Development and applications of high-frequency ESR up to 55 T

A multiextreme (high-field, low-temperature, high-pressure and nanoscale) electron spin resonance (ESR) measurement system is under development in Kobe. In this connection, our recent development is introduced and two applications of our high-frequency high-field ESR are described. High-frequency high-field ESR measurements of dioptase (Cu₆Si₆O₁₈·6H₂O), which has an interesting antiferromagnetic Cu²⁺ network, have been performed using a pulsed magnetic field of up to 55 T. Antiferromagnetic resonances (AFMR) are clearly observed at 4.2 K with the light sources of up to 1017 GHz. However, a deviation from the conventional two-sublattice AFMR theory is observed in the high field. Temperature dependence of the X-band and high-frequency ESR has been also observed in the triangular lattice antiferromagnet EtMe₃P[Pd(dmit)₂]₂ which shows the spin-Peierls-like transition below T _c = 25 K. The preliminary field dependence of the spin gap estimated from the analyses of our ESR results has been shown in connection with the previous magnetic susceptibility results.     

Microgravity experiments on droplet motion during flame spreading along three-fuel-droplet array

Flame spreading along a fuel droplet array at microgravity has been studied as a simple model of spray combustion. A three droplet array with a pendulum suspender was employed to investigate interactions between flame spreading and droplet motion in the array direction. Initial droplet diameter was 0.8 mm and fuel was n-heptane. A silicon carbide pendulum suspender of 15 μm in diameter and 30 mm in length was used for the third droplet. The first fixed droplet was ignited by electric spark. Behavior of the flame and the third droplet was observed using a high-speed video camera. Dimensionless span, which is the averaged droplet span divided by the averaged initial diameter of the three droplets, was varied from 2.7 to 10. Large displacement of the movable droplet was observed after group flame grew around the movable droplet. As the initial dimensionless span increased, the averaged droplet speed after the occurrence of flame spreading to the movable droplet increased steeply, taking the maximum value around 5 in initial dimensionless span, and then decreased gradually. The movable droplet advanced toward the second droplet in small spans and moved away from the second droplet in large spans. The direction of the motion changed around 4.6 in initial dimensionless span. Flame spread induction time from the second to the third droplet increased exponentially as the initial dimensionless span was increased. The induction time of flame spreading to a movable droplet was longer than that of flame spreading to a fixed droplet. From calculations of flame spreading along a 20-droplet array, it was predicted that the droplet speed nearly converged after flame spread to the sixteenth droplet. The maximum speed of the nineteenth droplet appeared around 7.5 in the initial dimensionless span.     

Long-range ordered magnet of a charge-transfer Ru2(4+)/TCNQ two-dimensional network compound

Two isostructural 2D assemblies composed of [Ru2(O2CCF3)4] and TCNQ or TCNQF4 in a 2:1 ratio were synthesized: [{Ru2(O2CCF3)4}2TCNQ].3(p-xylene) (1b) and [{Ru2(O2CCF3)4}2TCNQF4].3(p-xylene) (2). In 1b, the TCNQ moiety is assigned to be neutral because of no significant electron transfer from the Ru24+ units. Therefore, the magnetic property of 1b can be understood to be a paramagnetic nature of the isolated Ru24+ unit, while, a fully charge-transfer from the Ru2 units to the TCNQF4 molecules in 2 leads to charge delocalization spreading over the 2D network and allows a long-range magnetic order to occur. On the basis of an idea of the resonance scheme in charge-transfer D2A network systems, the first successful example of a charge-transferred magnet in the Ru2-TCNQ system was rationally designed by tuning redox between [Ru2]4+ and the TCNQ molecule changing from TCNQ to TCNQF4.     

Giant macrocycles composed of thiophene, acetylene, and ethylene building blocks

Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.     

Oxygen consumption of cell suspension in a poly(dimethylsiloxane) (PDMS) microchannel estimated by scanning electrochemical microscopy

A quantitative analysis of the oxygen concentration profile near a poly(dimethylsiloxane) (PDMS) microfluidic device was performed using scanning electrochemical microscopy (SECM). A microchannel filled with sodium sulfite (Na(2)SO(3)) aqueous solution was imaged by SECM, showing that the oxygen diffusion layer of the PDMS microchannel was observed to be hemicylindrical. Based on a theoretical analysis of the hemicylindrical diffusion layer of the microchannel, the total oxygen mass transfer rates of oxygen to the PDMS microchannel filled with the Na(2)SO(3) solution was calculated to be (4.01 +/- 0.30) x 10(-12) mol s(-1). This is the maximum value of the oxygen transfer rate for this PDMS microchannel device. The oxygen consumption rate increased almost linearly with the logarithm of the concentration of E. coli cells (10(6) approximately 10(8) cells). The respiratory activity for a single E. coli cell was estimated to be approximately 4.31 x 10(-20) mol s(-1) cell(-1).     

Steroidal glycosides and aromatic compounds from Smilax riparia

Two new steroidal glycosides named riparosides A (1) and B (2), and two aromatic compounds (3, 4), together with four known flavonoid derivatives have been isolated from the EtOH extract of the rhizomes and roots of Smilax riparia A. DC. The structure of riparoside A (1) was determined to be 3-O-alpha-L-rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->6)]-beta-D-glucopyranosyl 3beta,20alpha-dihydroxy-5alpha-furost-22(23)-ene 26-O-beta-D-glucopyranoside. Riparoside B (2) was characterized as 3-O-alpha-L-rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->6)]-beta-D-glucopyranosyl 3beta,16beta-dihydroxy-5alpha-pregnan-20-one 16-O-[5-O-beta-D-glucopyranosyl 5-hydroxy-4-methyl-pentanoic acid]-ester 26-O-beta-D-glucopyranoside. Compounds 3 and 4 were elucidated as a sucrosyl ferulic acid ester and 7-O-methyl-10-oxythymol gentiobioside, respectively.     

cis-to-trans isomerization promoted by pyridine as a crucial step for the selective preparation of trans-Pt(SAr)(Cl)(PAr'3)2

The general strategy for the syntheses of trans-Pt(SAr)(Cl)(PAr'3)2 (1) (Ar = Ph, C6H4-2-Me, C6H4-3-OMe C6H4-2-F, etc.; Ar' = Ph, C6H4-4-OMe, C6H4-4-Me, and C6H4-4-CF3) by the reaction of cis-PtCl2(PAr'3)2 with ArSH has been developed. The mechanistic investigation suggested that isomerization of cis-1 into trans-1 promoted by the combined use of C6H6 as a solvent and pyridine as a base was the key to the successful preparation of 1.     

Metal-organic frameworks from homometallic chains of nickel(II) and 1,4-cyclohexanedicarboxylate connectors: ferrimagnet-ferromagnet transformation

The hydrothermal reactions of nickel(II) nitrate with a mixture of the geometric cis and trans isomers of 1,4-cyclohexanedicarboxylic acid (1,4-chdc or C6H10(COOH)2) and a base yield three structurally different complexes, [Ni3(mu3-OH)2(mu4-cis-1,4-chdc)2(H2O)4].2H2O (1), [Ni(3)(mu3-OH)2(mu4-trans-1,4-chdc)2(H2O)4].4H2O (2), and [Ni(H2O)4(mu2-trans-1,4-chdc)], depending on the reaction conditions. The single-crystal X-ray structure analyses of 1 and 2 reveal segregation of the isomers and formation of frameworks based on infinite Ni3(OH)2(H2O)4 chains, acting as secondary building units, connected by either cis- or trans-chdc for 1 and 2, respectively. The frameworks sustain channels that house two or four water molecules, respectively, according to the size and shape of the channels that depend on the particular isomer. The structure of 3 consists of chains of square-planar Ni(H2O)4 bridged by trans-chdc. Magnetic data as a function of temperature and field of the virgin samples for 1 indicate long-range ordering (LRO) to a ferrimagnetic ground state at 2.1 K that is reversibly transformed into a ferromagnet below 4.4 K upon partial dehydration and rehydration. Powder X-ray diffraction of 1, in its virgin state, after dehydration and after rehydration, confirms the stability of the framework. The magnetic data for 2 tend toward a LRO state to possibly a ferrimagnet below 2 K. The temperature dependence of the susceptibility of the two compounds is accounted for by the presence of both ferro- and antiferromagnetic exchanges within each chain via Ni-O-Ni and Ni-O-C-O-Ni pathways and weak coupling between neighboring chains via the 1,4-chdc unit. 3 is a uniform s = 1 antiferromagnetic chain (J/kB = 2.27(1) K).     

Pattern-effect-free all-optical wavelength conversion using a hydrogenated amorphous silicon waveguide with ultra-fast carrier decay

Ultra-fast carrier decay, recently discovered in a hydrogenated amorphous silicon waveguide, can be exploited for pattern-effect-free all-optical signal processing based on optical Kerr nonlinearity. In this study, we utilized a 10 Gbit/s RZ-OOK data stream as a pump for degenerate four-wave mixing in a low-loss hydrogenated amorphous silicon waveguide. The propagation loss of the waveguide used was 1.0±0.2 dB/cm at 1550 nm. Unlike crystalline silicon waveguides, no noticeable difference was observed in the BER characteristics between the cases of PRBS 2(7)-1 and 2(31)-1.