region

We have mapped the entire TMC-1C region in the H13CO+ (J = 1-0) and CH3OH (JK = 20-10A+) lines at a grid spacing of 50'' with the 45 m telescope at Nobeyama Radio Observatory. We have also conducted high spatial resolution mapping observations of the TMC-1C region at a grid spacing of 34'' in both lines toward a 6' × 6' portion in the south and a 4' × 4' portion in the north. We found that the structure of TMC-1C is filamentary in both molecular lines. The size and position angle of the filament are 0.75 pc × 0.17 pc and 135°, respectively. The filament consists of dense (~105 cm-3) cores which are traced by either H13CO+ or CH3OH lines. We found that the distribution of cores seen in H13CO+ is quite different from the distribution of cores seen in CH3OH. The large velocity gradient analyses indicate that this difference is a result of the relative abundance variation between H13CO+ and CH3OH in the cores by about 1 order of magnitude. We have also carried out multitransitional observations of C3H2 (JK',K'' = 21,2-10,1 and 31,2-30,3) at two positions in the same cloud in order to estimate the molecular hydrogen densities for H13CO+ and CH3OH cores and found that the densities are around 105 cm-3 for both cores. These starless cores (no IRAS source), considered to be prestellar cores, seem to be at chemically different evolutionary stages; the H13CO+ cores are more evolved and closer to protostar formation than CH3OH cores. On the other hand, we found no difference in physical properties, i.e., the size, line width, and mass, between H13CO+ and CH3OH cores; the averages are about 0.07 pc, 0.3 km s-1, and 2 M☉, respectively.

Electron-phonon coupling in the metallic elements Al, Au, Na, and Nb: A first-principles study

We present an ab initio study of the electron-phonon coupling in some monatomic fcc and bcc metals. We employed a linear-response approach based on density-functional theory in the plane-wave pseudopotential representation to evaluate the phonon dispersion curves of Al, Au, Na, and Nb. We then studied the nonadiabatic behavior of the considered metals by determining the phonon linewidths due to the electron-phonon coupling and the Eliashberg and transport spectral function. We especially focused on the relevance of the different types of metallic bonds for these properties. We found remarkable differences in the phonon linewidths and spectral functions of elements with the same crystal structure, which is a subtle and important consequence of the different electronic structures. Finally, the spectral functions have been used to calculate the temperature dependence of the electrical and thermal resistivity. We compare our results to experimental data where available.

A study of dissolution characteristics and acid diffusion in chemically amplified DUV resist

The effects of dissolution characteristics and acid diffusion behavior on lithographic performance were evaluated in tert-butoxycarbonyl (t-BOC)-protected chemically amplified positive deep-ultraviolet (DUV) resists. The resists consisted of t-BOC-protected polyhydroxystyrene as a base resin and 2,4-dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). In particular, the line width difference between an isolated line and a dense line (iso/dense bias) was investigated by changing the post-exposure bake (PEB) temperature. As a result, clear relationships among dissolution characteristics, acid diffusion length, and iso/dense bias were obtained. Moreover, suitable dissolution characteristics and acid diffusion length for reducing iso/dense bias were clarified.

High-resolution angle-resolved photoemission from Cu(610)

Cu(610) has a mean terrace width of six atoms. Although the regular arrangement of steps was verified by SPALEED, no step-induced surface umklapp process could be identified in UPS spectra taken with HeI radiation. This fact allows an easy comparison with results from Cu(100). In particular, we demonstrate that the final state wave vector can be determined by triangulation using exclusively the Cu(610) surface, since equivalent k-space points contribute at different electron emission angles. However, spectra from equivalent points exhibit differences in the UPS linewidth and this gives additional information on the final state lifetime. Finally we discuss the modification of a Tamm state [its analogue is observed at M ̄ on the (100) surface] due to confinement by the steps.

Electron Spin Resonance, Electron-Nuclear Double Resonance and General Triple Resonance Studies on the Contributions to Line Broadening of CO2- in A-type Carbonated Apatites and Biocarbonates

Electron spin resonance (ESR), electron-nuclear double resonance (ENDOR) and general triple resonance were combined to study linewidth differences observed in the ESR spectra of CO2- species in calcium carbonate and carbonated apatite. In the latter compound, the motion and a distribution of g-factors (g-strain) are dominant contributions to the observed linewidth. The linewidth temperature behavior follows previous models for CO2- rotating in calcite. In apatite, these radicals rotate more freely and movement is not restricted to gxx-gzz plane. In carbonates theoretical fit of the linewidth at 9.5 and 34.0 GHz shows the existence of two orthorhombic spectra with slightly different g values and linewidths, which contribute to the observed linewidth difference between narrow and broad line species. Superhyperfine interactions with protons of water molecules, located probably near the second and the third nearest neighbor lattice sites, are responsible for minor contributions to line broadening of CO2- spectrum.

The effect of off-resonance radio frequency pulse saturation on fMRI contrast

This paper describes the use of off-resonance saturation to further manipulate the blood oxygenation level dependent (BOLD) contrast of fMRI. A customized narrow bandwidth radiofrequency pulse, applied with a range of frequency offsets prior to selection of each slice, was designed and incorporated into a gradient echo EPI sequence. This application takes advantage of the resonance frequency and linewidth differences between the oxygenated and deoxygenated state of blood in human brain during task activation and rest, and is capable of creating an enhancement in the contrast of the BOLD effect. Because of a possible contribution to the signal change from cerebro-spinal fluid, which has a much narrower linewidth and smaller frequency shift compared with the brain tissue, data were also collected using a nulling inversion pulse. The inversion pulse was applied before the off-resonance pulse and data acquisition to eliminate the CSF signal. Functional areas are thus more localized to the brain tissue.

Angle dependence of the ferromagnetic resonance linewidth in easy-axis and easy-plane single crystal hexagonal ferrite disks

Ferromagnetic resonance measurements were made as a function of the static external field angle for c-plane disks of single crystal flux grown manganese substituted barium M-type (Ba-M) and zinc Y-type (Zn-Y) hexagonal ferrites at 50 and 8.8 GHz, respectively. A shorted waveguide technique was used. Analysis of the FMR field versus angle results confirmed the operational assumption of a uniform mode response. For the easy-axis Ba-M disk, the linewidth was 69 Oe when the external field and magnetization vectors were perpendicular to the disk. The linewidth increased to a maximum measured value of 472 Oe when the magnetization was directed 45.4° from the sample normal. For the easy-plane Zn-Y disk, the linewidth had a minimum value of 18 Oe when the field and magnetization vectors were in-plane. The maximum linewidth was 391 Oe when the magnetization was directed 25.2° from the disk normal. The linewidths were larger than predicted for reasonable values of the Landau–Lifshitz damping and showed angle dependences which indicated nonintrinsic contributions to the loss. A modified two magnon scattering calculation based on the model of Sparks, Loudon, and Kittel was used to investigate these linewidth differences. The calculation included anisotropy modifications to the spin wave band for each material. The angle dependences of the excess linewidths show qualitative agreement with the two magnon predictions, with inhomogeneity sizes on the order of 1 and 0.25 μm and volume fractions of 0.01 and 0.005 for the Ba-M and Zn-Y disks, respectively.

Stark broadening observations for a cool, dense plasma

The impact-broadened linewidth of the Al II 467-nm line is compared with theory for ions embedded in plasma dense enough that the impact approximation becomes questionable, and where electron-electron correlations may be non-negligible. No significant difference in linewidth is found for plasmas in which the plasma parameter g is as large as 0.8.

Spectral parameters for quantitative mobility contrast in NMR imaging of solid polymers

Different procedures based on parameters of the wideline NMR absorption spectrum are presented to obtain localized molecular mobility contrast for imaging of solid polymers. For this purpose a 1H-NMR imaging technique with magic sandwich echoes is used for acquiring localized wideline spectra. With samples composed of polystyrene and high impact strength polystyrene, and polycarbonate and low density polyethylene a spatial difference in NMR absorption spectrum lineshape and linewidth is displayed. Furthermore, the spatial distribution of rigid and mobile domains in a heterogeneous polymer can be derived from the NMR spectral components. It is demonstrated that a van Vleck moment analysis can be performed from spatially resolved magic echo decays. The second ( M 2) and fourth ( M 4) moments of the rigid components show considerable variation with the spatial composition of the investigated samples.

Metal-ion binding properties of the transferrins: A vanadium-51 NMR study

Transferrins can bind a wide range of di- and trivalent metal ions. They have a bilobal structure where each domain contains a deep cleft that binds a metal ion along with a synergistic anion. In this work, the binding of vanadate as VO 2 + to the transferrins was studied by 51V quadrupolar central transition (QCT) NMR. Information about differences in the symmetry and motion of the bound metal ion was obtained from chemical shift and line width differences for serotransferrin (sTf), lactoferrin (lTf), and ovotransferrin (oTf). The effects of pH, ionic strength, and temperature on the 51V QCT NMR spectra of the bound VO 2 + cations showed that the N-lobe binding site of sTf is unique as compared to the other proteins. Properties of the quadrupolar central transition were also investigated, revealing that temperature, magnetic field strength, and NMR pulse angle all induce predictable changes on the second-order dynamic frequency shift, spectral line width, and optimal pulse angle in the 51V NMR spectra. Analysis of NMR spectra of V(V) 2-oTf and V(V) 2-sTf at three magnetic fields allowed an estimation of the quadrupolar coupling constants for these binding sites. This indicates that the degree of coordination symmetry in the binding sites is as follows: sTf N < sTf C < oTf N, C. Carbon-13 NMR studies revealed that VO 2 + binding, in contrast to di- and trivalent metal ions, has no requirement for a synergistic anion.