title: Mass-spectroscopic observations of glycine subjected to strong shock loading.
abstract: We have made time-of-flight mass-spectroscopic observations of 85/15 wt % water/glycine solutions and of crystalline alpha-glycine subjected to strong shock loading. The shockwaves were produced by placing the materials in contact with detonating solid explosives. In the solution observations, we have done experiments with glycine molecules composed of ordinary isotopes and with molecules labeled with (13)C, (15)N, and D atoms. The primary reason for conducting this research was to examine whether glycine molecules can survive exposure to strong shock loading, e.g., as might occur in the entry of a meteor into the earth's atmosphere. Our results show that glycine molecules can withstand the rigors of shock environments that generate pressure and temperature up to 180 kbar and 3200 K. Glycine in a 85 H(2)O/15 glycine wt % solution (i.e., one molecule of glycine to ca. 24 H(2)O molecules) exists primarily in its zwitterionic form. In both the solution and crystal experiments, we observed zwitterionic dimers, trimers, and, possibly, tetramers, after the materials were shocked. This implies that the solvating water molecules in the solution experiments must reside on the exterior of groups of solvated glycine molecules. We report quantum-chemical calculations, using density functional theory, that predict that two glycine zwitterions are bound together by ca. 15.72 kcal when immersed in an Onsager model of water. Our observations allow us to place lower-bound estimates on the lifetime of glycine zwitterions under our conditions. We have examined our data to determine whether dipeptide formation has occurred and found no evidence that it has. Compressible fluid-mechanical calculations were performed to estimate the pressures, temperatures, and the time scales present in the experiments.
authors.affiliation: MS P952, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA.
authors.forename: Ray
authors.initials: R
authors.lastname: Engelke
authors.forename: Normand C
authors.initials: NC
authors.lastname: Blais
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Sheffield
mesh_terms: D005118:Extraterrestrial Environment; D005998:Glycine / Q000737:chemistry*; D013058:Mass Spectrometry; D055595:Mechanical Phenomena; D008958:Models, Molecular; D008968:Molecular Conformation; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D005998:Glycine