Solid-state NMR adiabatic TOBSY sequences provide enhanced sensitivity for multidimensional high-resolution magic-angle-spinning 1H MR spectroscopy

We propose a solid-state NMR method that maximizes the advantages of high-resolution magic-angle-spinning (HRMAS) applied to intact biopsies when compared to more conventional liquid-state NMR approaches. Theoretical treatment, numerical simulations and experimental results on intact human brain biopsies are presented. Experimentally, it is proven that an optimized adiabatic TOBSY (TOtal through Bond correlation SpectroscopY) solid-state NMR pulse sequence for two-dimensional 1H-1H homonuclear scalar-coupling longitudinal isotropic mixing provides a 20%-50% improvement in signal-to-noise ratio relative to its liquid-state analogue TOCSY (TOtal Correlation SpectroscopY). For this purpose we have refined the C9(15)1 symmetry-based 13C TOBSY pulse sequence for 1H MRS use and compared it to MLEV-16 TOCSY sequence. Both sequences were rotor-synchronized and implemented using WURST-8 adiabatic inversion pulses. As discussed theoretically and shown in simulations, the improved magnetization-transfer comes from actively removing residual dipolar couplings from the average Hamiltonian. Importantly, the solid-state NMR techniques are tailored to perform measurements at low temperatures where sample degradation is reduced. This is the first demonstration of such a concept for HRMAS metabolic profiling of disease processes, including cancer, from biopsies requiring reduced sample degradation for further genomic analysis.     

Uniform-sign cross-peak double-quantum-filtered correlation spectroscopy

We detail the uniform-sign cross-peak double-quantum-filtered correlation spectroscopy (UC2QF COSY) experiment, a new through-bond correlation method for disordered solids. This experiment is a refocused version of the popular double-quantum-filtered correlation spectroscopy experiment in liquids. Its key feature is that it provides in-phase and doubly absorptive line shapes, which renders it robust for chemical shift correlation in solids. Both theory and experiment point to distinct advantages of this protocol, which are illustrated by several experiments under challenging conditions, including fast magic-angle spinning (30kHz), anisotropic molecular motion, and (13)C correlation spectroscopy at the natural abundance isotope level.     

Synthesis of strained cyclic peptides via an aza-Michael-acyl-transfer reaction cascade

A new method is presented to prepare strained lactams. Esterification of the C-terminus of a dipeptide with β-nitrostyrene or quinoline-type auxiliaries is followed by lactam formation by an intramolecular aza-Michael-acyl-transfer reaction cascade. Ultimately, the cyclic tetrapeptide cyclo[Phe-Tyr-Ala-Gly] has been prepared.     

A numerical solution of the coupled heat and mass transfer problem of non-planar solidification and melting of aqueous solutions

During freezing of aqueous solutions containing solutes like sodium chloride or glycerol, pure ice is the first solid phase to form. A numerical model is presented for the case of non-planar (dendritic) freezing, where local thermodynamic equilibrium can be assumed in the whole mushy region, allowing a one-dimensional treatment of the coupled heat and mass transfer in this region. Solute diffusion along the resulting interdendritic concentration gradient in the direction of freezing is taken into account by the model. With regard to the non-linear character of the matching condition between temperature and concentration an iterative method based on the Newton-algorithm was used to solve the system of the common non-linear heat and mass transfer equations, which were derived from the partial differential equations by a finite difference scheme. Varying the geometric and thermodynamic boundary conditions, a parameter study was performed for obtaining more information on heat transfer during thawing of regular-shaped samples (plate, cylinder, sphere). In particular, the warming rate distributions in containers filled with aqueous solution were determined, which are interesting parameters in the field of cryopreservation of biological material.Beim Gefrieren von wäßrigen Lösungen, die Substanzen wie Kochsalz oder Glyzerin enthalten, bildet sich als erste feste Phase reines Eis. Im Falle nichtplanarer (dendritischer) Erstarrung kann innerhalb der gesamten mushy region lokales thermodynamisches Gleichgewicht angenommen werden, wodurch eine eindimensionale Behandlung des gekoppelten Wärme- und Stofftransports in dieser Zone möglich wird. Dabei wird die Diffusion gelöster Stoffe entlang des resultierenden Konzentrationsgefälles im interdendritischen Zwischenraum berücksichtigt. Angeischts der nichtlinearen Anpassungsbedingung zwischen Temperatur und Konzentration wurde ein auf einem Newton-Algorithmus basierendes iteratives Verfahren verwendet, um die gewöhnlichen, nichtlinearen Wärme- und Stofftransportgleichungen zu lösen, die aus den partiellen Differentialgleichungen durch ein Finite-Differenzen-Verfahren gewonnen wurden. Unter Variation der geometrischen und thermodynamischen Randbedingungen wurde eine Parameterstudie mit dem Ziel durchgeführt, genaueren Einblick in das Auftauverhalten von Proben einfacher Geometrien (Platte, Zylinder, Kugel) zu gewinnen. Insbesondere wurden die Erwärmungsraten-Verteilungen in mit wäßriger Lösung geführten Containern bestimmt, die im Zusammenhang mit der Kryokonservierung biologischen Materials von Bedeutung sind.