The study of morphology and shape development has gained considerable interest in certain sciences, notably biology and geology. Liesegang experiments producing Co(OH)2 stratification are performed here, in one, two, and three dimensions for comparison of the pattern morphologies. We obtain well-resolved bands in one dimension, target patterns (rings) in two dimensions, and onion patterns (spherical shells) in three dimensions. The morphological characteristics of the various patterns (spacing coefficients, rate of growth of ring spacing with distance) were measured. The spacing ratio of the strata in the different spatial dimensions was found to be anticorrelated with the surface-to-volume ratio of the gel domain. Some studies featuring the importance of morphology in Liesegang systems are briefly surveyed.
Chitosan
oligosaccharide lactate (COL) has been modified to improve
water solubility of chitosan, especially for the uses in drug delivery
and biomedical applications. The present study reveals that self-assembly
of COL in solution forms nanoaggregates of size 10–30 nm with
a critical aggregation concentration (cac) of ∼5 μM.
Fluorescence quenching of pyrene establishes that one COL chain may
form around five independent hydrophobic microdomains during self-assembly
in solution that are crucial to drug–polymer contact. Interaction
of COL with a representative hydrophobic drug molecule, curcumin,
implies two different kinds of binding mechanisms of curcumin with
the pre- and nanoaggregated forms of COL, respectively. A strong ground
state interaction between curcumin and nanoaggregated COL has been
noted with an association constant of 3.91 × 104 L/mol
at 298 K. This association has been found to be diffusion controlled,
enthalpy driven, and as consequences of hydrophobic effects due to
van der Waals interactions. Increase in ionic strength, such as NaCl
concentration, in the medium pushes the hydrophobic chain of COL and
curcumin out from the solution by marginally lowering the cac and
increasing the size (∼30–60 nm) of the nanoaggregate;
thus, it also exponentially boosts the partition of curcumin into
COL nanoaggregates. However, similar increase in NaCl concentration
in the medium discourages contact of curcumin with preaggregated COL,
confirming an electrostatic interaction between curcumin and preaggregated
form of COL. This is further supported by FT-IR spectra. On the other
hand, hydrophobic bile salt surges both the cac and size of nanoaggregates
(∼100 nm), indicating bulky and hydrophobic cholate/deoxycholate
group cooperatively binds with COL and curcumin for which higher concentration
of COL is needed to accommodate bulky size of cholate/deoxycholate
and form large nanoaggregates. The present study also reports that
water vapor permeability of COL film declines linearly with curcumin
concentration under investigation due to blocking of the hydrophilic
part of COL by curcumin and hydrophobic nature of curcumin.
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