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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
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.
In areas with trillions of
coccolithophores, the waters will turn
an opaque turquoise from the dense
cloud of coccoliths. 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.
Nacre (mother of pearl) in
shells. Aragonite crystals
formed in layers separated by
protein sheets.
A diatom: porous silica shell
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
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)
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, so
lattice spacing = amino acid residue spacing
9) Inhibitors
Magnetotactic bacterial cell containign chains of magnetite
(Fe3O4) crystals, ~ 100nm in length.
Fig.6.4 shows different crystal morphologies of bacterial magnetite and
their indexed faces. Crystal growth at different planes will produce
various shapes.
General distribution of inorganic P with depth in the open ocean.
Example at left was data taken from October 1988 to February
1989 at Station ALOHA in the central North Pacific, as part of the
Hawaiian Ocean Time-series program
(http://hahana.soest.hawaii.edu/hot/hot-dogs/interface.html).
General distribution of inorganic P with depth in
the open ocean.
Example at left was data taken from October 1988
to February 1989 at Station ALOHA in the central
North Pacific, as part of the Hawaiian Ocean
Time-series program
(http://hahana.soest.hawaii.edu/hot/hotdogs/interface.html).
Why are these low near the surface?
From a report of:
BIOMOLECULAR SELF-ASSEMBLING MATERIALS
Scientific and Technological Frontiers,
Panel on Biomolecular Materials
Solid State Sciences Committee
Board on Physics and Astronomy
FIGURE 1 Illustration of the relationships
among various aspects of biomolecular
materials and their connections with the
life sciences.
Although still in its infancy, the
application of biological principles to the
development of new materials has
already been demonstrated. A nucleus of
broad-based research already exists,
involving a variety of disciplines including
chemistry, physics, biology, materials
science, and engineering.
The following specific examples of current research may help to give the reader an idea of the character of
this exciting field:
Polymer biosynthesis. Self-assembled monolayers and multilayers. Decorated membranes.
Mesoscopic organized structures. Biomineralization.
Biomolecular templates are being studied as nucleation devices for the synthesis of inorganic compounds with
unusual structures and high degrees of perfection. Examples include the epitaxial growth of carbonates
induced by molluscan shell protein and the intracellular synthesis of CdSe semiconductors.
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).
A and B –
SEM images recorded from barite
crystals grown at the interface between
water and hexane with stearic acid in the
organic phase at a supersaturation ratio of
ca. 50.
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 predefined 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.
Fig. 5 (a) Cellular film of manganese(III/IV) oxide
synthesized by reaction field templating in an oil
droplet biliquid foam. The framework has cell
sizes of 300 nm with continuous mineralized walls,
100 nm in thickness; note the additional higher-order
morphological features (circular pits) with
micrometre length scales, scale bar = 2 mm. (b)
Hollow spherical shell of calcium carbonate
(aragonite) formed by synthesizing a cellular
mineralized
film on polymer microspheres, scale bar = 200 nm.
(c) BaSO4 ‘tentacles’ formed from coaligned
crystalline nanofilaments produced by synthesis in
supersaturated microemulsions at room temperature,
scale bar = 500 nm. (d) Individual BaSO4
nanofilaments and a coiled morphological form
synthesized as in (c) scale bar = 200 nm. (e) Microskeletal calcium phosphate synthesized in frozen-oil
bicontinuous microemulsions, scale bar =
500 nm. ( f ) Silica microstructure produced by
alkoxide condensation reactions in bicontinuous
microemulsions, scale bar = 1 mm
Fig. 4 (a) Spiral outgrowth of calcium
carbonate formed by growing crystals in the
presence of 10 mg dm23 of a linear poly
a,b-aspartate of Mr
7100, scale bar 100 mm. (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) Self-assembled helical ribbon of a silicaphospholipid biphase, scale bar 200 mm. (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.