RIGHT AND LEFT: Geochemical Origins Of Life’s Homochirality
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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
February 28, 2008February 28, 2008Robert Hazen, Geophysical LaboratoryRobert Hazen, Geophysical Laboratory
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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
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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?
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Crystal-Molecule InteractionsCrystal-Molecule InteractionsCrystal-Molecule InteractionsCrystal-Molecule Interactions
• Formation of teeth and bones
• Biomineralization and biofilms
• Fossilization
• Weathering and soil formation
• Paints, glues, dyes
• Environmental monitoring and clean-up
• Nanotechnology
• Drug synthesis and purification
• Origins of life
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Crystal-Molecule InteractionsCrystal-Molecule InteractionsCrystal-Molecule InteractionsCrystal-Molecule Interactions
Huong et al. (2003) “Bone recognition mechanism ofHuong et al. (2003) “Bone recognition mechanism ofporcine osteocalcin from crystal structure” Nature 425:977-980.porcine osteocalcin from crystal structure” Nature 425:977-980.
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Central Assumptions ofCentral Assumptions ofOrigin-of-Life ResearchOrigin-of-Life ResearchCentral Assumptions ofCentral Assumptions ofOrigin-of-Life ResearchOrigin-of-Life Research
The first life forms were carbon-based.
Life’s origin was a chemical process that relied on water, air, and rock.
The origin of life required a sequence of emergent steps of increasing complexity.
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Life’s Origins:Life’s Origins:Four Emergent StepsFour Emergent Steps
Life’s Origins:Life’s Origins:Four Emergent StepsFour Emergent Steps
1. Emergence of biomolecules
2. Emergence of organized molecular systems
3. Emergence of self-replicating molecular systems
4. Emergence of natural selection
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Origin of Biomolecules: The Problem
Origin of Biomolecules: The Problem
A fundamental attribute of life is a high degree of molecular selectivity and organization, but prebiotic synthesis processes are indiscriminate.
What prebiotic processes might have contributed to such selection and organization?
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Biomolecular Selectivity:Biomolecular Selectivity:Amino AcidsAmino Acids
Biomolecular Selectivity:Biomolecular Selectivity:Amino AcidsAmino Acids
• 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
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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.
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Basic VocabularyBasic VocabularyBasic VocabularyBasic Vocabulary
Chiral = Enantiomeric = HandedChiral = Enantiomeric = Handed
“ “D” = “R” = Right-handedD” = “R” = Right-handed
“ “L” = “S” = Left-handedL” = “S” = Left-handed
Homochiral versus heterochiralHomochiral versus heterochiral
Racemic = mixture of left and rightRacemic = mixture of left and right
Symmetry Breaking = separate D/LSymmetry Breaking = separate D/L
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Chiral Purity is ImportantChiral Purity is ImportantChiral Purity is ImportantChiral Purity is Important
Smells like orangesSmells like oranges Smells like lemonsSmells like lemons
R-Limonene Mirror L-LimoneneR-Limonene Mirror L-Limonene
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Chiral Purity is ImportantChiral Purity is ImportantChiral Purity is ImportantChiral Purity is Important
N
O
O
HN
H N
O
O
NH
H
R-enantiomer
Analgesic (Good)
S-enantiomer
Teratogen (Bad)
ThalidomideThalidomide
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Chiral Purity is ImportantChiral Purity is ImportantChiral Purity is ImportantChiral Purity is Important
N
O
O
HN
H N
O
O
NH
H
R-enantiomer
Analgesic (Good)
S-enantiomer
Teratogen (Bad)
ThalidomideThalidomide
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Enantioselective ChemistryEnantioselective ChemistryEnantioselective ChemistryEnantioselective Chemistry
2. Enantioselective synthesis
Chiral catalystProchiral Reactants
Enantiomerically PureProducts
1. Enantioselective separation
Chiral reagentRacemic Mixture
Enantiomerically PureProduct
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Prebiotic Chiral SelectionPrebiotic Chiral SelectionPrebiotic Chiral SelectionPrebiotic Chiral Selection
• But life demonstrates a remarkable But life demonstrates a remarkable
degree of chiral selectivity.degree of chiral selectivity.
• Prebiotic synthesis processes produce Prebiotic synthesis processes produce
mixtures of left and right molecules.mixtures of left and right molecules.
What is the mechanism of What is the mechanism of
symmetry breaking?symmetry breaking?
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Previous HypothesesPrevious HypothesesPrevious HypothesesPrevious Hypotheses
Global Mechanisms:
• Selective synthesis or photolysis by CPR
• Parity violations in ß decay
Local Chiral Microenvironments:
• Chiral molecules, themselves
• Mineral surfaces
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Our Hypothesis: Minerals WorkOur Hypothesis: Minerals WorkOur Hypothesis: Minerals WorkOur Hypothesis: Minerals Work
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Our Hypothesis: Minerals WorkOur Hypothesis: Minerals WorkOur Hypothesis: Minerals WorkOur Hypothesis: Minerals Work
Aspartic acid on calcite
Lysine on quartz
TCA on calcite
TCA on feldspar
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ObjectivesObjectivesObjectivesObjectives
1. Examine the occurrence of chiral mineral surfaces in nature (Hazen 2004; Downs & Hazen 2004).
2. Demonstrate chiral selectivity by mineral surfaces (Hazen et al. 2001; Castro-Puyana et al. 2008).
3. Deduce mineral-molecule interactions (Asthagiri &
Hazen 2006; 2007).
4. Propose a general experimental research strategy (Hazen, Steele et al. 2005; Hazen 2006).
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1. Natural Chiral Surfaces1. Natural Chiral Surfaces1. Natural Chiral Surfaces1. Natural Chiral Surfaces
Crystal terminationCrystal termination
Stepped surfaceStepped surface
Kink siteKink site
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FCC(643) 346FCC
Chiral Single-Crystal Metal Surfaces
Mirror images are non-superimposable
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Chiral Surfaces Can SelectChiral Molecules
Chiral Surfaces Can SelectChiral Molecules
McFadden et al. (1996) “Adsorption of chiral alcohols on ‘chiral’ metal surfaces.” Langmuir 12, 2483-2487.
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Chiral AdsorptionChiral Adsorption
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Quartz – SiO2Quartz – SiO2
Quartz is the only common chiral rock-forming mineral
Right Left
Reports of successful chiral selections as early as the 1930s.
Yet all previous authors used powdered quartz!
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Quartz: Face-Specific AdsorptionQuartz: Face-Specific Adsorption
(10-11)
(01-11)
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Quartz Crystal FacesQuartz Crystal Faces
Courtesy of S. ParkerCourtesy of S. Parker
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Quartz – (100) FaceQuartz – (100) Face
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Quartz – (101) FaceQuartz – (101) FaceQuartz – (101) FaceQuartz – (101) Face
MIRRORMIRROR
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Quartz – (011) FaceQuartz – (011) FaceQuartz – (011) FaceQuartz – (011) Face
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Feldspar (110)Feldspar (110)Feldspar (110)Feldspar (110)
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Feldspar (110)Feldspar (110)Feldspar (110)Feldspar (110)
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Diopside – (110) FaceDiopside – (110) FaceDiopside – (110) FaceDiopside – (110) Face
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Diopside – (110) FaceDiopside – (110) FaceDiopside – (110) FaceDiopside – (110) Face
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Calcite – CaCOCalcite – CaCO33Calcite – CaCOCalcite – CaCO33
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Calcite – (214) FaceCalcite – (214) FaceCalcite – (214) FaceCalcite – (214) Face
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Chiral Indices: Calcite (104)Chiral Indices: Calcite (104)Chiral Indices: Calcite (104)Chiral Indices: Calcite (104)
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Chiral Indices: Calcite (214)Chiral Indices: Calcite (214)Chiral Indices: Calcite (214)Chiral Indices: Calcite (214)
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Table of Chiral IndicesTable of Chiral IndicesMineral Face Average Displ. Max. Displ.
Calcite (214) 0.93 1.81
Diopside (110)-c 0.53 0.85(110)-e 0.72 1.54
Copper (854) 0.84 1.29
Feldspar (110) 0.52 1.01
Quartz (100) 0.54 0.59(011) 0.36 0.46(101) 0 0
Downs & Hazen (2004) J. Molec. Catal.
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Table of Chiral IndicesTable of Chiral Indices
Mineral Face Average Displ. Max. Displ.
Calcite (214) 0.93 1.81
Diopside (110)-c 0.53 0.85(110)-e 0.72 1.54
Copper (854) 0.84 1.29
Feldspar (110) 0.52 1.01
Quartz (100) 0.54 0.59(011) 0.36 0.46(101) 0 0
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Table of Chiral IndicesTable of Chiral Indices
Mineral Face Average Displ. Max. Displ.
Calcite (214) 0.93 1.81
Diopside (110)-c 0.53 0.85(110)-e 0.72 1.54
Copper (854) 0.84 1.29
Feldspar (110) 0.52 1.01
Quartz (100) 0.54 0.59(011) 0.36 0.46(101) 0 0
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Conclusions 1: Chiral SurfacesConclusions 1: Chiral SurfacesConclusions 1: Chiral SurfacesConclusions 1: Chiral Surfaces
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.
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Glenn Goodfriend with Steve GouldGlenn Goodfriend with Steve Gould
2. Mineral Chiral Selection2. Mineral Chiral Selection2. Mineral Chiral Selection2. Mineral Chiral Selection
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Selective Adsorption on CalciteSelective Adsorption on CalciteSelective Adsorption on CalciteSelective Adsorption on Calcite
•CaCOCaCO33
•RhombohedralRhombohedral
•Common (214) formCommon (214) form
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GC AnalysisGC Analysis GC AnalysisGC Analysis
Aspartic acid doubletAspartic acid doublet
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GC AnalysisGC AnalysisGC AnalysisGC Analysis
Aspartic acid doubletAspartic acid doublet
~15 secondsSeparation
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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
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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.
Conclusions 2:Conclusions 2:Mineral Chiral SelectionMineral Chiral Selection
Conclusions 2:Conclusions 2:Mineral Chiral SelectionMineral Chiral Selection
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3. Modeling Mineral-Molecule 3. Modeling Mineral-Molecule InteractionsInteractions
3. Modeling Mineral-Molecule 3. Modeling Mineral-Molecule InteractionsInteractions
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?
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Modeling Mineral-Molecule Modeling Mineral-Molecule InteractionsInteractions
Modeling Mineral-Molecule Modeling Mineral-Molecule InteractionsInteractions
D-Alanine onD-Alanine on
Calcite (214)Calcite (214)
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Modeling Alanine on Calcite (214)Modeling Alanine on Calcite (214)Modeling Alanine on Calcite (214)Modeling Alanine on Calcite (214)
Use density functional theory (an accurate 1st
principles method) to model interactions.
As a first approximation ignore water (i.e., gas phase model).
Examine numerous plausible configurations.
The most stable configurations involve Ca-O bonding between calcite and carboxyl groups.
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D-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) Interactions
Begin by bringing a D-alanine molecule close to an unrelaxed calcite surface.
initial final H
N
C
O
Ca
initial final H
N
C
O
Ca
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D-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) InteractionsD-Alanine-Calcite (214) Interactions
The stable converged configuration reveals surface relaxation and Ca-O and O-H
interactions, but no strong third interaction.
initial final H
N
C
O
Ca
initial final H
N
C
O
Ca
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Alanine-Calcite (214) InteractionsAlanine-Calcite (214) InteractionsAlanine-Calcite (214) InteractionsAlanine-Calcite (214) Interactions
D-alanineD-alanine L-alanineL-alanine
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(D)-ASP (L)-ASP
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.
Aspartic Acid-Calcite (214) Aspartic Acid-Calcite (214) InteractionsInteractions
Aspartic Acid-Calcite (214) Aspartic Acid-Calcite (214) InteractionsInteractions
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Conclusions 3: Modeling Conclusions 3: Modeling Mineral-Molecule InteractionsMineral-Molecule Interactions
Conclusions 3: Modeling Conclusions 3: Modeling Mineral-Molecule InteractionsMineral-Molecule Interactions
Chiral interactions require Chiral interactions require three points of interaction.three points of interaction.
Which molecule sticks to Which molecule sticks to which surface is idiosyncratic.which surface is idiosyncratic.
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4. A General Research Strategy4. A General Research Strategy4. A General Research Strategy4. A General Research Strategy
How do we evaluate interactions among
the numerous possible mineral-molecule
pairs?
We need a combinatoric approach.
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Jake Maule, Andrew Steele and Rebecca Martin
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A Combinatoric StrategyA Combinatoric StrategyA Combinatoric StrategyA Combinatoric Strategy
ChipWriter
• Up to 126 minerals
• Up to 49,152 spots per
mineral
• Up to 96 different wells
• 100-micron spots
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A B CMicroarrays of Cy3-labeled asparagine, glutamine
and tyrosine on glass at 20 serial dilutions.
Each microarray was scanned simultaneously with 532nm/635nm lasers and the fluorescence emission was captured at the wavelength bands of 557-592nm
(Cy3) and 650-690nm (Cy5). Each image shows the intensity of Cy3/Cy5 fluorescent bands at a focal distance of 60m (left) and 120m (right).
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Microarrays of Cy3-labeled L-lysine on left- and right-handed quartz (100) faces at 8 serial dilutions. 150-micron spots.
A B
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Edward Vicenzi and Detlef RostToF-SIMS Lab, Smithsonian Institution
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ToF-SIMS
High-resolution ion fragment maps of
150-micron L-lysine spots on calcite (214).
X
X
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mass / u42.85 42.90 42.95 43.00 43.05 43.10 43.15
010
110
210
310
410
510
Inte
nsity
mass / u20 40 60 80 100 120 140 160 180 200 220 240 260 280
010
110
210
310
410
510
610
710
Inte
nsity
43Ca+ 42CaH+
C2H3O+
C2H5N+
C3H7+
L lysinecalcite
m/m ~ 8000 FWHM
300 AMU L-Lysine on Calcite (214)
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9 x 13 Array on 1 x 1 x 0.3 cm feldspar plate.
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AMINO ACIDS AND SUGARS ON FELDSPAR(010) Face – 1 x 1 cm plate
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Feldspar (010) in ToF-SIMS Sample Holder
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D-Lysine on Feldspar (010)
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DL-Xylose on Feldspar (010)
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mass / u42.85 42.90 42.95 43.00 43.05 43.10 43.15 43.20
010
110
210
310
410
510
Inte
nsi
ty
C2H5N (43.04)
C2H3O (43.02)
Key to Adsorbants----- arabinose
----- lyxose
----- ribose
----- xylose
----- lysine
Mass vs. Intensity for ~43 mass unit fragments
PentoseSugars
Amino Acid
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CONCLUSIONSCONCLUSIONS
• Microarray technology coupled with ToF-SIMS provides a powerful experimental means for combinatoric studies of mineral-molecule interactions.
• Many mineral surfaces have the potential for chiral selection of plausible prebiotic molecules.
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With thanks to:
NASA Astrobiology Institute National Science Foundation
Carnegie Institution of Washington