N-C bond formation of NO ligands on ruthenium complexes with concurrent vinylic C-H activation and subsequent proton-induced reactivities of the resulting nitrosovinyl species

The N-C coupling of ligating NO with 2-vinylpyridines, affording nitrosovinyl complexes, was found. This is of significance since the reaction process involves a C-H activation of the vinyl moiety and subsequent C-N bond formation. Furthermore, we show that the resulting nitrosovinyl complexes are chemically versatile and potentially valuable species. Protonation of the resulting nitrosovinyl complexes in refluxing alcohol afforded the alcohol-incorporated complexes, as well as the ketoimine species. It is interesting to note that a proton-induced reaction with PPh3 trapped their intermediates, leading to the explication of these reaction mechanisms.     

Tailor-Made Amino Acids and Fluorinated Motifs as Prominent Traits in Modern Pharmaceuticals

Structural analysis of modern pharmaceutical practices allows for the identification of two rapidly growing trends: the introduction of tailor-made amino acids and the exploitation of fluorinated motifs. Curiously, the former represents one of the most ubiquitous classes of naturally occurring compounds, whereas the latter is the most xenobiotic and comprised virtually entirely of man-made derivatives. Herein, 39 selected compounds, featuring both of these traits in the same molecule, are profiled. The total synthesis, source of the corresponding amino acids and fluorinated residues, and medicinal chemistry aspects and biological properties of the molecules are discussed.     

3-dynamic coloring of planar triangulations

An $r$-dynamic $k$-coloring of a graph $G$ is a proper $k$-coloring such that any vertex $v$ has at least $min\{r,{deg}_G\left(v\right)\}$ distinct colors in $N_G\left(v\right)$. The $r$-dynamic chromatic number${\chi }_r^d\left(G\right)$ of a graph $G$ is the least $k$ such that there exists an $r$-dynamic $k$-coloring of $G$.Loeb et al. (2018) showed that if $G$ is a planar graph, then ${\chi }_3^d\left(G\right)\le 10$, and there is a planar graph $G$ with ${\chi }_3^d\left(G\right)=7$. Thus, finding an optimal upper bound on ${\chi }_3^d\left(G\right)$ for a planar graph $G$ is a natural interesting problem. In this paper, we show that ${\chi }_3^d\left(G\right)\le 5$ if $G$ is a planar triangulation. The upper bound is sharp.     

Unusual behavior of nuclear relaxation in CeCu2Si2 “possible evidence for triplet superconductivity”

Nuclear relaxation of ⁶³Cu in the superconducting state of the Kondo-lattice system CeCu₂Si₂ has been studied with the use of the ⁶³Cu nuclear quadrupole resonance technique under zero field and down to 65mK. The nuclear spin-lattice relaxation rate (1/T₁) decreases drastically just below T_c=0.67 K down to 0.5T_c without the apparent enchanced behavior and then is found to be almost temperature independent below 0.3T_c. These results suggest that the superconductivity in CeCu₂Si₂ is not in the usual BCS regime. The analysis based upon the existing triplet pairing model with an anisotropic energy gap describes well the behavior from T_c down to 0.5T_c, while the temperature independence below 0.3T_c remains unexplained.     

Total synthesis of (±)-surugatoxin

Total synthesis of surugatoxin 1, isolated from the toxic Japanese ivory shell ($\text{Babylonia japonica}$), was achieved from 6-bromoisatin by stepwise ring construction involving two key steps: the stereospecific cyclization (9→10) and hydration (17→1).     

Oxygen isotope effect in high-T C superconductors: Cu nuclear quadrupole resonance relaxation rates

A scaling relationship has been observed between the⁶³Cu(2) spin-lattice relaxation rates 1/T ₁,(18) and 1/T ₁(16) observed in¹⁸O- and¹⁶O-exchanged YBa₂Cu₄O₈ and the normalized temperatureT/T _c(18 or 16). This relation implies thatT _C is decreased by the change in antiferromagnetic (AF) spin fluctuation rate. Thus oxygen isotope effect observed in high-T _C superconductors does not indicate any importance of electron-phonon interaction but it appears to originate from the change in AF fluctuations.