Probing proteins in solution by (129)Xe NMR spectroscopy.

The interaction of xenon with different proteins in aqueous solution is investigated by (129)Xe NMR spectroscopy. Chemical shifts are measured in horse metmyoglobin, hen egg white lysozyme, and horse cytochrome c solutions as a function of xenon concentration. In these systems, xenon is in fast exchange between all possible environments. The results suggest that nonspecific interactions exist between xenon and the protein exteriors and the data are analyzed in term of parameters which characterize the protein surfaces. The experimental data for horse metmyoglobin are interpreted using a model in which xenon forms a 1:1 complex with the protein and the chemical shift of the complexed xenon is reported (Locci et al., Keystone Symposia "Frontiers of NMR in Molecular Biology VI", Jan. 9--15, 1999, Breckenridge, CO, Abstract E216, p. 53; Locci et al., XeMAT 2000 "Optical Polarization and Xenon NMR of Materials", June 28--30, 2000, Sestri Levante, Italy, p. 46).

Molecular polarization and molecular chiralization: The first example of a chiralized xenon atom.

In this article we focus on the interaction between a chiral molecule and a single achiral molecule or an ensemble of achiral molecules. The desymmetrization of the achiral molecules resulting from this interaction is described as "chiralization." By analogy with electric polarization, we factorize chiralization into three factors, i.e., orientation, atomic, and electronic terms. Chiralization depends on the dipolar polarizability of the chiralized molecule but also on polarizabilities of higher order. The experimental part of this work is devoted to the electronic chiralization of a xenon atom and its observation by (129)Xe NMR spectroscopy. Copyright 2000 Wiley-Liss, Inc.

Correlation between sonoluminescence, sonochemistry and cavitation noise spectra.

The acoustic signal from the sonochemical production of H2O2 in water, as measured by the intensity and the width of the second harmonic, show a sensitive and correlated dependence to the presence of small amounts (millimolar range) of an anionic surfactant (SDS) in water. The graphic shows the link from the ultrasonic reaction to the measurable quantities. New possibilities to reliably control such processes is therefore opened.

About a double-body immersion horn system to be used for quantitative sonochemical studies

The majority of quantitative sonochemical studies in the 20-100-kHz frequency range are performed by using an immersion horn system. The new system described in this letter consists of a double immersion horn acted on by a single pair of piezoelectric ceramics. This instrument is well adapted to the quantitative measure of effects, i.e., variations in the rate constant of a specific reaction associated to the change of an experimental parameter. The gas effect, obtained by comparing the rate of a reaction under air and under argon, illustrates the efficiency of the system.

Study by (23)Na-NMR, (1)H-NMR, and ultraviolet spectroscopy of the thermal stability of an 11-basepair oligonucleotide.

23Na-NMR, (1)H-NMR, and ultraviolet (UV) spectroscopy have been used to study the thermal stability of the double helix structure of an 11-basepair oligonucleotide. The denaturation curves obtained by (23)Na-NMR and UV are analyzed using a two-state model. The melting temperature and DeltaH(0) obtained are identical within experimental error, suggesting that modifications in the ionic atmosphere, probed by (23)Na-NMR, and the modifications in the basepair stacking, probed by UV, occur at the same temperature. Additional dynamical information on the denaturation process has been obtained by (1)H-NMR: slow exchange is observed between the thymine methyl resonances, and the disappearance of imino protons shows that a single basepair opening does not contribute significantly to proton exchange.

Can monoatomic xenon become chiral?

A chiral host, cryptophane-A (1), makes even a monoatomic noble gas chiral. The interaction of xenon and 1 was monitored by (129) Xe NMR and in the presence of a chiral chemical shift reagent.

On the frequency and isotope effect in sonochemistry.

In the first part of the work, it was observed, by a relative method, that the Weissler reaction and the Br2-catalysed isomerisation of maleic acid into fumaric acid are faster at 20 kHz than at 1.7 MHz. The difference between the relative reaction rates can be considered as small when the two order magnitude difference between the two frequencies is taking into account. In the second part of the work, the frequency effect associated to an isotope effect was studied. The Weissler reaction was performed in H2O and D2O at 20 kHz and 1.7 MHz. The isotope effect is not the same at the two frequencies.

Binding of Ru(II) polyazaaromatic complexes to DNA: A 23Na NMR spin-lattice relaxation study.

The possibility of using sodium-23 spin-lattice relaxation rate measurements to probe the interaction modes of Ru11 polyazaaaromatic complexes with DNA is investigated. The following complexes are considered: Ru(phen)3(2+) (phen = 1.10-phenanthroline), Ru(phen)2HAT2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), and Ru(diMeTAP)3(2+) (diMeTAP = 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene). The addition of Ru(diMeTAP)3(2+) to a solution of NaDNA leads to a decrease in the sodium-23 spin-lattice relaxation rate (R1) similar to the effect observed upon addition of Mg2+. This indicates that Ru(diMeTAP)3(2+) interacts like Mg2+ with DNA and consequently that the electrostatic interaction dominates the association with DNA, Ru(phen)3(2+) and Ru(phen)2HAT2+ diminish R1 more efficiently than Mg2+, in a manner similar to ethidium bromide, which is known for its intercalation properties. Thus interactions other than electrostatic occur between these two complexes and DNA. These results are in agreement with data obtained from other techniques, according to which Ru(phen)3(2+) and Ru(phen)2HAT2+ are located partially inside the DNA double helix, in contrast to Ru(diMeTAP)3(2+) which remains in the ionic atmosphere around the phosphate backbone.