H. Zimmermann

The development of nuclear spins hyperpolarization, and the search for molecules that can be efficiently hyperpolarized is an active area in nuclear magnetic resonance. In this work we present a detailed study of SABRE SHEATH (signal amplification by reversible exchange in shield enabled alignment transfer to heteronuclei) experiments on ¹⁵N₂‐azobenzene. In SABRE SHEATH experiments the nuclear spins of the target are hyperpolarized through transfer of spin polarization from parahydrogen at ultralow fields during a reversible chemical process. Azobenzene exists in two isomers, trans and cis. We show that all nuclear spins in cis‐azobenzene can be efficiently hyperpolarized by SABRE at suitable magnetic fields. Enhancement factors (relative to 9.4 T) reach up to 3000 for ¹⁵N spins and up to 30 for the ¹H spins. We compare two approaches to observe either hyperpolarized magnetization of ¹⁵N/¹H spins, or hyperpolarized singlet order of the ¹⁵N spin pair. The results presented here will be useful for further experiments in which hyperpolarized cis‐¹⁵N₂‐azobenzene is switched by light to trans‐¹⁵N₂‐azobenzene for storing the produced hyperpolarization in the long‐lived spin state of the ¹⁵N pair of trans‐¹⁵N₂‐azobenzene.

Serial femtosecond crystallography (SFX) data were recorded at the European X-ray free-electron laser facility (EuXFEL) with protein microcrystals delivered via a microscopic liquid jet. An XFEL beam striking such a jet may launch supersonic shock waves up the jet, compromising the oncoming sample. To investigate this efficiently, we employed a novel XFEL pulse pattern to nominally expose the sample to between zero and four shock waves before being probed. Analyzing hit rate, indexing rate, and resolution for diffraction data recorded at MHz pulse rates, we found no evidence of damage. Notably, however, this conclusion could only be drawn after careful identification and assimilation of numerous interrelated experimental factors, which we describe in detail. Failure to do so would have led to an erroneous conclusion. Femtosecond photography of the sample-carrying jet revealed critically different jet behavior from that of all homogeneous liquid jets studied to date in this manner.

A method is implemented to perform “fast” adiabatic variation of the spin Hamiltonian by imposing the constant adiabaticity condition. The method is applied to improve the performance of singlet-state Nuclear Magnetic Resonance (NMR) experiments, specifically, for efficient generation and readout of the singlet spin order in coupled spin pairs by applying adiabatically ramped RF-fields. Test experiments have been performed on a specially designed molecule having two strongly coupled 13C spins and on selectively isotopically labelled glycerol having two pairs of coupled protons. Optimized RF-ramps show improved performance in comparison, for example, to linear ramps. We expect that the methods described here are useful not only for singlet-state NMR experiments but also for other experiments in magnetic resonance, which utilize adiabatic variation of the spin Hamiltonian.

In this article, we explore those factors that influence the orientational order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dimer and a related monomer thus enabling its behaviour to be controlled continuously, through its composition rather than chemical structure. Earlier studies have revealed that as the temperature is lowered in the nematic phase, the orientational order frequently passes through a maximum prior to the formation of the N_TB phase. A confirmative indication of this unusual behaviour is that the Haller function cannot fit this dependence over the entire nematic range; such behaviour is intriguing. In the N_TB phase, the measured order parameter is often insensitive to decreasing temperature for systems with strong N_TB–N transitions often associated with a narrow nematic range. For those mesogens with longer nematic ranges and hence weaker N_TB–N transitions, the order parameter decreases more markedly with temperature. As expected for the weak transitions, the behaviour of the order parameter is observed to be essentially continuous across the transition. Associated with the orientational order in the N_TB phase is the conical angle and an off-diagonal element of the Saupe ordering matrix.

The appearance of some special features in ²H-NMR spectra, which could not be explained by the conventional nematic order, was crucial for the discovery of the twist-bend nematic (N_TB) phase. Such features reflect the order and symmetry of the local environment of a probe and in principle their analysis can provide quantitative insights into the structural parameters of the phase. We have developed a methodology for the analysis of experimental data, different from the approaches that are normally used for two main reasons: (i) the structural features of the N_TB phase, specifically its local polarity, biaxiality and chirality, are consistently taken into account; (ii) the molecular features are introduced in a detailed way, through molecular modelling. We have applied this methodology to analyse ²H-NMR quadrupolar splittings for two representative systems, CB7CB and CB6OCB. The integration of theory, computational modelling and experiment allows us to extract quantitative information from the experimental data and to predict various properties, even not directly probed by measurements. We discuss how the molecular differences between CB7CB and CB6OCB translate into a different phase behaviour and we address issues concerning the distinguishing features of the N_TB phase, such as the definition of a local tilted director. Graphical Abstract

A 10-step synthesis of the antimalarial lead, ¹³ C ₁₈ -enriched plasmodione, and of seven putative metabolites is described.

We provide a detailed evaluation of nuclear magnetic resonance (NMR) parameters of the cis- and trans-isomers of azobenzene (AB). For determining the NMR parameters, such as proton–proton and proton–nitrogen J-couplings and chemical shifts, we compared NMR spectra of three different isotopomers of AB: the doubly ¹⁵N labeled azobenzene, ¹⁵N,¹⁵N′-AB, and two partially deuterated AB isotopomers with a single ¹⁵N atom. For the total lineshape analysis of NMR spectra, we used the recently developed ANATOLIA software package. The determined NMR parameters allowed us to optimize experiments for investigating singlet long-lived spin states (LLSs) of ¹⁵N spin pairs and to measure LLS lifetimes in cis-AB and trans-AB. Magnetization-to-singlet-to-magnetization conversion has been performed using the SLIC and APSOC techniques, providing a degree of conversion up to 17 and 24% of the initial magnetization, respectively. Our approach is useful for optimizing the performance of experiments with singlet LLSs; such LLSs can be exploited for preserving spin hyperpolarization, for probing slow molecular dynamics, slow chemical processes and also slow transport processes.