Farid Bensebaa

Cell adhesion peptide modification of gold-coated polyurethanes for vascular endothelial cell adhesion

Gold-coated polyurethanes were chemisorbed with three cell-adhesion peptides having an N-terminal cysteine: cys-arg-gly-asp (CRGD), cys-arg-glu-asp-val (CREDV), and the cyclic peptide cys-cys-arg-arg-gly-asp-try-leu-cys (CCRRGDWLC). The peptides were selected based on their presumed preferential interactions with the cell-surface integrins on vascular endothelial cells. The ability of the surfaces to support the preferential adhesion of human vascular endothelial cells was studied by comparing in vitro adhesion results for these cells with those from mouse 3T3 fibroblasts. Surface modification with the peptides was confirmed by water-contact angles and XPS. Surface morphology was determined by AFM and SEM. In vitro cell-culture studies in conjunction with plasma-protein adsorption and immunoblotting were performed on the various modified surfaces. The data suggest that peptide-modified surfaces have significant potential for supporting cell adhesion. Little or no cell adhesion was noted on gold- or cysteine-modified control surfaces. Human vascular endothelial cells showed the greatest adhesion to the CCRRGDWLC-modified surfaces, and the 3T3 fibroblasts adhered best to the CREDV-modified surfaces. Protein adsorption studies suggest that the preferential adsorption of the cell-adhesive proteins fibronectin and vitronectin is not likely mediating the differences noted. It is concluded that the cell-adhesive peptide-modified gold-coated polymers have significant potential for further development both as model substrates for fundamental studies and for use in biomaterials applications.

RAMAN CHARACTERIZATION OF METAL-ALKANETHIOLATES

Abstract Raman spectroscopy has been used to characterize neat alkanethiol and various metal-alkanethiolate materials. Neat alkanethiol gives rise to two CS stretching peaks at 662 and 735 cm −1 , assigned to gauche and trans rotamers respectively. Only one CS stretching peak positioned at 725 cm −1 was found from CuC 12 and AgC 12 layered compounds, implying the absence of gauche rotamer near the thiolate group. An all- trans conformation of the chain is inferred from the peak position values of the CC stretching modes of CuC 12 and AgC 12 layered compounds. Gauche rotamers were observed in silver colloids capped with alkanethiolate.

Green synthesis of tunable Cu(In1−xGax)Se2 nanoparticles using non-organic solvents

A green synthesis route of Cu(In1−xGax)Se2 nanoparticles with variable Ga content is described in this report for the first time. Only water and a minimum amount of energy input are used. Heating appropriate amounts of Cu, In, Ga and Se dispersed in an aqueous solution containing mercapto-acetic acid in a microwave oven gives rise to small and uniform nanoparticles. These new materials have been characterized to confirm composition, geometrical and structural properties. Transmission electron microcopy (TEM) confirmed size distribution around 4 nm. XRD confirmed the chalcopyrite structure with an average crystallite size of 3 nm. Atomic concentration and oxidation states of the different elements have been investigated using X-ray photoelectron spectroscopy (XPS). UV-visible absorption characterization confirmed the tunable optical properties of these materials. The proposed synthesis is scalable for commercial production with minimal environmental impact.

Microwave assisted synthesis of CdSe nanocrystals for straightforward integration into composite photovoltaic devices

A preparative route for a nanocrystalline CdSe/polymer nanocomposite that is easily integrated into photovoltaic device fabrication has been developed. Microwave assisted synthesis is used to initiate the reaction of relatively safe, inexpensive and air stable precursors. Particles size may be varied from 20 A to 60 A in diameter. The CdSe nanocrystals show near band-edge photoemission, are crystalline and may be incorporated into a poly(9,9-dioctylfluorene-2,7-diyl-alt-9-octylcarbazole-3,6-diyl) copolymer. This polymer/CdSe composite can be directly cast, without complicated work-up, for the preparation of photovoltaic devices.

Surface dipole layer potential induced ir absorption enhancement in n-alkanethiol SAMs on GaAs(001).

The work function of n-alkanethiol self-assembled monolayers (SAMs) prepared on the GaAs(001) surface was measured using the Kelvin probe technique yielding the SAM 2D dipole layer potential (DLP). Direct n-dependent proportionality between the DLP values and the C-H stretching mode infrared (IR) absorption intensities was observed, which supports a correspondence of reported IR enhancements with the electrostatic properties of the interface. X-ray photoelectron spectroscopy is also used to verify the work function measurements. In addition, the principal components of the refractive index tensor are shown to be n-invariant in the ordered SAM phase. Our results suggest that a local field correction to the transition dipole moment accounts for the observed increase in IR activity through an increase to the electronic polarizability.

Observation of surface enhanced IR absorption coefficient in alkanethiol based self-assembled monolayers on GaAs(001)

Alkanethiol self-assembled monolayers (SAMs) of various methylene group chain lengths [HS–(CH2)n–CH3] (n=9,11,13,15,17) were fabricated on the GaAs(001) surface followed by characterization using Fourier transform infrared spectroscopy. Modal analysis of the CH2 stretching mode region (2800–3000 cm−1) showed that linear scaling of the n-dependent factors accurately reproduced the spectral data, supporting a chain-length consistent physical model upon which a measurement of the absorption coefficient was based. Evaluated from the linearity of the absorbance data, a peak coefficient of 3.5×104 cm−1 was obtained and a domain for ordered self-assembly was assigned for values n>9. Compared with measurements of the absorption coefficient made in the liquid phase, the SAM phase coefficient was determined to be about six times greater. This enhancement effect is discussed in terms of contributions relating to the locally ordered environment and is largely attributed to the chemical properties of the interface. We...

Electro-optic investigation of the surface trapping efficiency in n-alkanethiol SAM passivated GaAs(001)

The electro-optic characteristics of the semi-insulating and n(+)-type GaAs(001) surfaces passivated with n-alkanethiol self-assembled monolayers were investigated using Kelvin probe surface photovoltage (SPV) and photoluminescence (PL) techniques. Referencing the equilibrium surface barrier height established in an earlier report, SPV measurements demonstrated a significant (>100 mV) increase in the non-equilibrium band-bending potential observed under low-level photo-injection. Modeling of the SPV accounts for these observations in terms of a large (>10(4)) decrease in the hole/electron ratio of surface carrier capture cross-sections, which is suggested to result from the electrostatic potential of the interfacial dipole layer formed upon thiol chemisorption. The cross-section effects are verified in the high-injection regime based on carrier transport modeling of the PL enhancement manifested as a reduction of the surface recombination velocity.

Surface chemistry of end cuts from Athabasca bitumen

Bitumen components, responsible for various processing problems, were analysed with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and photoacoustic Fourier transform infrared spectrometry (PAS-FTIR). These methods were selected because they can probe surfaces to different depths: ToF-SIMS explores the surface to a depth of ∼1 nm; XPS analyses a surface layer 7 nm deep; and PAS-FTIR probes layers several micrometres thick.

Step-scan Photoacoustic Fourier Transform and X-rays photoelectron spectroscopy of oil sands fine tailings: new structural insights

The chemical and physical properties of clay suspensions from oil sands have profound effect not only on the bitumen extraction process but also on the tailing treatment and reclamation. Step-scan Photoacoustic Fourier Transform Infrared (S2PAS-FTIR) has been used to characterize the properties of clay suspensions. The photoacoustic spectral features of the fine solids (FS) fraction were found to vary drastically with the modulation frequency. This is attributed to the increase in the relative amount of bitumen-like matter in the bulk. A similar behavior was observed on the bi-wetted solid (BWS) fraction, in spite of the fact that the variation as a function of the modulation frequency is less significant. No such change is observed on hydrophobic solid (HPS) sample. These observations allow us to refine our pictorial image of the bitumen fraction materials structure.

XPS study of the effect of the conditions of peptide chemisorption to gold and silver coated polymer surfaces

Chemisorption of peptides and active moieties onto gold and silver coated surfaces is an attractive method for studying the effect of fundamental surface properties on biological interactions. In theory, the monolayers formed have a high density of the active group of interest, and the relatively mild conditions associated with chemisorption should allow biological activity to be maintained. While the conditions for chemisorption are widely reported in the literature, significant differences exist between research groups and the effects of changing these conditions on the resultant surface have not been fully examined. Furthermore, comparisons have not been made between gold and silver as potential substrates in these applications. In the current work, glutathione and cysteine were chemisorbed onto gold- and silver-coated polymers. The effect of varying the chemisorption conditions was evaluated by XPS analysis of the resultant surfaces. Factors identified as having potentially significant effects on chemisorption procedure included chemisorption time, peptide concentration, peptide, pH of the chemisorption solution, mixing and material of the incubation container. Factor significance was evaluated using a two level fractional factorial design of experiments (DOE), with sulfur content determined by XPS used as a measure of chemisorption effectiveness. Significant differences were noted between the silver and gold-coated surfaces, with a higher amount of sulfur and hence, by inference, peptide found in general on silver surfaces reacted under identical conditions. On the gold surfaces, peptide concentration, peptide type, and chemisorption time were found to have a significant effect on the composition of the resulting surface. On the silver surfaces, factor specific differences were not as significant but there were a number of two factor interactions. The results provide further evidence of the differences in interactions with thiol between silver and gold and suggest that changes in the chemisorption conditions can dramatically affect the resultant surface composition.