Proton Line Research Articles

Neutron single-particle states populated via proton emission from146Tmand150Lu

Proton emission from the odd-odd nuclei ${}^{146}\mathrm{Tm}$ and ${}^{150}\mathrm{Lu}$ has been reinvestigated by means of the recoil mass spectrometer. In the ${}^{146}\mathrm{Tm}$ study, the strongest proton transitions at 1.12 MeV and at 1.19 MeV have been assigned to the decay of ${}^{146m}\mathrm{Tm}$ ${(T}_{1/2}=200\ifmmode\pm\else\textpm\fi{}10\mathrm{ms})$ and to the ${}^{146gs}\mathrm{Tm}$ decay ${(T}_{1/2}=80\ifmmode\pm\else\textpm\fi{}10\mathrm{ms}),$ respectively. Three new proton lines were identified at 0.89 MeV, 0.94 MeV, and 1.01 MeV. The observed decay pattern has been interpreted by using spherical estimates of emission probabilities. The decays of ${}^{146m,gs}\mathrm{Tm}$ to the $\ensuremath{\nu}{s}_{1/2}$ ${}^{145}\mathrm{Er}$ ground state and to excited neutron states originating from the $\ensuremath{\nu}{h}_{11/2}$ orbital are reported. This work represents the first observation of fine structure in proton emission from an odd-odd nucleus. In the ${}^{150}\mathrm{Lu}$ study, the proton energy and half-life values of ${E}_{p}=1277\ifmmode\pm\else\textpm\fi{}8\mathrm{keV}$ and ${T}_{1/2}{=39}_{\ensuremath{-}6}^{+8}\ensuremath{\mu}\mathrm{s}$ for the decay of ${}^{150m}\mathrm{Lu}$ were obtained with better precision, but no evidence for fine structure in the proton emission was found.

Selective polarization inversion of protons in rotating solids

The selective inversion of lines under phase modulated Lee–Goldburg (PMLG) decoupling in MAS proton spectroscopy is demonstrated. Short pulses inserted between consecutive PMLG irradiation intervals selectively invert the polarization of an on-resonance line while sustaining a high resolution proton evolution. The pulse scheme is combined with windowed-PMLG detection to obtain a one-dimensional high resolution spectrum with one of the proton lines inverted. Initial preparation of the protons in selectively inverted states can be used to follow the flow of polarization during spin diffusion. Examples of proton–proton spin exchange in alanine and histidine are demonstrated. Selective inversion is also used in conjunction with proton carbon LG-cross-polarization to achieve carbon spectra with lines characterized by different polarization states.

Centroid theory of transverse electron-proton two-stream instability in a long proton bunch

This paper presents an analytical investigation of the transverse electron-proton ($e\mathrm{\text{\ensuremath{-}}}p$) two-stream instability in a proton bunch propagating through a stationary electron background. The equations of motion, including damping effects, are derived for the centroids of the proton beam and the electron cloud by considering Lorentzian and Gaussian frequency spreads for the particles. For a Lorentzian frequency distribution, we derive the asymptotic solution of the coupled linear centroid equations in the time domain and study the $e\mathrm{\text{\ensuremath{-}}}p$ instability in proton bunches with nonuniform line densities. Examples are given for both uniform and parabolic proton line densities.

V34I and V34A substitutions within the factor XIII activation peptide segment (28-41) affect interactions with the thrombin active site

In the blood coagulation cascade, thrombin helps activate Factor XIII by cleaving the Factor XIII Activation Peptide at the R37-G38 peptide bond. The common polymorphism V34L yields a Factor XIII that is more easily activated than the wildtype enzyme. Peptides based on the Factor XIII (28-41) ((28)TVELQGVVPRGVNL(41)) sequence serve as an important model system for evaluating how to regulate thrombin activation of Factor XIII and subsequently fibrin clot character. Kinetic and NMR (1D proton line broadening and 2D transferred NOESY) studies have revealed that the P(4)-P(1) region of the activation peptides is critical for binding to the thrombin surface. These results have led to an interest in exploring two new mutations at the P(4) position including V34I and V34A. The V34I peptide was found to have the lowest K(m) of the peptides studied. However, unlike the V34L peptide, there are no P(4) to P(2) interactions observed in the transferred NOESY spectrum. The Leu thus promotes a bound conformation that cannot be achieved with the similar amino acid Ile. The V34A peptide exhibited a decrease in K(m) but also a substantial decrease in k(cat). With this smaller amino acid, 1D proton line broadening NMR studies indicate that further contact of the Q32 residue with the thrombin surface is now possible. From these studies, valuable kinetic and structural information is being obtained to characterize interactions between thrombin and the Factor XIII activation peptide.

Prompt proton decay scheme of (59)Cu.

Five prompt proton decay lines have been identified between deformed states in (59)Cu and three spherical states in (58)Ni by means of high-resolution in-beam particle-gamma gamma coincidence spectroscopy. The GAMMASPHERE array coupled to dedicated ancillary detectors including four Delta E-E silicon strip detectors was used to study high-spin states in (59)Cu. The multiple discrete proton lines are found to probe the wave functions of states in the decay-out regime of well- and superdeformed states.

Towards high-resolution 1H-NMR in biological membranes: magic angle spinning of bicelles

Proton line narrowing in biomembranes spun at the magic angle, for spinning speeds greater than 7 kHz, was investigated in two ways: increasing the field strength from 200 to 800 MHz and changing the membrane fluidity. The resolution that one can obtain on natural lipid membranes under the form of liposomes is 0.019 ppm at 800 MHz. On the other hand, spinning bicelles (disk-like model membranes made of synthetic long and short chain lipids) at the magic angle decreases the line width by an additional factor of 3 provided the bicelle is subjected to large orientational disorder. This leads to proton line widths of the order of 6 Hz at 500 MHz. The conjunction of high field, magic angle spinning and use of bicelle membranes should prove to be useful to solve membrane protein structure in a membrane environment.

NMR Studies of the Structure and Dynamics of Polymer Gels Based onN-Isopropylacrylamide (NiPAAm) and Methacrylic Acid (MAA)

A series of copolymer gels and interpenetrating networks (IPN) based on N-isopropylacrylamide (NiPAAm) and methacrylic acid (MAA) were synthesized and subsequently investigated by magic angle spinning 1H MAS, cross polarization 13C CP-MAS and pulse-saturation transfer 13C PST-MAS NMR. The structure of the interpenetrating networks is compared to that of the copolymer gels with the same composition. The study of the proton lines reveals low mobility of the chains in the copolymer gels and IPN with higher concentration of MAA, whereas those which are predominantly N iPAAm show higher mobility and therefore narrower proton lines. 13C CP-MAS revealed an interaction between the components of the IPNs. The PST-MAS technique was utilized to study the structure of the polymers in the gel phase. Copolymer gels exhibit some additional peaks in the carbonyl region due to the new chemical environment in the stereoregular sequences. In order to assure assignment, uncrosslinked copolymers with similar compositions as the copolymer gels were synthesized for comparative purposes and examined by conventional solution-state 13C NMR. A linear homopolymer of N iPAAm was synthesized inside of a P(MAA) gel. The polymer was extracted after the completion of the reaction and characterized by solution 13C NMR. About 24% of this P(N iPAAm) homopolymer could not be extracted presumably because of a strong hydrogen bonding or partial topological constrains. In the 13C NMR spectrum a new signal appeared in the carbonyl region due to MAA monomeric units. It may correspond to the methacrylic carbonyls interacting by hydrogen bonds with the amide groups.

Thrombin hydrolysis of V29F and V34L mutants of factor XIII (28-41) reveals roles of the P(9) and P(4) positions in factor XIII activation.

In blood coagulation, thrombin helps to activate factor XIII by cleaving the activation peptide at the R37-G38 peptide bond. The more easily activated factor XIII V34L has been correlated with protection from myocardial infarction. V34L and V29F factor XIII mutant peptides were designed to further characterize substrate binding to thrombin. HPLC kinetic studies have been carried out on thrombin hydrolysis of FXIII activation peptide (28-41), FXIII (28-41) V34L, FXIII (28-41) V29F, and FXIII (28-41) V29F V34L. The V34L mutations lead to improvements in both K(m) and k(cat) whereas the V29F mutation primarily affects K(m). Interactions of the peptides with thrombin have been monitored by 1D proton line broadening NMR and 2D transferred NOESY studies. The results were compared with previously published X-ray crystal structures of thrombin-bound fibrinogen Aalpha (7-16), thrombin receptor PAR1 (38-60), and factor XIII (28-37). In solution, the (34)VVPR(37) and (34)LVPR(37) segments of the factor XIII activation peptide serve as the major anchor points onto thrombin. The N-terminal segments are proposed to interact transiently with the enzyme surface. Long-range NOEs from FXIII V29 or F29 toward (34)V/LVPR(37) have not been observed by NMR studies. Overall, the kinetic and NMR results suggest that the factor XIII activation peptide binds to thrombin in a manner more similar to the thrombin receptor PAR1 than to fibrinogen Aalpha. The V29 and V34 positions affect, in different ways, the ability of thrombin to effectively hydrolyze the activation peptide. Mutations at these sites may prove useful in controlling factor XIII activation.

Solid-State Proton NMR Characterization of Ethylene Oxide and Propylene Oxide Random and Block Copolymer Composites with Poly(methyl silsesquioxanes)

Solid-state proton NMR with fast magic-angle sample spinning has been used to study the structure and dynamics of block and random ethylene oxide/propylene oxide copolymers in the bulk and as 30 wt % composites with poly(methyl silsesquioxane) which are precursors to nanoporous ultralow dielectric constant films. The NMR results for the bulk diblock copolymer show that the propylene oxide block is relatively mobile and the proton line widths are effectively narrowed with 12 kHz magic-angle sample spinning, while most of the signals for the semicrystalline ethylene oxide block are too broad to be observed under these conditions. Both the ethylene oxide and propylene oxide signals are observed in the 30 wt % composite, demonstrating that the formation of crystalline domains in the ethylene oxide block is inhibited in the composite. Dipolar filter NMR experiments show that the propylene oxide is less mobile than the ethylene oxide in the block copolymer composites, suggesting that the propylene oxide is near...

NMR study of the molecular nanomagnet[Fe8(N3C6H15)6O2(OH)12]⋅[Br8⋅9H2O]in the high-spin magnetic ground state

The magnetic molecular cluster $[{\mathrm{Fe}}_{8}({\mathrm{N}}_{3}{\mathrm{C}}_{6}{\mathrm{H}}_{15}{)}_{6}{\mathrm{O}}_{2}(\mathrm{OH}{)}_{12}{]}^{8+}[{\mathrm{Br}}_{8}\ensuremath{\cdot}9{\mathrm{H}}_{2}\mathrm{O}{]}^{8\ensuremath{-}},$ in short Fe8, has been investigated at low temperature by ${}^{1}\mathrm{H}$-NMR and relaxation measurements. Some measurements of ${}^{2}\mathrm{D}$-NMR in partially deuterated Fe8 clusters will also be reported. Upon decreasing temperature the NMR spectra display a very broad and structured signal which is the result of the internal local fields at the proton sites due to the local moments of the Fe(III) ions in the total $S=10$ magnetic ground state. The proton and deuteron NMR spectra have been analyzed and the different resonance peaks have been attributed to the different proton groups in the molecule. The simulation of the spectra by using a dipolar hyperfine field and the accepted model for the orientation of the Fe(III) local moments do not agree with the experiments even when the magnitude of the local Fe(III) moments is allowed to vary. It is concluded that a positive contact hyperfine interaction of the same order of magnitude as the dipolar interaction is present for all proton sites except the water molecules. The temperature and magnetic field dependence of the nuclear spin-lattice relaxation rate is ascribed to the fluctuations of the local Fe(III) moments, which follow rigidly the fluctuations of the total ground state magnetization of the nanomagnet. By using a simple model already utilized for the Mn12 cluster, we derive the value of the spin phonon coupling constant which determines the lifetime broadening of the different magnetic quantum number m substates of the $S=10$ ground state. It is shown that the lifetime broadening decreases rapidly on lowering the temperature. When the lifetime becomes longer than the reciprocal of the frequency shift of the proton lines a structure emerges in the NMR spectrum reflecting the ``frozen'' local moment configuration.

Improved resolution in proton NMR spectroscopy of powdered solids.

We present a new solid-state nuclear magnetic resonance experiment that yields, under CRAMPS decoupling conditions, a significant reduction in proton line widths for powdered organic solids. This experiment which relies on a constant-time acquisition of the proton transverse magnetization, removes the contribution of nonrefocusable broadening from the proton line widths. Although this new technique suffers from relatively low sensitivity, we demonstrate in this paper its feasibility on two model samples, L-alanine and the dipeptide Ala-Asp. In both cases a factor of between 2 and 3 in line width reduction is obtained for most of the proton resonances.

T-Site Trapped Molecular Hydrogen in Hot Wire a-Si:H

ABSTRACTProton NMR and proton-29Si double resonance NMR have been performed on hot wire a-Si:H films deposited from SiH4. Results are compared with those from conventional plasma enhanced chemical vapor deposition a-Si:H. Proton nutational angle studies and proton-29Si spin-echo double resonance (SEDOR) signals at 80 and 294 K indicate that a significant proton resonance population arises from T-site-trapped molecular H2. The hot wire films also display a ≥80 kHz FWHM uperbroad proton line and a sharp feature diamagnetically shifted by 25 ppm.

C30 Self-Assembled Monolayers on Silica, Titania, and Zirconia: HPLC Performance, Atomic Force Microscopy, Ellipsometry, and NMR Studies of Molecular Dynamics and Uniformity of Coverage

C30 self-assembled monolayers (SAMs) have been prepared on zirconia, titania, and two different silica gels by reacting C30 trichlorosilane with the humidified surfaces. 13C solid-state NMR spectroscopy indicated higher alkyl chain order on titania and zirconia materials than on the silica C30 phases. Order is inferred from the relative intensity of the main methylene carbon resonance assigned to an all-trans conformation. Carbon longitudinal relaxation time (T1C) data reveal that these ordered alkyl chains still have large-amplitude motions on submicrosecond time scales at ambient temperature. Since fast diffusional rotation about the chain axis is compatible with an all-trans conformation, T1C, carbon chemical shift, and proton line width data for the alkane rotator phase (C19) and the C30 phases were compared. Proton spin diffusion experiments were also conducted using an initial polarization gradient based on mobility differences. These experiments indicated both a higher mobility for the free end of ...

London penetration depth and coherence peak in ammonia-intercalated fulleride superconductors

The compound (NH3)xNaRb2C60 (x ∼ 1.6) has been studied by1H nuclear magnetic resonance. The proton line shows no shift at any temperature, while lineshape analysis of the low-temperature (30 K) spectra reveals the presence of a Knight shift interaction of pure anisotropic nature, whose amplitude has been estimated. Relaxation measurements show a single-exponential recovery of the magnetization at all investigated temperatures and fields. A Korringa behavior is observed below 65 K and a clear Hebel-Slichter coherence peak is detected just below Tc. The London penetration depth can be estimated from the line broadening observed below Tc, which yields λ ≈ 825 nm.

WIM/WISE NMR Studies of Chain Dynamics in Solid Polymers and Blends

Wideline separation (WISE) NMR with windowless isotropic mixing (WIM) is developed as a method to study the dynamics of polymers and blends. This experiment is designed to measure the dynamics of polymers through the proton lineshapes that are correlated with the carbon chemical shifts in two-dimensional NMR experiments. If the atoms experience large amplitude fluctuations that are fast compared to the dipolar broadening, then the proton lines will be narrowed relative to rigid solids. We have modified the WISE experiment by replacing the cross polarization step with WIM to quench spin diffusion during the cross polarization so that the proton linewidths can be directly related to the chain dynamics. Two-dimensional WIM/WISE has been used to measure the main-chain and side-chain dynamics in poly(n-butyl methacrylate) and blends of polystyrene and poly(vinyl methyl ether).

Sorption and diffusion of methanol and water in PVDF-g-PSSA and Nafion� 117 polymer electrolyte membranes

Sorption and diffusion properties of poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) and Nafion® 117 polymer electrolyte membranes were studied in water/methanol mixtures. The two types of membranes were found to have different sorption properties. The Nafion 117 membrane was found to have a maximum in-solvent uptake around 0.4 to 0.6 mole fraction of methanol, while the PVDF-g-PSSA membranes took up less solvent with increasing methanol concentration. The proton NMR spectra were recorded for membranes immersed in deuterated water/methanol mixtures. The spectra showed that the hydroxyl protons inside the membrane exhibit resonance lines different from the resonance lines of hydroxyl protons in the external solvent. The spectral features of the lines of these internal hydroxyl groups in the membranes were different in the Nafion membrane compared with the PVDF-g-PSSA membranes. Diffusion measurements with the pulsed field gradient NMR (PFG-NMR) method showed that the diffusion coefficient of the internal hydroxyl groups in the solvent immersed Nafion membrane mirrors the changes in the diffusion coefficients of hydroxyl and methyl protons in the external solvent. For the PVDF-g-PSSA membranes, a decrease in the diffusion coefficient of the internal hydroxyl protons was seen with increasing methanol concentration. These results indicate that the morphology and chemical structure of the membranes have an effect on their solvent sorption and diffusion characteristics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3277–3284, 2000

T-Site-Trapped Molecular Hydrogen in a-Si:H

ABSTRACTProton-29Si double resonance NMR measurements on high quality plasma-enhanced chemical vapor deposition a-Si:H deposited from SiH4 show that more than one third of the contained hydrogen is present as H2 molecules residing in the amorphous equivalent of T sites. The NMR signal from these trapped H2 appears in the narrow 4 kHz proton line, which arises from the less clustered hydrogen population. Very little of the molecular component is in the broad ~24 kHz line, which arises mostly from clustered hydrogen tightly bonded to silicon.

NMR study of role of the cross-relaxation effect in the cortex and the nucleus rabbit lens fragments

We have experimentally studied the coupling between the longitudinal magnetization of macromolecular protons and water protons in the cortex and the nucleus rabbit lens fragments (cross-relaxation). The NMR lines of water protons in the cortex and the nucleus of rabbit lens are inhomogenously broadened and relative narrow. We have assumed that the NMR line of crystalline protons in the lens is homogeneously broadened, very broad (the halfwidth order of 25 kHz) with small intensity. To detect the effect of cross-relaxation we adopted concept of the magnetization transfer used in magnetic resonance imaging. We irradiated the sample 20 kHz off resonance of the water protons with a train of low power RF pulses forming a selective saturation pulse and then after variable delay excited with a high-power 90°, detection pulse. Finally we have measured the sample NMR line intensity as a function of duration of selective pulse for several fixed delays between selective and detection pulses. We have found the significant difference between time constants of decays for the cortex and the nucleus. We attributed this difference to longer time of hydration water molecules in the cortex spend within proximity of the protein surface than in the nucleus. We have interpreted these finding as an effect of chemical protons exchange between macromolecular and water protons rather then cross-relaxation effects, and it is discussed in terms of the Lévy walk mechanism.

Pp→ppωreaction near threshold

We analyze the total cross section data for $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}\ensuremath{\omega}$ near threshold measured recently at SATURNE. Using an effective range approximation for the on-shell $\mathrm{pp}$ S-wave final-state interaction, we extract from these data the modulus $|\ensuremath{\Omega}|=0.53$ ${\mathrm{fm}}^{4}$ of the threshold transition amplitude \ensuremath{\Omega}. We present a calculation of various (tree-level) meson exchange diagrams contributing to \ensuremath{\Omega}. It is essential that $\ensuremath{\omega}$ emission from the anomalous $\ensuremath{\omega}\ensuremath{\rho}\ensuremath{\pi}$ vertex interferes destructively with \ensuremath{\omega} emission from the proton lines. The contribution of scalar $\ensuremath{\sigma}$-meson exchange to $\ensuremath{\Omega}$ turns out to be negligibly small. Without introducing off-shell meson-nucleon form factors the experimental value $|\ensuremath{\Omega}|=0.53$ ${\mathrm{fm}}^{4}$ can be reproduced with an $\ensuremath{\omega}N$-coupling constant of ${g}_{\ensuremath{\omega}N}=10.7.$ The results of the present approach agree qualitatively with the J\"ulich model. We also perform a combined analysis of the reactions $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}{\ensuremath{\pi}}^{0},$ $\mathrm{pn}{\ensuremath{\pi}}^{+},$ $\mathrm{pp}\ensuremath{\eta},$ $\mathrm{pp}\ensuremath{\omega},$ and $p\stackrel{\ensuremath{\rightarrow}}{n}\mathrm{pn}\ensuremath{\eta}$ near threshold.

Synthesis and characterization of novel biodegradable triblock copolymers from L‐Lactide, glycolide, and PPG

Copolymers with a PPG center block and two arms of random glycolide/lactide copolymers have been synthesized and characterized. Compared to random glycolide/lactide copolymers, these new polymers have high toughness and low elastic modulus.1 H-NMR spectral lines of glycolide CH2 protons of the copolymers are essentially identical. These materials show no crystallization transition in DSC thermograms and their melting points with respect to PLLA appeared at lower temperatures, indicating the pivotal role of the PPG center block in the copolymer. Degradation in aqueous media (pH = 6.9, 70°C) with stirring, subjected the two end blocks to hydrolytic degradation. The glycolyl ester bond cleavage was faster than for the lactyl ester bond. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 633–637, 1999