IR signature of the photoionization-induced hydrophobic-->hydrophilic site switching in phenol-Arn clusters

IR spectra of phenol-Arn (PhOH-Arn) clusters with n=1 and 2 were measured in the neutral and cationic electronic ground states in order to determine the preferential intermolecular ligand binding motifs, hydrogen bonding (hydrophilic interaction) versus pi bonding (hydrophobic interaction). Analysis of the vibrational frequencies of the OH stretching motion, nuOH, observed in nanosecond IR spectra demonstrates that neutral PhOH-Ar and PhOH-Ar2 as well as cationic PhOH+-Ar have a pi-bound structure, in which the Ar atoms bind to the aromatic ring. In contrast, the PhOH+-Ar2 cluster cation is concluded to have a H-bound structure, in which one Ar atom is hydrogen-bonded to the OH group. This pi-->H binding site switching induced by ionization was directly monitored in real time by picosecond time-resolved IR spectroscopy. The pi-bound nuOH band is observed just after the ionization and disappears simultaneously with the appearance of the H-bound nuOH band. The analysis of the picosecond IR spectra demonstrates that (i) the pi-->H site switching is an elementary reaction with a time constant of approximately 7 ps, which is roughly independent of the available internal vibrational energy, (ii) the barrier for the isomerization reaction is rather low(<100 cm(-1)), (iii) both the position and the width of the H-bound nuOH band change with the delay time, and the time evolution of these spectral changes can be rationalized by intracluster vibrational energy redistribution occurring after the site switching. The observation of the ionization-induced switch from pi bonding to H bonding in the PhOH+-Ar2 cation corresponds to the first manifestation of an intermolecular isomerization reaction in a charged aggregate.     

One-pot amidation of olefins through Pd-catalyzed coupling of alkylboranes and carbamoyl chlorides

A one-pot synthesis of C1-elongated amides starting from olefins and carbamoyl chlorides has been developed. Alkylboranes, generated by hydroboration of terminal olefins with 9-BBN-H, underwent smooth coupling with carbamoyl chlorides in the presence of palladium catalyst and Cs2CO3.     

Colloidal crystals of core-shell type spheres with poly(styrene) core and poly(ethylene oxide) shell

Elastic modulus and crystal growth kinetics have been studied for colloidal crystals of core–shell type colloidal spheres (diameter = 160–200 nm) in aqueous suspension. Crystallization properties of three kinds of spheres, which have poly(styrene) core and poly(ethylene oxide) shell with different oxyethylene chain length (n = 50, 80 and 150), were examined by reflection spectroscopy. The suspensions were deionized exhaustively for more than 1 year using mixed bed of ion-exchange resins. The rigidities of the crystals range from 0.11 to 120 Pa and from 0.56 to 76 Pa for the spheres of n = 50 and 80, respectively, and increase sharply as the sphere volume fraction increase. The g factor, parameter for crystal stability, range from 0.029 to 0.13 and from 0.040 to 0.11 for the spheres of n = 50 and 80, respectively. These g values indicate the formation of stable crystals, and the values were decreased as the sphere volume fraction increased. Two components of crystal growth rate coefficients, fast and slow, were observed in the order from 10⁻³ to 10¹ s⁻¹. This is due to the secondary process in the colloidal crystallization mechanism, corresponding to reorientation from metastable crystals formed in the primary process and/or Ostwald-ripening process. There are no distinct differences in the structural, kinetic and elastic properties among the colloidal crystals of the different core–shell size spheres, nor difference between those of core–shell spheres and silica or poly(styrene) spheres. The results are very reasonably interpreted by the fact that colloidal crystals are formed in a closed container owing to long-range repulsive forces and the Brownian movement of colloidal spheres surrounded by extended electrical double layers, and their formation is not influenced by the rigidity and internal structure of the spheres.     

Rheological properties of deionized Chinese ink

Rheological properties for Chinese ink in exhaustively deionized aqueous media were carefully examined. In the steady shear measurement, the shear viscosities of the ink could be well explained by considering the “effective” volume fraction of the particles in the ink including the electrical double layers and by using Einstein's equation for dilute suspension viscosity, when the particle volume fraction was substantially low. In the case that the volume fraction was higher, the shear viscosities showed extremely higher than those from Einstein's prediction, though the ink remained a Newtonian liquid. In the stress-strain measurement, the shear moduli were observed at strain smaller than 0.2. The “weak” aggregation among the particles in the ink under no shear or low shear rates was supported. It should be noted that the glue in the suspension plays an important role for the good liquidity of the ink and for the “weak” bridges among the particles resulting its good dispersion stability.     

O2 Binding and Dissociation and Ligand Exchange Reaction of O2 with CO in Polymer Composite Films of Hemoglobin

A polymer composite film of hemoglobin (Hb–polymer film) was prepared by the casting of an Hb–polymer mixed solution (weight ratio of Hb to polymer is 1 to 1). The percentages of O₂ and CO saturation of the Hb–dextran film were 46% and 70%, respectively. In the Hb solution, 100% saturation was observed for both ligands, and a humidified Hb–dextran film also showed 100% saturation. Water molecules would provide flexibility to the matrix polymer and promote a structural change in the Hb from a tense state (T) to a relaxed state (R). Thus the ligand binding to the Hb in the polymer films was strongly affected by the degree of interaction of Hb with the matrix polymers and the physical properties of the polymers. Inositol hexaphosphate (IHP) worked as an allosteric effector even in the solid polymer film and lowered the oxygen affinity of Hb. The O₂ transport through an Hb–polyethyleneimine (PEI) film with IHP showed the facilitated O₂ transport in comparison with the film without IHP because of the high dissociation rate of O₂ from Hb with IHP. © 1997 John Wiley & Sons, Ltd.     

Self-organized monolayer assemblies of octopusporphyrins: photoinduced electron transfer and O 2 coordination in aqueous media

Bolaamphiphilic tetraresorcinolporphyrins with eight long side chains (octopusporphyrins) and their metal complexes form monolayered assemblies in bulk aqueous solution. The nano-structure, the photoinduced electron transfers and the O₂ coordination of these octopusporphyrin assemblies are described. In the micellar fibers of 1a and 1b, a unique spherical arrangement of eight methyl groups on both sides of the porphyrin ring plane provides hydrophobic porphyrin centers which align in a string of pearls. Exciton calculations indicated a tilt stacking porphyrins arrangement with a separation of 11 Å. These fibers fluoresced strongly; electron transfer reaction was therefore observed between the porphyrin center and hydrophobic quenchers as well as hydrophilic quenchers. The fibers were also active as photocatalysts in the reduction of dimethylviologen by triethanolamine. Octopusporphyrins with different metal centers can also produce fibrous aggregates, for example, H₂P/Zn(II)P and Zn(II)P/Fe(III)P couples. The fluorescence quenching of Zn(II)P in the Zn(II)P/Fe(III)P hybrid fibers can be ascribed to the intermolecular electron transfer within the fibers. In H₂P/Zn(II)P couple, excitation energy transfer from excited Zn¹*P to H₂P occurred after photoexcitation. Octopusporphyrin with four dialkylglycerophosphocholine groups on both sides of the ring plane ( 2b ) forms spherical unilamellar vesicles. Based on cryomicroscopy, a white line was observed with a diameter of 15 Å in the middle of the membrane which are obviously a porphyrin layer with low molecular packing. The octopusheme ( 2c ) vesicles prepared in a similar manner with 20-fold excess molar coexistence of 1-dodecyl-2-methylimidazole (DMIm) can bind and release oxygen reversibly at 25°C. Moreover, water-soluble octopusporphyrin ( 3a ) produced fluorescent and non-fluorescent monolayer assemblies by anion exchange of the head groups, e.g. 3a with sodium perchlorate showed planar sheets. An exciton calculation is consistent with a two-dimensional arrangement with porphyrin separations of 25.6 and 17.4 Å in the x- and y-directions, respectively. External addition of negatively charged electron acceptors, naphtoquinone sulfonate and anthraquinone sulfonate, led to partial quenching of the fluorescence of the central porphyrin layer. The results have been evaluated using equations derived for this special quenching. © 1998 John Wiley & Sons, Ltd.     

Average Octet Radical Polymer: A Stable Polyphenoxyl with Star-Shaped π Conjugation

An average spin quantum number of 7/2 is displayed by the star-shaped, π-conjugated polyradical 1 , even with a spin concentration of 0.8 per monomer unit. Polymer 1 is stable at room temperature, and it is a powerful candidate for the synthesis of a feasible polymer with very high spin.     

Miscibility of sodium chloride and sodium dodecyl sulfate in the adsorbed film and aggregate

The adsorption, micelle formation, and salting out of sodium dodecyl sulfate in the presence of sodium chloride were studied from the viewpoint of their mixed adsorption and aggregate formation. The surface tension of aqueous solutions of a sodium chloride–sodium dodecyl sulfate mixture was measured as a function of the total molality and composition of the mixture. Phase diagrams of adsorption and aggregate formation were obtained by applying thermodynamic equations to the surface tension. Judging from the phase diagrams, sodium chloride and sodium dodecyl sulfate are miscible in the adsorbed film at very large composition of sodium chloride and in the salted-out crystalline particle, while they are immiscible in the micelle. The miscibilities in the adsorbed film, micelle, and crystalline particle increase in the following order: particle > adsorbed film > micelle. The difference in miscibility among the oriented states was ascribed to the difference in geometry between the adsorbed film and micelle and to the interaction between bilayer surfaces in the particle.     

Bond fluctuation of S/Se anchoring observed in single-molecule conductance measurements using the point contact method with scanning tunneling microscopy

Conductance was measured for the single molecules with S/Se anchoring on a Au surface using the point contact method with scanning tunneling microscopy that enables us to selectively perform a repeated analysis of a chosen target molecule. Apparent conductance changes observed in sequential measurements suggest the existence of bond fluctuation among the adsorption sites.