Microgels as drug carriers for sonopharmacology

The ultrasound-induced cleavage of covalent and non-covalent bonds to activate drugs (sonopharmacology) is a promising concept to gain control over the action of active pharmaceutical ingredients by an external trigger. Previously, linear polymer architectures bearing drug payloads were exploited for drug release by using the principles of polymer mechanochemistry. In this work, the carrier design is altered by the polymer topology to improve the ultrasound-triggered release of covalently anchored drugs from polymer scaffolds. We use microgels crosslinked by mechanoresponsive disulfides and copolymerized with Diels-Alder adducts of furylated payload molecules and acetylenedicarboxylate. Force-induced thiol formation induces a Michael-type addition liberating the payload from the microgels. The use of microgels significantly reduces sonication times compared to linear polymer chains and shields the cargo efficiently from non-triggered activation using ultrasound that produces inertial cavitation at a frequency of 20 kHz as model condition.     

Steplike transmission of light through a metal-dielectric multilayer structure due to an intensity-dependent sign of the effective dielectric constant

We numerically study light propagation through a specially designed nonlinear nanoscale metal-dielectric multilayer structure with a linear effective dielectric constant just below zero. The calculated dependence of the output intensity on the input intensity shows a steplike behavior. It rests upon an intensity-dependent change of the effective dielectric constant from negative (low-transmission state) to positive (high-transmission state) values, corresponding to a transition of the optical properties from metalliclike to dielectriclike. The study of the transient behavior of the structure demonstrates a switching time of around 1 ps.     

Aeolian transport of sand

The airborne transport of particles on a granular surface by the saltation mechanism is studied through numerical simulation of particles dragged by turbulent air flow. We calculate the saturated flux q_s and show that its dependence on the wind strength u_* is consistent with several empirical relations obtained from experimental measurements. We propose and explain a new relation for fluxes close to the threshold velocity u_t, namely, q_s=a(u_*-u_t)^α with α≈2. We also obtain the distortion of the velocity profile of the wind due to the drag of the particles and find a novel dynamical scaling relation. We also obtain a new expression for the dependence of the height of the saltation layer as function of the strength of the wind.     

2,2′‐Bipyridine‐Based Dendritic Structured Compounds for Second Harmonic Generation

Parallel alignment of dipolar electron‐donor–π‐bridge‐electron‐acceptor entities can strongly enhance their nonlinear optical properties. This favorable arrangement can be in principle achieved by linking these units covalently or through metal coordination. Four dipolar single‐strand chromophores decorated with a 5‐electron‐donor–5′‐electron‐acceptor‐modified 2,2′‐bipyridine functionality were synthesized. For two of these chromophores triple‐stranded dendritic structures were successfully formed. All of the compounds were characterized with respect to their linear and nonlinear optical properties. For the aldehyde derivatives an enhancement of the first hyperpolarizability of 4.5 rather than 3 was obtained when going from single to triple strands. Theoretical calculations with density functional theory suggest that interstrand transitions contribute to the optical properties of the dendritic structures.     

Rapid Autoxidation Forms Highly Oxidized RO2 Radicals in the Atmosphere

Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO₂ radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O₂ addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.     

Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds

In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity.     

Synthetic and Biological Studies on New Urea and Triazole Containing Cystobactamid Derivatives

Cystobactamids belong to the group of arene-based oligoamides that effectively inhibit bacterial type IIa topoisomerases. Cystobactamid 861-2 is the most active member of these antibiotics. Most amide bonds present in the cystobactamids link benzoic acids with anilines and it was found that some of these amide bonds undergo chemical and enzymatic hydrolysis, especially the one linking ring C with ring D. This work reports on the chemical synthesis and biological evaluation of thirteen new cystobactamids that still contain the methoxyaspartate hinge. However, we exchanged selected amide bonds either by the urea or the triazole groups and modified ring A in the latter case. While hydrolytic stability could be improved with these structural substitutes, the high antibacterial potency of cystobactamid 861-2 could only be preserved in selected cases. This includes derivatives, in which the urea group is positioned between rings A and B and where the triazole is found between rings C and D.     

Metal/Metal Redox Isomerism Governed by Configuration

A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ-η²-C,C′-κ²-S,P-C₂(PPh₂)S}Ru(η⁵-C₅H₅)(PPh₃)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ-η²-C,C′-κ²-S,P-C₂(PPh₂)S}Ru(η⁵-C₅H₅)-(PPh₃)], in which valence trapped W^III/Ru^II and W^II/Ru^III cationic species are at equilibrium.     

Quantum Defects as a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins

Single‐walled carbon nanotubes (SWCNTs) are a 1D nanomaterial that shows fluorescence in the near‐infrared (NIR, >800 nm). In the past, covalent chemistry was less explored to functionalize SWCNTs as it impairs NIR emission. However, certain sp³ defects (quantum defects) in the carbon lattice have emerged that preserve NIR fluorescence and even introduce a new, red‐shifted emission peak. Here, we report on quantum defects, introduced using light‐driven diazonium chemistry, that serve as anchor points for peptides and proteins. We show that maleimide anchors allow conjugation of cysteine‐containing proteins such as a GFP‐binding nanobody. In addition, an Fmoc‐protected phenylalanine defect serves as a starting point for conjugation of visible fluorophores to create multicolor SWCNTs and in situ peptide synthesis directly on the nanotube. Therefore, these quantum defects are a versatile platform to tailor both the nanotube's photophysical properties as well as their surface chemistry.