Probing the functionalization of gold surfaces and protein adsorption by PM-IRRAS

The control of morphology and coating of metal surfaces is essential for a number of organic electronic devices including photovoltaic cells and sensors. In this study, we monitor the functionalization of gold surfaces with 11-mercaptoundecanoic acid (MUA, HS(CH(2))(10)CO(2)H) and cysteamine, aiming at passivating the surfaces for application in surface plasmon resonance (SPR) biosensors. Using polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), cyclic voltammetry, atomic force microscopy and quartz crystal microbalance, we observed a time-dependent organization process of the adsorbed MUA monolayer with alkyl chains perpendicular to the gold surface. Such optimized condition for surface passivation was obtained with a systematic search for experimental parameters leading to the lowest electrochemical signal of the functionalized gold electrode. The ability to build supramolecular architectures was also confirmed by detecting with PM-IRRAS the adsorption of streptavidin on the MUA-functionalized gold. As the approaches used for surface functionalization and its verification with PM-IRRAS are generic, one may now envisage monitoring the fabrication of tailored electrodes for a variety of applications.

Molecular Ordering of Layer-by-Layer Polyelectrolyte Films Studied by Sum-Frequency Vibrational Spectroscopy

The molecular arrangement in organic thin films is crucial for their increasing technological applications. Here, we use vibrational spectroscopy by sum-frequency generation (SFG) to study the ordering of polyelectrolyte layers adsorbed on silica for all steps of layer-by-layer (LbL) self-assembly. In situ measurements during adsorption and rinsing showed that the adsorbed polymer has a disordered conformation and confirmed surface charge overcompensation upon polyelectrolyte adsorption by probing the interfacial electric field. In dry films, the polymer chains acquired a net orientational ordering, which was affected, however, by the adsorption of subsequent layers. Such a detailed characterization may allow the control of LbL film structure and functionality with unprecedented power.

Ni-Zn-Sm nanopowder ferrites: Morphological aspects and magnetic properties

Ni-Zn ferrites have been widely used in components for high-frequency range applications due to their high electrical resistivity, mechanical strength and chemical stability. Ni-Zn ferrite nanopowders doped with samarium with a nominal composition of Ni0.5Zn0.5Fe2-xSmxO4 (x = 0.0, 0.05, and 0.1 mol) were obtained by combustion synthesis using nitrates and urea as fuel. The morphological aspects of Ni-Zn-Sm ferrite nanopowders were investigated by X-ray diffraction, nitrogen adsorption by BET, sedimentation, scanning electron microscopy and magnetic properties. The results indicated that the Ni-Zn-Sm ferrite nanopowders were composed of soft agglomerates of nanoparticles with a high surface area (55.8-64.8 m(2)/g), smaller particles (18-20 nm) and nanocrystallite size particles. The addition of samarium resulted in a reduction of all the magnetic parameters evaluated, namely saturation magnetization (24-40 emu/g), remanent magnetization (2.2-3.5 emu/g) and coercive force (99.3-83.3 Oe). (c) 2007 Elsevier B. V. All rights reserved.

Modeling Adsorption Processes of Poly-p-phenylenevinylene Precursor and Sodium Acid Dodecylbenzenesulfonate onto Layer-by-Layer Films Using a Langmuir-type Metastable Equilibrium Model

The adsorption kinetics curves of poly(xylylidene tetrahydrothiophenium chloride) (PTHT), a poly-p-phenylenevinylene (PPV) precursor, and the sodium salt of dodecylbenzene sulfonic acid (DBS), onto (PTHT/DBS)(n) layer-by-layer (LBL) films were characterized by means of UV-vis spectroscopy. The amount of PTHT/DBS and PTHT adsorbed on each layer was shown to be practically independent of adsorption time. A Langmuir-type metastable equilibrium model was used to adjust the adsorption isotherms data and to estimate adsorption/desorption coefficients ratios, k = k(ads)/k(des), values of 2 x 10(5) and 4 x 10(6) for PTHT and PTHT/DBS layers, respectively. The desorption coefficient has been estimated, using literature values for poly(o-methoxyaniline) desorption coefficient, as was found to be in the range of 10(-9) to 10(-6) s(-1), indicating that quasi equilibrium is rapidly attained.

Adsorption kinetics and charge inversion in layer-by-layer films from nickel tetrasulfonated phthalocyanine and poly(allylamine hydrochloride)

Layer-by-layer (LBL) films of nickel tetrasulfonated phthalocyanine (NiTsPc) alternated with poly(allylamine hydrochloride) (PAH) have been prepared, whose surface charge has been evaluated using surface potential measurements. From adsorption kinetics results, we obtained the immersion time of similar to 40 s, which was used to assemble layers of NiTsPc. The effect of gold (Au) and aluminum (Al) electrodes on the charge behavior was examined. We found that the surface potential (i.e. surface charge) was inverted each time a layer of PAH was alternated with another of NiTsPc molecules for the two types of electrodes, which was attributed to charge overcompensation between positive charges of PAH molecules, and negative charges from NiTsPc molecules. (C) 2009 Elsevier B.V. All rights reserved.

Degradation and adsorption of AZO RR239 dye in aqueous solution by nanoscale zerovalent iron particles immobilized on sawdust

Carra sawdust pretrated with formaldehyde was used to adsorb RR239 (reactive azo dye) at varying pH and zerovalent iron (ZVI) dosage. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model. Batch experiments suggest that the decolorization efficiency was strongly enhanced with the presence of ZVI and low solution pH. The kinetics of dye sorption by mixed sorbent (5 g of sawdust and 180 mg of ZVI) at pH 2.0 was rapid, reaching more than 90% of the total discoloration in three minutes.

Identification of species formed after pyridine adsorption on iron, cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface-enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M(4)(py) (four metal atoms bonded to one py moiety) and M(4)(alpha-pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M(4)(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed alpha-pyridil species, as suggested previously. Copyright (C) 2009 John Wiley & Sons, Ltd.

Developing a fluorimetric sequential injection methodology to study adsorption/desorption of glyphosate on soil and sediment samples

This paper describes the development of a sequential injection method to automate the fluorimetric determination of glyphosate based on a first step of oxidation to glycine by hypochlorite at 48 degrees C, followed by reaction with the fluorogenic reagent o-phthaldialdehyde in presence of 2-mercaptoethanol in borate buffer (pH > 9) to produce a fluorescent 1-(2`-hydroxyethylthio)-2-N-alkylisoindole. The proposed method has a linear response for glyphosate concentrations between 0.25 and 25.0 mu mol L(-1), with limits of detection and quantification of 0.08 and 0.25 mu mol L(-1), respectively. The sampling rate of the method is 18 samples per hour, consuming only a fraction of reagents consumed by the chromatographic method based on the same chemistry. The method was applied to study adsorption/desorption properties in a soil and in a sediment sample. Adsorption and desorption isotherms were properly fitted by Freundlich and Langmuir equations, leading to adsorption capacities of 1384 +/- 26 and 295 +/- 30 mg kg(-1) for the soil and sediment samples, respectively. These values are consistent with the literature, with the larger adsorption capacity of the soil being explained by its larger content of clay minerals, while the sediment was predominantly sandy. (C) 2011 Elsevier B.V. All rights reserved.

Oxidation of anilinium ions intercalated in montmorillonite clay by electrochemical route

Resonance Raman, FTIR, X-ray diffraction, UV-vis-NIR, electron paramagnetic resonance, X-ray absorption at Si K-edge and electron microscopy were employed for characterizing the products formed through electrochemical oxidation of intercalated anilinium ions inside the cationic montmorillonite (MMT) clay. The layer silicate structure was not affected by the anilinium oxidation between the layers. The intercalated products present only an electronic absorption band at 400 nm, very low conductivity (ca. 10(-7) S cm(-1)) and their Raman spectrum displays bands, with high relative intensities, assigned to the benzidine dication, indicating that this product was formed in high amount. Nevertheless, bands that can be correlated to phenazine-like segments and 1,4-phenylenediamine repeat units (PANI like segments) are also observed. The very low EPR signal indicates that diamagnetic species are predominant. All results are compared to those obtained by anilinium-MMT chemically oxidized by persulfate and the differences are pointed out. (C) 2008 Elsevier B.V. All rights reserved.

Adsorption of 4-aminopyridine on Co and Ag electrodes probed by SERS

The adsorption of 4-aminopyridine (4-AP) on Co and Ag electrodes in acid or alkaline solutions of KCl and KI electrolyte salts were monitored by the Surface-enhanced Raman Spectroscopy (SERS) technique. The SERS intensity for the Ag electrode was in 2 orders of magnitude higher than for the Co electrode, due to the enhancement of the Raman cross-section on Ag by the surface-plasmon excitation. In acidic chloride medium (pH 4), the SERS results for Ag electrodes indicate that the protonated form of 4-AP (4-APH(+)) adsorbs in the potential range of -0.1 to -0.6 V (Ag broken vertical bar AgCl broken vertical bar KCl sat) through hydrogen-bonding between 4-APH(+) and Cl(-) adsorbed on the electrode surface: at more negative potentials the neutral form 4-AP is the predominant adsorbed species. For Co electrode in the same medium, only bands due to neutral 4-AP were observed in the spectra at -0.8 and -0.9 V. For more negative potentials bands assigned to both 4-AP and 4-AP surface complex are observed, with the lasts being enhanced, as the potentials are turned more negative. In alkaline chloride medium (pH 13), for less negative potentials the bands assigned to free 4-AP were observed in the spectra of both Ag and Co surfaces. For more negative potentials, only bands assigned to the 4-AP surface complex were observed. For 0.1 mol L(-1) KI acidic or alkaline solutions, bands assigned to 4-AP and 4-APH(+) were observed in a wider potential range than in chloride solutions. An adsorption scheme of 4-AP on Ag and Co is proposed for acidic and alkaline solutions. (C) 2010 Elsevier B.V. All rights reserved.

Microencapsulation of casein hydrolysate by complex coacervation with SPI/pectin

The aim of this work was to encapsulate casein hydrolysate by complex coacervation with soybean protein isolate (SPI)/pectin. Three treatments were studied with wall material to core ratio of 1:1, 1:2 and 1:3. The samples were evaluated for morphological characteristics, moisture, hygroscopicity, solubility, hydrophobicity, surface tension, encapsulation efficiency and bitter taste with a trained sensory panel using a paired comparison test. The samples were very stable in cold water. The hydrophobicity decreased inversely with the hydrolysate content in the microcapsule. Encapsulated samples had lower hygroscopicity values than free hydrolysate. The encapsulation efficiency varied from 91.62% to 78.8%. Encapsulated samples had similar surface tension, higher values than free hydrolysate. The results of the sensory panel test considering the encapsulated samples less bitter (P < 0.05) than the free hydroly-state, showed that complex coacervation with SPI/pectin as wall material was an efficient method for microencapsulation and attenuation of the bitter taste of the hydrolysate. (C) 2009 Elsevier Ltd. All rights reserved.

Study of the pozzolanic reaction kinetics in sugar cane bagasse-clay ash/calcium hydroxide system: kinetic parameters and pozzolanic activity

This paper presents a study of the pozzolanic reaction kinetics between calcium hydroxide and a mixture of sugar cane bagasse with 20 and 30% of clay, burned at 800 and 1000 degrees C (SCBCA) by electrical conductivity measurements. A kinetic-diffusive model produced in previous studies by some of the authors was used. The model was fitted to the experimental data, which allowed the computation of the kinetic parameters of the pozzolanic reaction (reaction rate constant and free energy of activation) that rigorously characterised the pozzolanic activity of the materials. The results show that SCBCA demonstrated reactivity and good pozzolanic qualities in the range 800-1000 degrees C.

Induction of neutralizing antibodies in mice immunized with an amino-terminal polypeptide of Streptococcus mutans P1 protein produced by a recombinant Bacillus subtilis strain

The oral pathogen Streptococcus mutans expresses a surface protein, P1, which interacts with the salivary pellicle on the tooth surface or with fluid-phase saliva, resulting in bacterial adhesion or aggregation, respectively. P1 is a target of protective immunity. Its N-terminal region has been associated with adhesion and aggregation functions and contains epitopes recognized by efficacious antibodies. In this study, we used Bacillus subtilis, a gram-positive expression host, to produce a recombinant N-terminal polypeptide of P1 (P1(39-512)) derived from the S. mutans strain UA159. Purified P1(39-512) reacted with an anti-full-length P1 antiserum as well as one raised against intact S. mutans cells, indicating preserved antigenicity. Immunization of mice with soluble and heat-denatured P1(39-512) induced antibodies that reacted specifically with native P1 on the surface of S. mutans cells. The anti-P1(39-512) antiserum was as effective at blocking saliva-mediated aggregation of S. mutans cells and better at blocking bacterial adhesion to saliva-coated plastic surfaces compared with the anti-full-length P1 antiserum. In addition, adsorption of the anti-P1 antiserum with P1(39-512) eliminated its ability to block the adhesion of S. mutans cells to abiotic surfaces. The present results indicate that P1(39-512), expressed and purified from a recombinant B. subtilis strain, maintains important immunological features of the native protein and represents an additional tool for the development of anticaries vaccines.

The role of citrate precursors on the morphology of lanthanide oxides obtained by thermal decomposition

Two series of lanthanide oxides with different morphologies were synthesized through calcinations of two types of citrate polymeric precursors. These oxides were characterized by XRD patterns, SEM electronic microscopy, and N(2) adsorption isotherms. SEM microscopy analysis showed that the calcination of crystalline fibrous precursors [Ln(2)(LH)(3)center dot 2H(2)O] (L = citrate) originated fibrous shaped particles. On the other hand, the calcination of irregular shaped particles of precursors [LnL center dot xH(2)O] originated irregular shaped particles of oxide, pointing out a morphological template effect of precursors on the formation of the respective oxides.

Adsorption of Pb(2+), Cu(2+) and Cd(2+) in FDU-1 silica and FDU-1 silica modified with humic acid

Ordered mesoporous silica with cubic structure, type FDU-1, was synthesized under strong acid media using B-50-6600 poly(ethylene oxide)-poly(butilene oxide)-poly(ethylene oxide) triblock copolymer (EO(39)BO(47)EO(39)) and tetraethyl orthosilicate (TEOS). Humic acid (HA) was modified to the synthesis process at a concentration of 1.5 mmol per gram of SiO(2). Thermogravimetry, small angle X-ray diffraction, nitrogen adsorption and high resolution transmission electron microscopy were used to characterize the samples. The pristine FDU-1 and FDU-1 with incorporated 1.5 mmol of HA were tested for adsorption of Pb(2+), Cu(2+) and Cd(2+) in aqueous solution. Incorporation of humic acid into the FDU-1 silica afforded an adsorbent with strong affinity for Cd(2+), Cu(2+) and Pb(2+) from single ion solutions. Adsorption of Cu(2+) was significantly enhanced after incorporation of humic acid, a fact that can be explained by the formation of complexes with carboxylic and phenolic groups at low concentrations of the metal cation. The results demonstrated the potential applicability of FDU-1 with incorporated HA in the removal of low concentrations of heavy metal cations from aqueous solution, such as wastewaters, after usual precipitation of metal hydroxides in alkaline medium and proper pH conditioning in the range between 6 and 7. (C) 2007 Elsevier Inc. All rights reserved.