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Kenzi Hori

Publications and source records attributed to Kenzi Hori.

7 recordsLinked to original sources
PubMed2005

Cholesterol-armed cyclens for helical metal complexes offering chiral self-aggregation and sensing of amino acid anions in aqueous solutions.

Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions.

Amino Acids↗
PubMed2002

Stable conformations of 12-crown-O3N and its Li+ complex in aqueous solution.

Stable conformations of 12-crown-O3N and its Li complexes in aqueous solution were investigated. To calculate the free energy differences of conformers of 12-crown-O3N and its Li+ complex, our procedure was to make use of two programs, CONFLEX and BOSS. The former generates conformers, and the latter calculates the differences in free energy of solvation between two conformers in aqueous solution. It was confirmed that the present procedure is applicable in solving the question of what is the most stable conformation of 12-crown-O3N in aqueous solution. Results of the calculations suggest that the order of stability for conformers in a vacuum is different from that in aqueous solution. It was also confirmed that the coordination geometry of solvent waters to Li+ changes depending on the distance between the cation and the crown ring.

Journal Article↗
PubMed1999

Side Arm Effects on Cyclen-Alkali Metal Cation Complexation: Highly Selective and Three-Dimensional Encapsulation of Na(+) Ion.

A variety of armed cyclens were prepared in which ester, amide, nitrile, and pyridine moieties were attached as cation-ligating side arms to a 12-membered ring. Ester-, amide-, and pyridine-armed cyclens nicely accommodated a Na(+) ion in a three-dimensional fashion and clearly discriminated the cation from Li(+) and K(+) ions. They extracted Na(+) ion more efficiently and selectively than common Na(+) ion-selective ligands. X-ray diffraction, FAB-MS, (23)Na NMR binding studies, and computer modeling experiments demonstrated that the cyclens having ester-, amide-, and pyridine-functionalized side arms formed highly selective encapsulated Na(+) complexes via a cooperative action of parent cyclen and side arms.

Journal Article↗
PubMed1999

Computer-Aided Reaction Design. Development of a New Facile Procedure to Synthesize 2-Mercapto-3-alkoxycarboxylate on the Basis of ab Initio Molecular Orbital Calculations.

This paper describes a new facial procedure to substitute a tosyloxy group in 2-(tosyloxy)alkanoate with SH(-) to yield 2-mercaptoalkanoate on the basis of ab initio MO calculations. Combination of substrate and solvent effects can control both reactivity and selectivity of reaction for 2-(tosyloxy)-3-alkoxycarboxylic acid which gave 2-mercapto-3-alkoxycarboxylic acid in good yield while its ethyl ester gave alpha,beta-unsaturated carboxylate ester as a main product. The difference of carboxylate moiety in the substrate causes remarkable change in reactivity and selectivity. To clarify origin of the difference, ab initio MO calculations in the gas phase and in DMF have been carried out. The solvent effect was considered at RHF/6-31+G with the IPCM-SCRF model. It was confirmed that the substrate with an ester fragment prefers the E1cB to the S(N)2 mechanism. In the transition state of the S(N)2 mechanism with a carboxylate ion fragment, the nucleophile SH(-) locates far from the reaction center due to the electrostatic repulsion between the COO(-) fragment and SH(-). This repulsion causes high activation barrier in the gas phase while polar solvent can reduce the barrier height. Therefore, reaction conditions can control reactivity of carboxylic acid. On the basis of analysis of the MO calculations, subsequent experiments were designed for a new dianion system to synthesize 2-pyrimidinylthio carboxylic acid from 2-tosyloxy carboxylate. We succeeded in developing a new facile method that the two reactions for thioether carried out in a one-pot procedure in excellent yield.

Journal Article↗
PubMed1997

A Theoretical and Experimental Study on Acid-Catalyzed Isomerization of 1-Acylaziridines to the Oxazolines. Reexamination of a Possible S(N)i Mechanism by Using ab Initio Molecular Orbital Calculations.

The S(N)i mechanism, which was previously proposed for the isomerization of 1-acylaziridines to the oxazolines, was reexamined theoretically by performing molecular orbital (MO) calculations of 1-formylaziridine and its derivatives as model compounds and experimentally by using 1(R)-[alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl]-2(S)-methylaziridine (5). At the MP2/6-31G//RHF/6-31G level, the activation energy was estimated to be 38.9 kcal mol(-1) for the S(N)i mechanism in which N-protonated 1-formylaziridine 8a(NH(+)) isomerizes to the N-protonated oxazoline 9a(NH(+)). Intrinsic reaction coordinate calculations showed that this reaction proceeds with retention of the ring carbon configuration. Methyl substitution in the aziridine ring reduces the activation energy by 10 kcal mol(-1). The ring closure of N-(2-chloroethyl)formamide (10a) to the oxazoline, which is a model reaction of the rate-determining step for the addition-elimination mechanism, was estimated to have an activation energy of 45.4 kcal mol(-1). The results of these MO calculations are consistent with the observation that the isomerization of the acylaziridine 5 to the oxazoline 6 is facilitated in the presence of weak nucleophiles such as with BF(3).OEt(2) while the formation of 6 is very slow in the presence of stronger nucleophiles such as p-toluenesulfonate. Both theoretical and experimental results suggest that the S(N)i mechanism explains well the isomerization of (R,S)-5 to the oxazoline with BF(3).OEt(2) in refluxing benzene.

Journal Article↗