spectra of 1 in CHCl3 in the presence of incremental amounts
of C60, exhibiting a substantial decrease of the Soret band as
well as an increase of a band at 450 nm. Since the van der Waals
diameter of C60 is about 1 nm,13 p–p stacking (sandwich
formation) between the bisporphyrins in 1 and fullerene is
likely (Fig. 4b). While these results are preliminary, they do
show that alternatingly functionalized celluloses are expected
to become a novel type of synthetic molecular receptors owing
to their inherent scaffolding properties.
Fig. 3 Schematic drawing of a cellulose helix that is left-handed, with
exactly three anhydroglucopyronose (AHG) residues per turn of the
helix. Two turns are shown, so that the first, fourth and seventh AHG
residue all have the same orientation. Each O6 is labeled, and every
other O6 has a circle around it to represent a porphyrin substituent.
Also shown are two ‘‘helical threads’’ that connect the O6 atoms.5
(A similar thread could connect any particular type of atom, as long as
the molecule is a helix.) One of the threads connects all of the O6
atoms, and it is left-handed. The other helix only connects the circled
O6 atoms, and it is right-handed. Since the CD measurements detect
only the chromophoric porphyrin rings at every second AHG unit, a
right-handed helix is reported, even though the helical thread through
all of the O6 (in every AHG unit) is left-handed.
In conclusion, we have demonstrated for the first time the
right-handedness of an alternatingly porphyrinated cellotriose.
This finding provides an excellent argument in favor of the high
application potential of alternatingly functionalized celluloses,
and a good strategy for the preparation of the corresponding
model compounds.
The authors thank Dr C. Obinger and Dr P. Furtmueller
(BOKU) for support for CD measurement and Dr A. Hofinger
(BOKU) for support for NMR measurement. The financial
support by the Austrian BMLFUW Ministry (Project
‘‘Multifunctional celluloses’’) is gratefully acknowledged.
K.S. acknowledges the Foundation of Yoshida Science and
Technologies.
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c
This journal is The Royal Society of Chemistry 2012
7674 Chem. Commun., 2012, 48, 7672–7674