Near-Infrared Light Activated Azo-BF₂ Switches

Increasing the electron density in BF₂-coodinated azo compounds through <i>para</i>-substitution leads to a bathochromic shift in their activation wavelength. When the substituent is dimethyl amine, or the like, the <i>trans</i>/<i>cis</i> isomerization process can be efficiently modulated using near infrared light. The electron donating capability of the substituent also controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the <i>cis</i> isomer, while the BF₂-coodination prevents reduction by glutathione

Visible Light Switching of a BF₂‑Coordinated Azo Compound

Here we report the synthesis and characterization of a BF₂–azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF₂, coupled with the extended conjugation of the NN π-electrons, increases the energy of the n−π* transitions and introduces new π-nonbonding (π_nb) to π* transitions that dominate the visible region. The well separated π_nb–π* transitions of the <i>trans</i> and <i>cis</i> isomers enable the efficient switching of the system by using only visible light. The complexation also leads to a slow <i>cis</i> → <i>trans</i> thermal relaxation rate (<i>t</i>_1/2 = 12.5 h). Theoretical calculations indicate that the absorption bands in the visible range can be tuned using different Lewis acids, opening the way to a conceptually new strategy for the manipulation of azo compounds using only visible light

Near-Infrared Light Activated Azo-BF₂ Switches

Increasing the electron density in BF₂-coodinated azo compounds through <i>para</i>-substitution leads to a bathochromic shift in their activation wavelength. When the substituent is dimethyl amine, or the like, the <i>trans</i>/<i>cis</i> isomerization process can be efficiently modulated using near infrared light. The electron donating capability of the substituent also controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the <i>cis</i> isomer, while the BF₂-coodination prevents reduction by glutathione

Visible Light Switching of a BF₂‑Coordinated Azo Compound

Here we report the synthesis and characterization of a BF₂–azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF₂, coupled with the extended conjugation of the NN π-electrons, increases the energy of the n−π* transitions and introduces new π-nonbonding (π_nb) to π* transitions that dominate the visible region. The well separated π_nb–π* transitions of the <i>trans</i> and <i>cis</i> isomers enable the efficient switching of the system by using only visible light. The complexation also leads to a slow <i>cis</i> → <i>trans</i> thermal relaxation rate (<i>t</i>_1/2 = 12.5 h). Theoretical calculations indicate that the absorption bands in the visible range can be tuned using different Lewis acids, opening the way to a conceptually new strategy for the manipulation of azo compounds using only visible light

Galvanic Replacement-Free Deposition of Au on Ag for Core–Shell Nanocubes with Enhanced Chemical Stability and SERS Activity

We report a robust synthesis of Ag@Au core–shell nanocubes by directly depositing Au atoms on the surfaces of Ag nanocubes as conformal, ultrathin shells. Our success relies on the introduction of a strong reducing agent to compete with and thereby block the galvanic replacement between Ag and HAuCl₄. An ultrathin Au shell of 0.6 nm thick was able to protect the Ag in the core in an oxidative environment. Significantly, the core–shell nanocubes exhibited surface plasmonic properties essentially identical to those of the original Ag nanocubes, while the SERS activity showed a 5.4-fold further enhancement owing to an improvement in chemical enhancement. The combination of excellent SERS activity and chemical stability may enable a variety of new applications

Transformation of Ag Nanocubes into Ag–Au Hollow Nanostructures with Enriched Ag Contents to Improve SERS Activity and Chemical Stability

We report a strategy to complement the galvanic replacement reaction between Ag nanocubes and HAuCl₄ with co-reduction by ascorbic acid (AA) for the formation of Ag–Au hollow nanostructures with greatly enhanced SERS activity. Specifically, in the early stage of synthesis, the Ag nanocubes are sharpened at corners and edges because of the selective deposition of Au and Ag atoms at these sites. In the following steps, the pure Ag in the nanocubes is constantly converted into Ag⁺ ions to generate voids owing to the galvanic reaction with HAuCl₄, but these released Ag⁺ ions are immediately reduced back to Ag atoms and are co-deposited with Au atoms onto the nanocube templates. We observe distinctive SERS properties for the Ag–Au hollow nanostructures at visible and near-infrared excitation wavelengths. When plasmon damping is eliminated by using an excitation wavelength of 785 nm, the SERS activity of the Ag–Au hollow nanostructures is 15- and 33-fold stronger than those of the original Ag nanocubes and the Ag–Au nanocages prepared by galvanic replacement without co-reduction, respectively. Additionally, Ag–Au hollow nanostructures embrace considerably improved stability in an oxidizing environment such as aqueous H₂O₂ solution. Collectively, our work suggests that the Ag–Au hollow nanostructures will find applications in SERS detection and imaging

Schematic representation of the lineage relationships of the cell types examined in these studies

<p><b>Copyright information:</b></p><p>Taken from "CNS progenitor cells and oligodendrocytes are targets of chemotherapeutic agents and "</p><p>http://jbiol.com/content/5/7/22</p><p>Journal of Biology 2006;5(7):22-22.</p><p>Published online 30 Nov 2006</p><p>PMCID:PMC2000477.</p><p></p> Pluripotent neuroepithelial stem cells (NSC) give rise to glial-restricted precursor (GRP) cells and neuron-restricted precursor (NRP) cells. NRP cells can give rise to multiple populations of neurons, whereas GRP cells give rise to astrocytes and oligodendrocyte-type-2 astrocytes (O-2A/OPCs). The O-2A/OPCs in turn give rise to oligodendrocytes. The progenitor cells that lie between NSCs and differentiated cell types, and are the major dividing cell population in the CNS, appear to be exceptionally vulnerable to the effects of chemotherapeutic agents. Also sharing this vulnerability are nondividing oligodendrocytes

Representative images of co-labeling for TUNEL and expression of cell type-specific antigens

<p><b>Copyright information:</b></p><p>Taken from "CNS progenitor cells and oligodendrocytes are targets of chemotherapeutic agents and "</p><p>http://jbiol.com/content/5/7/22</p><p>Journal of Biology 2006;5(7):22-22.</p><p>Published online 30 Nov 2006</p><p>PMCID:PMC2000477.</p><p></p> Despite the apparent labeling of nuclei with cell-type specific antibodies in dying cells (presumably due to the changes in antigen distribution associated with nuclear fragmentation), co-labeling was highly cell-type specific (see also Figure 7 for -stack analysis). NG2/TUNELcells from the CC. In this and subsequent rows, the first image is of TUNEL staining, the next two images are of staining for the proteins indicated, and the merged image is on the far right. DCX/TUNELcells from SVZ; GFAP/TUNELcell from DG. NeuN/TUNELcell from DG. In all merged images except (l) co-labeled cells show up as yellow; in (l) the nucleus of the co-labeled cell is green. Magnification 400×

Primary CNS cells are equally or more vulnerable to cytarabine than cancer cells

<p><b>Copyright information:</b></p><p>Taken from "CNS progenitor cells and oligodendrocytes are targets of chemotherapeutic agents and "</p><p>http://jbiol.com/content/5/7/22</p><p>Journal of Biology 2006;5(7):22-22.</p><p>Published online 30 Nov 2006</p><p>PMCID:PMC2000477.</p><p></p> Cells were plated on coverslips in 24-well plates at a density of 1,000 cells per well and allowed to grow for 24–48 h. On the basis of drug concentrations achieved in human patients, cells were exposed to cytarabine for 24 h. Cell survival and viability was determined after additional 24–48 h (see Materials and methods). Rat neural cell types studied included O-2A/OPCs, oligodendrocytes, GRP cells, NSCs and astrocytes. We also examined the T98 glioma cell line, a meningioma cell line, and the L1210 and EL-4 leukemia cell lines. To define the onset of cytarabine toxicity, cells were treated with cytarabine over a wide dose range (0.01–1 μM) extending downwards from the lower ranges achieved in high-dose therapy. Each experiment was carried out in quadruplicate and was repeated multiple times in independent experiments. Data represent mean of survival ± SEM, normalized to control values. There are no concentrations of cytarabine at which tumor cell lines were more sensitive O-2A/OPCs or oligodendrocytes