A series of controlled laboratory experiments are carried out in dual Teflon chambers to examine the presence of oligomers in secondary organic aerosols (SOA) from hydrocarbon ozonolysis as well as to explore the effect of particle phase acidity on SOA formation. In all seven hydrocarbon systems studied (i.e., alpha-pinene, cyclohexene, 1-methyl cyclopentene, cycloheptene, 1-methyl cyclohexene, cyclooctene, and terpinolene), oligomers with MW from 250 to 1600 are present in the SOA formed, both in the absence and presence of seed particles and regardless of the seed particle acidity. These oligomers are comparable to, and in some cases, exceed the low molecular weight species (MW < 250) in ion intensities in the ion trap mass spectra, suggesting they may comprise a substantial fraction of the total aerosol mass. It is possible that oligomers are widely present in atmospheric organic aerosols, formed through acid- or base-catalyzed heterogeneous reactions. In addition, as the seed particle acidity increases, larger oligomers are formed more abundantly in the SOA; consequently, the overall SOA yield also increases. This explicit effect of particle phase acidity on the composition and yield of SOA may have important climatic consequences and need to be considered in relevant models.

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Portions published previously in: Julian R. R.; Hodyss R.; Kinnear B.; Jarrold M. F.;Beauchamp J. L.

The free radical initiator Vazo 68 is coupled to a peptide and electrosprayed into an ion trap mass spectrometer. On collisional activation, the Vazo 68−peptide conjugate generates a free radical, which can be collisionally activated to cleave the peptide backbone. Mostly z-type fragments are formed, as in CAD of other radical peptides and ECD fragmentation. We present data for the Angiotensin II−Vazo 68 conjugate and discuss possible sites of H atom abstraction from the peptide. This experimental methodology for generating peptide fragments is a useful step toward the development of a completely gas-phase approach to protein sequencing.

The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigate the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We find that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some Martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multi-stage cooling of a thick magma body.

Portions previously published in: Julian R. R.; Hodyss R.; Beauchamp J. L. J. Am. Chem. Soc. 2001, 123, 3577-3583. IntroductionAmino acids are known to exist as zwitterions in solution, but conditions appropriate for stabilization of the zwitterionic form in the gas phase remain debatable. Studies of the gas phase acidity and basicity of glycine with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry have shown that the glycine zwitterion is unstable by ~84 kJ/mol. 1 Many recent calculations confirm that glycine is unlikely to exist in the gas phase as a zwitterion; 2 furthermore, the zwitterion is not even predicted to be a minima on the potential energy surface. Theory suggests that water molecules can stabilize the zwitterionic form of glycine in the gas phase, with recent calculations suggesting that two water molecules are required. 3 In contrast, recent experimental results suggest that the number of water molecules necessary to stabilize glycine as a zwitterion is five. The gas phase stability of the zwitterionic form of arginine is predicted to be much more favorable. The arginine zwitterion is created by transferring a proton from the Cterminus to the side chain (see 2.1 and 2.2). The nomenclature indicated for arginine structures 2.1-2.4 will be used in the present work. Arginine is the most basic amino acid (see Table 2.1). This high basicity increases the stability of zwitterionic arginine in the gas phase relative to other amino acids. However, recent experiments have shown that isolated arginine is not a zwitterion. Cavity-ring down laser absorption spectra of jetcooled arginine do not exhibit a peak corresponding to the calculated carboxylate asymmetric stretch of the zwitterion. 5 High level computations have confirmed that arginine (2.1) is more stable than zwitterionic arginine (2.2) in the absence of an 18 additional charge. 6 However, theory predicts that the zwitterionic arginine is only less stable than arginine by 4-12 kJ/mol, depending on the level of theory.6

A new method is introduced to determine the extent to which spontaneous chiral separation occurs in small noncovalently bound clusters. Soft-sampling electrospray ionization was used to transfer noncovalent complexes from solution to the gas phase. Mixing D and L enantiomers with one of the pair isotopically labeled reveals the effect of chirality on cluster stability. The observed cluster distribution is compared to the predicted statistical distribution to determine any preference for homo- or heterochirality. Arginine, for example, forms a stable trimer with no preference for the chirality of the individual amino acids. Serine, however, forms a protonated octamer with a pronounced preference for homochirality. The implications of these results for the structures of the complexes are discussed along with the broader implications for the origins of homochirality in living systems (homochirogenesis).

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