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Metastasized cancer cells have an increased resistance to therapies leading to a drastic decrease in patient survival rates. However, our understanding of the cause for this enhanced resistance is lacking. In this study, we report that physically tight confinement during cancer cell migration triggers therapeutic resistance and induces cancer stem cell-like behavior including up-regulation in efflux proteins and in cancer stem cell related markers. Moreover, the re-localization of Yes-associated protein (YAP) to the cell nucleus indicated an elevated level of cytoskeletal tension. The increased cytoskeletal tension suggested that mechanical interactions between cancer cells and tight surroundings during metastasis is one of the factors that contributes to therapeutic resistance and acquisition of cancer stem cell (CSC) like features. With this system and supporting data, we are able to study cells with therapeutic resistance and CSC-like properties for the future purpose of developing new strategies for the treatment of metastatic cancer.

Polymeric and oligomeric carbosilanes having Si atoms linked by methylene ( CH2 ) groups were used to prepare nano-sized tubules and bamboo-like SiC structures by both CVD and liquid precursor infiltration and pyrolysis inside of nanoporous alumina filter disks, followed by dissolution of the alumina template in HF(aq). These initially amorphous SiC structures were characterized by SEM, EMPA, TEM, and XRD. Typical outer diameters of the SiC nanotubes (NTs) were 200–300 nm with 20–40 nm wall thicknesses and lengths up to the thickness of the original alumina templates, ca. 60 μm. In the case of the CVD-derived SiC NTs, annealing these structures up to 1600 °C in an Ar atmosphere yielded a nanocrystalline β-SiC or β-SiC/C composite in the shape of the original NTs, while in the case of the liquid precursor-derived nanostructures, conversion to a collection of single crystal SiC nanofibers and other small particles was observed.

A homologous series of poly(n-alkylmethylsiloxanes), [SiMe(R)O]n, were prepared by cationic ring-opening polymerization (ROP) of cyclotrisiloxanes containing n-alkyl substituents, such as C2H5, n-C3H7, n-C4H9, n-C5H11, and n-C6H13, on the Si. The resultant polymers were characterized by NMR, GPC, and DSC measurements. All of these asymmetrically substituted polymers were obtained in high molecular weight form and were found to have an atactic configuration. Their glass transitions were found to increase smoothly from Et to n-Hex (i.e., −139, −120, −115, −111.9, and −108 °C, for Et to n-Hex, respectively). These Tgs are much lower than those of the corresponding polyolefins, [C(H)(R)CH2]n. Moreover, in the case of these polyolefins, the Tgs decrease continuously from R = Me to n-Hex. The calculated Tgs for the polysiloxanes that were obtained by using published empirical equations show the same general trend as the experimental values.

A general method for introducing various side chains onto a highly branched polysilaethylene (HBPSE) backbone is described. This method starts with a commercial oligomer mixture which has a highly ...

Polysilaethylene ([SiH2CH2]n) (PSE) and deuterated polysilaethylene ([SiD2CH2]n) have been examined by both vibrational spectroscopy and X-ray diffraction methods above and below the crystallization/melting transition at −20 °C. The results confirm previous indications that PSE crystallizes in an all-trans conformation analogous to that found for its all-carbon analog, polyethylene. Raman spectroscopy reveals the appearance of a sharp band at 706 cm-1 attributable to the symmetric Si−C stretching vibration when PSE is cooled below 0 °C, while wide-angle X-ray diffraction shows the existence of a crystalline form with a monoclinic unit cell (a = 5.70 A, b = 8.75 A, c = 3.25 A; γ = 97.5°) whose dimensions compare closely to the calculated repeat distance using the planar zigzag conformation of PSE. The calculation of the IR spectra by ab initio methods (Hartree−Fock level of theory) using the 3-21G* and 6-31G* basis sets agrees well with the experimental IR results. Through the use of the calculated IR spec...

The molecular structure of the monosilicon analog of poly(ethylene), poly(silylenemethylene), CH3[SiH2CH2]nSiH3, or poly(silaethylene) (PSE), was characterized by means of high-resolution 1H, 13C, ...

This chapter focuses on the application of such nucleophilic substitution reactions toward the synthesis of hyperbranched polycarbosilanes, with particular emphasis on those preparations that have resulted in relatively well characterized products. These syntheses are organized by the type of AB n monomer unit used (see Section 1.2), where A and B refer to the (C)X and (Si)X n , respectively, functional ends of the monomer unit and where the nature of the coupling reaction leads to entirely or primarily Si–C bond formation. In most cases, these are “one-pot” reactions that employ monomers that bear halogen or alkoxy groups on the C and Si ends of the unit. Indeed, hyperbranched polycarbosilanes have been described, in general, as “obtained in one synthetic step via a random, one-pot polymerization of multifunctional monomers of AB n type” [2]. Treatment of the AB n monomer with either elemental Mg or an organolithium reagent, ideally (but not always) forms a complexed carbanion (the nucleophile) by reaction with the C–X end of the monomer unit, resulting in an intermediate of the type, (X x M)CSiX n , where M = Mg or Li, X = halogen or alkoxy