Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR.

In DNP MAS NMR experiments at ∼80-110 K, the structurally important -CH and -NH signals in MAS spectra of biological samples disappear due to the interference of the molecular motions with the H decoupling. Here we investigate the effect of these dynamic processes on the NMR line shapes and signal intensities in several typical systems: (1) microcrystalline APG, (2) membrane protein bR, (3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD, and (5) the protonated and deuterated dipeptide N-Ac-VL over 78-300 K. In APG, the three-site hopping of the Ala-C peak disappears completely at 112 K, concomitant with the attenuation of CP signals from other C's and N's.

Optimizing water hyperpolarization and dissolution for sensitivity-enhanced 2D biomolecular NMR.

A recent study explored the use of hyperpolarized water, to enhance the sensitivity of nuclei in biomolecules thanks to rapid proton exchanges with labile amide backbone and sidechain groups. Further optimizations of this approach have now allowed us to achieve proton polarizations approaching 25% in the water transferred into the NMR spectrometer, effective water T1 times approaching 40s, and a reduction in the dilution demanded for the cryogenic dissolution process. Further hardware developments have allowed us to perform these experiments, repeatedly and reliably, in 5mm NMR tubes.

Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry.

We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide L-alanyl-L-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis.

Standard Thermodynamic Functions of Tripeptides -Formyl-l-methionyl-l-leucyl-l-phenylalaninol and -Formyl-l-methionyl-l-leucyl-l-phenylalanine Methyl Ester.

The heat capacities of tripeptides -formyl-l-methionyl-l-leucyl-l-phenylalaninol (-f-MLF-OH) and -formyl-l-methionyl-l-leucyl-l-phenylalanine methyl ester (-f-MLF-OMe) were measured by precision adiabatic vacuum calorimetry over the temperature range from = (6 to 350) K. The tripeptides were stable over this temperature range, and no phase change, transformation, association, or thermal decomposition was observed. The standard thermodynamic functions: molar heat capacity , enthalpy () - (0), entropy (), and Gibbs energy () - (0) of peptides were calculated over the range from = (0 to 350) K.

High frequency dynamic nuclear polarization.

During the three decades 1980-2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical, and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-γ nuclei such as the I = 1/2 species (13)C or (15)N.

Efficient, balanced, transmission line RF circuits by back propagation of common impedance nodes.

We present a new, efficient strategy for designing fully balanced transmission line RF circuits for solid state NMR probes based on back propagation of common impedance nodes (BPCIN). In this approach, the impedance node phenomenon is the sole means of achieving mutual RF isolation and balance in all RF channels. BPCIN is illustrated using a custom double resonance 3.

Dynamic Nuclear Polarization of Oxygen-17.

Oxygen-17 detected DNP NMR of a water/glycerol glass enabled an 80-fold enhancement of signal intensities at 82 K, using the biradical TOTAPOL. The >6,000-fold savings in acquisition time enables (17)O-(1)H distance measurements and heteronuclear correlation experiments. These experiments are the initial demonstration of the feasibility of DNP NMR on quadrupolar (17)O.

Dynamic nuclear polarization at 700 MHz/460 GHz.

We describe the design and implementation of the instrumentation required to perform DNP-NMR at higher field strengths than previously demonstrated, and report the first magic-angle spinning (MAS) DNP-NMR experiments performed at (1)H/e(-) frequencies of 700 MHz/460 GHz. The extension of DNP-NMR to 16.4 T has required the development of probe technology, cryogenics, gyrotrons, and microwave transmission lines.