Biomedical Engineering Reference
In-Depth Information
Fig. 2.19
Schematic
illustration of a statistical
distribution of fish-type ice
binding surfaces on a
low-index secondary surface,
inducing a
surface-reconstruction-type
effect while selecting the face
indices (
hkl
)
i
. Reprinted with
permission from ref. [
44
].
Copyright (2005) American
Chemical Society
a fish-type ice binding surface. By providing supplementary bonding in various
directions transverse to the existing strong bonding direction, the ice binding surface
modifies the surface orientation. Out of the numerous possibilities available for
the surface orientations parallel to the PBC, the specific face indices (
hkl
)
i
are
selected in Fig.
2.19
. Therefore, the indices of the observed ice facets are expected
to vary according to the specific properties of the ice binding surface of the AFP
and according to the changes in the ice binding surface caused by the experimental
conditions.
The available experimental results show that the morphological modification
mechanism of surface reconstruction is triggered by two variants of the fish-type
ice binding surface. The “one-dimensional” ice binding surface variant found in
fish-type I AFPs and AFGPs is characterized by one or more linearly extended
helices, having regularly spaced binding intervals in only one direction. It can align
its helix/helices along any one of several alternative lattice translations transverse to
the existing strong bonding direction, thus mimicking a second intersecting strong
bonding direction that is absent from the crystal structure. The bridged distances are
lattice periods between adjacent parallel PBCs. Therefore, surface reconstruction
through “supplementary inter
chain
bonding” is triggered by the 1D ice binding
surface variant. In globular type II and III AFPs, however, the “irregular” ice binding
surface variant consists of mixed ' and “ structures that are not 1D. It need not
either be planar or exhibit any spacing regularity in its binding sites in order to
function. It can align itself along numerous shorter distances in various directions.
It bridges intermolecular distances that need not be lattice translations, by linking
oxygen-oxygen pairs on adjacent parallel PBCs. So the irregular ice binding surface
variant can trigger surface reconstruction through “supplementary inter
molecular
bonding.”
It has been noted [
44
] that the geometrical differences between prismatic and
pyramidal faces become significant in comparing theoretical prediction against
experimental observation. The prism is an open form, implying that it can appear on
the crystal habit in combination with other forms but not by itself, for example,
