Zero- to Ultralow-Field NMR Spectroscopy of Small Biomolecules.

Nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique used to study chemicals and their transformations. However, high-field NMR spectroscopy necessitates advanced infrastructure, and even cryogen-free benchtop NMR spectrometers cannot be readily assembled from commercially available components. We demonstrate construction of a portable zero-field NMR spectrometer employing a commercially available magnetometer and investigate its applications in analytical chemistry.

Two-dimensional single- and multiple-quantum correlation spectroscopy in zero-field nuclear magnetic resonance.

We present single- and multiple-quantum correlation J-spectroscopy detected in zero (<1μG) magnetic field using a Rb vapor-cell magnetometer. At zero field the spectrum of ethanol appears as a mixture of C isotopomers, and correlation spectroscopy is useful in separating the two composite spectra. We also identify and observe the zero-field equivalent of a double-quantum transition in C-acetic acid, and show that such transitions are of use in spectral assignment.

Invited Review Article: Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic field.

We review experimental techniques in our laboratory for nuclear magnetic resonance (NMR) in zero and ultralow magnetic field (below 0.1 μT) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free Rb atomic magnetometer. The typical sensitivity is 20-30 fT/Hz for signal frequencies below 1 kHz and NMR linewidths range from Hz all the way down to tens of mHz.

C-Decoupled J-Coupling Spectroscopy Using Two-Dimensional Nuclear Magnetic Resonance at Zero-Field.

We present a two-dimensional method for obtaining C-decoupled, H-coupled nuclear magnetic resonance (NMR) spectra in zero magnetic field using coherent spin-decoupling. The result is a spectrum determined only by the proton-proton J-coupling network. Detection of NMR signals in zero magnetic field requires at least two different nuclear spin species, but the proton J-spectrum is independent of isotopomer, thus potentially simplifying spectra and thereby improving the analytical capabilities of zero-field NMR.

Antisymmetric Couplings Enable Direct Observation of Chirality in Nuclear Magnetic Resonance Spectroscopy.

Here we demonstrate that a term in the nuclear spin Hamiltonian, the antisymmetric J-coupling, is fundamentally connected to molecular chirality. We propose and simulate a nuclear magnetic resonance (NMR) experiment to observe this interaction and differentiate between enantiomers without adding any additional chiral agent to the sample. The antisymmetric J-coupling may be observed in the presence of molecular orientation by an external electric field.

Nuclear magnetic resonance at millitesla fields using a zero-field spectrometer.

We describe new analytical capabilities for nuclear magnetic resonance (NMR) experiments in which signal detection is performed with chemical resolution (via spin-spin J couplings) in the zero to ultra-low magnetic field region, below 1μT. Using magnetic fields in the 100μT to 1mT range, we demonstrate the implementation of conventional NMR pulse sequences with spin-species selectivity.

Transition-Selective Pulses in Zero-Field Nuclear Magnetic Resonance.

We use low-amplitude, ultralow frequency pulses to drive nuclear spin transitions in zero and ultralow magnetic fields. In analogy to high-field NMR, a range of sophisticated experiments becomes available as these allow narrow-band excitation. As a first demonstration, pulses with excitation bandwidths 0.

REACTION DYNAMICS. Spectroscopic observation of resonances in the F + H2 reaction.

Photodetachment spectroscopy of the FH2(-) and FD2(-) anions allows for the direct observation of reactive resonances in the benchmark reaction F + H2 → HF + H. Using cooled anion precursors and a high-resolution electron spectrometer, we observe several narrow peaks not seen in previous experiments. Theoretical calculations, based on a highly accurate F + H2 potential energy surface, convincingly assign these peaks to resonances associated with quasibound states in the HF + H and DF + D product arrangements and with a quasibound state in the transition state region of the F + H2 reaction.