Current trends in green sample preparation before liquid chromatographic bioanalysis

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Synthesis and characterization of modular polyphosphonate homopolymers and copolymers

Linear polyphosphonates with the generic formula –[P(Ph)(X)OR′O]_n– (X = S or Se) have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and a diol (HOR′OH = 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, tetraethylene glycol, or 1,12-dodecanediol) followed by reaction with a chalcogen. Random copolymers have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and mixture of two of the diols in a 2:1:1 mol ratio followed by reaction with a chalcogen. Block copolymers with the generic formula –[P(Ph)(X)OR′O]_{(x + 2)} –[P(Ph)(X)OR′O]_{(x + 3)}– (X = S or Se) have been synthesized by the polycondensations of Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers with HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers followed by reaction with a chalcogen. The Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers are prepared by the reaction of an excess of P(Ph)(NEt₂)₂ with a diol while the HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers are prepared by the reaction of P(Ph)(NEt₂)₂ with an excess of the diol. In each case the excess, x is the same and determines the average block sizes. All of the polymers were characterized using ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, TGA, DSC, and SEC. ³¹P{¹H} NMR spectroscopy demonstrates that the random and block copolymers have the expected arrangements of monomers and, in the case of block copolymers, verifies the block sizes. All polymers are thermally stable up to ~300°C, and the arrangements of monomers in the copolymers (block vs. random) affect their degradation temperatures and T_g profiles. The polymers have weight average MWs of up to 3.8 × 10⁴ Da.     

EBC-232 and 323: A Structural Conundrum Necessitating Unification of Five In Silico Prediction and Elucidation Methods

Structurally unique halimanes EBC-232 and EBC-323, isolated from the Australian rainforest plant Croton insularis, proved considerably difficult to elucidate. The two diastereomers, which consist an unusual oxo-6,7-spiro ring system fused to a dihydrofuran, were solved by unification and consultation of five in silico NMR elucidation and prediction methods [i.e., ACDLabs, olefin strain energy (OSE), DP4, DU8+ and TD DFT CD]. Structure elucidation challenges of this nature are prime test case examples for empowering future AI learning in structure elucidation.     

Ruthenium (II) complexes bearing thioether-appended α-iminopyridine ligands: Arene precursors permit access to κ2-N,N and κ3-N,N,S complexes

Herein we report the preparation of a series of Ru(II) complexes featuring α-iminopyridine ligands bearing thioether functionality (NNS^R, where R = Me, CH₂Ph, Ph). Metallation using [(p-cymene)RuCl]₂ permits access to Ru complexes with a κ²-N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p-cymene moiety is displaced, and the ligand adopts a κ³-N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNS^Me)Ru (NCMe)₂Cl]Cl. The κ²-N,N-Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec-phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S-Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.     

Mathematical analysis of the dynamics of COVID-19 in Africa under the influence of asymptomatic cases and re-infection

Coronavirus pandemic (COVID-19) hit the world in December 2019, and only less than 5% of the 15 million cases were recorded in Africa. A major call for concern was the significant rise from 2% in May 2020 to 4.67% by the end of July 15, 2020. This drastic increase calls for quick intervention in the transmission and control strategy of COVID-19 in Africa. A mathematical model to theoretically investigate the consequence of ignoring asymptomatic cases on COVID-19 spread in Africa is proposed in this study. A qualitative analysis of the model is carried out with and without re-infection, and the reproduction number is obtained under re-infection. The results indicate that increasing case detection to detect asymptomatically infected individuals will be very effective in containing and reducing the burden of COVID-19 in Africa. In addition, the fact that it has not been confirmed whether a recovered individual can be re-infected or not, then enforcing a living condition where recovered individuals are not allowed to mix with the susceptible or exposed individuals will help in containing the spread of COVID-19.     

Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

By exploring lithium–bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium–bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium–bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et₂O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et₂O yielded almost double the conversion of cyclic products than in THF.