Background: As the end product of the bacterial fermentation of dietary fiber in the colonic lumen, sodium butyrate (NaBt) has been reported to exert antitumor effects on colorectal cancer (CRC). In addition to functioning as a histone deacetylase (HDAC) inhibitor, NaBt also regulates the expression of microRNAs (miRNAs) to inhibit CRC cell proliferation. Yet, the mechanisms involved are not completely understood. Here we investigate whether NaBt regulates miR-203 to inhibit CRC growth and explore the promising target gene of miR-203 in CRC cells. Methods: We conducted qRT-PCR and Western blotting assays to evaluate the effects of NaBt on the expression of miR-203 and NEDD9 in HT-29 and Caco-2 cell lines. The promising target gene of miR-203 was predicted by miRNA target prediction and dual luciferase reporter assay. CRC Cell proliferation, colony formation, cell apoptosis and cell invasion assays were performed to explore the effect of NaBt, miR-203 and NEDD9 on HT-29 and Caco-2 cell lines. Results: The results showed that NaBt increased the expression of miR-203 to induce CRC cell apoptosis as well as inhibit cell proliferation, colony formation and cell invasion. Moreover, we determined that the NEDD9 was a target gene of miR-203. NEDD9 partially overcame the inhibitory effects of miR-203 on CRC cell colony formation and invasion. Conclusions: NaBt could induce CRC cell apoptosis, inhibit CRC cell proliferation, colony formation and invasion through miR-203/NEDD9 cascade. The present study may enrich the mechanisms underlying the process that NaBt exerts anti-tumor effects on CRC cells.

This work provides insight into carrier dynamics in a model photoelectrochemical system comprised of a semiconductor, metal oxide, and metal. To isolate carrier dynamics from catalysis, a common catalytic metal (Pt) is used in concert with an outer-sphere redox couple. Silicon (111) substrates were surface-functionalized with electronegative aryl moieties (p-nitrophenyl and m-dinitrophenyl). A mixed monolayer using p-nitrophenyl/methyl exhibited high surface quality as determined by X-ray photoelectron spectroscopy (low surface SiO x content) and low surface recombination velocity. This substrate also exhibited the expected positive surface dipole, as evidenced by rectifying J–V behavior on p-type substrates, and by positive photovoltage measured by surface photovoltage spectroscopy. Its close molecular relative m-dinitrophenyl exhibited poor electronic surface quality as indicated by high SiO x coverage and high surface recombination velocities (S > 3000 cm s–1). Photoelectrochemical J–V measurements of p-type Si-functionalized surfaces in contact with a high concentration (50 mM) of methyl viologen (MV2+) in aqueous media revealed V OC values that are correlated with the measured barrier heights. In contrast, low-concentration (1.5 mM) MV2+ experiments revealed significant contributions from surface recombination. Next, the electronic and (photo)­electrochemical properties were studied as a function of ALD metal oxide deposition (TiO2, Al2O3) and Pt deposition. For the m-dinitrophenyl substrate, ALD deposition of both TiO2 and Al2O3 (150 °C, amorphous) decreased the surface recombination velocity. Surprisingly, this TiO2 deposition resulted in negative shifts in V OC for all surfaces (possibly ALD-TiO2 defect band effects). However, Pt deposition recovered the efficiencies beyond those lost in TiO2 deposition, affording the most positive V OC values for each substrate. Overall, this work demonstrates that (1) when carrier collection is kinetically fast, p-Si(111)–R devices are limited by thermal emission of carriers over the barrier, rather than by surface recombination. And (2) although TiO2|Pt improves the PEC performance of all substrates, the beneficial effects of the underlying (positive) surface dipole are still realized. Lastly (3) Pt deposition is demonstrated to provide beneficial charge separation effects beyond enhancing catalytic rates.

No abstract

The energy conversion efficiency of tandem photocatalysts for the overall water splitting reaction (OWS) is currently limited by our understanding of carrier separation and recombination in such systems. What is the effect of the solid–solid and solid–liquid interfaces on the carrier dynamics, and how do the photovoltage and catalytic activity depend on the light intensity? In order to address these issues, we report here on the light intensity-dependent water splitting activity and open circuit potential (OCP) measurements for a core–shell tandem made from bismuth vanadate (BiVO4) microparticles and ruthenium-loaded rhodium-doped strontium titanate (Ru-SrTiO3:Rh) nanoparticles. The measurements identify three operational regimes of the tandem: a threshold intensity of 8–14 mW cm–2 below which no OWS occurs, a regime of strongly increasing apparent quantum efficiency (AQE) (17.7–70.2 mW cm–2), and a regime of nearly constant AQE (>171 mW cm–2). Open circuit potential measurements of the separate BiVO4 and Ru-SrTiO3:Rh absorbers in dilute H2SO4 solution (pH 3.5) confirm photoanodic behavior for BiVO4 and photocathodic behavior for Ru-SrTiO3:Rh and provide the light intensity dependent quasi-Fermi energies for the majority carriers in each material. The data allows modeling of the charge transfer dynamics in the tandem. In the dark, the materials form a weak p/n-junction which causes minority carrier recombination at the tandem contact and impedes the function of the photocatalyst under low light flux. At higher light intensity, charge separation of the tandem is increasingly controlled by minority carrier transfer at the solid/liquid contacts. As a result, majority carriers can flow to the SrTiO3:Rh/BiVO4 interface and recombine there and help equilibrate the majority carrier Fermi levels of both absorbers to a common value. The resulting shift of the band edges of both absorbers improves the rectifying character of the solid–liquid contacts and is the basis for the increase of the AQE from 0 to 1.11% (400 nm). Above 171 mW cm–2, the AQE of the tandem remains nearly constant and becomes limited by intrinsic lattice and interfacial recombination of the two absorbers, by the low absorption coefficient of SrTiO3:Rh, and by the slow water oxidation kinetics of the BiVO4 surface. Finally, under very strong illumination, the H2/O2 back reaction becomes rate-limiting. These insights will be useful for the optimization of OWS tandem photocatalysts, especially under light limiting conditions.

S-doped Na2Ti6O13@TiO2 (S-TTO) core-shell nanorods, with exposed anatase TiO2 {101} facets, were synthesized by a facile calcination method. It was found that the addition of thiourea as the sulfur precursor was beneficial for the formation of anatase TiO2 with a better crystallinity and the doped sulfur atoms favorably stabilized the anatase structure. The substitution of Ti(4+) by S(6+) in the lattice of S-TTO gave rise to the visible light response and increased the amount of active groups typically as a hydroxyl radical adsorbed onto the catalyst surface. With the formation of the Ti-O-S bond, partial electrons could be transferred from S to O atoms. The electron-deficient S atoms might capture e(-) and thus inhibit the recombination of photogenerated electron-hole pairs. Meanwhile, a closely contacted interface was formed between Na2Ti6O13 and anatase TiO2, resulting in a nanoscale heterojunction structure to speed up the separation rate of photogenerated charge carriers. The exposed anatase {101} facets could act as possible reservoirs of the photogenerated electrons, yielding a highly reactive surface for the reduction of O2 to O2˙(-) and thus the decrease of recombination probability of electron-hole pairs. In addition, the anisotropically shaped titanate nanorods provided a pathway for the quick transport of charge carriers throughout the longitudinal direction. The combined effects of S doping, nano-heterojunction formation and morphology engineering led to an obviously enhanced photocatalytic performance for the degradation of methylene blue (MB) solution under visible light irradiation. The corresponding photocatalytic mechanism was investigated and discussed in detail. The present work may provide an insight into the fabrication of delicate composite photocatalysts with excellent performance.