Download Mineral Surface

Mineral Surface
bulk vs surface
dangling bonds
reactivity of mineral surface
pH and ionic strength
Origin of First cell
role of minerals in
Urey-Miller experiments
chiral selection on mineral surfaces
mineral energy source
clay “vesicles” as cell membranes
Atoms on calcite (CaCO3)
15 nm x-y; 1Å height
Source: Asylum Research
For an atom at a surface of a crystal, the
surface coordination number is always
less than the bulk coordination number.
CN of Na in bulk = 6
CN of Na at surface <6
Origin of charge at mineral surfaces
Pauling’s Rules – neutral charge of cation on per bond basis
Na = octahedral coordination, +1: 1/6 per bond
Fe = octahedral coordination, +3: +3/6 = 0.5 per bond
Si = tetrahedral coordination, +4: +4/4 = 1 per bond
Good reference: Notes from Prof. Stephen A. Nelson
_
O_
+ Si + _
_ + + O_
_O _
_O
central, bridging
oxygen is satisfied but
other oxygen atoms
are not
tetrahedral
(SiO4)-4
“dangling” bonds
at edges
X
Fe
CN = 6
Goethite (FeOOH)
*double chain of octahedral
1 = singly coordinated surface O
2 = doubly coordinated surface O
3 = triply coordinated surface O
-2 + 0.5 + 1 = -0.5
singly
coordinated O
-2 + 0.5 + 0.5 + 1 = 0
doubly
coordinated O
-2 + 0.5 + 0.5 + 0.5 = -0.5
triply
coordinated O
pH dependence of mineral surface charge
ΞSiOH+
<> ΞSiO + H+
Favored at low pH b/c Le Chatelier's principle
*add protons the reaction proceeds to left
1.0 ΞSiO-
ΞSiOH+
0.5 “pzc”
0 pH pzc Point-of-zero charge of common minerals
Mineral
pzc
Chrysotile
>10
α-Al2O3
9.1
α-Fe2O3
8.5
γ-AlOOH
8.2
α-FeOOH
7.8
β-MnO2
7.2
Kaolinite
4.6
δ-MnO2
2.8
Montmorill.
2.5
SiO2
2.0
+ _ Stumm, Chemistry of the Solid-Water Interface 1992
Impact of ionic strength mineral surface charge
Electrical double layer in which excess
negative charge on surface is balance by
excess cations from solution.
*Thickness of this double layer depends upon
ionic strength.
For water at room temperature in monovalent
electrolyte, the Debye length is:
κ-1 (nm) = 0.304 / (ionic strength)-0.5
Some examples…
High I.S. = 0.1M then 0.96 nm
Low I.S.= 0.0001M then 30.4 nm
The “edge effect” of mineral surfaces
Greater diversity and density of organisms at the interface of two habitats.
Origin of life on Earth
*role of minerals
Brock Biology of Microorganisms
Role of mineral surfaces in origin of life
Origin of life
*Emergence or formation of biomolecules
What was the ultimate source of amino acids, etc?
Role of minerals in origin of life
Urey-Miller Experiment – use simple compounds to build larger
biomolecules like proteins
*Problem: amino acids quickly destroyed by
nitrites that were also formed.
Role of minerals in origin of life
Urey-Miller Experiment – use simple compounds to build larger
biomolecules like proteins
Jeffrey Bada repeated the experiments in the
presence of iron and carbonate minerals, which
may have been present on the early Earth.
Amino acids were again formed but this time they
were stable b/c the minerals “neutralized” the
nitrites. In particular, calcite (CaCO3) played a
key role.
Cleaves et al. 2008 Orig Life Evol Biosph
Role of minerals in origin of life
Pyrite (FeS2)
Metabolism in primitive organisms
H2 used to
create pmf
FeS
!"
Elemental S
Takes energy to organize inherently
disorganized molecules.
Oxygen was NOT available to
earliest cells, but FeS was common.
This reactions goes on as long as
there is a supply of FeS.
Many Archaea can carry out this
reaction
Brock Biology of Microorganisms
Hydrothermal vent
http://www.youtube.com/watch?v=D69hGvCsWgA
Role of minerals in origin of life
Emergence of chirality. Many of life’s macromolecules use chiral building
blocks.
Pre-biotic synthesis of biomolecules produces left and right-handed
molecules.
What selects for chirality?
1
1
2
C
4
3
(L)-enantiomer
C
4
2
3
(R)-enantiomer
Role of minerals in origin of life
Quartz (SiO2)
Left
Right
Quartz is the most common mineral on Earth.
Quartz has chiral faces.
Calcite (CaCO3)
Calcite also has chiral faces.
Aspartic acid (negative charge aa) adsorption to different faces on calcite.
D/L value = 1 value for aspar8c acid in experimental solu8on Hazen et al., 2001 PNAS
Role of minerals in origin of life
Formation of clay armored bubbles
*create an “inside” and “outside”
1.  Drop clay suspension on
glass slide.
2.  Add another slide on top.
3.  This traps air bubbles
4.  Rub slides back & forth.
5.  Bubbles coat with clay.
broken
clay vesicle
20 μ Authors suggest that this mimics natural motion of sliding rocks or pebbles under
influence of tides.
Subramaniam et al. 2011 Soft Matter
concentration of dextran is
similar inside and outside
concentration of fluorophore
is excluded from interior
monomers of oleate enter clayvesicle and then self-assemble
into liposome
All scale bars 10 µm