Core/valence partition and relativistic effects in effective potentials for transition metals

Two different versions, relativistic and nonrelativistic, of the “shape-consistent” effective potential (EP ) formalism are analyzed in ab initio calculations for transition metals. The influence of alternative core/valence partitions on the reliability of the procedure is discussed. The accuracy of EP results for transition metals is shown to depend on adequate choices of the valence subspace and proper inclusion of relativistic effects.     

Elimination of autofluorescence background from fluorescence tissue images by use of time-gated detection and the AzaDiOxaTriAngulenium (ADOTA) fluorophore

Sample autofluorescence (fluorescence of inherent components of tissue and fixative-induced fluorescence) is a significant problem in direct imaging of molecular processes in biological samples. A large variety of naturally occurring fluorescent components in tissue results in broad emission that overlaps the emission of typical fluorescent dyes used for tissue labeling. In addition, autofluorescence is characterized by complex fluorescence intensity decay composed of multiple components whose lifetimes range from sub-nanoseconds to a few nanoseconds. For these reasons, the real fluorescence signal of the probe is difficult to separate from the unwanted autofluorescence. Here we present a method for reducing the autofluorescence problem by utilizing an azadioxatriangulenium (ADOTA) dye with a fluorescence lifetime of approximately 15 ns, much longer than those of most of the components of autofluorescence. A probe with such a long lifetime enables us to use time-gated intensity imaging to separate the signal of the targeting dye from the autofluorescence. We have shown experimentally that by discarding photons detected within the first 20 ns of the excitation pulse, the signal-to-background ratio is improved fivefold. This time-gating eliminates over 96 % of autofluorescence. Analysis using a variable time-gate may enable quantitative determination of the bound probe without the contributions from the background.     

Size‐Selective Encapsulation of Hydrophobic Guests by Self‐Assembled M4L6 Cobalt and Nickel Cages

Subtle differences in metal–ligand bond lengths between a series of [M₄L₆]^4? tetrahedral cages, where M=Fe^II, Co^II, or Ni^II, were observed to result in substantial differences in affinity for hydrophobic guests in water. Changing the metal ion from iron(II) to cobalt(II) or nickel(II) increases the size of the interior cavity of the cage and allows encapsulation of larger guest molecules. NMR spectroscopy was used to study the recognition properties of the iron(II) and cobalt(II) cages towards small hydrophobic guests in water, and single‐crystal X‐ray diffraction was used to study the solid‐state complexes of the iron(II) and nickel(II) cages.     

Preparation and Characterization of Compositions Based on PbO-MgO-Nb2O5 Using the Sol-Gel Method

Lead Magnesium Niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), is an important relaxor ferroelectric material. A significant problem exists, however, in the preparation of this material: it is very difficult to prepare pure phase, without the presence of a pyrochlore impurity phase which degrades the dielectric properties. Depending on the processing conditions, the amount of pyrochlore phase varies.Considering the ternary diagram PbO-MgO-Nb₂O₅, different compositions have been prepared by a simple sol-gel method at room temperature using Pb(CH₃COO)₂, Mg(CH₃COO)₂, Nb(OC₂H₅)₅ as precursors. After the heat treatment, the samples obtained were analyzed by XRD and EPMA with the purpose of studying the compositions formed.From the analysis of these results, it seems to be that the appearance of pyrochlore can be related to the reactivity of the MgO and/or the presence of other phases of the binary system PbO-Nb₂O₅. An excess of Pb and Mg is necessary for compositions to be formed near the PMN. The control of the amount of these two elements is very important because an excess of MgO would lead to rich compositions in Mg as a secondary phase.     

Surfacial carbonized palygorskite as support for high-performance Pt-based electrocatalysts

Pt nanoparticles deposited on a low-cost, surfacial, carbonized palygorskite (Pt/C-PLS) prepared by carbonizing sucrose were evaluated as a methanol oxidation catalyst for direct methanol fuel cells. Transmission electron microscopy and Fourier transfrom infrared spectrophotometry analyses revealed that carbon was formed on the surface of PLS and that free silica presented in the C-PLS support. The catalytic activity of methanol oxidation of Pt/C-PLS was higher than that of Pt/C, and the former catalyst had better CO tolerance.     

Philicity of Acetonyl and Benzoyl Radicals: A Comparative Experimental and Computational Study

In this work, the reactivities of acetonyl and benzoyl radicals in aromatic substitution and addition reactions have been compared in an experimental and computational study. The results show that acetonyl is more electrophilic than benzoyl, which is rather nucleophilic. A Hammett plot analysis of the addition reactions of the two radicals to substituted styrenes clearly support the nucleophilicity of benzoyl, but in the case of acetonyl, no satisfactory linear correlation with a single substituent-related parameter was found. Computational calculations helped to rationalize this effect, and a good linear correlation was found with a combination of polar parameters (σ⁺) and the radical stabilization energies of the formed intermediates. Based on the calculated philicity indices for benzoyl and acetonyl, a quantitative comparison of these two radicals with many other reported radicals is possible, which may help to predict the reactivities of other aromatic radical substitution reactions.     

Brodie's or Hummers’ Method: Oxidation Conditions Determine the Structure of Graphene Oxide

Synthesis and studies of graphite oxide started more than 150 years ago and turned into a boom by the measurements of the outstanding physical properties of graphene. A series of preparation protocols emanated trying to optimize the synthesis of graphene oxide in order to obtain a less defective material, as source for graphene. However, over-oxidation of the carbon framework hampered establishing structure-property relationships. Here, the fact that two different synthetic methods for graphene oxide preparation lead to very similar types of graphene oxide with a preserved graphene lattice is demonstrated. Either sodium chlorate in nitric acid (similar to Brodie's method) or potassium permanganate in sulfuric acid (similar to Hummers’ method) treatment are possible; however, reaction conditions must be controlled. With a preserved carbon lattice analytical differences between the samples relate to the altered on-plane functionality. Consequently, terming preparation protocols “according to Brodie's/Hummers’ method” is not sufficient.     

Design,Synthesis, and Phenotypic Profiling of Pyrano‐Furo‐Pyridone Pseudo Natural Products

Natural products (NPs) inspire the design and synthesis of novel biologically relevant chemical matter, for instance through biology‐oriented synthesis (BIOS). However, BIOS is limited by the partial coverage of NP‐like chemical space by the guiding NPs. The design and synthesis of “pseudo NPs” overcomes these limitations by combining NP‐inspired strategies with fragment‐based compound design through de novo combination of NP‐derived fragments to unprecedented compound classes not accessible through biosynthesis. We describe the development and biological evaluation of pyrano‐furo‐pyridone (PFP) pseudo NPs, which combine pyridone‐ and dihydropyran NP fragments in three isomeric arrangements. Cheminformatic analysis indicates that the PFPs reside in an area of NP‐like chemical space not covered by existing NPs but rather by drugs and related compounds. Phenotypic profiling in a target‐agnostic “cell painting” assay revealed that PFPs induce formation of reactive oxygen species and are structurally novel inhibitors of mitochondrial complex I.     

The synthesis of cyclic polymers by olefin metathesis: Achievements and challenges

Cyclic polymers have drawn considerable interest for their peculiar physical properties in comparison to linear polymers, despite their equivalent compositions. Synthetically, cyclic polymers can be accessed through either macrocyclic ring‐closure or by ring‐expansion polymerization, but the main challenge with either method is the production of highly pure cyclic polymer samples. This highlight describes advances in the area of cyclic polymer synthesis, with a particular focus on ring‐expansion metathesis polymerization. Methods for characterizing cyclic polymers and assessing their purity are also discussed in order to emphasize the need for additional robust and reliable methods for synthesizing and studying topologically complex macromolecules. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 228–242     

A Fluorescent Activatable AND‐Gate Chemokine CCL2 Enables In Vivo Detection of Metastasis‐Associated Macrophages

We report the novel chemical design of fluorescent activatable chemokines as highly specific functional probes for imaging subpopulations of immune cells in live tumours. Activatable chemokines behave as AND‐gates since they emit only after receptor binding and intracellular activation, showing enhanced selectivity over existing agents. We have applied this strategy to produce mCCL2‐MAF as the first probe for in vivo detection of metastasis‐associated macrophages in a preclinical model of lung metastasis. This strategy will accelerate the preparation of new chemokine‐based probes for imaging immune cell function in tumours.