Photoblinking and photobleaching of rylene diimide dyes

We investigate photoblinking and photobleaching of perylene diimide (PDI) and its higher homologue terrylene diimide (TDI). Single molecule fluorescence trajectories of the dye molecules embedded in PMMA under ambient conditions exhibit "on"-"off" blinking in the time range from ms to s. Due to the limited statistics of individual trajectories we construct ensemble distributions of "on" and "off" times which follow power laws with similar power law coefficients (m(on) ≈ 1.18, m(off) ≈ 1.31). The blinking is attributed to reversible formation of radical cations which are presumably created by electron transfer from higher excited triplet states T(n) of the molecules to acceptor levels in the PMMA host. This view is corroborated by the properties of TDI, which blinks at an excitation wavelength of 520 nm but does not at lower energy excitation (647 nm). In line with this observation, T(1)-T(n) absorption data of TDI (and PDI) indicate that above a certain illumination wavelength population of higher excited triplet states T(n) does not occur, preventing blinking. It is furthermore argued that the long-lived dark ("off") states, i.e. the radical cations, are precursors for the photobleaching process of the dye molecules. Consequently, the photobleaching quantum yield Y(bl) for TDI is very small at an excitation wavelength of 647 nm (Y(bl) = 2 × 10(-10)) but increases by two orders of magnitude at 520 nm (Y(bl) = 2 × 10(-8)), which lies in the range observed for PDI investigated with an excitation wavelength of 488 nm. Additional studies of a PDI-TDI donor-acceptor dyad give further insights into the blinking and bleaching processes. Important findings include the observation of power law blinking of TDI and PDI (after bleaching of TDI) with similar coefficients as found for the isolated chromophores. Furthermore, in the dyad the photostability of TDI decreases due to efficient population of the states T(n) by singlet-triplet annihilation, while that of PDI (after bleaching of TDI) is the same as for the isolated dye. These findings support the conclusions drawn for the isolated chromophores, in particular the involvement of the triplet manifold in the blinking (and bleaching) behavior.     

Controlled manipulation of multiple cells using catalytic microbots

Self-propelled microjet engines (microbots) can transport multiple cells into specific locations in a fluid. The motion is externally controlled by a magnetic field which allows to selectively load, transport and deliver the cells.     

ChemInform Abstract: Polychloride Monoanions from [Cl3]‐ to [Cl9]‐: A Raman Spectroscopic and Quantum Chemical Investigation.

Polychloride monoanions [Cl_n]^‐ (n = 3, 5, 7, 9) stabilized by quaternary ammonium salts are obtained through the addition or condensation of an excess of dry chlorine to [NMe₄]Cl, [NEt₄]Cl, [NPr₄]Cl, or [NBu₄]Cl and characterized by Raman spectroscopy and state‐of‐the‐art quantum chemical calculations up to the CCSD(T) level.     

New tetramethylthiepinium (TMTI) for copper-free click chemistry

A new derivative of the strained 3,3,6,6-tetramethylthiacycloheptyne (TMTH) bearing a functional handle is reported. Following an optimized synthesis, the handle was introduced by mild alkylation of the sulphur atom. The resulting functionalized strained 4,5-didehydro-3,3,6,6-tetramethyl-2,3,6,7-tetrahydrothiepinium (TMTI) proved to be stable and underwent extremely fast [3+2] cycloaddition reaction with benzyl azide in both organic and aqueous solvents. The reaction was equally efficient in cell lysate and serum and therefore opens interesting prospects for chemical-biology applications.     

Peptide-antibody complex as handle for single-molecule cut & paste

Molecule-by-molecule arrangement of proteins, for example, in enzymatic networks of predefined composition and proximity, is a major goal that may be accomplished by the single-molecule cut-and-paste technique (SMC&P). For this purpose, co-expressed anchors and handles as protein tags should be employed. As a first step in this direction, the authors develop an SMC&P design which exploits an antibody-peptide complex as a molecular handle.     

Comparative study using Raman microspectroscopy reveals spectral signatures of human induced pluripotent cells more closely resemble those from human embryonic stem cells than those from differentiated cells

Raman microspectroscopy is a non-destructive, label-free optical technique that offers information-rich molecular analysis of living cells. We report here the first Raman spectral study of human induced pluripotent stem cells (hiPSCs), and compare their Raman features to those of human embryonic stem cells (hESCs) and differentiated progeny of hESCs. Raman spectra from 687 cm(-1) to 1073 cm(-1) were collected from living hiPSCs, hESCs and hESCs non-specifically differentiated for 20 days. Spectra of hiPSCs and hESCs were found to be highly similar, and both were distinguishable from differentiated hESCs in terms of relative Raman peak intensities and variances. Principal component analysis (PCA) of the spectra demonstrated a clear discrimination between hiPSCs and differentiated hESCs. These results suggested that reprogramming returned human somatic cells to a state where the overall cellular composition was similar to that of human embryonic stem cells. Some metabolic differences between the two groups of pluripotent cells could be inferred, however it was unclear whether or not these differences were related to reprogramming.