Pyrolysis of Alkanes: A Computational Approach.

In this study, we investigate the kinetic and thermodynamic aspects of thermal cracking reactions of short paraffin chains by density functional theory (DFT) methods. The thermal cracking reactions have been modeled for a series of shorter unbranched alkanes at 673 K by following a free-radical mechanism. Benchmark calculations have been carried out with different functionals (B3LYP, M06-2X, PBE0, BMK, B3PW91) and basis sets (6-31G(d,p), 6-311+G(d,p)) to determine the most suitable DFT method, and the results were compared to the available experimental data. Computations were also performed at the CBS-QB3 level to evaluate the accuracy of the DFT method. The thermodynamic and kinetic properties of the initiation, hydrogen atom transfer (HAT), and decomposition (ß-scission) reactions are intensely discussed to better understand the trends in product distributions at high temperatures. Evans-Polanyi (EP) relations have been used to build a linear relationship between the enthalpy of reactions and their activation energies; this process may be useful for the determination of the kinetic parameters of longer paraffin chains as well. Finally, the preexponential factors of short-chain paraffin have been calculated and classified based on the identity of the radicalic products. The latter, together with the activation energies derived from the EP relations can be used safely for the prediction of the rate constants for long paraffin chains.

Array-based sensing of purine derivatives with fluorescent dyes.

Natural and synthetic purine derivatives such as caffeine, theophylline, 6-mercaptopurine and 8-chlorotheophylline are important drugs. Due to the structural similarity of these compounds, it is intrinsically difficult to prepare chemosensors for their selective optical detection. Here, we describe a sensor array which can be used to differentiate pharmacologically important purine derivatives with good accuracy. The array is composed of four polysufonated fluorescent dyes, all of which can bind purines viaπ-stacking interactions. The complexation of the analytes results in partial quenching of the fluorescence. The fluorescence response of the four dyes provides a characteristic signal pattern, enabling the identification of thirteen purine derivatives at low millimolar concentration. Furthermore, it is possible to use the array for obtaining information about the quantity and purity of purine samples.

Correction: Pattern-based sensing of aminoglycosides with fluorescent amphiphiles.

[This corrects the article DOI: 10.1039/C4SC00737A.].

Selective detection of Al(3+) and citric acid with a fluorescent amphiphile.

An amphiphilic fluorescent dye with a disulfonated BODIPY head group and a heptadecyl side chain is described. In buffered aqueous solution, the amphiphile can form aggregates with a critical micelle concentration of ∼20 µM. The aggregation of the dye is associated with a strong quenching of its fluorescence. Al(3+) promotes aggregation, whereas other metal ions have a much smaller effect, in particular when histidine is added as masking agent. The Al(3+)-induced aggregation can be used to sense Al(3+) in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that a dye-Al(3+) mixture can be used as a sensing ensemble for the detection of citric acid. The assay allows quantifying the citric acid content of commercial beverages such as energy drinks.

Atropisomeric dyes: axial chirality in orthogonal BODIPY oligomers.

A dissymmetrically substituted orthogonal BODIPY dimer and an orthogonal BODIPY trimer exist as two stable conformers, which are in fact atropisomeric enantiomers. The racemic mixture can be separated by HPLC using a chiral stationary phase. These enantiomeric derivatives hold great potential as chiral agents in asymmetric synthesis, fluorogenic/chromogenic sensing, and biological applications.

Tetrastyryl-BODIPY-based dendritic light harvester and estimation of energy transfer efficiency.

Versatile BODIPY dyes can be transformed into bright near-IR-emitting fluorophores by quadruple styryl substitutions. When clickable functionalities on the styryl moieties are inserted, an efficient synthesis of a light harvester is possible. In addition, clear spectral evidence is presented showing that, in dendritic light harvesters, calculations commonly based on quantum yield or emission lifetime changes of the donor are bound to yield large overestimations of energy transfer efficiency.

Fluorescence sensing of spermine with a frustrated amphiphile.

A charge-frustrated amphiphile composed of a pyrene-1,3,6-trisulfonate head group and an eicosane side chain can be used as a fluorescence chemosensor for spermine. The sensor allows the detection of spermine down to the nanomolar concentration range with good selectivity over closely related biogenic amines such as spermidine.

From virtual to physical: integration of chemical logic gates.

Integration by parts: advanced information processing at the molecular level requires integrated logic gates, which has to date been possible only virtually. Now, two independently working AND molecular logic gates are brought together by "click" chemistry to form integrated logic gates which respond exactly as predicted from such an integration scheme.