Clustering of Uracil Molecules on Ice Nanoparticles

Abstract

We generate a molecular beam of ice nanoparticles (HO), N̅ ≈ 130-220, which picks up several individual gas phase uracil (U) or 5-bromouracil (BrU) molecules. The mass spectra of the doped nanoparticles prove that the uracil and bromouracil molecules coagulate to clusters on the ice nanoparticles. Calculations of U and BrU monomers and dimers on the ice nanoparticles provide theoretical support for the cluster formation. The (U)H and (BrU)H intensity dependencies on m extracted from the mass spectra suggest a smaller tendency of BrU to coagulate compared to U, which is substantiated by a lower mobility of bromouracil on the ice surface. The hydrated U·(HO)H series are also reported and discussed. On the basis of comparison with the previous experiments, we suggest that the observed propensity for aggregation on ice nanoparticles is a more general trend for biomolecules forming strong hydrogen bonds. This, together with their mobility, leads to their coagulation on ice nanoparticles which is an important aspect for astrochemistry.

Uptake of Hydrogen Bonding Molecules by Benzene Nanoparticles

“… 42 Nevertheless, we have observed coagulation of some molecules on ice nanoparticles, as well. 43 , 44 …”

Mass spectrometry of aerosol particle analogues in molecular beam experiments

“…However, if the binding energy of a molecular dimer was greater than the molecule‐water interaction, the dimers (and other small clusters) were generated even on the ice nanoparticles as shown in our experiments with 2‐hydroxypyridine and 2‐pyridone on ice nanoparticles . Also uracil has recently been demonstrated to generate clusters on ice nanoparticles . These experiments might be important in the context of origins of life in the universe where biomolecular synthesis on interstellar ices was proposed …”

“…[123][124][125] For water clusters, it was used to deposit different molecules on them including atmospherically relevant species such as N x O y based molecules, 126 hydrogen halides, 99,100,127 and freons 87 for photodissociation studies, and other molecules. 67,128 Also organic and more complex molecules including biomolecules [129][130][131][132][133][134] were deposited on water clusters via the pickup technique. If the beam passes through two (or more) pickup cells in series, different molecules can be deposited on the clusters and chemical reactions could be triggered by photons or electrons on the nanoparticles.…”

“…133 Also uracil has recently been demonstrated to generate clusters on ice nanoparticles. 134 These experiments might be important in the context of origins of life in the universe where biomolecular synthesis on interstellar ices was proposed. 136…”

Pickup and reactions of molecules on clusters relevant for atmospheric and interstellar processes

“…40,174,[201][202][203] Similarly, we observed coagulation of uracil and 5-bromouracil on (H 2 O) N . 204 Thus the observed propensity for aggregation on ice nanoparticles seems to be a more general trend for molecules forming strong hydrogen bonds among themselves, e.g., biomolecular analogues. Recently, we have observed also pyruvic and valeric acid coagulating on (H 2 O) N .…”