Adsorption of enterobactin to metal oxides and the role of siderophores in bacterial adhesion to metals

The potential contribution of chemical bonds formed between bacterial cells and metal surfaces during biofilm initiation has received little attention. Previous work has suggested that bacterial siderophores may play a role in bacterial adhesion to metals. It has now been shown using in situ ATR-IR spectroscopy that enterobactin, a catecholate siderophore secreted by Escherichia coli, forms covalent bonds with particle films of titanium dioxide, boehmite (AlOOH), and chromium oxide-hydroxide which model the surfaces of metals of significance in medical and industrial settings. Adsorption of enterobactin to the metal oxides occurred through the 2,3-dihydroxybenzoyl moieties, with the trilactone macrocycle having little involvement. Vibrational modes of the 2,3-dihydroxybenzoyl moiety of enterobactin, adsorbed to TiO(2), were assigned by comparing the observed IR spectra with those calculated by the density functional method. Comparison of the observed adsorbate IR spectrum with the calculated spectra of catecholate-type [H(2)NCOC(6)H(3)O(2)Ti(OH)(4)](2-) and salicylate-type [H(2)NCOC(6)H(3)O(2)HTi(OH)(4)](2-) surface complexes indicated that the catecholate type is dominant. Analysis of the spectra for enterobactin in solution and that adsorbed to TiO(2) revealed that the amide of the 2,3-dihydroxybenzoylserine group reorientates during coordination to surface Ti(IV) ions. Investigation into the pH dependence of enterobactin adsorption to TiO(2) surfaces showed that all 2,3-dihydroxybenzoyl groups are involved. Infrared absorption bands attributed to adsorbed enterobactin were also strongly evident for E. coli cells attached to TiO(2) particle films. These studies give evidence of enterobactin-metal bond formation and further suggest the generality of siderophore involvement in bacterial biofilm initiation on metal surfaces.     

Adsorption to metal oxides of the Pseudomonas aeruginosa siderophore pyoverdine and implications for bacterial biofilm formation on metals

The initiation of biofilm formation is poorly understood, and in particular, the contribution of chemical bond formation between bacterial cells and metal surfaces has received little attention. We have previously used in situ infrared spectroscopy to show, during the initial stages of Pseudomonas aeruginosa biofilm formation, the formation of coordinate covalent bonds between titanium dioxide particle films and pyoverdine, a mixed catecholate and hydroxamate siderophore. Here we show using infrared spectroscopy that pyoverdine can also form covalent bonds with particle films of Fe2O3, CrOOH, and AlOOH. Adsorption to the metal oxides through the catechol-like 2,3-diamino-6,7-dihydroxyquinoline part of pyoverdine was most evident in the infrared spectrum of the adsorbed pyoverdine molecule. Weaker infrared absorption bands that are consistent with the hydroxamic acids of pyoverdine binding covalently to TiO2, Fe2O3, and AlOOH surfaces were also observed. The adsorption of pyoverdine to TiO2 and Fe2O3 surfaces showed a pH dependence that is indicative of the dominance of the catechol-like ligand of pyoverdine. Infrared absorption bands were also evident for pyoverdine associated with the cells of P. aeruginosa on TiO2 and Fe2O3 surfaces and were notably absent for genetically modified cells unable to synthesize or bind pyoverdine at the cell surface. These studies confirm the generality of pyoverdine-metal bond formation and suggest a wider involvement of siderophores in bacterial biofilm initiation on metals.     

A biomimetic principle for the chemical modification of metal surfaces: synthesis of tripodal catecholates as analogues of siderophores and mussel adhesion proteins

By following a biomimetic design principle, tetravalent scaffolds based on an adamantyl and trisalkylmethyl core structure have been synthesized. These scaffolds have been coupled to three catecholamines, thus resembling the characteristic tripodal recognition motif of many natural metal binders, such as mussel adhesion proteins and siderophores, for example, enterobactin. Besides this tripodal recognition element, our scaffolds provide a fourth position for the conjugation of effector molecules. These effectors can be conjugated through biocompatible conjugation techniques to the scaffold and can be used to tailor the properties of different metal surfaces for a range of applications, for example, in implant engineering. Herein, we describe the synthesis of several tripodal metal binders and their immobilization on TiO(2) surfaces by using a simple dip-coating procedure. Furthermore, we demonstrate the conjugation of our surface binders to the dye eosin Y as an effector molecule by peptide coupling. The resulting surfaces have been analyzed by using ellipsometry, time-of-flight secondary ion mass spectrometry, IR spectroscopy, and contact-angle measurements to confirm the specific loading on TiO(2) films and nanoparticles with our trivalent surface binders. As a proof of concept, we have demonstrated the functionalization of TiO(2) nanoparticles with the eosin Y dye.     

The impact of ultraviolet light on bacterial adhesion to glass and metal oxide-coated surface

Biofouling of glass and quartz surfaces can be reduced when the surface is coated with photocatalytically active metal oxides, such as TiO2 (anatase form) or SnO2. We measured the attachment of eight strains of bacteria to these two metal oxides (TiO2 and SnO2), and to an uncoated glass (control; designated Si-m) before and after exposure to UV light at wavelengths of 254 nm (UVC) or 340 nm UV (UVA). TiO2-coated surfaces were photocatalytically active at both 254 and 340 nm as evidenced by a decrease in the water contact angle of the surface from 59 degrees +/-2 to <5 degrees. The water contact angle of the SnO2 surface was reduced only at 254 nm, while contact angle of the Si-m glass surface was not altered by light of either wavelength. Bacterial adhesion decreased by 10-50% to photocatalyzed glass surfaces. In all cases, bacteria exposed to the UV light were completely killed due to a combination of exposure to UV light and the photocatalytic activity of the glass surfaces. These results show that UV light irradiation of TiO2-coated surfaces can be an effective method of reducing bacterial adhesion.     

Adsorption of 2-chloropyridine on oxides--an infrared spectroscopic study

The adsorption of 2-chloropyridine on SiO(2), TiO(2), ZrO(2), SiO(2)-Al(2)O(3) and H-mordenite has been studied by IR spectroscopy. The different modes of interaction with oxide surfaces, i.e. hydrogen-bonding and adsorption at Br?nsted or Lewis acid sites, was modelled by ab initio calculations at the B3LYP/DZ+(d) level. Adsorption on SiO(2) results in hydrogen bonding to surface hydroxyl groups, whereas the spectra obtained following adsorption on TiO(2) and ZrO(2) display evidence for electron transfer at Lewis acidic surface sites. Protonation of 2-chloropyridine at Br?nsted acidic sites was detected only for adsorption on SiO(2)-Al(2)O(3) and H-mordenite, indicating the presence of Br?nsted acidic sites on these oxide surfaces with pK(a) values 相似文献   

Tin oxide-surface modified anatase titanium(IV) dioxide with enhanced UV-light photocatalytic activity

[Sn(acac)(2)]Cl(2) is chemisorbed on the surfaces of anatase TiO(2)via ion-exchange between the complex ions and H(+) released from the surface Ti-OH groups without liberation of the acetylacetonate ligand (Sn(acac)(2)/TiO(2)). The post-heating at 873 K in air forms tin oxide species on the TiO(2) surface in a highly dispersed state on a molecular scale ((SnO(2))(m)/TiO(2)). A low level of this p block metal oxide surface modification (~0.007 Sn ions nm(-2)) accelerates the UV-light-activities for the liquid- and gas-phase reactions, whereas in contrast to the surface modification with d block metal oxides such as FeO(x) and NiO, no visible-light response is induced. Electrochemical measurements and first principles density functional theory (DFT) calculations for (SnO(2))(m)/TiO(2) model clusters (m = 1, 2) indicate that the bulk (TiO(2))-to-surface interfacial electron transfer (BS-IET) enhances charge separation and the following electron transfer to O(2) to increase the photocatalytic activity.     

ATR-FTIR spectroscopy reveals bond formation during bacterial adhesion to iron oxide

The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces was examined using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. When live Shewanella oneidensis, Pseudomonas aeruginosa, and Bacillus subtilis cells were introduced to a horizontal hematite (alpha-Fe(2)O(3))-coated internal reflection element (IRE), FTIR peaks emerged corresponding to bacterial phosphate group binding. These IR peaks were not observed when bacteria were introduced to the uncoated ZnSe IRE. When cells were added to colloidal suspensions of alpha-Fe(2)O(3) at pH 7, spectra included peaks corresponding to P-OFe and nu(COOH), the latter being attributed to bridging of carboxylate at mineral surface OH groups. Selected model organic compounds with P-containing functionalities (phenylphosphonic acid [PPA], adenosine 5'-monophosphate [AMP], 2'-deoxyadenyl(3'-->5')-2'-deoxyadenosine [DADA], and deoxyribonucleic acid [DNA]) produce spectra with similar peaks corresponding to P-OFe when adsorbed to alpha-Fe(2)O(3). The data indicate that both terminal phosphate/phosphonate and phosphodiester groups, either exuded from the cell or present as surface biomolecules, are involved in bacterial adhesion to Fe-oxides through formation of innersphere Fe-phosphate/phosphonate complexes.     

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO₂ metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the “stickiest” sites. Application of a TiO₂-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.     

Zinc(II) tetraarylporphyrins anchored to TiO2, ZnO, and ZrO2 nanoparticle films through rigid-rod linkers

A series of six Zn(II) tetraphenylporphyrins (ZnTPP), with a phenyl (P) or oligophenyleneethynylene (OPE = (PE) n ) rigid-rod bridge varying in length (9-30 A) and terminated with an isophthalic acid (Ipa) anchoring unit, were prepared as model dyes for the study of sensitization processes on metal oxide semiconductor nanoparticle surfaces (MO(n) = TiO(2), ZnO, and insulating ZrO(2)). The dyes were designed such that the electronic properties of the central porphyrin chromophore remained consistent throughout the series, with the rigid-rod anchoring unit allowing each porphyrin unit to be located at a fixed distance from the metal oxide nanoparticle surface. Electronic communication between the porphyrin and the rigid-rod unit was not desired. Rigid-rod porphyrins ZnTPP-Ipa, ZnTPP-P-Ipa, ZnTPP-PE-Ipa, ZnTPP-(PE)(2)-Ipa, ZnTPP-(PE)(3)-Ipa, and ZnTMP-Ipa (with mesityl substituents on the porphyrin ring) were synthesized using combinations of mixed aldehyde condensations and Pd-catalyzed cross-coupling reactions. Their properties, in solution and bound, were compared with that of Zn(II) 5,10,15,20-tetra(4-carboxyphenyl)porphyrin ( p-ZnTCPP) as the reference compound. Solution UV-vis and steady-state fluorescence spectra for all six rigid-rod-Ipa porphyrins were almost identical to each other and to that of p-ZnTCPP. Cyclic voltammetry and differential pulse voltammetry scans of the methyl ester derivatives of the six rigid-rod-Ipa porphyrins, recorded in dichloromethane/electrolyte, exhibited redox behavior typical of ZnTPP porphyrins, with the first oxidation in the range +0.99 to 1.09 V vs NHE. All six rigid-rod-Ipa porphyrins and p-ZnTCPP were bound to metal oxide (MO(n) = TiO(2), ZnO, and insulating ZrO(2)) nanoparticle films. The Fourier transform infrared attenuated total reflectance spectra of all compounds bound to MO n films showed a broad band at 1553-1560 cm(-1) assigned to the v(CO(2)(-)) asymmetric stretching mode. Splitting of the Soret band into two bands at 411 and 423 nm in the UV-vis spectra of the bound compounds, and broadening and convergence of both fluorescence emission bands in the fluorescence spectra of the porphyrins bound to insulating ZrO(2) were also observed. Such changes were less evident for ZnTMP-Ipa, which has mesityl substituents on the porphyrin ring to prevent aggregation. Steady-state fluorescence emission of rigid-rod-Ipa porphyrins bound to TiO(2) and ZnO through the longest bridges (>14 A) showed residual fluorescence emission, while fluorescence quenching was observed for the shortest compounds.     

Bacterial adhesion to glass and metal-oxide surfaces

Metal oxides can increase the adhesion of negatively-charged bacteria to surfaces primarily due to their positive charge. However, the hydrophobicity of a metal-oxide surface can also increase adhesion of bacteria. In order to understand the relative contribution of charge and hydrophobicity to bacterial adhesion, we measured the adhesion of 8 strains of bacteria, under conditions of low and high-ionic strength (1 and 100 mM, respectively) to 11 different surfaces and examined adhesion as a function of charge, hydrophobicity (water contact angle) and surface energy. Inorganic surfaces included three uncoated glass surfaces and eight metal-oxide thin films prepared on the upper (non-tin-exposed) side of float glass by chemical vapor deposition. The Gram-negative bacteria differed in lengths of lipopolysaccharides on their outer surface (three Escherichia coli strains), the amounts of exopolysaccharides (two Pseudomonas aeruginosa strains), and their known relative adhesion to sand grains (two Burkholderia cepacia strains). One Gram positive bacterium was also used that had a lower adhesion to glass than these other bacteria (Bacillus subtilis). For all eight bacteria, there was a consistent increase in adhesion between with the type of inorganic surface in the order: float glass exposed to tin (coded here as Si-Sn), glass microscope slide (Si-m), uncoated air-side float glass surface (Si-a), followed by thin films of (Co(1-y-z)Fe(y)Cr(z))3O4, Ti/Fe/O, TiO2, SnO2, SnO2:F, SnO2:Sb, A1(2)O3, and Fe2O3 (the colon indicates metal doping, a slash indicates that the metal is a major component, while the dash is used to distinguish surfaces). Increasing the ionic strength from 1 to 100 mM increased adhesion by a factor of 2.0 +/- 0.6 (73% of the sample results were within the 95% CI) showing electrostatic charge was important in adhesion. However, adhesion was not significantly correlated with bacterial charge and contact angle. Adhesion (A) of the eight strains was significantly (P < 10(-25)) correlated with total adhesion free energy (U) between the bacteria and surface (A = 2162e(-1.8U)).Although the correlation was significant, agreement between the model and data was poor for the low energy surfaces (R2 = 0.68), indicating that better models or additional methods to characterize bacteria and surfaces are still needed to more accurately describe initial bacterial adhesion to inorganic surfaces.     

Vibrational characteristics of outer-sphere surface complexes: example of sulfate ions adsorbed onto metal (hydr)oxides

The vibrational characteristics of outer-sphere complexes of sulfate at several mineral oxide-water interfaces were investigated by in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. In the IR spectra obtained from surface outer-sphere complexes, only one peak of the asymmetric stretching vibrational mode υ(3) similar to that of free sulfate ion SO(4)(2-) in aqueous solution is observed. However, on the investigated (hydr)oxide surfaces of Al(3+), Ti(4+), Fe(2+/3+), Cr(3+), Ce(4+), Cu(2+), Y(3+), Zn(2+), and Nd(3+), a shift of up to 14 cm(-1) was found, which was correlated to the polarizing power of the metal cations. A high polarizing power was found to result in a stronger shift of υ(3) compared to that of the aqueous SO(4)(2-) ion. Furthermore, the impact of the metal oxide structure on the characteristics of the formed outer-sphere complex was negligible because different Al and Fe (hydr)oxides did not show any changes in the respective IR spectra. Finally, the ionic strength (1-10(-4) M) and pH (6.8-3.1) have been modified to change the surface potential, showing no direct influence on the spectra (i.e., on the geometry of the outer-sphere complex).     

Electronic coupling in iron oxide-modified TiO2 leads to a reduced band gap and charge separation for visible light active photocatalysis

In recent experiments Tada et al. have shown that TiO(2) surfaces modified with iron oxide display visible light photocatalytic activity. This paper presents first principles simulations of iron oxide clusters adsorbed at the rutile TiO(2) (110) surface to elucidate the origin of the visible light photocatalytic activity of iron oxide modified TiO(2). Small iron oxide clusters adsorb at rutile (110) surface and their presence shifts the valence band so that the band gap of the composite is narrowed towards the visible, thus confirming the origin of the visible light activity of this composite material. The presence of iron oxide at the TiO(2) surface leads to charge separation, which is the origin of enhanced photocatalytic efficiency, consistent with experimental photoluminesence and photocurrent data. Surface modification of a metal oxide is thus an interesting route in the development of visible light photocatalytic materials.     

First-principles analyses and predictions on the reactivity of barrier layers of Ta and TaN toward organometallic precursors for deposition of copper films

We present theoretical studies based on first-principles density functional theory calculations on the mechanisms of chemical vapor deposition of Cu-hexafluoracetylacetonato-trimethylvinylsilane (Cu(hfac)(tmvs)) on tantalum surfaces. This process has been used in the past to grow copper films via a disproportionation reaction and was found to exhibit adhesion problems. We show that the Ta surfaces are highly reactive and that the organic ligands in a copper precursor would undergo spontaneous decomposition upon contact with the Ta substrates. This may lead to contamination of the metal surfaces caused by the formation of carbide, fluoride, oxide species, or other fragments of the copper precursor on the barrier layer. We propose a practical solution for these adhesion problems caused by the CVD process by passivating the metal surfaces with N(2) to reduce their activity toward the precursor. Our extensive first-principles molecular dynamics simulations under typical deposition conditions predict that, for properly passivated TaN surfaces, only the copper atoms are firmly adsorbed on the surface, with loose Cu-ligand bonds. The ligands are sufficiently stable on these passivated surfaces, remaining slightly above the surface due to the repulsion between the electron-rich N-layer and the electron-rich ligand groups, and subsequently liberated upon the disproportionation reaction.     

Titanium oxide complexes with dinitrogen. Formation and characterization of the side-on and end-on bonded titanium oxide-dinitrogen complexes in solid neon

The reactions of titanium oxide molecules with dinitrogen have been studied by matrix isolation infrared spectroscopy. The titanium monoxide molecule reacts with dinitrogen to form the TiO(N(2))(x) (x = 1-4) complexes spontaneously on annealing in solid neon. The TiO(η(1)-NN) complex is end-on bonded and was predicted to have a (3)A' ground state arising from the (3)Δ ground state of TiO. Argon doping experiments indicate that TiO(η(1)-NN) is able to form complexes with one or more argon atoms. Argon atom coordination induces a large red-shift of the N-N stretching frequency. The TiO(η(2)-N(2))(2) complex was characterized to have C(2v) symmetry, in which both the N(2) ligands are side-on bonded to the titanium metal center. The tridinitrogen complex TiO(η(1)-NN)(3) most likely has C(3v) symmetry with three end-on bonded N(2) ligands. The TiO(η(1)-NN)(4) complex was determined to have a C(4v) structure with four equivalent end-on bonded N(2) ligands. In addition, evidence is also presented for the formation of the TiO(2)(η(1)-NN)(x) (x = 1-4) complexes, which were predicted to be end-on bonded.     

Adsorption and conformation behavior of biotinylated fibronectin on streptavidin-modified TiO(X) surfaces studied by SPR and AFM

It is well-known that protein-modified implant surfaces such as TiO(2) show a higher bioconductivity. Fibronectin is a glycoprotein from the extracellular matrix (ECM) with a major role in cell adhesion. It can be applied on titanium oxide surfaces to accelerate implant integration. Not only the surface concentration but also the presentation of the protein plays an important role for the cellular response. We were able to show that TiO(X) surfaces modified with biotinylated fibronectin adsorbed on a streptavidin-silane self-assembly multilayer system are more effective regarding osteoblast adhesion than surfaces modified with nonspecifically bound fibronectin. The adsorption and conformation behavior of biotinylated and nonbiotinylated (native) fibronectin was studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM). Imaging of the protein modification revealed that fibronectin adopts different conformations on nonmodified compared to streptavidin-modified TiO(X) surfaces. This conformational change of biotinylated fibronectin on the streptavidin monolayer delivers a fibronectin structure similar to the conformation inside the ECM and therefore explains the higher cell affinity for these surfaces.     

A citric acid-derived ligand for modular functionalization of metal oxide surfaces via "click" chemistry

Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.     

Au <--> N synergy and N-doping of metal oxide-based photocatalysts

N-doping of titania makes photocatalytic activity possible for the splitting of water, and other reactions, under visible light. Here, we show from both theory and experiment that Au preadsorption on TiO2 surfaces significantly increases the reachable amount of N implanted in the oxide. The stabilization of the embedded N is due to an electron transfer from the Au 6s levels toward the N 2p levels, which also increases the Au-surface adhesion energy. Theoretical calculations predict that Au can also stabilize embedded N in other metal oxides with photocatalytic activity, such as SrTiO3 and ZnO, producing new states above the valence band or below the conduction band of the oxide. In experiments, the Au/TiN(x)O(2-y) system was found to be more active for the dissociation of water than TiO2, Au/TiO2, or TiO(2-y). Furthermore, the Au/TiN(x)O(2-y) surfaces were able to catalyze the production of hydrogen through the water-gas shift reaction (WGS) at elevated temperatures (575-625 K), displaying a catalytic activity superior to that of pure copper (the most active metal catalysts for the WGS) or Cu nanoparticles supported on ZnO.     

Selective catalytic oxidation of ethanol to acetic acid on dispersed Mo-V-Nb mixed oxides

The direct oxidation of ethanol to acetic acid is catalyzed by multicomponent metal oxides (Mo-V-NbO(x)) prepared by precipitation in the presence of colloidal TiO(2) (Mo(0.61)V(0.31)Nb(0.08)O(x)/TiO(2)). Acetic acid synthesis rates and selectivities (~95 % even at 100 % ethanol conversion) were much higher than in previous reports. The presence of TiO(2) during synthesis led to more highly active surface areas without detectable changes in the reactivity or selectivity of exposed active oxide surfaces. Ethanol oxidation proceeds via acetaldehyde intermediates that are converted to acetic acid. Water increases acetic acid selectivity by inhibiting acetaldehyde synthesis more strongly than its oxidation to acetic acid, thus minimizing prevalent acetaldehyde concentrations and its intervening conversion to CO(x). Kinetic and isotopic effects indicate that C-H bond activation in chemisorbed ethoxide species limits acetaldehyde synthesis rates and overall rates of ethanol conversion to acetic acid. The VO(x) component in Mo-V-Nb is responsible for the high reactivity of these materials. Mo and Nb oxide components increase the accessibility and reducibility of VO(x) domains, while concurrently decreasing the number of unselective V-O-Ti linkages in VO(x) domains dispersed on TiO(2).     

TiO2表面氧空位对Rup2P/TiO2/ITO薄膜电极光致电荷转移的影响

采用改性的TiCl4水解法制备出三种不同表面性质的TiO2-X(X=5,10,20,X表示加入NaOH的浓度,单位为mo·lL-1)样品.利用(1,10-邻菲咯啉)2-2-(2-吡啶基)苯咪唑钌混配配合物(Rup2P)作为敏化剂,制备出Rup2P/TiO2-5/ITO(铟锡金属氧化物)、Rup2P/TiO2-10/ITO和Rup2P/TiO2-20/ITO表面敏化薄膜电极.测试结果表明三种薄膜电极的光电转换效率Rup2P/TiO2-10/ITO最高,Rup2P/TiO2-20/ITO次之,Rup2P/TiO2-5/ITO最低.利用吸收光谱、表面光电压(SP)谱、荧光光谱和表面光电流作用谱等分析了Rup2P和三种TiO2的能带结构和表面性质;利用光致循环伏安和表面光电流作用谱研究了三种Rup2P/TiO2-X/ITO薄膜电极的光致界面电荷转移过程.结果表明,在光致界面电荷转移过程中,TiO2层表面氧空位对Rup2P/TiO2-X/ITO薄膜电极光致电荷转移产生重要影响.并进一步讨论了Rup2P/TiO2-X/ITO薄膜电极的光电流产生机理.     

Force measurements of bacterial adhesion on metals using a cell probe atomic force microscope

The adhesion of microbial cells to metal surfaces in aqueous media is an important phenomenon in both the natural environment and engineering systems. The adhesion of two anaerobic sulfate-reducing bacteria (Desulfovibrio desulfuricans and a local marine isolate) and an aerobe (Pseudomonas sp.) to four polished metal surfaces (i.e., stainless steel 316, mild steel, aluminum, and copper) was examined using a force spectroscopy technique with an atomic force microscope (AFM). Using a modified bacterial tip, the attraction and repulsion forces (in the nano-Newton range) between the bacterial cell and the metal surface in aqueous media were quantified. Results show that the bacterial adhesion force to aluminum is the highest among the metals investigated, whereas the one to copper is the lowest. The bacterial adhesion forces to metals are influenced by both the electrostatic force and metal surface hydrophobicity. It is also found that the physiological properties of the bacterium, namely the bacterial surface charges and hydrophobicity, also have influence on the bacteria-metal interaction. The adhesion to the metals by Pseudomonas sp. and D. desulfuricans was greater than by the marine SRB isolate. The cell-cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Cell probe atomic force microscopy has provided some useful insight into the interactions of bacterial cells with the metal surfaces.