Photochemical Modification Research Articles

Polymeric Tissue Culture Substrates patterned by UV Irradiation

ABSTRACTWe studied the physico/chemical effects of deep UV irradiation of polystyrene, PMMA and polycarbonate with respect to cell adhesion and protein immobilization. Photochemical modifications of the polymer surfaces yielded unstable peroxides and carboxylic acid groups. Patterned protein adsorbates were realized by coupling via carbodiimid activation of the COOH moieties. We have immobilized enzymes and antibodies. It was observed that hepatoma cells (HepG2) and fibroblasts (L929) adhered in the presence of serum proteins in the culture medium on the irradiated regions of the substrate without any further treatment.

Photochemical modification of some polynaphthalimides

A series of polynaphthalimdes from dinaphthalene dianhydride and aromatic diamines mainly with alkyl substituents at ortho position to amine groups along with the model compounds has been synthesized using one-step high temperature polycondensation. It was found that in the case of the model compounds and the polymers synthesized from diamines with alkyl groups having at a carbon two hydrogen atoms, cyclodehydration process can take place during heating or UV irradiation and formation of additional cycle of pyrrole structure was observed. The polynaphthalimides synthesized from aromatic diamines substituted with alkyl groups can be modified under heating or UV irradiation, towards additional ring formation of pyrrole type, which causes an increase of the polymers glass transition temperatures.

Photochemical modification of poly(ether sulfone) and sulfonated poly(sulfone) nanofiltration membranes for control of fouling by natural organic matter

Poly(ether sulfone) and sulfonated poly(sulfone) nanofiltration membranes were modified by UV irradiation and UV-assisted graft polymerization of N-vinyl-2-pyrrolidinone (NVP) as a strategy for mitigating fouling by naturally-occurring organic compounds (NOM) found in surface waters. Exposure to UV (254 nm) alone increased membrane hydrophilicity, interpreted in terms of either the contact angle, θ, or surface wettability (cos θ). It was possible to increase cos θ above 0.94. FTIR analysis suggests that this was due, in part, to the formation of surface hydroxyl groups. The membrane structure was opened, as evidenced by increased clean water permeability. Fouling by natural organic matter (isolated from a surface water source using reverse osmosis) was reduced significantly, but conditions that minimized fouling also decreased solute (NOM as organic carbon) rejection. In contrast, it is possible to identify UV-assisted graft polymerization reaction conditions which significantly reduced fouling, with clean water permeability and solute rejection similar to as-received membranes. When short reaction times (10 s) were used, clean water permeability decreased and solute rejection increased, presumably as a result of pore blockage by graft polymer chains. The opposite behavior in each respect was observed for long irradiation time (180 s); however, while fouling tendency was reduced relative to as-received membranes, it was not reduced to the same extent as membranes irradiated for 60 s. This observation could be explained by an increase in pore fouling resulting from increased access to enlarged pores by larger molecular weight natural organic matter components.

Characterisation of fresh particulate vehicular exhausts near a Paris high flow road

Simultaneous continuous measurements of PM 2.5, PM 10, black carbon mass (BCae), Black smoke (BS) and particle number density ( N) were conducted in the close vicinity of a high traffic road around Paris during a three-month period beginning in August 1997. In parallel some aerosol collection was performed on filters in order to assess the black carbon (BC), organic carbon (OC) and water soluble organic fractions (WSOC) of the freshly emitted traffic aerosols. The high hourly concentrations of PM 2.5 (39±20 μg m −3), BCae (14±7 μg m −3), and N (220,000±115,000 cm −3), were found to be well correlated with each other. On average PM 2.5 represented 66±13% of PM 10 and appears to be composed primarily of BC (43±20%). On the contrary no correlation was found between PM 2.5 and the coarse (PM 10–PM 2.5) mass fractions which was attributed to resuspension processes by vehicles. Black carbon mass concentrations obtained from both filter analyses (BC) and Aethalometre data (BCae) show a good agreement suggesting that the Aethalometre calibration based on a black carbon specific attenuation coefficient ( σ) of 19 m 2 g −1 is well adapted to nearby roadside measurements. Daily BC (used as a surrogate for fine particles) concentrations and wind speed were found to be anti-correlated. Average daily variations of BC could be related to traffic intensity and regime as well as to the boundary layer height. As expected for freshly emitted traffic aerosols, filter analyses indicated a high BC/TC ratio (29±5%) and a low mean WSOC/OC ratio (12.5±5%) for the bulk aerosol. For these two ratios no day/night differences were observed, the sampling station being probably too close to traffic to evidence photochemical modification of the aerosol phase. Finally, a linear relationship was found between BC and BS hourly concentrations (BC=0.10×BS+1.18; r 2=0.93) which offers interesting perspectives to retrieve BC concentrations from existing BS archives.

Photochemical modification of the lower critical solution temperature of cinnamoylated poly(N-2-hydroxypropylmethacrylamide) in water

Partial modification of the nonionic polymer poly(N-2-hydroxy-propylmethacrylamide) by cinnamate produces stimuli-responsive copolymers. The hydrophobic character of the cinnamate chromophore induces not only a lower critical solution temperature (LCST) in water, but renders additionally the polymers photoresponsive. For moderate cinnamate contents of 9 mol-%, the photoisomerization of the trans-cinnamate to cis-cinnamate groups allows to switch the LCST by irradiation, whereas for higher cinnamate contents of 21 mol-%, irradiation leads to intra- and intermolecular photocrosslinking.

Modification of cyclic nucleotide-gated ion channels by ultraviolet light.

We irradiated cyclic nucleotide-gated ion channels in situ with ultraviolet light to probe the role of aromatic residues in ion channel function. UV light reduced the current through excised membrane patches from Xenopus oocytes expressing the alpha subunit of bovine retinal cyclic nucleotide-gated channels irreversibly, a result consistent with permanent covalent modification of channel amino acids by UV light. The magnitude of the current reduction depended only on the total photon dose delivered to the patches, and not on the intensity of the exciting light, indicating that the functionally important photochemical modification(s) occurred from an excited state reached by a one-photon absorption process. The wavelength dependence of the channels' UV light sensitivity (the action spectrum) was quantitatively consistent with the absorption spectrum of tryptophan, with a small component at long wavelengths, possibly due to cystine absorption. This spectral analysis suggests that UV light reduced the currents at most wavelengths studied by modifying one or more "target" tryptophans in the channels. Comparison of the channels' action spectrum to the absorption spectrum of tryptophan in various solvents suggests that the UV light targets are in a water-like chemical environment. Experiments on mutant channels indicated that the UV light sensitivity of wild-type channels was not conferred exclusively by any one of the 10 tryptophan residues in a subunit. The similarity in the dose dependences of channel current reduction and tryptophan photolysis in solution suggests that photochemical modification of a small number of tryptophan targets in the channels is sufficient to decrease the currents.

Effects of ultraviolet modification on the gating energetics of cyclic nucleotide-gated channels.

Middendorf et al. (Middendorf, T.R., R.W. Aldrich, and D.A. Baylor. 2000. J. Gen. Physiol. 116:227-252) showed that ultraviolet light decreases the current through cloned cyclic nucleotide-gated channels from bovine retina activated by high concentrations of cGMP. Here we probe the mechanism of the current reduction. The channels' open probability before irradiation, P(o)(0), determined the sign of the change in current amplitude that occurred upon irradiation. UV always decreased the current through channels with high initial open probabilities [P(o)(0) > 0.3]. Manipulations that promoted channel opening antagonized the current reduction by UV. In contrast, UV always increased the current through channels with low initial open probabilities [P(o)(0) < or = 0.02], and the magnitude of the current increase varied inversely with P(o)(0). The dual effects of UV on channel currents and the correlation of both effects with P(o)(0) suggest that the channels contain two distinct classes of UV target residues whose photochemical modification exerts opposing effects on channel gating. We present a simple model based on this idea that accounts quantitatively for the UV effects on the currents and provides estimates for the photochemical quantum yields and free energy costs of modifying the UV targets. Simulations indicate that UV modification may be used to produce and quantify large changes in channel gating energetics in regimes where the associated changes in open probability are not measurable by existing techniques.

Multiphoton-Excited Fluorescence Imaging and Photochemical Modification of Dye-Doped Polystyrene Microsphere Arrays

The use of nonlinear optical methods for thin-film polymeric materials modification and characterization is explored. Ordered 3-dimensional (3-D) dye-doped polystyrene microsphere arrays are photobleached and imaged in these studies. Efficient, irreversible photochemical bleaching of the dye within individual 0.5 and 1 μm diameter microspheres occurs when 810 nm light from a mode-locked Ti:sapphire laser is focused to an ∼400 nm diameter spot within the spheres. Photobleaching is shown to result from three-photon absorption and may involve ionization of the dye. The three-photon-induced photochemistry is dramatically more efficient than that resulting from single-photon excitation. Imaging of the unbleached and bleached arrays is accomplished by monitoring the two-photon-excited fluorescence from the dye. Both the nonlinear photobleaching and imaging methods provide inherent depth-discriminating capabilities, allowing for high-resolution 3-D control of the volume modified and imaged. The results suggest t...

Modification of collagen films by ultraviolet irradiation

This work describes photochemical modification of collagen films, which are widely used in medical and consumer applications. Modification of collagen films by UV irradiation (254 nm) was investigated using differential scanning calorimetry and scanning electron microscopy. It was found that the denaturation temperature of collagen decreased during irradiation and the surface of the films was changed. Changes of denaturation temperature and surface of films under UV irradiation point to the loss of water bonded to collagen. This is confirmed by IR spectra.

Alignment of liquid crystals on a photosensitive substrate studied by surface optical second-harmonic generation

The adsorption kinetics and orientational ordering of 4(')-n-octyl-4-cyanobiphenyl (8CB) liquid crystal films evaporated onto photosensitive poly(vinyl-cinnamate) (PVCN) substrates were investigated by surface optical second-harmonic generation. The adsorption rate of the first monolayer decreases with increasing degree of photochemical modification of the polymer. The in-plane orientational anisotropy of the 8CB films grown on unidirectionally photopolymerized PVCN substrates is considerably lower than the intrinsic surface orientational anisotropy of these substrates, which can explain the generally found weak surface anchoring of liquid crystals on PVCN alignment layers.

Mechanical and optical manipulation of porphyrin rings at the submicrometre scale

Scanning probe microscopes (SPMs) and especially the atomic force microscope (AFM) can be used as tools for modifying surface structures on the submicrometre and even nanometre scale. For this purpose an advanced interface has been developed to facilitate these manipulations and greatly increase the number of possible applications. In this paper this interface (the nanoManipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM imaging, manipulations and fluorescence imaging of the same area on the sample. The new setup is tested on ringlike structures of a porphyrin derivative (BP6). A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resolution attainable in these kind of experiments could go down below 100 nm and is primarily determined by the tip and sample geometry. Comparable with this experiment is the application of a near-field scanning optical microscope (NSOM) to make photochemical modifications. Using the excitation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Application on the BP6 rings led to a modification of 280 nm wide. AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the possible applications of the techniques and may ultimately go down to the single-molecule level.

A comparative study of the photochemical modifications effected in the UV laser ablation of doped polymer substrates

The photochemical modifications induced by excimer 248 nm ablation of PMMA films doped with organic compounds exemplifying different photoreactivities are presented. The employed dopants were naphthalene and the photosensitive bromo- and iodonaphthalene. The comparison of the three systems shows that ablation with nanosecond (30 ns) pulses results in significant modifications of the photosensitive halonaphthalene dopants, including an increase in their photolysis yields and the formation of additional products. In sharp contrast, in the ablation with 500 fs pulses, photochemical modifications are found to be limited.

Structural studies of supramolecular β-cyclodextrin complexes with butyrophenone and valerophenone: an explanation for photochemical reaction modification

Download options Please wait... Supplementary files Preparation and crystallisation of β-CD complexes with aryl alkyl ketones; crystallographic and photochemical studies DOC (560K) Crystal data TXT (112K) Article information DOI https://doi.org/10.1039/B002828M Article type Communication Submitted 31 Mar 2000 Accepted 05 Apr 2000 First published 05 May 2000 Download Citation Chem. Commun., 2000, 857-858 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Structural studies of supramolecular β-cyclodextrin complexes with butyrophenone and valerophenone: an explanation for photochemical reaction modification T. J. Brett and J. J. Stezowski, Chem. Commun., 2000, 857 DOI: 10.1039/B002828M To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Tom J. Brett John J. Stezowski

UV laser ablation of halonaphthalene-doped PMMA: chemical modifications above versus below the ablation threshold

Laser-induced fluorescence is employed to monitor the photochemical modifications that bromo- and iodonaphthalene incorporated in PMMA films undergo following ablation at 248 nm. Following irradiation at low fluences with nanosecond pulses, photolysis of the dopants is found to result in the formation of naphthalene-like photoproducts, whereas above the threshold additional products are observed. Based on concentration studies, these are tentatively ascribed to species containing two naphthyl groups. In close correspondence to the formation of the new species, the photolysis yields for both dopants are found to increase sharply above the threshold. Finally, the nature and extent of these photochemical effects is indicated to depend sensitively on the laser pulse width. The mechanistic implications of these results are discussed.

Photochemical effects in the UV laser ablation of polymers: Implications for laser restoration of painted artworks

The photochemical modifications induced in the UV ablation of molecular substrates are examined in model systems of polymer films (PMMA) doped with a highly photosensitive organic pigment (1-iodonaphthalene). Ablation by nanosecond laser pulses at 248 nm is shown to result in an increase of photolysis yields and in the efficient formation of new products. In sharp contrast, photoproduct formation in the corresponding ablation with 500 fs pulses is well defined and limited. Thus, besides its well-acknowledged thermal advantage, fs ablation is shown to provide a high degree of control over the induced photochemical modifications. The results of the study are correlated with the specific procedures that have been defined for the efficient restoration of painted surfaces with minimal photochemical modification to the substrate.

Feasibility of molecular-resolution fluorescence near-field microscopy using multi-photon absorption and field enhancement near a sharp tip

Aperture-based near-field microscopy suffers from fundamental limitations imposed by the electromagnetic skin depth of the aperture material and a rapidly decreasing throughput as the aperture is made smaller. Apertureless approaches without these limitations have been demonstrated for coherent imaging but are not easily applicable to incoherent processes such as fluorescence or Raman scattering and to photochemical surface modification. Using multi-photon processes in conjunction with the field enhancement that occurs at a sharp tip in close apposition to a substrate should permit substantial localization of absorption and excitation to a nm sized volume. The expected enhancement of the optical field at the tip edge is calculated here for various combinations of metallic and nonmetallic tip and substrate materials. It is estimated that when using 100 fs pulses repeating at 100 MHz average laser powers of about 10 mW should be sufficient to reach saturating field strengths for three-photon absorption. Steady state and instantaneous temperature rises at the tip are estimated and found likely not to be a limiting factor. Fluorescence quenching is expected to limit the resolution achievable with metallic tips to about 5 nm, but tips made from highly refracting insulators or semiconductors should allow truly molecular resolution.

Isolation of Cross-Coupling Products in Model Studies on the Photochemical Modification of Proteins by Tiaprofenic Acid

To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C–C- and C–O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol–DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol–(D)TPA cross-coupling may be relevant to the understanding of drug–protein photobinding.

Isolation of Cross-Coupling Products in Model Studies on the Photochemical Modification of Proteins by Tiaprofenic Acid

To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C–C- and C–O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol–DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol–(D)TPA cross-coupling may be relevant to the understanding of drug–protein photobinding.

Excimer Laser-Induced Photochemical Surface Modification of Plastics.

Photo-induced surface modification of plastics was accomplished with an ArF excimer laser in the presence ofchemical solutions. The chemical stability of the plastics is attributed to the presence of C-H, C-F or C=Obonds. Mechanism of this surface modification is to pull the terminal atoms from C-H or C-F bond in theplastic surface and to substitute the functional group for the dangling bond of C. In this treatment, the chemicalsolution was sandwiched between the sample surface and silica glass window by capillary phenomenon. Then, the solution and sample surface were excited with UV photons. In addition, the sample surface was dehydrogenatedor defluorinated by the H or B atoms which were photodissociated from H2O or B (OH) 3 in an aqueous solution, and the photodissociated OH radicals were substituted for unbonding chain of C. As a result, the plasticssurface were photochemically modified to have hydrophilic, oleophilic or metallic properties.

Cytotoxicity and mutagenicity of UVB assessed using cultured rat fibroblast.

A retroviral vector carrying both positive (neo) and negative (herpes simplex virus thymidine kinase or HSV-tk) selection markers was constructed as a substrate for mutational assay in mammalian cells. Using a population of rat fibroblast cells carrying a single copy per cell of retroviral DNA randomly integrated in their chromosomes, we examined the cytotoxic and mutagenic activities of ultraviolet light (UV) at four wavelengths (254, 290, 300, and 320 nm). The action spectra for these activities are similar to some of the previously reported spectra for photochemical DNA modifications, erythema, cell killing, and mouse skin carcinogenesis, except at 290 and 320 nm. At 290 nm, no significant mutagenicity was observed. At 320 nm, both cytotoxic and mutagenic activities were 10 times higher than the values expected from the absorption spectrum for DNA and the action spectrum for bacterial inactivation and mutagenesis. Structural comparison of some of the HSV-tk mutants obtained after irradiation with 300 and 320 nm UV revealed partially different patterns of mutation specificity, suggesting the involvement of multiple molecular mechanisms in the genotoxicity associated with this range of UV.