Photochemical synthesis of α-oxygenated benzothiophenedioxides

The photochemical synthesis of 1-hydroxy[b]benzo-1,3-dihydrothiophene-2,2-dioxides from orthomethylbenzaldehyde and its analogs is described. Some of the chemistry of these α-oxygenated sulfones, including exchange of the 1-hydroxy group with various alkoxy groups and the thermal reversion of these oxygenated derivatives to trappable 1-alkoxy-substituted o-quinodimethanes has been investigated.     

Controlled process for polymer micromachining using designed pulse trains of a UV solid state laser

A flexible workstation equipped with a solid state laser operating at 266 nm wavelength was used to machine holes in polyethylene terephthalate, polyimide and polycarbonate. An optical pulse picker was employed to reduce the high repetition rates of the laser, while a breakthrough sensor was used to avoid over-drilling of through holes. For each material, different repetition rates and designed pulse trains were tested to improve feature quality and process efficiency. Although the three polymers had very different reactions at this wavelength they all showed an improvement in feature quality with decreasing repetition rate due to a reduction in thermal effects. Up to 10 kHz the average depth per pulse remained unchanged and afterwards a slight increase was observed but this was accompanied by large uncertainties. Bursts of pulses at 40 kHz inserted inside the low repetition rate pulse train reduced the drilling time and the amount of debris redeposited without affecting the feature quality. It was found that a number of cleaning pulses after perforation eliminates the heat affected zone around exits. Holes with entrance diameters below 20 μm and exit diameters as small as 2 μm were obtained with high repeatability.     

Comprehensive and High‐Throughput Exploration of Chemical Space Using Broadband 19F NMR‐Based Screening

Fragment‐based lead discovery has become a fundamental approach to identify ligands that efficiently interact with disease‐relevant targets. Among the numerous screening techniques, fluorine‐detected NMR has gained popularity owing to its high sensitivity, robustness, and ease of use. To effectively explore chemical space, a universal NMR experiment, a rationally designed fragment library, and a sample composition optimized for a maximal number of compounds and minimal measurement time are required. Here, we introduce a comprehensive method that enabled the efficient assembly of a high‐quality and diverse library containing nearly 4000 fragments and screening for target‐specific binders within days. At the core of the approach is a novel broadband relaxation‐edited NMR experiment that covers the entire chemical shift range of drug‐like ¹⁹F motifs in a single measurement. Our approach facilitates the identification of diverse binders and the fast ligandability assessment of new targets.     

Histidine-based salt as an ionic tag for proline: application in enantioselective cross aldol reaction in ionic liquids

Abstract

A new ionic-liquid supported aminocatalyst was synthesized by the peptide coupling of proline on a ring-dialkylated histidine salt serving as ionic support. The catalytic activity and enantioselectivity of the obtained dipeptide catalyst were evaluated in the enantioselective cross aldol reaction of substituted benzaldehyde derivatives with acetone, in organic solvent and in ionic liquids, and both were found to be significantly higher in ionic liquids than in organic solvents. The [bmim][OTf] – catalyst system could be recycled for up to five cycles without any loss in activity.     

Rapid Synthesis of Zwitterionic Phosphonium Benzoates by a Three‐Component Coupling Involving Phosphines,Arynes and CO2

A mild and easy to perform multicomponent coupling involving phosphines, arynes generated from 2‐(trimethylsilyl)aryl triflates, and CO₂ allowing the transition‐metal‐free synthesis of zwitterionic phosphonium benzoates has been developed. The reaction proceeds via the generation of 1 : 1 zwitterionic intermediates from phosphines and arynes followed by the interception with CO₂ to deliver the carboxylates in moderate to good yields instead of the anticipated benzooxaphosphol‐3(1H)‐ones.     

Structural development of mercaptophenol self-assembled monolayers and the overlying mineral phase during templated CaCO3 crystallization from a transient amorphous film

Formation of biomineral structures is increasingly attributed to directed growth of a mineral phase from an amorphous precursor on an organic matrix. While many in vitro studies have used calcite formation on organothiol self-assembled monolayers (SAMs) as a model system to investigate this process, they have generally focused on the stability of amorphous calcium carbonate (ACC) or maximizing control over the order of the final mineral phase. Little is known about the early stages of mineral formation, particularly the structural evolution of the SAM and mineral. Here we use near-edge X-ray absorption spectroscopy (NEXAFS), photoemission spectroscopy (PES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to address this gap in knowledge by examining the changes in order and bonding of mercaptophenol (MP) SAMs on Au(111) during the initial stages of mineral formation as well as the mechanism of ACC to calcite transformation during template-directed crystallization. We demonstrate that formation of ACC on the MP SAMs brings about a profound change in the morphology of the monolayers: although the as-prepared MP SAMs are composed of monomers with well-defined orientations, precipitation of the amorphous mineral phase results in substantial structural disorder within the monolayers. Significantly, a preferential face of nucleation is observed for crystallization of calcite from ACC on the SAM surfaces despite this static disorder.     

Porphyrin-diones and porphyrin-tetraones: reversible redox units being localized within the porphyrin macrocycle and their effect on tautomerism

Porphyrin-2,3-diones and porphyrin-2,3,7,8- and porphyrin-2,3,12,13-tetraones were shown to have a redox-active unit that can function independently of the macrocycle at large. Electroreduction of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin-2,3-diones [(P-dione)M] and the corresponding -2,3,12,13-tetraones [L-(P-tetraone)M] and -2,3,7,8-tetraones [C-(P-tetraone)M], where M = 2H, CuII, ZnII, NiII, and PdII was investigated and the products were characterized by ESR and thin-layer UV-visible spectroelectrochemistry. Electrochemical and spectroelectrochemical data show that the first two reductions of the porphyrin-diones and the first three reductions of the porphyrin-tetraones occur at the dione units. This was confirmed by ESR spectra of first reduction products which show that the electron spin is totally localized on a semidione unit, independent of the central metal ion and of the number and location of dione units. ESR spectra of the radical anions derived from free-base porphyrin-2,3-dione [(P-dione)2H] and porphyrin-2,3,12,13-tetraone [L-(P-tetraone)2H] confirm the trans-arrangement of the two inner protons and their location on nonsubstituted pyrrolic rings, thereby maintaining an 18-atom 18-pi electron bacteriochlorin-like aromatic delocalization pathway. The redox unit is not similarly isolated in the corner free-base porphyrin-2,3,7,8-tetraone [C-(P-tetraone)2H]. A one-electron reduction of C-(P-tetraone)2H leads to the formation of a tautomer with trans inner hydrogens with one residing on the N of the ring with the reduced unit as the only detectable product. This process is favorable because it creates a more delocalized 18-atom 18-pi electron aromatic pathway. This result is consistent with the measured redox potentials which show the first reduction of C-(P-tetraone)2H to be substantially easier than (P-dione)2H or L-(P-tetraone)2H.