A hexagonal prismatic porphyrin array: synthesis, STM detection, and efficient energy hopping in near-infrared region

A belt-shaped hexagonal cyclic porphyrin array 2 that comprises of six meso-meso, beta-beta, beta-beta triply linked diporphyrins 3 bridged by 1,3-phenylene spacers is prepared by oxidation from cyclic dodecameric array 1 consisting of six meso-meso directly linked diporphyrins 4 with DDQ and Sc(OTf)3. The absorption spectrum of 2 is similar to that of the constituent subunit 3 but shows a slight red-shift for the Q-bands in near-infrared (NIR) region, indicating the exciton coupling between the neighboring diporphyrin chromophores. Observed total exciton coupling energies in the absorption spectra were largely matched with the calculated values based on point-dipole exciton coupling approximation. It was found that the experimental exciton coupling strength (292 cm(-1)) of the Q-band in 2 is slightly larger than the calculated one (99 cm(-1)), indicating that the electronic communications are enhanced through 1,3-phenylene linkers in hexameric macromolecule. A rate of the excitation energy hopping (EEH) that occurs in 2 at the lowest excited singlet state in the near-infrared region has been determined to be (1.8 ps)(-1) on the basis of the pump-power dependent femtosecond transient absorption (TA) and the transient absorption anisotropy (TAA) decay measurements. The 2 times faster EEH rate of 2 than that of 1 (4.0 ps)(-1) mainly comes from involving through-bond energy transfer among diporphyrin subunits via 1,3-phenylene bridges as well as F?rster-type through-space EEH processes. STM measurement of 2 in the Cu(100) surface revealed that it takes several discrete conformations with respect to the relative orientation of neighboring diporphyrins. Collectively, an effective EEH in the NIR region is realized in 2 due largely to the intensified oscillator strength in the S(1) state (Q-band) and the close proximity held by 1,3-phenylene spacers.     

Changes in carbon and nitrogen stable isotopes of chironomid larvae during growth, starvation and metamorphosis

We conducted experiments to determine isotope changes in the deposit-feeding chironomid larvae Chironomus acerbiphilus during feeding, starvation and metamorphosis. Isotope changes in chironomid larvae occurred mainly during growth and rarely afterward. This finding indicates that chironomid isotope turnover mainly occurs in conjunction with growth and suggests that chironomid larvae only break down newly assimilated food for energy during periods of no growth. Chironomid delta(13)C values significantly increased throughout the starvation experiment, indicating that chironomids preferentially break down components with lower delta(13)C content during starvation. We found significant changes in chironomid isotope ratios ((15)N enrichment) during pupation. This evidence suggests that the physiological condition of animals (such as during an active growth phase or pre- or post-molting) is important to their stable isotope ratios.     

Which is reactive in alkaline solution, boronate ion or boronic acid? Kinetic evidence for reactive trigonal boronic acid in an alkaline solution

That boronic acid is a reactive species toward a diol moiety even in an alkaline solution and that the boronate ion is not very reactive were demonstrated by the estimated upper limit of the rate constants for the reactions of some boronic acids with 2,2'-biphenol and 2,3-dihydroxynaphthalene in a neutral-alkaline solution, which will correct a common misunderstanding in boron chemistry and would renew the idea of effective boronic acid sensor design for carbohydrates.     

gem-Difluorocyclopropane as core molecule candidate for liquid crystal compounds

The synthesis of a novel chiral gem-difluorocyclopropane building block has been accomplished using chemo-enzymatic reaction protocol; the prochiral diol of 1,4-bis(2,2-difluoro-3-(hydroxymethyl)cyclopropyl)benzene (5) was converted to the corresponding chiral diacetate by Pseudomonas lipase (lipase SL-25, Meito)-catalyzed transesterification with vinyl acetate as acyl donor with >99% enantiomeric excess. Various types of diesters or dialkyl ether were prepared from the diol and their helical twisting power (HTP) was evaluated by addition of 1.0 wt% to a non-chiral nematic liquid crystal host; the HTP was significantly dependent on the structure of ester or ether moieties and diester of diol 5 with isopropylfumalic acid showed the largest HTP.     

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.     

Dynamic processes in endocytic transformation of a raft-exhibiting giant liposome

The dynamic response of a raft-exhibiting giant liposome to external stimuli, such as the addition of Triton X-100 or osmotic stress, was studied. We observed that daughter vesicles are generated inside of the liposome through endocytic budding. It was found that the budding to generate daughter vesicles is classified into two different routes, simple budding through the invagination of a whole raft and budding from the boundary of a raft accompanied by waving motion. Smaller rafts show a preference for simple budding, whereas large rafts mainly adopt the other process. We discuss the mechanism of this difference in terms of the kinetic pathway of internalization by considering the line energy and bending energy of the membrane.     

Photoisomerizable DNA Ligands. A Simple Method to Probe the Regions of AT-Rich Sequences

The dramatic effect of the microenvironment on the mechanism and quantum yield of photoisomerization have been widely evidenced; therefore, one can expect that the DNA matrix can modulate photoisomerization of properly designed ligands, and it may have an analytical importance.     

Electrochemical DNA Sensor Using Ferrocenyl Naphthalene Diimide Ligand

Searching for the method for gene detection is vitally important with the development of genetic diagnosis. Generally gene detection is carried out by the judgment of existence of signal of DNA probe (labeled complementary sequence) bound to target DNA sequence. Since sample DNA is immobilized on the solid support, non-bound DNA probe is washed out from the support.     

Reversible structural phase transition in Ni-Mn-Ga alloys in a magnetic field

In Ni_2+x Mn_1?x Ga shape-memory ferromagnetic alloys with coincident magnetic and structural phase transitions, a reversible structural field-induced phase transition was observed at constant temperature and pressure in magnetic fields of about 10 T. Computational results are in qualitative agreement with experiment.     

A finite element analysis of mach reflection by using the Boussinesq equation

The numerical analysis of ‘Mach reflection’, which is the reflection of an obliquely incident solitary wave by a vertical wall, is presented. For the mathematical model of the analysis, the two-dimensional Boussinesq equation is used. In order to solve the equation in space, the finite element method based on the linear triangular element and the conventional Galerkin method is applied. The combination of explicit and semi-implicit schemes is employed for the time integration. Moreover, one of the treatments for the open boundary condition, in which the analytical solution of the linearized Boussinesq equation in the outside domain is linked to the discrete values of velocity and water elevation in the inside domain, is applied for the modeling of the Mach reflection problem. © 1998 John Wiley & Sons, Ltd.