Comblike Ionic Complexes of Poly(gamma-glutamic acid) and Alkanoylcholines Derived from Fatty Acids
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Tipus de documentArticle
Data publicació2013-02-15
EditorAmerican Chemical Society (ACS)
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Abstract
A series of ionic complexes with almost stoichio-
metric composition have been
“
synthesized
”
from bacterial poly(
γ
-
glutamic acid) and alkanoylcholines derived from fatty acids with
12, 14, 16, and 18 carbon atoms. The complexes were stable up to
temperatures close to 200
°
C and were non-water-soluble but
readily soluble in organic solvents. In the solid state they adopted
the biphasic structure typical of comblike systems with the
polypeptide chains arranged in sheets and periodically separated
by a para
ffi
nic phase which was partially crystallized for C14, C16,
and C18. The window width of the layered structure was
estimated by SAXS to be within the 3.6
−
4.5 nm range, and WAXS showed that the alkyl tails were crystallized in a hexagonally
packed lattice with a
d
100
spacing of 0.41 nm. These complexes displayed reversible melting of the para
ffi
nic phase in the 40
−
65
°
C range at temperatures with values increasing with the length of the alkanoyl group. A slight expansion of the intersheet
distance occurred at melting followed by contraction upon heating at higher temperatures but without signi
fi
cant alteration of the
layered structure. The
13
C CP-MAS NMR analysis revealed the underlying polymethylene
anti
-to-
gauche
conformational
conversion that takes place at the thermal transition. An energy-based simulation study of the crystallization process a
ff
orded a
molecular picture of the complex and evidenced the favoring e
ff
ect of the choline structure on the packing of the alkyl side
CitacióTolentino, A. [et al.]. Comblike Ionic Complexes of Poly(gamma-glutamic acid) and Alkanoylcholines Derived from Fatty Acids. "Macromolecules", 15 Febrer 2013, vol. 46, núm. 4, p. 1607-1617.
ISSN0024-9297
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