Molecular motor-functionalized porphyrin macrocycles

International audienceMolecular motors and switches change conformation under the influence of an external stimulus, e.g. light. They can be incorporated into functional systems, allowing the construction of adaptive materials and switchable catalysts. Here, we present two molecular motor-functionalized porphyrin macrocycles for future photo-switchable catalysis. They display helical, planar and point chirality, and are diastereomers, which differ in the relativeorientation of the motor and macrocyclic components. Fluorescence, UV-vis, and 1H NMR experiments reveal that the motor-functionalized macrocycles can bind and thread different variants of viologen guests, including a one-side blocked polymeric one of 30 repeat units. The latter feature indicates that the motor systems can find the open end of a polymer chain, thread on it, and move along the chain to eventually bind at the viologen trap, opening possibilities for catalytic writing on single polymer chains via chemical routes

Correctly validating results from single molecule data: the case of stretched exponential decay in the catalytic activity of single lipase B molecules

The question of how to validate and interpret correctly the waiting time probability density functions (WT-PDFs) from single molecule data is addressed. It is shown by simulation that when a stretched exponential WT-PDF, with a stretched exponent alfa and a time scale parameter tau, generates the off periods of a two-state trajectory, a reliable recovery of the input WT-PDF from the trajectory is obtained even when the bin size used to define the trajectory, dt, is much larger than the parameter tau. This holds true as long as the first moment of the WT-PDF is much larger than dt. Our results validate the results in an earlier study of the activity of single Lipase B molecules and disprove recent related critique

The LHCb upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

Host-guest complexes with tuneable solid state structures

Molecular clip receptors with long hydrocarbon tails self-assemble and form lamellar thin solid films, the architecture and properties of which can be fine-tuned by complexation of guest molecules

Self-assembled structures from an amphiphilic multiblock copolymer containing rigid semiconductor segments

An amphiphilic multiblock copolymer comprising nearly monodisperse poly(ethylene oxide) segments (M-w/M-n = 1.03) and polydisperse poly(methylphenylsilane) (PMPS) segments (M-w/M-n = 2.0) forms a variety of well-defined morphologies such as vesicles, micellar rods, and helices upon aggregation in water-based solvent systems, despite this polydisperse character. Since polysilanes show sigma -conjugation in the main chain, the optical and electronic properties of the described block copolymer depend on its confomational behavior. It is demonstrated by microscopic and spectroscopic techniques that the conformations of the PMPS backbone can be controlled through manipulation of the aggregation behavior, i.e., by the choice of the solvent composition

Lamellar organic thin films through self-assembly and molecular recognition

Molecular clips possessing U-shaped cavities have been functionalized on their convex side with long aliphatic tails. These molecules form dimers which self-assemble into malleable lamellar thin films. Upon addition of a guest (methyl 3,5-dihydroxybenzoate), a 1:1 host-guest complex is formed, which prohibits clip dimerization. As a result, the lamellar structure of the material is lost. Complexation of 3,5-dihydroxybenzoic acid in the clip results in host-guest complexes which dimerize by hydrogen bonding interactions between the carboxylic acid functions of the bound guests. This dimerization restores the lamellar type architecture of the material

Synthesis and physical properties of a porphyrin cavity based on glycoluril

The synthesis, conformational behavior and binding properties of a porphyrin host based on glycoluril are described. In solution it exists as a mixture of three slowly exchanging conformers, of which the populations can be controlled by temperature. The receptor binds potassium ions and methyl viologen by an induced-fit mechanism

Optical transduction of chemical sensing by thin films of colour reagents and molecular receptors using piezo-optical and surface plasmon resonance methods

Two novel chemical sensing systems using thin organic films have been elaborated and compared, one involving well established colour reagents used with a novel piezo-optical transduction system and the other using alkylviologen films for molecular recognition of phenols, with transduction via surface plasmon resonance (SPR) techniques. In the piezo-optical technique, chopped light absorbed by the thin sensing film deposited on piezoelectric polyvinylidene fluoride (PVDF) is converted into heat by non-radiative decay. This expands the film, stressing the PVDF and generating an electric charge which is measured using a lock-in amplifier. The signal dependence on optical absorption length, thermal diffusion length, film uniformity and porosity, chopper frequency and amplifier phase synchronisation are reviewed. The design and selection of molecular receptors for phenols, and the fabrication of thin films suitable for SPR, are described together with results demonstrating response patterns to different phenols and products of atmospheric aging of phenol solutions. The relative advantages of these two very different generic transduction techniques for organic thin film sensing layers are discussed with reference to the data presented on the selected sensing systems