In situ measurements of the interaction force between surfaces hydrophobized by physical adsorption of surfactants in solutions and the direct observation of the morphology of adsorbed surfactants were conducted for trimethylammonium chlorides with alkyl chains of six different lengths, using a tapping mode AFM. It is found that (1) a strong and long-range attractive force with a discontinuous step is observed, when surfactants with a sufficiently long alkyl chain are employed, (2) the bubblelike domains and the corresponding force curves are obtained directly, (3) the long-range interaction never appears when a completely air-free solution of surfactants is prepared, and (4) the usual degassing method of solutions does not necessarily guarantee that surfactant solutions are degassed when they contain stabilized bubbles. Hence, it is concluded that the long-range attraction is attributable to the gas bridge formed between surfaces due to the coalescence of stabilized microscopic bubbles on the surfaces which are introduced in the preparation process of the solution.
4H-1-benzopyran-4-ones (chromones) are important naturally-distributing compounds. As compared with flavones, isoflavones and 2-styrylchromones, there are only few papers of 3-styrylchromones that have been published. We have previously reported that among fifteen 3-styrylchromone derivatives, three new synthetic compounds that have OCH3 group at the C-6 position of chromone ring, (E)-3-(4-hydroxystyryl)-6-methoxy-4H-chromen-4-one (compound 11), (E)-6-methoxy-3-(4-methoxystyryl)-4H-chromen-4-one (compound 4), (E)-6-methoxy-3-(3,4,5-trimethoxystyryl)-4H-chromen-4-one (compound 6) showed much higher cytotoxicities against four epithelial human oral squamous cell carcinoma (OSCC) lines than human normal oral mesenchymal cells. In order to further confirm the tumor specificities of these compounds, we compared their cytotoxicities against both human epithelial malignant and non-malignant cells, and then investigated their effects on fine cell structures and metabolic profiles and cell death in human OSCC cell line HSC-2. Cytotoxicities of compounds 4, 6, 11 were assayed with MTT method. Fine cell structures were observed under transmission electron microscope. Cellular metabolites were extracted with methanol and subjected to CE-TOFMS analysis. Compounds 4, 6, 11 showed much weaker cytotoxicity against human oral keratinocyte and primary human gingival epithelial cells, as compared with HSC-2, confirming their tumor-specificity, whereas doxorubicin and 5-FU were highly cytotoxic to these normal epithelial cells, giving unexpectedly lower tumor-specificity. The most cytotoxic compound 11, induced the mitochondrial vacuolization, autophagy suppression followed by apoptosis induction, and changes in the metabolites involved in amino acid and glycerophospholipid metabolisms. Chemical modification of lead compound 11 may be a potential choice for designing new type of anticancer drugs.
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