Heteronuclear transfers from labile protons in biomolecular NMR: Cross polarization, revisited

Cross‐Polarization Schemes for Improved Heteronuclear Transfers Involving Labile Protons in Biomolecular Solution NMR

“…Figure 4 explores this aspect of the CP process with three variants introduced in Figure 1, as clarified by Liouville-space simulations. These numerical calculations accounted for chemical exchange, spin relaxation, and RF waveforms centered on-resonance with the labile proton; [15] in addition, a 4 ppm offset between the H N and the water resonance (498 MHz) was considered. The introduction of this offset, akin to that arising in alanine, drops the maximum achievable 15 N enhancement from the � 100 % value arising in the absence of chemical shifts (Figure 7 in ref.…”

“…15 N transfer experiments were Figure 3. 15 N-detected CP experiments measured on L-alanine at pH 2.1 and at three different temperatures, using the indicated sequences (498 MHz NMR). Shown on top are the approximate solvent exchange rates of the 1 Hs serving as source of polarization, as estimated by 1 H line shape analyses.…”

“…Biomolecular NMR experiments often demand enhancing the sensitivity of low-γ nuclei by polarization transfers from protons, as well as using polarization transfers to correlate different nuclear species with one another. [1][2][3][4][5][6] Both the sensitivity enhancing and the multinuclear correlation aspects of these polarization transfers play central roles in tackling the structures and dynamics of proteins and nucleic acids, and often involve bonded 1 H/ 15 N spin pairs belonging to amide, amine, or imino groups. [6][7][8] These polarization transfers are usually achieved by a series of pulses and RFfree evolution periods, as in the INEPT pulse block used in 1 HÀ 15 N HSQC experiments.…”

“…[17] This demand can be difficult or impossible to fulfill in bioNMR experiments, where the use of high fields leads to large 1 H N À 1 H water chemical shift differences, and the use of cryogenically-cooled probes limits the γB 1 fields that can be achieved on the low-frequency channels. For the particular setup to be considered here, the maximum safe 15 N field that can be deposited without causing RF arcing is γ N B 1,N /2π � 3.5 kHz; the HH γ H B 1,H = γ N B 1,N condition thus requires setting the 1 H RF γ H B 1,H /2π to � 3.5 kHz, a field that is insufficient for providing an effective, simultaneous spinlocking of the water and amide/amine/imino resonances. Paradoxically, considerably stronger γ H B 1,H fields are achievable in high-field cryogenically-cooled probes, but these are incompatible with the HH-imposed demands.…”

Restore High-Resolution Nuclear Magnetic Resonance Spectra from Inhomogeneous Magnetic Fields Using a Neural Network

“…It provides detailed information about chemical shifts, J -coupling, and relaxation rates and has been widely used in chemical analysis, structural biology, and life sciences. − The spectral resolution and signal-to-noise ratio are crucial criteria for the quality of the NMR spectra. With the continuous development of NMR equipment hardware (e.g., a stronger superconducting magnet and a cryogenic probe) and experimental techniques (e.g., cross-polarization and hyperpolarization), sensitivity has been greatly improved in modern NMR spectroscopy. On the other hand, the resolution of NMR spectra is also highly valued.…”