Transcript Biomineralization - Bryn Mawr College

Biomineralization
what?
• Relatively new branch of study in bioinorganic
• Extends beyond ‘biocoordination chem’ focusing on M + L
• Extends length range of bio and inorg interplay
• Interfaces with “hot” area of nano structures/devices/materials
• Inorganic structures combined with an organic matrix
Biomineralization
The bottom line?
• Organic layers or limits between crystals gives flexibility
• Patterning from carboxylate arrays
• Highly Controlled precipitation
• Involve complicated Equilbria
Biomineralization
which?
Major materials are:
(see Table VI.1)
Calcium carbonate - crystalline as CaCO3 (calcite, aragonite)
amorphous as CaCO3.hydrate
Calcium phosphate- crystalline as Ca10(PO4)6(OH)2 (hydroxyapatite)
crystalline as Ca8(PO4)6(H)2 (octacalcium phosphate)
Silica
Iron oxides
amorphous SiO2.hydrate
magnetite Fe3O4
Geothite, lepidocrocite
ferrihydrite Fe2O3. hydrate
Biomineralization
requirements
Low solubility: Ca2+ preferred to Mg2+
High lattice stabilities: Ca10(PO4)6(OH)2 preferred to MgO
Thermodynamically stable:
Recall:
Lattice Enthalpy DHlattice ~ Lattice Energy, U
U=
N Z+ Z- A e2
4 p eo d
(1 - n)
N is Avogadro’s # 6.022 x 1023 ion pairs/mol
Z+ Z- is the charge product
A is the Madelung constant
e2 and eo are charge on e- and permittivity constants
d is the distance (cm) between r+ and rn is a number, Born constant
Biomineralization
uses
Major materials are:
(see Table VI.1)
CaCO3 (calcite, aragonite)
structural support
amorphous as CaCO3.hydrate
Ca storage
Ca10(PO4)6(OH)2 (hydroxyapatite)
structural support, mech. strength
Ca8(PO4)6(H)2 (octacalcium phosphate)
precursor
SiO2.hydrate
structural support
magnetite Fe3O4
orientation
Geothite, lepidocrocite
teeth
ferrihydrite Fe2O3. hydrate
Fe storage
Morphogenesis: Pattern and Form in Biomineralization
Fig. 2 (a) Magnesium calcite
polycrystalline concretion
from the red coral Corallium
rubrum showing irregular
surfaces protuberances,
scale bar 10 mm.
(b) the biomineral is
patterned by radial and
tangential constraints to give
the wheel-like architecture.
(d) Radiolarian microskeleton consisting of a
continuous spheroidal
framework of amorphous
silica, scale bar 10 mm.
(e) Radiolarian microskeleton showing how the
hollow porous silica
microshell is structurally
connected to an internal set
of radially-directed
mineralized spicules; scale
same as in (d).
From S. Mann, 1997
The combination of inorganic structure
with organic matrix can increase the
strength.
The organic matrix:
• Limits dimension of crystal
• Reduces voids in crystal
• Inhibits cracks
• Matrix absorbs, dissipates energy
• Patterning
Nacre (mother of pearl) in
shells. Aragonite crystals
formed in layers separated by
protein sheets.
Like any other type of phytoplankton, coccolithophores
are one-celled marine plants that live in large numbers
throughout the upper layers of the ocean. Unlike any other
plant in the ocean, coccolithophores surround themselves
with a microscopic plating made of limestone (calcite).
These scales, known as coccoliths, are shaped like
hubcaps and are only three one-thousandths of a millimeter
in diameter.
What coccoliths lack in size they
make up in volume. At any one time
a single coccolithophore is attached
to or surrounded by at least 30
scales. Additional coccoliths are
dumped into the water when the
coccolithophores multiply asexually,
die or simply make too many scales.
Scientists estimate that the
organisms dump more than 1.5
million tons (1.4 billion kilograms) of
calcite a year, making them the
leading calcite producers in the
ocean. In large numbers,
coccolithophores dump tiny white
calcite plates by the bucketful into
the surrounding waters and
completely change its hue. In areas
with trillions of coccolithophores, the
waters will turn an opaque turquoise
from the dense cloud of coccoliths.
Biomineralization
context
Major role in carbon cycle:
Ca2+ + HCO3  CaCO3 + CO2 + H2O
Calcification can parallel photosynthetic activity:
As carbon dioxide is removed, equilibrium shifts favoring carbonate.
CaCO3 deposited within cells: coral reefs.
Example of biomineralization as a secondary effect.
Another is FeS from sulfate reducing bacteria.
Biologically Induced Biomineralization
Biologially Induced Biomineralization
characteristics
Results from other metabolic processes
Not controlled
Amorphous or heterogeneous structures
Biologially Controlled Biomineralization
characteristics
• Highly regulated processes
• Examples: bone, teeth, shells, having specific functions
• Well-defined structures (crystallinity), and shapes
• Formed in vesicle compartments = functions like a flask!
• Epitaxy control: matches dimensions of lattice to the
amino acid template
Fig. VI.5 : Controls of biomineralization from supersaturated solutions
1) Gating via membrane pumps and redox processes
2) complexations w/ solubilizing agents
3) enzyme controlled concentrations
4) ionic strength (common ion effect) and activities
5) pH
6) organic matrix- mediation insoluble organic compartments
7) matrix mediated nucleation, regulated direction of lattice growth
8) Epitaxy control: match dimension of crystal to pattern of template, lattice spacing = amino acid residue spacing
9) Inhibitors
C
chelation
activity
redox
ionic strength
pH
Fig.6.4 shows different crystal morphologies of bacterial magnetite and
their indexed faces. Crystal growth at different planes will produce
various shapes.
How complicated shapes are formed
Use of specific residues as template
 Asp – rich protein
Ca2+
How complicated shapes are formed
Like a cast made from a mold
Fig. 6.10 Cell Walls, intracellular organelles and cellular assemblages act
as scaffolds for microtubules (MT) which in turn are used as directing agents
for the patterns of vesicles (V) involved in biomineralization (B).
From S. Mann 1997
Magnetotactic bacterial cell containing chains of magnetite
(Fe3O4) crystals, ~ 100nm in length. Organized along cell
walls in vesicles, added sequentially to align magnetic units.
From a report of:
BIOMOLECULAR SELF-ASSEMBLING MATERIALS
Scientific and Technological Frontiers
Examples of current
research inf this
exciting field:
Polymer
biosynthesis.
Self-assembled
monolayers and
multilayers.
Decorated
membranes.
Mesoscopic
organized
structures.
Biomineralization.
FIGURE 1 Illustration of the relationships among various aspects of biomolecular materials and their connections
with the life sciences. A nucleus of broad-based research already exists, involving a variety of disciplines
including chemistry, physics, biology, materials science, and engineering.
Debabrata R. Ray, Ashavani Kumar, Satyanarayana Reddy, S. R. Sainkar, N. R. Pavaskar and Murali Sastry*
Materials Chemistry Division, National Chemical Laboratory, Pune, India CrystEngComm, 2001, 3, 213-216
Development of protocols to grow crystals of controllable structure, size, morphology
and superstructures of pre-defined organizational order is an important goal in crystal engineering with
tremendous implications in the ceramics industry. Lured by the exquisite control that biological organisms exert over mineral
nucleation and growth by a process known as biomineralization, materials scientists are trying to understand biomineralization
and, thereby, develop biomimetic approaches for the synthesis of advanced ceramic materials.
SEM images recorded from barite
crystals grown at the interface
between water and hexane with
stearic acid in the organic phase.
SEM images of BaSO4 crystals grown at the water–
chloroform
interface with stearic acid (images A and B) and
octadecylamine (images C and D) as the templating
molecules in the organic phase.
In the case of octadecylamine, the molecules at the interface
would be positively charged at pH = 6.2 and therefore, the
sulfate ions would be bound at the interface rather than Ba2+
ions as was the case with stearic acid molecules. We were
interested in seeing whether the order of complexation of the
ionic species prior to crystallization affected the morphology
of the barite crystals grown at the liquid–
liquid interface. As
mentioned earlier, chloroform is denser than water and
therefore the orientation of both the stearic acid and
octadecylamine molecules at the liquid–
liquid interface would
be opposite to that in the case of water–
hexane (below).
Fig. 4
(a) Spiral outgrowth of calcium carbonate
formed by growing crystals in the
presence of 10 mg dm3 of a linear poly aspartate of Mr 7100, scale bar 100 mm.
(b) (b) Hierarchical morphology of BaSO4
crystals formed in a 0.5 mM aqueous
solution of polyacrylate of Mr 5100;
scale bar 10 mm. The cone-shaped units
develop on the rim of pre-existing cones,
and each cone consists of myriad BaSO4
nanofilaments (inset, scale bar 1 mm).
(c) (c) Self-assembled helical ribbon of a
silica-phospholipid biphase, scale bar
200 mm.
(d) (d) Thin section showing a continuous
silica framework produced by bacterial
templating. The porous channels (white
circles) are viewed end-on and are
approximately 500 nm in width, scale
bar 500 nm
A Hypothetical Model for Dental Enamel
Biomineralization
1. Amelogenins are synthesized and secreted
by ameloblast cells.
2. Amelogenin molecules assemble into nanosphere structures approximately 20 nm in
diameter with an anionic (negatively charged)
surface.
3. The nanospheres interact electrostatically
with the elongating surfaces of the enamel
crystalites, acting as 20nm spacers that prevent
crystal-crystal fusions. Enzymes (Proteinase-1)
eventually digest away the charged surface of the
nanospheres, producing hydrophobic
nanospheres that further assemble and stabilize
the growing crystalites.
4. Finally, other enzymes (Proteinase-2)
degrade the hydrophobic nanospheres,
generating amelogenin fragments and other
unidentified products (?), which are resorbed by
the ameloblasts.
5. As the amelogenin nanosphere protection is
removed, crystallites thicken and eventually may
fuse into mature enamel.