Control of the Aggregation Properties of Tris(maltohexaose)-Linked Porphyrins with an Alkyl Chain
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Mikata, Yuji; Sawaguchi, Taichi; Kakuchi, Toyoji; Gottschaldt, Michael; Schubert, Ulrich S.; Ohi, Hiromi; Yano, Shigenobu
- Abstract:
- A series of porphyrins with three maltohexaose units and one
alkyl chain (ethyl, butyl, hexyl, decyl, and hexadecyl) has
been synthesized. Aggregation properties were investigated
by absorbance and circular dichroism (CD) spectra. These
trismaltohexaosylated tetraphenylporphyrins exhibited high
water solubility. Although these porphyrins exhibited sharp
Soret bands in DMSO solution, the Soret band broadened in
a concentration-dependent manner in aqueous solution. This
is the result of the aggregation of porphyrin molecules in
aqueous solution. Interestingly, trismaltohexaosylated porphyrins
with long alkyl chains of a certain length exhibited
a broad Soret band in water without concentration dependency
due to the stability of such aggregates. The CD spectra were silent in DMSO solution in all porphyrin derivatives,
indicating that the maltohexaose moiety does not interact
with the porphyrin chromophore in the monomeric state.
However, in water, a splitting Cotton effect was observed at
the Soret band. Intensity of this CD signal decreased as the
length of the alkyl chain was extended. These observations
show the formation of a chiral, face-to-face aggregate, in
which the porphyrin rings are in close proximity to each
other for short alkyl chain derivatives. The porphyrin derivatives
with long alkyl chains exhibit edge-to-edge aggregation,
where hydrophobic interaction of the alkyl chains separates
the porphyrin chromophores.
- Year:
- 2010
- Type of Publication:
- Article
- Keywords:
- Carbohydrates; Porphyrinoids; Aggregation; Noncovalent interactions; Circular dichroism
- Journal:
- European Journal of Organic Chemistry
- Volume:
- -
- Pages:
- 663 - 671