Influence of the variance of degree distributions on the evolution of cooperation in complex networks

We study how initial network structure affects the evolution of cooperation in a spatial prisoner’s dilemma game. The network structure is characterized by various statistical properties. Among those properties, we focus on the variance of the degree distribution, and inquire how it affects the evolution of cooperation by three methods of imitation. For every method, it was found that a scale-free network does not always promote the evolution of cooperation, and that there exists an appropriate value of the variance, at which cooperation is optimal.     

Stereoselective Synthesis of cis,cis‐Configured Perhydroquinoxaline‐5‐Carbonitrile from Cyclohex‐2‐en‐1‐ol

cis,cis‐Configured perhydroquinoxaline‐5‐carbonitrile 10 was synthesized stereoselectively by ditosylation of trans,cis‐2,3‐dihydroxycyclohexane‐1‐carbonitrile 4 and subsequent reaction with ethylenediamine. The diol precursor 4 was stereoselectively obtained by regioselective opening of the epoxide 3 with KCN in water avoiding hazardous Et₂AlCN.     

Superionic Conduction in Co‐Vacant P2‐NaxCoO2 Created by Hydrogen Reductive Elimination

The layered P2‐Na_xMO₂ (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2‐Na_xCoO₂ created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm^?1 at 25 °C. Using in situ synchrotron X‐ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na_0.61(H₃O)_0.18Co_0.93O₂. Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co‐stoichiometric compound Na_x(H₃O)_yCoO₂ does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.     

Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

Electron ionization induced metastable decompositions of isomeric trimethylsilylmethanol, (CH3)3SiCH2OH, and methoxytrimethylsilane, (CH3)3SiOCH3

The metastable decompositions of trimethylsilylmethanol, (CH₃)₃SiCH₂OH (MW: 104, 1) and methoxytrimethylsilane, (CH₃)₃SiOCH₃ (MW: 104, 2) upon electron ionization have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectroscopy and D labeling. The metastable ions of 1 ^·+ decompose to give the fragment ions m/z 89 (CH ₃ ^· loss) and 73 (^·CH₂OH loss), whereas those of 2 ^·+ only yield the fragment ion m/z 89 (CH ₃ ^· loss). The latter fragment ion is generated by loss of a methyl radical from the trimethylsilyl group via a simple cleavage reaction as shown by D labeling. However, the fragment ions m/z 89 and 73 from 1 ^·+ are generated following an almost statistical exchange of the original methyl and methylene hydrogen atoms in the molecular ion as shown also by D labeling. This exchange indicates a complex rearrangement of the molecular ion of 1 ^·+ prior to metastable decomposition for which as key step a 1,2-trimethylsilyl group migration from carbon to oxygen is suggested. A different behavior is also found between the source-generated m/z 89 ions from 1 ^·+ which decompose in the metastable time region to give ions m/z 61 by loss of ethylene and those from 2 ^·+ which decompose in the metastable region to yield ions m/z 59 by elimination of formaldehyde.     

Homohelicity induction of propylene-linked zinc bilinone dimers by complexation with chiral amine and α-amino esters. Preorganization of structurally coupled homohelical subunits

Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters.     

Photoelectrochemistry of p-type Cu2O semiconductor electrode in ionic liquid

We investigated the photoelectrochemical characteristics and photo-stability of Cu₂O layered on a copper plate using a hydrophobic ionic liquid. Our findings revealed that Cu₂O is stable under white light irradiation, provided water is removed from the electrolyte. Methyl viologen derivative, a well-established electron acceptor, was introduced to the ionic liquid electrolyte, allowing the photo-induced electron transfer reaction at the Cu₂O/electrolyte interface to be characterized. The methyl viologen derivative exhibited two distinct redox reactions at −0.56 V and −0.98 V vs. Ag/AgCl, clearly indicating that no dimer formation or co-proportionation reaction occurred. The excessive photocurrents being continuously generated resulted from a viable photo-induced electron transfer reaction from the Cu₂O to the acceptor. However, in contrast, the reduction of the Cu₂O by water in the aqueous solution causes this electron transfer to be inhibited. We further demonstrate that these findings are vital to understanding the role of the Cu₂O and its photoelectrochemical applications.     

Single-wall carbon nanotubes supported platinum nanoparticles with improved electrocatalytic activity for oxygen reduction reaction

Significant enhancement in the electrocatalytic activity of Pt particles toward oxygen reduction reaction (ORR) has been achieved by depositing them on a single wall carbon nanotubes (SWCNT) support. Compared to a commercial Pt/carbon black catalyst, Pt/SWCNT films cast on a rotating disk electrode exhibit a lower onset potential and a higher electron-transfer rate constant for oxygen reduction. Improved stability of the SWCNT support is also confirmed from the minimal change in the oxygen reduction current during repeated cycling over a period of 36 h. These studies open up ways to utilize SWCNT/Pt electrocatalyst as a cathode in the proton-exchange-membrane-based hydrogen and methanol fuel cells.     

Dihydroxyacetone variants in the organocatalytic construction of carbohydrates: mimicking tagatose and fuculose aldolases

Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase.     

Biosynthetic Conclusions from the Functional Dissection of Oxygenases for Biosynthesis of Actinorhodin and Related Streptomyces Antibiotics

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Highlights? ActVA-ORF5 is a flavin-dependent monooxygenase required for actinorhodin biosynthesis ? ActVA-ORF5 and its three close homologs were functionally dissected ? ActVA-ORF5 and Gra-21 are bifunctional at C-6/C-8, while Med-7 acts only for C-6 ? AlnT exhibits different regiospecificity for oxidation of tricyclic substrates