Photochemical Modification Research Articles

Photochemical surface modification and characterization of double-decker-shaped polysilsesquioxane hybrid thin films

The surface modification of a double-decker-shaped polysilsesquioxane (DDPSQ) film by deep ultraviolet (UV) irradiation (λ = 185 and 254 nm) was studied in the presence of atmospheric oxygen at room temperature. The change in the surface structure of a DDPSQ hybrid film was observed by means of contact angle measurements, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Exposure to deep UV light was found to convert the surface of DDPSQ film from hydrophobic to hydrophilic due to the formation of silanol groups (Si–OH) on the DDPSQ film. Measurements of FT-IR and XPS indicate that the Si–O–Si cage structure of DDPSQ was converted to the Si–O–Si network structure of SiO2 through cleavage of the Si–O–Si cage with deep UV irradiation. The irradiated DDPSQ film surface is very smooth with a root-mean-square (RMS) roughness of 0.34 nm. Moreover, to demonstrate the effect of surface modification of a DDPSQ film on the adhesion of metals, we fabricated silver (Ag) micropatterns on the deep UV modified DDPSQ film by laser-induced pyrolysis of a film prepared from liquid-dispersed Ag nanoparticles. The Ag micropatterns show an excellent adhesion to the modified DDPSQ surface as assessed by the Scotch tape test.

Photochemical Modification of Diamond and Related Materials with Fluorine Functionalities

Photolysis of perfluoroazooctane with diamond and related materials, such as diamond powders, films, diamond-like carbon (DLC) and nanodiamond films, led to a chemical modification of the surface to introduce perfluorooctyl functional groups, confirmed by means of FT-IR, XPS, Raman and TOF-SIMS measurements. The diamond and related materials modified with fluorine moieties showed an improvement of frictional property and a reduction of surface energy evaluated by contact angle to water, compared with pristine diamond, DLC and nanodiamond films. The results on the values of water contact angle depending on irradiation time are consistent with those of F/C ratio of fluorinated diamond and related materials by monitoring with XPS.

Assessing Native and Non-native Conformational States of a Protein by Methylene Carbene Labeling: The Case ofBacillus licheniformisβ-Lactamase

Much knowledge of protein folding can be derived from the examination of the nature and size of solvent-exposed surfaces along conformational transitions. We exploit here a general photochemical modification with methylene carbene of the accessible surface area (ASA) of the polypeptide chain. Labeling of Bacillus licheniformis beta-lactamase (BL-betaL) with 1 mM 3H-diazirine yielded 8.3 x 10(-3) mol CH2/mol protein, in agreement with the prediction for an unspecific surface labeling phenomenon. The unfolded state U in 7 M urea was labeled 60% more than the native state N. This result lies well below the increment of ASA expected from theoretical estimates and points to the presence of residual organization in state U and/or of cavities or crevices favoring the partition of the reagent in state N. A partially folded state I was demonstrated from two sequential transitions occurring at 1.5-3.0 M and 3.5-6.5 M urea. This technique shows a close correlation with optical probes most sensitive to changes in tertiary structure, a statement supported by the fact that the largest change occurs along the N-I portion of the N-I-U transition and along the acid pH-induced N-A transition. In the latter case, state A is labeled 70% more than state N, an increment consistent with the loosening of tight interactions in the core of the protein. Fragmentation of labeled BL-betaL into peptides provides a sequential map of solvent accessibility. Thus, amino acid residues pertaining to the Omega-loop and to helices alpha5 and alpha6 line the major cavity of the protein, that is big enough to lodge the diazirine reagent. Methylene labeling, by introducing an original (and perhaps unique) experimental measurement of ASA, enlightens subtle aspects of complex transitions and makes possible a comparative structural characterization of the native as well as non-native states.

Polymeric photoacid generators for direct photochemical modification of surface

AbstractTo achieve easy spin coating and enhanced efficiency in the photolithographic process for the direct photochemical modification of surface, we incorporated photoacid generator (PAG) into polymer backbone. Bis‐(4‐hydroxy‐phenyl)‐(4‐methoxy‐3,5‐dimethyl‐phenyl)‐sulfonium chloride was synthesized as a monomer, and was polymerized with sebacoyl chloride and terephthaloyl chloride. The resulting polymeric PAG in chloride salt form was converted to the p‐toluenesulfonate and 1‐naphthol‐5‐sulfonate forms with ion‐exchange reactions. By the photolithographic process with the polymeric PAG, the protecting groups of the linker molecules self‐assembled onto a glass plate were micropatterned to produce an amine pattern for the microarray of oligonucleotides. The acids generated from the polymeric PAG effectively deprotect the acid‐labile protecting groups of the linker molecules through a chemical amplification process in the exposed region. After the treatment of the patterned amino groups with a fluorescent dye, the pattern profiles were observed with a fluorescence scanner. The fluorescence image reveals a well‐defined pattern at a micro level, which clearly indicates that the polymeric PAGs have a great potential in photochemical surface modification for the microarray of oligonucleotides. Copyright © 2007 John Wiley & Sons, Ltd.

Photochemical modification of single-walled carbon nanotubes with amino functionalities and their metal nanoparticles attachment

A useful method for sidewall modification of SWNTs with amino-containing substituents was developed by the use of radical process of photolysis of acetonitrile. The covalent functionalization was confirmed by means of Raman, XPS, FT-IR, mass and UV–Vis–NIR measurements. Subsequent treatments of amino-containing substituents-modified SWNTs with silver nanoparticles gave an attachment of silver on the surface of SWNTs through the amino linkage.

Tracing terrigenous dissolved organic matter and its photochemical decay in the ocean by using liquid chromatography/mass spectrometry

Reversed-phase liquid chromatography/mass spectrometry (LC/MS) is introduced as a new molecular fingerprinting technique for tracing terrigenous dissolved organic matter (DOM) and its photochemical decay in the ocean. DOM along a transect from the mangrove-fringed coast in Northern Brazil to the shelf edge was compared with mangrove-derived porewater DOM exposed to natural sunlight for 2–10 days in a photodegradation experiment. DOM was isolated from all samples via solid-phase extraction (C18) for LC/MS analysis. DOM in the estuary and ocean showed a bimodal mass distribution with two distinct maxima in the lower m/ z range from 400 to 1000 Da (intensity-weighted average of 895 Da). Terrigenous porewater DOM from the mangroves was characterized by a broad molecular mass distribution over the detected range from 150 to 2000 Da (intensity-weighted average of 1130 Da). Polar compounds, i.e., those that eluted early in the reversed-phase chromatography, absorbed more UV light and had on average smaller molecular masses than the more apolar compounds. After 10 days of irradiation (∼ 70 kWh/m 2), mangrove DOM resembled open-ocean DOM in its mass distribution (intensity-weighted average of 885 Da). In addition, a large fraction of UV-absorbing compounds, which were present in mangrove samples but absent in offshore samples, were not detected after photodegradation. However, the bimodal mass distribution in ocean waters was not reproduced during photodegradation. This mass distribution is certainly a reflection of specific molecular properties of marine DOM which systematically differed from the mangrove samples. The molecular patterns of DOM in the ocean did not show significant contribution of terrigenous DOM, which is in contrast to previous stable carbon isotope analysis. If, however, photochemical modifications of the terrigenous component are considered as an additional mechanism besides simple mixing of two end members (marine and mangrove), the observed molecular patterns of oceanic DOM are consistent with the contribution of terrigenous DOM in these samples. In order to explore the molecular mass information, the mass spectra of the different samples were compared through multivariate statistics. Cluster analyses and multi-dimensional scaling (MDS) revealed significant differences between mangrove and oceanic DOM that successively disappeared in the course of the photodegradation experiment. With help of discriminant analyses, the similarity between photodegraded mangrove DOM and open-ocean DOM could be confirmed on an individual m/ z level. Though conventional ion trap mass spectrometry (resolving power of ∼ 1000) does not resolve the complexity of DOM at the level of single molecules, it does provide detailed molecular fingerprints. This molecular fingerprinting technique provides a means to trace DOM and modifications in its molecular structure in aquatic systems.

A Simple Photomask with Photoresist Mask Layer for Ultraviolet-Photolithography and Its Application for Selectively Photochemical Surface Modification of Polymers

According to ultraviolet (UV) spectroscopic studies, a positive AZ photoresist film thicker than 10 (m can hardly transmit UV lights of wavelengths 200–285 nm. A simple photomask for UV photolithography was prepared using a quartz glass plate coated with a light-obstructing film of positive AZ photoresist, and the quality of the photomask and fidelity of the pattern transferred by the photomask were evaluated. The developed AZ photoresist photomask was used for fabrication of gold microelectrode on polycarbonate (PC) sheets. PC sheetswere exposed to the UV lights emitted from a low-pressure mercury lamp and passed through the photomask. The PC sheets were subjected to selective surface photolysis in the exposed area. After a series of wet chemical reactions, nano gold particles serving as the catalyst for electroless plating were deposited on the irradiated area. Gold microelectrodes were then generated by immersing the selectively activated PC sheet in an electroless gold plating bath for a specific time. Without need for a clean room, the photomasks can be prepared by a chemist in a common chemical laboratory with low-cost materials and simple procedures.

F2 Laser Photochemical Welding of Aligned Silica Microspheres to Silicone Rubber

Precisely aligned transparent fused-silica (SiO2) microspheres 2.5 µm in diameter were nonthermally welded to silicone rubber by 157 nm F2-laser-induced photochemical modification of the silicone into silica. A short exposure to the F2 laser of ∼10 mJ/cm2 single-pulse fluence, 10 Hz pulse repetition rate and 600 pulses was required for sufficient photochemical welding. The welding strength depended on the extent of the silica formation, which was controlled by F2 laser exposure. Silica formation occurred even in silicone underneath the microspheres due to the F2 laser decomposition of oxygen molecules dissolved in the silicone. A cross-sectional atomic force microscope image of silicone underneath the microspheres after welding revealed that a large contact area between the silicone and the microspheres was formed. After welding, the aligned silica microspheres were butt-coupled to a tapered silica optical fiber ∼2.5 µm in diameter for optical waveguide applications. The alignment was found to have the capability of guiding red (635 nm)-wavelength light.

Photochemical writing of silica optical waveguides in silicone rubber by F2 laser

Photochemical writing of silica (SiO2) optical waveguides in silicone [(SiO(CH3)2)n] rubber has been successfully demonstrated by 157-nm F2 laser-induced photochemical modification of silicone into silica. The 2-mm-thick or ∼40- m-thick silicone rubber was exposed to F2 laser through a thin (∼0.2 mm) air layer. A proximity Cr-on-CaF2 photomask with 8- to 16- m-wide slits controlled the exposure size to define the width of the silica waveguides. A laser processing window to generate crack-free waveguides with good optical transparency was found by varying the number laser pulse, pulse repetition rate and single pulse laser fluence. Otherwise, rapid or excess exposure of the F2 laser caused cracking of the silica waveguides. The waveguides were found to guide both red (635-nm) and infrared (1550- nm) wavelength light with propagation loss estimated to be ∼15 and ∼6 dB/cm, respectively. Most of the loss originates in Rayleigh scattering from numerous inclusions originally present in the commercial 2-mm-thick silicone rubber.

Photochemical welding of silica optical components to silicone rubber by F2 laser

Photochemical welding of fused silica glass to silicone rubber has been demonstrated by 157-nm F2 laser-induced photochemical modification of the silicone surface in contact with the glass. Fused-silica coverslips (150 m thick), silica optical fibres (125 µm diameter), and 2.9- µm diameter microspheres were successfully welded onto 2-mm-thick silicone rubber by irradiating the silicone surface through the partially transparent glasses. Sufficient photochemical conversion for strong welding was provided by multiple exposures of tens to thousands of pulses in a narrow optimized fluence window near ∼6-mJ/cm2 per pulse.

Electrospun aliphatic polycarbonates as tailored tissue scaffold materials

Two different aliphatic polycarbonates were synthesised from CO 2 and the respective epoxides. Poly(propyl carbonate) (PPC) was prepared by heterogeneous catalysis with zinc glutarate. Poly(cyclohexyl carbonate) (PCHC) was prepared via living copolymerisation homogeneously catalysed by a 3-amino-2-cyanoimidoacrylate zinc acetate complex and subjected to electrospinning. The obtained nanofibres had a well-defined morphology free of beads along the fibres and with slightly porous structures on their surface. Subsequently, low-power deep UV irradiations, previously applied for photochemical surface modifications of two-dimensional and three-dimensional scaffolds from biostable polymers, were performed. Here, an effect on surface and bulk properties of PPC nanofibres was observed. Surface modifications of both polymers affected plasma protein adsorption. Photochemical bulk modifications observed for the first time on PPC nanofibres are indicating the possibility of spatial control of biodegradation rates, hence allow for control of the progression of host/implant interactions in vivo. In particular PPC was used for cell culture of L929 fibroblasts and primary rat hepatocytes. Even delicate primary cells showed good adhesion to the scaffolds and high viability.

VUV-photon Induced Formation of Hydrophilic and Hydrophobic Micro Domains Structure on Intraocular Lens Surface for Blocking after Cataract

ABSTRACTA micro domain structure, which hydrophilic and hydrophobic groups were arrayed alternately, was formed on the surface of an intraocular lens [IOL] by using ultra violet rays [VUV]. With this technique, the IOL that is free from fibrin has been developed. In order to substitute the hydrophilic groups in matrix-form on the surface, an ArF laser light was then irradiated on the hydrophobic surface in the presence of water for the −OH groups, through the 50-micrometer dot-patterned reticle. With this selective photochemical surface modification, the hydrophilic and hydrophobic groups were arrayed alternately on the sample surface. The modified IOL was soaked in 0.1-wt % fibrin solutions, and the fibrin-sticking rate was measured by using an infrared spectroscopy [FT-IR]. It results that the absorption coefficient of amide band reached to 0.0006, decreasing to one-six of non-treatment sample's.

Photochemical Modification of Diamond Films with Sulfur-Containing Functionalities

Photolysis of cyclic disulfides in the presence of diamond films led to a surface modification that introduced thioalkylthiol functional groups, as confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The S/C ratio of sulfur-modified diamond films depends on irradiation time, as monitored by XPS. Through thioalkylthiol moieties, the attachment of gold nanoparticles using a self-assembly process was performed on diamond surfaces.

Photochemistry of refractive index structures in poly(methyl methacrylate) by femtosecond laser irradiation

Femtosecond, subablation threshold photomodification of poly(methyl methacrylate) (PMMA) at 387 nm is explored to enable fabrication of optical components. Volatile fragment analysis (thermal desorption gas chromatography-mass spectrometry) and molecular weight distribution monitoring (size exclusion chromatography) suggest photochemical modification, involving direct cleavage of the polymer backbone and propagation via chain unzipping under formation of monomers, similar to the pyrolytic degradation of PMMA. Waveguides were produced in undoped, clinical-grade PMMA, showing an increased refractive index in the laser focal region (Dnmax=4x10(-3)).

Effect of the surface modification of polymer membranes on their microbiological fouling

Composite polymer membranes with chemically different surfaces are prepared by the photochemical modification of Millipore microfiltration poly(vinylidene fluoride) and polysulfone membranes using 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-hydroxyethyl methacrylate, and 2-(dimethylamino)ethyl methacrylate quaternized with methyl chloride. It is shown that, during the filtration of an E. coli suspension, the membrane flux substantially decreases with time owing to the fouling of the membrane surface by bacterial cells. The membranes with the hydrophilic surface are less susceptible to fouling than hydrophobic membranes, while the ability to recover the performance upon washing is higher for the membranes with a chemically neutral surface than for charged membranes. It is shown that the susceptibility of membranes to microbiological fouling reduces with a decrease in the roughness of the membrane surface. It is established that the membranes modified with the quaternized 2-(dimethylamino)ethyl methacrylate possess antibacterial properties. These membranes proved to be the most efficient in the filtration of natural surface water in a noncontinuous regime, a result that is explained by the ability of membranes to prevent the formation of a fouling biofilm on their surfaces.

Inactivation des agents pathogènes dans les produits sanguins labiles : sécurité transfusionnelle et impact économique

The safety of labile blood products (red blood cell concentrates, platelet concentrates and plasma) is currently ensured by medical and biological donor selection measures. Nonetheless, in addition to the residual risk of bacterial injection of platelet concentrates and parasitic infection of red cell concentrates, there is the emerging danger associated with new viruses. Pathogen inactivation based on chemical or photochemical genomic modifications is a broad-spectrum approach. These techniques are already used to inactivate plasma, and are being developed or application to platelet and erythrocyte concentrates. Universal inactivation of all labile blood products should be possible in a few years' time, but clinical and hemovigilance studies must first show that the biological properties and therapeutic efficacy of these products are not markedly affected, and that the methods used do not lead to long-term toxicity.

Stimulation of metazooplankton by photochemically modified dissolved organic matter

We examined the response of bacteria and proto- and metazooplankton to photomodified dissolved organic matter (DOM). Sterile filtered water from a eutrophic and a humic lake, that was either exposed to artificial ultraviolet (UV) radiation or kept dark, was added to semicontinuous laboratory microcosms that lasted for 7 weeks. Bacterial production responded positively to photochemical modification of DOM regardless of lake type. Final heterotrophic biomass (bacteria1proto1metazooplankton) was 47 ± 5 and 37 ± 5 µg carbon (C) L−1 in microcosms with UVexposed and unaltered eutrophic water DOM and 15 ± 4 and 11 ± 2 µg C L−1 in microcosms with UV-exposed and unaltered humic water DOM, respectively. For the eutrophic water, there were no significant differences in proto- or metazooplankton biomasses between microcosms receiving UV-exposed or nonexposed DOM. Differences between eutrophic water microcosms were not significant when flagellates, ciliates, cladocerans, and copepods were examined separately. In microcosms with UV-exposed humic water, biomasses of heterotrophic flagellates, rotifers, nauplii, and cladocerans were higher than in those with nonexposed DOM. Higher final metazooplankton biomass following addition of UV-exposed humic water indicates that photochemically modified DOM can be effectively transferred through the microbial loop.

Photochemical modification of nanodiamond films with perfluorooctyl functionalities

Photolysis of perfluoroazooctane in the presence of nanodiamond films on Si substrate resulted in surface modification with perfluorooctyl functional groups, which was confirmed by means of FT-IR, XPS, Raman and TOF-SIMS measurements. The nanodiamond films modified with fluorine moieties show a reduction of the surface energy in comparison with pristine nanodiamond film. The contact angle of chemically modified nanodiamond film to water is 124°, comparable to that of polytetrafluoroethylene (103°). In the case of nanodiamond films deposited on glass substrate with a transparent property, this chemical modification would not influence the transparency of nanodiamond films, showing > 87% transmittance in the region of > 400 nm wavelength.

Pesticide-mediated homeostatic modulation in arthropods

The term hormesis was coined to describe a phenomenon where exposure to high levels of stressors is inhibitory whereas low (mild, sublethal, and subtoxic) doses are stimulatory. The stimulatory effects are believed to be the result of compensatory biochemical processes following a destabilization of normal homeostasis. Exposure of arthropods to mild levels of chemical stressors (i.e., pesticides) may result in enhanced reproduction that has been associated along with other factors with pest outbreaks and resurgences. Hormesis, however, cannot be claimed for cases in which the observed stimulatory effects were due to exposure of non-target pests (i.e., mites) to pesticides (DDT, carbaryl, insecticidal pyrethroids or imidacloprid). Pesticides applied to non-target pests cannot be regarded as stressors since inhibition or mortality at very high doses can hardly be observed and measured. Pesticide-induced homeostatic modulation (PIHM) is suggested as a broader term to include both hormesis and stimulatory effects of pesticides on non-target pests. The specific role played by PIHM in inducing pest outbreaks in agroecosystems is difficult to evaluate as other complex environmental factors are most likely involved. The time factor is significant where applied pesticides undergo physical dissipation as well as biological, chemical, and/or photochemical modifications. A delay in outbreaks may be anticipated as arthropod pests exposed to effective residues and degradation products will be subjected to PIHM resulting in enhanced reproduction. Knowledge about hormesis and PIHM has practical aspects for designing pest control strategies and pest resistance management practices.

UV Assisted Surface Modification of Polystyrene in the Presence of Trialkylsilanes

AbstractSummary: A process for the photochemical modification of polystyrene (PS) surfaces employing organosilane compounds has been developed. Polystyrene was irradiated in presence of trialkylsilanes [ethyldimethylsilane (EDMS), trimethylsilane (TrMS)]. UV irradiation was carried out with a medium pressure (MP) Hg lamp and a 193 nm ArF* excimer laser. FT‐IR and X‐ray photoelectron spectroscopy (XPS) evidenced that after irradiation alkylsilyl groups were covalently bond to the polymer surface. Contact angle measurements proved a significant lowering in surface energy of polystyrene as a result of the photomodification process. When EDMS was used as photoreactive reagent, the introduction of SiH groups onto the polymer surface was also found. The introduction of SiH bonds onto polymer surfaces provides new possibilities for further surface functionalization. Atomic force microscopy (AFM) showed that Hg lamp irradiation does not exert significant changes in surface topography, while 193 nm excimer laser irradiation leads to surface corrugation. Summing up, it is demonstrated that organosilanes can be employed in UV reactions to attach silyl and also SiH groups onto polystyrene surfaces. Possible reaction mechanisms are discussed. magnified image