PubMed Health⌕ Search

Biomedical subjects

Kazushi Kinbara

Publications and source records attributed to Kazushi Kinbara.

15 recordsLinked to original sources
PubMed2007

Crystallographic and chiroptical studies on tetraarylferrocenes for use as chiral rotary modules for molecular machines.

A crystal structure of the racemic form of chiral molecular scissors 1 with a trans configuration at the azobenzene unit (rac-trans-1), in which the scissors adopt a closed geometry with two blade phenyl groups that overlap each other, was successfully determined. X-ray crystallographic determination of the structure of (1S,1'S)-10, which is a derivative of the key precursor of trans-1, was also successful. On the basis of the crystal structure of (1S,1'S)-10, the absolute configuration of 1 and related molecular machines, such as molecular pedal 2, and self-locking rotor 3, which all contain a chiral tetrasubstituted ferrocene module, were determined. A correlation between the absolute configuration and the circular dichroism properties of these molecular machines and their synthetic precursors was also determined.

Journal Article↗
PubMed2007

Catalysis of a peptidic micellar assembly covalently immobilized within mesoporous silica channels: importance of amphiphilic spatial design.

A mesostructured silica/organic composite 1-MS, constructed from a rodlike micelle of amino acid amphiphile 1 that has a condensable head group and that can be used as a template, was found to be able to catalyze the acetalization of cyclohexanone, in ethanol at 25 degrees C (50% in 12 h), whereas no reaction took place with unfunctionalized mesoporous silica. In sharp contrast, hydrolytic removal of the C16 alkyl tail of immobilized 1 resulted in the complete disappearance of the catalytic activity, which suggests the importance of a hydrophobic inner domain for the admission of cyclohexanone. Unsupported peptide amphiphile 2, under identical conditions to those above, was inefficient for acetalization regardless of the absence (2% in 24 h) or presence of mesoporous silica (7% in 24 h). Reference composite 2-MS, which is a noncovalently immobilized peptidic micelle, was virtually inactive (1% in 24 h). These observations indicate the importance of covalent immobilization of the peptidic rod micelle for catalysis. Mesostructured silicate 3-MS hybridized with a nonpeptidic, ammonium ion amphiphile (3) showed a certain catalytic activity, but the yield (12% in 24 h) of the acetal was much lower than that achieved by using 1-MS as the catalyst. Amorphous silica with immobilized 1 on its surface was much less active than 1-MS for acetalization (5% in 24 h).

Acetals↗
PubMed2006

A self-locking molecule operative with a photoresponsive key.

Rotary host 1, composed of a ferrocene unit as a rotary module, is conformationally locked internally in apolar solvents such as benzene by a double intramolecular Zn-N coordination between the zinc porphyrin and aniline units, attached to each cyclopentadienyl (Cp) ring. Upon addition of the cis form of 1,2-bispyridylethylene (cis-2) to (+)-1 ([cis-2]/[(+)-1] = 5.0), an enantiomer of 1, the intramolecular Zn-N coordination bonds in (+)-1 are readily cleaved to form an externally locked, cyclodimeric one-to-one complex (+)-1 subset cis-2, accompanying a rotation of the ferrocene module, as visualized by CD spectroscopy. In contrast, use of trans-2, in place of cis-2, under otherwise identical conditions to the above, did not result in releasing the internal double lock of (+)-1. Such a large difference between the isomers of 2 in the affinity toward host 1, along with their capabilities of photochemical interconversion, allowed for the demonstration of a reversible self-locking operation of 1. Namely, the externally locked state of 1, as in the form of 1 supersetcis-2, spontaneously retrieves the internally locked state, after the release of 2 from 1 upon cis-to-trans photochemical isomerization of ligating 2, while the backward photochemical isomerization of 2 in the presence of 1 results in switching of 1 to its externally locked state.

Aniline Compounds↗
PubMed2006

Mechanical twisting of a guest by a photoresponsive host.

Molecular analogues of a variety of mechanical devices such as shuttles, brakes, unidirectional rotors and tweezers have been created. But these 'molecular machines' have not yet been used to mechanically manipulate a second molecule in a controlled and reversible manner. Here we show that light-induced scissor-like conformational changes of one molecule can give rise to mechanical twisting of a non-covalently bound guest molecule. To realize this coupling of molecular motions, we use a previously designed system: a ferrocene moiety with an azobenzene strap, each end of which is attached to one of the two cyclopentadienyl rings of the ferrocene unit, acts as a pivot so that photoisomerization of the strap rotates the ferrocene rings relative to each other and thereby also changes the relative position of two 'pedal' moieties attached to the ferrocene rings. We translate this effect into intermolecular coupling of motion by endowing the pedals with binding sites, which allow the host system to form a stable complex with a bidentate rotor molecule. Using circular dichroism spectroscopy, we show that the photoinduced conformational changes of the host are indeed transmitted and induce mechanical twisting of the rotor molecule. This design concept, which significantly extends the successful coupling of motion beyond the intramolecular level seen in synthetic allosteric receptors, might allow for the remote control of molecular events in larger interlocked molecular systems.

Journal Article↗
PubMed2006

Semibiological molecular machine with an implemented "AND" logic gate for regulation of protein folding.

A semibiological molecular machine with an implemented "AND" logic gate was developed, which was capable of controlling the folding process of proteins in response to ATP and light as input stimuli. The molecular design made use of a genetically engineered chaperonin GroEL bearing, at both entrance parts of its cylindrical cavity, cysteine residues, which were functionalized by an azobenzene derivative to construct photoresponsive mechanical gates (azo-GroEL). This engineered chaperonin trapped denatured green fluorescent protein (GFP(denat)) and prohibited its refolding. However, when hosting azo-GroEL detected ATP (input stimulus 1) and UV light (input stimulus 2) at the same time, it quickly released GFP(denat) to allow its refolding. In contrast, reception of either input stimulus 1 or 2 resulted in only very slow or no substantial refolding of GFP(denat). Implementation of such "AND" logic gate mechanisms in mechanically driven biomolecular systems is an important step toward the design of secured drug delivery systems.

Adenosine Triphosphatases↗
PubMed2005

Synthesis, absolute configuration, and application of enantiopure trans-1-aminobenz[f]indan-2-ol.

Both novel enantiopure trans-1-aminobenz[f]indan-2-ols (4) were obtained from the racemate by the diastereomeric salt formation with (+)- and (-)-dibenzoyltartaric acids (8), respectively, and the absolute configuration of the enantiomer 4 in the less-soluble diastereomeric salt of racemic 4 with (+)-8 was determined to be (1S,2S) by an X-ray crystallographic analysis. The chiral recognition ability of the enantiopure amino alcohol was examined for the enantioseparation of racemic 2-arylalkanoic acids by the diastereomeric salt formation. The role of the naphthylene group of the amino alcohol was found to be closely associated with the stabilization of the crystal by CH/pi interactions on the basis of an X-ray crystallographic study.

Amino Alcohols↗
PubMed2004

Rational design of CH/pi interaction sites in a basic resolving agent.

A novel synthetic basic resolving agent, cis-1-aminobenz[f]indan-2-ol (ABI), was rationally designed by introducing effective CH/pi interaction sites to cis-1-aminoindan-2-ol (AI), whose chiral recognition ability has been reported from our laboratory. ABI was applicable to a wide variety of racemic arylalkanoic acids and showed moderate to excellent chiral recognition ability, which was obviously higher than that of AI. The fundamental and important role of CH/pi interactions, such as tunable CH(sp(2))/pi and CH(sp(3))/pi interactions, in the chiral recognition by ABI was revealed by X-ray crystallographic study.

Journal Article↗
PubMed2003

Synthesis and structure of macrocyclic bis(hydroxynaphthoic amide)s connected by an achiral or chiral diamine.

Macrocyclic bis(hydroxynaphthoic amide)s 6, connected by an achiral or chiral diamine, were synthesized by the tandem Claisen rearrangement. CD spectra, X-ray crystallographic analyses, and variable-temperature NMR measurements of the chiral bis(hydroxynaphthoic amide)s revealed that the two hydroxynaphthalene rings in these macrocycles adopt a twisted conformation both in solution and in the crystalline state because of the steric hindrance between the two hydroxynaphthalene rings and that the chirality of the twisted conformation is generated by that of the chiral linker. Theoretical calculations revealed that the chiral linker works effectively to favor energetically one conformer of the diastereomers, although a flipping process was possible and can be observed to occur on the NMR time scale in variable-temperature experiments.

Journal Article↗
PubMed2003

Chaperonin-mediated stabilization and ATP-triggered release of semiconductor nanoparticles.

Various properties of semiconductor nanoparticles, including photoluminescence and catalytic activity, make these materials attractive for a range of applications. As nanoparticles readily coagulate and so lose their size-dependent properties, shape-persistent three-dimensional stabilizers that enfold nanoparticles have been exploited. However, such wrapping approaches also make the nanoparticles insensitive to external stimuli, and so may limit their application. The chaperonin proteins GroEL (from Escherichia coli) and T.th ('T.th cpn', from Thermus thermophilus HB8) encapsulate denatured proteins inside a cylindrical cavity; after refolding, the encapsulated proteins are released by the action of ATP inducing a conformational change of the cavity. Here we report that GroEL and T.th cpn can also enfold CdS semiconductor nanoparticles, giving them high thermal and chemical stability in aqueous media. Analogous to the biological function of the chaperonins, the nanoparticles can be readily released from the protein cavities by the action of ATP. We expect that integration of such biological mechanisms into materials science will open a door to conceptually new bioresponsive devices.

Adenosine Diphosphate↗
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↗