Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

Photoactive metal complexes employing Earth‐abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non‐innocence to tune the luminescence and photochemistry of the excited state of the [CrN₆] chromophore [Cr(tpe)₂]³⁺ with close to octahedral symmetry (tpe=1,1,1‐tris(pyrid‐2‐yl)ethane). [Cr(tpe)₂]³⁺ exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)₂]³⁺ are redox non‐innocent, leading to reversible reductive chemistry. The excited state redox potential and lifetime of [Cr(tpe)₂]³⁺ surpass those of the classical photosensitizer [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) enabling energy transfer (to oxygen) and photoredox processes (with azulene and tri(n‐butyl)amine).     

Porous Media Characterization Using Minkowski Functionals: Theories,Applications and Future Directions

An elementary question in porous media research is in regard to the relationship between structure and function. In most fields, the porosity and permeability of porous media are properties of key interest. There is, however, no universal relationship between porosity and permeability since not only does the fraction of void space matter for permeability but also the connectivity of the void fraction. With the evolution of modern day X-ray microcomputed tomography (micro-CT) and advanced computing, it is now possible to visualize porous media at an unprecedented level of detail. Approaches in analyzing micro-CT data of porous structures vary in the literature from phenomenological characterization to network analysis to geometrical and/or topological measurements. This leads to a question about how to consistently characterize porous media in a way that facilitates theoretical developments. In this effort, the Minkowski functionals (MF) emerge from the field of statistical physics where it is evident that many physical processes depend on the geometry and topology of bodies or multiple bodies in 3D space. Herein we review the theoretical basis of the MF, mathematical theorems and methods necessary for porous media characterization, common measurement errors when using micro-CT data and recent findings relating the MF to macroscale porous media properties. This paper is written to provide the basics necessary for porous media characterization and theoretical developments. With the wealth of information generated from 3D imaging of porous media, it is necessary to develop an understanding of the limitations and opportunities in this exciting area of research.

     

Dissecting Fragment-Based Lead Discovery at the von Hippel-Lindau Protein:Hypoxia Inducible Factor 1α Protein-Protein Interface

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Highlights? Inhibitors of pVHL:HIF-1α interaction are ligand-efficient and retain binding mode ? Ro3-compliant fragments of these inhibitors are not hits in biophysical screens ? Successful hit fragments break the Ro3 and target at least two subsites at the PPI ? Integration of GE and GLE analyses provide methodology to probe hot spots at a PPI     

Measuring the range of plasmonic interaction

When gold nanoparticles are covered with nanometric layers of transparent polyelectrolytes, the plasmon absorption spectrum A(λ) increases by a factor of approximately three and shifts to the red. These modifications of dissipative experimental observables stop when the cover layer thickness approaches the particle diameter. Spectral modifications of dispersive parameters like the reflection R, however, keep changing with increasing cover layer thickness. The shift of the plasmon resonance caused by two interacting particle layers is studied as a function of the separating distance between the two layers. We discuss these observations in the context of an effective medium theory and conclude that it can only be applied for a layer thickness on the order of the particle diameter.     

On the diameter of partition polytopes and vertex-disjoint cycle cover

We study the combinatorial diameter of partition polytopes, a special class of transportation polytopes. They are associated to partitions of a set X = {x ₁, . . . , x _n } of items into clusters C ₁, . . . , C _k of prescribed sizes κ ₁ ≥ · · · ≥ κ _k . We derive upper bounds on the diameter in the form of κ ₁ + κ ₂, n ? κ ₁ and ${\lfloor \frac{n}{2} \rfloor}$ . This is a direct generalization of the diameter-2 result for the Birkhoff polytope. The bounds are established using a constructive, graph-theoretical approach where we show that special sets of vertices in graphs that decompose into cycles can be covered by a set of vertex-disjoint cycles. Further, we give exact diameters for partition polytopes with k = 2 or k = 3 and prove that, for all k ≥ 4 and all κ ₁, κ ₂, there are cluster sizes κ ₃, . . . , κ _k such that the diameter of the corresponding partition polytope is at least ${\lceil \frac{4}{3} \kappa_2 \rceil}$ . Finally, we provide an ${O(n(\kappa_1 + \kappa_2(\sqrt{k} - 1)))}$ algorithm for an edge-walk connecting two given vertices of a partition polytope that also adheres to our diameter bounds.