Excited State Engineering in Ag29 Nanocluster through Peripheral Modification with Silver(I) Complexes for Bright Near-Infrared Photoluminescence.

The optical property of an ionic metal nanocluster (NC) is affected by the ionic interaction with counter ions. Here, we report that the modification of trianionic [Ag29(BDT)12(TPP)4]3- NC (BDT: 1.3-benzenedithiol; TPP: triphenylphosphine) with silver(I) complexes led to the intense photoluminescence (PL) in the near-infrared (NIR) region. The binding of silver(I) complexes to the peripheral region of Ag29 NC is confirmed by the single-crystal X-ray diffraction (SCXRD) measurement, which is further supported by electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy. The change of excited-state dynamics by the binding of silver(I) complexes is discussed based on the results of a transient absorption study as well as temperature-dependent PL spectra and PL lifetime measurements. The modification of Ag29 NCs with cationic silver(I) complexes is considered to give rise to a triplet excited state responsible for the intense NIR PL. These findings also afford important insights into the origin of the PL mechanism as well as the possible light-driven motion in Ag29-based NCs.

Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-ß-diketonate Ligands and Circularly Polarized Luminescence Study.

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-EuIII 6(TTP)8(OH2)6Na4] n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-EuIII 4(TTP)4(bipy)4(MEK)2(OH2)2 tetrahedral clusters, and (c) the achiral crystal structure of the [EuIII 2(BTP)4(OH2)2Na2] n coordination polymer (where BTP = dianionic bis-ß-diketonate, TTP = trianionic tris-ß-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic EuIII products. The conglomerate crystallization of [EuIII 6(TTP)8(OH2)6Na4] n appears to be caused by the presence of the sodium, Na+ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na+ ions. All the EuIII compounds exhibit characteristic red luminescence (5D0 → 7FJ, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral EuIII 6(TTP)8(OH2)6Na4] n species, displaying a |g lum| value in the range of 0.15 to 0.68 at the 5D0 → 7F1 emission band. Subtle changes of the [EuIII 6(TTP)8(OH2)6Na4] n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

Tetrathienyl Corannulene Compounds with Highly Sensitive Photochromism.

We have designed and synthesized photochromic tetrathienyl corannulene compounds, 1,2,7,8-tetrakis(2-methyl-5-phenylthiophen-3-yl)corannulene (1) and 1,2,7,8-tetrakis(2,4-dimethyl-5-phenylthiophen-3-yl)corannulene (2), by fusing two units of photochromic terarylene with a curved aromatic corannulene with a promising antenna effect. Compound 1 exhibited highly sensitive photoreactivity, with a large molar absorption coefficient of 8.2×104  M-1 cm-1 and practically photon-quantitative photocyclization. On the other hand, a terarylene derivative with a planar aromatic phenanthrene, 9,10-bis(2,4-dimethyl-5-phenylthiophen-3-yl)phenanthrene (4) showed no photoreactivity. The reason for such a difference was attributed to the predominance of the photoreactive atropisomers amplified by energy migration, and the shortened distance between reactive carbons induced by the curved structure.

The emergence of intense near-infrared photoluminescence by photoactivation of silver nanoclusters.

Photoirradiation of a pyridine solution of Ag29 nanoclusters (NCs) with red photoluminescence (PL) at 680 nm activated intense PL in the near infrared (NIR) region, giving a PL quantum yield (PLQY) of 33% at 770 nm. The use of Au-doped silver NCs further boosted the PLQY to more than 45% at 800 nm. Photoirradiation is considered to induce a change in the charge localization in the NCs, leading to the formation of NIR emitting sites.

Visible Circularly Polarized Luminescence of Octanuclear Circular Eu(III) Helicate.

This work reports on the structural and photophysical characterization of D4-symmetrical octanuclear circular LnIII helicates, [(R)- or (S)-iPr-Pybox]8(LnIII)8(THP)8 (where Ln = Eu and Tb, THP = trianionic tris-ß-diketonate, and iPr-Pybox = chiral bis(4-isopropyl-2-oxazolinyl)pyridine). X-ray crystallographic analysis revealed that the octanuclear circular helicate possesses square antiprism architecture and consists of four [(R)- or (S)-iPr-Pybox]2LnIII2(THP)2 asymmetric units arranged in a closed ring form. Ligand-to-ligand interactions between the THP and the iPr-Pybox ligands have successfully directed formation of enantiopure, homoconfigurational (Δ,Δ,Δ,Δ,Δ,Δ,Δ,Δ)-R and (Λ,Λ,Λ,Λ,Λ,Λ,Λ,Λ)-S isomers. All of the nonacoordinated LnIII ions are identical and exhibit a distorted capped square antiprism (CSAP) geometry. Upon excitation of the ligand absorption band (λ = 360 nm), the circular helicates display characteristic EuIII (red, 5D0 → 7FJ, J = 0-4) or TbIII (green, 5D4 → 7FJ, J = 6-3) core f-f luminescence. The overall emission quantum yields of the circular EuIII and TbIII helicates are 0.145 and 0.0013, respectively, in chloroform. The EuIII and TbIII complexes exhibit remarkable circularly polarized luminescence (CPL) activity at their magnetic dipole transition with observed luminescence dissymmetry factors |glum| of 1.25 (5D0 → 7F1, λ = 592 nm) and 0.25 (5D4 → 7F5, λ = 541 nm), respectively. Exceptional |glum| values of the circular EuIII helicates highlight the visible intensity difference between left and right circularly polarized emissions of R and S isomers in chloroform and PMMA thin film.

Self-assembled Tetranuclear EuIII Complexes with D2- and C2h-Symmetrical Square Scaffold.

Three new tetranuclear europium(III) alternating circular helicates, (2-PhRRRR/2-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BPP)6, (2-iPrRRRR/2-iPrSSSS) [(R)- or (S)-iPr-Pybox]4EuIII4(BPP)6, and (3-PhRRRR/3-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BHP)6, are presented with their structural and chiroptical characterization (BPP and BHP = bis-ß-diketonates; Pybox = chiral bis(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-ß-diketonates and Pybox ligands produce different bis-ß-diketonates arrangements around four EuIII ions and, thus, their specific symmetry in the final tetranuclear complexes. 2-PhRRRR/2-PhSSSS and 3-PhRRRR/3-PhSSSS are recognized as D2-symmetry, while 2-iPrRRRR/2-iPrSSSS self-assemblies possess pseudo C2h-symmetry. Due to different molecular symmetry, 2-PhRRRR/2-PhSSSS and 2-iPrRRRR/2-iPrSSSS crystals display different ligands orientation in their EuIII coordination spheres. The presence of pseudo σh-mirror symmetry in 2-iPrRRRR/2-iPrSSSS promotes a pair of distinguishable EuIII geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f-f transitions in the EuIII core. The EuIII self-assemblies exhibit intense CPL with different observed |glum| values (2-PhRRRR/2-PhSSSS ∼ |0.31|, 2-iPrRRRR/2-iPrSSSS ∼ |0.08|, 3-PhRRRR/3-PhSSSS ∼ |0.31| in chloroform).

Photo-Lewis Acid Generator Based on Radical-Free 6π Photo-Cyclization Reaction.

We present here a new photo-active molecule which acts as a photo-Lewis acid generator (PLAG) based on photo-chemical 6π-percyclization. Photo-illumination of the PLAG molecule produces a condensed aromatic carbocation with a triflate counteranion, which exhibits Lewis acid chemical catalytic reactivity such as initiation of the polymerization of epoxy monomers and catalysis of Mukaiyama-aldol reactions. The terminal-end structure in the epoxy polymerization was modified with the Lewis acid fragment. The carbocation induced the Mukaiyama-aldol reaction as a new photo-gated system with remarkably high catalytic reactivity and turnover numbers higher than 60. The photo-chemical quantum yield of the carbocation generation is 50%, which is considerably higher than obtained with most Brønsted photo-acid generators.

A novel tumor-promoting function residing in the 5' non-coding region of vascular endothelial growth factor mRNA.

BACKGROUND: Vascular endothelial growth factor-A (VEGF) is one of the key regulators of tumor development, hence it is considered to be an important therapeutic target for cancer treatment. However, clinical trials have suggested that anti-VEGF monotherapy was less effective than standard chemotherapy. On the basis of the evidence, we hypothesized that vegf mRNA may have unrecognized function(s) in cancer cells. METHODS AND FINDINGS: Knockdown of VEGF with vegf-targeting small-interfering (si) RNAs increased susceptibility of human colon cancer cell line (HCT116) to apoptosis caused with 5-fluorouracil, etoposide, or doxorubicin. Recombinant human VEGF165 did not completely inhibit this apoptosis. Conversely, overexpression of VEGF165 increased resistance to anti-cancer drug-induced apoptosis, while an anti-VEGF165-neutralizing antibody did not completely block the resistance. We prepared plasmids encoding full-length vegf mRNA with mutation of signal sequence, vegf mRNAs lacking untranslated regions (UTRs), or mutated 5'UTRs. Using these plasmids, we revealed that the 5'UTR of vegf mRNA possessed anti-apoptotic activity. The 5'UTR-mediated activity was not affected by a protein synthesis inhibitor, cycloheximide. We established HCT116 clones stably expressing either the vegf 5'UTR or the mutated 5'UTR. The clones expressing the 5'UTR, but not the mutated one, showed increased anchorage-independent growth in vitro and formed progressive tumors when implanted in athymic nude mice. Microarray and quantitative real-time PCR analyses indicated that the vegf 5'UTR-expressing tumors had up-regulated anti-apoptotic genes, multidrug-resistant genes, and growth-promoting genes, while pro-apoptotic genes were down-regulated. Notably, expression of signal transducers and activators of transcription 1 (STAT1) was markedly repressed in the 5'UTR-expressing tumors, resulting in down-regulation of a STAT1-responsive cluster of genes (43 genes). As a result, the tumors did not respond to interferon (IFN)alpha therapy at all. We showed that stable silencing of endogenous vegf mRNA in HCT116 cells enhanced both STAT1 expression and IFNalpha responses. CONCLUSIONS: These findings suggest that cancer cells have a survival system that is regulated by vegf mRNA and imply that both vegf mRNA and its protein may synergistically promote the malignancy of tumor cells. Therefore, combination of anti-vegf transcript strategies, such as siRNA-based gene silencing, with anti-VEGF antibody treatment may improve anti-cancer therapies that target VEGF.