Biomedical Engineering Reference
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structure and activities of lipid A-diphosphate, the experiments were repeated in the
presence of 150 µM Mg
2+
in the same crystallization environment. Even at this Mg
2+
concentration no changes in the above findings were observed. However, recrystal-
lization experiments in the presence of higher amounts of Mg
2+
(150 mM) revealed
aragonite to be the major polymorph of the precipitated CaCO
3
(Faunce and Paradies,
2008).
The crystalline CaCO
3
particles that formed remained well separated between the
interfaces of the lipid A-diphosphate assemblies and the aqueous surrounding. The
CD spectrum between 210 and 500 nm did not change with time or [Ca
2+
] at either
pH. This indicated that no changes in the secondary structures of the template oc-
curred upon crystallization. Accordingly, no contamination of lipid A-diphosphate by
the CaCO
3
crystals was detected from MALDI-TOF-MS and LC-MS analyses. Inter-
particle interactions at a well-defined screening length
k
-1/2
~ 9.5 nm (surface charge
density)
between the template, crystals and water may have arisen. This would be from
a balance between long-range attractive and repulsive forces at the above screening
length. Roughness-induced capillary effects (Hashmi et al., 2005) and irregular menis-
cus defects may explain the prevalence of the observed vaterite cluster at high-volume
fractions, in the subphase. Loose aggregates of vaterite formed at high-volume frac-
tions by suppressing the growth of calcite.
The development of a specific well-formed mineral layer by the various poly-
morphs of CaCO
3,
with lipid A-diphosphate as a template may cause direct resistance
to viral and bacterial invasion and/or penetration with respect to CAM activity. The
CAM activity was not changed in the presence of 10 µM to 5 mM CaCl
2
at pH 8.5,
thus underlining the importance of the physical behavior of lipid A-diphosphate at
high pH. However, it was significantly altered in the presence of 10 mM CaCl
2
but
revealed no further increase in CAM activity.
lipid a-phosphate assemblies at ph 8.0-9.0
The solution structure of lipid A-diphosphate at an alkaline pH that is pH 8.5-9.0 was
of considerable importance for a number of reasons, which are as follows: (i) potential
production of vaccines; (ii) compounds known to bind to LPS or lipid A-diphosphate
at pH 8.0; (iii) chain length-dependent agglutination of oligosaccharide clustering at
alkaline pH by multivalent anion binding (Christ et al., 1994), (iv) inactivation of
endotoxins by cationic surfactants in the textile, cleaning and disposal processes in
hospitals and nursing homes, and (v) neutralizing the endotoxic structure of lipid A-
diphosphate with cationic complexes (Paradies et al., 2003). The solutions of lipid
A-diphosphate at pH 8.5 showed significantly lower solubility than organic salts with
for example cetylpyridinium, cetyltrimethyl-ammonium, triethylamine, dihexadecyl-,
or didecyldimethylammonium than one would expect. The physical behavior of dis-
persions of lipid A-diphosphate at alkaline pH was highly warranted, therefore, pre-
liminary results of this system at pH 8.0 at 25°C presented. The influence of a variable
charge on lipid A-phosphates, particularly, for lipid A-diphosphate
,
was more subtle to
study and difficult to access experimentally because of the chemical instability at an
alkaline pH over certain time periods. Counterion condensation played a significant
role as shown for example micelles by Bucci et al. (1991), Yamanaka et al. (1999)
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