Tuning energy transfer in switchable donor-acceptor systems

The synthesis and characterisation of a coumarin-dithienylcyclopentene-coumarin symmetric triad (CSC) and a perylene bisimide-dithienylcyclopentene-coumarin asymmetric triad (PSC) are reported. In both triads the switching function of the photochromic dithienylcyclopentene unit is retained. For CSC an overall 50% quenching of the coumarin fluorescence is observed upon ring-closure of the dithienylcyclopentene component, which, taken together with the low PSS (<70%), indicates that energy transfer quenching of the coumarin component by the dithienylcyclopentene in the closed state is efficient. Upon ring opening of the dithienylcyclopentene unit the coumarin emission is restored fully. The PSC triad shows efficient energy transfer from the coumarin to the perylene bisimide unit when the dithienylcyclopentene unit is in the open state. When the dithienylcyclopentene is in the closed (PSS) state a 60% decrease in sensitized perylene bisimide emission intensity is observed due to competitive quenching of the coumarin excited state and partial quenching of the perylene excited state by the closed dithienylcyclopentene unit. This modulation of energy transfer is reversible over several cycles for both the symmetric and asymmetric tri-component systems.     

Counterion effect on the spin-transition properties of the cation [Fe(btzx)3]2+ (btzx=m-Xylylenebis(tetrazole))

The influence of the counteranion on the structure and the spin-transition properties of original 1D bis(tetrazole) Fe(II) systems, namely [Fe(btzx)(3)]X(2) (X=PF(6) (-) (1), CF(3)SO(3) (-) (2) and ClO(4) (-) (3); btzx=m-xylylenebis(tetrazole)) is studied. The X-ray crystal structures of compounds 1 and 2 are described in detail. These structures present a solvent molecule encapsulated within pockets formed by btzx ligands along the 1D coordination chains. Compound 2 is shown to be the first structurally characterised alternating HS-LS 1D spin-transition system (HS=high spin, LS=low spin). The magnetic susceptibility measurements of all three compounds are compared. The degree of completion and the transition temperature are both drastically influenced by the counterion used, while surprisingly, the cooperative nature of the transition is not affected by the choice of counterion. Compounds 1 and 2 are further studied by M?ssbauer spectroscopy and their distinct LIESST properties are compared.     

Quantitative prediction of amyloid fibril growth of short peptides from simulations: calculating association constants to dissect side chain importance

Quantitative prediction of the fibril growth properties of different peptides is conducted with a molecular dynamics approach. Association constants of small peptides used as a model for amyloid formation are calculated, and the results show very good agreement with experiments. Also the free-energy differences associated with two important interactions that characterize fibril growth, namely cross-beta-sheet and lateral interactions, are obtained. These two interactions show different dependencies on the physicochemical properties of the side chains, explaining the variation in fibril morphologies between different peptides.     

Stereoselective and efficient synthesis of (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-ol

[reaction: see text] Two short and efficient synthesis routes have been developed for bis-THF-alcohol 2, a key building block of the investigational HIV protease inhibitor TMC114 (1). Using S-2,3-O-isopropylideneglyceraldehyde (4) as the source of chirality, both routes are based on a diastereoselective Michael addition of nitromethane to give predominantly the syn congeners 6 followed by a Nef oxidation and cyclization to afford lactone acetals 8, which are reduced and cyclized to give 2.     

Possibilities and limitations of quadrupole mass spectrometric detector in fast gas chromatography

In this work the application and limitations of a common bench top quadrupole mass spectrometer was evaluated for the qualitative and quantitative measurement of n-alkanes and pesticides of a wide range of volatilities and polarities with fast GC separations using 0.15 mm I.D. narrow-bore capillary columns. It was found that the spectra acquisition rate has a great impact on sensitivity (peak areas, peak shapes and S/N ratios). The quality of the obtained spectra is not significantly influenced in the full scan monitoring mode for the fastest scan rates. For quantitative analysis a selected ion monitoring mode is able to acquire the sufficient number of data-points for the proper peak shape reconstruction and good repeatability of peak areas measurements expressed by RSD (< 5%) for all tested dwell times shorter than 75 ms. However, for shorter dwell times, S/N ratio is lower, while peak areas are not influenced.     

Determining the intermolecular structure in the S0 and S1 states of the phenol dimer by rotationally resolved electronic spectroscopy.

The rotationally resolved UV spectra of the electronic origins of five isotopomers of the phenol dimer have been measured. The complex spectra are analyzed using a fitting strategy based on a genetic algorithm. The intermolecular geometry parameters have been determined from the inertial parameters for both electronic states and compared to the results of ab initio calculations. In the electronic ground state, a larger hydrogen-bond length than in the ab initio calculations is found together with a smaller tilt angle of the aromatic rings, which shows a more pronounced dispersion interaction. In the electronically excited state, the hydrogen-bond length decreases, as has been found for other hydrogen-bonded clusters of phenol, and the two aromatic rings are tilted less toward each other.     

A comprehensive model for simulating the interaction of water with solid surfaces in fire suppression environments

A novel framework for sprinkler-based fire suppression modeling has been developed that includes detailed interaction of water with solid surfaces. This model builds on the fire growth model (FireFOAM) previously developed at FM Global. The fundamental film-transport equations for mass continuity, momentum, and energy have been formulated and implemented in an open-source CFD code (OpenFOAM®) and subsequently coupled with FireFOAM. Water transport, as would occur in a fire suppression environment, is tracked along solid surfaces. Interaction of the water with the solid surfaces in the form of cooling and pre-wetting is represented. Coupling between the film-transport model and the gas-phase and condensed-phase regions has been specified through interfacial transport models. Model validation for vaporization and conjugate heat transfer is shown for a surrogate fire environment. Radiation heat transfer is applied to a vertical panel with water flowing down the surface. Heat fluxes range from 5 to 33 kW/m² and water flow rates range from 2 to 52 g/m/s.     

Exploration of branching topology effects on polymer melt rheology using hierarchical calculation schemes

Hierarchical computational schemes based on tube theories enable calculation of rheological properties for polymers of arbitrary topology. In this study, such a scheme is used to systematically explore key rheological features of model long-chain branched systems. Empirical relations between molecular structure and rheology typically use overall molar mass and branching averages as structural variables, due to lack of knowledge on details of the topological structure or to limited structural variability between available experimental samples. The present approach clarifies the effect of additional structural variation beyond overall molar mass and branching level. For the polymer structures under consideration, arm length is found to dominate zero-shear viscosity, whereas the recoverable compliance scales with the ratio of total molar mass and backbone molar mass. Different topologies are found to lead to a different shear thinning/elasticity balance. The simulation approach provides clear hints for polymer designers that look to obtain specific property balances via topological modifications. This complements the classical empirical approach. Merging the different approaches is expected to synergistically speed up new product development.