Photochemical Modification Research Articles

Diffusion and Interaction Dynamics of Individual Membrane Protein Complexes Confined in Micropatterned Polymer‐Supported Membranes

Micropatterned polymer-supported membranes (PSM) are established as a tool for confining the diffusion of transmembrane proteins for single molecule studies. To this end, a photochemical surface modification with hydrophobic tethers on a PEG polymer brush is implemented for capturing of lipid vesicles and subsequent fusion. Formation of contiguous membranes within micropatterns is confirmed by scanning force microscopy, fluorescence recovery after photobleaching (FRAP), and super-resolved single-molecule tracking and localization microscopy. Free diffusion of transmembrane proteins reconstituted into micropatterned PSM is demonstrated by FRAP and by single-molecule tracking. By exploiting the confinement of diffusion within micropatterned PSM, the diffusion and interaction dynamics of individual transmembrane receptors are quantitatively resolved.

Polyoxometalate-Modified Boron-Doped Diamond Electrodes

Polyoxometalates were immobilized on a boron-doped diamond (BDD) surface modified by a photochemical modification method. The BDD surface was first modified with allyltriethylammonium bromide (ATAB) to form surface quaternary ammonium groups. The ATAB–BDD was then immersed in a phosphomolybdic acid (H3PMo12O40, denoted as PMo12) solution to fabricate PMo12-adsorbed ATAB–BDD (PMo12–ATAB–BDD). The electrostatic interaction between PMo12 and the quaternary ammonium group on ATAB–BDD is considered to be critical to the stable immobilization. Polyoxometalate-modified BDD was also fabricated from phosphonic-acid-terminated BDD. BDD was first modified with vinylphosphonic acid (VPA), followed by the reaction of the surface phosphonic acid groups with ammonium molybdate to generate a lacunary phosphomolybdic acid (PMox) group. Although the coverage of the PMox group on PMox–BDD was less than that of PMo12–ATAB–BDD, PMox–BDD was found to be more stable to potential cycling than PMo12–ATAB–BDD, indicating that covalent modification methods are effective for creating stable functional groups on diamond.

Surface modification of poly(ethylene terephthalate) fabric via photo-chemical reaction of dimethylaminopropyl methacrylamide

Photo-chemical reactions and surface modifications of poly(ethylene terephthalate) (PET) fabrics with the monomer dimethylaminopropyl methacrylamide (DMAPMA) and benzophenone (BP) as photo-initiator using a broad-band UV lamp source were investigated. The tertiary amino groups of the grafted poly(DMAPMA) chains were subsequently quaternized with alkyl bromides of different chain lengths to establish antibacterial activity. The surface composition, structure and morphology of modified PET fabrics were characterized by Fourier transform infrared spectroscopy (FTIR/ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). To evaluate the amount of quaternary and tertiary ammonium groups on the modified surface, PET was dyed with an acid dye which binds to the ammonium groups. Therefore, the color depth is a direct indicator of the amount of ammonium groups. The resulting antibacterial activity of the modified PET fabrics was tested with Escherichia coli. The results of all experiments show that a photochemical modification of PET is possible using DMAPMA, benzophenone and UV light. Also, the quaternization of tertiary amino groups as well as the increase in antibacterial activity of the modified PET by the established quaternary ammonium groups were successful.

Direct Nanopatterning Into Conjugated Polymers Using Interference Crosslinking

AbstractNanoscale photonic structures are patterned directly by exposing a thin film of conjugated polymer to the interference pattern of UV laser beams, thus inducing crosslinking between the polymer molecules in the bright fringes. The crosslinked polymer molecules become indissolvable in organic solvent due to the localized photochemical modification, enabling successful lift‐off of the soft grating structures. The resultant nanodevice exhibits excellent chemical and physical stability. This demonstrates the high spatial resolution of the crosslinking process and introduces a direct nanofabrication technique, which may be utilized in the design of optoelectronic and laser devices.

Role of Solvent–Oxygen Ion Pairs in Photooxidation of CdSe Nanocrystal Quantum Dots

Understanding the mechanisms for photodegradation of nanocrystal quantum dots is an important step toward their application in real-world technologies. A usual assumption is that photochemical modifications in nanocrystals, such as their photooxidation, are triggered by absorption of a photon in the dot itself. Here, we demonstrate that, contrary to this commonly accepted picture, nanocrystal oxidation can be initiated by photoexcitation of solvent-oxygen ion pairs that relax to produce singlet oxygen, which then reacts with the nanocrystals. We make this conclusion on the basis of photolysis studies of solutions of CdSe nanocrystals. Our measurements indicate a sharp spectral onset for photooxidation, which depends on solvent identity and is 4.8 eV for hexane and 3.4 eV for toluene. Importantly, the photooxidation onset correlates with the position of a new optical absorption feature, which develops in a neat solvent upon its exposure to oxygen. This provides direct evidence that nanocrystal photooxidation is mediated by excitation of solvent-oxygen pairs and suggests that the stability of the nanocrystals is defined by not only the properties of their surfaces (as has been commonly believed) but also the properties of their environment, that is, of the surrounding solvent or matrix.

IMMOBILIZATION OF POLYSACCHARIDE DERIVATIVES ON POLYURETHANE SURFACE THROUGH LAYER-BY-LAYER SELF-ASSEMBLY AND PHOTOCHEMICAL MODIFICATION

Polysaccharide derivatives were immobilized on the surface of polyurethane(PU) through layer-by-layer self-assembly technique and photochemical modification method.At first,azido-chitosan(AzCS) was synthesized and immobilized on the polyurethane substrates by UV irradiation.Then,lentinan sulfate(LS) and azido-chitosan were alternatively deposited on the polyurethane substrates through layer-by-layer self-assembly technique.Finally,the self-assembled multilayers were cross-linked by UV irradiation.From above steps,the polysaccharide derivatives modified polyurethanes were prepared.The surface properties of the modified polyurethanes were evaluated by infrared spectroscopy,UV-Vis spectroscopy,X-ray photoelectron spectroscopy and water contact angle measurement.The antibacterial activity against Escherichia coli and blood compatibility of unmodified and modified PU were tested in vitro,respectively.The results showed that the water contact angle of the modified surfaces decreased gradually during the successive buildup of the multilayers.The hemolysis test and platelet adhesion test both indicated that the blood compatibility of PU surfaces was improved after surface modification.Moreover,the modified surfaces showed antibacterial activity against Escherichia coli.The number of viable Escherichia coli on the modified surface decreased by 49%.Thus,the surface modification of polysaccharide derivatives through layer-by-layer self-assembly and photochemical modification not only improves the hydrophilicity and hemocompatibility of the modified PU,but also introduces special antibacterial bioactivity onto the modified surfaces.

REMOVED: High Performance Gas Separation Membrane from a Polymer of Intrinsic Microporosity by Photochemical Surface Modification

This article has been removed: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). This article has been removed at the request of the Executive Publisher. This article has been removed because it was published without the permission of the author(s).

Self-alignment of Gold Nanoparticles through the Control of Particle-substrate and Particle-particle Interactions

Gold (Au) nanostructures have been fabricated on various substrates, such as Si, ITO and quartz glass, through the position-selective deposition of Au nanoparticles. This self-aligned deposition of the nanoparticles is promoted through the electrostatic interaction between the nanoparticles and the deposition sites, which are charged negatively and positively, respectively. Prior to the nanoparticle deposition, the positively charged sites where covered with aminosilane self-assembled monolayer had been constructed on the substrate with an artificial pattern design by a lithographic method. A photolithographic process, which was based on direct photochemical modification of organic substances induced by irradiating with a vacuum ultra-violet (VUV) light, was employed so that sub-μm features down to 500nm have been successfully fabricated and provided as templates for aligning Au nanoparticles. The second method for patterning was electrochemical line drawing using a scanning probe microscope. One-dimensional arrays of Au nanoparticles with a line thickness of a single nanoparticle diameter have been successfully fabricated. In addition, by replacing a surface charged layer consisting of citric acid molecules surrounding the Au nanoparticles with alkanethiol molecules, the Au nanoparticles were neutralized so that the fabricated Au nanoparticle array in which most of the nanoparticles were separated each other was re-organized to a more closely packed structure.

Laser Wavelength Dependence on Photochemical Surface and Interface Modifications of Aluminum Thin Films on Silica Glass

Photochemical surface and interface modifications of Al thin films on silica glass were successfully carried out using a 157 nm F2 laser for micropatterning. The surface modification phenomenon was discussed in relation to by changing the laser wavelength using a 193 nm ArF laser or a 266 nm neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. The ArF laser could induce the surface modification of Al thin films to form a protective Al2O3 layer resistant to KOH aqueous solution, similarly to the F2 laser. However, the mechanical hardness of the ArF-laser-irradiated sample was clearly lower than that of the F2-laser-irradiated sample. The origin of the surface modification was examined by irradiating the F2 laser in vacuum. The interface modification phenomenon was analyzed by X-ray photoelectron spectroscopy in the three cases. The adhesion strengths of the samples were also compared. The 266 nm Nd:YAG laser was not effective for the present photochemical modifications.

Sensitive Electrochemical Detection of Glucose at Glucose Oxidase-Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode

Electrochemical detection of glucose was achieved at a glucose oxidase (GOx)-cobalt phthalocyanine (CoPc)-modified boron-doped diamond (BDD) electrode without any additional electron mediator in the electrolyte solution. The surface of the hydrogen-terminated BDD thin film prepared by microwave plasma-assisted CVD was modified with 4-vinylpyridine (4VP) via photochemical modification. The 4VP-BDD was then immersed in a CoPc solution to obtain CoPc-BDD. A poly(p-phenylenediamine) (PPD) thin film containing GOx was coated on the CoPc-BDD electrode surface via electropolymerization. At the GOx/PPD-CoPc-BDD electrode, anodic current for glucose oxidation was observed with a sigmoidal voltammetric curve, indicating successful electron mediation of H2O2generated as the result of glucose oxidation at GOx. The signal-to-background ratio for voltammetric current of glucose detection was larger at the GOx/PPD-CoPc-BDD electrode than at the GOx/PPD-modified platinum electrode due to the smaller background current of the modified BDD electrode.

Photolysis of Recombinant Human Insulin in the Solid State: Formation of a Dithiohemiacetal Product at the C-Terminal Disulfide Bond

Exposure of protein pharmaceuticals to light can result in chemical and physical modifications, potentially leading to loss of potency, aggregation, and/or immunogenicity. To correlate these potential consequences with molecular changes, the nature of photoproducts and their mechanisms of formation must be characterized. The present study focuses on the photochemical degradation of insulin in the solid state. Solid insulin was characterized by solid-state NMR, polarized optical microscopy and scanning electron microscopy; various insulin preparations were exposed to UV light prior to product analysis by mass spectrometry. UV-exposure of solid human insulin results in photodissociation of the C-terminal intrachain disulfide bond, leading to formation of a CysS(•) thiyl radical pair which ultimately disproportionates into thiol and thioaldehyde species. The high reactivity of the thioaldehyde and proximity to the thiol allow the formation of a dithiohemiacetal structure. Dithiohemiacetal is formed during the UV-exposure of both crystalline and amorphous insulin. Dithiohemiacetals represent novel structures generated through the photochemical modification of disulfide bonds. This is the first time that such structure is identified during the photolysis of a protein in the solid state.

Thin-film solar-chemical battery: Photo-charging and discharging in amorphous AgAsS2 films

We have fabricated a rechargeable photo-chemical battery using ion-hole conducting AgAsS2 films. An asymmetrically-electroded Al/AgAsS2/SnO2 yields photocurrents and upon illumination it is concomitantly charged up. When the illumination is stopped, the stack discharges electricity into an external circuit. This photo-charging and discharging phenomenon is attributed to a photo-chemical modification of Ag-ion distribution in amorphous AgAsS2.

Photo-chemical Surface Modification for the Control of Protein Adsorption on Textile Substrates

Cell growth on fiber surfaces is an important aspect of many applications of technical textiles. The need to prevent clogging in artificial blood vessels or in textiles used for blood or water filtration as well as the anti-fouling properties of outdoor technical textiles are examples in this context. Since the adsorption of proteins forms the initial step of cell growth, a promising way to avoid biofouling is to prohibit protein adsorption by means of a suitable, permanent and non-toxic surface functionalization. Today, the deposition of poly(ethylene glycol)s (PEGs) is a well-known approach to decrease non-specific protein adsorption. In this work, a photo-chemical method to graft or cross-link PEGs on fiber surfaces was studied. Monomethacrylated PEG300MA and PEG2080MA as well as dimethacrylated PEG400DMA and PEG600DMA were considered, the numbers indicate average molar mass in g/mol. Textile fabrics made of poly(ethylene terephthalate) (PET) were impregnated with solutions of the PEGs and irradiated using either a KrCl* or a XeCl* excimer lamp (emission wavelengths 222 or 308 nm, respectively). Surface properties of the treated textiles were characterized as a function of process conditions using various surface sensitive analyses. UV cross-linking of PEG400DMA resulted in the deposition of a thick layer which effectively masked the texture of the fabric and its pore system. Much less coverage was observed in case of monomethacrylated PEGMAs, with a significant reduction in drop penetration time already after deposition of a marginal layer (less than 0.01 mg/mg). Highest reductions in adsorption of bovine serum albumin (BSA) were observed for samples prepared using PEG300MA or PEG400DMA under conditions where also the drop penetration time was at its minimum. The longer chain PEG2080MA was less effective. All results show clearly that the protein adsorption tendency can be significantly reduced by choice of suitable combinations of PEGylated monomer and UV irradiation conditions.

Photochemical modification of diamond powder with sulfur functionalities and its behavior on gold surfaces

A useful method of modifying the surface of diamond powders with sulfur-containing functionalities was developed by the use of the photolysis of elemental sulfur. The introduction of sulfur-containing functional groups on the diamond surfaces was confirmed by means of XPS, DRIFT and mass spectroscopy analyses. The sulfur-modified diamond powders exhibited surface-attachment behavior to gold surfaces through the sulfur-containing linkage. In brief, exposure of the modified diamond powders to gold colloids resulted in gold nanoparticles being attached to the diamond powders. Treatment of the modified diamond powders with gold thin film on Si substrate afforded alignment of surface-attached diamond powders through sulfur linkages by self-assembly.

Formation of Transparent SiO2 Protective Layer on Polycarbonate by 157 nm F2 Laser for Lightweight Automobile Window

A transparent, hard silica glass (SiO2) layer was formed on a conventional protective coat made of silicone ([SiO(CH3)2]n) on a polycarbonate plate by the 157 nm F2 laser-induced photochemical modification of silicone into SiO2. An optimum laser irradiation time of the F2 laser was found to form a crack-free SiO2 layer. The high optical transparency of the samples in the visible light region remained unchanged after the F2 laser irradiation. In the Taber abrasion test, the SiO2 layer markedly reduced the number of scratches, resulting in a low haze value. The haze values of the samples also depend on the thickness of the silicone protective coat underneath the SiO2 protective layer. As a result, the difference of haze value (δHz) was successfully reduced to 3.6%, compared with these of the nonirradiated sample and a bare polycarbonate plate of approximately 11.3 and 41.3%, respectively, which is comparable to the case of a bare silica glass of approximately 1.6%. In addition, the thickness of the SiO2 protective layer was estimated to be approximately 0.44 µm for the 30-s laser irradiation by immersing the samples in 1 wt % hydrogen fluoride aqueous solution and measuring the depth using a surface profilometer.

ChemInform Abstract: Zr-Catalyzed Kinetic Resolution of Allylic Ethers and Mo-Catalyzed Chromene Formation in Synthesis. Enantioselective Total Synthesis of the Antihypertensive Agent (S,R,R,R)-Nebivolol.

The first enantioselective total synthesis of the antihypertensive agent (S,R,R,R)-nebivolol (3) is described. The synthesis includes the efficient (EBTHI)Zr-catalyzed kinetic resolutions of cycloheptenyl styrenyl ethers 8 and 16, which are subsequently treated with 4 mol % Mo(CHCMe2Ph)(N(2,6-(i-Pr)2C6H3))(OCMe(CF3)2)2 to afford chiral nonracemic 2-substituted chromenes (R,R)-9 and (S,R)-17. Since the present retrosynthetic analysis dissects the molecule into two chromene fragments, both the (R) and (S) antipodes of (EBTHI)Zr catalyst are required. Accordingly, Buchwald's efficient resolution process is used to resolve rac-(EBTHI)ZrCl2 (from catalytic hydrogenation of commercially available rac-(EBI)ZrCl2), such that the two requisite transition metal chiral catalysts are obtained by a single process. Other noteworthy features of the synthesis include a highly efficient, regio- and stereoselective Pd-catalyzed opening of cyclic allylic epoxide 7 with diaryloxystannane 15 and a photochemical modification o...

Photochemical modification of single-walled carbon nanotubes using HPHMP photoinitiator for enhanced organic solvent dispersion

Photochemical modification of single-walled carbon nanotubes (SWCNTs) was carried out by covalent attachment of 2-propanol-2-yl radicals on the surface of SWCNTs, which were engendered by the photolysis of 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (HPHMP) under ultraviolet (UV) light. Pristine single-walled carbon nanotubes (p-SWCNTs) were dispersed in acetone along with HPHMP photoinitiator. After that, the mixture was irradiated by UV light to generate the free radicals which were introduced onto the surface of SWCNTs. The modification of SWCNTs was supported by UV/visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermal gravimetric analysis–mass spectrometry (TGA–MS), and transmission electron microscopy (TEM). UV/visible results revealed the loss of van Hove singularities due to covalent modification. The modification was further verified by FT-IR showing the signals at 3421 and 1100 cm−1 due to stretching and bending of O–H group, respectively. Moreover, other peaks at 2927 and 2858 cm−1 indicated the asymmetric and symmetric stretching modes of aliphatic C–H bond, respectively. Raman spectra illustrated that the intensity ratio of the tangential mode to the disorder mode (IG/ID), for modified SWCNTs (F-SWCNTs), decreased nearly four times than p-SWCNTs. TGA–MS also evidenced the signal corresponding to m/z 59 at 400 °C indicating the presence of 2-propanol-2-yl groups. TEM and dispersibility data demonstrated that the sidewall modification detached the bundled structure, enhanced the dispersion in common organic solvents and retained the original size of SWCNTs without hefty modification, which could cut or damage the nanotubes.

The use of model probes for assessing in depth modifications induced during laser cleaning of modern paintings

The cleaning of over-paint layers is a usual requirement to be met in the conservation of modern paintings. In most cases, acrylics or other related compounds must be removed without affecting the original painting. The elucidation of the extent of any photochemical or structural modification induced to the substrate following laser irradiation is a crucial challenge for the broader implementation of such laser cleaning strategies into the conservation practice. To achieve this, a methodology based on the use of a sensitive photochemical and photomechanical model system is introduced. A probe consisting of a polymeric material (e.g., Paraloid B72) doped with aromatic photo-sensitizers (e.g., POPOP) of known photochemistry and coated with uniform acrylic layer effectively simulates the real case scenario. Following laser irradiation, a variety of spectroscopic techniques including single or multiphoton laser-induced fluorescence and third-harmonic generation are employed for the assessment of any photochemical and structural modification induced in the bulk material. Practical issues related to the laser parameters employed will be presented, and the potential for a more general applicability of this methodology in the laser cleaning of modern paintings will be discussed.

Effect of TiO<SUB>2</SUB> Nanoparticles on the Interface in the PET-Rubber Composites

Usually, ceramic powders (SiO2, ZnO) are used as fillers for enhancing rubber mechanical strength. Poly-ethylene terephthalate (PET)-rubber nanocomposites were prepared by compression molding using titanium oxide (TiO2) nanoparticles as low content fillers (<2% wt). The interface properties of PET-rubber nanocomposites were studied before and after keeping the samples under UV-radiation for a week. UV-radiation has interesting potential for the photochemical modification of polymers and TiO2. The influence of UV radiation on the properties of the interface polymer-TiO2 nanoparticles was evaluated. The impact of nanoparticle aggregates on the nanometer to micrometer organization of PET-rubber composites was studied with Atomic Force Microscopy (AFM). The interface properties were explained by measuring the contact angles and surface tensions. The interactions between components of nanocomposites were investigated with Fourier Transform-Infrared (FTIR) and the effects of TiO2 nanoparticle on the interfaces and composites crystalline structure were evaluated by X-ray diffraction (XRD). The results proved that the TiO2 nanoparticles, in different weight percentages, did not alter the nanocomposites crystallinity or the average crystallites size, but improve the interface properties.

Recent Studies of Laser Science in Paintings Conservation and Research

The removal of aged and deteriorated molecular overlayers from the surface of paintings is a delicate and critical intervention in Cultural Heritage (CH) conservation. This irreversible action gets particularly complicated given the multitude of materials that may be present within a painted work of art (often in ultrathin layers or traces), as well as the exceptional sensitivity of the original surfaces to environmental conditions such as heat, light, and so on. Lasers hold an important role among the available cleaning methodologies, as they enable high control and accuracy, material selectivity, and immediate feedback. Still, prior to their implementation, it is imperative to optimize the cleaning parameters, so to ensure that any potential implications to the remaining materials are minimal and well understood. Toward this aim, research at IESL-FORTH is focused on both refining and continuously updating the laser-cleaning protocols (by introducing novel laser technologies into the field, i.e., ultrashort laser pulses), as well as on investigating and studying the nature and extent of laser-induced physicochemical alterations to the involved materials. In this Account, extended work for the understanding of ultraviolet (UV) laser ablation of polymers is presented. Emphasis is placed on the use of model systems (polymers doped with chromophores of known photochemistry) to examine the in-depth laser-induced modifications at the processed surfaces and thus to illustrate the dependence of their nature and extent on laser parameters and material properties. Furthermore, studies for the potential use of femtosecond UV pulses to overcome certain limitations involved with the nanosecond ablation of molecular overlayers from CH surfaces are highlighted. In particular, it is demonstrated that in the femtosecond regime any chemical modifications are, qualitatively and quantitatively, highly defined, limited and nearly independent of the material properties, such as the absorptivity and the degree of polymerization/molecular weight. Thus, they can be highly potent in the treatment of molecular substrates, enabling new material processing schemes that have not been possible with nanosecond laser technology, as for example, processing of ultrathin varnish layers. Finally, a sensitive indicator is introduced to elucidate the extent of any photochemical or structural modification induced at the substrate on the process of the laser-assisted removal of overpaints. A realistic scenario of an overlayered modern painting is simulated by a sensitive polymer film covered with acrylic paint. The indicator is doped with photosensitizers of known photochemistry and strong fluorescence emission, which allow the employment of laser induced fluorescence (LIF) for the detection of any chemical modifications generated into the substrate during laser cleaning. In addition, nonlinear microscopy techniques are successfully employed to examine the extent of these modifications. The suggested methodology is proven to reliably and accurately detect potential changes, and thus, it can serve as a monitoring tool to fine-tune the cleaning protocol and safeguard the original painting.