Hydrophilic Carotenoids: Carotenoid Aggregates - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 31

3 Hydrophilic Carotenoids:

Carotenoid Aggregates

Hans-Richard Sliwka, Vassilia Partali,
and Samuel F. Lockwood

CONTENTS
3.1 Introduction ............................................................................................................................ 31
3.2 Natural Hydrophilic Carotenoids ........................................................................................... 33
3.3 Synthetic Hydrophilic Carotenoids ........................................................................................ 33
3.4 Surface Properties................................................................................................................... 40
3.5 Aggregate Structure................................................................................................................ 42
3.6 Aggregate Stability ................................................................................................................. 50
3.7 Biophysical and Biological Activity of Hydrophilic Carotenoids and
Carotenoid Aggregates ........................................................................................................... 51
3.8 Possible Additional Commercial and Scientii c Application.................................................. 53
3.9 Conclusions............................................................................................................................. 53
Acknowledgments ............................................................................................................................ 54
References ........................................................................................................................................ 54

3.1 INTRODUCTION
At i rst glance, the designation “hydrophilic carotenoid” may appear to be an oxymoron. Therefore,
the phrase requires more precision: a hydrophilic carotenoid is a highly unsaturated compound,
synthetic or natural, which has particular functional groups generating substantial water afi nity
for the compound. What then is a “carotenoid aggregate”? This term has somehow evaded accurate
characterization. In the same sense that a carotenoid protein (carotenoprotein) is not formed by con-
jugation with carotenoid amino acids, but rather is an inclusion of a carotenoid or carotenoids within
a protein macrostructure (Dreon et al. 2007), a carotenoid aggregate is not necessarily understood
as an aggregate of pure carotenoids. In fact, many of the investigated carotenoid aggregates consist
of carotenoids enclosed in vesicles of common surfactants (Burke et al. 2001, Chen and Djuric
2001). We will henceforth use the expression “carotenoid aggregate” in a strict manner: carotenoid
aggregates are supramolecular assemblies of carotenoid compounds in water and nothing
else . This implies that the carotenoid molecules adhere mutually in a “self-aggregating” process.
Another equally justii ed designation perhaps would be “self-assembling.” However, expressed in
colloquial style, molecules self-assemble on a surface, forming two-dimensional self-assembling
monolayers or Langmuir-Blodgett i lms (Wolf et al. 1937, Tomoaia-Cotisel and Quinn 1998, Ion
et al. 2002, Liu et al. 2002, Miyahara and Kurihara 2004, Foss et al. 2006a). Self-aggregation cre-
ates three-dimensional objects or structures. Self-aggregation and self-assembly describe the more
general phenomena of self-organization, which is explained within the framework of supramolecu-
lar chemistry (Wolf et al. 1937, Lehn 1988, Zana 2004). Intermolecular associations, which create
aggregates, can induce properties in the resulting multimolecular structure remarkably different

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