Influence of free-space calibration using He on the measurement of adsorption isotherms

It is well known that helium (He) molecules that remain inside micropores after free-space calibration at a low temperature (77.4 K) affect the shape of an adsorption isotherm, especially in a very low relative pressure region. This negative effect of the remaining He leads to a misunderstanding of the porous characteristics, such as micropore size distribution and surface properties. However, it is still believed that such erroneous interpretations are limited to narrow microporous materials such as activated carbon and measurements at low temperatures, namely the measurement of the adsorption of N₂ and Ar at their boiling points. Here we report a systematic investigation of the influence of free-space calibration using He on microporous, mesoporous and non-porous materials. Zeolite Y, mesoporous silica, carbon black and aerosil 200 were used for the measurements. N₂, H₂O and CO₂ adsorption isotherms were measured at 77.4, 298 and 298 K, respectively. Free-space calibration was carried out before and after the isotherm measurement for each sample. Although the influence of the He that remained in the sample was small for the non-porous sample, the shape of the isotherms for the other samples in a low relative pressure region was rather affected by the timing of the free-space calibration even for the mesoporous sample, and at an ambient temperature.     

Total synthesis of (+/-)-hedychilactone B: stepwise allenoate diene cycloaddition to prepare trimethyldecalin systems

[reaction: see text] The total synthesis of the diterpene hedychilactone B 1 is reported. The exo adduct 4x, the major product of the stepwise [4+2] cycloaddition of the diene 2 and the allenoate 3, has been converted into 1 via 7 steps, among them a key nonconjugative hydrolysis of a gamma-methylene silyl enol ether and an E-selective olefination.     

Rh-catalyzed cyclization of diynes and enynes initiated by carbonyl-directed activation of aromatic and vinylic C-H bonds

The Rh-catalyzed hydroarylative and hydrovinylative cyclization of diynes with aryl ketones or enones gave monocyclic 1,3-dienes. Enynes also underwent the same reaction and chiral products were obtained with high ee using a chiral Rh catalyst. Carbonyl-directed activation of aromatic and vinylic C-H bonds is likely the initial step in the present transformation.     

Kondo universal scaling for a quantum dot coupled to superconducting leads

We study competition between the Kondo effect and superconductivity in a single self-assembled InAs quantum dot contacted with Al lateral electrodes. Because of Kondo enhancement of Andreev reflections, the zero-bias anomaly develops side peaks, separated by the superconducting gap energy Delta. For ten valleys of different Kondo temperature T(K) we tune the gap Delta with an external magnetic field. We find that the zero-bias conductance in each case collapses onto a single curve with Delta/k(B)T(K) as the only relevant energy scale, providing experimental evidence for universal scaling in this system.     

Optimum speech level to minimize listening difficulty in public spaces

For ideal speech communication in public spaces, it is important to determine the optimum speech level for various background noise levels. However, speech intelligibility scores, which is conventionally used as the subjective listening test to measure the quality of speech communication, is near perfect in most everyday situations. For this reason, it is proposed to determine optimum speech levels for speech communication in public spaces by using listening difficulty ratings. Two kinds of listening test were carried out in this work. The results of the tests and our previous work [M. Morimoto, H. Sato, and M. Kobayashi, J. Acoust. Soc. Am. 116, 1607-1613 (2004)] are jointly discussed for suggesting the relation between the optimum speech level and background noise level. The results demonstrate that: (1) optimum speech level is constant when background noise level is lower than 40 dBA, (2) optimum speech level appears to be the level, which maintains around 15 dBA of SN ratio when the background noise level is more than 40 dBA, and (3) listening difficulty increases as speech level increases under the condition where SN ratio is good enough to keep intelligibility near perfect.     

Effects of frequency characteristics of reverberation time on listener envelopment

Spatial impression perceived in a listening space comprises at least two components: one is auditory (apparent) source width (ASW) and the other is listener envelopment (LEV). Both ASW and LEV are affected not only by temporal but also by spatial structures of reflections. It has been clarified that ASW for symphony music is significantly affected by low-frequency components of source signals and reflections, but not by their high-frequency components. The objective of this work is to investigate whether LEV is affected by the frequency characteristics of source signals and reverberation sounds, which are known to contribute to the creation of LEV. In this study, three experiments were performed to clarify the effects of reverberation time (RT) and its frequency characteristics on LEV. In contrast to the case of ASW, the experimental results show that RTs both at high and low frequencies affect LEV.     

Sensitive and selective determination of peptides,PG and PGP,using a novel fluorogenic reagent 4-chlorobenzene-1,2-diol

A novel fluorometric method was developed for the sensitive and selective detection of Pro-Gly (PG) and Pro-Gly-Pro (PGP) using 4-chlorobenzene-1,2-diol (4-CBD) as a fluorogenic reagent. The reaction was performed at 37°C for 30 min in the presence of a borate buffer (pH 7.0) and sodium periodate. The resulting fluorescence intensity was measured using a spectrofluorometer with excitation and emission wavelengths of 450 nm and 535 nm. To obtain a stable fluorescent signal and maximise its intensity, different reaction conditions such as the concentrations of the reagents, the reaction time, and the pH were optimised. Under the optimised conditions, a linear relationship was obtained between fluorescence intensity and peptide concentrations from 1.0–40.0 µmol L^?1 with a limit of detection of 1.0 µmol L^?1 (S/N = 3). Both PG and PGP generated a strong signal out of all the peptides tested and no other biogenic substances such as amino acids or proteins produced any fluorescence. The reaction thus developed is simple, rapid, selective, and sensitive. It can be applied to the determination of peptides as biomarkers or substrates.     

The Synthesis and Dynamic Structures of Multinuclear Complexes of Large Porphyrinoids Expanded by Phenylene and Thienylene Spacers

1,3‐Bis(2‐pyrryl)benzene was used to prepare dibenziamethyrin, in which two pyrrole units of [24]amethyrin(1.0.0.1.0.0) are replaced by benzene. 1,4‐Bis(2‐pyrryl)benzene, 2,5‐bis(2‐pyrryl)thiophene, and 4,4′‐bis(2‐pyrryl)biphenyl were also used in place of 2,2′‐bipyrrole to give expanded analogues of [24]rosarin(1.0.1.0.1.0) and [32]octaphyrin(1.0.1.0.1.0.1.0). These large porphyrinoids can incorporate multiple metal units of Rh(CO)₂ and Pd(π‐allyl) with considerable deviation of the metal atoms from the dipyrrin planes, evidenced by X‐ray crystallography. The coordinated Rh(CO)₂ group shuttled between both sides of the macrocycle; the rate was dependent on the spacer, ring size, and number of metal atoms. Variable temperature ¹H NMR spectroscopy showed that the tris‐rhodium complexes of the expanded rosarins with 1,4‐phenylene or 2,5‐thienylene spacers adopt a C_3v‐symmetric form and a C_s‐symmetric form as a result of the Rh(CO)₂ groups hopping through the macrocycle cavity. The C_3v‐symmetric form has a greater dipole moment and, therefore, is favored in solvents of greater polarity. The Rh(CO)₂ groups in the tris‐rhodium complex of the expanded rosarin with 4,4′‐biphenylene spacers hop so fast that an averaged spectral pattern (D_3h) was seen in the ¹H NMR spectrum, even at ?60 °C. Expanded octaphyrins with 1,4‐phenylene and 2,5‐thienylene spacers bind four Rh(CO)₂ groups outside the macrocycle cavity to form a D_2d‐symmetric saddle‐shaped structure that did not show any dynamic behavior on the NMR timescale, even at 80 °C. This tetranuclear complex is one of the largest porphyrinoid metal complexes characterized by X‐ray crystallography to date.     

Total Synthesis and Biological Evaluation of the Antibiotic Lysocin E and Its Enantiomeric,Epimeric, and N‐Demethylated Analogues

Lysocin E, a macrocyclic peptide, exhibits potent antibacterial activity against methicillin‐resistant Staphylococcus aureus (MRSA) through a novel mechanism. The first total synthesis of lysocin E was achieved by applying a full solid‐phase strategy. The developed approach also provides rapid access to the enantiomeric, epimeric, and N‐demethylated analogues of lysocin E. Significantly, the antibacterial activity of the unnatural enantiomer was comparable to that of the natural isomer, suggesting the absence of chiral recognition in its mode of action.