Energy transfer reaction of cationic porphyrin complexes on the clay surface: effect of sample preparation method

Photochemical energy transfer of non-aggregated cationic porphyrins on an anionic-type clay (Smecton SA) surface was investigated. The efficiency of energy transfer and excited-state quenching in the absence of energy transfer were evaluated at various loading levels of porphyrin on the clay surface and were found to be significantly affected by the loading level. As the latter increased, both energy transfer efficiency and excited-state quenching increased. Judging from the dependency of energy-transfer efficiency on the porphyrin loading level, a partially clustered structure, but without aggregation, of porphyrins on the clay surface is proposed.     

Chelate and intramolecular ion-pair formation: A guiding concept for structure/selectivity relationships in the liquid-liquid extraction of alkali and alkaline earth metal ions by anionic crown ether derivatives

Crown ether dyes with pendent anionic side-arms were synthesized for extractionspectrophotometry of alkali and alkaline earth metal ions. Dramatic changes in metal selectivity were obtained simply by changing the nature of the anionic side-arm on the same crown ether skeleton. A structure/metal selectivity relationship is discussed in detail in terms of “chelate” and “intramolecular ion-pair” formation. Small metal cations (high charge density) are preferred in the extraction by a crown ether reagent with a charge-localized anionic side-arm through the formation of a “chelate”. Large metal cations (low charge density) are preferred in the extraction by reagents with a charge-delocalized anionic side-arm through the formation of an “intramolecular ion-pair”. Steric restrictions imposed by the side-arm on the metal ion approaching the crown ether are also important factor in controlling the selectivity of these reagents.     

Photochemical valence tautomerization of berberinephenolbetaines to 8,14-cycloberbines,versatile aziridine derivatives for spirobenzylisoquinolines

Irradiation of the berberinephenolbetaines ($\text{8}$$\text{a}$, $\text{8}$$\text{b}$, and $\text{8}$$\text{c}$) effected valence tautomerization to give the 8,14-cycloberbines ($\text{9}$$\text{a}$, $\text{9}$$\text{b}$, and $\text{9}$$\text{c}$), the aziridine derivatives, in high yield. The 8,14-cycloberbines were efficiently converted to the spirobenzylisoquinolines by regioselective C bond cleavage.     

Nucleophilic additions of arylzinc compounds to aldehydes mediated by CrCl(3): efficient and facile synthesis of functionalized benzhydrols, 1(3H)-isobenzofuranones, benzyl alcohols, or diaryl ketones

In the presence of a stoichiometric amount of CrCl(3) and trimethylchlorosilane (TMSCl), nucleophilic addition of arylzinc compounds 1c-h to arylaldehydes 2a,b,g smoothly proceeded at room temperature to yield corresponding benzhydrols 4a-f in good yields. From arylzinc compounds 1a,b, 3-aryl-1(3H)-isobenzofuranones 3a-f were given by the CrCl(3)-mediated reaction with arylaldehydes 2a-f. Diaryl ketones 5a-e were obtained in good yields by the addition of excess amount of benzaldehyde as an oxidant to the resulting solution after the CrCl(3)-mediated reaction between arylzinc compounds 1c-g and arylaldehydes 2b,g was completed. In the nucleophilic additions of arylzinc compounds 1a,d,f to alkyladehydes 6b-f, the treatment of arylzinc compounds with CrCl(3) was required prior to the addition of the aldehydes in order to prevent the fast protodezincation of arylzinc compounds by the enolizable aldehydes. In these CrCl(3)-mediated nucleophilic additions of arylzinc compounds to aldehydes, arylchromium(III) species are probably reactive intermediates.     

Ruthenium‐Catalyzed Cycloisomerization of 2,2′‐Diethynyl‐ biphenyls Involving Cleavage of a Carbon–Carbon Triple Bond

A ruthenium complex catalyzes a new cycloisomerization reaction of 2,2′‐diethynylbiphenyls to form 9‐ethynylphenanthrenes, thereby cleaving the carbon–carbon triple bond of the original ethynyl group. A metal–vinylidene complex is generated from one of the two ethynyl groups, and its carbon–carbon double bond undergoes a [2+2] cycloaddition with the other ethynyl group to form a cyclobutene. The phenanthrene skeleton is constructed by the subsequent electrocyclic ring opening of the cyclobutene moiety.     

Trifluoroethylxanthate as an Analytical Reagent: AAS of Zinc,Antimony and Lead After Coprecipitation of Their Trifluoroethylxanthates onto Microcyrstalline Naphthalene

Abstract

A sensitive method has been developed for the direct atomic absorption spectrometric determination of zinc, antimony and lead after coprecipitation of their trifluoroethylxanthates onto microcrystalline naphthalene. The metal xanthates are quantitatively coprecipitated over the pH ranges: Zn, 5.9–8.4; Sb, 4.0–6.0 and Pb, 4.0–11.0. The solid mass consisting of the metal complex and naphthalene is dissolved in DMF. This solution is aspirated into an air-acetylene flame at 213.9, 217.6 and 217.0nm for Zn, Sb and Pb, respectively. Beer's law is obeyed in the concentration range 2–50, 3–90 and 5–60 μg of Zn, Sb and Pb, respectively in 10ml of the final DMF solution. RSDs are at the ± (0.5–0.6)% level (n=10). The concentration for 1% absorption is 0.019, 0.035 and 0.060μg/ml for Zn, Sb and Pb, respectively. The method is suitable for the preconcentration of the metals from a larger volume of the aqueous phase, and has been employed for their determination in standard reference materials. It may be employed for the simultaneous determination of Zn, Pb and Sb in a solution by pH control.     

Single-Round DNA Aptamer Selection by Combined Use of Capillary Electrophoresis and Next Generation Sequencing: An Aptaomics Approach for Identifying Unique Functional Protein-Binding DNA Aptamers

In DNA aptamer selection, existing methods do not discriminate aptamer sequences based on their binding affinity and function and the reproducibility of the selection is often poor, even for the selection of well-known aptamers like those that bind the commonly used model protein thrombin. In the present study, a novel single-round selection method (SR-CE selection) was developed by combining capillary electrophoresis (CE) with next generation sequencing. Using SR-CE selection, a successful semi-quantitative and semi-comprehensive aptamer selection for thrombin was demonstrated with high reproducibility for the first time. Selection rules based on dissociation equilibria and kinetics were devised to obtain families of analogous sequences. Selected sequences of the same family were shown to bind thrombin with high affinity. Furthermore, data acquired from SR-CE selection was mined by creating sub-libraries that were categorized by the functionality of the aptamers (e. g., pre-organized aptamers versus structure-induced aptamers). Using this approach, a novel fluorescent molecular recognition sensor for thrombin with nanomolar detection limits was discovered. Thus, in this proof-of-concept report, we have demonstrated the potential of a “DNA Aptaomics” approach to systematically design functional aptamers as well as to obtain high affinity aptamers.     

The potential use of electrospun polylactic acid nanofibers as alternative reinforcements in an epoxy composite system

This pilot study elaborates the development of novel epoxy/electrospun polylactic acid (PLA) nanofiber composites at the fiber contents of 3, 5, and 10 wt % to evaluate their mechanical and thermal properties using flexural tests and differential scanning calorimetry (DSC). The flexural moduli of composites increase remarkably by 50.8 and 24.0% for 5 and 10 wt % fiber contents, respectively, relative to that of neat epoxy. Furthermore, a similar trend is also shown for corresponding flexural strengths being enhanced by 31.6 and 4.8%. Fractured surface morphology with scanning electron microscopy (SEM) confirms a full permeation of cured epoxy matrix into nanofiber structures and existence of nondestructive fibrous networks inside large void cavities. The glass transition temperature (T_g) of composites increases up to 54–60 °C due to embedded electrospun nanofibers compared to 50 °C for that of epoxy, indicating that fibrous networks may further restrict the intermolecular mobility of matrix in thermal effects. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 618–623     

Palladium complexes bearing an N‐heterocyclic carbene–sulfonamide ligand for cooligomerization of ethylene and polar monomers

Herein, we report the synthesis of palladium complexes bearing an N‐heterocyclic carbene (NHC)‐sulfonamide bidentate ligand and their application in ethylene oligomerization and ethylene/polar monomer cooligomerization. These catalysts could smoothly catalyze ethylene oligomerization and ethylene/methyl acrylate cooligomerization albeit the performance was lower compared to that of a NHC–phenoxide catalyst. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 474–477