Applications of tritium NMR to macromolecules: a study of two nucleic acid molecules

Tritium NMR: A compilation of data and a practical guide

The present review is focused on experimental methods and structural applications of tritium NMR. It consists of five parts covering accordingly, introduction, brief overview, early (based on the papers appearing before 2000), more recent (based on the papers appeared in the interim of 2000 to 2015), and recent (based on the papers that appeared after 2015) reports. A special interest in this review is focused on practical aspects of tritium NMR spectroscopy, which is thoroughly illustrated by its numerous applications in chemistry and biochemistry.

Intermolecular Overhauser effects in fluoroalcohol solutions of cyclo-alanylglycine

Interactions between the diketopiperazine cyclo-alanylglycine and four fluorinated alcohols in water-fluoroalcohol mixtures were examined by (1)H[(19)F] intermolecular nuclear Overhauser effects (NOE) experiments. The alcohols studied were trifluoroethanol, hexafluoroacetone trihydrate, 1,1,1,3,3,3-hexafluoroisopropanol and perfluoro-t-butanol. The experimental methods used permit detection of solvent-solute NOEs of 0.1% or less. Solute and solvent diffusion coefficients were determined and apparent molecular radii of the fluoroalcohols estimated. Using these data, it was shown that observed (1)H[(19)F] intermolecular NOEs are consistent with expectations based on theory. A method for extending conventional theory to take into account the shape of a solute and the exposure of its hydrogens to solvent is described. This approach gives reasonable agreement with experimental results, particularly if it is assumed that solute-solvent interactions take place in such a way that the fluorines of a fluoroalcohol are preferentially oriented toward the solute during solute-solvent encounters. The results support the suggestion that intermolecular (1)H[(19)F] NOEs may become a useful tool for studies of peptide and protein conformations in fluoroalcohol-water solvent mixtures.

The residence time of the bound water in the hydrophobic minor groove of the carbocyclic-nucleoside analogs of Dickerson-Drew dodecamers

The residence time of the bound water molecules in the antisense oligodeoxyribonucleotides containing 7'-alpha-methyl (TMe) carbocyclic thymidines in duplex (I), d5'(1C2G3C4G5A6A7TMc8TMe9C10G11C12G)23', and 6'-alpha-hydroxy (TOH) carbocyclic thymidines in duplex (II), d5'(1C2G3C4G5AOH6AOH7TOH8 TOH9C10G11C12G)2(3), have been investigated using a combination of NOESY and ROESY experiments. Because of the presence of 7'-alpha-methyl groups of TMe in the centre of the minor groove in duplex (I), the residence time of the bound water molecule is shorter than 0.3 ns. The dramatic reduction of the residence time of the water molecule in the minor groove in duplex (I) compared with the natural counterpart has been attributed to the replacement of second shell of hydration and disruption of hydrogen-bonding with 04' in the minor groove by hydrophobic alpha-methyl groups, as originally observed in the X-ray study. This effect could not be attributed to the change of the width of the minor groove because a comparative NMR study of the duplex (I) and its natural counterpart showed that the widths of their minor grooves are more or less unchanged (r.m.s.d change in the core part is <0.63A). For duplex (II) with polar 6'-alpha-hydroxyl groups pointed to the minor groove, the correlation time is much longer than 0.36 ns as a result of the stabilising hydrogen-bonding interaction with N3 or 02 of the neighbouring nucleotides.

Solvent magnetization artifacts in high-field NMR studies of macromolecular hydration

With the use of high magnetic fields and improved quality factor ratings of the probeheads in modern NMR spectrometers, radiation damping becomes more and more important. In addition, the demagnetizing field effect from protonated solvents gains significance with the increase of the magnetic field strength. During a typical NMR pulse sequence the magnetic fields caused by these effects become time-dependent, which makes the system nonlinear and may, for example, measurably influence the precession frequencies of all nuclei in the sample. Since radiation damping can affect signals that are several kilohertz away from the solvent resonance, the amplitude, phase, and frequency of the desired signals can be disturbed so as to give rise to spectral artifacts. In particular when difference methods are used to obtain the final spectrum, the data sets may be severely deteriorated by such artifacts. This paper investigates effects from the demagnetizing field and from radiation damping with a selection of pulse sequences in use for studies of macromolecular hydration, and strategies are described for the detection and elimination of the ensuing artifacts.