Manuela List

Silver and Gold Complexes with a New 1,10‐Phenanthroline Analogue N‐Heterocyclic Carbene: A Combined Structural, Theoretical, and Photophysical Study

Unusual coordination for gold: an imidazolium salt was synthesized and used as a precursor for an N-heterocyclic carbene, which can be considered as the carbene analogue of 1,10-phenanthroline. Like the diimine congener, this ligand gives luminescent metal complexes. Remarkably, the Au(III) complex features a gold atom in an unusual environment: it is surrounded by six donor atoms, two of which interact electrostatically with the Au atom.

Copper(II) complexes with imino phenoxide ligands: synthesis, characterization, and their application as catalysts for the ring-opening polymerization of rac-lactide

Four new copper complexes based on bidentate imino phenoxide ligands were synthesized and characterized by IR, UV–Vis spectroscopy, ESI mass spectrometry, single crystal X-ray diffraction, and electrochemistry. The crystal structures revealed that the copper(II) atoms are surrounded by phenolate oxygen and imine nitrogen atoms of two ligands in a distorted square-planar geometry. The existence of ligand-centered, as well as Cu(II)-centered quasi-reversible and reversible redox reactions are observed in the cyclic voltammetry experiments of all the complexes. All complexes are able to catalyze the ring-opening polymerization of rac-lactide yielding polymers with moderate molecular weights and moderately broad molecular weight distributions.Graphical abstract

Analysis of methylated melamines in reaction mixtures by CZE‐MS

A fast and reliable method based on CZE coupled to Q‐TOF MS for the analysis of methylated melamines is presented. Experiments with UV detection were performed using BGE containing formic acid and TFA to optimize electrophoretic conditions and to achieve baseline separation. Employing a TFA‐based electrolyte containing 80% ACN and MS detection, nine different methyl melamines were determined in real samples, which were produced by catalytic hydrogenation of melamine/formaldehyde reaction mixtures. The use of a Q‐TOF MS resulted in LOD better than 0.01 mg/L for all compounds and high mass accuracy with mass errors lower than 2.3 ppm.

N-Methylmelamines: Synthesis, Characterization, and Physical Properties

N-Methylmelamines have recently gained importance as valuable compounds for manufacturing modified melamine formaldehyde resins and other polymer building blocks. A great advantage of these polymers is the reduction of the carcinogenic formaldehyde. Selecting the polymerization processes (e.g., substance polymerization, polymerization in solution) and controlling the polymerization reaction and properties of these novel materials requires knowledge of the properties of the individual melamine derivatives used as new building blocks. All possible permutations of N-methylmelamines were prepared, and reaction progress was monitored by GC/MS. 2,4,6-Tris(dimethylamino)-1,3,5-triazine was prepared to complete the series; this is, however, also a possible byproduct in various synthesis routes. The reaction conditions were optimized to obtain high yields of each derivative with the highest possible purity. The substances were characterized by NMR and IR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. In addition, physical properties, such as solubility, melting points, and pKb values, were determined. The number of amino-, methylamino-, and dimethylamino groups has a significant effect on these properties. In summary, we found that by increasing the number of amino- and methylamino groups, solubility and pKb increase. With increasing number of amino groups, the compounds tend to form hydrogen bonds, and thus, the melting point shifts to higher temperature ranges where they start to decompose.

Palladium complexes containing imino phenoxide ligands: synthesis, luminescence, and their use as catalysts for the ring-opening polymerization of rac-lactide

The preparation, structural characterization, luminescence, and catalytic activity of three palladium(II) complexes bearing imino phenoxide ligands are reported. The X-ray studies revealed that the complexes are mononuclear with palladium centres coordinated in a square-planar coordination environment. Two of the complexes are emissive in solution at room temperature. The catalytic activities towards the ring-opening polymerization of rac-lactide (rac-LA) were tested. Polymers with moderate molecular weights and relatively broad dispersity (Ð) were obtained. Kinetic studies revealed that the polymerization followed first-order kinetics.Graphical abstract

Synthesis and Characterization of Silver(I) and Gold(I) Complexes Bearing a Pyrido-annelated N-Heterocyclic Carbene: A Rare Example of a Cocrystal Containing Two Different Gold(I) Complexes

Abstract The cyclohexyl-substituted imidazo[1,5-a]pyridin-2-ium hexafluorophosphate, 2a, has been prepared as precursor for the respective pyrido-annelated N-heterocyclic carbene. [(NHC)2Ag]PF6, 3, has been synthesized by the reaction of 2a with AgCl=KOH in dichloromethane (DCM). Unexpectedly, the reaction of 3 with (tht)AuBr yielded both (NHC)AuBr and [(NHC)Au(tht)]PF6 which formed a 1 : 1 cocrystal (4a,b). The complexes are aggregated to infinite chains, which are governed by both π-π stacking and weak aurophilic interactions. Subsequent oxidation of the co-crystalline material with CsBr3 gave (NHC)AuBr3, 5. All compounds were characterized by NMR spectroscopy, mass spectrometry and elemental analysis. Additionally, compounds 2a and 5 were investigated by electronic spectroscopy: 2a behaves like a typical aromatic compound exhibiting absorption and fluorescence bands attributable to π-π* transitions. The Au(III) complex 5 exhibits ligand-centered fluorescence at room temperature and both ligand-centered fluorescence and a weak phosphorescence at 77 K.

Edible Insects and Other Chitin-Bearing Foods in Ethnic Peru: Accessibility, Nutritional Acceptance, and Food-Security Implications

Abstract. This study concerns the ecological and economic features of a particular category of complementary foods in ethnic Peru—comprising of insects, crustaceans, snails, and mushrooms— grouped as chitin-bearing foods (CBFs). Data collection was through participatory methods and semistructured interviews with 242 individuals in eight communities/villages from four ethnic populations. We found that, in Peruvian Amazonian Amerindian communities, CBFs are the most relevant protein source during the rainy season. Shrimp (Macrobrachium sp.), crab (Hypolobocera peruviana), palmweevil (Rhynchophorus palmarum), leaf-cutter ants (Atta cephalotes), and Lepidoptera larvae are common in the Amazonian diet. In Awajún and Ashaninka communities, most interviewed subjects declared significant consumption of CBFs, while a low percentage ate vertebrates every week during the rainy season and even in the dry season. In contrast, highland Quechua people occasionally consume larvae of Lepidoptera and Coleoptera and Quechua-Lamas populations (in the Amazonian region from historical times) consume the most accessible CBFs on a weekly basis. Traditional technologies and methods of semi-cultivation are evidence of a growing economic interest for CBFs. Relevant species have a high nutritional value in terms of chitin, fatty acids, and proteins, as well a high acceptance by the indigenous population. We conclude that Amazonian Amerindians manage these foods not only as a remedy for food shortage during the rainy season, but also as a stable forest resource and year-round agricultural by-product. We conclude that these traditional food practices should be incorporated within local and national agri-food policies to develop their economic potential and bring their social benefits into rural and peri-urban areas of Peru.

Synthesis, crystal structures and blue emission of zinc(II) halide complexes of 1-alkyl-imidazole and (–)-nicotine

Abstract Zn(II) halide complexes of the form L2ZnX2 (X=Cl, Br, I) containing bio-relevant or bio-related ligands like 1-alkyl-imidazoles (alkyl=methyl, ethyl and iso-propyl) or (–)-nicotine are presented. All complexes were characterized by 1H NMR spectroscopy, mass spectrometry and elemental analysis. The molecular structures of the majority of complexes were determined by single crystal X-ray diffraction. The zinc ion exists in a tetrahedral environment coordinated by two halide anions and two nitrogen atoms of the N-heterocycles. Upon photoexcitation the nicotine complexes feature a blue emission which we tentatively assign to phosphorescence.

Synthesis, Characterization and Luminescence of Silver(I) and Gold(I) Complexes Bearing a Diethyl Acetal Functionalized N-Heterocyclic Carbene

1-(2,2ʹ-Diethoxyethyl)-3-methyl-imidazolium bromide, 1, has been prepared and used as a precursor for the synthesis of the corresponding silver bromide complex [(NHC)2Ag][AgBr2], 2. Transmetallation of 2 with (tht)AuBr (tht = tetrahydrothiophene) yields (NHC)AuBr, 3. The solid-state structures of 2 and 3 have been determined by single-crystal X-ray diffraction revealing a loose aggregation of the complexes by weak metal-metal interactions. Due to the presence of these contacts, both complexes are emissive in the solid state. Graphical Abstract Synthesis, Characterization and Luminescence of Silver(I) and Gold(I) Complexes Bearing a Diethyl Acetal Functionalized N-Heterocyclic Carbene