Expression of proteins of interest in food

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Design, Synthesis and Properties of ‘Photochromic Torsional Switches’ (PTS)

The geometrical arrangement of the p-orbitals in organic semiconductors plays a pivotal role for the optoelectronic properties of the resulting bulk materials.[1] Control over the π-bond geometry, e.g. the planarity, of an extended conjugated system offers the possibility to modulate the effective conjugation length of a π-system, thus, allowing for the tuning of optical and electronic properties.[1,2] A promising way to reversibly modulate the orientation of the p-orbitals in a conjugated strucrure is to incorporate photochromic segments onto the ‘backbone’ of the π-system. Attempts to use photochromic molecules as monomer units in a polymer chain have shown that the photo-reversibility efficiency decreases inversely with the enhancement of the π-conjugation.[3] In the present work we report on a novel molecular architecture, referred to as a ‘photochromic torsional switch’ (PTS), which can overcome the limits of todays photochromic dyes towards their incorporation into extended π-system. The aforementioned molecular structure consists of a polymerizable bithiophene unit able to mechanically change its π-system planarity in response to a photochromic isomerization of a laterally attached azobenzene unit. In the dark and upon exposure of visible light, the azobenzene moiety assumes its extended trans conformation, thus, forcing the bithiophene backbone to twist out of coplanarity (dihedral angle from 50° to 68°). By contrast, exposure to UV light results in isomerization of the azobenzene unit to the cis conformation, which allows the bithiophene fragment to assume a planar, π-conjugated conformation (dihedral angles from 150° to 168°). The PTS architectures, proposed in this work, represent a new generation of photochromic dyes that can allow for the preparation of ‘conjugated photochromic polymers’, and help to gain deeper understanding of the correlation between molecular conformation and optoelectronic properties of π-conjugated macromolecules

Excitation polarization provides structural resolution of individual non-blinking nano-objects.

We propose to combine the method of fluorescence intensity centroid localization with rotation of the plane of excitation polarization. Polarized light interacts selectively with differently oriented fluorophores; thus yielding topological information on the nanometer scale, without any need for fluorophore blinking. The method is applicable to photostable individual systems, when most of the traditional super-resolution methods fail. A theoretical study is supported by experiments on 30 nm long cyclodextrin-encapsulated single polyrotaxane conjugated polymer chains

Regioselectivity in arene-catalyzed reductive lithiation of acetals of chlorobenzaldehydes

The regioselectivity of arene-catalyzed reductive lithiation of acetals of chlorobenzaldehydes strongly depends on the form of lithium metal employed as a reducing agent. According to previous findings, naphthalene catalyzed reductions run in the presence of lithium powder (high Na content) led to competitive metalations of both aromatic carbon-chlorine and benzylic carbon-oxygen bonds. At variance with these results, naphthalene catalyzed reductions run in the presence of lithium wire (either high or low Na content) led to highly regioselective metalation of aromatic carbon-chlorine bonds. These results disclose new possibilities of selective applications of arene-catalyzed reductive lithiation reactions. (c) 2005 Elsevier Ltd. All rights reserved

Self-Assembled Monolayers as Patterning Tool for Organic Electronic Devices

The patterning of functional materials represents a crucial step for the implementation of organic semiconducting materials into functional devices. Classical patterning techniques such as photolithography or shadow masking exhibit certain limitations in terms of choice of materials, processing techniques and feasibility for large area fabrication. The use of self-assembled monolayers (SAMs) as a patterning tool offers a wide variety of opportunities, from the region-selective deposition of active components to guiding the crystallization direction. Here, we discuss general techniques and mechanisms for SAM-based patterning and show that all necessary components for organic electronic devices, i.e., conducting materials, dielectrics, organic semiconductors, and further functional layers can be patterned with the use of self-assembled monolayers. The advantages and limitations, and potential further applications of patterning approaches based on self-assembled monolayers are critically discussed

Inhomogeneous Quenching as a Limit of the Correlation Between Fluorescence Polarization and Conformation of Single Molecules

The photophysical properties of conjugated polymers (CPs) largely depend on the interactions between the CP and its environment. We present a study of two polymers with identical conjugated backbones, bare and insulated, that showed different fluorescence excitation modulation depth histograms. However, the polarization differences are not related to differences in conformation, as commonly believed, but to the existence of "dark" chromophores in the bare polymer that are statically quenched. This results in inhomogeneous quenching of the polymer chain that breaks the correlation between excitation fluorescence polarization and conjugated polymer chain conformation

Photo-induced fluorescence quenching in conjugated polymers dispersed in solid matrices at low concentration

When isolated conjugated polymer (CP) chains are studied by single molecule spectroscopy, excitation power density in the range of 10-1000 W cm -2 is normally used. We show that at such excitation power densities the fluorescence ability of CPs is significantly reduced. A new methodological approach allowed us to measure the fluorescence quantum yield (QY) of thin matrix polymer films doped with fluorophores at very low concentration using fluorescence microscopy. Fluorescence QYs of different conjugated polymers (P3HT, MEH-PPV, PFBV and cyclodextrin-coated PFBV-Rtx) and a reference perylene diimide dye dispersed in the PMMA matrix were measured as a function of the excitation power density that ranged from ∼10-4 to 100 W cm -2. Already at an excitation power of 0.1 W cm-2 (the power density of the sunlight at the Earth) a detectable reduction of the fluorescence QY was observed for most of the polymers. The origin of the QY reduction is exciton annihilation by photo-generated triplet and/or change-transfer states. Insulation by cyclodextrin was found to decrease significantly the effect of non-emissive quenching states. This journal is © the Partner Organisations 2014