Anthracene-Based Cyclophanes with Selective Fluorescent Responses for TTP and GTP: Insights into Recognition and Sensing Mechanisms

Three anthracene-based cyclophanes were synthesized and their binding properties towards nucleoside triphosphates were studied. A new polycyclic amine derived from dearomatized anthracene was identified as a major side product in the cyclization reaction between 9,10-anthracenedicarboxaldehyde and diethylenetriamine. Its structure was determined by single-crystal X-ray analysis. The cyclophanes were found to form 1:1 complexes with all nucleoside triphosphates as well as with pyrophosphate in a buffered aqueous solution at pH 6.2. A turn-on fluorescence response was observed for all nucleotides except for GTP, which demonstrated strong fluorescence quenching. The strongest turn-on fluorescence was observed for the largest receptor 3 in the presence of thymidine triphosphate (TTP). Based on the NMR and fluorescence experiments, two major binding modes for nucleotide complexes were identified.     

Electronic Push–Pull Modulation by Peripheral Substituents in Pentaaryl Boroles

Establishing access to a bulky tetraaryl dilithiobutadiene (Ph*C)₄Li₂ (Ph*=3,5-tBu₂(C₆H₃)) allowed for the synthesis of five-membered heterocycles with incorporated main-group elements. Along with an amino borole, a set of substituted pentaaryl boroles (Ph*C)₄BAr has been synthesized. The examination of their absorption spectra and computational studies by means of DFT granted insight into the influence of peripheral substituents on the electronic features of the parent pentaphenyl borole (PhC)₄BPh. Introduction of the more electron-rich Ph* residue at the carbon atoms increases the HOMO energy, redshifting the visible π/π*-absorption bands compared with the parent pentaphenyl borole. The influence on the frontier orbitals of three different boron-bound aryls with electronically modulating substituents in the remote 3,5-positions Ar=3,5-R₂-C₆H₃ (R=Me, H, CF₃) was studied. The substituents were found to increase (+I effect, Me) or decrease (−I effect, CF₃) the LUMO energy, thus directly affecting the visible absorption spectra. This represents the first study on HOMO–LUMO-gap adjustments by a combined push–pull approach of a substituted pentaphenylborole.     

Electrochemical Reduction of N2 to NH3 at Low Potential by a Molecular Aluminum Complex

Electrochemical generation of ammonia (NH₃) from nitrogen (N₂) using renewable electricity is a desirable alternative to current NH₃ production methods, which consume roughly 1 % of the world's total energy use. The use of catalysts to manipulate the required electron and proton transfer reactions with low energy input is also a chemical challenge that requires development of fundamental reaction pathways. This work presents an approach to the electrochemical reduction of N₂ into NH₃ using a coordination complex of aluminum(III), which facilitates NH₃ production at −1.16 V vs. SCE. Reactions performed under ¹⁵N₂ liberate ¹⁵NH₃. Electron paramagnetic resonance spectroscopic characterization of a reduced intermediate and investigations of product inhibition, which limit the reaction to sub-stoichiometric, are also presented.     

Tailoring the Grain Boundary Chemistry of Polymeric Carbon Nitride for Enhanced Solar Hydrogen Production and CO2 Reduction

Photocatalytic water splitting is a promising and clean way to mimic plant photosynthesis in a sustainable manner. Improvements of the quantum efficiency and optical absorption in the relevant range are necessary steps to approach practicality. Herein, we reported that these issues can be readily addressed when 5‐aminotetrazole, a monomer with high nitrogen content, is used for the synthesis of carbon nitride. The molten salt mixture NaCl/KCl is used as a high‐temperature solvent to tailor the grain boundary structure and chemistry. Visible light quantum efficiency for H₂ production of 0.65 could be obtained in the presence of K₂HPO₄ as a double layer modifier. This value is very high, considering that this number depends on light to charge couple conversion, charge localization, as well as a successful oxidation and reduction reaction.     

A new class of flexure-free torsional vibrations of annular rods

It is shown that the system of partial differential equations governing small amplitude vibrations of an elastic ring has solutions describing motions in which the axial curve C of the ring remains rigid, but executes a rocking motion while the cross-sections undergo torsional rotations about C that vary periodically both in time and in distance along C. This type of flexure-free torsional vibration can occur both in rings that are stress-free in a circular equilibrium configuration and in rings formed by bringing together and sealing, with or without the addition of twist, the ends of rods that are stress-free when straight.

---

Sommario Si mostra che le equazioni che governano le oscillazioni di piccola ampiezza di travi elastiche anulari hanno soluzioni che corrispondono a moti nei quali l'asse C della trave è sottoposto a un'oscillazione rigida e le sezioni trasversali subiscono una rotazione torsionale che varia periodicamente nel tempo e con l'ascissa lungo C. Questo tipo di vibrazione torsionale, non accompagnata da flessione dell'asse, si presenta sia quando la configurazione anulare è priva di sforzi sia quando tale configurazione può pensarsi ottenuta inflettendo una trave che in uno stato privo di sforzi è ad asse rettilineo, imprimendo ad essa una eventuale deformazione torsionale, e collegando fra loro le sue estremità.

     

On the Distribution and Scaling of Convective Wavespeeds in the Shear Layers of Heated Supersonic Jets

The noise generated by supersonic plumes is of growing concern given the enormous peak noise intensity radiated by tactical aircraft engines. A key component of this noise is the enhanced radiation of mixing noise caused by large scale eddies convecting supersonically relative to the surrounding quiescent medium. As very little data exist for eddy convection in high Reynolds number, supersonic plumes, our current ability to develop concepts that alter compressible eddy convection is limited. Herein we present new experimental data of eddy convective wavespeeds in the developing shear layer of supersonic heated jets. A new scaling of the wavespeed in radial similarity coordinates is proposed which takes into account the influence of the ratio of static densities between the jet and ambient streams. In particular, we observe a structural change in wavespeed spectra at the end of the potential core—in addition to high turbulence levels, the potential core breakdown region can have enhanced eddy wavespeeds, increasing noise radiation efficiency. The results provide a first examination of the interplay of density ratio effects and the dynamic breakdown process of the potential core in supersonic jets—physics integral to the noise generation process.