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Takuzo Aida

Publications and source records attributed to Takuzo Aida.

66 records · Page 4Linked to original sources
PubMed2003

Light-driven open-close motion of chiral molecular scissors.

The first example of "light-driven chiral molecular scissors" (1), which consists of 1,1',3,3'-tetraarylferrocene as a pivot part and azobenzene as a driving part, was synthesized. Absorption, circular dichroism (CD), and 1H NMR spectral studies on the photoinduced isomerization process of an enantiomer of 1 agreed well with a prediction by a DFT calculation, where a motion of the handles via light-driven contraction/expansion of the connecting azobenzene strap was transformed, through a pivotal motion of the ferrocene unit, into an open-close motion of the blade parts.

Journal Article↗
PubMed2002

Homochiral supramolecular polymerization of an "S"-shaped chiral monomer: translation of optical purity into molecular weight distribution.

An "S"-shaped chiral motif of a p-xylylene-bridged bis(cyclic dipeptide) (1), having four hydrogen-bonding amide functionalities, formed a homochiral supramolecular polymer in solution. X-ray crystallography of a slightly modified version of 1 for an enhanced crystallinity showed one-dimensional columnar assemblies via four double hydrogen-bonding interactions. Model studies with half-protected analogues of 1 indicated a nearly perfect enantioselectivity in hydrogen-bonding dimerization. When 1 was not racemic but enriched in either of the enantiomers, a supramolecular polymer with a bimodal molecular weight distribution resulted, due to the formation of two homochiral polymers with different molecular weights. By taking advantage of this, separation of optically pure 1 from an enantiomerically unbalanced mixture was possible by means of size-exclusion chromatography.

Chromatography, Gel↗
PubMed2002

A supramolecular oscillator composed of carbon nanocluster C(120) and a rhodium(III) porphyrin cyclic dimer.

A rhodium(III) porphyrin cyclic dimer (1) included carbon nanocluster C120 (2) to form a pi-electronic supramolecular complex (1 superset2), in which 2 oscillated back and forth within its cavity. Spectroscopic titration of 1 with 2 and line shape analysis on variable-temperature 1H NMR spectral profiles of 1 superset2 and reference inclusion complexes in toluene-d8, chlorobenzene-d5, and dichlorobenzene-d4 indicated that the association constant (Kassoc) of 1 superset2 and oscillation activity of included 2 are both larger as the affinity of the solvent toward fullerenes is smaller. The DeltaS values for the oscillation were all positive, indicating that the oscillation of 2 involves desolvation of a protruding C60 moiety of included 2 from the host cavity.

Journal Article↗
PubMed2002

Steric control of organic transformation by a dendrimer cage: organocobalt dendrimer porphyrins as novel coenzyme B(12) mimics.

Cobalt(II) complexes of poly(aryl ester) dendrimer porphyrins (m-[Gn]TPP)Co(II) and (p-[Gn]TPP)Co(II) (n = 0-3) underwent AIBN-initiated alkylation (AIBN = 2,2'-azobis(isobutyronitrile)) at the metal center with propargyl alcohol in CDCl(3) at 60 degrees C, where the dendritic substituents did not affect the overall conversion rate but selectivity of the alkylation. With the largest (m-[G3]TPP)Co(II), a single organocobalt(III) species (Co(III)-C(=CH(2))CH(2)OH, 4) was selectively formed in 91% yield, due to a steric protection of 4 by the large dendrimer cage from the access of another molecule of cobalt porphyrin species. In contrast, with other cobalt(II) porphyrins, isomerized compounds such as Co(III)-C(CH(3))=CHOH (5) and Co(III)-CH(CH(3))CHO (6) were formed in addition to 4. A stereochemical investigation with (m-[G3]TPP)Co(II) using AIBN-d(12), in place of nondeuterated AIBN, demonstrated that the alkylation (cobalt(III) hydride addition to propargyl alcohol) is selective to a trans adduct. Results also indicated that this addition step does not involve external activation of propargyl alcohol.

Alkylation↗
PubMed2002

Dendritic multiporphyrin arrays as light-harvesting antennae: effects of generation number and morphology on intramolecular energy transfer.

A series of star- and cone-shaped dendritic multiporphyrin arrays, (nPZn)4PFB and (nPZn)1PFB, respectively, that contain energy-donating dendritic zinc porphyrin (PZn) wedges of different numbers (n = 1, 3, and 7) of the PZn units, attached to an energy-accepting free-base porphyrin (PFB) core, were synthesized by a convergent growth approach. For the cone-shaped series ((nPZn)1PFB), the efficiency of energy transfer (phi ENT) from the photoexcited PZn units to the focal PFB core, as evaluated from the fluorescence lifetimes of the PZn units, considerably decreased as the generation number increased: (1PZn)1PFB (86%), (3PZn)1PFB (66%), and (7PZn)1PFB (19%). In sharp contrast, the star-shaped series ((nPZn)4PFB) all showed high phi ENT values: (1PZn)4PFB (87%), (3PZn)4PFB (80%), and (7PZn)4PFB (71%). Energy transfer efficiencies of (3PZn)4-ester-PFB, (1PZn)4-ester-PFB, and (3PZn)1-ester-PFB, whose dendritic PZn wedges are connected by an ester linkage to the PFB core, were almost comparable to those of the corresponding ether-linked versions. Fluorescence depolarization (P) studies showed much lower P values for star-shaped (7PZn)4PFB and (3PZn)4PFB than cone-shaped (7PZn)1PFB and (3PZn)1PFB, respectively, indicating a highly efficient energy migration among the PZn units in the star-shaped series. Such a morphology-assisted photochemical event is probably responsible for the excellent light-harvesting activity of large (7PZn)4PFB molecules.

Energy Transfer↗
PubMed2002

Iron complexes capped with dendrimer-appended triazacyclononanes as the novel spatially encumbered models of non-heme iron proteins.

Poly(benzyl ether) dendrimers with a 1,4,7-triazacyclononane (TACN) focal core (Ln(3)TACN, 2a-4a) and nondendritic L1(3)TACN (1a), upon reaction with FeCl(2), followed by NaOAc and NH(4)PF(6), afforded mononuclear iron(II) complexes [Fe(II)(eta(2)-OAc)(Ln(3)TACN)](+) (1b-4b), which were oxidized under O(2) to form dinuclear (mu-O)(mu-OAc)(2)diiron(III) complexes (1c-4c) in 54-74% isolated yields. The formation of 1c-4c obeyed second-order kinetics with respect to 1b-4b, respectively, where the observed rate constants (k(2)) were clearly dependent on the generation number of the dendritic substituents. Photoirradiation of 1c-4c in the presence of NaOAc gave diiron(II) complexes (1d-4d), which were reoxidized to 1c-4c by O(2), following first-order kinetics with respect to 1d-4d, respectively. The crystal structure of nondendritic 1cshowed that the diiron(III) center is surrounded by an aromatic wall of the six 3,5-dimethoxybenzyl substituents, while spectroscopic profiles of dendritic 2c-4c suggested that the geometries of their diiron(III) centers are little different from that of 1c. The diiron(III) center of the largest 4c was highly robust toward alkaline hydrolysis and also insulated electrochemically.

Binding Sites↗
PubMedDate not supplied

Light-harvesting ionic dendrimer porphyrins as new photosensitizers for photodynamic therapy.

Photodynamic therapy (PDT) is a promising therapeutic modality for treatment of solid tumors. In this study, third-generation aryl ether dendrimer porphyrins (DPs) with either 32 quaternary ammonium groups (32(+)DPZn) or 32 carboxylic groups (32(-)DPZn) were evaluated as a novel, supramolecular class of photosensitizers for PDT. DPs showed a different cell-association profile depending on the positive or negative charge on the periphery, and both DPs eventually localized in membrane-limited organelles. In contrast, protoporphyrin IX (PIX), which is a hydrophobic and relatively low molecular weight photosensitizer used as a control in this study, diffused through the cytoplasm except the nucleus. Confocal fluorescent imaging using organelle-specific dyes indicated that PIX induced severe photodamage to disrupt membranes and intracellular organelles, including the plasma membrane, mitochondrion, and lysosome. On the other hand, cells treated with DPs kept the characteristic fluorescent pattern of such organelles even after photoirradiation. However, notably 32(+)DPZn achieved remarkably higher (1)O(2)-induced cytotoxicity against LLC cells than PIX. Furthermore, both dendrimer porphyrins had far lower dark toxicity as compared with PIX, demonstrating their highly selective photosensitizing effect in combination with a reduced systemic toxicity.

Cell Membrane↗