305
somes or lipidic bilayers with incorporated foreign molecules
or other materials [4, 5, 11, 19].
9. This preliminary isotherm scan, running at temperatures
before the unfolding transition begins, minimizes baseline
artifacts that can be induced by the thermal shock involved in
the loading of the sample or reference cells [24].
10. Repeating the scanning cycles is necessary, in order to investigate the presence or the absence of the reversibility of the phenomena. Usually, the test for reversibility is to perform two
DSC scans and check that the second scan gives all of the
endotherm observed in the first scan [25].
11. ΔΗ reflects the total heat energy uptake by the sample undergoing the transition, depending on the amount of sample
present in the active volume of the DSC cell, and should be
normalized according to the sample size [24].
12. The ΔΤ 1/2 reflects the sharpness of the curve and is correlated
with the cooperativity between the different materials of the
bilayer. In the presence of foreign molecules, an increase of ΔΤ 1/2
possibly implies decrease of the cooperativity.
13. The second heating and cooling run are taken into account as
presenting results.
14. Three representative literature case studies, including examples of drugs, cyclodextrin complexes, polymers and dendrimers incorporated into lipidic bilayers, have been chosen, in
order to clarify how the obtained DSC data can be explained:
(a) In the first presented example, Liossi et al. [17] used DSC
technique in order to investigate the interactions of irbesartan
drug
and
irbesartan–2-hydroxypropyl-βcyclodextrin (HP-β-CD) complex with dipalmitoyl
phosphatidylcholine (DPPC) lipidic bilayers by applying
two different preparation protocols (see Note 6). The DSC
results are presented in Fig. 2 and Table 1. Analytically, the
presence of irbesartan drug alone resulted in a reduction
of the T m , narrowing of the transition width of the main
phase transition, and abolishment of the pre- transition, while
it did not affect ΔΗ m considerably. These data indicate a
strong effect on the head-group region of lipid bilayers.
Contrariwise in the case of HP-β-CD incorporation, both
the pre-transition and the main transition are lowered by a
few degrees, indicating a smaller perturbation and a
decrease of the packing density of the lipids, but not so
intensively. In combination with SAXS and solid-state
NMR spectroscopy results, DSC results showed that the
HP-β-CD sits on the liposomal surface. In addition, the
pure drug exerted significant differences on the membrane
internalization compared to the encapsulated drug into
the HP-β-CD, as reflected by the different calorimetric
data and the combinational biophysical experiments, proDSC on Liposomes and Bilayers Incorporating Drugs and Biomaterials
somes or lipidic bilayers with incorporated foreign molecules
or other materials [4, 5, 11, 19].
9. This preliminary isotherm scan, running at temperatures
before the unfolding transition begins, minimizes baseline
artifacts that can be induced by the thermal shock involved in
the loading of the sample or reference cells [24].
10. Repeating the scanning cycles is necessary, in order to investigate the presence or the absence of the reversibility of the phenomena. Usually, the test for reversibility is to perform two
DSC scans and check that the second scan gives all of the
endotherm observed in the first scan [25].
11. ΔΗ reflects the total heat energy uptake by the sample undergoing the transition, depending on the amount of sample
present in the active volume of the DSC cell, and should be
normalized according to the sample size [24].
12. The ΔΤ 1/2 reflects the sharpness of the curve and is correlated
with the cooperativity between the different materials of the
bilayer. In the presence of foreign molecules, an increase of ΔΤ 1/2
possibly implies decrease of the cooperativity.
13. The second heating and cooling run are taken into account as
presenting results.
14. Three representative literature case studies, including examples of drugs, cyclodextrin complexes, polymers and dendrimers incorporated into lipidic bilayers, have been chosen, in
order to clarify how the obtained DSC data can be explained:
(a) In the first presented example, Liossi et al. [17] used DSC
technique in order to investigate the interactions of irbesartan
drug
and
irbesartan–2-hydroxypropyl-βcyclodextrin (HP-β-CD) complex with dipalmitoyl
phosphatidylcholine (DPPC) lipidic bilayers by applying
two different preparation protocols (see Note 6). The DSC
results are presented in Fig. 2 and Table 1. Analytically, the
presence of irbesartan drug alone resulted in a reduction
of the T m , narrowing of the transition width of the main
phase transition, and abolishment of the pre- transition, while
it did not affect ΔΗ m considerably. These data indicate a
strong effect on the head-group region of lipid bilayers.
Contrariwise in the case of HP-β-CD incorporation, both
the pre-transition and the main transition are lowered by a
few degrees, indicating a smaller perturbation and a
decrease of the packing density of the lipids, but not so
intensively. In combination with SAXS and solid-state
NMR spectroscopy results, DSC results showed that the
HP-β-CD sits on the liposomal surface. In addition, the
pure drug exerted significant differences on the membrane
internalization compared to the encapsulated drug into
the HP-β-CD, as reflected by the different calorimetric
data and the combinational biophysical experiments, proDSC on Liposomes and Bilayers Incorporating Drugs and Biomaterials