Dealing with a local heating effect when measuring catalytic solids in a reactor with Raman spectroscopy

In continuation of our previous work on the applicability of the G(R(infinity)) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr(6+) in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 degrees C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard.     

Topology and geometry of the Berkovich ramification locus for rational functions, II

This article is the second installment in a series on the Berkovich ramification locus for nonconstant rational functions $\varphi \in k(z)$ . Here we show the ramification locus is contained in a strong tubular neighborhood of finite radius around the connected hull of the critical points of $\varphi $ if and only if $\varphi $ is tamely ramified. When the ground field $k$ has characteristic zero, this bound may be chosen to depend only on the residue characteristic. We give two applications to classical non-Archimedean analysis, including a new version of Rolle’s theorem for rational functions.     

Chemistry of Crosslinking Processes for Self‐Healing Polymers

Recent developments in material design have seen an exponential increase of polymers and polymer composites that can repair themselves in response to damage. In this review, a distinction is made between extrinsic materials, where the self‐healing property is obtained by adding healing agents to the material to be repaired, and intrinsic materials, where self‐healing is achieved by the material itself through its chemical nature. An overview of the crosslinking chemistries used in self‐healing materials will be given, discussing the advantages and drawbacks of each system. The review is not only aiming to enable researchers to compare their ongoing research with the state‐of‐the‐art but also to serve as a guide for the newcomers, which allows for a selection of the most promising self‐healing chemistries.     

Spatially Resolved Genetic Analysis of Tissue Sections Enabled by Microscale Flow Confinement Retrieval and Isotachophoretic Purification

We have developed a method for spatially resolved genetic analysis of formalin‐fixed paraffin‐embedded (FFPE) cell block and tissue sections. This method involves local sampling using hydrodynamic flow confinement of a lysis buffer, followed by electrokinetic purification of nucleic acids from the sampled lysate. We characterized the method by locally sampling an array of points with a circa 200 μm diameter footprint, enabling the detection of single KRAS and BRAF point mutations in small populations of RKO and MCF‐7 FFPE cell blocks. To illustrate the utility of this approach for genetic analysis, we demonstrate spatially resolved genotyping of FFPE sections of human breast invasive ductal carcinoma.     

An Octa-Urea [Pd2L4]4+ Cage that Selectively Binds to n-octyl-α-D-Mannoside

Designing compounds for the selective molecular recognition of carbohydrates is a challenging task for supramolecular chemists. Macrocyclic compounds that incorporate isophtalamide or bisurea spacers linking two aromatic moieties have proven effective for the selective recognition of all-equatorial carbohydrates. Here, we explore the molecular recognition properties of an octa-urea [Pd₂L₄]⁴⁺ cage complex ( 4 ). It was found that small anions like NO₃⁻ and BF₄⁻ bind inside 4 and inhibit binding of n-octyl glycosides. When the large non-coordinating anion ‘BAr^F’ was used, 4 showed excellent selectivity towards n-octyl-α-D-Mannoside with binding in the order of K_a≈16 M⁻¹ versus non-measurable affinities for other glycosides including n-octyl-β-D-Glucoside (in CH₃CN/H₂O 91 : 9).     

Metric properties of the tropical Abel–Jacobi map

Let Γ be a tropical curve (or metric graph), and fix a base point p∈Γ. We define the Jacobian group J(G) of a finite weighted graph G, and show that the Jacobian J(Γ) is canonically isomorphic to the direct limit of J(G) over all weighted graph models G for Γ. This result is useful for reducing certain questions about the Abel–Jacobi map Φ _p :Γ→J(Γ), defined by Mikhalkin and Zharkov, to purely combinatorial questions about weighted graphs. We prove that J(G) is finite if and only if the edges in each 2-connected component of G are commensurable over ℚ. As an application of our direct limit theorem, we derive some local comparison formulas between ρ and \varPhi_p^*(r){\varPhi}_{p}^{*}(\rho) for three different natural “metrics” ρ on J(Γ). One of these formulas implies that Φ _p is a tropical isometry when Γ is 2-edge-connected. Another shows that the canonical measure μ _Zh on a metric graph Γ, defined by S. Zhang, measures lengths on Φ _p (Γ) with respect to the “sup-norm” on J(Γ).     

A Water Soluble Pd2L4 Cage for Selective Binding of Neu5Ac

The sialic acid N-acetylneuraminic acid (Neu5Ac) and its derivatives are involved in many biological processes including cell-cell recognition and infection by influenza. Molecules that can recognize Neu5Ac might thus be exploited to intervene in or monitor such events. A key obstacle in this development is the sparse availability of easily prepared molecules that bind to this carbohydrate in its natural solvent; water. Here, we report that the carbohydrate binding pocket of an organic soluble [Pd₂L₄]⁴⁺ cage could be equipped with guanidinium-terminating dendrons to give the water soluble [Pd₂L₄][NO₃]₁₆ cage 7 . It was shown by means of NMR spectroscopy that 7 binds selectively to anionic monosaccharides and strongest to Neu5Ac with K_a=24 M⁻¹. The cage had low to no affinity for the thirteen neutral saccharides studied. Aided by molecular modeling, the selectivity for anionic carbohydrates such as Neu5Ac could be rationalized by the presence of charge assisted hydrogen bonds and/or the presence of a salt bridge with a guanidinium solubilizing arm of 7 . Establishing that a simple coordination cage such as 7 can already selectively bind to Neu5Ac in water paves the way to improve the stability, affinity and/or selectivity properties of M₂L₄ cages for carbohydrates and other small molecules.     

Topology and geometry of the Berkovich ramification locus for rational functions, I

We initiate a detailed study of the ramification locus for projective endomorphisms of the Berkovich projective line—the non-Archimedean analog of the Riemann sphere.