Synthesis and redox behavior of ruthenocene-terminated oligoenes: characteristic and stable two-electron redox system and lower potential shift of the two-electron oxidation wave with elongating conjugation

Ruthenocene-terminated butadienes and hexatrienes were prepared by the Wittig reaction of 3-ruthenocenyl-2-propenals with ruthenocenylmethylphosphonium salts and the Mukaiyama coupling of the propenals, respectively. Cyclic voltammetry of these complexes indicated that they were involved in a stable two-electron redox process. The oxidation potentials for ruthenocene-terminated oligoenes shifted progressively to lower potential with the increasing CH==CH units as follows: Rc--Rc (0.32 V)>RcCH==CHRc (+0.09 V)>Rc(CH==CH)(2)Rc (-0.06 V)>Rc(CH==CH)(3)Rc (-0.07 V), (Rc=ruthenocene). The tendency is in remarkable contrast to that in the successive one-electron redox process. These complexes were chemically oxidized to give stable crystalline solids, whose structures were confirmed by NMR spectroscopy and X-ray analysis to be oligoene analogues of a bis(fulvene) complex, for example, [(eta(5)-C(5)Me(5))Ru[mu(2)-eta(6):eta(6)-C(5)H(4)CH(CH==CH)(n)CHC(5)H(4)]Ru(eta(5)-C(5)Me(5))](2+) (n=1 or 2). The DFT calculation of the two-electron-oxidized species reproduced well the fulvene-complex structure for the ruthenocene moieties. Since both the neutral and oxidized species are stable and chemically reversible, this redox system may be serviceable as a two-electron version of the ferrocene one-electron redox system.     

Acid-base equilibria of various oxidation states of aqua-ruthenium complexes with 1,10-phenanthroline-5,6-dione in aqueous media

Syntheses and pH dependent electrochemical properties of aqua-ruthenium(II) complexes, [Ru(trpy)(PDA-N,N')(OH2)](ClO4)2 ([1](ClO4)2) and [Ru(trpy)(PD-N,N')(OH2)](ClO4)2 ([2](ClO4)2) (trpy = 2,2':6',2'-terpyridine, PDA = 6-acetonyl-6-hydroxy-1,10-phenanthroline-5-one, PD = 1,10-phenanthroline-5,6-dione) are presented. Treatment of [Ru(trpy)(PD-N,N')Cl](PF6) with AgClO4 in a mixed solvent of acetone and H2O selectively produced the acetonyl-PD complex [1](ClO4)2, and the similar treatment in a mixed solvent of 2-methoxyethanol and H2O gave the PD complex [2](ClO4)2. The molecular structures of both complexes were determined by X-ray structural analysis. The proton dissociation constants of various oxidations state of [1]2+ and [2]2+ were evaluated by simulation of E(1/2) values of those redox potentials depending on pH. The simulation revealed that the acetonyl-PD complex [1]2+ underwent successive Ru(II)/Ru(III) and Ru(III)/Ru(IV) redox couples though the two redox reactions were not separated in the cyclic voltammograms. The redox behavior of [2]2+ in H2O is reasonably explained by not only the similar successive metal-centered redox reactions but also simultaneous two-electron quinone/catechol redox couple of the PD ligand including the contribution of hydration on a carbonyl carbon.     

Hydrothermal routes to prepare nanocrystalline mesoporous SnO2 having high thermal stability

We report simple hydrothermal routes to prepare thermally stable SnO2 particles having high specific surface areas and mesoporosity. The preparation method includes a new combination of synthetic processes: hydrolysis of tin(IV) chloride at 95 degrees C in the absence of alkaline solutions (aqueous NH3 or NaOH), formation of nanocrystalline SnO2, and subsequent hydrothermal treatments at temperatures between 100 and 200 degrees C. After annealing treatments of the hydrothermally treated SnO2 particles at 400 or 500 degrees C, their crystallite sizes remained smaller than 7.7 nm and their specific surface areas were still higher than 110 m2/g, indicative of the high thermal stability against particle growth and sintering. Furthermore, mesoporosity evolved with a relatively narrow pore size distribution typically in the range of 3.0-4.3 nm. The effects of the hydrothermal treatment were explained by uniformization of the particle size that was beneficial to the suppression of particle growth.     

Which genetic marker for which conservation genetics issue?

Conservation genetics focuses on the effects of contemporary genetic structuring on long-term survival of a species. It helps wildlife managers protect biodiversity by identifying a series of conservation units, which include species, evolutionarily significant units (ESUs), management units (MUs), action units (AUs), and family nets (FNs). Although mitochondrial DNA (mtDNA) evolves 5-10 times faster than single-copy nuclear DNA (scnDNA), it records few traces of contemporary events. Thus, mtDNA can be used to resolve taxonomic uncertainties and ESUs. Variable number of tandem repeats (VNTRs) evolve 100-1000 times faster than scnDNA and provide a powerful tool for analyzing recent and contemporary events. VNTR analysis techniques include polymerase chain reaction (PCR)-based microsatellite assays and oligonucleotide probing. Size homoplasy problems in PCR-based microsatellite assays can strongly affect the inference of recent population history. The high homozygosity in endangered species is reflected in a relatively low number and level of variability in microsatellite loci. This combined with "allelic dropout" and "misprinting" errors contributes to the generation of highly biased genetic data following analyses of natural populations. Thus, in conservation genetics, microsatellites are of limited use for identifying ESUs, MUs, and AUs. In contrast to PCR-based microsatellite analysis, oligonucleotide probing avoids errors resulting from PCR amplification. It is particularly suitable for inferring recent population history and contemporary gene flow between fragmented subpopulations. Oligonucleotide fingerprinting generates individual-specific DNA banding patterns and thus provides a highly precise tool for monitoring demography of natural populations. Hence, DNA fingerprinting is powerful for distinguishing ESUs, MUs, AUs, and FNs. The use of oligonucleotide fingerprinting and fecal DNA is opening new areas for conservation genetics.     

Preparation of ureido group bearing polymers and their upper critical solution temperature in water

Poly(2‐ureidoethylmethacrylate) (PUEM_n) was synthesized via reversible addition‐fragmentation chain transfer (RAFT) radical polymerization and following polymer reaction. We prepared two PUEM_n samples with different degrees of polymerization (n = 100 and 49). The polymers exhibited upper critical solution temperature (UCST) in phosphate‐buffered saline (PBS) solution. The phase separation temperature (T_p) in PBS can be controlled ranging from 17 to 55 °C by changing molecular weight of the polymer, polymer concentration, and adding NaCl concentration. The polymers in PBS formed coacervate drops by liquid–liquid phase separations below T_p. Results of the dielectric relaxation measurement, the hydration number per monomeric unit was 5 above T_p. Based on a fluorescence study, the polymer formed slightly hydrophobic environments below T_p. The liquid–liquid phase separation was occurred presumably because of weak hydrophobic interactions and intermolecularly hydrogen bonding interactions between the pendant ureido groups. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2845–2854     

Hydration effect on the ion-pair extraction of lithium picrate by hydrophobic benzo-15-crown-5 ether into various less-polar diluents.

The ion-pair formation constant (K(MLA)(0) in mol(-1) dm(3)) for Li(B15C5)(+) with a picrate ion (Pic(-)) in water was determined by potentiometry with a K(+)-selective electrode at 25 degrees C and an ionic strength of 0, where B15C5 denotes benzo-15-crown-5 ether. Using the concentration equilibrium constants, K(MLA), estimated from this value, the extraction constants (mol(-2) dm(6) unit) of about ten diluents were re-calculated from previously reported extraction data. Also, the distribution constants of an ion-pair complex, Li(B15C5)Pic, between water and the diluents were re-estimated. A disagreement in the determined K(MLA) value between a solvent-extraction method and potentiometry was explained in terms of the Scatchard-Hildebrand equation; it came from the fact that the hydration of Li(I) in Li(B15C5)Pic was larger than that of free B15C5 in water. Then, the previously determined value by the former method was re-estimated using the potentiometric K(MLA) value.     

A polyrotaxane gel using boronic acid-appended γ-cyclodextrin as a hybrid cross-linker

A boronic acid-appended γ-cyclodextrin (BA-CyD) was synthesized as a hybrid cross-linker of polyvinyl alcohol (PVA) to form a new type of hydrogel. The CyD moiety of BA-CyD forms an inclusion complex with the PVA chain to produce a mechanically interlocking structure. At the same time, the BA moiety of BA-CyD forms covalent bonds with the 1,3-diol moieties of PVA. On the basis of these two modes of interaction, the hybrid cross-linker connects two PVA chains, thus resulting in the formation of a hydrogel. To investigate the possibility of this hydrogel becoming the basis for an intelligent material for drug delivery, sugar-responsive drug release from the hydrogel was demonstrated.     

Universal power laws in the threshold network model: A theoretical analysis based on extreme value theory

We theoretically and numerically investigated the threshold network model with a generic weight function where there were a large number of nodes and a high threshold. Our analysis was based on extreme value theory, which gave us a theoretical understanding of the distribution of independent and identically distributed random variables within a sufficiently high range. Specifically, the distribution could be generally expressed by a generalized Pareto distribution, which enabled us to formulate the generic weight distribution function. By using the theorem, we obtained the exact expressions of degree distribution and clustering coefficient which behaved as universal power laws within certain ranges of degrees. We also compared the theoretical predictions with numerical results and found that they were extremely consistent.