Dipyridylketone as a versatile ligand precursor for new cationic heteroleptic cyclometalated iridium complexes

Three new bis-cyclometalated iridium(III) complexes, of general formula [Ir(2-phenylpyridine)(2)(L)](+), are reported. The compounds contain a dipyridine-type ligand (L) derived from di-2-pyridylketone (dipyridin-2-ylmethanol, 2,2'-(hydrazonomethylene)dipyridine and 3-hydroxy-3,3-di(pyridine-2-yl)propanenitrile) and were synthesized through two different reaction pathways. The alternative synthetic pathway herein proposed, namely the direct reactions on the complex [Ir(2-phenylpyridine)(2)(2,2'-dipyridylketone)](+), overcame the inconveniences encountered with the standard reaction between the dimeric precursor [Ir(2-phenylpyridine)(2)(μ-Cl)](2) and the ancillary ligands (L). The photophysical characterization of the iridium complexes reveals that modifications on the ancillary ligand introduce large changes in the photophysical behaviour of the complexes. High emission quantum yield is associated with the presence of a saturated carbon between the two pyridyl moieties: [Ir(2-phenylpyridine)(2)(2,2'-dipyridylketone)](+) and [Ir(2-phenylpyridine)(2)(2,2'-(hydrazonomethylene)dipyridine)](+) are extremely low emissive, while [Ir(2-phenylpyridine)(2)(dipyridin-2-ylmethanol)](+) and [Ir(2-phenylpyridine)(2)(3-hydroxy-3,3-di(pyridine-2-yl)propanenitrile)](+) are good photoemitters. DFT and TD-DFT calculations confirmed the mixed LC/MLCT character of the excited states involved in the absorption and emission processes and highlighted the role of the π-conjugation between the two subunits of the ancillary ligand in determining the nature of the LUMO.     

Divergent and solvent dependent reactions of 4-ethoxycarbonyl-3-methyl-1-tert-butoxycarbonyl-1,2-diaza-1,3-diene with enamines

Starting from 1-tert-butyloxycarbonyl-3-methyl-4-ethoxycarbonyl-1,2-diaza-1,3-diene and β,β,β and α,β-substituted enamines a careful choice of solvents and temperatures allows the divergent synthesis of 5,6-dihydro-4H-pyridazines, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester, and 1-amino-pyrroles. Moreover, some interesting conclusions about the mechanism(s) of the reaction have been drawn by careful analysis of products' structure and distribution. Thus, the reaction may proceed through a stereospecific [4+2] cycloaddition mechanism giving rise to 5,6-dihydro-4H-pyridazines or by simple addition or domino addition/cyclization pathways affording, respectively, 2-(1-N-boc-hydrazono-ethyl)-4-pyrrolidin-1-yl-but-3-enoic acid ethyl ester and 1-amino-pyrroles (formally the [3+2] cycloaddition product).     

Tuning the spin-transition properties of pyrene-decorated 2,6-bispyrazolylpyridine based Fe(II) complexes

Two 2,6-bispyrazolylpyridine ligands (bpp) were functionalized with pyrene moieties through linkers of different lengths. In the ligand 2,6-di(1H-pyrazol-1-yl)-4-(pyren-1-yl)pyridine (L1) the pyrene group is directly connected to the bpp moiety via a C-C single bond, while in the ligand 4-(2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)benzyl-4-(pyren-1-yl)butanoate (L2) it is separated by a benzyl ester group involving a flexible butanoic chain. Subsequent complexation of Fe(II) salts revealed dramatic the influence of the nature of the pyrene substitution on the spin-transition behaviour of the resulting complexes. Thus, compound [Fe(L1)(2)](ClO(4))(2) (1) is blocked in its high spin state due to constraints caused by a strong intermolecular π-π stacking in its structure. On the other hand, the flexible chain of ligand L2 in compounds [Fe(L2)(2)](ClO(4))(2) (2) and [Fe(L2)(2)](BF(4))(2)·CH(3)CN·H(2)O (3) prevents structural constraints allowing for reversible spin transitions. Temperature-dependent studies of the photophysical properties of compound 3 do not reveal any obvious correlation between the fluorescence of the pyrene group and the spin state of the spin transition core.     

Structure-based approach for identification of novel phenylboronic acids as serine-β-lactamase inhibitors

β-Lactamases are bacterial enzymes conferring resistance to β-lactam antibiotics in clinically-relevant pathogens, and represent relevant drug targets. Recently, the identification of new boronic acids (i.e. RPX7009) paved the way to the clinical application of these molecules as potential drugs. Here, we screened in silico a library of ~1400 boronic acids as potential AmpC β-lactamase inhibitors. Six of the most promising candidates were evaluated in biochemical assays leading to the identification of potent inhibitors of clinically-relevant β-lactamases like AmpC, KPC-2 and CTX-M-15. One of the selected compounds showed nanomolar K _i value with the clinically-relevant KPC-2 carbapenemase, while another one exhibited broad spectrum inhibition, being also active on Enterobacter AmpC and the OXA-48 class D carbapenemase.     

New organic nitrates. II. Synthesis of 2H-pyrido[2,3-e]-1,3-oxazine-2,4(3H)-diones, 2H-pyrido[4,3-e]-1,3-oxazine-2,4(3H)-diones, 2H-pyrido[4,3-e]-1,3-oxazin-4(3H)-ones, 2H-thieno[2,3-e]-1,3-oxazin-4(3H)-ones and 2H-thieno[3,4-e]-1,3-oxazin-2,4(3H)-diones

The preparation and the physico-chemical characterization of 2H-pyrido[2,3-e]-1,3-oxazine-2,4(3H)-diones, 2H-pyrido[4,3-e]-1,3-oxazine-2,4(3H)-diones, 2H-pyrido[4,3-e]-1,3-oxazin-4(3H)-ones, 2H-thieno[2,3-e]-1,3-oxazin-4(3H)-ones and 2H-thieno[3,4-e]-1,3-oxazine-2,4(3H)-diones are reported.     

Direct mass spectrometry of polymers. XIV. Thermal fragmentation processes in poly-schiff bases

The thermal fragmentation processes in poly-Schiff bases have been investigated by direct pyrolysis–mass spectrometry. The mass spectral data show that the thermal fragmentation occurring in the polymers under investigation is characterized by hydrogen transfer reactions. In the case of a totally aromatic poly-Schiff base (polymer I ), the thermal fragmentation process involves hydrogen transfer irom the methyne group with formation of fragments bearing nitrile and/or phenyl end groups. In the case of aromatic-aliphatic poly-Schiff bases (polymers II–IV ), the hydrogen transfer process occurs from the aliphatic methylene groups. The latter process involves a lower energy and therefore occurs at lower temperatures with respect to the totally aromatic polymer I , with formation of thermal fragments bearing olefin and/or imine end groups. Beside these fragments, several thermal fragmentation compounds are also evolved by multiple hydrogen transfer reactions.     

Synthesis of 4,5-dihydro-2,4-benzoxazepin-3( 1H)ones and 1,3,4,5-tetrahydro-2,4-benzoxazepines

o- Aminomethylbeiizyl alcohols (X) easily cyclize with phosgene in an aqueous alkaline medium to form 4,5-dihydro-2,4-benzoxazepin-3(1H)ones (IV) and with aldehydes in acidic conditions to yield 1,3,4,5-tetrahydro-2,4-benzoxazepines (V). The characteristics and chemical behaviour of these new heterocyclic ring systems are reported.     

Practical aspects of chemometrics for oil spill fingerprinting

Tiered approaches for oil spill fingerprinting have evolved rapidly since the 1990s. Chemometrics provides a large number of tools for pattern recognition, calibration and classification that can increase the speed and the objectivity of the analysis and allow for more extensive use of the available data in this field. However, although the chemometric literature is extensive, it does not focus on practical issues that are relevant to oil spill fingerprinting. The aim of this review is to provide a framework for the use of chemometric approaches in tiered oil spill fingerprinting and to provide clear-cut practical details and experiences that can be used by the forensic chemist. The framework is based on methods for initial screening, which include classification of samples into oil type, detection of non matches and of weathering state, and detailed oil spill fingerprinting, in which a more rigorous matching of an oil spill sample to suspected source oils is obtained. This review is intended as a tutorial, and is based on two examples of initial screening using respectively gas chromatography with flame ionization detection and fluorescence spectroscopy; and two of detailed oil spill fingerprinting where gas chromatography-mass spectrometry data are analyzed according to two approaches: The first relying on sections of processed chromatograms and the second on diagnostic ratios.