Astragalus is the largest genus in Leguminosae. Several molecular studies have investigated the potential adulterants of the species within this genus; nonetheless, the evolutionary relationships among these species remain unclear. Herein, we sequenced and annotated the complete chloroplast genomes of three Astragalus species—Astragalus adsurgens, Astragalus mongholicus var. dahuricus, and Astragalus melilotoides using next-generation sequencing technology and plastid genome annotator (PGA) tool. All species belonged to the inverted repeat lacking clade (IRLC) and had similar sequences concerning gene contents and characteristics. Abundant simple sequence repeat (SSR) loci were detected, with single-nucleotide repeats accounting for the highest proportion of SSRs, most of which were A/T homopolymers. Using Astragalus membranaceus var. membranaceus as reference, the divergence was evident in most non-coding regions of the complete chloroplast genomes of these species. Seven genes (atpB, psbD, rpoB, rpoC1, trnV, rrn16, and rrn23) showed high nucleotide variability (Pi), and could be used as DNA barcodes for Astragalus sp. cemA and rpl33 were found undergoing positive selection by the section patterns in the coded protein. Phylogenetic analysis showed that Astragalus is a monophyletic group closely related to the genus Oxytropis within the tribe Galegeae. The newly sequenced chloroplast genomes provide insight into the unresolved evolutionary relationships within Astragalus spp. and are expected to contribute to species identification.
Silica
xerogels were synthesized via the hydrolysis and condensation
of tetraethyl orthosilicate (TEOS) under the catalysis of n-butylamine (BA), followed by drying the formed wet gel
under ambient pressure at 120 °C. The solvents (water and ethanol)
and catalyst enclosed in wet gels were recovered during the drying
process. It was found that the relative percentage of ethanol in the
recovered liquids increased, while those of water and butylamine decreased.
The recovered liquids were directly used for four runs, and then the
contents of BA, H2O, and TEOS were adjusted to maintain
the reactant ratios to be the same as those in the first run, facilitating
a fast sol and gel formation. Totally 12 silica xerogels with high
degree of three-dimensional Si–O–Si network were synthesized.
The results indicate that all the silica xerogels are composed of
aggregated particles sized 20–250 nm, resulting in porous networks
with specific area, pore volume, and pore diameter in the range of
290–690 m2/g, 1.54–2.40 cm3/g,
and 17.4–68.2 nm, respectively. The compositional change in
the recovered liquids, the drying time, and the volume of wet gel
had influence on the aggregation, degree of condensation, and surface
area of the cyclically synthesized xerogels. The synthesis route not
only saves resources but also does not generate any waste, providing
a sustainable sol−gel way to synthesize materials.
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