An Efficient, Robust New Scheme for Establishing Broadband Homonuclear Correlations in Biomolecular Solid State NMR (original) (raw)
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Research Square (Research Square), 2023
A recently developed homonuclear dipolar recoupling scheme, Adiabatic Linearly FREquency Swept reCOupling (AL FRESCO), was applied to record two-dimensional (2D) 15 N-15 N correlations on uniformly 15 N-labeled GB1 powders. A major feature exploited in these 15 N-15 N correlations was AL FRESCO's remarkably low RF power demands, which enabled seconds-long mixing schemes when establishing direct correlations. These 15 N-15 N mixing schemes proved efficient regardless of the magic-angle spinning (MAS) rate and, being nearly free from dipolar truncation effects, they enabled the detection of long-range, weak dipolar couplings, even in the presence of strong short-range dipolar couplings. This led to a connectivity information that was significantly better than that obtained with spontaneously proton-driven, 15 N spin-diffusion experiments. An indirect approach producing long-range 15 N-15 N correlations was also tested, relying on short (ms-long) 1 H N-1 H N mixings schemes while applying AL FRESCO chirped pulses along the 15 N channel. These indirect mixing schemes produced numerous long-distance Ni-Ni±n (n = 2 − 5) correlations, that might be useful for characterizing three-dimensional arrangements in proteins. Once again, these AL FRESCO mediated experiments proved more informative than variants based on spin-diffusion-based 1 H N-1 H N counterparts.
Broadband Dipolar Recoupling for Magnetization Transfer in Solid-State NMR Correlation Spectroscopy
ChemPhysChem, 2008
Recent developments in solid-state nuclear magnetic resonance have opened the way to detailed structural and dynamic analysis of crystalline and non-crystalline biological solids. In isotopically enriched molecules of biological interest, 13 C-13 C magnetization transfer via spin-exchange processes (also called spin diffusion) allows one both to assign the resonances and to determine internuclear distances. Chemical-shift correlation experiments commonly employed for such purposes exploit different means of compensating for the energy imbalances of 13 C spins with different resonance frequencies and use a variety of recoupling schemes which inhibit the quenching of homo-and heteronuclear dipolar interactions by magic angle spinning (MAS). Spin exchange can be promoted by any of three methods: 1) Proton-driven spin diffusion (PDSD) which does not require any radio-frequency (RF) irradiation and relies on line broadening due to carbon-proton dipolar couplings, so that its efficiency strongly depends on the spinning frequency and on local motions. 2) Rotor-driven spin exchange which occurs in rotational resonance (R 2 ) methods, and does not use any RF irradiation either. It strongly favors flip-flop processes between pairs of 13 C spins which have a difference in isotropic chemical shifts that matches an integer multiple of the spinning frequency. 3) RF-driven spin exchange which relies on homo-and heteronuclear recoupling of the dipolar interactions. A wide range of recoupling sequences has been developed, including a number of broadband homonuclear recoupling schemes. For optimal performance, especially at high MAS frequencies, most known recoupling methods require high RF power which can lead to excessive sample heating at longer transfer times. Some dipolar recoupling methods employ reduced RF power on 13 C or on 1 H, like dipolar assisted rotational resonance (DARR) [21] or RF-assisted diffusion (RAD) experiments with RF amplitudes adjusted to the spinning frequency n r . This enhances 13 C-13 C spin exchange through recoupling of homo-and heteronuclear dipolar interactions. In fact, rotary resonance recoupling (R 3 ) using various ratios n = n 1H /n r = 1/2, 1 and 2 leads to the restoration of different anisotropic spin interactions. However, the efficiency of rotary resonance recoupling, including DARR/RAD-like experiments, is critically dependent on resonance offsets and on the homogeneity of the RF fields, and may lead to non-uniform 13 C-13 C spin exchange between various sites.
The Journal of Physical Chemistry Letters, 2010
We present a novel solid-state NMR method for heteronuclear dipolar recoupling without decoupling. The method, which introduces the concept of exponentially modulated rf fields, provides efficient broadband recoupling with large flexibility with respect to hetero-or homonuclear applications, sample spinning frequency, and operation without the need for highpower 1 H decoupling. For previous methods, the latter has been a severe source of sample heating which may cause detoriation of costly samples. The so-called EXPonentially mOdulated Recoupling Technique (EXPORT) is described analytically and numerically, and demonstrated experimentally by 1D 13 C spectra and 2D 13 C-15 N correlation spectra of 13 C, 15 N-labeled samples of GB1, ubiquitin, and fibrils of the SNNFGAILSS fragment of amylin. Through its flexible operation, robustness, and strong performance, it is anticipated that EXPORT will find immediate application for both hetero-and homonuclear dipolar recoupling in solid-state NMR of 13 C, 15 Nlabeled proteins and compounds of relevance in chemistry.
Journal of Magnetic Resonance, 2009
H-1 H decoupling CRAMPS 2D 1 H-1 H single-quantum-doublequantum spectra wDUMBO Double-quantum recoupling Homonuclear correlation Rotor-synchronised symmetry sequences a b s t r a c t Two-dimensional 1 H homonuclear correlation NMR spectra of solids of biological interest have been recorded at high magnetic fields (14.1 and 18.8 T) and MAS rates up to 67 kHz, using RN m n symmetrybased homonuclear recoupling and CRAMPS decoupling; this method affords exceptional spectral resolution and is well suited to probe 1 H-1 H proximities in powdered solids.
Chemical Physics Letters, 2004
We present a new solid-state NMR pulse sequence that accomplishes efficient broad-band dipolar recoupling in systems with small dipolar couplings and large chemical shift anisotropies. The method involves a supercycled symmetry-based recoupling sequence incorporated in a constant-interval data acquisition strategy. The supercycle removes destructive higher-order average Hamiltonian terms, and makes the method more robust at long time intervals. We demonstrate 38.4% double-quantum filtering efficiency on diammonium [1,4-13 C 2 ]-fumarate in which the internuclear distance, as estimated by X-ray diffraction, is 387.8 pm. The estimated 13 C-13 C dipolar coupling was )136.5 AE 5.1 Hz, corresponding to an internuclear distance of 382.5 AE 4 pm.
Chem. Sci., 2011
We introduce a new experiment, which makes use of Spin State Selective manipulations to perform sensitive and resolved through-bond correlations in organic and biological solids at high-fields and under ultra-fast MAS. The scheme is the shortest and most sensitive through-bond correlation method introduced so far in solids, yields resolved fingerprints of uniformly 13 C-labeled biomolecules, and constitutes a tool to highlight slight static structural disorder around crystallographically equivalent molecules in microcrystalline samples.
2012
We report novel symmetry-based radio-frequency (rf) pulse sequences for efficient excitation of doublequantum (2Q) coherences under very fast (>60 kHz) magic-angle spinning (MAS) conditions. The recursively generated pulse-scheme series, R2 1 2 p R2 À1 2 p ðp ¼ 1; 2; 3; . . .), offers broadband 13 C-13 C recoupling in organic solids at a very low rf power. No proton decoupling is required. A high-order average Hamiltonian theory analysis reveals a progressively enhanced resonance-offset compensation for increasing p, as verified both by numerical simulations and 2Q filtration NMR experiments on 13 C 2 -glycine, [2,3-13 C 2 ]alanine, and [U-13 C]tyrosine at 14.1 T and 66 kHz MAS, where the pulse schemes with p P 3 compare favorably to current state-of-the-art recoupling options.
Restoring symmetry in two-dimensional solid-state NMR correlation spectra
Chemical Physics Letters, 2012
The intrinsic asymmetry of 2D solid-state homonuclear NMR correlation spectra that arises from a nonuniform preparation of the magnetization can be removed by equilibrating the magnetization in the initial stage of the experiments through dipolar recoupling induced by PARIS or PARISxy schemes. Both methods ensure magnetization exchange with modest radio-frequency amplitudes and permit one to create an initial state that restores the symmetry about the main diagonal of 2D spectra of uniformly labeled biomolecules. This improves the determination of structural and kinetic information. Both recoupling schemes may also be used to record nearly quantitative peak amplitudes in 1D cross-polarization magic-angle-spinning spectra.