General Catalytic Methylation of Amines with Formic Acid under Mild Reaction Conditions

A general catalytic protocol for the methylation of amines has been developed applying, for the first time, formic acid as the C₁ building block and silanes as reducing agents. A broad range of aromatic and aliphatic, both primary and secondary, amines has been converted to the corresponding tertiary amines including [N‐¹³C]‐labelled drugs in good to excellent yields under mild conditions.     

Albumin–Folate Conjugates for Drug‐targeting in Photodynamic Therapy

Photodynamic therapy (PDT) is based on the cytotoxicity of photosensitizers in the presence of light. Increased selectivity and effectivity of the treatment is expected if a specific uptake of the photosensitizers into the target cells, often tumor cells, can be achieved. An attractive transporter for that purpose is the folic acid receptor α (FRα), which is overexpressed on the surface of many tumor cells and mediates an endocytotic uptake. Here, we describe the synthesis and photobiological characterization of polar β‐carboline derivatives as photosensitizers covalently linked to folate‐tagged albumin as the carrier system. The particles were taken up by KB (human carcinoma) cells within <90 min and then co‐localized with a lysosomal marker. FRα antibodies prevented the uptake and also the corresponding conjugate without folate was not taken up. Accordingly, a folate‐albumin‐β‐carbolinium conjugate proved to be phototoxic, while the corresponding albumin–β‐carbolinium conjugates without FA were nontoxic, both with and without irradiation. An excess of free folate as competitor for the FRα‐mediated uptake completely inhibited the photocytotoxicity. Interestingly, the albumin conjugates are devoid of photodynamic activity under cell‐free conditions, as shown for DNA as a target. Thus, phototoxicity requires cellular uptake and lysosomal degradation of the conjugates. In conclusion, albumin–folate conjugates appear to be promising vehicles for a tumor cell targeted PDT.     

Hydrogenation of Esters to Alcohols Catalyzed by Defined Manganese Pincer Complexes

The first manganese‐catalyzed hydrogenation of esters to alcohols has been developed. The combination of Mn(CO)₅Br with [HN(CH₂CH₂P(Et)₂)₂] leads to a mixture of cationic and neutral Mn PNP pincer complexes, which enable the reduction of various ester substrates, including aromatic and aliphatic esters as well as diesters and lactones. Notably, related pincer complexes with isopropyl or cyclohexyl substituents showed very low activity.     

A soft XAS transmission cell for operando studies

A new cell for operando soft X‐ray absorption spectroscopy in transmission mode is presented. Developed for investigations on solar water‐splitting catalysts, the cell allows the study of solid films in direct contact with electrolyte solution while applying voltage and visible light. The design is optimized for fast sample exchange and the simultaneous measurement of fluorescence and transmission signal. The capability of the cell is presented on a manganese oxide (MnO_x) film, where electronic structure changes are monitored during forward and backward potential changes. Detailed information about the varying contributions of several Mn oxidation states during this process was revealed.     

Identities for Generalized Appell Functions and the Blow-up Formula

In this paper, we prove identities for a class of generalized Appell functions which are based on the \({{\rm A}_2}\) root lattice. The identities are reminiscent of periodicity relations for the classical Appell function and are proven using only analytical properties of the functions. Moreover, they are a consequence of the blow-up formula for generating functions of invariants of moduli spaces of semi-stable sheaves of rank 3 on rational surfaces. Our proof confirms that in the latter context, different routes to compute the generating function (using the blow-up formula and wall-crossing) do arrive at identical q-series. The proof also gives a clear procedure on how to prove analogous identities for generalized Appell functions appearing in generating functions for sheaves with rank \({r>3}\).     

Alternating current techniques in scanning electrochemical microscopy (AC-SECM)

Alternating current scanning electrochemical microscopy (AC-SECM) is a growing branch within the variety of SECM methods. This review covers publications involving AC-SECM from its beginning to date. The findings of several research groups are thematically structured along with the specific experimental procedures. This should enable researchers to rationally choose purposeful parameters for their AC-SECM experiments.     

Synthesis and cannabinoid receptor activity of ketoalkenes from Echinacea pallida and nonnatural analogues

Despite its popularity and widespread use, the efficacy of Echinacea products remains unclear and controversial. Among the various compounds isolated from Echinacea, ketoalkenes and ketoalkenynes exclusively found in the pale purple coneflower (E. pallida) are major components of the extracts. In contrast to E. purpurea alkamides, these compounds have not been synthesized and studied for immunostimulatory effects. We present a practical and useful synthetic approach to the ketoalkenes using palladium-catalyzed cross-coupling reactions and the pharmaceutical results at the human cannabinoid receptors. The synthetic route developed provides overall good yields for the ketoalkenes and is applicable to other natural products with similar 1,4-diene motifs. No significant activity was observed at either receptor, indicating that the ketoalkenes from E. pallida are not responsible for immunomodulatory effects mediated via the cannabinergic system. However, newly synthesized non-natural analogues showed micro-molar potency at both cannabinoid receptors.