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fatty acyl chainlength. These observations suggest that the
higher incremental values of transition enthalpy (⌬Hinc),
contributed by each methylene unit in the DAEs, are a
consequence of the closer chain packing.
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Differential scanning calorimetric studies on the thermotropic
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It was reported earlier that 1,3-diacylglycerols exhibit
higher transition temperature, transition enthalpy, and
transition entropy as compared with 1,2-diacylglycerols (36,
47). In 1,2-diacylglycerols, the acyl chains lie side by side
and have a hairpin conformation (39, 40), whereas 1,3-
diacylglycerols form an extended structure with the two
chains separated in a ‘V’ formation with a dihedral angle of
94° between the two acyl chain planes (36). It was proposed
that the V-shape conformation results in a more comfortable
chain packing in 1,3-diacylglycerols as compared with 1,2-
diacylglycerols (36). In DAEs, the two chains are oriented
with respect to each other at an angle of 110–113°, adopting
an L-shaped geometry, which may further assist better pack-
ing. Our data also support that, compared with hairpin con-
formation, the lipid molecules pack better in a V- or
L-shaped conformation. This may be reflected in higher
⌬Hinc, ⌬Sinc for DAEs as compared with NAEs. It may also be
noted that transition temperatures of DAEs are higher com-
pared with diacylglycerols of same fatty acyl chainlength,
although for the same acyl chains, the latter have higher
molecular weights as compared with the former.
CONCLUSIONS
A homologous series N-, O-diacylethanolamines, which
are biologically relevant lipids, were synthesized in this
study and their thermotropic phase transitions were char-
acterized by differential scanning calorimetry. A linear
dependence was observed in the thermodynamic param-
eters, ⌬Ht and ⌬St, associated with the chain-melting
phase transitions. Crystal structures of three compounds
in this lipid series, namely, DDEA, DLEA, and DMEA,
were solved by single crystal X-ray diffraction. The struc-
ture clearly demonstrates that the conformation of N-acyl
chain in DAEs is very similar to that found in different
NAEs. All the three DAEs adopt an ‘L’ shape, which may
assist better packing with higher ⌬Hinc values as com-
pared with NAEs. Studies aimed at understanding the
interaction of these molecules with other membrane
lipids would be expected to provide clues to understand
their role in biological membranes. Such studies are cur-
rently underway in our laboratory.
15. Kamlekar, R. K., S. Satyanarayana, D. Marsh, and M. J. Swamy.
2007. Miscibility and phase behavior of N-acylethanolamine/
diacylphosphatidylethanolamine binary mixtures of matched acyl
chainlengths (N=14, 16). Biophys. J. 92: 3968–3977.
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cholesterol (1:1) complex: first evidence from differential scan-
ning calorimetry, fast-atom-bombardment mass spectrometry and
computational modeling. FEBS Lett. 531: 343–347.
17. Kamlekar, R. K., M. S. Chandra, T. P. Radhakrishnan, and M. J.
Swamy. 2009. Interaction of N-myristoylethanolamine with cho-
lesterol investigated in a Langmuir film at the air-water interface.
Biophys. Chem. 139: 63–69.
18. Swamy, M. J., M. Ramakrishnan, D. Marsh, and U. Würz.
2003. Miscibility and phase behaviour of binary mixtures of
N-palmitoylethanolamine and dipalmitoylphosphatidylcholine.
Biochim. Biophys. Acta. 1616: 174–183.
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physico-chemical aspects of N-biotinyl phosphatidylethanolamines,
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Calorimetry and structure of N-, O-diacylethanolamines
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