Low-temperature heat capacity of room-temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Heat capacities of liquid, stable crystal, and liquid-quenched glass of a room-temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide were measured between 5 and 310 K by adiabatic calorimetry. Heat capacity of the liquid at 298.15 K was determined for an IUPAC project as (631.6 +/- 0.5) J K(-1) mol(-1). Fusion was observed at T(fus) = 272.10 K for the stable crystalline phase, with enthalpy and entropy of fusion of 28.34 kJ mol(-1) and 104.2 J K(-1) mol(-1), respectively. The purity of the sample was estimated as 99.83 mol % by the fractional melting method. The liquid could be supercooled easily and the glass transition was observed around T(g) approximately 183 K, which was in agreement with the empirical relation, T(g) approximately ((2)/(3)) T(fus). The heat capacity of the liquid-quenched glass was larger than that of the crystal as a whole. In the lowest temperature region, however, the difference between the two showed a maximum around 6 K and a minimum around 15 K, at which the heat capacity of the glass was a little smaller than that of crystal.     

Bidirectional and colorimetric recognition of sodium and potassium ions

Host 1 based on the phenolphthalein skeleton and two crown ether moieties demonstrated opposite behaviors toward sodium and potassium cations caused by bidirectional complexation. [reaction: see text]     

Laminar–Turbulent Intermittency in Annular Couette–Poiseuille Flow: Whether a Puff Splits or Not

Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette–Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette–Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.     

Biphenyl ether and biphenyl quinolizidine lactone alkaloids from Heimia salicifolia

Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions.     

Deduction of channel-length distribution from isothermal thermogravimetry

A possible deduction is proposed of channel length distribution in one-dimensional porous materials from the kinetic data obtained in isothermal thermogravimetry (TG). The method utilizes the absorption/desorption of small molecules into one-dimensional nano-channel. In the surface-controlled absorption/desorption, the second derivative with respect to time is directly proportional to the channel-length distribution function. Even in the diffusion-controlled case, the second derivative with respect to the square root of time gives rough information on the distribution function.     

NMR studies on effects of temperature, pressure, and fluorination on structures and dynamics of alcohols in liquid and supercritical states

We measured 1H NMR chemical shifts (delta H) and 1H and 2H NMR spin-lattice relaxation times (1H- and 2H-T1) of methanol, ethanol, 2-propanol, 2,2,2-trifluoroethanol, and 1,1,1,3,3,3-hexafluoro-2-propanol in the temperature range from 298 to 673 K at reduced pressures ( Pr = P/ Pc) of 1.22 and 3.14. The delta H values showed that the degree (X HB) of hydrogen bonding decreased in the order of methanol > ethanol >2-propanol > H2O, and that the hydrogen bonding was much affected by fluorination, because of the intramolecular H-F interactions in supercritical (sc) states. Moreover, 1H- T 1 measurements revealed that the relaxation processes of OH groups in nonfluoroalcohols are controlled by dipole-dipole (DD) and spin-rotation (SR) mechanisms below and above the critical temperature (Tc), while the cross-correlation effects connected with intramolecular DD interactions between a carbon atom and an adjacent proton played an important role for hydrocarbon groups (CHn, n = 1-3) under sc conditions. This interpretation was also supported by two other results. The first is that the intramolecular H-F interactions strongly inhibit the internal rotation of CH and CH2 groups of sc fluoroalcohols, and the second is that the molecular reorientational correlation times (tauc(D)) obtained from 2H- T 1 values of deuterated hydrocarbon groups (CDn ) at temperatures above T c have significantly less temperature dependence than those of OD groups. Actually, the apparent activation energy (DeltaEa) for molecular reorientational motions in sc alcohols was smaller compared with liquid alcohols, being about 1 order of magnitude.     

Metal ion-dependent fluorescent dynamics of photoexcited zinc-porphyrin and zinc-myoglobin modified with ethylenediaminetetraacetic acid

The reconstituted zinc-myoglobin (ZnMb) dyads, ZnMb-[M(II)(edta)], have been prepared by incorporating a zinc-porphyrin (ZnP) cofactor modified with ethylenediaminetetraacetic acid (H(4)edta) into apo-Mb. In case of the monomeric ZnP(edta) cofactor coordinated by one pyridine molecule, ZnP(py)(edta), a spontaneous 1:1 complex with a transient metal ion was formed in an aqueous solvent, and the photoexcited singlet state of ZnP, (1)(ZnP)*, was quenched by the [Cu(II)(edta)] moiety through intramolecular photoinduced electron-transfer (ET) reaction. The rate constant for the intramolecular quenching ET (k(q)) at 25 degrees C was successfully obtained as k(q) = 5.1 x 10(9) s(-1). In the case of Co(2+), Ni(2+), and Mn(2+), intersystem crossing by paramagnetic effect was mainly considered between (1)(ZnP)* and the [M(II)(edta)] complex. For the ZnMb-[M(II)(edta)] systems, the intramolecular ET reaction between the excited singlet state of (1)(ZnMb)* and the [Cu(II)(edta)] moieties provided the slower quenching rate constant, k(q) = 2.1 x 10(8) s(-1), compared with that of the ZnP(py)(edta) one. Kinetic studies also presented the efficient fluorescence quenching of the (1)(ZnMb)*-[Co(II)(edta)] dyad. Our study clearly demonstrates that wrapping of the ZnP cofactor by the apoprotein matrix and synthetic manipulation at the Mb surface ensure metal ion-sensitive fluorescent dynamics of ZnMb and provides valuable information to elucidate the complicated mechanism of the biological photoinduced ET reactions of hemoproteins.     

Visualization and laser measurements on the flow field and sand movement on sand dunes with porous fences

The installation of windbreak sand fences around sand dunes is one of the most promising methods to suppress windblown sand movement. In the study reported in this paper, we investigated the influence and validity of a small fence mounted on a model sand dune, in order to understand the fence’s suppression mechanism on the sand movement. The flow field around the dune and the process of sand-dune erosion were measured using LDV, PIV, and laser-sheet visualization techniques. A non-porous fence was found to suppress sand movements in its upstream area, but to enhance erosion downstream of the fence. This intensive erosion was caused by separated shear flow from the leading edge of the fence. In this study, four levels of porosity rate of the fence were tested. The fence-porosity dependences of the turbulent flow field and the erosion were discussed. The shapes of eroded sand dunes were found to depend on the porosity rate. The relationship between the sand-dune erosion and the flow field around the dune was illustrated with schematic diagrams. We concluded that the most desirable fence porosity should be 30% in order to avoid dune erosion if installed at a middle height on the stoss surface of a dune. This porosity provides a mean velocity reduction with avoiding a separated flow, although the flow bleeding through the porous fence is accompanied by grid turbulence and induces serious erosion in a narrow space behind the fence. Furthermore, we confirmed that the empirical correlation of the critical friction velocity can be applied to sand movements influenced by a fence.     

Reconstruction of Scalar Source Intensity Based on Sensor Signal in Turbulent Channel Flow

We consider a turbulent channel flow, where a scalar point source with a time-harmonic intensity releases a substance that can be modeled as a passive scalar. With the source location known, our objective is to estimate the time history of the source intensity based on sensor measurements at different locations downstream of the source by adopting an adjoint approach. It is shown that the proposed algorithm reproduces the original coherent sinusoidal wave of the scalar source accurately from the chaotic scalar signals measured by our sensors. By systematically changing the source-sensor distance and the pulsation frequency of the source, we clarify how these two factors affect the estimation accuracy. The proposed scheme is also applicable to estimation with multiple sensors. We demonstrate that increasing the number of sensors improves the estimation greatly when the scalar is released from a source away from the wall, where large-scale eddies dominate the scalar dispersion. In contrast, the estimation performance remains poor even with multiple sensors when the scalar source is located near the wall, where the source information is quickly lost due to the strong turbulence activity and the scalar diffusion in the near-wall region.