Publisher Correction: Micelles from gemini.

In the version of this Research Highlight originally published, the text 'Now, Nishioka et al. have shown that carefully designed gemini amphiphiles can also form micelles' should have read 'Now, Nishioka et al. have shown that aromatic gemini amphiphiles can form monodisperse micelles'. This has now been corrected.

Photolysis of endoperoxides in the presence of nitroxides: a laser flash photolysis study with optical and ESR detection.

Time-resolved electron paramagnetic resonance spectroscopy, transient absorption, and phosphorescence spectroscopy were used to investigate the spin polarization of a nitroxide free radical induced by interaction with singlet oxygen ((1)O2). The latter was generated by photolysis of endoperoxides of two anthracene derivatives. Although both anthracene endoperoxides are structurally similar, opposite spin polarization of the nitroxide was observed. Photolysis of one endoperoxide leads to absorptive nitroxide spin polarization due to interaction with the generated (1)O2. Photolysis of the other endoperoxide generated emissive nitroxide spin polarization, probably due to interaction of the endoperoxide triplet states with nitroxides.

Time-resolved EPR study of singlet oxygen in the gas phase.

X-band EPR spectra of singlet O2((1)Δg) and triplet O2((3)Σg(-)) were observed in the gas phase under low molecular-oxygen pressures PO2 = 0.175-0.625 Torr, T = 293-323 K. O2((1)Δg) was produced by quenching of photogenerated triplet sensitizers naphthalene C8H10, perdeuterated naphthalene, and perfluoronaphthalene in the gas phase. The EPR spectrum of O2((1)Δg) was also observed under microwave discharge. Integrated intensities and line widths of individual components of the EPR spectrum of O2((3)Σg(-)) were used as internal standards for estimating the concentration of O2 species and PO2 in the EPR cavity. Time-resolved (TR) EPR experiments of C8H10 were the main focus of this Article. Pulsed irradiation of C8H10 in the presence of O2((3)Σg(-)) allowed us to determine the kinetics of formation and decay for each of the four components of the O2((1)Δg) EPR signal, which lasted for only a few seconds. We found that the kinetics of EPR-component decay fit nicely to a biexponential kinetics law. The TR EPR 2D spectrum of the third component of the O2((1)Δg) EPR spectrum was examined in experiments using C8H10. This spectrum vividly presents the time evolution of an EPR component. The largest EPR signal and the longest lifetime of O2((1)Δg), τ = 0.4 s, were observed at medium pressure PO2 = 0.4 Torr, T = 293 K. The mechanism of O2((1)Δg) decay in the presence of photosensitizers is discussed. EPR spectra of O2((1)Δg) evidence that the spin-rotational states of O2((1)Δg) are populated according to Boltzmann distribution in the studied time range of 10-100 ms. We believe that this is the first report dealing with the dependence of O2((1)Δg) EPR line width on PO2 and T.

Controlled doping in thin-film transistors of large contorted aromatic compounds.

Bigger and better: The new thin-film organic material octabenzcircumbiphenyl (OBCB; see scheme) forms an active layer in a field effect transistor, which can be switched simultaneously with two different inputs, that is, electrical bias and protonation.

New rhodamine nitroxide based fluorescent probes for intracellular hydroxyl radical identification in living cells.

The synthesis, characteristics, and biological applications of a series of new rhodamine nitroxide fluorescent probes that enable imaging of hydroxyl radicals (•OH) in living cells are described. These probes are highly selective for •OH in aqueous solution, avoiding interference from other reactive oxygen species (ROS), and they facilitate •OH imaging in biologically active samples. The robust nature of these probes (high specificity and selectivity, and facile synthesis) offer distinct advantages over previous methods for •OH detection.

EPR analysis and DFT computations of a series of polynitroxides.

Polynitroxides with varying numbers of nitroxide groups (one to four) derived from different aromatic core structures show intramolecular electron spin-spin coupling. The scope of this study is to establish an easy methodology for extracting structural, dynamical, and thermodynamical information from the EPR spectra of these polynitroxides which might find use as spin probes in complex systems, such as biological and host/guest systems, and as polarizing agents in dynamic nuclear polarization (DNP) applications. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level provided information on the structural details such as bond lengths and angles in the gas phase, which were compared with the single crystal X-ray diffraction data in the solid state. Polarizable continuum model (PCM) calculations were performed to account for solvent influences. The electron paramagnetic resonance (EPR) spectra of the polynitroxides in chloroform were analyzed in detail to extract information such as the percentages of different conformers, hyperfine coupling constants a, and rotational correlation times τ(c). The temperature dependence on the line shape of the EPR spectra gave thermodynamic parameters ΔH and ΔS for the conformational transitions. These parameters were found to depend on the number and relative positions of the nitroxide and other polar groups.

Electric-field-induced fluorescence quenching in polyfluorene, ladder-type polymers, and MEH-PPV: evidence for field effects on internal conversion rates in the low concentration limit.

Electric field-induced fluorescence quenching has been measured for a series of conjugated polymers with applications in organic light-emitting diodes. Electrofluorescence measurements on isolated chains in a glassy matrix at 77 K show that the quenching efficiency for poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is an order of magnitude larger than that for either a ladder-type polymer (MeLPPP) or polyfluorene (PFH). This effect is explained in terms of the relatively high probability of field-enhanced internal conversion deactivation in MEH-PPV relative to either MeLPPP or PFH. These data, obtained under dilute sample conditions such that chain-chain interactions are minimal, are contrasted with the much higher quenching efficiencies observed in the corresponding polymer films, and several explanations for the differences are considered. In addition, the values of the change in dipole moment and change in polarizability on excitation (|Δµ| and tr(Δα), respectively) are reported, and trends in these values as a function of molecular structure and chain length are discussed.

Electroabsorption of dimers containing MM (M = Mo, W) quadruply bonded units: insights into the electronic structure of neutral coupled redox centers and their relationship with mixed valence ions.

The electroabsorption spectra for the metal-to-ligand charge transfer transition in complexes containing oxalate and terephthalate bridged MM quadruply bonded units, [(MM)(pivalate)(3)](2)-mu(2)-BR, where M = Mo or W and BR = oxalate or terephthalate, are reported. The measured magnitude of the change in dipole moment (|Deltamu|) and the change in polarizability (Deltaalpha) that accompany this electronic transition are found to be small and not to follow the behavior expected on the basis of the two-state model. In addition, the trend in the value of Deltaalpha for the neutral states is mirrored by the trend in the degree of electronic coupling (H(AB)) for the strongly coupled mixed valence states formed by the same complexes in their singly oxidized states.

New melanic pigments in the human brain that accumulate in aging and block environmental toxic metals.

Neuronal pigments of melanic type were identified in the putamen, cortex, cerebellum, and other major regions of human brain. These pigments consist of granules 30 nm in size, contained in organelles together with lipid droplets, and they accumulate in aging, reaching concentrations as high as 1.5-2.6 microg/mg tissue in major brain regions. These pigments, which we term neuromelanins, contain melanic, lipid, and peptide components. The melanic component is aromatic in structure, contains a stable free radical, and is synthesized from the precursor molecule cysteinyl-3,4-dihydroxyphenylalanine. This contrasts with neuromelanin of the substantia nigra, where the melanic precursor is cysteinyl-dopamine. These neuronal pigments have some structural similarities to the melanin found in skin. The precursors of lipid components of the neuromelanins are the polyunsaturated lipids present in the surrounding organelles. The synthesis of neuromelanins in the various regions of the human brain is an important protective process because the melanic component is generated through the removal of reactive/toxic quinones that would otherwise cause neurotoxicity. Furthermore, the resulting melanic component serves an additional protective role through its ability to chelate and accumulate metals, including environmentally toxic metals such as mercury and lead.