A series of 10-arylflavins (10-phenyl-, 10-(2',6'-dimethylphenyl)-, 10-(2',6'-diethylphenyl)-, 10-(2',6'-diisopropylphenyl)-, 10-(2'-tert-butylphenyl)-, and 10-(2',6'-dimethylphenyl)-3-methylisoalloxazine (2 a-f)) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with (1)H-DOSY NMR spectroscopic experiments in CD(3)CN, CD(3)CN/D(2)O (1:1), and D(2)O confirm the decreased ability of 10-arylflavins 2 to form aggregates relative to tetra-O-acetyl riboflavin (1). 10-Arylflavins 2 a-d do not interact by π-π interactions, which are restricted by the 10-phenyl ring oriented perpendicularly to the isoalloxazine skeleton. On the other hand, N3-H⋅⋅⋅O hydrogen bonds were detected in their crystal structures. In the structure of 10-aryl-3-methylflavin (2 f) with a substituted N3 position, weak C-H⋅⋅⋅O bonds and weak π-π interactions were found. 10-Arylflavins 2 were tested as photoredox catalysts for the aerial oxidation of 4-methoxybenzyl alcohol to the corresponding aldehyde (model reaction), thus showing higher efficiency relative to 1. The quantum yields of 4-methoxybenzyl alcohol oxidation reactions mediated by arylflavins 2 were higher by almost one order of magnitude relative to values in the presence of 1.

This article presents an investigation of the sensing properties of chemiresistors based on Cu 2 O/CuO core−shell nanowires containing p−p′ heterojunctions. The nanowires were synthesized by a conventional hydrothermal method and used for the detection of ethanol and nitrogen dioxide, reducing and oxidizing agents, respectively. To unravel the chemical processes connected with gas detection, an in situ approach was applied. This approach was based on near-ambient pressure X-ray photoelectron spectroscopy combined with simultaneous monitoring of sensor responses. The in situ measurements were performed during exposure to the analytes at a total pressure of 0.05−1.05 mbar and 450 K and were correlated with chemiresistor response measurements carried out at a standard pressure and under an ambient atmosphere. The study revealed that heterojunction treatment with ethanol vapors, accompanied by partial reduction of the nanowires, is the key step to obtaining chemiresistors with good sensing performance. While the untreated heterojunctions exhibited poor n-type sensing responses, the treated ones showed significantly improved p-type responses. The treated sensors were characterized by a stable baseline, high reversibility, detection limits estimated as 50 ppm for ethanol and 100 ppb for nitrogen dioxide, and with response times in tens of seconds. In all cases, we propose a band scheme of Cu 2 O/CuO heterojunctions and a gas-sensing mechanism.

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To identify as many solid forms of active pharmaceutical ingredient (API) as possible and to monitor their cocrystallization potential, synthetic methods are needed. According to API properties (solubility, melting point, stability), suitable screening methods have to be considered. In this study, the performance of most of the commonly available cocrystallization techniques such as neat grinding, liquid-assisted grinding, slurrying, co-melting, and slow evaporation was compared. We applied them to four pharmaceutical cocrystals of trospium chloride (TCl, a muscarinic antagonist urinary antispasmodic) with adipic (AD), glutaric (GA), oxalic (OX), and salicylic acids (SA), which were identified as hits from previous slow evaporation experiments. Their structures were determined by single-crystal X-ray diffraction (TCl-SA and TCl-OX cocrystals) or from powder X-ray diffraction data (TCl-AD and TCl-GA cocrystals). Other methods to characterize the cocrystal phases were applied ( 1 H NMR, DSC, IR, and Raman spectroscopy). Comparison of cocrystallization methods and of the prepared cocrystals was discussed.