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Nuclear magnetic resonance spectroscopy (NMR) is a valuable analytical tool with applications in a vast array of research fields from chemistry and biology to medicine and beyond. NMR is renowned for its straightforward data interpretation and quantitative properties, making it attractive for pharmacokinetic applications, where drug metabolism pathways, concentrations, and kinetics need to be evaluated. However, pharmacologically active compounds and their metabolites in biofluids often appear in minute concentrations, well below the detection limit of NMR. Herein, we demonstrate how parahydrogen hyperpolarization overcomes this sensitivity barrier, allowing us to detect mid-nanomolar concentrations of a drug and a drug metabolite in a biofluid matrix. The performance of the method is demonstrated by monitoring nicotine and cotinine urinary elimination, reflected by their concentrations in urine during the onset and withdrawal from nicotine consumption. An NMR limit of detection of 0.1 μM and a limit of quantitation of 0.7 μM is achieved in a practical pharmacokinetics scenario where precise quantitative and qualitative analysis is desired.

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We report on high-resolution variable-temperature '^C magic-angle-spinning NMR spectra of the organic superconductor /3L-(ET)2I3. Broadening of the resonances is observed when lowering the temperature, with onset near the incommensurate phase transition around 180 K inducing a static crystallographic disorder. The NMR line shape displays directly the spin distribution function in space. The results give evidence of weak Anderson localization. The theory of the Knight shift distribution in 2D disordered metal is presented. We determine the impurity scattering time of conduction electrons and use it to discuss the suppression of the superconducting transition temperature by the localization.

We report the 87 Rb nuclear magnetic resonance (NMR) results in a recently synthesized Na 5 RbCu 4 ðAsO 4 ÞCl 2 . This complex novel two-dimensional (2D) cuprate is an unique magnetic material, which contains layers of coupled Cu 4 O 4 tetramers. In zero applied magnetic field, it orders antiferromagnetically via a second-order low-entropy phase transition at T N ¼ 15ð1Þ K. We characterize the ordered state by 87 Rb NMR, and suggest for it a non-collinear rather than collinear arrangement of spins. We discuss the properties of Rb nuclear site and point out the new structural phase transition(s) around 74 and 110 K. r Occurrence of high-temperature superconductivity in doped spin-1 2 square planar antiferromagnets has stimulated the search for new families of low-dimensional magnetic materials. We have studied the compound Na 5 RbCu 4 ðAsO 4 ÞCl 2 , whose spin exchange interactions are confined to 2D layers. The compound has a layered structure comprised of square Cu 4 O 4 tetramers [1]. The Cu ions are divalent and the system behaves as a low-dimensional S ¼ 1 2 antiferromagnet. Spin exchange in Na 5 RbCu 4 ðAsO 4 ÞCl 2 appears to be quasi-2D and nonfrustrated [2].In this report we present 87 Rb nuclear magnetic resonance (NMR) results of the compound. The experiments are performed in B 0 ¼ 8:45 and 14.1 T magnetic field in a temperature (T) range 4oTo300 K. A single crystal of Na 5 RbCu 4 ðAsO 4 ÞCl 2 ð1 Â 1 Â 0:2 mm 3 Þ was used.NMR spectra of 87 Rb ðI ¼ 3 2 ) central transition ðAE 1 2 3 Ç 1 2 Þ in Fig. 1(left) for the orientation of a crystal B 0 kb show a direct observation of the transition into the AFM ordered phase below 14.3 K. The splitting of the resonance line corresponds to the local hyperfine field of AE 8 mT due to the static magnetic moments at the tetramers coppers. The spectra in Fig. 1 (right) for B 0 ? b orientation do not show any measurable splitting in this T-range. From such orientation dependence one can conclude that in the AFM ordered phase the magnetic moments are aligned along the b-axis of the crystal, i.e., perpendicular to the tetramer plane. Rb sites in the lattice neighbor to four nearest coppers belonging to two sides of the two adjacent (along b) tetramers. These four coppers need to create a hyperfine field at Rb site in b-direction (or in opposite direction). A possible arrangement for that would be if the two magnetic moments of the tetramer sides along c-axis have "" or ## alignment (insert of Fig. 1). That peculiar magnetic structure may result from strongly different superexchange couplings J a and J c between the coppers of a given tetramer [2].A closer look to the spectra in AFM phase indicates that the real magnetic structure of the compound is not simple at all. The complicated double-horn line shape with ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ -see front matter r