Elizabeth A. Frank

Detection and possible origins of aminomalonic acid in protein hydrolysates

Aminomalonic acid (Ama) was first detected in alkaline hydrolysates of proteins in 1984. In this work we describe our search for the origin of aminomalonic acid in alkaline hydrolysates of proteins. We have developed a technique for quantitation of aminomalonic acid based upon gas chromatography/mass spectrometry. Using this technique, we find approximately 0.3 Ama/1000 amino acids in hydrolysates of Escherichia coli protein. We have demonstrated that Ama is not formed from any of the 20 major amino acids during the hydrolysis procedure. Furthermore, the amount of Ama found does not depend on the presence of small amounts of O2 during the hydrolysis. Thus far, we have not been able to demonstrate an artifactual origin for Ama. The results described above suggest that Ama may indeed be a constituent of proteins before the hydrolysis procedure. Possible origins of Ama include errors in protein synthesis and oxidative damage to amino acid residues in proteins.

Evaluating an impact origin for Mercury's high‐magnesium region

During its four years in orbit around Mercury, the MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft’s X-Ray Spectrometer revealed a large geochemical terrane in the northern hemisphere that hosts the highest Mg/Si, S/Si, Ca/Si, and Fe/Si and lowest Al/Si ratios on the planet. Correlations with low topography, thin crust, and a sharp northern topographic boundary led to the proposal that this high-Mg region (HMR) is the remnant of an ancient, highly degraded impact basin. Here we use a numerical modeling approach to explore the feasibility of this hypothesis and evaluate the results against multiple mission-wide datasets and resulting maps from MESSENGER. We find that a ~3000-km diameter impact basin easily exhumes Mg-rich mantle material but that the amount of subsequent modification required to hide basin structure is incompatible with the strength of the geochemical anomaly, which is also present in maps of Gamma Ray and Neutron Spectrometer data. Consequently, the high-Mg region is more likely to be the product of high-temperature volcanism sourced from a chemically heterogeneous mantle than the remains of a large impact event. (178 words)

Thermal effects of late accretion to the crust and mantle of Mercury

Abstract Impact bombardment on Mercury in the solar systems late accretion phase (ca. 4.4–3.8 Ga) caused considerable mechanical, chemical and thermal reworking of its silicate reservoirs (crust and mantle). Depending on the frequency, size and velocity of such impactors, effects included regional- and global-scale crustal melting, and thermal perturbations of the mercurian mantle. We use a 3D transient heating model to test the effects of two bombardment scenarios on early (pre-Tolstojan) Mercurys mantle and crust. Results show that rare impacts by the largest (≳100 km diameter) bodies deliver sufficient heat to the shallow mercurian mantle producing high-temperature ultra-magnesian (komatiitic s.s.) melts. Impact heating leading to effusive (flood) volcanism can account for the eponymous “high-magnesium region” (HMR) observed during the MErcury Surface, Space Environment, GEochemistry Ranging (MESSENGER) mission. We find that late accretion to Mercury induced volumetrically significant crustal melting (≤58 vol.%), mantle heating and melt production, which, combined with extensive resurfacing (≤100%), also explains why its oldest cratering record was effectively erased, consistent with crater-counting statistics.