Tetsuo Kuwabara

Condensation of alcohol over solid-base catalyst to form higher alcohols

Condensations of various primary alcohols (C2-C5) with methanol were carried out at atmospheric pressure over various metal oxides having a solid-base property. The reactions gave one or two carbon higher alcohol than the reacted primary alcohol. MgO catalyst was most active for the reaction and yielded the alcohol products in high selectivity (> 80%). Based on the results of the exchange reaction between methyl hydrogen of methanol over MgO surface, it is concluded that a rapid hydride transfer between adsorbed alcohol and adsorbed carbonyl is responsible for the selective formation of alcohols.

Solid base-catalyzed reaction of nitriles with methanol to form α,β-unsaturated nitriles. II, Surface base property and reaction mechanism

Abstract Solid acid and base properties of magnesium oxides activated by transition metal ions, MMgO, which are effective catalysts for the reaction of nitriles with methanol to form corresponding α,β-unsaturated nitriles, were studied by temperature-programmed desorption of CO2 and the reaction of isopropyl alcohol, and the reaction mechanism was studied by isotopic tracer methods. The surface base property of magnesium oxide was modified by the addition of a metal ion; the addition of a metal ion with larger ionic radius than Mg2+ increases the amount of surface base site, whereas the addition of a metal ion with an ionic radius smaller than that of Mg2+ induces surface acid sites without any appreciable changes in the amount of surface base site. Active catalysts were formed in the latter case but not in the former case. It was thought that a surface acid property as well as a surface base property played an important role in the course of the reaction. Reaction of deuterium-substituted acetonitrile and methanol revealed that the exchange reaction between hydroxyl hydrogen of methanol and methyl hydrogen of acetonitrile took place readily under the conditions of acrylonitrile synthesis and the isotopic distribution in acetonitrile after the reaction was very close to that of isotopic equilibrium. No exchange reaction between methyl hydrogen of methanol and that of acetonitrile was observed. It was found, on the other hand, that the isotopic exchange reaction between methyl hydrogen of deuterated methanol and light methanol can occur under the same conditions. The reaction mechanism appears to be dehydrogenation of methanol to adsorbed formaldehyde which then reacts with the acetonitrile anion and, after dehydration, yields acrylonitrile.

Classification of DNA-binding mode of antitumor and antiviral agents by the electrochemiluminescence of ruthenium complex.

The DNA-binding mode of antitumor and antiviral agents has been evaluated by electrochemiluminescence (ECL) of tris(1,10-phenanthroline)-ruthenium complex (Ru(phen)(3)(2+)) in the presence of oxalate ion in pH 7.3 Tris buffer solution. An emission of Ru(phen)(3)(2+) was observed repeatedly with a voltage above 1000mV subjected to a potential sweep from 0 to 1250mV. The addition of lambdaDNA into the solution containing 1 micro M of Ru(phen)(3)(2+) caused the decrease in the ECL intensity, which became half at a DNA concentration of 20 micro M. This is due to the binding of Delta-type of Ru(phen)(3)(2+) with DNA in the major groove of DNA. When the various concentrations of the drug were added to the solution containing 1& micro M Ru(phen)(3)(2+), the ECL intensity was not affected by the concentration of the drug in the absence of DNA. In the presence of DNA (10 micro M), however, two ECL emission patterns were observed when the concentration of the drug was varied. The pattern that the ECL intensity increased with increasing the drug concentration was observed for cisplatin, daunomycin, and DC92-B. This may have resulted from the DNA binding of the drug with a major groove site, where Ru(phen)(3)(2+) should bind. Ru(phen)(3)(2+) nonbinding to DNA might exist in the bulk solution and exhibits ECL emission. The drug exhibiting the drug-concentration-dependent ECL is classified as a drug with a major groove binding character. The addition of drugs, such as mitomycin C and duocarmycin SA, did not cause a change in the ECL intensity even in the presence of DNA. This result indicates that these drugs bind to DNA with minor groove binding. Since similar trends were observed for actinomycin D, distamycin A, doxorubicin, and chromomycin A3; these drugs are also considered as minor groove binding agents. All these results demonstrate that the DNA-binding mode of the drug can be evaluated easily by utilizing the ECL of Ru(phen)(3)(2+), which is used as the sensing probe.

A low-pressure guerbet reaction over magnesium oxide catalyst

Propan-1-ol and 2-methylpropan-1-ol were synthesized selectively by the catalytic reaction of methanol and ethanol over magnesium oxide.

Photochromism of Viologens Included in Crown Ether Cavity

Abstract The effect of a π-electron–donating macrocyclic molecule on the photochromic behavior of viologen derivatives was investigated in a thin polymer film. The intermolecular interactions between the viologens and the macrocyclic molecule were investigated in a solution before photoirradiation. In acetone, benzylviologens, N,N′-dibenzyl-4,4′-bipyridinium hexafluorophosphate (1) and N,N′-dibenzyl-trans-1,2-bis(4-pyridinium)ethylene hexafluorophosphate (2) each derived from 4,4′-bipiyridine and trans-1,2-bis(4-pyridyl)ethylene, respectively, form an inclusion complex with p-benzocrown ether (3) with binding constants of ca 200 M−1, which was driven by a charge transfer interaction. The peak wavelength of the charge transfer absorption band was at 453 and 421 nm for the inclusion complexes of 1 and 2 with 3, respectively. Upon photoirradiation to the polymer film containing 1, the film changed color from colorless to blue, associated with the reduction of 1 from the dication to the radical cation. The original dication was recovered after 120 min. The addition of 3 into the film containing 1 caused not only the color change from colorless to yellow, associated with the charge transfer interaction between 1 and 3 before photoirradiation, but also an acceleration in the bleaching rate of the photoreduced 1. When p-dimethoxybenzene (4) was used as an acyclic analog of 3, a negligible change in the photochromic behavior of 1 was observed. Similar effect of 3 on the photochromic behavior of 2 was observed. These results imply that the π-electron–donating macrocyclic molecule causes a faster bleaching of photoreduced viologens by forming the inclusion complex.

Color-modulation by Additives for Photochromism of Cyclic Viologen Derivatives

Abstract Two cyclic viologen derivatives were prepared in order to investigate their photochromic properties in a thin polymer film. The absorption peaks of photoreduced cyclic viologen units were shifted to the red side by the inclusion of indole or 1,4-dimethoxybenzene, although those of photoreduced acyclic analogues were not shifted in the presence of the guests.

Guest-induced colour changes and molecule-sensing abilities of p-nitrophenol-modified cyclodextrins

Two p-nitrophenol modified β-CDs (1, 2) were synthesized in order to assess colour changes induced by host–guest complexation as well as to investigate their conformations and binding properties as colour changeable indicators for the presence of organic molecules in pH neutral aqueous solutions. Host 3, which has an α-CD in place of the β-CD of 1, was also synthesized for comparison. The induced circular dichroism spectra of 1–3 suggest that the p-nitrophenol unit of 1 and 3 is not completely included in their CD cavities and that of 2 is fully included in its β-CD cavity. The spectra of 1–3 in the presence of guest supported these results, slightly enhancing the absolute intensities for 1 and 3 and decreasing the intensity for 2. The guest-induced conformation changes of 1–3 caused the colour to change from yellow to colourless, which is associated with the conversion of the appending moiety from phenolate anion to neutral phenol species at pH 5.10 for 1 and 3 and at pH 6.50 for 2. The binding constants of 1 were markedly larger than those for 2, reflecting that the p-nitrophenol moiety of 1 acts as an effective hydrophobic cap while that of 2 acts as an intramolecular inhibitor upon guest accommodation. These results demonstrate that various colour changeable indicators for molecules which work under neutral conditions may be constructed on the basis of the appropriate design of the appending part in dye-modified cyclodextrins.

Supramolecular thermochromism of a dye-appended β-cyclodextrin

A β-cyclodextrin derivative 1 bearing a dye moiety reveals thermochromism; the mechanism is based on an equilibrium shift in its host–guest complexation, occurring in the range 25–65 °C in a 10% ethylene glycol aqueous solution.

Ion Sensing by Charge Transfer Absorption Variations of Benzocrown–Bipyridinium Conjugates with an Alkyl Chain

Two benzocrown ether-bipyridinium conjugates, 1 and 2, each having a different length of alkyl chains with butyl and dodecyl groups, respectively, have been synthesized for the purpose of developing a new guest-responsive color-change chemosensor. Both 1 and 2 showed yellow colors with broad absorption bands around 400 nm in acetonitrile. These are associated with the intramolecular charge transfer (CT) absorption, in which the benzocrown ether and bipyridinium units act as the donor and acceptor, respectively. Upon addition of the guest; such as Na(+), they faded in color due to the blue shift in their intramolecular charge transfer absorption bands. These are associated with the formation of 1:1 host-guest inclusion complex. Analogues, 3 and 4, both being similar in structure to 1 and 2 with non-crown ether unit, also showed intramolecular CT absorptions around 400 nm, but did not change their absorption spectra upon addition of the guest because of the lack of guest-binding abilities. The guest-induced color change of 1 and 2 can be used for alkali and alkaline metal ion sensing. Both 1 and 2 could detect divalent cations such as Mg(2+) and Ca(2+) rather than univalent ones, Li(+), Na(+), K(+), Rb(+), and Cs(+). Although a marked difference between 1 and 2 was not observed in their guest sensing abilities, the remarkable recognition of 1 and 2 for Mg(2+) and Ca(2+) was found compared with that of 5, which has benzyl unit instead of alkyl chains of 1 and 2. The sensitivity values of 1 and 2 were roughly proportional to their binding constants, as shown by the binding constants with Li(+), Na(+), Mg(2+), and Ca(2+) with the values of 910, 260, 820, and 2300 M(-1) for 1 and 930, 290, 1270, and 2790 M(-1) for 2, while the binding constants of 5 were estimated to be 930, 440, 210, and 1200 M(-1) for Li(+), Na(+), Mg(2+), and Ca(2+), respectively. The limit concentration of detection of 2 for Ca(2+) was estimated to be 0.016 mM, which was the smallest value in this system.

Rapid Communication Effect of Alkali Metal Ions on Photochromic Behavior of Bisviologen‐incorporated Oligo‐oxyethylene Units ¶

Two bisviologen derivatives, 1,11‐bis(N‐propyl‐4,4′‐bipyridinium)‐3,6,9‐trioxaundecane tetrakis‐(hexafluorophosphate) (1) and 1,8‐bis(N‐propyl‐4,4′‐bipyridinium)‐3,6‐dioxaoctane tetrakis‐(hexafluorophosphate) (2), each incorporating trioxaundecane and dioxaoctane groups between two viologen units, respectively, were prepared so that their photochromic behavior in the absence and the presence of alkali metal ions in a thin polymer film could be investigated. Photoirradiation of the films containing 1 and 2 caused color changes from pale yellow to blue, associated with the photoinduced reduction of the viologen units from the dication to the radical cation. The addition of alkali metal ions, especially, K+ and Na+, caused change in the spectra of the photoreduced viologen radical cation for 1 and 2, respectively, because of the increase in the fractional amplitude for the dimer component of the radical cation rather than the monomer one. This may be related to the guest‐induced conformational change of 1 and 2, in which the alkali metal ion is surrounded by the oligo‐oxyethylene unit of 1 and 2. The regulation in photochromic properties of viologen derivatives can be achieved by addition of alkali metal ions.