Photo-induced electron transfer in supramolecular materials of titania nanostructures and cytochrome c

In the present paper, we report on the molecular interaction and photochemistry of TiO2 nanoparticles (NPs) and cytochrome c systems for understanding the effects of supramolecular organization and electron transfer by using two TiO2 structures: P25 TiO2 NPs and titanate nanotubes. The adsorption and reduction of cytochrome c heme iron promoted by photo-excited TiO2, arranged as P25 TiO2 NPs and as nanotubes, were characterized using electronic absorption spectroscopy, thermogravimetric analysis, and atomic force microscopy. In an aqueous buffered suspension (pH 8.0), the mass of cytochrome c adsorbed on the P25 TiO2 NP surface was 2.3 fold lower (0.75 μg m−2) than that adsorbed on the titanate nanotubes (1.75 μg m−2). Probably due to the high coverage of titanate nanotubes by adsorbed cytochrome c, the low amount of soluble remaining protein was not as efficiently photo-reduced by this nanostructure as it was by the P25 TiO2 NPs. Cytochrome c, which desorbed from both titanium materials, did not exhibit changes in its redox properties. In the presence of the TiO2 NPs, the photo-induced electron transfer from water to soluble cytochrome c heme iron was corroborated by the following findings: (i) identification by EPR of the hydroxyl radical production during the irradiation of an aqueous suspension of TiO2 NPs, (ii) impairment of a cytochrome c reduction by photo-excited TiO2 in the presence of dioxane, which affects the dielectric constant of the water, and (iii) change in the rate of TiO2-promoted cytochrome c reduction when water was replaced with D2O. The TiO2-promoted photo-reduction of cytochrome c was reverted by peroxides. Cytochrome c incorporated in the titanate nanotubes was also reversibly reduced under irradiation, as confirmed by EPR and UV-visible spectroscopy21974177426CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP475235/2010-0; 2011/01541-0Sem informação2008/04849-0; 2009/15558-1; 2011/01541-

Evaluation of Cyclodextrins as Environmentally Friendly Wettability Modifiers for Enhanced Oil Recovery

In the present work, the use of Cyclodextrins (CDs) as wettability modifiers for enhanced oil recovery (EOR) was evaluated. Cyclodextrins (CDs) are cyclic oligosaccharides that form inclusion complexes with various organic molecules, including n-alkanes. Wettability was evaluated through the contact angle (θ) of an n-dodecane drop in contact with a quartz surface and immersed in a 0.6 M NaCl aqueous solution containing the CDs. The quartz surface was functionalized with octadecyltrichlorosilane (OTS), rendering the surface oil-wet (C18-quartz). Here, the n-dodecane, the saline solution and the C18-quartz represent the oil, the reservoir brine and an oil-wet rock surface, respectively. In the absence of CDs, the n-dodecane drops spread well over the C18-quartz, showing that the surface was oleophilic. In the presence of CDs, remarkable effects on the wettability were observed. The most dramatic effects were observed with α-cyclodextrin (α-CD), in which case the C18-quartz surface changed from oil-wet (θ = 162°) in the absence of CD to water-wet (θ = 33°) in the presence of 1.5% (w/v) α-CD. The effects of the CDs can be explained by the formation of surface-active inclusion complexes between the CDs and n-dodecane molecules. The CD inclusion complexes can be regarded as pseudo-surfactants, which are less harmful to the environment than the traditional surfactants employed by the petroleum industry

Characterization of a Perylenediimide Self-Assembled Monolayer on Indium Tin Oxide Electrodes Using Electrochemical Impedance Spectroscopy

Self-assembled monolayers (SAMs) of <i>N,N</i>′-bis­(2-phosphonoethyl)-3,4,9,10-perylenediimide (PPDI), a perylene dye substituted with phosphonic acid groups, were deposited on indium tin oxide (ITO) substrates. Dye deposition was confirmed by UV–visible absorption spectroscopy and by electrochemical methods. Electrochemical characterization of the SAM was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Two reversible redox waves were observed by CV for the PPDI monolayer, corresponding to <i>E</i>_1/2 = −0.49 V (radical anion formation) and <i>E</i>_1/2 = −0.90 V (dianion formation). The effect of applied bias on the EIS response was studied, comparing a region where PPDI was not reduced (applied bias = 0 V) with a region within the redox window of the imide (applied bias = −0.6 V). The EIS results were analyzed using either impedance (Nyquist and Bode) or capacitance (Cole–Cole) diagrams. Capacitance plots were shown to be by far more sensitive to study the faradaic activity of the SAM, allowing the determination of both the pseudocapacitance (<i>C</i>_pc) for charging the monolayer and the heterogeneous electron transfer rate constant (<i>k</i>_et) from the electrode to the SAM. A molecular coverage of 7 × 10^–11 mol/cm² was calculated for the SAM from the pseudocapacitance. A value of <i>k</i>_et = 41 s^–1 was obtained, consistent with literature data for similar systems

Color-Tunable Fluorescence and White Light Emission from Mesoporous Organosilicas Based on Energy Transfer from 1,8-Naphthalimide Hosts to Perylenediimide Guests

The present work reports Förster resonance energy transfer (FRET) from 1,8-naphthalimide (NI) donors bound to the pore walls of mesoporous silicas to perylenediimide (PDI) acceptors doped into the mesochannels. Mesoporous organosilicas containing covalently bound NI were synthesized by co-condensation of tetraethylorthosilicate (TEOS) with N-(3-(triethoxysilyl)­propyl)-1,8-naphthalimide (TEPNI) in the presence of a block copolymer surfactant as a template. The resulting materials were highly ordered, presenting a 2D hexagonal structure, and displayed easily tunable optical properties, which could be controlled by the amount of NI in the sample. A sample prepared from a diluted TEPNI solution (SBANId) presented a blue, monomerlike emission. In contrast, when a concentrated TEPNI solution was used, the resulting material (SBANIc) displayed a green, excimerlike emission. For the FRET studies, N,N′-bis­(2,6-dimethylphenyl)-3,4,9,10-perylenediimide was doped into the pores of the SBANI samples from chloroform solutions. When excited at the NI absorption maximum (350 nm), PDI-doped SBANIc showed intense quenching of the NI emission band, even at very low PDI doping, with quenching efficiencies reaching nearly 80% with only 0.6 mol % PDI (PDI/NI ≈ 1:170). The emission of PDI was observed at higher doping ratios, even though the PDI hardly absorbs at 350 nm, thus evidencing FRET from the host NI to the guest PDI. SBANI materials with a suitable amount of the PDI dopant displayed a white emission, spanning the whole visible spectrum

A Novel Synthesis Route of Mesoporous gamma Alumina from Polyoxohydroxide Aluminum

Mesoporous gamma-aluminas (gamma-Al2O3) were synthesized starting from an unusual precursor of polyoxohydroxide aluminum (POHA). This precursor was obtained from aluminum oxidation in alkaline water-ethanol solvent in the presence of d-glucose that induces the formation of a gel, which leads to the POAH powder after ethanolic treatment Precipitated POHAs were calcined at different temperatures (300, 400, 700 and 900 degrees C) resultmg m the metastable gamma-Al(2)0(3) phase. Whereas at 300 degrees C no gamma-Al(2)0(3) phase was formed, unexpectedly, mesoporous gamma-Al(2)0(3) was obtained at 400 degrees C having a high specific surface area (282 m(2)/g) and a narrow pore size distribution At higher temperatures, the aluminas had the expected decrease in surface area 166 m(2)/g (700 degrees C) and 129 m(2)/g (900 degrees C), respectively The structural change from POHA to alumina calcined at 400 degrees C occurs directly without the need to isolate the hydroxide or oxyhydroxide aluminum precursors Both POHA and transition aluminas were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), N-2 sorption and Scanning Electron Microscopy (SEM) These findings show an alternative route to produce high standard aluminas.Fundacao de Apoio a Pesquisa do Estado de Sao Paulo - FAPESPCAPESCNPqUniv Sao Paulo, Dept Engn Quim DEQ, Escola Engn Lorena, Estr Municipal Campinho S-N, BR-12602810 Lorena, SP, BrazilUniv Fed Sao Paulo UNIFESP, Dept Ciencias Exatas & Terra, Rua Sao Nicolau 210, BR-09913030 Diadema, SP, BrazilUniv Fed ABC, Ctr Engn Modelagem & Ciencias Sociais Aplicadas, Santo Andre, SP, BrazilUniv Sao Paulo, Inst Quim, Ave Prof Lineu Prestes 748, BR-05508900 Sao Paulo, SP, BrazilUniv Sao Paulo, Escola Engn Lorena, Polo Ind, Dept Engn Mat DEMAR, Gleba Al-6 S-N, BR-12602810 Lorena, SP, BrazilUniv Fed Sao Paulo UNIFESP, Dept Ciencias Exatas & Terra, Rua Sao Nicolau 210, BR-09913030 Diadema, SP, BrazilFAPESP: 2015/06064-6, 2013/08166-5, 2016/05496-2Web of Scienc

Zirconium phosphonate/1,4,5,8-naphthalenediimides self-assembled films

The formation and characterization of self-assembled films of zirconium phosphonate / N,N'-di(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (DPN) is presented. The films were produced on glass substrates by deposition of alternating layers of Zr+4 and DPN. Films containing up to 16 layers on each side of the substrate were obtained and monitored by absorption spectroscopy and ellipsometry. When irradiated, the initially colorless films turned to a persistent pinky color reminiscent of that of DPN anion radical. These films are a promising material to the development of photovoltaic devices

A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum

<div><p>Mesoporous gamma-aluminas (γ-Al2O3) were synthesized starting from an unusual precursor of polyoxohydroxide aluminum (POHA). This precursor was obtained from aluminum oxidation in alkaline water-ethanol solvent in the presence of d-glucose that induces the formation of a gel, which leads to the POAH powder after ethanolic treatment. Precipitated POHAs were calcined at different temperatures (300, 400, 700 and 900 °C) resulting in the metastable γ-Al2O3 phase. Whereas at 300 °C no γ-Al2O3 phase was formed, unexpectedly, mesoporous γ-Al2O3 was obtained at 400 ºC having a high specific surface area (282 m2/g) and a narrow pore size distribution. At higher temperatures, the aluminas had the expected decrease in surface area: 166 m2/g (700 °C) and 129 m2/g (900 °C), respectively. The structural change from POHA to alumina calcined at 400 ºC occurs directly without the need to isolate the hydroxide or oxyhydroxide aluminum precursors. Both POHA and transition aluminas were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 sorption and Scanning Electron Microscopy (SEM). These findings show an alternative route to produce high standard aluminas.</p></div

Covalent attachment of 3,4,9,10-perylenediimides onto the walls of mesoporous molecular sieves MCM-41 and SBA-15

This work describes the covalent grafting of 3,4,9,10-perylenediimides (PDI), which are fluorescent dyes with very interesting optical properties, onto the walls of mesoporous molecular sieves MCM-41 and SBA-15. The mesoporous materials were first treated with 3-aminopropyltriethoxysilane (APTES) in anhydrous toluene, generating amine-containing surfaces. The amine-containing materials were then reacted with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCA), generating surface-grafted PDI. Infrared spectra of the materials showed that the reaction with amino groups took place at both anhydride ends of the PTCA molecule, resulting in surface attached diimides. No sign of unreacted anhydride groups were found. The new materials, designated as MCMN2PDI and SBAN(2)PDI, presented absorption and emission spectra corresponding to weakly coupled PDI chromophores, in contrast to the strongly coupled rings usually found in solid PDI samples. The materials showed a red fluorescence, which could be observed by the naked eye under UV irradiation or with a fluorescence microscope. The PDI-modified mesoporous materials showed electrical conductivity when pressed into a pellet. The results presented here show that the new materials are potentially useful in the design of nanowires. (C) 2007 Elsevier Inc. All rights reserved