Self-assembled monolayer electrode of a diiron complex with a phenoxo-based dinucleating ligand: observation of molecular oxygen adsorptionldesorption in aqueous media

The phenoxo-based dinucleating ligand, 2,6-bis[bis(6-pivalamido-2-pyridylmethyl)amino-methyl-4-aminophenol (1), and its Fe2(II) complex, [Fe2(II)(1)(PhCOO)2](CF3SO3) (2), were prepared and 2 deposited on the Au surface (2/Au) is much more stable than in solution and exhibits redox behavior in aqueous media as well as reversible adsorption/desorption of oxygen at room temperature.     

Theoretical investigations for zinc blende-wurtzite polytypism in GaAs layers at Au/GaAs(1 1 1) interfaces

The zinc blende (ZB)-wurtzite (W) polytypism of GaAs layers at the Au/GaAs(1 1 1)B interfaces is investigated based on total-energy electronic-structure calculations within density functional theory. The calculations for the abrupt interfaces including a GaAs top layer with ZB and W stacking sequences reveal that the ZB sequence is energetically favorable, but the energy of W sequence with an interstitial Au atom at the top GaAs layer of the interface is lower than that of ZB sequence. This is because electrons accumulate around the interstitial region due to the hybridization between Au-6s and As-4p orbitals, resulting in the reduction of Ga-As bond charges. As a result, the relative stability at the top GaAs layer is determined by the electrostatic energy due to ionic charges. The results imply that the stabilization of W sequence at the Au catalyst-semiconductor interfaces as well as that on the nanowire faces are the origins for the appearance of W segments in NWs, qualitatively consistent with experiments.     

Re-examination of terminal relaxation behavior of high-molecular-weight ring polystyrene melts

For high-molecular-weight (M) ring polymers with low contamination of linear chains, recent viscoelastic tests revealed broad terminal relaxation associated with no clear entanglement plateau. This relaxation behavior is qualitatively similar to that deduced from molecular models (double-folded lattice-animal model and the fractal loopy globule model) for entangled ring polymers, but quantitatively important differences are also noted: For example, the full terminal relaxation of those polymers is slower than the model prediction. This study re-examined the viscoelastic data of entangled high-M ring polystyrene (PS) samples (coded as R-240; M = 244×10³) specifically for two points: the purity of the ring samples after the viscoelastic tests and the molecular origin of the stress. For the first point, the R-240 samples contaminated with linear chains at low but different levels were prepared by tuning either the purification efficiency or the retention time of the sample at high temperature (T) before/during the viscoelastic test. The fraction w _L of the linear contaminant, determined after the viscoelastic measurement, was ranging from 0.7 to 4.9%, and the extrapolation of the modulus data to w _L = 0 gave the data for the ideally pure ring melt. This pure ring melt exhibited broad terminal relaxation that started faster but completed slower compared to the model prediction, indicating that the ring relaxation is not well described by the current model(s) even in the absence of linear contaminant. For the second point, dynamic birefringence measurements were conducted for the R-240 samples with w _L = 4.6 and 1.0%. These samples obeyed the stress-optical rule, and their stress-optical coefficient was indistinguishable from that for linear PS samples, revealing that the stress of the ring PS chains reflects the orientational anisotropy of the chains (as is the case also for linear chains). The relaxation behavior of pure ring PS melt is discussed on the basis of these findings, with the focus being placed on the ring-ring threading not considered in the models.     

Flow pattern and boiling heat transfer of CO2 in horizontal small-bore tubes

Increasing attention has been focused on carbon dioxide (CO₂) heat pump system where the temperature level is rather low, while the operating pressure is rather high. In this system, the density difference between vapor and liquid becomes rather small, which significantly affects flow patterns. Low surface tension and latent heat also have significant influence on two-phase flow patterns and heat transfer. This paper describes experimental and numerical investigation on flow patterns and heat transfer characteristics of boiling flow CO₂ at high pressure in horizontal small-bore tubes ranging from 1.0 mm to 3.0 mm I.D. Even though the density difference is rather small at high pressure, phase stratification takes place, which leads to the intermittent dryout at the upper wall. So far developed discrete bubble model by the authors for vertical flows is modified so as to include horizontal flow mechanisms. The predicted flow patterns with this new model agree on the whole with the experimental observation.     

An XAFS study of the S–Se exchange during the reaction of selenophene over Mo sulfide catalysts

The S–Se exchange during the hydrode-selenium (HD-Se) reaction of selenophene was investigated over MoS₂/Al₂O₃ and intrazeolite Mo sulfide clusters. The local structure of Se incorporated into the Mo sulfide catalysts was studied by means of Se K-edge XAFS. It was found that the capacity of S–Se exchange during the HD-Se reaction and dynamic behavior of Se incorporation strongly depend on the cluster size of Mo sulfides.     

Characterization of metabolites of a novel histamine H(2)-receptor antagonist, lafutidine, in human liver microsomes by liquid chromatography coupled with ion trap mass spectrometry

The metabolism of lafutidine in human liver microsomes was studied using liquid chromatography/ion trap mass spectrometry with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources. A total of 14 metabolites were identified including hydroxylated lafutidine and sulfonyl lafutidine as the major metabolites. The chemical properties and the MS(n) behaviors of lafutidine and all of its identified metabolites were studied in detail. Lafutidine had a fragmentation pattern as a result of homolytic bond cleavage in the MS/MS spectrum. This cleavage can form an odd-electron ion with the loss of furan-2-ylmethyl radical (-81 Da with a proton shift), which then sequentially loses neutral groups in the MS(3) spectrum. This fragmentation sequence was also observed from the metabolites with the unchanged sulfinyl moiety. When the sulfinyl moiety was oxidized to the sulfonyl moiety, this fragmentation sequence did not exist, which could be used to identify S-oxidation metabolites of lafutidine. In general, N-oxides could produce distinct [M+H-O](+) ions under LC/APCI-MS due to the thermal activation in the desolvation region of the API source, which could be used to identify N-oxidation metabolites of lafutidine. In order to avoid the possibility of false positives, the MS/MS spectrum of the [M+H-O](+) ion was compared with that of the non-N-oxidation metabolites or parent drug in the APCI source. If they were consistent, the structure could be finally confirmed. The exact masses for lafutidine and lafutidine N-oxide fragment ions were determined using an LTQ/Orbitrap mass spectrometer.     

Strain-Induced Ring Expansion Reactions of Calix[3]pyrrole-Related Macrocycles

The recent discovery of calix[3]pyrrole, a porphyrinogen-like tripyrrolic macrocycle, has provided an unprecedented strain-induced ring expansion reaction into calix[6]pyrrole. Here, we synthesized calix[n]furan[3-n]pyrrole (n=1∼3) macrocycles to investigate the reaction scope and mechanism of the ring expansion. Single crystal X-ray analysis and theoretical calculations revealed that macrocyclic ring strain increases as the number of inner NH sites increases. While calix[1]furan[2]pyrrole exhibited almost quantitative conversion into calix[2]furan[4]pyrrole within 5 minutes, less-strained calix[2]furan[1]pyrrole and calix[3]furan were inert. However, N-methylation of calix[2]furan[1]pyrrole induced a ring-expansion reaction that enabled the isolation of a linear reaction intermediate. The mechanism analysis revealed that the ring expansion consists of regioselective ring cleavage and subsequent cyclodimerization. This reaction was further utilized for synthesis of calix[6]-type macrocycles.