Observation of strong low-lying E1 strength in the two-neutron halo nucleus 11Li

An exclusive measurement has been made of the Coulomb dissociation of the two-neutron halo nucleus 11Li at 70 MeV/nucleon at RIKEN. Strong low-energy (soft) E1 excitation is observed, peaked at about Ex = 0.6 MeV with B(E1) = 1.42(18) e2fm2 for Erel < or = 3 MeV, which was largely missed in previous measurements. This excitation represents the strongest E1 transition ever observed at such low excitation energies. The spectrum is reproduced well by a three-body model with a strong two-neutron correlation, which is further supported by the E1 non-energy-weighted cluster sum rule.     

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.     

Synthesis of a novel star-shaped dendrimer by radial-growth polymerization of sarcosine N-carboxyanhydride initiated with poly(trimethyleneimine) dendrimer

A novel AB_n-type dendrimer/linear polymer block copolymer, i.e., poly(trimethyleneimine) dendrimer-block-(polysarcosine)₆₄ ( 1 ), was synthesized by ring-opening polymerization of sarcosine N-carboxyanhydride initiated with the 64-NH₂-terminal poly(trimethyleneimine) dendrimer as a macroinitiator. 1 has narrow molecular weight distributions (M_w/M_n = 1.0₁–1.0₃, by size exclusion chromatography) and controlled polysarcosine chain lengths (by varying the monomer/dendrimer feed molar ratios). Small-angle neutron scattering (SANS) data obtained in D₂O solution of 1 (DP's of polysarcosine = 2.0 and 24) fitted well with a Guinier plot of a spherical particle, and gave diameters of 44 and 100 Å, respectively.     

Binding of poly(amido amine) dendrimer to sodium hyaluronate in aqueous NaCl solution

Binding of poly(amido amine) dendrimer to sodium hyaluronate (NaHA) in aqueous 0.25 M NaCl solution has been investigated by static light scattering. It was observed that the apparent weight-average molecular weight and the radius of gyration increase with the ratio of NH(2) terminal groups in the dendrimer to the carboxylate groups in the NaHA, [NH(2)]/[COO(-)]. Up to [NH(2)]/[COO(-)]=31, the observed variation of molecular weight was reproduced by the "average binding" model, where an average number of dendrimers binds to each NaHA chain. Based on the "critical binding" model, the maximum number, n(max), of dendrimers which can bind to a NaHA chain was calculated to be n(max)=300 for a solution of [NH(2)]/[COO(-)]=56. The obtained value corresponds to the binding of one dendrimer per 1.5 repeating units on a NaHA chain. It is suggested from the observed radius of gyration that, while the dendrimer-NaHA complexes of [NH(2)]/[COO(-)] up to 5 maintain a wormlike character similar to NaHA without bound dendrimers, those of [NH(2)]/[COO(-)] above 10 behave like rigid rods. It is concluded that the hydrogen-bonding interaction, besides the electrostatic interaction, should play an important role in the formation of the NaHA-dendrimer complexes.     

Diels-alder reaction of (E)-4-(2-nitroethenyl)-1H-imidazoles and methyl (E)-3-(1-imidazol-4-yl)propenoates

Diels-Alder reaction of methyl (E)-3-(1H-imidazol-4-yl)propenoates 2, 3a-c and (E)4-(2-nitroethenyl)-1H-imidazoles 3d,e with 2,3-dimethyl-1,3-butadiene, cyclopentadiene, and cyclohexa-1,3-diene gave the corresponding cycloadducts 6–9 .     

Heterogeneously catalyzed aerobic oxidative biaryl coupling of 2-naphthols and substituted phenols in water

The oxidative coupling reaction can efficiently be promoted by supported ruthenium catalyst Ru(OH)x/Al2O3. A variety of 2-naphthols and substituted phenols can be converted to the corresponding biaryl compounds in moderate to excellent yields using molecular oxygen as a sole oxidant in water without any additives. The catalysis is truly heterogeneous in nature, and Ru(OH)x/Al2O3 can easily be recovered after the reaction. The catalyst can be recycled seven times with the maintenance of the catalytic performance, and the total turnover number reaches up to 160. The results of competitive coupling reactions suggest that the present oxidative biaryl coupling reaction proceeds via the homolytic coupling of two radical species and the Ru(OH)x/Al2O3 catalyst acts as an one-electron oxidant. Two radical species are coupled to give the corresponding biaryl product, and the one-electron reduced catalyst is reoxidized by molecular oxygen. The amounts of O(2) uptake and H(2)O formation were almost one-quarter and one-half the amount of substrate consumed, respectively, supporting the reaction mechanism. The kinetic data and kinetic isotope effect show that the reoxidation of the reduced catalyst is the rate-limiting step for the coupling reaction.     

One-shot block copolymerization

This paper describes a new method of the preparation of block copolymer, in which a mixture of two monomers is subjected to polymerization (simultaneous feeding) by the aid of an initiator. The new method is performed with the polymerization of a family of 2-oxazolines, which proceeds via electrophilic propagating species, cation or covalent bond having electrophilic reactivity. The key to the block copolymer formation with one-shot feeding of monomers is the difference of reactivity of polymerization (nucleophilicity) between the two monomers. First the monomer of higher reactivity is polymerized to completion, and then the monomer of decreased reactivity is polymerized starting from the propagating species of the first polymerization. For the high selectivity of the production of block copolymer, each of two propagations should be of “living mechanism”. Two combinations of monomers, i.e., 2-methyl-2-oxazoline/2-(heptafluoro-n-propyl)-2-oxazoline and 2-phenyl-2-oxazoline/2-(pentafluoroethyl)-2-oxazoline, together with an initiator of methyl tosylate were found to follow the pattern of the new process. Block copolymer of the former monomers' combination was water-soluble, and its aqueous solution showed an excellent value of surface tension.