Facile,single-pot preparation of nanoporous SiO2 particles (carrier) with AgNPs at core and crust for controlled disinfectant release

This study demonstrates a novel, facile and one-pot approach to synthesize silica nanoparticles with silver at core and crust (SiNP-AgCC). A modified Stöber method was used to make SiNP-AgCC. A significant reduction in the size of SiO₂ nanoparticles was seen, with 2–5 nm AgNPs being uniformly distributed on the surface and 10–20 nm AgNPs in the center. A typical mesoporous SiO₂ particle (SiNP) produced using the Stöber method was transformed to nanoporous SiO₂ by this modified Stöber method. Nanoporous SiO₂ particles with silver in the center are advantageous for slow and consistent Ag⁺ release, which was confirmed by Ag⁺ ion release test. Antibacterial activities of the samples were tested to evaluate the disinfection performance of the samples on gram-negative bacteria (Escherichia coli) using disk diffusion and the LB-agar method. SiNP-AgCC showed prolonged silver release for more than 20 days and improved antibacterial properties even after five days of incubation.     

Problem-independent nonlinear switch for newly designed WENO-BO-Z scheme

The uniformly third-order WENO-BO-Z scheme has been proposed previously in an attempt to restore third-order accuracy at the second-order critical point via the reduction of nonlinear dissipation followed by the modification of nonlinear weights as well as to improve the intermediate bandwidth property of the linear optimal stencil of the classical WENO-JS scheme with respect to both dispersion and dissipation. However, a problem-dependent nonlinear switch was employed to turn on in the intermediate range of wavenumbers to avoid unnecessary nonlinear adaption of the WENO scheme and was mainly dependent on the trial-and-error threshold value of a switch parameter. In order to avoid the problem-dependent nature of this switch, a problem-independent nonlinear switch is suggested and investigated in this work. Benchmark problems, ranging from non-broadband to broadband, are solved using the WENO-BO-Z scheme, and a comparison of the suggested switch with the problem-dependent switch is made.     

Hydrodynamic analysis of electrostatic counter-streaming instability in a spin-polarized electron–positron–ion plasma

In this study, we present linear analysis of electrostatic counter-streaming instability in spin-polarized electron–positron–ion (e-p-i) plasma. With the aid of the separate spin evolution-quantum hydrodynamic (SSE-QHD) model, we derive the dispersion relation of counter-streaming instability. We numerically solve the dispersion and find four wave solutions: Langmuir wave, positron acoustic mode, and two electron and positron spin-dependent waves. It is noted that coupling of streaming and spin effects excites Langmuir instability and positron acoustic mode instability. However, in the absence of spin effect, only Langmuir instability will survive in e-p-i plasma. We have also discussed the effects of positron concentration, streaming speed, and spin polarization on the real frequency of waves and the growth rate. The present study may be helpful for understanding longitudinal wave propagation and instabilities in dense magnetized environments.     

The quettamines: a new class of isoquinoline alkaloids

Three quettamine type alkaloids, which incorporate either a benzofuran or a dihydrobenzofuran moiety within the molecular framework, have been obtained from $\text{Berberis}$$\text{baluchistanica}$. These are dihydrosecoquettamine ($\text{1}$), secoquettamine ($\text{2}$), and quettamine chloride ($\text{3}$). Alkaloids $\text{1}$ and $\text{3}$ are racemates. Hofmann degradation of quettamine ($\text{3}$) provides secoquettamine ($\text{2}$) and the styrene $\text{4}$ which has a trans relationship between the hydrogens at C-1 and C-α, thus indicating the identical stereochemistry in quettamine. Emde reduction of quettamine leads to dihydrosecoquettamine ($\text{1}$) and the stilbene $\text{5}$. Two other polar alkaloids in the plant are (+)-armepavine methochloride ($\text{6}$) and oblongine chloride ($\text{7}$). An oblongine type alkaloid must be the biogenetic precursor for the quettamines. Arguments are presented favoring direct oxidative coupling in the biogenesis of the cularine alkaloids.     

Pyridylethyl: A versatile protecting group. Part II. The protection of heterocyclic N-H groups

Pyrrole, indole, carbazole and imidazole have been protected as N-[2-(4-pyridyl)ethyl] derivatives. Deprotection occurred under mild conditions after quaternisation. 3-Bromoindole was prepared by bromin-ation of the protected parent indole.     

Microbial Transformation of Isolongifolen‐4‐one

The microbial transformation of (+)‐isolongifolen‐4‐one ( 4 ) by a number of fungi by means of a standard two‐stage fermentation technique afforded (7R)‐12‐hydroxyisolongifolen‐4‐one ( 5 ), (7S)‐13‐hydroxyisolongifolen‐4‐one ( 6 ), (11R)‐11‐hydroxyisolongifolen‐4‐one ( 7 ), (10R)‐10‐hydroxyisolongifolen‐4‐one ( 8 ), and (9R)‐9‐hydroxyisolongifolen‐4‐one ( 9 ) (Scheme). All five metabolites were found to be new, and metabolites 6 and 9 showed potent tyrosinase inhibitory activity (Table 1). The metabolites and their derivatives were characterized on the basis of spectroscopic and single‐crystal X‐ray‐diffraction techniques.     

Microbial transformation of (+)-androsta-1 ,4-diene-3,17-dione by Cephalosporium aphidicola

Fermentation of (+)-androsta-1,4-diene-3,17-dione ([structure: see text]) with Cephalosporium aphidicola for 8 days yielded oxidative and reductive metabolites, androst-4-ene-3,17-dione ([structure: see text]), 17beta-hydroxyandrosta-1,4-diene-3-one ([structure: see text]), 11alpha-hydroxyandrosta-1,4-diene-3,17-dione ([structure: see text]), 11alpha-hydroxyandrost-4-ene-3,17-dione ([structure: see text]), 11alpha,17beta-dihydroxyandrost-4-ene-3-one ([structure: see text]) and 11alpha,17beta-dihydroxyandrosta-1,4-diene-3-one ([structure: see text]). The fermentation of [structure: see text] with Fusarium lini also yielded metabolites [structure: see text]. The structures of these metabolites were elucidated on the basis of spectroscopic techniques.