Ultralong coherence times in the purely electronic zero-phonon line emission of single molecules

We report the observation of ultralong coherence times in the purely electronic zero-phonon line emission of single terrylenediimide molecules at 1.4 K. Vibronic excitation and spectrally resolved detection with a scanning Fabry-Perot spectrum analyzer were used to measure a linewidth of 65 MHz. This is within a factor of 1.6 of the transform limit. It therefore indicates that single molecule emission may be suited for applications in linear optics quantum computation. Additionally it is shown that high resolution spectra taken with the spectrum analyzer allow for the investigation of fast spectral dynamics in the emission of a single molecule.Comment: to appear in Applied Physics Letter

Precise quantification of silica and ceria nanoparticle uptake revealed by 3D fluorescence microscopy

Particle_in_Cell-3D is a powerful method to quantify the cellular uptake of nanoparticles. It combines the advantages of confocal fluorescence microscopy with fast and precise semi-automatic image analysis. In this work we present how this method was applied to investigate the impact of 310 nm silica nanoparticles on human vascular endothelial cells (HUVEC) in comparison to a cancer cell line derived from the cervix carcinoma (HeLa). The absolute number of intracellular silica nanoparticles within the first 24 h was determined and shown to be cell type-dependent. As a second case study, Particle_in_Cell-3D was used to assess the uptake kinetics of 8 nm and 30 nm ceria nanoparticles interacting with human microvascular endothelial cells (HMEC-1). These small nanoparticles formed agglomerates in biological medium, and the particles that were in effective contact with cells had a mean diameter of 417 nm and 316 nm, respectively. A significant particle size-dependent effect was observed after 48 h of interaction, and the number of intracellular particles was more than four times larger for the 316 nm agglomerates. Interestingly, our results show that for both particle sizes there is a maximum dose of intracellular nanoparticles at about 24 h. One of the causes for such an interesting and unusual uptake behavior could be cell division

Totalsynthese invers prenylierter Bromindole aus dem Moostierchen Flustra foliacea

The marine bryozoan Flustra foliacea is known as source of unique brominated indole alkaloids. Flustra alkaloids are structurally related to the highly toxic acetylcholinesterase inhibitor physostigmine which is clinically tested as a possible remedy for Alzheimer's disease. The concentration of those natural products can vary strongly, depending on location and season. Thus, exploration of the total synthesis of the Flustra alkaloids is required for any detailed analysis of their biological activity. As a recent member of the family, we isolated deformyl-flustrabromine (dFBr) which shows promising activity at the nicotinic acetylcholine receptor (nAChR). Deformylflustrabromine may be a biosynthetic precursor of other Flustra alkaloids such as flustraminol A. An efficient first total synthesis of dFBr and three of its congeners has been developed. Key step of the synthesis is the inverse prenylation at the indole 2-position. When treated with tert-BuOCl and prenyl[9-BBN], Nb-Formyl-Nb-methyl-tryptamine cleanly reacts affording the inversely 2-prenylated compound in a yield of 75 %. However, inverse prenylation of the indole 2-position was not suitable for the 6-brominated analog, synthesized via the Batcho-Leimgruber route. The influence of 6-bromination on the reactivity of several indoles was investigated confirming that deactivating effect. For the synthesis of dFBr we had to turn back to non-brominated indoles. Surprisingly good regioselectivity for the indole 6-position was observed on monobromination of the corresponding, 2-inversely prenylated indole precursor with one equivalent of NBS in HOAc/HCO2H (3:1). The product flustrabromine crystallizes as the E-rotamer. Alkaline hydrolysis afforded deformylflustrabromine which was synthesized within four steps and an overall yield of 53 % starting from Nb-methyl-tryptamine. Now, gram quantities of material are accessible for further biological studies. During this study, interesting formation of traces of inversely prenylated THF was observed. This phenomenon has been further studied by performing the actual reaction in the absence of indole derivatives. It was possible to convert unsubstituted tetrahydrofuran to the 2-inversely prenylated compound simply by treatment with NCS and prenyl[9-BBN] at room temperature, in a yield of 88 %. This is a new reaction

Switching first contact: photocontrol of E. coli adhesion to human cells

We have shown previously that carbohydrate-specific bacterial adhesion to a non-physiological surface can be photocontrolled by reversible E/Z isomerisation using azobenzene-functionalised sugars. Here, this approach is applied to the surface of human cells. We show not only that bacterial adhesion to the azobenzene glycoside-modified cell surface is higher in the E than in the Z state, but add data about the specific modulation of the effect

Indistinguishable Photons from a Single Molecule

We report the results of coincidence counting experiments at the output of a Michelson interferometer using the zero-phonon-line emission of a single molecule at $1.4 K$. Under continuous wave excitation, we observe the absence of coincidence counts as an indication of two-photon interference. This corresponds to the observation of Hong-Ou-Mandel correlations and proves the suitability of the zero-phonon-line emission of single molecules for applications in linear optics quantum computation.Comment: To appear in Phys. Rev. Let

Metal-Enhanced Fluorescence of Chlorophylls in Single Light-Harvesting Complexes

Ensemble and single-molecule spectroscopy demonstrates that both emission and absorption of peridinin−chlorophyll−protein photosynthetic antennae can be largely enhanced through plasmonic interactions. We find up to 18-fold increase of the chlorophyll fluorescence for complexes placed near a silver metal layer. This enhancement, which leaves no measurable effects on the protein structure, is observed when exciting either chlorophyll or carotenoid and is attributed predominantly to an increase of the excitation rate in the antenna. The enhancement mechanism comes from plasmon-induced amplification of electromagnetic fields inside the complex. This result is an important step toward applying plasmonic nanostructures for controlling the optical response of complex biomolecules and improving the design and functioning of artificial light-harvesting systems

Bisacylphosphane oxides as photo-latent cytotoxic agents and potential photo-latent anticancer drugs

Bisacylphosphane oxides (BAPOs) are established as photoinitiators for industrial applications. Light irradiation leads to their photolysis, producing radicals. Radical species induce oxidative stress in cells and may cause cell death. Hence, BAPOs may be suitable as photolatent cytotoxic agents, but such applications have not been investigated yet. Herein, we describe for the first time a potential use of BAPOs as drugs for photolatent therapy. We show that treatment of the breast cancer cell lines MCF-7 and MDA-MB-231 and of breast epithelial cells MCF-10A with BAPOs and UV irradiation induces apoptosis. Cells just subjected to BAPOs or UV irradiation alone are not affected. The induction of apoptosis depend on the BAPO and the irradiation dose. We proved that radicals are the active species since cells are rescued by an antioxidant. Finally, an optimized BAPO-derivative was designed which enters the cells more efficiently and thus leads to stronger effects at lower doses