A series of indolocarbazole–pyridine (IP) oligomers were prepared that fold into helical conformations, and their folding features in solution and in the solid state were revealed. Helical folding ...of these IP foldamers is induced by dipolar interactions through the ethynyl bond and π-stacking between two repeating units. Upon helical folding, 1H NMR signals of aromatic protons were significantly shifted upfield by Δδ = 0.5–2.2 ppm. In addition, hypochromic shifts and fluorescence quenching were observed in the absorption and emission spectra. X-ray crystal structures clearly demonstrated that IP foldamers folded to helical structures with cylindrical internal cavities wherein 3 or 5 water molecules were occupied by hydrogen-bonding interactions in a 1-D array, reminiscent of transmembrane water channels, called aquaporins.
The helical handedness excess of an indolocarbazole-pyridine hybrid oligomer capable of folding into a stable helical structure was achieved up to 96% by rational modification of terminal chiral ...residues.
Indolocarbazole-pyridine hybrid foldamers are strongly fluorescent in an extended random conformation, but the fluorescence is completely quenched upon folding to a helical conformation due to the ...compact stacking between aryl planes in the backbone. Anion binding disturbs the helical conformation, thus regenerating the fluorescence of the foldamers. This unique property has been utilized to develop a fluorescence turn-on probe for anions such as sulfate and fluoride.
N-(p-Methoxycarbonylbenzyl) triazole (BTz) substituents have been introduced to Ni(II) porphyrins (NiPs), in which their modulated axial-coordination processes have been investigated. For this ...study, the two types of ligands, neutral pyridine versus anionic cyanide, were employed to investigate an effect of BTz substituents. The unique microenvironments given by the BTz substituents provided two different effects on the axial-coordination processes of NiPs on the ground and excited states: (1) steric shielding and (2) donation of hydrogen-bonding sites. The steric shielding diminished the binding affinity of pyridine, while the cooperation of hydrogen bonds extraordinarily strengthened the binding affinity of CN–. Interestingly, it was observed that the binding of CN– with the supporting of BTz substituents accompanied nonplanar distortion of NiPs. Such conformational change perturbed the electronic structure of NiPs, which gave rise to the modulation of coordination processes of NiPs in the excited state. As a consequence, photoinudced ligand binding and releasing processes of four- and six-coordinated NiPs were changed into the dominant photoinduced ligand releasing process.
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Phosphorylcholine-substituted silsesquioxanes were synthesized via the UV-initiated thiol-ene ‘click’ reaction of octakis(3-mercaptopropyl)octasilsesquioxane (POSS-SH) with ...2-methacryloyloxyethylphosphorylcholine or allylphosphorylcholine in mixed (DMF/MeOH) solvents, respectively. In addition, the crystal structures of POSS-SH and MPC were first determined.
A cobalt (Co) supramolecular triple-stranded helicate, Co8(PDA)6(Br-PTA)3(DMF)4(H2O)2 (1) (PDA = 2,6-pyridinedicarboxylate, Br-PTA = 5-bromoisophthalate, DMF = dimethylformamide), is successfully ...synthesized and fully characterized. The solid-state structure of 1 shows that four cobalt atoms are coordinated by three PDA ligands to form a tetranuclear cobalt cluster with three extension points and the ditopic Br-PTA ligands interlink two basic assembly units. In crystal packing, the bromo group is surrounded by the cavity-like tetranuclear cobalt cluster, which acts as a metallocavitand, to generate a unique cage-like crystal packing geometry. The isomorphous molecular cage, which exhibits a similar crystal-packing geometry as observed in 1, is also successfully isolated. This is an unusual example of a highly symmetric cage-like crystal packing architecture, resulting from the interaction among metallocavitands of in situ generated supramolecular modules.
The α/β-peptide 11/9-helix and the β-peptide 12/10-helix belong to "mixed" helices, in which two types of hydrogen bonds with opposite directionality alternate along the helical axis.
...-2-Aminocyclohexanecarboxylic acid (
-ACHC) is known to promote these mixed helices and stabilize the helical propensity more than other acyclic β-residues. Application of a mixed-helical backbone still requires sufficient solubility in aqueous solution. In this regard, we chose
-4-aminopiperidine-3-carboxylic acid (
-APiC) as a foldamer building block that can provide both sufficient aqueous solubility and mixed-helical propensity. Conformational analyses of α/β- and β-peptides containing a
-APiC residue by circular dichroism spectroscopy and single-crystal X-ray crystallography suggest that the incorporation of
-APiC instead of
-ACHC can enhance the aqueous solubility of the mixed-helical peptides without any adverse effect on helical folding. In addition, the ratio between right- and left-handed 12/10-helices of β-peptides can be rationalized by relative energies between the local conformations of the
-APiC residue.
The α/β-peptide 11/9-helix and the β-peptide 12/10-helix belong to "mixed" helices, in which two types of hydrogen bonds with opposite directionality alternate along the helical axis.
cis
...-2-Aminocyclohexanecarboxylic acid (
cis
-ACHC) is known to promote these mixed helices and stabilize the helical propensity more than other acyclic β-residues. Application of a mixed-helical backbone still requires sufficient solubility in aqueous solution. In this regard, we chose
cis
-4-aminopiperidine-3-carboxylic acid (
cis
-APiC) as a foldamer building block that can provide both sufficient aqueous solubility and mixed-helical propensity. Conformational analyses of α/β- and β-peptides containing a
cis
-APiC residue by circular dichroism spectroscopy and single-crystal X-ray crystallography suggest that the incorporation of
cis
-APiC instead of
cis
-ACHC can enhance the aqueous solubility of the mixed-helical peptides without any adverse effect on helical folding. In addition, the ratio between right- and left-handed 12/10-helices of β-peptides can be rationalized by relative energies between the local conformations of the
cis
-APiC residue.
cis
-4-Aminopiperidine-3-carboxylic acid (
cis
-APiC) enhances the aqueous solubility of 11/9-helical α/β-peptides and 12/10-helical β-peptides with no adverse effect on helical folding.
A cobalt (Co) supramolecular triple-stranded helicate, Co
8
(PDA)
6
(
Br
-PTA)
3
(DMF)
4
(H
2
O)
2
(
1
) (PDA = 2,6-pyridinedicarboxylate,
Br
-PTA = 5-bromoisophthalate, DMF = dimethylformamide), is ...successfully synthesized and fully characterized. The solid-state structure of
1
shows that four cobalt atoms are coordinated by three PDA ligands to form a tetranuclear cobalt cluster with three extension points and the ditopic
Br
-PTA ligands interlink two basic assembly units. In crystal packing, the bromo group is surrounded by the cavity-like tetranuclear cobalt cluster, which acts as a metallocavitand, to generate a unique cage-like crystal packing geometry. The isomorphous molecular cage, which exhibits a similar crystal-packing geometry as observed in
1
, is also successfully isolated. This is an unusual example of a highly symmetric cage-like crystal packing architecture, resulting from the interaction among metallocavitands of
in situ
generated supramolecular modules.
The generation of cage-like crystal packing geometry of TSHs in the solid state induced by the host-guest interactions among metallocavitands.
