NMR Quantum Logic Gates for Homonuclear Spin Systems

If NMR systems are to be used as practical quantum computers, the number of coupled spins will need to be so large that it is not feasible to rely on purely heteronuclear spin systems. The implementation of a quantum logic gate imposes certain constraints on the motion of those spins not directly involved in that gate, the so-called "spectator" spins; they must be returned to their initial states at the end of the sequence. As a result, a homonuclear spin system where there is appreciable coupling between every pair of spins would seem to require a refocusing scheme that doubles in complexity and duration for every additional spectator spin. Fortunately, for the more realistic practical case where long-range spin-spin couplings can be neglected, simpler refocusing schemes can be devised where the overall duration of the sequence remains constant and the number of soft pulses increases only linearly with the number of spectator spins. These ideas are tested experimentally on a six qubit system: the six coupled protons of inosine.Comment: 11 pages LaTeX plus 6 fig

Uniform water-mediated saturation transfer: a sensitivity-improved alternative to WaterLOGSY

In the study of small molecule ligands and candidate macromolecular targets, water spins in long-lived association with macromolecules (proteins or nanoparticles) constitute a remarkable source of magnetization that can be exploited to reveal ligand-target binding. In this work we show how the selective saturation of water spins complemented with adiabatic off-resonance spin-locks can remove the NOE contribution of bulk water in the final difference spectrum, leading to uniformly enhanced signals that reveal weak ligand-target interactions

Increasing sensitivity and versatility in NMR supersequences with new HSQC-based modules

The sensitivity-enhanced HSQC, as well as HSQC-TOCSY, experiments have been modified for incorporation into NOAH (NMR by Ordered Acquisition using 1H detection) supersequences, adding diversity for 13C and 15N modules. Importantly, these heteronuclear modules have been specifically tailored to preserve the magnetisation required for subsequent acquisition of other heteronuclear or homonuclear modules in a supersequence. In addition, we present protocols for optimally combining HSQC and HSQC-TOCSY elements within the same supersequences, yielding high-quality 2D spectra suitable for structure characterisation but with greatly reduced experiment durations. We further demonstrate that these time savings can translate to increased detection sensitivity per unit time

Line narrowing in spectra of proteins dissolved in a dilute liquid crystalline phase by band-selective adiabatic decoupling: Application to 1HN-15N residual dipolar coupling measurements

Residual heteronuclear dipolar couplings obtained from partially oriented protein samples can provide unique NMR constraints for protein structure determination. However, partial orientation of protein samples also causes severe 1 H line broadening resulting from residual 1 H- 1 H dipolar couplings. In this communication we show that band-selective 1 H homonuclear decoupling during data acquisition is an efficient way to suppress residual 1 H- 1 H dipolar couplings, resulting in spectra that are still amenable to solution NMR analysis, even with high degrees of alignment. As an example, we present a novel experiment with improved sensitivity for the measurement of one-bond 1 H N - 15 N residual dipolar couplings in a protein sample dissolved in magnetically aligned liquid crystalline bicelles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43042/1/10858_2004_Article_254694.pd

Recording 13 C- 15 N HMQC 2D sparse spectra in solids in 30 s

International audienc

Magnetization transfer to enhance NOE cross-peaks among labile protons: applications to imino–imino sequential walks in SARS-CoV-2-derived RNAs

2D NOESY plays a central role in structural NMR spectroscopy. We have recently discussed methods that rely on solvent-driven exchanges to enhance NOE correlations between exchangeable and non-exchangeable protons in nucleic acids. Such methods, however, fail when trying to establish connectivities within pools of labile protons. This study introduces an alternative that also enhances NOEs between such labile sites, based on encoding a priori selected peaks by selective saturations. The resulting selective magnetization transfer (SMT) experiment proves particularly useful for enhancing the imino–imino cross-peaks in RNAs, which is a first step in the NMR resolution of these structures. The origins of these enhancements are discussed, and their potential is demonstrated on RNA fragments derived from the genome of SARS-CoV-2, recorded with better sensitivity and an order of magnitude faster than conventional 2D counterparts