Steady state effects in PGSE NMR diffusion experiments

The Determination of Sucrose Content in Maple Sap Using Time-Domain Magnetic Resonance

The natural variation of sucrose concentration in maple tree sap is investigated using time-domain magnetic resonance (MR). The current study, which includes a concise introduction to the relevant MR properties, is a demonstration of principle showing how the relaxation time constant T ₂ and the self-diffusion coefficient relate to the amount of sucrose and ionic content present in the collected sap samples. T ₂ and self-diffusion coefficient for maple saps from six different trees, each sampled weekly in the spring of 2019, were measured using MR. The results were plotted against the sucrose concentration of each sample with the aim of determining if either quantity could serve as the basis for a non-invasive sucrose measurement for maple trees. The T ₂ relaxation time constant was found not to be a reliable proxy for sucrose content in maple sap as it showed sensitivity to the slight changes in sap chemistry throughout the season and natural variation from tree to tree. The diffusion coefficient, determined through a standard pulsed-gradient spin-echo experiment, was insensitive to the changes in sap chemistry and showed a strong relationship to sucrose content. A diffusion measurement is thus proposed as the most suitable candidate for a non-invasive sucrose measurement for maple tree sap.

Explicit phenomenological solutions for magnetization exposed to an arbitrary NMR diffusion steady state pulse sequence

Explicit phenomenological solutions to recurrence relations for the bulk transverse and longitudinal magnetization found using the Torrey-Bloch equations with relaxation effects are used to investigate nuclear magnetic resonance (NMR) diffusion measurements. Of particular interest are steady state NMR (self-)diffusion measurements that reduce experimental time that can extend the techniques to quickly reacting systems. The solutions for bulk transverse and longitudinal magnetization presented here are used to investigate the average behavior of the transverse and longitudinal magnetization in forming a steady state and are used to derive new expressions for the steady state longitudinal magnetization. These solutions can be applied to a noninteracting spin 1/2 ensemble undergoing free diffusion exposed to an arbitrary NMR pulse sequence containing arbitrary magnetic field gradient waveforms. The closed algebraic form method presented here has an advantage over iterative procedures for calculating transverse and longitudinal magnetization for the analysis and development of steady state pulse sequences. Previous theoretical results for steady state diffusion measurements are also reproduced. The Mathematica code for these solutions is provided in the supplementary material.

Synthesis, self-assembly and Langerin recognition studies of a resorcinarene-based glycocluster exposing a hyaluronic acid thiodisaccharide mimetic

Herein, we report the synthesis of an octavalent glycocluster exposing a thiodisaccharide mimetic of the repetitive unit of hyaluronic acid, βSGlcA(1 → 3)βSGlcNAc, constructed on a calix[4]resorcinarene scaffold by CuAAC reaction of suitable precursors. This glycocluster showed a strong tendency toward self-aggregation. DOSY-NMR and DLS experiments demonstrated the formation of spherical micelles of d ≅ 6.2 nm, in good agreement. TEM micrographs showed the presence of particles of different sizes, depending on the pH of the starting solution, thus evidencing that the negative charge on the micelle surface due to ionization of the GlcA residues plays an important role in the aggregation process. STD-NMR and DLS experiments provided evidence of the interaction between the synthetic glycocluster and Langerin, a relevant C-type lectin. This interaction was not observed in the STD-NMR experiments performed with the basic disaccharide, providing evidence of a multivalent effect.

Exchange-modified DOSY experiments. the use of chiral solvating agents and lanthanide shift reagents as matrices

(S)-BINOL and Eu(fod)₃ were tried as matrices to improve DOSY performance and D^t and MW prediction power on small organic molecules.

Counterion Transport and Transference Number in Aqueous and Nonaqueous Short-Chain Polyelectrolyte Solutions

Nonaqueous polyelectrolyte solutions have recently been proposed as potential battery electrolytes due to their unique ability to tune the mobility of the anion relative to that of the electrochemically active lithium ion. This could potentially be used to study the effect of concentration polarization during battery charge, a major limiting factor in achieving fast charge rates that is caused by high anion mobility. An important consideration in the design of polyelectrolyte solutions for battery applications is the solubility of the polymer in battery-relevant carbonate blend solvents. Little is understood from a transport perspective, however, about the importance of designing the polymer to be solvophillic or if it is sufficient to obtain solubility through the incorporation of appended ions alone (as with polystyrene sulfonate in water). Using a model polysulfone-based system without added salt, we investigate the conductivity, viscosity, and diffusion of polyelectrolyte solutions over a range of concentrations and molecular weights in dimethyl sulfoxide (DMSO) and water. In both solvents, sulfonated polysulfone is readily soluble and the charged group is known to dissociate, but the neutral backbone polymer is only soluble in DMSO. We find marked differences in the transport behavior of polymer solutions prepared from the two solvents, particularly at high concentrations. Comparing this transport behavior to that of the monomer in solution demonstrates a larger decrease in lithium motion in DMSO than in water, even though the bulk viscosity in water increases far more rapidly. This study sheds light on the important parameters for optimizing polyelectrolyte solution transport in different solvents.

Shortening NMR experimental times

Conventionally, arrayed nuclear magnetic resonance experiments, such as diffusion and relaxation, are performed with the same number of scans (NS) at each iteration despite the signal-to-noise ratio being more than sufficient for many of the iterations. Here, we propose a simple yet effective approach that significantly shortens experimental times by varying NS through the arrayed experiments while keeping the signal-to-noise ratio essentially the same and retaining experimental accuracy.

Physical characterization using diffusion NMR spectroscopy

NMR diffusion measurements (or dNMR) provide a powerful tool for analysis of solution organization and microgeometry of the environment by probing random molecular motion. Being a very versatile method, dNMR can be applied to a large variety of samples and systems. Here, a brief introduction into dNMR and a summary of recent advances in the field are presented. The research topics include restricted diffusion, anisotropic diffusion, polymer dynamics, solution structuring and dNMR method development. The dNMR studied systems include plants, cells (cell models), liquid crystals, polymer solutions, ionic liquids, supercooled solutions, untreated water, amino acid solutions and more. It is demonstrated how a variety of dNMR methods can be applied to a system to extract the data on particular structures present among, formed by or surrounding the diffusing particles. It is also demonstrated how dNMR methods can be developed to allow probing larger geometries, low sample concentrations and faster processes. Copyright © 2016 John Wiley & Sons, Ltd.