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Cleveland Barlow posted an update 6 months, 1 week ago
Lignin is the richest source of renewable aromatics and has immense potential for replacing synthetic chemicals. The limited functionality of lignin is, however, challenging for its potential use, which motivates research for creating advanced functional lignin-derived materials. Here, we present an aqueous-based acid precipitation method for preparing functional lignin nanoparticles (LNPs) from carboxymethylated or carboxypentylated lignin. We observe that the longer grafted side chains of carboxypentylated lignin allow for the formation of larger LNPs. The functional nanoparticles have high tolerance against salt and aging time and well-controlled size distribution with Rh ≤ 60 nm over a pH range of 5-11. We further investigate the layer-by-layer (LbL) assembly of the LNPs and poly(allylamine hydrochloride) (PAH) using a stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D). Results demonstrate that LNPs made of carboxypentylated lignin (i.e., PLNPs with the adsorbed mass of 3.02 mg/m2) form a more packed and thicker adlayer onto the PAH surface compared to those made of carboxymethylated lignin (i.e., CLNPs with the adsorbed mass of 2.51 mg/m2). The theoretical flux, J, and initial rate of adsorption, (dΓ/dt)0, analyses confirm that 22% of PLNPs and 20% of CLNPs arriving at the PAH surface are adsorbed. The present study provides a feasible platform for engineering LNPs with a tunable size and adsorption behavior, which can be adapted in bionanomaterial production.The 2-fold reduction of B2X4(NHC)2 (X = Cl, Br, I; NHC = (un)saturated N-heterocyclic carbene) yields the corresponding green-colored 1,2-dihalodiborenes B2X2(NHC)2, the 11B NMR resonances of which are strongly upfield-shifted upon descending the halide group. The diborenes crystallize as the trans isomers, with relatively short B═B double bonds (1.513(9) to 1.568(4) Å). Cyclic voltammetric experiments with these diborenes reveal reversible one-electron oxidation processes to the corresponding diboron radical cation (E1/2 = -1.16 to -1.50 V); the reducing power of B2X2(NHC)2 increasing with the electronegativity of the halide and for the less π-accepting unsaturated NHCs. The main UV-vis absorption (393-463 nm), which corresponds mainly to a highest occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO) transition, undergoes a blueshift upon descending the halide group and shows some dependence on the stereoelectronics of the NHC ligands. Computational analyses show that the HOMO of B2X2(NHC)2 is mostly localized on the B═B π bond, with the contribution from halide p orbitals decreasing down the group, and the saturated NHCs affording some π-bonding delocalization over the B-CNHC bonds. The calculated HOMO and LUMO energies decrease upon descending the halide group, while the HOMO-LUMO gap also decreases, correlating well with the cyclovoltammetry and UV-vis data. The reactions of B2Br2(NHC)2 with elemental sulfur and red selenium lead to the formation of the corresponding diborathiiranes and seleniranes, respectively, which were characterized by NMR and UV-vis spectroscopy, cyclic voltammetry, and X-ray diffraction analyses. In one case, an additional one-electron oxidation yields a unique cyclic B2Se radical cation. Computational analyses show that the localization of the HOMO and HOMO – 1 of the diboraseleniranes is inverted compared to the diborathiiranes.Research in natural products, the genetically encoded small molecules produced by organisms in an idiosyncratic fashion, deals with molecular structure, biosynthesis, and biological activity. selleck chemicals Bioinformatics analyses of microbial genomes can successfully reveal the genetic instructions, biosynthetic gene clusters, that produce many natural products. Genes to molecule predictions made on biosynthetic gene clusters have revealed many important new structures. There is no comparable method for genes to biological activity predictions. To address this missing pathway, we developed a machine learning bioinformatics method for predicting a natural product’s antibiotic activity directly from the sequence of its biosynthetic gene cluster. We trained commonly used machine learning classifiers to predict antibacterial or antifungal activity based on features of known natural product biosynthetic gene clusters. We have identified classifiers that can attain accuracies as high as 80% and that have enabled the identification of biosynthetic enzymes and their corresponding molecular features that are associated with antibiotic activity.Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.An efficient transition-metal-free decarboxylative cyclization of N-arylacrylamides with 2,2-difluoro-2-(phenylthio)acetic acid for the construction of thiodifluoroindoleone derivatives is described. This strategy features stable and readily available substrates, mild reaction conditions, and transition-metal-free catalysts. Notably, this protocol has successfully applied to synthesis of gem-difluoroalkenes, which exist in numerous biologically active compounds.
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