The optoacoustic layering effect and thickness measurements

Summary The value of optoacoustic spectroscopy as a technique for the quantitative non-destructive determination of thickness of surface layers is examined by reference to two systems. In one, carbon deposits on a nickel-alumina catalyst with graphite filler, it is shown that the deposit can be detected, and its thickness estimated by application of a simple equation. The relationship does not hold for different thicknesses of the transparent polymer melinex above 40 m. It is argued that because the optoacoustic signal has complex origins, reliable quantitative relationships are difficult to establish. However, it is confirmed that qualitative analysis of subcutaneous layers by OAS, is relatively straightforward.

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Der optoakustische Schichteffekt und Messungen von Schichtdicken

Zusammenfassung Der Nutzen der optoakustischen Spektroskopie für die quantitative zerstörungsfreie Bestimmung von Oberflächenschichtdicken wird an Hand von zwei verschiedenen Systemen untersucht. Im Falle von Kohlenstoffablagerungen auf einem Ni-Al₂O₃-Katalysator mit Graphitmatrix konnte die Dikke der Ablagerung mit Hilfe einer einfachen Gleichung bestimmt werden. Jedoch konnte diese Beziehung bei dem transparenten Polymer Melinex für Schichtdicken über 40 m nicht angewendet werden. Wegen der komplexen Ursachen des optoakustischen Signals ist es schwierig, zuverlässige quantitative Beziehungen aufzustellen. Für qualitative Schichtuntersuchungen kann die Methode aber nützlich sein.

     

Remote Loading of Small‐Molecule Therapeutics into Cholesterol‐Enriched Cell‐Membrane‐Derived Vesicles

The increasing popularity of biomimetic design principles in nanomedicine has led to therapeutic platforms with enhanced performance and biocompatibility. This includes the use of naturally derived cell membranes, which can bestow nanocarriers with cell‐specific functionalities. Herein, we report on a strategy enabling efficient encapsulation of drugs via remote loading into membrane vesicles derived from red blood cells. This is accomplished by supplementing the membrane with additional cholesterol, stabilizing the nanostructure and facilitating the retention of a pH gradient. We demonstrate the loading of two model drugs: the chemotherapeutic doxorubicin and the antibiotic vancomycin. The therapeutic implications of these natural, remote‐loaded nanoformulations are studied both in vitro and in vivo using animal disease models. Ultimately, this approach could be used to design new biomimetic nanoformulations with higher efficacy and improved safety profiles.     

Real‐Time Control of the Enantioselectivity of a Supramolecular Catalyst Allows Selecting the Configuration of Consecutively Formed Stereogenic Centers

The enantiomeric state of a supramolecular copper catalyst can be switched in situ in ca. five seconds. The dynamic property of the catalyst is provided by the non‐covalent nature of the helical assemblies supporting the copper centers. These assemblies are formed by mixing an achiral benzene‐1,3,5‐tricarboxamide (BTA) phosphine ligand (for copper coordination) and both enantiomers of a chiral phosphine‐free BTA co‐monomer (for chirality amplification). The enantioselectivity of the hydrosilylation reaction is fixed by the BTA enantiomer in excess, which can be altered by simple BTA addition. As a result of the complete and fast stereochemical switch, any combination of the enantiomers was obtained during the conversion of a mixture of two substrates.     

Self‐Assembled Zinc/Cystine‐Based Chloroplast Mimics Capable of Photoenzymatic Reactions for Sustainable Fuel Synthesis

Prototypes of biosystems provide good blueprints for the design and creation of biomimetic systems. However, mimicking both the sophisticated natural structures and their complex biological functions still remains a great challenge. Herein, chloroplast mimics have been fabricated by one‐step bioinspired amino acid mineralization and simultaneous integration of catalytically active units. Hierarchically structured crystals were obtained by the metal‐ion‐directed self‐assembly of cystine (the oxidized dimer of the amino acid cysteine), with a porous structure and stacks of nanorods, which show similar architectural principles to chloroplasts. Porphyrins and enzymes can both be encapsulated inside the crystal during mineralization, rendering the crystal photocatalytically and enzymatically active for an efficient and sustainable synthesis of hydrogen and acetaldehyde in a coupled photoenzymatic reaction.     

Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

In a comparative study of the electrocatalytic CO₂ reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO₂ becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO₂. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.