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Carboxylic Acid Initiated Organocatalytic Ring-Opening Polymerization of N-Sulfonyl Aziridines: An Easy Access to Well-Controlled Polyaziridine-Based Architectural and Functionalized Polymers(Macromolecules, American Chemical Society (ACS), 2019-11-11) [Article]A highly easy and efficient metal-free methodology for the synthesis of polyaziridine-based polymers with controlled architectures and desired functionalities was developed by organocatalytic ring-opening polymerization (ROP) of N-sulfonyl aziridines with a carboxylic acid as initiator. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (MTBD) and phosphazene t-Bu-P4 organocatalysts have demonstrated high catalytic efficiency in connection with the controlled/living character of the ROP of 2-methyl-N-tosylaziridines (TsMAz) initiated by benzoic acid. Aryl carboxylic acids bearing an azido or a hydroxyl group as well as bio-derived vanillic acid and syringic acid and alkyl- and alkenyl-substituted carboxylic acids, such as acetic acid, palmitic acid, and methacrylic acid, can all initiate the ROP of TsMAz toward well-defined P(TsMAz)s. α,ω-Diamino telechelic, star-shaped P(TsMAz)s, and poly(styrene-co-methacrylic acid)-graft-poly(2-methyl-N-tosylaziridine) [P(St-co-MAA)-g-P(TsMAz)] have been conveniently synthesized from the corresponding multicarboxyl (macro)initiators. Finally, this protocol has been applied for the synthesis of a linear photoresponsive P(TsMAz) and an aggregation-induced emission (AIE)-active 4-arm P(TsMAz) star from the corresponding functionalized carboxylic acids.
A direct fluorescent signal transducer embedded in a DNA aptamer paves the way for versatile metal-ion detection(Sensors and Actuators B: Chemical, Elsevier BV, 2019-11-07) [Article]Using DNA aptamers as sensors for metal ions provide a variety of applications in biology and industry. Many of these sensors are based on guanine-rich DNA sequences that undergo conformational changes upon metal-ion binding. However, these sensors require an exogenous reporter that can recognize such DNA conformational changes and transduce the signal. Here, we bypass the exogenous reporter by embedding a signal transducer in the guanine-rich DNA aptamer that measures directly the DNA conformational changes upon metal-ion binding. Our signal transducer is an environmentally sensitive Cy3 fluorescent dye that is internally coupled to the DNA aptamer. We demonstrate the applicability of our embedded-signal transducer approach using a known potassium-responding aptamer. We next demonstrate the versatility of this approach by designing an aptamer sensor that can detect potassium ions in the low micro-molar range and with high selectivity against a wide range of ions including sodium. The aptamer accurately measured potassium ions concentration in a variety of aqueous and biological test samples. Our embedded-signal transducer approach will pave the way for the development of aptamer sensors for a variety of ligands.
Draft Genome Sequence of Methanobacterium sp. Strain 34x, Reconstructed from an Enriched Electromethanogenic Biocathode(Microbiology Resource Announcements, American Society for Microbiology, 2019-11-06) [Article]A draft genome sequence of Methanobacterium sp. strain 34x was reconstructed from the metagenome of an enriched electromethanogenic biocathode operated in a microbial electrosynthesis (MES) reactor. Methanobacterium sp. strain 34x has 68.98% nucleotide-level genomic similarity with the closest related methanogen available with a whole-genome assembly, Methanobacterium lacus strain AL-21. This genome will provide insight into the functional potential of methanogens at the biocathodes of MES systems.
Parameter and differentiation order estimation for a two dimensional fractional partial differential equation(Journal of Computational and Applied Mathematics, Elsevier BV, 2019-11-06) [Article]This paper deals with the estimation of coefficients and differentiation orders for two-dimensional fractional partial differential equations. Recently, a hybrid method based on modulating functions has been proposed by the authors to estimate the coefficients and a differentiation order for a one dimensional fractional advection dispersion equation in Aldoghaither et al. (2015). We propose to extend this method to the two-dimensional case. First, the coefficients are estimated using a modulating functions method, where the problem is transferred into solving a system of algebraic equations. Then, the modulating functions method combined with a Newton algorithm is proposed to estimate the coefficients and the differentiation orders simultaneously. Numerical example is presented with noisy measurements to show the effectiveness and the robustness of the method.
Lower crustal heterogeneity beneath the northern Tibetan Plateau constrained by GPS measurements following the 2001 Mw7.8 Kokoxili earthquake(Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 2019-11-06) [Article]We use Global Positioning System (GPS) measurements across the Xidatan segment of the Kunlun fault in the Tibetan Plateau to investigate the surface deformation following the 2001 Mw 7.8 Kokoxili earthquake. We find significant post-seismic deformation during the period 2007-2015, characterized by an asymmetric shear across the 2001 rupture, with average velocities reaching ~10 mm/yr about 30-45 km south of the coseismic rupture. We also find that the postseismic transients diffused away from the coseismic rupture through time, with a shift of the maximum transient rates from ~20-30 km south of the rupture in 2001-2002 to ~30-45 km in 2007-2015. Viscoelastic relaxation is the dominant physical process during the period 2007-2015. The estimated effective viscosity of the lower crust beneath the Songpan-Ganzi terrane is 2×1018-3×1018 Pa s from the 2001-2002 data, and it has increased to ~2×1019 Pa s for the period 6 to 14 years after the event. The large asymmetry in the postseismic deformation field indicates a laterally heterogeneous lower crust beneath the northern Tibetan Plateau. Viscoelastic relaxation models show that the viscosity of the lower crust beneath the Qaidam basin is ~2 and ~4 times larger than the viscosity of the lower crust beneath the Songpan-Ganzi terrane in 2001-2002 and 2007-2015, respectively. Based on these data and results from previous studies, we postulate that the Kunlun fault itself is not the unique rheological boundary and that additional domains with viscosity increasing from the Qiangtang terrane to the Qaidam basin appear to be required.