Distinctive Signatures of the Spin- and Momentum-Forbidden Dark Exciton States in the Photoluminescence of Strained WSe2 Monolayers under Thermalization.

With both spin and valley degrees of freedom, the low-lying excitonic spectra of photoexcited transition-metal dichalcogenide monolayers (TMDC-MLs) are featured by rich fine structures, comprising the intravalley bright exciton states as well as various intra- and intervalley dark ones. The latter states can be classified as those of the spin- and momentum-forbidden dark excitons according to the violated optical selection rules. Because of their optical invisibility, these two types of the dark states are in principle hardly observed and even distinguished in conventional spectroscopies although their impacts on the optical and dynamical properties of TMDC-MLs have been well noticed. In this Letter, we present a theoretical and computational investigation of the exciton fine structures and the temperature-dependent photoluminescence spectra of strained tungsten diselenide monolayers (WSe2-MLs) where the intravalley spin-forbidden dark exciton lies in the lowest exciton states and other momentum-forbidden states are in the higher energies that are tunable by external stress. The numerical computations are carried out by solving the Bethe-Salpeter equation for an exciton in a WSe2-ML under the stress-control in the tight-binding scheme established from the first principle computation in the density functional theory. According to the numerical computation and supportive model analysis, we reveal the distinctive signatures of the spin- and momentum-forbidden exciton states of strained WSe2-MLs in the temperature-dependent photoluminescences and present the guiding principle to infer the relative energetic locations of the two types of dark excitons.

Proteomic survey of copper-binding proteins in Arabidopsis roots by immobilized metal affinity chromatography and mass spectrometry.

To plants, copper is vitally essential at low concentrations but extremely toxic at elevated concentrations. Plants have evolved a suite of mechanisms that modulate the uptake, distribution, and utilization of copper ions. These mechanisms require copper-interacting proteins for transporting, chelating, and sequestrating copper ions. In this study, we have systematically screened for copper-interacting proteins in Arabidopsis roots via copper-immobilized metal affinity chromatography (Cu-IMAC). We also compared Arabidopsis root metalloproteomes with affinity to Cu-IMAC and Zn-IMAC. From the identities of 38 protein spots with affinity to Cu-IMAC, 35 unique proteins were identified. Functional classification of these proteins includes redox/hydrolytic reactions, amino acid metabolism, glutathione metabolism, phosphorylation, translation machinery, membrane-associated proteins, and vegetative storage proteins. Potential copper-interacting motifs were predicted and scored. Six candidate motifs, H-(X)5 -H, H-(X)7 -H, H-(X)12 -H, H-(X)6 -M, M-(X)7 -H, and H-(X)3 -C, are present in Cu-IMAC-isolated proteins with higher frequency than in the whole Arabidopsis proteome.

Site-selective DNA photocleavage involving unusual photoinitiated tautomerization of chiral tridentate vanadyl(V) complexes derived from N-salicylidene alpha-amino acids.

The titled vanadyl(V) complexes serve as efficient reagents for cleaving supercoiled plasmid DNA by photoinitiation. Complex 3d, derived from 2-hydroxy-1-naphthaldehyde and l-phenylalanine, exhibits a unique wedge feature, inducing a site-selective photocleavage at the C22-T23 of the bulge backbone for a HIV-27 DNA system at 0.1-5 muM. Transient absorption experiments for 3d indicate the involvement of LMCT with concomitant tautomerization, leading to an o-quinone-methide V-bound hydroxyl species responsible for the cleavage profiles. [structure: see text]