Enhancing effect of phenylboronic acid compounds and their interactions with the diol groups of saccharides in a capillary electrophoresis-chemiluminescence detection system.

In our previous study, we proposed molecular recognition of mono- and disaccharides making use of the interaction between their diol groups and p-iodophenylboronic acid in capillary electrophoresis with a chemiluminescence detection system. Here, to extend our knowledge of molecular recognition, we first examined the enhancing effects of four phenylboronic acid compounds other than p-iodophenylboronic acid i.e., 4-biphenylboronic acid, 4-octyloxyphenyl-boronic acid, 3-octyloxyphenylboronic acid, and 4-dodecyloxyphenylboronic acid, for luminol-hydrogen peroxide-horseradish peroxidase reaction in the capillary electrophoresis-chemiluminescence detection system. Only 4-biphenylboronic acid showed an enhancing effect similar to that of p-iodophenylboronic acid; the effect was determined over the range of 0.5-10 microM in this system. Second, we estimated the apparent stability constants between the diol groups of saccharides (1-methyl-D-glucoside, D-saccharose, and D-fructose) and the boronic acid moieties of the two enhancers, p-iodophenylboronic acid and 4-biphenylboronic acid. The apparent binding constants obtained here provided insight to confirm the principle of molecular recognition for the saccharides examined here.     

Thermo-responsive mending of polymers crosslinked by thermally reversible covalent bond: Polymers from bisfuranic terminated poly(ethylene adipate) and tris-maleimide

Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels-Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) (PEAF₂) and a tris-maleimide, M₃. When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60 °C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60 °C. So, the PEAF₂ network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus.     

Regularized logistic discrimination with basis expansions for the early detection of Alzheimer’s disease based on three-dimensional MRI data

In recent years, evidence has emerged indicating that magnetic resonance imaging (MRI) brain scans provide valuable diagnostic information about Alzheimer’s disease. It has been shown that MRI brain scans are capable of both diagnosing Alzheimer’s disease itself at an early stage and identifying people at risk of developing Alzheimer’s. In this article, we have investigated statistical methods for classifying Alzheimer’s disease patients based on three-dimensional MRI data via L2-type regularized logistic discrimination with basis expansions. Preceding studies adopted an open approach when applying three-dimensional data analysis. Our proposed classification model with dimension reduction techniques offers discriminant functions with excellent prediction performance in terms of sensitivity and specificity.     

Confocal Raman and electronic microscopy studies on the topotactic conversion of calcium carbonate from Pomacea lineate shells into hydroxyapatite bioceramic materials in phosphate media

Conversion of Pomacea lineate shells into hydroxyapatite (HA) bioceramic materials was investigated by their in vitro treatment with phosphate solutions, at room temperature. Confocal Raman microscopy revealed that the conversion proceeds at distinct rates through the nacreous or periostracum sides of the shell. The conversion can be accelerated using powdered samples, yielding biocompatible materials of great interest in biomedicine.     

Effects of extension or prevention of pi-conjugation on photoinduced electron transfer processes of ferrocene-oligothiophene-fullerene triads

Photoinduced electron-transfer processes of alkyl-inserted ferrocene-trimethylene-oligothiophene-fullerene (Fc-tm-nT-C60) linked triads and directly linked ferrocene-oligothiophene-fullerene(Fc-nT-C60) triads were investigated using time-resolved fluorescence and transient absorption spectroscopic methods. In nonpolar solvent, the energy-transfer (EN) process occurred from 1nT* to C60 for both triads, without forming the charge-separated (CS) state. In polar solvent, the initial CS state, Fc-tm-nT(*+)-C60(*-), was formed via Fc-tm-nT-1C60 after the EN process from 1nT by photoexcitation of the nT moiety and after direct photoexcitation of the C60 moiety. For Fc-tm-nT(*+)-C60(*-), the positive charge shifted from the nT(*+) moiety to the Fc moiety, producing the final CS state, Fc(*+)-tm-nT-C60(*-), which lasted for 22-330 ns by changing nT from 4T to 12T. For Fc-nT-C60 in polar solvent, the CS state, in which the radical cation is delocalized on both Fc and nT moieties ((Fc-nT)(*+)-C60(*-)), was formed immediately after direct photoexcitation of the nT and C60 moieties. The lifetimes of (Fc-nT)(*+)-C60(*-) were estimated to be 0.1-50 ns by changing nT from 4T to 12T. The longer lifetimes of Fc(*+)-tm-nT-C60(*-) than those of (Fc-nT)(*+)-C60(*-) are caused by the insertion of the trimethylene chain to prevent the pi-conjugation between the Fc and nT moieties. The lifetimes for Fc(*+)-tm-nT-C60(*-) and (Fc-nT)(*+)-C60(*-) are prolonged by changing nT from 4T to 12T. For the charge-recombination process of Fc(*+)-tm-nT-C60(*-), the damping factor was evaluated to be 0.10 A(-1). For (Fc-nT)(*+)-C60(*-), the oxidation potentials of the nT moieties control the electron-transfer process with reflecting stabilization of the radical cations of the nT moieties.     

Photoinduced processes in a tricomponent molecule consisting of diphenylaminofluorene-dicyanoethylene-methano[60]fullerene

Photoinduced intramolecular processes in a tricomponent molecule C60(>(CN)2-DPAF), consisting of an electron-accepting methano[60]fullerene moiety (C60>) covalently bound to an electron-donating diphenylaminofluorene (DPAF) unit via a bridging dicyanoethylenyl group [(CN)2], were investigated in comparison with (CN)2-DPAF. On the basis of the molecular orbital calculations, the lowest charge-separated state of C60(>(CN)2-DPAF) is suggested to be C60*-(>(CN)2-DPAF*+) with the negative charge localized on the fullerene cage, while the upper state is C60(>(CN)2*--DPAF*+). The excited-state events of C60(>(CN)2-DPAF) were monitored by both time-resolved emission and nanosecond transient absorption techniques. In both nonpolar and polar solvents, the excited charge-transfer state decayed mainly through initial energy-transfer process to the C60 moiety yielding the corresponding 1C60, from which charge separation took place leading to the formation of C60*-(>(CN)2-DPAF*+) in a fast rate and high efficiency. In addition, multistep charge separation from C60(>(CN)2*--DPAF*+) to C60*-(>(CN)2-DPAF*+) may be possible with the excitation of charge-transfer band. The lifetimes of C60*-(>(CN)2-DPAF*+) are longer than the previously reported methano[60]fullerene-diphenylaminofluorene C60(>(C=O)-DPAF) with the C60 and DPAF moieties linked by a methanoketo group. These findings suggest an important role of dicyanoethylenyl group as an electron mediating bridge in C60(>(CN)2-DPAF).     

Synthesis and photophysical properties of two dual oligothiophene-fullerene linkage molecules as photoinduced long-distance charge separation systems

To further extend photoinduced charge separation previously observed for oligothiophene-fullerene dyads (nT-C60), we have studied two novel dual oligothiophene-fullerene triads, 8T-4T-C60 and 4T-8T-C60, where quaterthiophene (4T) and octithiophene (8T) are linked by a trimethylene chain and either one is attached to a fullerene (C60). The cyclic voltammograms and electronic absorption spectra of these triad compounds indicated no electronic interactions among the three components. On the other hand, the emission spectra were markedly perturbed by electron transfer and/or energy transfer from the oligothiophene to fullerene. Detailed comparisons between the emission spectra of the triads (8T-4T-C60 and 4T-8T-C60) and the dyads (4T-C60 and 8T-C60) suggest that the additionally attached octithiophene or quaterthiophene in the triads is involved in the photophysical decay mechanism, and the 8T-4T-C60 triad undergoes photoinduced electron transfer leading to long-distance charge separation. This was actually corroborated by observation of the specific bands due to 8T*+-4T-C60*- species in the transient absorption spectra after photoexcitation of the octithiophene. The sandwich device based on the 8T-4T-C60 triad produced a more effective photovoltaic response to visible light owing to the contribution of the additional octithiophene chromophore compared to that using the dyad 4T-C60. On the other hand, the 4T-8T-C60-based device demonstrated a rather poorer photovoltaic performance when compared to the 8T-C60 device.     

Synthesis of heterometal cluster complexes by the reaction of cobaltadichalcogenolato complexes with groups 6 and 8 metal carbonyls

Metalladichalcogenolate cluster complexes [{CpCo(S2C6H4)}2Mo(CO)2] (Cp = eta(5)-C5H5) (3), [{CpCo(S2C6H4)}2W(CO)2] (4), [CpCo(S2C6H4)Fe(CO)3] (5), [CpCo(S2C6H4)Ru(CO)2(P(t)Bu3)] (6), [{CpCo(Se2C6H4)}2Mo(CO)2] (7), and [{CpCo(Se2C6H4)}(Se2C6H4)W(CO)2] (8) were synthesized by the reaction of [CpCo(E2C6H4)] (E = S, Se) with [M(CO)3(py)3] (M = Mo, W), [Fe(CO)5], or [Ru(CO)3(P(t)Bu3)2], and their crystal structures and physical properties were investigated. In the series of trinuclear group 6 metal-Co complexes, 3, 4, and 7 have similar structures, but the W-Se complex, 8, eliminates one cobalt atom and one cyclopentadienyl group from the sulfur analogue, 4, and does not satisfy the 18-electron rule. 1H NMR observation suggested that the CoW dinuclear complex 8 was generated via a trinuclear Co2W complex, with a structure comparable to 7. The trinuclear cluster complexes, 3, 4, and 7, undergo quasi-reversible two-step one-electron reduction, indicating the formation of mixed-valence complexes Co(III)M(0)Co(II) (M = Mo, W). The thermodynamic stability of the mixed-valence state increases in the order 4 < 3 < 7. In the dinuclear group 8 metal-Co complexes, 5 and 6, the CpCo(S2C6H4) moiety and the metal carbonyl moiety act as a Lewis acid character and a base character, respectively, as determined by their spectrochemical and redox properties. Complex 5 undergoes reversible two-step one-electron reduction, and an electron paramagnetic resonance (EPR) study indicates the stepwise reduction process from Co(III)Fe(0) to form Co(III)Fe(-I) and Co(II)Fe(-I).