A Theoretical Study on the Photodissociation of Acetone: Insight into the Slow Intersystem Crossing and Exploration of Nonadiabatic Pathways to the Ground State

Structures of transition states (TSs) and minima on seam of crossing (MSXs) for potential energy surfaces (PESs) of acetone of the S₀, S₁, and T₁ states were explored. On the basis of the results, we propose a new mechanism, slow intersystem crossing from S₁ to T₁ without seam of crossing, followed by CH₃ dissociation via a TS on T₁; this slow pathway will be overtaken by a more efficient S₁ pathway for higher energy. This is consistent with the observed long lifetime of the S₁ species. Moreover, four channels, including three new ones, were found to regenerate the ground state acetone from the S₁ PES, and they all may be involved in the roaming channel that has been proposed recently as a new route of CO generation in a 230 nm photolysis. There are significant differences in MSX structures and energies between the present CASPT2 results and previous CASSCF results

Anionic Polymerization Mechanism of Acrylonitrile Trimer Anions: Key Branching Point between Cyclization and Chain Propagation

A cluster anion of vinyl compounds in the gaseous phase has served as one of the simplest microscopic models of the initial stages of anionic polymerization. Herein, we describe our investigations into the initial stage mechanisms of anionic polymerization of acrylonitrile (AN; CH₂CHCN) trimer anions. While the cyclic oligomer is found in mass and photoelectron spectroscopic studies of (AN)₃^–, only the chain oligomer is found in the infrared photodissociation (IRPD) spectrum of Ar-tagged (AN)₃^–. On the basis of the calculated polymerization pathway of (AN)₃^–, we consider that the chain oligomers are the reaction intermediates in the cyclization of (AN)₃^–. The rotational isomerization of the (AN)₃^– chain oligomer is found to be the bottleneck in the cyclization of (AN)₃^–. To form the (AN)₄^– chain oligomer by chain propagation, the addition of an AN molecule to (AN)₃^– should occur prior to the rotational isomerization. We conclude that the rotational isomerization in the (AN)₃^– chain oligomer is the key branching point between cyclization (termination) or chain propagation in the anionic polymerization

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Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition

An anthryl-substituted exocyclic silene, 3-silylene-2-silaaziridine, was synthesized by isomerization of the corresponding disilacyclopropanimine. The UV–vis spectrum of the silene shows a distinct intramolecular charge transfer (ICT) transition from the π orbital of the SiC double bond to the π* orbital of the anthryl moiety. The relatively high-lying π­(SiC) orbital of the 3-silylene-2-silaaziridine moiety and the low-lying π* orbital of the anthryl group would be responsible for the distinct ICT band

Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition

An anthryl-substituted exocyclic silene, 3-silylene-2-silaaziridine, was synthesized by isomerization of the corresponding disilacyclopropanimine. The UV–vis spectrum of the silene shows a distinct intramolecular charge transfer (ICT) transition from the π orbital of the SiC double bond to the π* orbital of the anthryl moiety. The relatively high-lying π­(SiC) orbital of the 3-silylene-2-silaaziridine moiety and the low-lying π* orbital of the anthryl group would be responsible for the distinct ICT band

Effect of Oral Administration of Metronidazole or Prednisolone on Fecal Microbiota in Dogs

<div><p>Gastrointestinal microbiota have been implicated in the pathogenesis of various gastrointestinal disorders in dogs, including acute diarrhea and chronic enteropathy. Metronidazole and prednisolone are commonly prescribed for the treatment of these diseases; however, their effects on gastrointestinal microbiota have not been investigated. The objective of this study was to evaluate the effects of these drugs on the gastrointestinal microbiota of dogs. Metronidazole was administered twice daily at 12.5 mg/kg to a group of five healthy dogs, and prednisolone at 1.0 mg/kg daily to a second group of five healthy dogs for 14 days. Fecal samples were collected before and after administration (day 0 and 14), and 14 and 28 days after cessation (day 28 and 42). DNA was extracted, and the bacterial diversity and composition of each sample were determined based on 16S ribosomal RNA (rRNA) gene sequences using next-generation sequencing (Illumina MiSeq). In the group administered metronidazole, bacterial diversity indices significantly decreased at day 14, and recovered after the cessation. Principal coordinates analysis and hierarchical dendrogram construction based on unweighted and weighted UniFrac distance matrices revealed that bacterial composition was also significantly altered by metronidazole at day 14 compared with the other time points. The proportions of Bacteroidaceae, Clostridiaceae, Fusobacteriaceae, Lachnospiraceae, Ruminococcaceae, Turicibacteraceae, and Veillonellaceae decreased, while Bifidobacteriaceae, Enterobacteriaceae, Enterococcaceae, and Streptococcaceae increased at day 14 and returned to their initial proportions by day 42. Conversely, no effect of prednisolone was observed on either the bacterial diversity or composition. Reducing pathogenic bacteria such as Fusobacteria and increasing beneficial bacteria such as <i>Bifidobacterium</i> through the administration of metronidazole may be beneficial for promoting gastrointestinal health; however, further investigations into the effects on diseased dogs are needed.</p></div

Relative proportions of the most predominant bacterial taxa in the dogs with metronidazole administration.

<p>Taxa observed in at least three of five dogs with the proportion of >1% (either day 0, 14, 28, or 42) were included in this table.</p><p>*Significantly different from day 0 (<i>P</i><0.05).</p>†<p>Significantly different from day 14 (<i>P</i><0.05).</p><p>Relative proportions of the most predominant bacterial taxa in the dogs with metronidazole administration.</p

Hierarchical dendrogram and fecal microbial composition of each sample at the phylum level.

<p>Figures were constructed using unweighted UniFrac distances. (A) Result of dogs administered metronidazole. This dendrogram showed that the samples obtained at day 14 were clustered. (B) Result of dogs administered prednisolone. No clustering was observed at any time points.</p

Effect of metronidazole and prednisolone on bacterial diversity indices.

<p>Data represents mean ± SD.</p><p>*Significantly different from day 0 (<i>P</i><0.05).</p>†<p>Significantly different from day 14 (<i>P</i><0.05).</p><p>Effect of metronidazole and prednisolone on bacterial diversity indices.</p

Principal coordinates analysis (PCoA) of V4 16S rRNA genes from canine fecal samples.

<p>Figures were calculated using unweighted UniFrac distances. (A) Result of dogs administered metronidazole. Metronidazole-affected samples (blue, day 14) were separated from the other samples, primarily along PCoA axis 1 (accounting for 33.94% of all variability among samples). (B) Result of dogs administered prednisolone. Prednisolone administration did not induce alteration of bacterial composition.</p