A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent-Induced Increase of the Enantiomerization Barrier in 1-Aza-[5]helicene

Helicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors.[1] Synthetic protocols were developed to obtain helicenes with skeletons consisting of ortho-fused benzene rings or analogue structures incorporating a heteroatom, as in thiophene-, furane-, or pyridine-containing helicenes.[2] In recent years, a repertoire of synthetic strategies was developed to access all monoaza[5]helicenes as well as some diaza[ 5]helicenes.[3] The properties of these materials are related to the stereodynamics of these helical chiral compounds. By exploration of the unexpected broad range of physicochemical properties of aza[n]helicenes it was realized that there is an opportunity to modulate a specific property by controlled design of the position of the N atoms in the helical molecular frame. In this contribution, we show a complete stereodynamic characterization of monoaza[5]-helicenes combining enantioselective dynamic HPLC and DFT calculations. At variance with previous theoretical calculations[4], 1-aza[5]helicene shows a surprisingly high enantiomerization barrier, which is triggered by specific solvent interactions. [5] References [1] a) H. A. Staab, M. A. Zirnstein, C. Krieger, Angew. Chem. Int. Ed. Engl. 1989, 28, 86–88; Angew. Chem. 1989, 101, 73– 75;b) T. R. Kelly, Acc. Chem. Res. 2001, 34, 514 –522; c) T. J. Wigglesworth, D. Sud, T. B. Norsten, V. S. Lekhi, N. R. Branda, J. Am. Chem. Soc. 2005, 127, 7272 – 7273; d) L. Vyklicky´, S. H. Eichhorn, T. J. Katz, Chem. Mater. 2003, 15, 3594 –3601; e) M. Gingras, Chem. Soc. Rev. 2013, 42, 1051– 1095. [2] a) M. Gingras, Chem. Soc. Rev. 2013, 42, 968–1006; b) M. Gingras, G. F_lix, R. Peresutti, Chem. Soc. Rev. 2013, 42, 1007 –1050; c) Y. Shen, C.-F. Chen, Chem. Rev. 2012, 112, 1463– 1535. [3] a) C. Bazzini, S. Brovelli, T. Caronna, C. Gambarotti, M. Giannone, P. Macchi, F. Meinardi, A. Mele, W. Panzeri, F. Recupero, A. Sironi, Eur. J. Org. Chem. 2005, 1247 – 1257; b) S. Abbate, C. Bazzini, T. Caronna, F. Fontana, C. Gambarotti, F. Gangemi, G. Longhi, A. Mele, I. Natali Sora, W. Panzeri, Tetrahedron 2006, 62,139 –148; c) T. Caronna, F. Fontana, A. Mele, I. Natali Sora, W. Panzeri, L. Vigan_, Synthesis 2008, 413– 416; d) T. Caronna, S. Gabbiadini, A. Mele, F. Recupero, Helv. Chim. Acta 2002, 85, 1 –8; e) T. Caronna, F. Castiglione, F. Fontana, D. Mendola, I. Natali Sora, Molecules 2012, 17, 463 –479. [4] S. Abbate, C. Bazzini, T. Caronna, F. Fontana, F. Gangemi, F. Lebon, G. Longhi, A. Mele, I. Natali Sora, Inorg. Chim. Acta 2007, 360, 908 –912. [5] T. Caronna, A. Mele, A. Famulari, D. Mendola, F. Fontana, M. Juza, M. Kamuf, K. Zawatzky, and O. Trapp, Chem. Eur. J. 2015, 21, 1–7

Multiple points of view of heteronuclear NOE: long range vs short range contacts in pyrrolidinium based ionic liquids in the presence of Li salts.

The nuclear Overhauser enhancement (NOE) is a powerful tool of NMR Spectroscopy extensively used to gain structural information in ionic liquids (ILs). A general model for the distance dependence of intermolecular NOE in ILs was recently proposed showing that NOE spots beyond the first solvation shell and accounts for long-range effects. This conclusion prompted for a deep rethinking of the NOE data interpretation in ILs. In this paper we present an extensive and quantitative study of N-propyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI), the homologue with bis(fluorosulfonyl)imide (PYR13FSI), and their mixtures with LiTFSI based on {1H-19F} and {1H-7Li}NOE correlation experiments (HOESY). The former is mainly tuned on long-range interactions, the latter on short-range ones, due to the small and large Larmor frequency differences of the involved nuclei. The collected data are discussed in two different way: long-range {1H-19F}NOEs spot on the polar/apolar domains within the ILs, whereas short-range (e.g. regarding the first coordination shell) {1H-7Li}NOEs describe the contacts between first neighbors, with interesting correlation with the distances’ statistics derived by crystallographic data of related systems

Polydisperse methyl β-cyclodextrin–epichlorohydrin polymers: variable contact time 13C CP-MAS solid-state NMR characterization

The polymerization of partially methylated β-cyclodextrin (CRYSMEB) with epichlorohydrin was carried out in the presence of a known amount of toluene as imprinting agent. Three different preparations (D1, D2 and D3) of imprinted polymers were obtained and characterized by solid-state 13C NMR spectroscopy under cross-polarization magic angle spinning (CP-MAS) conditions. The polymers were prepared by using the same synthetic conditions but with different molar ratios of imprinting agent/monomer, leading to morphologically equivalent materials but with different absorption properties. The main purpose of the work was to find a suitable spectroscopic descriptor accounting for the different imprinting process in three homogeneous polymeric networks. The polymers were characterized by studying the kinetics of the cross-polarization process. This approach is based on variable contact time CP-MAS spectra, referred to as VCP-MAS. The analysis of the VCP-MAS spectra provided two relaxation parameters: TCH (the CP time constant) and T1ρ (the proton spin-lattice relaxation time in the rotating frame). The results and the analysis presented in the paper pointed out that TCH is sensitive to the imprinting process, showing variations related to the toluene/cyclodextrin molar ratio used for the preparation of the materials. Conversely, the observed values of T1ρ did not show dramatic variations with the imprinting protocol, but rather confirmed that the three polymers are morphologically similar. Thus the combined use of TCH and T1ρ can be helpful for the characterization and fine tuning of imprinted polymeric matrices

Calcium acamprosate: a triclinic polymorph

The title compound, poly[bis­(μ3-4-acetamido­propane­sulfon­ato)­calcium], [Ca(C5H10NO4S)2]n, is a triclinic polymorph of the previously reported monoclinic structure [Toffoli et al. (1988 ▶). Acta Cryst. C44, 1493–1494]. The triclinic modification was found to have an all-trans configuration of the acetamido­propane chain, in contrast with the monoclinic polymorph which shows an angle of 74.66 (8)° between the S—C—C—C chain plane and that of the amide group. The Ca2+ cation is situated on an inversion centre and is hexa­coordinated by six O atoms belonging to different anions in a distorted octa­hedral geometry. This arrangement leads to a layered structure parallel to (011). The layers are held together by N—H⋯O hydrogen bonds and by short C—H⋯O inter­actions, both involving the sulfonate O atoms not coordinated to the Ca2+ cations. The structure was determined from a crystal twinned by non-merohedry [twin law (00, 00, −0.335 −0.85 1), with a fractional contribution of the minor twin domain of 46.7 (1)%]

Transport properties of ibuprofen encapsulated in cyclodextrin nanosponge hydrogels: A proton HR-MAS NMR spectroscopy study

The chemical cross-linking of β-cyclodextrin (β-CD) with ethylenediaminetetraacetic dianhydride (EDTA) led to branched polymers referred to as cyclodextrin nanosponges (CDNSEDTA). Two different preparations are described with 1:4 and 1:8 CD-EDTA molar ratios. The corresponding cross-linked polymers were contacted with 0.27 M aqueous solution of ibuprofen sodium salt (IP) leading to homogeneous, colorless, drug loaded hydrogels. The systems were characterized by high resolution magic angle spinning (HR-MAS) NMR spectroscopy. Pulsed field gradient spin echo (PGSE) NMR spectroscopy was used to determine the mean square displacement (MSD) of IP inside the polymeric gel at different observation times td. The data were further processed in order to study the time dependence of MSD: MSD = f(td). The proposed methodology is useful to characterize the different diffusion regimes that, in principle, the solute may experience inside the hydrogel, namely normal or anomalous diffusion. The full protocols including the polymer preparation and purification, the obtainment of drug-loaded hydrogels, the NMR sample preparation, the measurement of MSD by HR-MAS NMR spectroscopy and the final data processing to achieve the time dependence of MSD are here reported and discussed. The presented experiments represent a paradigmatic case and the data are discussed in terms of innovative approach to the characterization of the transport properties of an encapsulated guest within a polymeric host of potential application for drug delivery

Insights into the Complexation Mechanism of a Promising Lipophilic PyTri Ligand for Actinide Partitioning from Spent Nuclear Fuel

The challenging issue of spent nuclear fuel (SNF) management is being tackled by developing advanced technologies that point to reduce environmental footprint, long-term radiotoxicity, volumes and residual heat of the final waste, and to increase the proliferation resistance. The advanced recycling strategy provides several promising processes for a safer reprocessing of SNF. Advanced hydrometallurgical processes can extract minor actinides directly from Plutonium and Uranium Reduction Extraction raffinate by using selective hydrophilic and lipophilic ligands. This research is focused on a recently developed N-heterocyclic selective lipophilic ligand for actinides separation to be exploited in advanced Selective ActiNide EXtraction (SANEX)- like processes: 2,6-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)pyridine (PyTri-Ethyl-Hexyl-PTEH). The formation and stability of metal−ligand complexes have been investigated by different techniques. Preliminary studies carried out by electrospray ionization mass spectrometry (ESI−MS) analysis enabled to qualitatively explore the PTEH complexes with La(III) and Eu(III) ions as representatives of lanthanides. Time-resolved laser fluorescence spectroscopy (TRLFS) experiments have been carried out to determine the ligand stability constants with Cm(III) and Eu(III) and to better investigate the ligand complexes involved in the extraction process. The contribution of a 1:3 M/L complex, barely identified by ESI−MS analyses, was confirmed as the dominant species by TRLFS experiments. To shed light on ligand selectivity toward actinides over lanthanides, NMR investigations have been performed on PTEH complexes with Lu(III) and Am(III) ions, thereby showing significant differences in chemical shifts of the coordinating nitrogen atoms providing proof of a different bond nature between actinides and lanthanides. These scientific achievements encourage consideration of this PyTri ligand for a potential large-scale implementation

Unraveling the degradation mechanism in FIrpic based Blue OLEDs: II. Trap and detect molecules at the interfaces

The impact of organic light emitting diodes (OLEDs) in modern life is witnessed by their wide employment in full-color, energy-saving, flat panel displays and smart-screens; a bright future is likewise expected in the field of solid state lighting. Cyclometalated iridium complexes are the most used phosphorescent emitters in OLEDs due to their widely tunable photophysical properties and their versatile synthesis. Blue-emitting OLEDs, suffer from intrinsic instability issues hampering their long term stability. Backed by computational studies, in this work we studied the sky-blue emitter FIrpic in both ex-situ and in-situ degradation experiments combining complementary, mutually independent, experiments including chemical metathesis reactions, in liquid phase and solid state, thermal and spectroscopic studies and LC-MS investigations. We developed a straightforward protocol to evaluate the degradation pathways in iridium complexes, finding that FIrpic degrades through the loss of the picolinate ancillary ligand. The resulting iridium fragment was than efficiently trapped "in-situ" as BPhen derivative 1. This process is found to be well mirrored when a suitably engineered, FIrpic-based, OLED is operated and aged. In this paper we (i) describe how it is possible to effectively study OLED materials with a small set of readily accessible experiments and (ii) evidence the central role of host matrix in trapping experiments.Comment: 13 pages, 6 figure

Enzymatic Baeyer-Villiger oxidation of steroids with cyclopentadecanone monooxygenase

Peer reviewed: YesNRC publication: Ye

Identifying priority areas for spatial management of mixed fisheries using ensemble of multi‐species distribution models

Spatial fisheries management is widely used to reduce overfishing, rebuild stocks, and protect biodiversity. However, the effectiveness and optimization of spatial measures depend on accurately identifying ecologically meaningful areas, which can be difficult in mixed fisheries. To apply a method generally to a range of target species, we devel- oped an ensemble of species distribution models (e-SDM) that combines general ad- ditive models, generalized linear mixed models, random forest, and gradient-boosting machine methods in a training and testing protocol. The e-SDM was used to integrate density indices from two scientific bottom trawl surveys with the geopositional data, relevant oceanographic variables from the three-dimensional physical-biogeochemi- cal operational model, and fishing effort from the vessel monitoring system. The de- termined best distributions for juveniles and adults are used to determine hot spots of aggregation based on single or multiple target species. We applied e-SDM to juvenile and adult stages of 10 marine demersal species representing 60% of the total demer- sal landings in the central areas of the Mediterranean Sea. Using the e-SDM results, hot spots of aggregation and grounds potentially more selective were identified for each species and for the target species group of otter trawl and beam trawl fisheries. The results confirm the ecological appropriateness of existing fishery restriction areas and support the identification of locations for new spatial management measures

Identifying priority areas for spatial management of mixed fisheries using ensemble of multi‐species distribution models

Spatial fisheries management is widely used to reduce overfishing, rebuild stocks, and protect biodiversity. However, the effectiveness and optimization of spatial measures depend on accurately identifying ecologically meaningful areas, which can be difficult in mixed fisheries. To apply a method generally to a range of target species, we developed an ensemble of species distribution models (e-SDM) that combines general additive models, generalized linear mixed models, random forest, and gradient-boosting machine methods in a training and testing protocol. The e-SDM was used to integrate density indices from two scientific bottom trawl surveys with the geopositional data, relevant oceanographic variables from the three-dimensional physical-biogeochemical operational model, and fishing effort from the vessel monitoring system. The determined best distributions for juveniles and adults are used to determine hot spots of aggregation based on single or multiple target species. We applied e-SDM to juvenile and adult stages of 10 marine demersal species representing 60% of the total demersal landings in the central areas of the Mediterranean Sea. Using the e-SDM results, hot spots of aggregation and grounds potentially more selective were identified for each species and for the target species group of otter trawl and beam trawl fisheries. The results confirm the ecological appropriateness of existing fishery restriction areas and support the identification of locations for new spatial management measures