Thomas Bräuniger

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Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.

Greatly increased toughness of infiltrated spider silk.

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.

Improved Proton Decoupling in NMR Spectroscopy of Crystalline Solids Using the SPINAL-64 Sequence

Summary. The performance of three different spin decoupling schemes, CW, TPPM, and SPINAL-64 is compared, by recording proton decoupled 13C NMR spectra of a crystalline glycine sample, with 20% isotopic labelling. At a magnetic field of B0 = 14.1 T, the two phase modulated pulse schemes, TPPM and SPINAL-64, are shown to give decisively better results than CW decoupling, and the SPINAL-64 sequence is found to perform better than TPPM. It is suggested that in NMR of crystalline solids, SPINAL-64 offers a viable and competitive alternative to the well established TPPM decoupling technique, especially at higher magnetic fields.

Swept-frequency two-pulse phase modulation (SWf-TPPM) sequences with linear sweep profile for heteronuclear decoupling in solid-state NMR

Recently, a pulse scheme for heteronuclear spin decoupling in solid‐state NMR, called swept‐frequency two‐pulse phase modulation (SWf‐TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency‐sweep profile can be varied to achieve optimal efficiency for crystalline and liquid‐crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SWf‐TPPM sequences with tangential sweep profiles (SWftan‐TPPM) and linear sweep profiles (SWflin‐TPPM). Using the 13CH2 resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut‐off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise. Copyright

Efficient 5QMAS NMR of spin-5/2 nuclei: use of fast amplitude-modulated radio-frequency pulses and cogwheel phase cycling.

We report here an efficient multiple-quantum magic-angle spinning (MQMAS) pulse sequence involving fast amplitude-modulated (FAM) radio-frequency pulses for excitation and conversion of five-quantum (5Q) coherences of spin-5/2 nuclei. The use of a FAM-I type pulse train for the conversion of 5Q into 1Q coherences proves to be easier to implement experimentally than the earlier suggested use of a FAM-II type sequence [J. Magn. Reson. 154 (2002) 280], while delivering at least equal signal enhancement. Results of numerical simulations and experimental 27Al 5QMAS spectra of aluminium acetylacetonate for different excitation and conversion schemes are compared to substantiate these claims. We also demonstrate the feasibility of acquiring 5QMAS spectra of spin-5/2 systems using cogwheel phase cycling [J. Magn. Reson. 155 (2002) 300] to select the desired coherence pathways. A cogwheel phase cycle of only 57 steps is shown to be as effective as the minimum conventional nested 77-step phase cycle.

Frequency-swept pulse sequences for 19F heteronuclear spin decoupling in solid-state NMR.

Heteronuclear spin decoupling pulse sequences in solid-state NMR have mostly been designed and applied for irradiating 1H as the abundant nucleus. Here, a systematic comparison of different methods for decoupling 19F in rigid organic solids is presented, with a special emphasis on the recently introduced frequency-swept sequences. An extensive series of NMR experiments at different MAS frequencies was conducted on fluorinated model compounds, in combination with large sets of numerical simulations. From both experiments and simulations it can be concluded that the frequency-swept sequences SWf-TPPM and SWf-SPINAL deliver better and more robust spin decoupling than the original sequences SPINAL and TPPM. Whereas the existence of a large chemical shift anisotropy and isotropic shift dispersion for 19F does compromise the decoupling efficiency, the relative performance hierarchy of the sequences remains unaffected. Therefore, in the context of rigid organic solids under moderate MAS frequencies, the performance trends observed for 19F decoupling are very similar to those observed for 1H decoupling.

Improving sensitivity and resolution of MQMAS spectra: a 45Sc-NMR case study of scandium sulphate pentahydrate.

To efficiently obtain multiple-quantum magic-angle spinning (MQMAS) spectra of the nuclide 45Sc (I=7/2), we have combined several previously suggested techniques to enhance the signal-to-noise ratio and to improve spectral resolution for the test sample, scandium sulphate pentahydrate (ScSPH). Whereas the 45Sc-3QMAS spectrum of ScSPH does not offer sufficient resolution to clearly distinguish between the 3 scandium sites present in the crystal structure, these sites are well-resolved in the 5QMAS spectrum. The loss of sensitivity incurred by using MQMAS with 5Q coherence order is partly compensated for by using fast-amplitude modulated (FAM) sequences to improve the efficiency of both 5Q coherence excitation and conversion. Also, heteronuclear decoupling is employed to minimise dephasing of the 45Sc signal during the 5Q evolution period due to dipolar couplings with the water protons in the ScSPH sample. Application of multi-pulse decoupling schemes such as TPPM and SPINAL results in improved sensitivity and resolution in the F(1) (isotropic) dimension of the 5QMAS spectrum, the best results being achieved with the recently suggested SW(f)-TPPM sequence. By numerical fitting of the 45Sc-NMR spectra of ScSPH from 3QMAS, 5QMAS and single-quantum MAS at magnetic fields B(0)=9.4 T and 17.6 T, the isotropic chemical shift delta(iso), the quadrupolar coupling constant chi, and the asymmetry parameter eta were obtained. Averaging over all experiments, the NMR parameters determined for the 3 scandium sites, designated (a), (b) and (c) are: delta(iso)(a)=-15.5+/-0.5 ppm, chi(a)=5.60+/-0.10 MHz, eta(a)=0.06+/-0.05; delta(iso)(b)=-12.9+/-0.5 ppm, chi(b)=4.50+/-0.10 MHz, eta(b)=1.00+/-0.00; and delta(iso)(c)=-4.7+/-0.2 ppm, chi(c)=4.55+/-0.05 MHz, eta(c)=0.50+/-0.02. The NMR scandium species were assigned to the independent crystallographic sites by evaluating their experimental response to proton decoupling, and by density functional theory (DFT) calculations using the PAW and GIPAW approaches, in the following way: Sc(1) to (c), Sc(2) to (a), and Sc(3) to (b). The need to compute NMR parameters using an energy-optimised crystal structure is once again demonstrated.

A combined 14N/27Al nuclear magnetic resonance and powder X-ray diffraction study of impurity phases in β-sialon ceramics

Beta-sialons are ceramic phases occurring in the SiO(2)-Si(3)N(4)-AlN-Al(2)O(3) system. A series of samples with differing compositions has been investigated by magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy and powder X-ray diffraction (XRD). Although the constituent nitrogen nuclei occupy positions of low symmetry in the beta-sialon structure, 14N NMR spectra could be recorded for the samples examined. The origin of the 14N signal could be traced to the presence of an aluminium nitride (AlN) impurity phase with the help of 27Al NMR and XRD results. Similarly, the existence of Al(2)O(3) grains could be readily detected for a number of samples. Thus, the combination of 14N and 27Al NMR is shown to be an especially effective tool in identifying and characterizing impurity phases in sialon ceramics, complementing the results obtained from standard XRD analysis.

Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in solid-state NMR of spin-7/2 nuclei.

We here investigate the sensitivity enhancement of central-transition NMR spectra of quadrupolar nuclei with spin-7/2 in the solid state, generated by fast amplitude-modulated RF pulse trains with constant (FAM-I) and incremented pulse durations (SW-FAM). Considerable intensity is gained for the central-transition resonance of single-quantum spectra by means of spin population transfer from the satellite transitions, both under static and magic-angle-spinning (MAS) conditions. It is also shown that incorporation of a SW-FAM train into the excitation part of a 7QMAS sequence improves the efficiency of 7Q coherence generation, resulting in improved signal-to-noise ratio. The application of FAM-type pulse trains may thus facilitate faster spectra acquisition of spin-7/2 systems.

19F-decoupling of half-integer spin quadrupolar nuclei in solid-state NMR: application of frequency-swept decoupling methods.

In solid-state NMR studies of minerals and ion conductors, quadrupolar nuclei like (7)Li, (23)Na or (133)Cs are frequently situated in close proximity to fluorine, so that application of (19)F decoupling is beneficial for spectral resolution. Here, we compare the decoupling efficiency of various multi-pulse decoupling sequences by acquiring (19)F-decoupled (23)Na-NMR spectra of cryolite (Na(3)AlF(6)). Whereas the MAS spectrum is only marginally affected by application of (19)F decoupling, the 3Q-filtered (23)Na signal is very sensitive to it, as the de-phasing caused by the dipolar interaction between sodium and fluorine is three-fold magnified. Experimentally, we find that at moderate MAS speeds, the decoupling efficiencies of the frequency-swept decoupling schemes SW(f)-TPPM and SW(f)-SPINAL are significantly better than the conventional TPPM and SPINAL sequences. The frequency-swept sequences are therefore the methods of choice for efficient decoupling of quadrupolar nuclei with half-integer spin from fluorine.