Asymmetric Pd(II)-Catalyzed C−O,C−N,C−C Bond Formation Using Alkenes as Substrates: Insight into Recent Enantioselective Developments

This Review summarizes the advances in the catalytic enantioselective mono- and difunctionalization of alkenes, highlighting the fundamental role of ligands. Several types of asymmetric reactions have been developed involving different bonds formation, C−O, C−N and C−C, highlighting the urgency to go ahead in the search for new ligands and synthetic methodologies in order to improve the control over the reaction selectivity and activity and thus, to increase the applications in the synthesis of heterocyclic scaffolds and biologically active compounds. The Review is organized into paragraphs, which discuss the type of bond formed during the nucleopalladation, C−O, C−N, C−C bonds, and the type of reaction involved.     

Miniaturized diode laser module emitting green light at 532 nm with a power of more than 900 mW for next-generation holographic displays

We present a micro-integrated laser module based on an amplified diode laser and second harmonic generation which is a promising candidate for a green light source in next-generation 3D holographic displays. The light emitted by the amplified laser has a wavelength of 1064 nm, reaches a power up to 8.2 W and has a long coherence length of >400 m. For second harmonic generation, we tested two geometries of periodically poled lithium niobate crystals in single pass: a bulk crystal and a planar waveguide crystal. With the planar waveguide crystal, we achieve an output power >900 mW and a coherence length >20 m at a wavelength of 532 nm.     

Iridoidic pattern in endemic Sardinian plants: the case of Galium species

The monoterpenoid fractions of three endemic Galium ssp. (Rubiaceae) from Sardinia Island were examined and compared with the iridoidic pattern yet known in Galium species. This comparison evidenced theirs endemic characters. In particular, in G.corsicum and in G. glaucophyllum loganic acid was isolated and identified for the first time in Galium genus. In G. schmidii a rare iridoid is present, 10-hydroxy-loganin, whose presence in this genus was evidenced only in G. mollugo and loganin isolated for the first time.     

Two‐Dimensional Infrared Spectroscopy Reveals the Structure of an Evans Auxiliary Derivative and Its SnCl4 Lewis Acid Complex

Determining the structure of reactive intermediates is the key to understanding reaction mechanisms. To access these structures, a method combining structural sensitivity and high time resolution is required. Here ultrafast polarization‐dependent two‐dimensional infrared (P2D‐IR) spectroscopy is shown to be an excellent complement to commonly used methods such as one‐dimensional IR and multidimensional NMR spectroscopy for investigating intermediates. P2D‐IR spectroscopy allows structure determination by measuring the angles between vibrational transition dipole moments. The high time resolution makes P2D‐IR spectroscopy an attractive method for structure determination in the presence of fast exchange and for short‐lived intermediates. The ubiquity of vibrations in molecules ensures broad applicability of the method, particularly in cases in which NMR spectroscopy is challenging due to a low density of active nuclei. Here we illustrate the strengths of P2D‐IR by determining the conformation of a Diels–Alder dienophile that carries the Evans auxiliary and its conformational change induced by the complexation with the Lewis acid SnCl₄, which is a catalyst for stereoselective Diels–Alder reactions. We show that P2D‐IR in combination with DFT computations can discriminate between the various conformers of the free dienophile N‐crotonyloxazolidinone that have been debated before, proving antiperiplanar orientation of the carbonyl groups and s‐cis conformation of the crotonyl moiety. P2D‐IR unequivocally identifies the coordination and conformation in the catalyst–substrate complex with SnCl₄, even in the presence of exchange that is fast on the NMR time scale. It resolves a chelate with the carbonyl orientation flipped to synperiplanar and s‐cis crotonyl configuration as the main species. This work sets the stage for future studies of other catalyst–substrate complexes and intermediates using a combination of P2D‐IR spectroscopy and DFT computations.     

Identification and quantification of six major α-dicarbonyl process contaminants in high-fructose corn syrup

High-fructose corn syrup (HFCS) is a widely used liquid sweetener produced from corn starch by hydrolysis and partial isomerization of glucose to fructose. During these processing steps, sugars can be considerably degraded, leading, for example, to the formation of reactive α-dicarbonyl compounds (α-DCs). The present study performed targeted screening to identify the major α-DCs in HFCS. For this purpose, α-DCs were selectively converted with o-phenylendiamine to the corresponding quinoxaline derivatives, which were analyzed by liquid chromatography with hyphenated diode array-tandem mass spectrometry (LC-DAD-MS/MS) detection. 3-Deoxy-D-erythro-hexos-2-ulose (3-deoxyglucosone), D-lyxo-hexos-2-ulose (glucosone), 3-deoxy-D-threo-hexos-2-ulose (3-deoxygalactosone), 1-deoxy-D-erythro-hexos-2,3-diulose (1-deoxyglucosone), 3,4-dideoxyglucosone-3-ene, methylglyoxal, and glyoxal were identified by enhanced mass spectra as well as MS/MS product ion spectra using the synthesized standards as reference. Addition of diethylene triamine pentaacetic acid and adjustment of the derivatization conditions ensured complete derivatization without de novo formation for all identified α-DCs in HFCS matrix except for glyoxal. Subsequently, a ultra-high performance LC-DAD-MS/MS method was established to quantify 3-deoxyglucosone, glucosone, 3-deoxygalactosone, 1-deoxyglucosone, 3,4-dideoxyglucosone-3-ene, and methylglyoxal in HFCS. Depending on the α-DC compound and concentration, the recovery ranged between 89.2% and 105.8% with a relative standard deviation between 1.9% and 6.5%. Subsequently, the α-DC profiles of 14 commercial HFCS samples were recorded. 3-Deoxyglucosone was identified as the major α-DC with concentrations up to 730 μg/mL HFCS. The total α-DC content ranged from 293 μg/mL to 1,130 μg/mL HFCS. Significantly different α-DC levels were not detected between different HFCS specifications, but between samples of various manufacturers indicating that the α-DC load is influenced by the production procedures.     

Hybrid UV-cured organic–inorganic IPNs

Hybrid organic–inorganic UV-cured coatings based on interpenetrating polymer networks (IPN) were prepared starting by an equimolar methacrylate-epoxy UV-curable mixture (bisphenol-A-diglycidyl dimethacrylate/bisphenol-A-diglycidyl ether, abbreviated as BisGMA/BADGE), in the presence of tetrafunctional silane monomer tetrakis(methacryloyloxy-ethoxy)silane (TetMESi) as inorganic precursor. The photocuring kinetics of the BisGMA/BADGE IPN monomer mixture were strongly affected by the order of the cure of the individual components. Addition of TetMESi resulted in higher degrees of reaction. DMTA of the BisGMA/BADGE IPN suggest a two phase structure. The rubbery modulus of the hydrolysed BisGMA/BADGE/TetMESi systems increased as the level of TetMESi was raised in the formulation due primarily to the significant reinforcing effect of the nano-silica particles. TGA of the BisGMA/BADGE IPN showed three degradation stages with no residual char but the hydrolysed BisGMA/BADGE/TetMESi systems formed a carbonaceous silica char which increased in mass as the level of TetMESi was raised. The two phase morphology of the BisGMA/BADGE IPN was confirmed by FE-SEM analysis. For IPNs prepared with TetMESi, SiO₂ particles are evident in the FE-SEM image and have diameters in the nanometric size range.     

Intramolecular 1,8-hydrogen atom transfer reactions in disaccharide systems containing furanose units

A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4-C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric d-furanoses. d-xylo- and d-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas d-arabino- and d-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively.     

Reflectometric interference spectroscopy (RIfS) as a new tool to measure in the complex matrix milk at low analyte concentration

Measurements in complex matrices like milk still present a challenge in biosensor development. This is especially important when using a label-free detection method or when measuring low analyte concentrations. The direct optical method reflectometric interference spectroscopy (RIfS) was used for investigating matrix effects in immunoassay development. Furthermore, approaches to reduce these effects have been established. As a model system, the hormone testosterone has been chosen because this immunoassay has been well characterized in buffer. In a first step, the immunoassay for the detection of testosterone in buffer was improved beyond former published results. Therefore, the sensor surface was optimized, resulting in a fivefold lower limit of detection (70.2 ng L⁻¹) and limit of quantification (130.0 ng L⁻¹). Additionally, the assay time could be reduced to 15 min. Consequently, we used this improved assay to investigate matrix effects of whole pasteurized bovine milk. To minimize these effects, the surface chemistry was adapted and a suitable evaluation method was established, reducing the effects of Tyndall scattering and nonspecific binding to the sensor surface. These improvements allow for very reliable quantitative measurements in milk. The assay developed required no sample pretreatment and allowed for the regeneration of the sensor surface so that calibration could be performed on one chip. The calibration in milk (3.5% fat) resulted in a limit of detection of 94.4 ng L⁻¹ and a limit of quantification of 229.3 ng L⁻¹. Furthermore, recovery rates between 70% and 120% could be obtained. Thus, for the first time, an analyte in the matrix milk was successfully quantified with RIfS at low concentrations.     

Excitonic luminescence of hemiporphyrazines

Metal-free hemiporphyrazine (HpH(2)) is a notoriously insoluble material possessing interesting photophysical properties. Here we report the synthesis, structure, and photophysical properties of an octahedral zinc trans-ditriflate hemiporphyrazine complex "HpH(2)Zn(OTf)(2)" that contains a neutral hemiporphyrazine ligand. The photophysical properties of hemiporphyrazine are largely unaffected by introduction of zinc(II) triflate, but a dramatic increase in solubility is observed. HpH(2)Zn(OTf)(2) therefore provides a convenient model system to evaluate the impact of aggregation on the photophysical properties of hemiporphyrazine. Soluble aggregates and crystalline materials containing planar hemiporphyrazines exhibit relatively strong absorbance of visible light (450-600 nm) and red luminescence (600-700 nm). Hemiporphyrazine monohydrate (HpH(2)·H(2)O), in contrast, has a nonplanar "saddle-shaped" conformation that exhibits very little absorbance of visible light in solution or in the solid state. Upon photoexcitation at 380 nm, HpH(2)Zn(OTf)(2) and HpH(2) exhibit multiwavelength emissions centered at 450 and 650 nm. Emissions at 450 nm are highly anisotropic, while emissions at 650 nm are fully depolarized with respect to a plane-polarized excitation source. Taken together, our results suggest that excitonic coupling of aggregated and crystalline hemiporphyrazines results in increased absorbance and emission of visible light from S(0) ? S(1) transitions that are usually symmetry forbidden in isolated species. In contrast to previously proposed theories involving excited-state intramolecular proton transfer, we propose that the multiple-wavelength luminescent emissions of HpH(2)Zn(OTf)(2) and HpH(2) are due to emissive S(1) and S(2) states in aggregated and crystalline hemiporphyrazines. These results may provide a better understanding of the nonlinear optical properties of these materials in solution and in the solid state.