Joined: June 2008
|Quote (Alan Fox @ Feb. 21 2011,04:13)|
|So cycles of wetting and drying at the margin of salt water pools could in theory, if amino acids ware present, result in the build-up of random sequences. Has any experiment been tried or proposed?|
PS Thanks for responses, Guys.
Yes, they have been done. BA^77 has a quotemine of a study of dilute salty water favoring AAs over peptides. It is a real scientific paper by a couple of guys who favor eutectic ice OOL theories. I think the references in that paper contain a paper about more concentrated salt conditions. I know I've read it. Basically, when the water molecule comes out, it gets grabbed by the sodium and chloride ions and isn't available to break the peptide bond.
Free energy relationships in aqueous amino acid and peptide solutions containing sodium chloride
Eugene E. Schrier and R. A. Robinson
Journal of Solution Chemistry
Volume 3, Number 7, 493-501, DOI: 10.1007/BF00648134
Three systems of the type amino acid or peptide-sodium chloride-water have been investigated over wide solute molality ranges using the isopiestic vapor pressure method. The amino acid employed was L-alpha-alanine, while the peptides were diglycine and triglycine. Equations were obtained for the activity coefficients of these compounds in the salt solutions in terms of the molalities of the solutes. The trace activity coefficients of the peptides were negative at low salt molality and became positive as the salt molality was increased. The limiting interaction parameters were calculated for the systems using the Kirkwood ion-dipole expression and empirical quantities derived from previous work to obtain the salt effect on the nonpolar and amide portion of the molecule. Good agreement was obtained between the calculated values and the experimental results in the case of diglycine, but they diverged in the case of triglycine. The calculated value for L-alpha-alanine is in poorer agreement with the experimental value than for the other amino acids studied previously.
Key words Amino acids - peptides - diglycine - triglycine - isopiestic method - ion-dipole interactions - NaCl
Presented in part at the Second International Conference on Calorimetry and Thermodynamics, Orono, Maine, July 1971.
Wow that is old, almost old enough for a creationist to believe!
Newer, but still science from the previous century:
(This is the cite that speaks directly to your question.)
Origins of Life and Evolution of Biospheres
Volume 23, Number 3, 167-176, DOI: 10.1007/BF01581836
Evaporation cycle experiments — A simulation of salt-induced peptide synthesis under possible prebiotic conditions
Somporn Saetia, Klaus R. Liedl, Artur H. Eder and Bernd M. Rode
Evaporation cycles applied to dilute solutions of amino acids, Cu(II) and NaCl lead to peptides within 1–3 days. This simulation of possible coastal or laguna processes in a primitive earth environment gives further indications towards the relevance of the salt-induced peptide formation reaction in chemical evolution. The experiments were successfully applied to glycine, alanine, aspartic and glutamic acid. Besides isolated amino acids, also their mixtures with glycine as reaction partner were studied, leading to peptides for all of the aforementioned substances, as well as for valine and proline, which do not dimerize alone. Sequence preferences and some conservation of optical purity were observed.
A follow-up study showing synergies of multiple AAs in the mix:
Origins of Life and Evolution of Biospheres
Volume 29, Number 5, 463-471, DOI: 10.1023/A:1006583311808
Mutual Amino Acid Catalysis in Salt-Induced Peptide Formation Supports this Mechanism's Role in Prebiotic Peptide Evolution
Yuttana Suwannachot and Bernd M. Rode
The presence of some amino acids and dipeptides under the conditions of the salt-induced peptide formation reaction (aqueous solution at 85 °C, Cu(II) and NaCl) has been found to catalyze the formation of homopeptides of other amino acids, which are otherwise produced only in traces or not at all by this reaction. The condensation of Val, Leu and Lys to form their homodipeptides can occur to a considerable extent due to catalytic effects of other amino acids and related compounds, among which glycine, histidine, diglycine and diketopiperazine exhibit the most remarkable activity. These findings also lead to a modification of the table of amino acid sequences preferentially formed by the salt-induced peptide formation (SIPF) reaction, previously used for a comparison with the sequence preferences in membrane proteins of primitive organisms
Dude, its got, like, its own acronym!
More from the Rode group. Discussion of SIPF starts on page 9 of the PDF. Now claiming some effect on the growth of homochirality. Woot!
I’m referring to evolution, not changes in allele frequencies. - Cornelius Hunter
I’m not an evolutionist, I’m a change in allele frequentist! - Nakashima