The rutile form of titanium dioxide (r-TiO 2 ) usually shows a photocatalytic activity lower than that of anatase-TiO 2 (a-TiO 2 ). Nevertheless, there are numerous examples of sometimes unexpectedly high activity of r-TiO 2 . This material may appear to be particularly useful when a noncomplete and selective photocatalytic oxidation of organic substrates is required. On the basis of literature examples and our own studies, we compare the photocatalytic activities of r-TiO 2 , a-TiO 2 , and r-TiO 2 /a-TiO 2 composites. Because of a significantly better oxygen adsorption at the surface of r-TiO 2 and a lower redox potential of the excited electron, more efficient O 2•− production takes place at the surface of rutile. As a consequence, generation of 1 O 2 (involving O 2 reduction and the subsequent oxidation of superoxide) and reduction of H 2 O 2 to OH − and HO • are also favored with this material. Therefore, r-TiO 2 can be considered to be a particularly good photocatalyst for activation of molecular oxygen. On the other hand, a-TiO 2 appears to be a stronger oxidant. In its presence, efficient HO • generation (the result of water or surface hydroxyl group oxidation) and oxidation of H 2 O 2 to O 2•− are observed.
The exclusion of charged fluorescent dyes by intact cells has become a well-established assay for determining viability of cells. In search for a non-invasive fluorescent probe capable of long-term monitoring of cell death in real-time, we evaluated a new anthracycline derivative DRAQ7. The novel probe does not penetrate the plasma membrane of living cells but when the membrane integrity is compromised, it enters and binds readily to nuclear DNA to report cell death. It proved to be non-toxic to a panel of cancer cell lines grown continuously for up to 72 hours and did not induce any detectable DNA damage signaling when analyzed using laser scanning microscopy and flow cytometry. DRAQ7 provided a sensitive, real-time readout of cell death induced by a variety of stressors such as hypoxia, starvation and drug-induced cytotoxicity. The overall responses to anti-cancer agents and resulting pharmacological dose-response profiles were not affected by the growth of tumor cells in the presence DRAQ7. Moreover, we for the first time introduced a near real-time microflow cytometric assay based on combination of DRAQ7 and mitochondrial inner membrane potential (ΔΨm) sensitive probe TMRM. We provide evidence that this low-dosage, real-time labeling procedure provides multi-parameter and kinetic fingerprint of anti-cancer drug action.
A density functional theory (DFT) study was performed on a collection of clinically approved drugs, or Known Drug Space (KDS), to determine the statistical distribution of four properties: dipole moment (DM), polarisability (POL), ionisation potential (IP) and electron affinity (EA). The DM and POL are linked to cell permeability of drugs whereas IP and EA reflect their redox stability thus ease of metabolism. A benchmarking exercise showed a good correlation between experimental values and their predicted counterparts. It was found that KDS occupies the volume of chemical space defined by: DM≤10 D, POL≤68 Å(3) , IP 6.0-9.0 V and EA-1.5-2.0 eV. Only 16 % of the drugs are outside one or more of these parameters. Three categories based on known oral absorption and bioavailability (low/medium/high) were established and compared. Predominately, drugs designated as 'low' were found outside the established parameters. The properties were compared with mainstream molecular descriptors and a strong correlation was seen for POL to MW (r(2) =0.899), which can explain the success of the latter since POL reflects the ability of molecules to interact with polar and non-polar environments such as water and interior of a membrane.
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