Shrong-Shi Lin

Demicellization of a Mixture of Cationic−Anionic Hydrogenated/Fluorinated Surfactants through Selective Inclusion by α- and β-Cyclodextrin

The interactions between alpha- and beta-cyclodextrin (alpha-/beta-CD) and an equimolar mixture of octyltriethylammonium bromide (OTEAB) and sodium perfluorooctanoate (SPFO) were studied by 1H and 19F NMR, surface tension, conductivity, and dynamic light scattering. It was shown that beta-CD could destroy the mixed micelles of OTEAB-SPFO by selective inclusion of SPFO. As beta-CD was added, the system was observed to undergo a process like this: beta-CD preferentially included SPFO to form 1:1 beta-CD/SPFO complexes. As the inclusion of SPFO was almost saturated, the mixed micelles broke and all OTEAB was released and exposed to aqueous surroundings. Then 1:1 beta-CD/OTEAB and 2:1 beta-CD/SPFO complexes significantly formed simultaneously. Contrary to beta-CD, alpha-CD exhibited selective inclusion to OTEAB and only weak association with SPFO. alpha-CD could also destroy the mixed micelles of OTEAB-SPFO; however, the demicellization ability of alpha-CD is much smaller than that of beta-CD. These conclusions were also well supported by the calculations of binding constants and DeltaG degrees . Different from the complexes of CD/conventional surfactants, the complexes of beta-CD/SPFO or alpha-CD/OTEAB formed by selective inclusion of CD in the mixed cationic-anionic surfactants may have contributed to the surface activity of the aqueous mixtures. The complexes of alpha-CD/OTEAB showed much more significant contribution to the surface activity than that of the complexes of beta-CD/SPFO.

How does structure determine organic reactivity? Partitioning of carbocations between addition of nucleophiles and deprotonation

Publisher Summary This chapter reviews the results of the studies of the kinetics and products of stepwise nucleophilic substitution and elimination reactions of alkyl derivatives, focuses on factors that control the rate constant ratio k s / k p for the partitioning of carbocations, and provides an understanding of how the absolute rate constants k s and k p that constitute this ratio, change with changing carbocation structure. The analyses presented in the chapter are possible because of some recent experimental results that include: determinations of absolute rate constants with values up to k s = 10 10 s -1 for the reaction of carbocations with water and other nucleophilic solvents, determination of the large values of the rate constant ratio k s / k p from the low yields of alkene product, kinetic studies of stepwise hydration reactions of alkenes, and recent characterization of carbocations that partition to form an alkene. The chapter also discusses the explanations for the large changes in the rate constant ratio for the partitioning of carbocations between reaction with BrOnsted and Lewis bases that result from small changes in carbocation structure.

Bio-inspired protein-gold nanoconstruct with core-void-shell structure: beyond a chemo drug carrier

Chemotherapy has been widely used in clinical practice for cancer treatment. A major challenge for a successful chemotherapy is to potentiate the anticancer activity, whilst reducing the severe side effects. In this context, we design a bio-inspired protein-gold nanoconstruct (denoted as AFt-Au hereafter) with a core-void-shell structure which exhibits a high selectivity towards carcinoma cells. Anticancer drug 5-fluorouracil (5-FU) can be sequestered into the void space of the construct to produce an integrated nanoscale hybrid AFt-AuFU that exhibits an increased cellular uptake of 5-FU. More importantly, AFt-Au, serving as a bio-nano-chemosensitizer, renders carcinoma cells more susceptible to 5-FU by cell-cycle regulation, and thus, leads to a dramatic decrease of the IC50 value (i.e. the drug concentration required to kill 50% of the cell population) of 5-FU in HepG2 cells from 138.3 μM to 9.2 μM. Besides HepG2 cells, a remarkably enhanced anticancer efficacy and potentially reduced side effects are also achieved in other cell lines. Our further work reveals that the drug 5-FU is internalized into cells with AFt-Au primarily via receptor-mediated endocytosis (RME). After internalization, AFt-AuFU colocalizes with lysosomes which trigger the release of 5-FU under acidic conditions. Overall, our approach provides a novel procedure in nanoscience that promises an optimal chemotherapeutic outcome.