The Reaction of Muonium with Hydrogen Peroxide in Aqueous Solution.

Rate constants for the reactions of muonium (Mu) (the ultralight isotope of the hydrogen atom) with H O in H O and D O in D O have been determined at various temperatures and pH (pD) values. The data are consistent with the three reactions: , , and the equivalent for the deuterated entities. A significant positive H/D isotope effect was found for the undissociated peroxide, while for the anions the effect was negligible or slightly in the opposite direction.

Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy.

In addition to their importance as abundant hydrocarbon deposits in nature, clathrate hydrates are being studied as potential media for hydrogen and carbon dioxide storage and as "nano-reactors" for small molecules. However, little is known about the behavior of reactive species in such materials. We have employed muon spin spectroscopy to characterize various organic free radicals that reside as isolated guests in structure II clathrates.

Proton, muon and ¹³C hyperfine coupling constants of C₆₀X and C₇₀X (X = H, Mu).

The reaction of H atoms with fullerene C70 has been investigated by identifying the radical products formed by addition of the atom muonium (Mu) to the fullerene in solution. Four of the five possible radical isomers of C70Mu were detected by avoided level-crossing resonance (μLCR) spectroscopy, using a dilute solution of enriched (13)C70 in decalin. DFT calculations were used to predict muon and (13)C isotropic hyperfine constants as an aid to assigning the observed μLCR signals.

Organic free radicals in clathrate hydrates investigated by muon spin spectroscopy.

Very little is known about the behavior of free H atoms and small organic radicals inside clathrate hydrate structures despite the relevance of such species to combustion of hydrocarbon hydrates. Muonium is an H atom analog, essentially a light isotope of hydrogen, and can be used to probe the chemistry of H atoms and transient free radicals. We demonstrate the first application of muon spin spectroscopy to characterize radicals in clathrate hydrates.

Sequence-dependent structural dynamics of primate adenosine-to-inosine editing substrates.

Humans have the highest level of adenosine-to-inosine (A-to-I) editing amongst primates, yet the reasons for this difference remain unclear. Sequence analysis of the Alu Sg elements (A-to-I RNA substrates) corresponding to the Nup50 gene in human, chimp, and rhesus reveals subtle sequence variations surrounding the edit sites. We have developed three constructs that represent human (HuAp5), chimp (ChAp5), and rhesus (RhAp5) Nup50 Alu Sg A-to-I editing substrates.

A silyl radical formed by muonium addition to a silylene.

Muonraker: irradiation of the stable silylene N,N'-bis(2,6-diisopropylphenyl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene with muons produced a radical that was identified as the monomeric muonium adduct from its muon spin rotation (μSR) spectrum. The muon hyperfine constant for this radical is 931 MHz, the largest ever recorded for a free radical.

Hyperfine coupling in methyl radical isotopomers.

The hyperfine coupling constants (hfcs) of two methyl radical isotopomers, CH2Mu and CD2Mu, have been measured over a wide range of temperature in ketene and ketene-d2, from which the radicals were generated. The magnitudes of the hfcs of these muoniated methyl radical isotopomers are larger than those of CH3 and CD3 due to larger zero-point energy in the out-of-plane bending mode. In contrast to CH3 and CD3, where the coupling constants become smaller with increasing temperature, the negative hfcs of the muoniated radicals were found to increase in magnitude (become more negative) with temperature, passing through a maximum near the boiling point of ketene.

Organic free radicals in superheated water studied by muon spin spectroscopy.

There is a pressing need to identify and monitor reaction intermediates in water at high temperatures and pressures, but conventional techniques have limited capability for studying transient free radicals under such challenging conditions. Apparatus has now been developed to permit muon avoided-level crossing spectroscopy (muLCR) of organic free radicals in superheated water. The combination of muLCR with transverse-field muon spin rotation (TF-muSR) provides the means to identify and characterize free radicals via their nuclear hyperfine coupling constants.

The reactions of imidazol-2-ylidenes with the hydrogen atom: a theoretical study and experimental confirmation with muonium.

The possible radicals resulting from hydrogen atom addition to the imidazole rings of 1,3-bis(isopropyl)-4,5-dimethylimidazol-2-ylidene (1) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (2) have been studied by means of density functional calculations (B3LYP). The calculations included solvent effects estimated via the polarized continuum model (PCM) and an empirical treatment of vibrational averaging of hyperfine constants. Addition of a hydrogen (or muonium) atom to the carbeneic carbon of 1,3-bis(isopropyl)-4,5-dimethylimidazol-2-ylidene was found to give a radical 60.

Enolization of acetone in superheated water detected via radical formation.

Muoniated free radicals have been detected in muon-irradiated aqueous solutions of acetone at high temperatures and pressures. At temperatures below 250 degrees C, the radical product is consistent with muonium addition to the keto form of acetone. However, at higher temperatures, a different radical was detected, which is attributed to muonium addition to the enol form.