The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Robert G. Griffin - One of the best experts on this subject based on the ideXlab platform.
-
Rapid 3D MAS NMR Spectroscopy at Critical Sensitivity
2010Co-Authors: Yoh Matsuki, Robert G. Griffin, Matthew T. Eddy, Judith HerzfeldAbstract:&A however, C detection is inherently less sensitive than H detection. Second, slower relaxation and the need for high-power H decoupling in solids necessitate longer recycle delays. For these reasons, employing three or more dimensions in MAS NMR experiments has not yet become common practice. In solution NMR, more efficient acquisition has relied on non-uniform sampling (NUS), which has been successfully applied to multidimensional experiments on larger systems. Although extending NUS to MAS NMR would be of enormous practical importance, the application of conventional NUS methods to MAS NMR has been limited by the specific problem of accurately modeling weak signals in noisy spectra, in addition to the general problems of quantitative spectral reconstruction and slow computation. The lower sensitivity in MAS NMR experiments requires an unprecedented robustness of any NUS method to minimize artifacts. Herein, we address these challenges with SIFT (spectroscopy by integration of frequency and time domain information), a rapid and model-free method for computing a NMR spectrum from a NUS time-domain dataset. SIFTworks by replacing missing information in the time domain with a priori knowledge of “dark” regions in the frequency domain; that is, those regions known to contain no NMR signals. The frequency domain information, assimilated by a very rapid computational process, obviates some time-domain sampling with no sacrifice in resolution and no modeling bias. We previously used SIFT to process 2D NUS N-HSQC solution data, where dark regions created by over-sampling were utilized to replace up to 75% of the uniform timedomain data points. We demonstrate the effectiveness of the SIFT method in solids, using dark regions resulting from the need for Rotor-synchronized sampling in the indirect dimensions. Unlike other NUS data processing methods that actively model signals to reconstruct a spectrum, SIFT suppresses the sampling noise by using only definitive information from the dark spectral areas. Thus, SIFT avoids bias from subjective discrimination between weak signals and noise, and reconstructs missing time data points with high fidelity, as if they had been actually recorded. These favorable properties make SIFT uniquely suited for processing NUS data in the sensitivity-limited regime. To demonstrate the application of SIFT to NUS MAS NMR, we recorded a 3D NCOCX spectrum (Figure 1a ) of a microcrystalline, uniformly [N,C]-labeled sample of the b1 domain of protein G (GB1) at high digital resolution (1.1 ppm for F1, 0.7 ppm for F2, before zero-filling). For both t1 and t2, the dwell time was synchronized to three times the Rotor Period, 3/nR (bandwidth equal to nR/3 Hz), in order to fold the
-
Dipolar recoupling in solid state NMR by phase alternating pulse sequences.
Journal of magnetic resonance (San Diego Calif. : 1997), 2008Co-Authors: J. Lin, Robert G. Griffin, Marvin J. Bayro, Navin KhanejaAbstract:Abstract We describe some new developments in the methodology of making heteronuclear and homonuclear recoupling experiments in solid state NMR insensitive to rf-inhomogeneity by phase alternating the irradiation on the spin system every Rotor Period. By incorporating delays of half Rotor Periods in the pulse sequences, these phase alternating experiments can be made γ encoded. The proposed methodology is conceptually different from the standard methods of making recoupling experiments robust by the use of ramps and adiabatic pulses in the recoupling Periods. We show how the concept of phase alternation can be incorporated in the design of homonuclear recoupling experiments that are both insensitive to chemical shift dispersion and rf-inhomogeneity.
-
recoupling of heteronuclear dipolar interactions with rotational echo double resonance at high magic angle spinning frequencies
Journal of Magnetic Resonance, 2000Co-Authors: Christopher P. Jaroniec, Judith Herzfeld, Brett A. Tounge, Chad M. Rienstra, Robert G. GriffinAbstract:Abstract Heteronuclear dipolar recoupling with rotational-echo double-resonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the Rotor Period (10–60%). We demonstrate, in two model 13C–15N spin systems, [1-13C, 15N] and [2-13C, 15N]glycine, that REDOR ΔS/S0 curves acquired at high MAS rates and relatively low recoupling fields are nearly identical to the ΔS/S0 curve expected for REDOR with ideal δ-function pulses. The only noticeable effect of the finite π pulse length on the recoupling is a minor scaling of the dipolar oscillation frequency. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different π pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar oscillation frequency by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx-4) both the frequency and amplitude of the oscillation are expected to change.
-
Recoupling of heteronuclear dipolar interactions with rotational-echo double-resonance at high magic-angle spinning frequencies.
Journal of magnetic resonance (San Diego Calif. : 1997), 2000Co-Authors: Christopher P. Jaroniec, Judith Herzfeld, Brett A. Tounge, Chad M. Rienstra, Robert G. GriffinAbstract:Heteronuclear dipolar recoupling with rotational-echo double-resonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the Rotor Period (10-60%). We demonstrate, in two model (13)C-(15)N spin systems, [1-(13)C, (15)N] and [2-(13)C, (15)N]glycine, that REDOR DeltaS/S(0) curves acquired at high MAS rates and relatively low recoupling fields are nearly identical to the DeltaS/S(0) curve expected for REDOR with ideal delta-function pulses. The only noticeable effect of the finite pi pulse length on the recoupling is a minor scaling of the dipolar oscillation frequency. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different pi pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar oscillation frequency by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx-4) both the frequency and amplitude of the oscillation are expected to change.
-
Homonuclear correlation spectroscopy in rotating solids
Chemical Physics Letters, 1992Co-Authors: R.g.s. Spencer, Andrew E. Bennett, Robert G. GriffinAbstract:Abstract A two-dimensional homonuclear correlation experiment for magic angle spinning NMR spectroscopy of polycrystalline solids is described. The approach involves application of a multiple pulse mixing Period that scales chemical shifts to zero, thereby removing the barrier to spin exchange among interacting nuclei. Transfer of spin coherence is achieved by a transverse mixing sequence in which eight π pulses, πx-πx-πy-πy-π−y-π−y-π−x-π−x, are applied per Rotor Period. Spectra of triply-labeled 1,2,3-13C3-D,L-alanine are presented, which demonstrate correlations among all three carbon spins.
Clare P Grey - One of the best experts on this subject based on the ideXlab platform.
-
19F/23Na multiple quantum cross polarization NMR in solids
The Journal of Chemical Physics, 2000Co-Authors: Kwang Hun Lim, Clare P GreyAbstract:19F→23Na triple quantum (TQ) cross polarization (TQCP) experiments and numerical simulations have been performed on the oxyfluoride NaMoO3F. Due to the orientation dependence of the quadrupolar tensor and thus the TQ nutation frequency (ωs,nut), only a fraction of the spins in the powder can match the Hartmann–Hahn condition at the same time, for a fixed 19F rf field strength (ω1I). Numerical simulations of the static TQCP process, for different single crystallite orientations, demonstrate that the most efficient TQCP occurs for parts of the powder where the quadrupolar splitting, Q′, is largest, and where the TQ coherences are pure eigenstates of the system, even though ωs,nut is smallest for these orientations. Under magic angle spinning (MAS) conditions, ωs,nut becomes time dependent and again, efficient TQCP is observed at times during the Rotor Period where Q′ is largest. TQCP intensities for different crystallites were calculated as a function of ω1I, for fixed 23Na rf field strengths, to obtain TQC...
-
INEPT Experiments Involving Quadrupolar Nuclei in Solids
Journal of Magnetic Resonance, 1998Co-Authors: Clare P GreyAbstract:Abstract Coherence transfer from quadrupolar 27 Al ( I = 5 2 ) nuclei to 31 P ( I = 1 2 ) via INEPT experiments is investigated. 27 Al → 31 P INEPT experiments on a (CH 3 ) 3 P–AlCl 3 complex in zeolite NaX are performed, and the results demonstrate that the 31 P INEPT signals strongly depend on whether or not the 27 Al pulses are applied synchronously with the Rotor Period, and on the length of the 27 Al pulses. A density-matrix calculation involving the use of the spin operators for spin 3 2 and 1 2 nuclei has been performed to help understand the evolution behavior of the density matrix under the influence of the quadrupolar interaction, the dipolar and J -couplings, and the pulse lengths applied to the quadrupolar nuclei. The theoretical predictions obtained from these calculations are consistent with the INEPT experimental observations.
-
Analysis of the anisotropic dimension in the RIACT (II) multiple quantum MAS NMR experiment for I = 3/2 nuclei.
Solid state nuclear magnetic resonance, 1998Co-Authors: Kwang Hun Lim, Clare P GreyAbstract:Abstract Numerical simulations of the anisotropic dimension of the Rotation-Induced Adiabatic Coherence Transfer (RIACT) MQ experiment have been performed as a function of the asymmetry parameter, η , for different spacings between the triple quantum (3Q) excitation and 3Q to single quantum (1Q) reconversion pulses. Large distortions of the spectra are observed, in comparison to the spectra obtained with 1D MAS NMR methods. The method is very sensitive to the relative orientation of the quadrupolar tensor and Rotor axis, and signal can only be obtained from a maximum of 60% of the powder. The intensity varies with the spacing between the two pulses, t 1 , reaching a minimum of 30% when t 1 is either a multiple of a full Rotor Period ( nτ r ) or for ( n +1/2) Rotor Periods, for pulse lengths ( τ 1SL ) of a quarter of a Rotor Period. The maximum of 60% is obtained when t 1 = nτ r − τ 1SL . Experimental spectra were acquired for anhydrous Na 2 HPO 4 . Good fits were obtained between the experimental and simulated spectra, even for the non-Rotor synchronized experiment, by choosing fixed values of t 1 . The simulations allowed the quadrupole coupling constants and asymmetry parameters to be extracted from the experimental data.
-
Optimizing the13C–14N REAPDOR NMR Experiment: A Theoretical and Experimental Study☆
Journal of magnetic resonance (San Diego Calif. : 1997), 1998Co-Authors: Hsien-ming Kao, Clare P Grey, Lamy J Chopin, Terry GullionAbstract:Abstract The optimum 14 N pulse lengths in the 13 C– 14 N rotational-echo adiabatic-passage double-resonance (REAPDOR) NMR experiment are determined from calculations and from experiments on samples of glycine and l -alanine. The REAPDOR experiment utilizes the adiabatic passages that 14 N spins make between the 14 N Zeeman energy levels during the application of a single, short 14 N radiofrequency pulse. Use of a short 14 N irradiation time of less than one-quarter of a Rotor Period ensures that the number of 14 N spins that undergo more than one passage is minimized. This simplifies calculations describing 13 C dipolar dephasing and provides better agreement between calculations and experiments. Recovery of the 13 C– 14 N dipolar couplings and 14 N quadrupolar coupling constants and asymmetry parameters is described.
-
14N Population transfers in two-dimensional 13C14N1H triple-resonance magic-angle spinning nuclear magnetic resonance spectroscopy
Solid state nuclear magnetic resonance, 1995Co-Authors: Clare P Grey, Astrid P.a.m. Eijkelenboom, Wiebren S. VeemanAbstract:Abstract A two-dimensional (2D) experiment has been used to show that 14N irradiation and magic-angle spinning (MAS) results in population transfers between the 14N Zeeman levels. This experiment was applied to a sample of N-acetyl- d,l -valine, a material where asymmetric doublets resulting from 13C14N dipolar coupling are clearly resolved in the 13C spectrum at a field of 7 T for carbon atoms directly bonded to the nitrogen atom. The 13C transverse magnetization was allowed to evolve in the F1 and F2 dimensions, and the 14N spins were irradiated during the mixing Period. Cross-peaks were observed in the 2D C spectrum between the two peaks of the CH asymmetric doublet. Since one peak of the doublet results primarily from coupling to the ¦0〉 state and the other peak from coupling to the ¦ − 1〉 and ¦ + 1〉 states, population changes between the 14N Zeeman levels have occurred during the mixing Period. These population transfers are a consequence of the time dependence of the 14N quadrupole splitting Q under MAS conditions and 14N irradiation. Level anti-crossings of the 14N Zeeman levels occur at the zero-crossings of Q, and a continuous and slow change in Q will result in the transfer of 14N populations between the different Zeeman levels. If these passages are adiabatic, then the system returns to its original state after two zero-crossings. This is consistent with the experimental observation that the intensities of the cross-peaks for 14N irradiation are greater for half a Rotor Period than a full Rotor Period.
L. Emsley - One of the best experts on this subject based on the ideXlab platform.
-
Quantitative analysis of backbone dynamics in a crystalline protein from nitrogen-15 spin-lattice relaxation.
Journal of the American Chemical Society, 2005Co-Authors: N. Giraud, M. Blackledge, M. Goldman, A. Bockmann, A. Lesage, F. Penin, L. EmsleyAbstract:A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one Rotor Period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the Rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein.
-
Quantitative analysis of backbone dynamics in a crystalline protein from nitrogen-15 spin-lattice relaxation.
Journal of the American Chemical Society, 2005Co-Authors: N. Giraud, M. Blackledge, M. Goldman, A. Bockmann, A. Lesage, F. Penin, L. EmsleyAbstract:A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one Rotor Period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the Rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein.A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one Rotor Period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the Rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein.
Jean-paul Amoureux - One of the best experts on this subject based on the ideXlab platform.
-
Broadband excitation in solid-state NMR using interleaved DANTE pulse trains with N pulses per Rotor Period
Journal of magnetic resonance (San Diego Calif. : 1997), 2013Co-Authors: Julien Trébosc, Olivier Lafon, Diego Carnevale, Simone Ulzega, Geoffrey Bodenhausen, Jean-paul AmoureuxAbstract:N abstract We analyze the direct excitation of wide one-dimensional spectra of nuclei with spin I = 1/2 or 1 in rotat- ing solids submitted to pulse trains in the manner of Delays Alternating with Nutations for Tailored Exci- tation (DANTE), either with one short Rotor-synchronized pulse of duration sp in each of K Rotor Periods ðD K 1 Þ or with N interleaved equally spaced pulses sp in each Rotor Period, globally also extending over K
-
Broadband excitation in solid-state NMR using interleaved DANTE pulse trains with N pulses per Rotor Period.
Journal of Magnetic Resonance, 2013Co-Authors: Julien Trébosc, Olivier Lafon, Diego Carnevale, Simone Ulzega, Geoffrey Bodenhausen, Jean-paul AmoureuxAbstract:: We analyze the direct excitation of wide one-dimensional spectra of nuclei with spin I=1/2 or 1 in rotating solids submitted to pulse trains in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE), either with one short Rotor-synchronized pulse of duration τp in each of K Rotor Periods (D1(K)) or with N interleaved equally spaced pulses τp in each Rotor Period, globally also extending over K Rotor Periods (DN(K)). The excitation profile of DN(K) scheme is a comb of rf-spikelets with NνR=N/TR spacing from the carrier frequency, and a width of each spikelet inversely proportional to the length, KTR, of DN(K) scheme. Since the individual pulse lengths, τp, are typically of a few hundreds of ns, DN(K) scheme can readily excite spinning sidebands families covering several MHz, provided the rf carrier frequency is close enough to the resonance frequency of one the spinning sidebands. If the difference of isotropic chemical shifts between distinct chemical sites is less than about 1.35/(KTR), DN(K) scheme can excite the spinning sidebands families of several sites. For nuclei with I=1/2, if the homogeneous and inhomogeneous decays of coherences during the DANTE sequence are neglected, the K pulses of a D1(K) train have a linearly cumulative effect, so that the total nutation angle is θtot=K2πν1τp, where ν1 is the rf-field amplitude. This allows obtaining nearly ideal 90° pulses for excitation or 180° rotations for inversion and refocusing across wide MAS spectra comprising many spinning sidebands. If one uses interleaved DANTE trains DN(K) with N>1, only spinning sidebands separated by intervals of NνR with respect to the carrier frequency are observed as if the effective spinning speed was NνR. The other sidebands have vanishing intensities because of the cancellation of the N contributions with opposite signs. However, the intensities of the remaining sidebands obey the same rules as in spectra obtained with νR. With increasing N, the intensities of the non-vanishing sidebands increase, but the total intensity integrated over all sidebands decreases. Furthermore, the NK pulses in a DN(K) train do not have a simple cumulative effect and the optimal cumulated flip angle for optimal excitation, θtot(opt)=NK2πν1τp, exceeds 90°. Such DN(K) pulse trains allow achieving efficient broadband excitation, but they are not recommended for broadband inversion or refocusing as they cannot provide proper 180° rotations. Since DN(K) pulse trains with N>1 are shorter than basic D1(K) sequences, they are useful for broadband excitation in samples with rapid homogeneous or inhomogeneous decay. For nuclei with I=1 (e.g., for (14)N), the response to basic D1(K) pulse train is moreover affected by inhomogeneous decay due to 2nd-order quadrupole interactions, since these are not of rank 2 and therefore cannot be eliminated by spinning about the magic angle. For large quadrupole interactions, the signal decay produced by second-order quadrupole interaction can be minimized by (i) reducing the length of DN(K) pulse trains using N>1, (ii) fast spinning, (iii) large rf-field, and (iv) using high magnetic fields to reduce the 2nd-order quadrupole interaction.
-
Uniform broadband excitation of crystallites in rotating solids using interleaved sequences of delays alternating with nutation.
Journal of Magnetic Resonance, 2012Co-Authors: Veronika Vitzthum, Julien Trébosc, Olivier Lafon, Simone Ulzega, Jean-paul Amoureux, Marc A Caporini, Geoffrey BodenhausenAbstract:In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N>1, one obtains 'DANTE-N' sequences comprising N pulses per Rotor Period that extend over K Rotor Periods. Optimized interleaved DANTE schemes with N>1 are shorter than basic DANTE-1 sequences with N=1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N>1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide (14)N sites in peptides at B(0)=18.8T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency ν(rot), as if the samples were rotating at Nν(rot). We show applications to direct detection of nitrogen-14 nuclei with spin I=1 subject to large quadrupole interactions, using fast magic angle spinning (typically ν(rot)⩾60kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses.
-
Uniform broadband excitation of crystallites in rotating solids using interleaved sequences of delays alternating with nutation.
Journal of magnetic resonance (San Diego Calif. : 1997), 2012Co-Authors: Veronika Vitzthum, Julien Trébosc, Olivier Lafon, Simone Ulzega, Jean-paul Amoureux, Marc A Caporini, Geoffrey BodenhausenAbstract:In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N > 1, one obtains 'DANTE-N' sequences comprising N pulses per Rotor Period that extend over K Rotor Periods. Optimized interleaved DANTE schemes with N > 1 are shorter than basic DANTE-1 sequences with N = 1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N > 1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide N-14 sites in peptides at B-0 = 18.8 T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency nu(rot), as if the samples were rotating at N nu(rot). We show applications to direct detection of nitrogen-14 nuclei with spin I = 1 subject to large quadrupole interactions, using fast magic angle spinning (typically nu(rot) >= 60 kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses. (C) 2012 Elsevier Inc. All rights reserved.
-
Broadband excitation in solid-state NMR of paramagnetic samples using Delays Alternating with Nutation for Tailored Excitation ('Para-DANTE')
Chemical Physics Letters, 2012Co-Authors: Diego Carnevale, Veronika Vitzthum, Julien Trébosc, Olivier Lafon, Jean-paul Amoureux, Geoffrey BodenhausenAbstract:This Letter shows that interleaved sequences of short pulses in the manner of 'Delays Alternating with Nutation for Tailored Excitation' (DANTE) with N = 1,2,3 . . . equidistant pulses per Rotor Period extending over K Rotor Periods can be used to excite, invert or refocus a large number of spinning sidebands of spin-1/2 nuclei in paramagnetic samples where hyperfine couplings lead to very broad spectra that extend over more than 1 MHz. The breadth of the response is maintained for rf-field amplitudes as low as 30 kHz since it results from cumulative effects of individual pulses with very short durations.
Chad M. Rienstra - One of the best experts on this subject based on the ideXlab platform.
-
J-Based 3D sidechain correlation in solid-state proteins
Physical chemistry chemical physics : PCCP, 2009Co-Authors: Ye Tian, Chad M. Rienstra, Lingling Chen, Dimitri Niks, J. Michael Kaiser, Jinfeng Lai, Michael F. Dunn, Leonard J. MuellerAbstract:Scalar-based three-dimensional homonuclear correlation experiments are reported for 13C sidechain correlation in solid-state proteins. These experiments are based on a sensitive constant-time format, in which homonuclear scalar couplings are utilized for polarization transfer, but decoupled during chemical shift evolution, to yield highly resolved indirect dimensions and band selectivity as desired. The methods therefore yield spectra of high quality that give unique sets of sidechain correlations for small proteins even at 9.4 Tesla (400 MHz 1H frequency). We demonstrate versions of the pulse sequence that enable correlation from the sidechain to the backbone carbonyl as well as purely sidechain correlation sets; together these two data sets provide the majority of 13C–13C correlations for assignment. The polarization transfer efficiency is approximately 30% over two bonds. In the protein GB1 (56 residues), we find essentially all cross peaks uniquely resolved. We find similar efficiency of transfer (∼30%) in the 140 kDa tryptophan synthase (TS), since the relaxation rates of immobilized solid proteins are not sensitive to global molecular tumbling, as long as the correlation time is much longer than the magic-angle spinning Rotor Period. In 3D data sets of TS at 400 MHz, some peaks are resolved and, in combination with higher field data sets, we anticipate that assignments will be possible; in this vein, we demonstrate 2D 13C–13C spectra of TS at 900 MHz that are well resolved. These results together provide optimism about the prospects for assigning the spectra of such large enzymes in the solid state.
-
Band-selective ^13C Homonuclear 3D Spectroscopy for Solid Proteins at High Field with Rotor-synchronized Soft Pulses
Journal of Biomolecular NMR, 2006Co-Authors: Donghua H. Zhou, Kathryn D. Kloepper, Kem A. Winter, Chad M. RienstraAbstract:We demonstrate improved 3D ^13C–^13C–^13C chemical shift correlation experiments for solid proteins, utilizing band-selective coherence transfer, scalar decoupling and homonuclear zero-quantum polarization transfer. Judicious use of selective pulses and a z-filter Period suppress artifacts with a two-step phase cycle, allowing higher digital resolution in a fixed measurement time. The novel correlation of C^ali–C^ali–CX (C^ali for aliphatic carbons, CX for any carbon) reduces measurement time by an order of magnitude without sacrificing digital resolution. The experiment retains intensity from side-chain carbon resonances whose chemical shift dispersion is critical to minimize spectral degeneracy for large proteins with a predominance of secondary structure, such as β-sheet rich fibrillar proteins and α-helical membrane proteins. We demonstrate the experiment for the β1 immunoglobulin binding domain of protein G (GB1) and fibrils of the A30P mutant of α-synuclein, which is implicated in Parkinson’s disease. Selective pulses of duration comparable the Rotor Period give optimal performance, but must be synchronized with the spinning in non-trivial ways to minimize chemical shift anisotropy recoupling effects. Soft pulses with a small bandwidth-duration product are best for exciting the ~70 ppm bandwidth required for aliphatic-only dimensions.
-
Selective refocusing pulses in magic-angle spinning NMR: Characterization and applications to multi-dimensional protein spectroscopy
Journal of magnetic resonance (San Diego Calif. : 1997), 2006Co-Authors: Benjamin J. Wylie, Chad M. RienstraAbstract:Abstract Band-selective pulses are frequently used in multi-dimensional NMR in solution, but have been used relatively less often in solid-state NMR applications because of the complications imposed by magic-angle spinning. In this work, we examine the frequency profiles and the refocusing efficiency of several commonly employed selective general rotation π pulses through experiments and numerical simulations. We demonstrate that highly efficient refocusing of transverse magnetization can be achieved, with experiments that agree well with numerical simulations. We also show that the rotational echo is shifted by a half Rotor Period if a selective pulse is applied over an integer number of Rotor Periods. Appropriately synchronizing indirect evolution Periods with selective pulses ensures proper phasing of cross peaks in 2D spectra. The improved performance of selective pulses in multi-dimensional protein spectroscopy is demonstrated on the 56-residue β1 immunoglobulin binding domain of protein G (GB1).
-
recoupling of heteronuclear dipolar interactions with rotational echo double resonance at high magic angle spinning frequencies
Journal of Magnetic Resonance, 2000Co-Authors: Christopher P. Jaroniec, Judith Herzfeld, Brett A. Tounge, Chad M. Rienstra, Robert G. GriffinAbstract:Abstract Heteronuclear dipolar recoupling with rotational-echo double-resonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the Rotor Period (10–60%). We demonstrate, in two model 13C–15N spin systems, [1-13C, 15N] and [2-13C, 15N]glycine, that REDOR ΔS/S0 curves acquired at high MAS rates and relatively low recoupling fields are nearly identical to the ΔS/S0 curve expected for REDOR with ideal δ-function pulses. The only noticeable effect of the finite π pulse length on the recoupling is a minor scaling of the dipolar oscillation frequency. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different π pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar oscillation frequency by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx-4) both the frequency and amplitude of the oscillation are expected to change.
-
Recoupling of heteronuclear dipolar interactions with rotational-echo double-resonance at high magic-angle spinning frequencies.
Journal of magnetic resonance (San Diego Calif. : 1997), 2000Co-Authors: Christopher P. Jaroniec, Judith Herzfeld, Brett A. Tounge, Chad M. Rienstra, Robert G. GriffinAbstract:Heteronuclear dipolar recoupling with rotational-echo double-resonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the Rotor Period (10-60%). We demonstrate, in two model (13)C-(15)N spin systems, [1-(13)C, (15)N] and [2-(13)C, (15)N]glycine, that REDOR DeltaS/S(0) curves acquired at high MAS rates and relatively low recoupling fields are nearly identical to the DeltaS/S(0) curve expected for REDOR with ideal delta-function pulses. The only noticeable effect of the finite pi pulse length on the recoupling is a minor scaling of the dipolar oscillation frequency. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different pi pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar oscillation frequency by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx-4) both the frequency and amplitude of the oscillation are expected to change.
