ACTA BIOLOGICA CRACOVIENSIA

16 TH INTERNATIONAL SYMPOSIUM ON CAROTENOIDS
ed ethanol, it forms predominantly H-aggregates with absorption
peak at 390 nm, but J-aggregates coexist in the sample as evidenced
by weak absorption band around 510 nm. Excited-state
dynamics are significantly changed upon aggregation. Excitation
of H-aggregates at 400 nm reveals prolongation of the S 1 lifetime
as compared with monomer (38 vs. 24 ps). In addition, contrary
to monomers, transient signal of ACOA aggregates does not decay
within 100 ps, indicating presence of long-lived species, most
likely a triplet state generated by singlet-singlet homofission.
ACOA also forms H-aggregates when attached to TiO 2 film. As
observed earlier for monomeric ACOA-TiO 2 system in colloidal
solution (Pan et al., 2002), excitation of ACOA aggregate on TiO 2
film generates ACOA radical on sub-picosecond time scale due to
electron injection from the S 2 state. Contrary to monomeric
ACOA, however, the ACOA aggregate also exhibits a slower phase
of electron injection that may occur from the S 1 state of the ACOA
aggregate.
REFERENCES
PAN J, BENKÖ G, XU Y, PASCHER T, SUN L, SUNDSTRÖM V, POLÍVKA T. 2002.
Photoinduced electron transfer between a carotenoid and TiO2 nanoparticle. J. Am. Chem. Soc. 124: 13949-13957.
Exceptional molecular organization of
canthaxanthin in lipid membranes
Agnieszka Sujak
Department of Physics, University of Life Sciences in Lublin,
Poland
Canthaxanthin (β, β-carotene 4, 4' dione) is a carotenoid pigment
widely distributed in nature. It is found in green algae, bacteria,
crustaceans, and fish. In the last 30 years it has been a popular
E161g food additive and cosmetic colorant due to a very attractive
color.
There are many reports on undesirable health effects caused
mainly by the formation of canthaxanthin crystals in the macula
lutea membranes of the retina, called canthaxanthin retinopathy.
Our experiments done on model systems indicate an exceptional
molecular organization of canthaxanthin in lipid membranes
as well as a very strong effect of this carotenoid on the
physical properties of the lipid membranes.
It has been found that the canthaxanthin localization and orientation
in the model lipid membranes depends strongly on its
concentration. The mean angle between the dipole transition
moment and the axis normal to the plane of the DPPC membrane
was determined as 20°- at 0.5 mol% which confirms vertical orientation
of the axis connecting opposite keto-groups of the xanthophyll
at the 4 and 4' positions and 47°- at 2 mol% of canthaxanthin,
which implies the possibility that canthaxanthin incorporated
into lipid membranes can be distributed in such a way that
its small fraction can be oriented parallel to the plane of the lipid
membrane.
Strong interactions between canthaxanthin and lipids were
found under experimental conditions. For model DPPC lipid
membranes and canthaxanthin concentration below 1 mol% significant
changes in the membrane properties were observed, in
some cases at the pigment concentration as low as 0.05 mol%
with respect to lipid. Based on experimental data on phosphatidylcholines
several molecular mechanisms of canthaxanthin
action can be listed such as strong van der Waals interactions
between polyene chain of canthaxanthin and the lipid alkyl
chains, modifications of the lipid properties in its polar zone,
introduction of a new thermotropic phases upon the incorporation
of canthaxanthin, formation of the hydrogen bonds between
canthaxanthin keto- groups and the C=O group of lipid or hydro-
gen bonds between the canthaxanthin polyene chain and water.
Two last mechanisms can have a crucial significance in formation
of molecular aggregates of canthaxanthin leading to further development
of canthaxanthin- induced retinopathy.
The cis-carotenoid-membrane interactions
SESSION 8
Justyna Widomska 1 , Witold K. Subczynski 2 ,
Wiesław I. Gruszecki 3 , Kazimierz Strzałka 4
1Department of Biophysics, Medical University of Lublin, Poland,
jwidomska@gmail.com
2Department of Biophysics, Medical College of Wisconsin, USA,
subczyn@mcw.edu
3Deparment of Biophysics, Institute of Physics, Maria Curie-
Skłodowska University, Poland, wieslaw.gruszecki@umcs.pl
4Department of Plant Physiology and Biochemistry, Jagiellonian
University, Krakow, Poland, strzalka@mol.uj.edu.pl
The heterogeneity of carotenoids is greatly increased by the existence
of their geometrical isomers. Carotenoid geometry is a factor
that determines their solubility and orientation in the lipid memebrane
as well as antioxidant capacities and bioavailability. The
polyene-chain double-bonds present in carotenoids can exist in
mono-cis, poly-cis, or all-trans configurations; however the vast
majority of naturally occurring carotenoids exist in the thermodynamically
more stable all-trans conformation rather than in cis
configuration. Trans-cis conversion occurs at elevated temperature
and/or in the presence of intensive light and triplet sensitizers.
The role of the all-trans carotenoids in the modulation of the
physical properties of lipid membranes has been a subject of
research for the last three decades. Effects of trans-carotenoids
on the structural and dynamic properties of lipid bilayers have
been studied with application of various techniques, such as differential
scanning calorimetry, fluorescence, electron spin resonance
and nuclear magnetic resonance spectroscopy, diffractometry,
and others. However, the effect of the cis-isomers of
carotenoids on the membrane properties is less investigated.
Our results indicate that the cis-isomers of xanthophylls, similarly
to the trans-isomer adopt a transmembrane orientation and
do not show a tendency to organize into high aggregates as trans
configuration. Molecules of carotene in form trans and cis are
distributed homogeneously without any well-defined orientation
within the membrane. The influence of this nonpolar carotenoid
on the memebrane properties is negligible and such effects can be
related to the low solubility of carotene in the lipid bilayers.
Supported by the POL-POSTDOC III grant no. PBZ/MNiSW/07/2006/01
of the Polish Ministry of Higher Education and Science.
Structural aspects of antioxidant activity of
lutein in models of photoreceptor membranes
Anna Wisniewska-Becker1 , Grzegorz Nawrocki1,2 ,
Mariusz Duda1 , Witold K. Subczynski3 1 Department of Biophysics, Faculty of Biochemistry, Biophysics
and Biotechnology, Jagiellonian University, ul. Gronostajowa 7,
30-387 Krakow, Poland, anna.m.wisniewska@uj.edu.pl,
mariusz.duda@uj.edu.pl
2 Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow
32/46, 02-668 Warsaw, Poland, nawrocki@ifpan.edu.pl
3 Department of Biophysics, Medical College of Wisconsin, 8701
Watertown Plank Road, Milwaukee, WI 53226 USA,
subczyn@mcw.edu
It was shown that in membranes containing domains, such as
raft-forming mixtures (composed of dioleoylphosphatidylcholine
106 ACTA BIOLOGICA CRACOVIENSIA Series Botanica