Polymer-Metal Bilayer with Alkoxy Groups for Antibacterial Improvement

Many bio-applicable materials, medical devices, and prosthetics combine both polymer and metal components to benefit from their complementary properties. This goal is normally achieved by their mechanical bonding or casting only. Here, we report an alternative easy method for the chemical grafting of a polymer on the surfaces of a metal or metal alloys using alkoxy amine salt as a coupling agent. The surface morphology of the created composites was studied by various microscopy methods, and their surface area and porosity were determined by adsorption/desorption nitrogen isotherms. The surface chemical composition was also examined by various spectroscopy techniques and electrokinetic analysis. The distribution of elements on the surface was determined, and the successful bonding of the metal/alloys on one side with the polymer on the other by alkoxy amine was confirmed. The composites show significantly increased hydrophilicity, reliable chemical stability of the bonding, even interaction with solvent for thirty cycles, and up to 95% less bacterial adhesion for the modified samples in comparison with pristine samples, i.e., characteristics that are promising for their application in the biomedical field, such as for implants, prosthetics, etc. All this uses universal, two-step procedures with minimal use of energy and the possibility of production on a mass scale.

Monitoring the Lifetime of Photoexcited Electrons in a Fresh and Bulk Reduced Rutile TiO2 Single Crystal. Possible Anisotropic Propagation

Defects (oxygen vacancies and interstitial cations) in oxide semiconductors have recently been invoked as a key property behind increased photocatalytic reaction rates. In this work, we have monitored by transient absorption spectroscopy (TAS) excited electrons in the conduction band decaying into the invoked traps to extract their lifetime using a rutile single crystal instead of the more conveniently used powder homologue. This is preferred in order to rule out grain boundary, degree of crystallinity, and size effects among other parameters that would obscure the results. It was found, in the energy region investigated (1.3-1.8 eV), that the lifetime of excited electrons is about four times shorter for the bulk defect crystal when compared to the fresh one. This indicates that the created defects (mostly oxygen defects and interstitial Ti cations) are unlikely to contribute to reaction rate enhancement.

A computational study of the interaction of oxygenates with the surface of rutile TiO2(110). Structural and electronic trends

A variety of OH containing molecules in their different modes of adsorption onto the rutile TiO₂(110) are studied by means of density functional theory. A special focus is given to ethanol, ethylene glycol and glycerol. The different species were analyzed with respect to the adsorption energy, work function, and atomic Bader charges. Our results show that dissociated adsorption is favored in all cases. Within these modes, the strongest binding is observed in the case of bidentate fully dissociated adsorption, followed by bidentate partially dissociated then the monodentate dissociated modes. The dependence is also noted upon charge transfer analysis. Species adsorbing with two dissociated OH groups show a negative charge which is roughly twice as large compared to those exhibiting only one dissociated group. In the case of molecular adsorption, we find a small positive charge on the adsorbate. The change in work functions obtained is found to be negative in all studied cases. We observe a trend of the work function change being more negative for glycerol (3 OH groups) followed by ethylene glycol (2 OH groups) and the remaining alcohols (1 OH group), thus indicating that the number of OH groups present is an important factor in regards to work function changes. For the complete series of adsorbates studied (methanol, ethanol, isopropanol, ethylene glycol, glycerol, hydrogen peroxide and formic acid) there is a linear relationship between the change in the work function and the adsorption energy for the molecular adsorption mode. The relationship is less pronounced for the dissociated adsorption mode for the same series.

Photo-catalytic hydrogen production over Au/g-C3N4: effect of gold particle dispersion and morphology

Metal/semiconductor interactions affect electron transfer rates and this is central to photocatalytic hydrogen ion reduction. While this interaction has been studied in great detail on metal oxide semiconductors, not much is known of Au particles on top of polymeric semiconductors. The effects of gold nanoparticle size and dispersion on top of g-C3N4 were studied by core and valence level spectroscopy and transmission electron microscopy in addition to catalytic tests. The as-prepared, non-calcined catalysts displayed Au particles with uniform dimension (mean particle size = 1.8 nm) and multiple electronic states: XPS Au 4f7/2 lines at 84.9 and 87.1 eV (each with a spin-orbit splitting of 3.6-3.7 eV). These particles, which did not show localized surface plasmon resonance (LSPR), before the reaction, doubled in size after the reaction giving a pronounced LSPR at about 550 nm. The effect of the heating environment on these particles (in air or in H2) was further investigated. While heating in H2 gave Au nanoparticles of different shapes, heating under O2 gave exclusively spherical particles. Similar activity towards photocatalytic hydrogen ion reduction under UV excitation was seen in both cases, however. XPS Au 4f analyses indicated that an increase in deposition time, during catalyst preparation, resulted in an increase in the initial fraction of oxidized gold particles, which were easily reduced under hydrogen. The valence band region for Au/gC3N4 was further studied in an effort to compare it to what is already known for Au/metal oxide semiconductors. A shift of over 2 eV for the Au 5d doublets was noticed between reduced and oxidized gold particles with mean particle sizes between 2 and 6 nm, which is consistent with the final state effect. A narrow range of gold loading for optimal catalytic performance was seen, where it seems that a density of one Au particle per 10 × 10 nm2 is the most suitable. Particle size and shape had a minor effect on performance, which may indicate the absence of a plasmonic effect on the reaction rate.

Photo-thermal reactions of ethanol over Ag/TiO2 catalysts. The role of silver plasmon resonance in the reaction kinetics

Photo-thermal catalytic reactions of ethanol over Ag/TiO₂ were conducted in order to probe into the role of plasmonic resonance response in the reaction kinetics.

Up-conversion luminescence coupled to plasmonic gold nanorods for light harvesting and hydrogen production

The conversion of infrared light to visible-light which allows a larger fraction of sun-light to be used is needed to improve light-harvesting. In this work a tri-functional material composed of an up-converter (NaYF₄-Yb-Tm), plasmonic gold nanorods and CdS was made photocatalytically active using 980 nm wavelength light for the reduction of H⁺ to H₂.

Positive variation of the MRI signal via intramolecular inclusion complexation of a C-2 functionalized β-cyclodextrin

The synthesis of a contrast agent based on a β-cyclodextrin is reported. An enhancement of relaxivity in the presence of an intramolecular inclusion complex is observed.

A DFT study on carbon monoxide adsorption onto hydroxylated α-Al₂O₃(0001) surfaces

The adsorption of CO onto the hydroxylated α-Al2O3(0001) surface was studied using density functional theory (DFT). Dissociated adsorption of water was found to be stable, with an adsorption energy (Ea) of 1.62 eV at θ(water) = 0.75. The most stable hydroxylation form on the clean surface was found to be in the 1-2 dissociation configuration, where the OH group binds to a surface Al ion and the H ion binds to one of the three equivalent surface O ions. The adsorption energy of CO was found to be dependent on the degree of pre-hydroxylation of the surface as well as on the CO coverage. The highest adsorption energy of CO was found when θ(CO) = 0.25 on a pre-hydroxylated surface with θ(water) = 0.25; Ea = 0.57 eV. The adsorption energy of CO decreased upon increasing the degree of pre-hydroxylation. The vibrational frequency of ν(CO) was also computed and in all cases it was blue shifted with respect to gas-phase CO. The shift, Δν, decreased with increasing CO coverage but increased with increasing surface hydroxylation. A comparison with available experimental work is discussed.

Hydrogen Production from Ethanol. Comparing Thermal Catalytic Reactions to Photo-catalytic Reactions

Hydrogen production from renewables such as bio-ethanol is one of the most promising processes for energy carriers in a sustainable way. In this work we review and compare two catalytic systems: one based on thermal activation over bimetallic catalysts (Rh-Pd/CeO2) and the other over photo-excited semiconductor catalysts (Au/TiO2 anatine, rutile and anatase/rutile). It is found that the hydrogen yield is far higher on the thermally activated catalysts (at 773K) when compared to that of the photo-exited catalysts (at room temperature); about 60 times. However, the photo-excited catalysts are a promising way to create a fully sustainable system for future applications if the complete removal of hydrogen atoms from water and ethanol are obtained at room temperature.

Ethanol photo-oxidation on a rutile TiO2(110) single crystal surface

The reaction of ethanol has been studied on the surface of rutile TiO(2)(110) by Temperature Programmed Desorption (TPD), online mass spectrometry under UV excitation and photoelectron spectroscopy while the adsorption energies of the molecular and dissociative modes of ethanol were computed using the DFT/GGA method. The most stable configuration is the dissociative adsorption in line with experimental results at room temperature. At 0.5 ML coverage the adsorption energy was found equal to 80 kJ mol(-1) for the dissociative mode (ethoxide, CH(3)CH(2)O(a) + H(a)) followed by the molecular mode (67 kJ mol(-1)). The orientation of the ethoxides along the [001] or [110] direction had minor effect on the adsorption energy although affected differently the Ti and O surface atomic positions. TPD after ethanol adsorption at 300 K indicated two main reactions: dehydration to ethylene and dehydrogenation to acetaldehyde. Pre-dosing the surface with ethanol at 300 K followed by exposure to UV resulted in the formation of acetaldehyde and hydrogen. The amount of acetaldehyde could be directly linked to the presence of gas phase O(2) in the vacuum chamber. The order of this photo-catalytic reaction with respect to O(2) was found to be 0.5. Part of acetaldehyde further reacted with O(2) under UV excitation to give surface acetate species. Because the rate of photo-oxidation of acetates (acetic acid) was slower than that of ethoxides (ethanol), the surface ended up by being covered with large amounts of acetates. A reaction mechanism for acetaldehyde, hydrogen and acetate formation under UV excitation is proposed.

Photoreaction of the rutile TiO2(011) single-crystal surface: reaction with acetic acid

The reaction of acetic acid with stoichiometric and reduced rutile TiO(2)(011) single-crystal surfaces has been studied under dark and UV illumination conditions. The surface coverage after the dissociative adsorption of acetic acid with respect to Ti was found to be 0.55. Monitoring XPS Ti, O, and C lines revealed that the surface population decreased incrementally with temperature up to 650 K. The decrease in the slope of both the -CH(3)- and -COO- XPS peaks was not monotonic and followed two slopes in agreement with TPD results. The first channel involves the removal of surface acetates to acetic acid by recombinative desorption, and the second mainly involves dehydration to ketene. UV-light illumination was conducted at 300 K in the absence and presence of molecular oxygen at different pressures: in the 10(-6)-10(-9) Torr range. Acetate species were found to decrease with illumination time, and their decrease is seen to be dependent on the oxygen pressure. Plausible decomposition pathways are presented. Deliberately reducing the surface by electron bombardment prior to the adsorption of acetic acid did not affect the photoreaction rate within the experimental limits.

Ab initio study of surface acid-base reactions. The case of molecular and dissociative adsorption of ammonia on the (011) surface of rutile TiO2

The interaction of ammonia molecules with Lewis acid centers (Ti4+ metal ions) of the (011) surface of rutile TiO2 is investigated by density functional theory in order to understand, from first principle, the nature of acid-base reactions on solid surfaces. Unlike the rutile (110) surface that contains alternating rows of 5-fold and 6-fold Ti atoms, all Ti atoms of the (011) surface are 5-fold coordinated. This surface has shown considerable activity for numerous chemical reactions and is thus an ideal prototype. At 1/2 monolayer coverage, with respect to surface Ti atoms, the adsorption energy is found to be equal to 100 kJ mol-1, and drops to 58 kJ mol-1 at one monolayer coverage. Analysis of the electronic density of states (DOS) revealed information regarding the mode of adsorption. In particular, the nitrogen 3a1 and 2a1 orbitals appear to undergo significant changes upon adsorption, in agreement with photoelectron spectroscopy studies. Dissociative adsorption was also investigated on the same surface. Both NH2(Tis) + H(Os) and NH(Tis) + 2H(Os) modes of dissociative adsorption, where s stands for surface, are found to be less stable than the molecular (non dissociated) adsorption.

Photocatalysis and the origin of life: synthesis of nucleoside bases from formamide on TiO2(001) single surfaces

We report the conversion of a large fraction of formamide (NH(2)CHO) to high-molecular-weight compounds attributed to nucleoside bases on the surface of a TiO(2) (001) single crystal in ultra-high vacuum conditions. If true, we present previously unreported evidence for making biologically relevant molecules from a C1 compound on any single crystal surface in high vacuum and in dry conditions. An UV light of 3.2 eV was necessary to make the reaction. This UV light excites the semiconductor surface but not directly the adsorbed formamide molecules or the reaction products. There thus is no need to use high energy in the form of photons or electrical discharge to make the carbon-carbon and carbon-nitrogen bonds necessary for life. Consequently, the reaction products may accumulate with time and may not be subject to decomposition by the excitation source. The formation of these molecules, by surface reaction of formamide, is proof that some minerals in the form of oxide semiconductors are active materials for making high-molecular-weight organic molecules that may have acted as precursors for biological compounds required for life in the universe.

Coupling of carbon monoxide molecules over oxygen-defected UO2(111) single crystal and thin film surfaces

While coupling reactions of carbon-containing compounds are numerous in organometallic chemistry, they are very rare on well-defined solid surfaces. In this work we show that the reductive coupling of two molecules of carbon monoxide to C2 compounds (acetylene and ethylene) could be achieved on oxygen-defected UO2(111) single crystal and thin film surfaces. This result allows in situ electron spectroscopic investigation of a typical organometallic reaction such as carbon coupling and extends it to heterogeneous catalysis and solids. By using high-resolution photoelectron spectroscopy (HRXPS) it was possible to track the changes in surface states of the U and O atoms as well as identify the intermediate of the reaction. Upon CO adsorption U cations in low oxidation states are oxidized to U4+ ions; this was accompanied by an increase of the O-to-U surface ratios. The HRXPS C 1s lines show the presence of adsorbed species assigned to diolate species (-OCH=CHO-) that are most likely the reaction intermediate in the coupling of two CO molecules to acetylene and ethylene.

Reactions of glutaric acid on the TiO2(001) single crystal. Effect of surface reduction on the reaction pathway

The detailed reaction of glutaric acid (a C(5) dicarboxylic acid) has been studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Upon adsorption at 300 K, both carboxylic acid functions are deprotonated to give adsorbed glutarate species. The reaction of these species differs significantly on the oxidized surface from that on the reduced surface. On the oxidized surface, two competing reactions are seen: (i) decomposition to two molecules of CO and one molecule of propene and (ii) dehydration to ketene. Upon sputtering with hydrogen ions (reducing the surface states of Ti ions and implanting hydrogen atoms in the lattice), the main observed reaction is reduction to the dialdehyde and the dialcohol. The yield of these two products, not seen on the oxidized surface, reaches 80% on the highly reduced surface. Another compound is seen on the reduced surface with m/z = 70. The analysis of its fragmentation pattern tends to assign it to cyclopentane that is formed by an intramolecular reductive coupling reaction on the O-defect sites.

Reactions of ammonia on stoichiometric and reduced TiO(2)(001) single crystal surfaces

The reaction of NH(3) on the surface of the 011-faceted structure of the TiO(2)(001) single crystal is studied and compared to that on the O-defected surface. Temperature-programmed desorption (TPD) conducted after NH(3) adsorption at 300 K shows only molecular desorption at 340 K. Modeling of TPD signals as a function of surface coverage indicated that the activation energy, E(d), and pre-exponential factor, v(eff), decrease with increasing coverage. Near zero surface coverage, E(d) was found to be equal to 92 kJ/mol and v(eff) to be close to 10(13) /s. Both parameters decreased to approximately 52 kJ/mol and approximately 10(7) /s at saturation coverage. The decrease is due to a repulsive interaction of adsorbed NH(3) molecules on the surface. Computing of the TPD results show that saturation is obtained at 1/2 monolayer coverage (referred to Ti atoms). Both the amount and shape of NH(3) peak change on the reduced (Ar(+)-sputtered) surfaces. The desorption peak at 340 K is considerably attenuated on mildly reduced surfaces (TiO( approximately )(1.9)) and has totally disappeared on the heavily reduced surfaces (TiO(1.6)(-)(1.7)), where the main desorption peak is found at 440 K. This 440-K desorption is most likely due to NH(x) + H recombination resulting from ammonia dissociation upon adsorption on Ti atoms in low oxidation states.

Selective modulation of P-glycoprotein's ATPase and anion efflux regulation activities with PKC alpha and PKC epsilon in Sf9 cells

The modulation of P-glycoprotein's (Pgp) ATPase activity and its ability to regulate swelling-activated 125I efflux, by PKC alpha and PKC epsilon, was examined in insect cells. Recombinant baculovirus was used to express human Pgp in Sf9 cells and Pgp was also coexpressed with either PKC alpha or PKC epsilon. ATPase assays showed the enzyme activity of Pgp to be elevated during co-expression with the Ca2+ dependent isoform PKC alpha, but not with the Ca2+ independent variant PKC epsilon. Furthermore, neither isoform, when co-expressed with Pgp, altered the swelling-activated efflux of 125I from Sf9 cells. However, in cells co-expressing Pgp/PKC (alpha or epsilon), pre-treatment with the phorbol ester TPA significantly reduced the swelling-activated 125I efflux with both PKC isoforms. Our results suggest that phosphorylation with the Ca2+ independent variant PKC epsilon does not regulate the ATPase activity of Pgp and that stimulation of PKC with TPA alters the swelling-activated efflux of anions from insect cells expressing Pgp.

HIV-1 reverse transcriptase is phosphorylated in vitro and in a cellular system

Phosphorylation modulates the activity of many proteins that interact with nucleic acids including DNA and RNA polymerases. The HIV-1 reverse transcriptase (RT) is essential during the replicative cycle of the HIV-1 virus. HIV-1 RT has several potential sites for phosphorylation that could regulate its activities. In this work, the phosphorylation of HIV-1 RT is examined in vitro and in vivo, to evaluate any role for this modification in regulating RT metabolism. Recombinant unphosphorylated HIV-1 RT heterodimer expressed in bacteria can be phosphorylated in vitro by several purified mammalian protein kinases. Seven kinases were tested, and five of these enzymes phosphorylated HIV-1 RT. Using an insect baculovirus expression system, the 66 kDa HIV-1 RT was also phosphorylated in vivo. However, HIV-1 RT immunoprecipitated from H9-lymphoma cells infected with HIV-1 showed negligible phosphorylation. Our results indicate that purified HIV-1 RT can be phosphorylated by several mammalian protein kinases in vitro and during expression in baculovirus infected insect cells.