Exclusion of aromatic radical cations from cyclodextrin nanocavity studied by pulse radiolysis

The influence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the one-electron oxidation reaction of aromatic sulfides (S) with Br2*- and the decay process of the S radical cation (S*+) was investigated by pulse radiolysis. The dissociation kinetics of S*+ from the CD cavity was examined in terms of the apparent equilibrium constants (Kapp) for the formation and decay processes of S*+. Inhibition of the one-electron oxidation reaction of S by Br2*- was clearly observed in the presence of HP-beta-CD. On the basis of a comparison between the determined Kapp values, it was found that the binding ability of S*+ with HP-beta-CD is much lower than that of S, because of the hydrophobic nature of the cavity. The formation process of the dimer radical cation of 4-(methylthio)phenylmethanol ((MTPM)2*+), which is generated between MTPM(*+) and neutral MTPM in solution, was also inhibited by the addition of HP-beta-CD.     

Low temperature heat capacities of mechanically alloyed La-doped PbWO4 system

Heat capacity measurements were carried out on Pb_1-xLa_xWO_4+x/2 (x=0.2) and Pb_1-xLa_2x/3WO₄ (x=0.2, 0.5) solid solutions prepared by sintering and mechanical alloying (MA) methods. For all the solid solutions, sintered samples showed slightly larger heat capacity around 100 K in comparison with MA samples, which was presumably caused by the excitation of mobile oxide ion motion. For sintered scheelite-type structured PbWO₄s, high-temperature synthesis introduced oxide ion interstitials even for the Pb_1-xLa_2x/3WO₄ system, which resulted in the excess heat capacity at low temperature for excitation. On the other hand, for the samples prepared by room-temperature MA technique, oxide ion seemed to occupy the regular sites rather than interstitial ones and excess heat capacities were not observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of highly stabilized intramolecular dimer radical cation and pi-complex of [3n]cyclophanes (n = 3, 5, 6) during pulse radiolysis

Formation of radical cation and charge-transfer complex of [3n]cyclophanes (n = 3, 5, 6) was investigated by transient absorption spectroscopy during pulse radiolysis. Radical cations of [3n]cyclophanes showed the charge resonance band around 700 nm which exhibited a blue-shift as the number of trimethylene bridges increased, indicating formation of highly stabilized intramolecular dimer radical cation of [3n]cyclophanes. The absorption peak of the charge-transfer complex with chlorine atom also showed the shift in accord with the oxidation potential of [3n]cyclophanes.     

Thermodynamic Properties of Alkanediols+Acetates at 298.15 K

In this work we present experimental values of the density, refractive index, speed of sound, isentropic compressibility and liquid-liquid equilibria of the binary mixtures (methyl acetate, ethyl acetate, propyl acetate, and butyl acetate) with (1,2-ethanediol, 1,2-propanediol, or 1,3-propanediol) at 298.15 K and atmospheric pressure, as a function of mole fraction. From the experimental values, the corresponding excess and deviation values were computed (excess molar volumes, changes of refractive index on mixing, and changes of isentropic compressibility), variable-degree polynomials being fitted to the results. The validity of different estimation methods for predicting the experimental values of physical properties was tested. The limiting partial excess molar volume of the components in each binary mixture was determined by means of predetermined Redlich-Kister parameters. Group contribution method (UNIFAC-Dortmund) was applied in order to compare their capability in predicting the experimental equilibria values. This revised version was published online in July 2006 with corrections to the Cover Date.     

An efficient synthesis of a class of novel N‐Alkyl‐N‐aryl‐4‐hydroxy‐1‐methyl‐2‐oxo‐1,2‐dihydro‐3‐quinolinecarbothioamides

The novel title compounds have been prepared in high yield by an optimized amide coupling followed by a Dieckmann cyclization. Additionally, this new route is amenable to preparative scale synthesis.     

Synthesis of a Ni Complex Chelated by a [2.2]Paracyclophane-Functionalized Diimine Ligand and Its Catalytic Activity for Olefin Oligomerization

A diimine ligand having two [2.2]paracyclophanyl substituents at the N atoms (L1) was prepared from the reaction of amino[2.2]paracyclophane with acenaphtenequinone. The ligand reacts with NiBr₂(dme) (dme: 1,2-dimethoxyethane) to form the dibromonickel complex with (R,R) and (S,S) configuration, NiBr₂(L1). The structure of the complex was confirmed by X-ray crystallography. NiBr₂(L1) catalyzes oligomerization of ethylene in the presence of methylaluminoxane (MAO) co-catalyst at 10–50 °C to form a mixture of 1- and 2-butenes after 3 h. The reactions for 6 h and 8 h at 25 °C causes further increase of 2-butene formed via isomerization of 1-butene and formation of hexenes. Reaction of 1-hexene catalyzed by NiBr₂(L1)–MAO produces 2-hexene via isomerization and C12 and C18 hydrocarbons via oligomerization. Consumption of 1-hexene of the reaction obeys first-order kinetics. The kinetic parameters were obtained to be ΔG^‡ = 93.6 kJ mol⁻¹, ΔH^‡ = 63.0 kJ mol⁻¹, and ΔS^‡ = −112 J mol⁻¹deg⁻¹. NiBr₂(L1) catalyzes co-dimerization of ethylene and 1-hexene to form C8 hydrocarbons with higher rate and selectivity than the tetramerization of ethylene.     

Particle size effect on the new phase transition in a tridymite compound, CsCoPO4

A new phase transition (III–IV) was found at 311 K in CsCoPO₄ by DSC measurements. The crystal structure of all the phases, I–IV, in CsCoPO₄ was studied by synchrotron-radiation X-ray powder diffraction. The diffractometry revealed that CsCoPO₄ had the same crystal structure as that of corresponding phases in CsZnPO₄. An extremely large particle size effect was found on III–IV phase transition in CsCoPO₄; the phase transition enthalpy decreases with decreasing the particle size around 0.1 mm. Such large particle size effects had been also observed in CsZnPO₄. However, no III–IV phase transition was observed in the particle smaller than 0.1 mm of CsZnPO₄, while such a critical size was not found in CsCoPO₄.     

Photocatalytic cleavage of single TiO2/DNA nanoconjugates

TiO(2)/DNA nanoconjugates were successfully fabricated by using the catechol moiety as a binding functional group, which was confirmed by steady-state absorption and fluorescence spectroscopies. Upon UV irradiation, the photocatalytic cleavage of the TiO(2)/DNA nanoconjugates was observed at the single-molecule level by using wide-field fluorescence microscopy. The decrease in the number of conjugates, which was estimated from the luminescent spots due to semiconductor quantum dots modified at the DNA strand, was significantly inhibited by a single A/C mismatch in the DNA sequences. This result strongly suggests that the migration of holes, which are injected from the photoexcited TiO(2) into the DNA, through the DNA bases plays an important role in the photocatalytic cleavage of the conjugates. The influences of the photogenerated reactive oxygen species (ROS) on the cleavage efficiency were also examined. According to the experimental results, it was concluded that oxidation of the catechol moiety and/or the DNA damage are key reactions in this process.     

Sulfonated Pyrene as a Photoregulator for Single-Stranded DNA Looping

Controlling the conformation and function of biomolecules through photoregulators holds great promise as a spatiotemporally controllable tool for disease control. In addition, introducing photoregulators into biomolecules has also found applications in constructing smart nanomaterials. In spite of the astonishing advances that have been made in the past few years, realizing highly controllable and efficient regulation over the conformation and function of biomolecules under physiological conditions is still challenging. Herein, sulfonated pyrene SPy was synthesized and used as a photoregulator to control the looping of single-stranded DNAs (ssDNAs) in aqueous solution. Due to its water solubility, SPy merits use in the study of biomolecules in aqueous solution. The looping of the doubly SPy -modified ssDNAs is stimulated by irradiation and regulated by SPy . Photoionization generates the radical cation of SPy ( SPy ^.+). The association of SPy ^{. +} with its neutral counterpart, SPy , gives rise to the dimer radical cation of SPy ( SPy₂ ^{. +} ). During the association process, the stabilization energy released to form SPy₂ ^{. +} provides a driving force for the looping of ssDNAs. Conversely, the formed loop conformations were trapped by the formation of SPy₂ ^{. +} , and this allowed the looping dynamics to be investigated. The results reported herein suggest potential of SPy as a photoregulator for controlling the conformation and function of biomolecules under physiological conditions.