RIGHT AND LEFT: RIGHT AND LEFT: Geochemical Origins Geochemical Origins Of Life’s Homochirality Of Life’s Homochirality United States Naval Observatory United States Naval Observatory February 28, 2008 February 28, 2008 Robert Hazen, Geophysical Laboratory Robert Hazen, Geophysical Laboratory
72
Embed
RIGHT AND LEFT: Geochemical Origins Of Life’s Homochirality
RIGHT AND LEFT: Geochemical Origins Of Life’s Homochirality. United States Naval Observatory February 28, 2008 Robert Hazen, Geophysical Laboratory. Research Collaborators. Carnegie Institution Hugh Churchill H. James Cleaves George Cody G ö zen Ertem Tim Filley - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
RIGHT AND LEFT:RIGHT AND LEFT:
Geochemical OriginsGeochemical Origins
Of Life’s HomochiralityOf Life’s Homochirality
RIGHT AND LEFT:RIGHT AND LEFT:
Geochemical OriginsGeochemical Origins
Of Life’s HomochiralityOf Life’s HomochiralityUnited States Naval ObservatoryUnited States Naval Observatory
Research CollaboratorsResearch CollaboratorsResearch CollaboratorsResearch CollaboratorsCarnegie Institution Hugh Churchill H. James Cleaves George Cody Gözen Ertem Tim Filley Rebecca Martin Jake Maule Andrew SteeleGeorge Washington Univ. Glenn Goodfriend Henry TengUniv. of Delaware Donald Sparks
Univ. of Arizona Robert T. DownsGeorge Mason University Harold MorowitzJohns Hopkins University Dimitri Sverjensky Caroline Jonsson Christopher Jonsson Carnegie-Mellon University Aravind Asthagiri David ShollSmithsonian Institution Ed VicenziSpanish Astrobiology Inst. Antonio Salgado-Serrano
Two QuestionsTwo Questions(Possibly Related)(Possibly Related)
Two QuestionsTwo Questions(Possibly Related)(Possibly Related)
2. What processes selected life’s idiosyncratic molecules?
1. How do crystals interact with organic molecules?
• Only 20 biological amino Only 20 biological amino acids compared to >90 in acids compared to >90 in Murchison meteoriteMurchison meteorite
• Only Only -H amino acids (i.e., -H amino acids (i.e., no no -methyl amino acids) -methyl amino acids)
• Homochirality – L>>RHomochirality – L>>R
Biological HomochiralityBiological HomochiralityBiological HomochiralityBiological HomochiralityMany of life’s essential molecules are chiral.Many of life’s essential molecules are chiral.
42
C
3
1
(L)-enantiomer(L)-enantiomer
42
C
3
1
(R)-enantiomer(R)-enantiomer
How did life on Earth become homochiral?How did life on Earth become homochiral?
Annual sales of chiral pharmaceuticals Annual sales of chiral pharmaceuticals approaches $200 billion.approaches $200 billion.
Chiral mineral surfaces are common. hiral mineral surfaces are common.
In oxides and silicates, larger chiral In oxides and silicates, larger chiral indices are often associated with the indices are often associated with the presence of both terminal cations and presence of both terminal cations and anions. anions.
Relatively large chiral indices are Relatively large chiral indices are often associated with stepped and often associated with stepped and kinked surfaces.kinked surfaces.
Glenn Goodfriend with Steve GouldGlenn Goodfriend with Steve Gould
2. Mineral Chiral Selection2. Mineral Chiral Selection2. Mineral Chiral Selection2. Mineral Chiral Selection
Selective Adsorption on CalciteSelective Adsorption on CalciteSelective Adsorption on CalciteSelective Adsorption on Calcite
•CaCOCaCO33
•RhombohedralRhombohedral
•Common (214) formCommon (214) form
GC AnalysisGC Analysis GC AnalysisGC Analysis
Aspartic acid doubletAspartic acid doublet
GC AnalysisGC AnalysisGC AnalysisGC Analysis
Aspartic acid doubletAspartic acid doublet
~15 secondsSeparation
Chiral Selection on CalciteChiral Selection on CalciteChiral Selection on CalciteChiral Selection on Calcite
D excess D excess
L excess L excess
Hazen et al. (2001) Hazen et al. (2001) PNASPNAS
Calcite (214) crystal surfaces select D- and L-aspartic acid.
We do not observe selective adsorption of glutamic acid or alanine on calcite.
Maximum selective adsorption occurs on terraced crystal faces. This fact suggests that chiral selection may occur along linear features.
The alignment of chiral amino acids on calcite may lead to homochiral polymerization.
Why do D- and L-amino acids bind differently Why do D- and L-amino acids bind differently (aspartic acid versus alanine on calcite)?(aspartic acid versus alanine on calcite)?
Experiments do not tell us much except that Experiments do not tell us much except that there may be an electrostatic contribution.there may be an electrostatic contribution.
Can modeling shed light on specific atomic-Can modeling shed light on specific atomic-scale interactions?scale interactions?
The most stable configuration found for D- and L-The most stable configuration found for D- and L-aspartic acid on calcite (214) surface. The D aspartic acid on calcite (214) surface. The D
enantiomer is favored by 8 Kcal/mol. enantiomer is favored by 8 Kcal/mol.