Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies

Details Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.286s&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 286

Computer Science

Scientific paper

The wide acceptance of the parent body aqueous alteration hypothesis to explain the presence of hydrated silicate minerals on carbonaceous chondrite meteorites has led a number of researchers to investigate the suggestion that some of the organic compounds in these meteorites were produced during the silicate mineral alteration event (Bunch and Chang, 1980; Peltzer et al., 1984; Cronin, 1989; Shock and Schulte, 1990). Much of the interest has focused on the mechanisms of amino acid formation, the most favored of which is Strecker synthesis (Peltzer et al., 1984; Cronin, 1989; Kerridge, 1990). The observation of ammonium-bearing minerals in several carbonaceous chondrites (Zolensky and McSween, 1988), as well as the possible detection of the same minerals on asteroids (King et al., 1992), may allow explicit coupling of Strecker synthesis reactions with mineral alteration by aqueous fluids on meteorite parent bodies. In one path of Strecker synthesis, aldehydes or ketones react with HCN and ammonia in aqueous solution to produce amino acids. In the absence of ammonia in the initial reaction step, Strecker synthesis will produce hydroxy acids. This process has also been invoked to explain the presence of hydroxy acids on carbonaceous chondrites (Peltzer et al., 1984). The potential for Strecker synthesis of amino and hydroxy acids can be evaluated from values of the Gibbs free energy of the overall reactions deltaG (sub)r degrees. At 25 degrees C and 1 bar, calculated values of deltaG (sub)r degrees are negative for many examples of overall Strecker synthesis reactions, indicating that these reactions are energetically favored at these conditions. Oxygen isotope systematics indicate that aqueous alteration of carbonaceous chondrites occurred at temperatures from 0 degrees to ~150 degrees C (Clayton and Mayeda, 1984). Values of deltaG (sub)r degrees for reactions involving aqueous organic compounds can be calculated at elevated temperature using standard state properties from the literature together with equations, data and parameters provided by Shock and Helgeson (1990) and Shock (1992). We have used correlation algorithms developed by Shock and Helgeson (1990) to estimate equation-of-state parameters for aqueous aldehydes and HCN. These data and parameters, together with those for aqueous amino acids from Shock and Helgeson (1990), hydroxy acids from Shock (1992) and NH(sub)3 (aq) from Shock et al. (1989) were used to calculate values of deltaG (sub)r degrees for Strecker synthesis reactions at elevated temperatures. All the reactions we have investigated thus far are energetically favored over the entire range of temperatures considered. These preliminary results suggest that Strecker synthesis during aqueous alteration may account for the amino acids and hydroxy acids observed in carbonaceous chondrites. Testing this hypothesis, however, requires simultaneous solution of mass-action and mass-balance equations, together with constraints on initial activities of aldehydes and HCN in the aqueous phase. The presence of these compounds in interstellar space (Turner, 1989) and their inferred concentrations in comets provide constraints on these variables. Additionally, the coupled equilibria between the amino and hydroxy acids produced by Strecker synethesis allow evaluation of the activity of NH(sub)3 (ag). References: Bunch T. E. and Chang S. (1980) Geochim. Cosmochim. Acta 44, 1543-1577; Clayton R. N. and Mayeda T. K. (1984) Earth Planet. Sci. Lett. 67, 151-161; Cronin J. R. (1989) Adv. Space Res. 9, 5964; Kerridge J. F. (1991) Origins of Life 21, 19-29; King T. V. V., Clark R. N., Calvin W. M., Sherman D. M., and Brown R. H. (1992) Science 255, 1551-1553; Peltzer E. T., Bada J. L., Schlesinger G., and Miller S. L. (1984) Adv. Space Res. 4, 69-74; Shock E. L. (1992) Amer. J. Sci., submitted; Shock E. L. and Helgeson H. C. (1990) Geochim. Cosmochim. Acta 54, 2009-2036; Shock E. L., Helgeson H. C., and Sverjensky D. A. (1989) Geochim. Cosmochim. Acta 53, 2157-2183; Shock E. L and Schulte M. D. (1990) Nature 343, 728-731; Turner B. E. (1989) Space Sci. Rev. 51, 235-337; Zolensky M. E. and McSween H. Y. (1988) In Meteorites and the Early Solar System (eds J. F. Kerridge and M. S. Matthews), pp. 114-143. Univ. Arizona Press, Arizona.

Affiliated with

Also associated with

No associations

Rating

Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1209636