Radical cation formation in characterization of novel C3-symmetric disks and their precursors by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Four C3-symmetrical tris(dipeptide) disks and their precursors were characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). The C3-symmetrical disks were based on a benzene-1,3,5-triscarboxamide core extended by oligopeptides with trialkoxyanilide tails. The results indicate that MALDI TOF MS is a powerful and straightforward analytical technique for characterizing C3-symmetrical disks and their precursors. Clear (pseudo)-molecular ion peaks could readily be identified. It is remarkable that strong radical ion signals were observed for all the compounds, including the anilines that were expected to be protonated prior to laser irradiation using acidic MALDI matrixes. Possible mechanisms for radical ion formation were investigated with the employment of radical scavengers, with various matrixes and with direct laser desorption/ionization (LDI). Most likely the radicals are formed by losing one electron from the aniline nitrogen and stabilized by conjugation through the phenyl ring. It appears that direct photo/thermal ionization of analytes is an important route for the radical ion formation of the compounds with trialkoxy aniline/anilide groups.     

A group electronegativity equalization scheme including external potential effects

By calculating the electron affinity and ionization energy of different functional groups, CCSD electronegativity values are obtained, which implicitly account for the effect of the molecular environment. This latter is approximated using a chemically justified point charge model. On the basis of Sanderson's electronegativity equalization principle, this approach is shown to lead to reliable "group in molecule" electronegativities. Using a slight adjustment of the modeled environment and first-order principles, an electronegativity equalization scheme is obtained, which implicitly accounts for the major part of the external potential effect. This scheme can be applied in a predictive manner to estimate the charge transfer between two functional groups, without having to rely on cumbersome calibrations. A very satisfactory correlation is obtained between these charge transfers and those obtained from an ab initio calculation of the entire molecule.     

Chiral poly(ureidophthalimide) foldamers in water

Poly(ureidophthalimide)s decorated with hydrophilic side chains, that ensure solubility in aqueous media, have been synthesized and characterized by UV/Vis and circular dichroism (CD) spectroscopy. Temperature and concentration dependent CD measurements in water have revealed an almost temperature and concentration independent Cotton effect, indicative for a strong intramolecular organization. Similar studies in THF demonstrate the dynamic nature of the secondary architecture, a characteristic of foldamers. In addition, the bisignated Cotton effect in water is opposite in sign to that in THF, suggestive for a solvent-dependent preference for one helical handedness. Mixing experiments prove the dominance of water in determining the handedness of the helical architecture. The solvent allows for control over the helical architecture and thus governs the supramolecular synthesis.     

Analysing steady-state simulation output using vector autoregressive processes with exogenous variables

A simulation study often requires computation of a point estimate and confidence region for the steady-state mean of a stochastic output process. The literature offers a variety of statistical techniques, including replication/deletion, the batch-means method, and spectrum analysis. We present a new multivariate output-analysis technique that is based on the general autoregressive time-series model with exogenous variables to set up a joint confidence region for the steady-state mean. We demonstrate our technique by an extensive computational experiment, and show that it performs at least as well as other output-analysis techniques, without having some of their drawbacks.     

Taming of Furfurylidenes by Chiral Bismuth-Rhodium Paddlewheel Catalysts. Preparation and Functionalization of Optically Active 1,1-Disubstituted (Trifluoromethyl)cyclopropanes

Although 2-furyl-carbenes (furfurylidenes) are prone to instantaneous electrocyclic ring opening, chiral [BiRh]-paddlewheel complexes empowered by London dispersion allow (trifluoromethyl)furfurylidene metal complexes to be generated from a bench-stable triftosylhydrazone precursor. These reactive intermediates engage in asymmetric [2+1] cycloadditions and hence open entry into valuable trifluoromethylated cyclopropane or -cyclopropene derivatives in optically active form, which are important building blocks for medicinal chemistry but difficult to make otherwise.     

Metal-Free Electrocatalytic Diacetoxylation of Alkenes

1,2-Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2-dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom-efficient reactant. This transition metal-free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst-free conditions. The synthetic method is extensively investigated with cyclic voltammetry.