Anisotropic expansion of a spherical M2L4 coordination capsule through the elongation of the ligand led to a new M2L'4 capsule. The expanded capsule provides an elliptical cavity encircled by polyaromatic frameworks with large openings and thereby can encapsulate elliptical fullerene C70 and monofunctionalized fullerene C60 in high yields. In addition, selective formation of a new M2L2L'2 capsule occurs by mixing the original M2L4 and expanded M2L'4 capsules in a 1:1 ratio upon addition of C60 or monofunctionalized C60 as a template molecule.
Tropomyosin
(Tpm) is a two-stranded parallel α-helical coiled-coil
protein, and studying its structure is crucial for understanding the
nature of coiled coils. Previously, we found that the N-terminal half
of the human skeletal muscle α-Tpm (α-Tpm 140) was less
structurally stable in the presence of phosphate ions than the coiled-coil
protein carrier (CCPC) 140 variant with 18 mutated residues, in which
all amino acid residues located at the interface between the two α-helices
were completely conserved. A classical hypothesis explains that interhelical
interactions stabilize the coiled-coil structure. In this study, we
tested the hypothesis that the structural stability of Tpm and its
variant is governed by the binding of multivalent ions that form a
bridge between charged side chains located at positions b, c, and f of the heptad repeat
on a single α-helical chain. We found that the structural stability
of α-Tpm 140 and CCPC 140 markedly increased upon addition of
divalent cations and divalent anions, respectively. We also clarified
that the structural stability of the α-Tpm 140/CCPC 140 heteromeric
coiled-coil molecule was governed by the stability of a less stable
α-helical chain. These results demonstrated that the entire
structural stability of Tpm is determined by the stability of a single
α-helix. Our findings provide new insights into the study of
the structure of coiled-coil proteins.
Host–Guest Systems Anisotropic expansion of a spherical M2L4 coordination capsule through the elongation of the ligand led to a new M2L′4 capsule. The expanded capsule provides an elliptical cavity encircled by polyaromatic frameworks with large openings and thereby can encapsulate elliptical fullerene C70 and monofunctionalized fullerene C60 in high yields. For more information see the Communication by M. Yoshizawa et al. on
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