Photoinduced Crosslinking Reaction Research Articles

Photopolymerized Features via Beam Pen Lithography as a Novel Tool for the Generation of Large Area Protein Micropatterns.

A cantilever-free scanning probe lithography (CF-SPL)-based method for the rapid polymerization of nanoscale features onasurfacevia crosslinking and thiol-acrylate photoreactions is described, whereinthenanoscale position, height, and diameter of each feature can be finely and independently tuned. With precise spatiotemporal control over the illumination pattern, beam pen lithography (BPL) allows for the photo-crosslinking of polymers into ultrahigh resolution features over centimeter-scale areas using massively parallel >160 000 pen arrays of individually addressable pens that guide and focus light onto the surface with sub-diffraction resolution. The photoinduced crosslinking reaction of the ink material, which is composed of photoinitiator, diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, poly(ethylene glycol) diacrylate, and thiol-modified functional binding molecules (i.e., thiol-PEG-biotin or 16-mercaptohexanoic acid), proceeds to ≈80% conversion with UV exposure (72mWcm-2 ) for short time periods (0.5s). Such polymer patterns are further reacted with proteins (streptavidin and fibronectin) to yield protein arrays with feature arrangements at high resolution and densities controlled by local UV exposure. This platform, which combines polymer photochemistry and massive arrays of scanning probes, constitutes a new approach to making biomolecular microarrays in a high-throughput and high-yielding manner, opening new routes for biochip synthesis, bioscreening, and cell biology research.

Injectable and In Situ Gelling Dextran Derivatives Containing Hydrolyzable Groups for the Delivery of Large Molecules.

Recently, we reported the synthesis and characterization of a new dextran derivative obtained by grafting polyethylene glycol methacrylate to a polysaccharide backbone through a carbonate bond. This moiety was introduced because it allows for the fabrication, through a photo-induced crosslinking reaction, of biodegradable hydrogels particularly suitable for the release of high molecular weight molecules. Here, we investigate the influence of the oxyethylene chain length and the molecular weight of the starting dextran on the main properties of the polymeric solutions as well as those of the corresponding hydrogels. All synthesized polymeric derivatives were characterized by FTIR, NMR, and rheological analyses. The photo-crosslinking reaction of the polymers allowed us to obtain biodegradable networks tested for their mechanical properties, swelling, and degradation behavior. The results showed that both the oxyethylene chain length as well as the molecular weight of the starting dextran influenced swelling and degradation of the hydrogel network. As a consequence, the different behaviors in terms of swelling and degradability were able to affect the release of a large model molecule over time, making these matrices suitable candidates for the delivery of high molecular weight drug substances.

Preparation of Linear Cryogel Arrays as a Microfluidic Platform for Immunochromatographic Assays

We describe a new microfluidic platform to perform immunochromatographic assays. The platform consists of a linear assembly of small, porous cryogel monoliths functionalized with various biomolecules. The cryogels are anchored in an optically transparent capillary, which serves as the microfluidic carrier. This assembly enables fluid flow by capillary action and simple optical detection. Using an in situ preparation method, individual compartments are generated from small plugs of polymer solutions that are transformed into small individually functionalized cryogel monoliths through a photoinduced cross-linking reaction. In the same reaction step, the monoliths are firmly anchored to the surface of the capillary. As proof-of-concept, a prototype platform is successfully used for the detection of the inflammatory marker interleukin 6 via a sandwich immunoassay. We observe excellent assay performance metrics that include high sensitivity, good linearity, and low variation. We also demonstrate fluid transport solely by passive means, which is a critical attribute for point-of-care diagnostics.

A General Strategy to Enhance the Performance of Dye-Sensitized Solar Cells by Incorporating a Light-Harvesting Dye with a Hydrophobic Polydiacetylene Electrolyte-Blocking Layer.

A unique strategy to suppress charge recombination effectively and enhance light harvesting in dye-sensitized solar cells (DSSCs) is demonstrated by the design of a new dipolar organic dye functionalized with a diacetylene unit, which is capable of undergoing a photoinduced crosslinking reaction to generate a hydrophobic polydiacetylene layer. The polydiacetylene layer serves as an electrolyte-blocking layer that effectively blocks the approach of the oxidized redox mediator and suppresses the dark current, and also plays a role in light harvesting owing to efficient energy transfer to the dipolar dyes. A 15 % efficiency improvement was achieved on going from the monomer dye (JSC =13.5 mA cm-2 , Voc =0.728 V, fill factor=0.73, η=7.17 %) to the crosslinked dye (JSC =14.9 mA cm-2 , Voc =0.750 V, fill factor=0.74, η=8.27 %) under AM 1.5 conditions.

A theoretical study of the light-induced cross-linking reaction of 5-fluoro-4-thiouridine with thymine

In contrast to photophysics of thio-substituted nucleobases, their photoinduced cross-linking reactions with canonical nucleobases remain scarcely investigated computationally. In this work, we have adopted combined CASPT2/PCM//CASSCF and B3LYP-D3/PCM electronic structure methods to study this kind of photochemical reaction of 5-fluoro-4-thiouridine (truncated 5-fluoro-1-methyl-4-thiouracil used in calculations) and 1-methylthymine (referred to as thymine for clarity hereinafter). On the basis of CASPT2/PCM computed results, we have proposed two efficient excited-state relaxation pathways to populate the lowest T1 state of the complex of 5-fluoro-1-methyl-4-thiouracil and thymine from its initially populated S2(1ππ*) state. In the first one, the S2 system first hops to the S1 state via an S2/S1 conical intersection, followed by a direct S1 → T1 intersystem crossing process enhanced by large S1/T1 spin-orbit coupling. In the second path, the resultant S1 system first jumps to the T2 state, from which an efficient T2 → T1 internal conversion occurs. The T1 cross-linking reaction is overall divided into two phases. The first phase is a stepwise and nonadiabatic photocyclization reaction, which starts from the T1 complex and ends up with an S0 thietane intermediate. The second phase is a thermal reaction. The system first rearranges its four- and six-membered rings to form three new rings; then, an S0 fluorine atom transfer occurs, followed by the formation of photoproducts. Finally, the present work paves the way for studying light-induced cross-linking reactions of thionucleobases with canonical bases in DNA and RNA.

Photoactivated immobilization of single-stranded DNAs on a psoralen-functionalized surface under low pH conditions

Single stranded DNA was photo-patterned on a psoralen-functionalized surface and conjugated with a psoralen-modified enzyme. Photoreactions between the single-stranded DNA and psoralen-functionalized materials were found to be significantaly influenced by pH, showing high efficientcy only under acidic conditions. Specifically, the photopattering of single-stranded DNA probes, such as polythymine, polyadenine, polycytosine, and polyguanine, on a psoralen-functionalized amino-dextran surface under various pH conditions (pH 3.36–8.80) showed that the polythymine probes had the highest immobilization efficiency at pH 3.36. The effect of pH was further confirmed by photopatterning the single-stranded DNA probes using the photomask. While almost no pattern was observed on the psoralen surface at pHs greater than 5.5, much more visible patterns were observed as the pH was decreased below 5.5. As a result of the irradiation of polyT15 and polyA15-labeled DNA probes, the photopatterns formed by the irradiation of polythymine probes were found to be associated with the cross-linking between the thymine and the psoralen moieties. Finally, additional studies showed that psoralen could be used as the reactive center in the photo-induced cross-linking reaction between DNA and the model protein, horseradish peroxidase (HRP).

Effects of Congo Red on Aβ1−40 Fibril Formation Process and Morphology

Alzheimer's disease (AD), an age-related neurodegenerative disorder, is the most common form of dementia, and the seventh-leading cause of death in the United States. Current treatments offer only symptomatic relief; thus, there is a great need for new treatments with disease-modifying potential. One pathological hallmark of AD is so-called senile plaques, mainly made up of β-sheet-rich assemblies of 40- or 42-residue amyloid β-peptides (Aβ). Hence, inhibition of Aβ aggregation is actively explored as an option to prevent or treat AD. Congo red (CR) has been widely used as a model antiamyloid agent to prevent Aβ aggregation. Herein, we report detailed morphological studies on the effect of CR as an antiamyloid agent, by circular dichroism spectroscopy, photo-induced cross-linking reactions, and atomic force microscopy. We also demonstrate the effect of CR on a preaggregated sample of Aβ(1-40). Our result suggests that Aβ(1-40) follows a different path for aggregation in the presence of CR.

Synthesis and Photoinduced Cross-linking Reactions of 4,5′,8-Trimethylpsoralen-incorporated Oligodeoxyribonucleotide

Abstract Photo-induced cross-linking reaction at a certain position in nucleic acids, occurring in a sequence specific manner, would be the key to inhibitor the growth of carcinoma cells, which has a point mutation in the ras gene. We newly synthesized 4,5′,8-trimethylpsoralen nucleoside and examined its photoinduced cross-linking activities in DNA duplexes after UVA irradiation.

Influence of sample composition and processing parameters on the UV cure of clear coatings

Photocurable systems consist of functional macromolecules, which undergo polymerization and a photoinduced crosslinking reaction under UV irradiation. Radiation-curable coatings have gained importance because they are environmentally friendly and save more energy than conventional heat-curable processes. The performance of UV-curable coatings depends on their formulation and cure quality. The quality of UV radiation cure depends on lamp characteristics, photoinitiator (PI) content, film thickness, curing environment, substrate and temperature. The aim of this study was to evaluate the influence of coating thickness and UV radiation dose, as well as coating characteristics such as PI content and stabilizer additive composition, on the curing process.

A New Class of Photoactivatable and Cleavable Derivatives of Neurotoxin II from Naja naja oxiana. Synthesis, Characterisation, and Application for Affinity Labelling of the Nicotinic Acetylcholine Receptor from Torpedo californica

A new series of photoactivatable and cleavable derivatives of neurotoxin II from the cobra Naja naja oxiana is investigated which can be used for mapping the surface topology of the nicotinic acetylcholine receptor from Torpedo electric tissue. The preparation and characterisation of five toxin derivatives, each with a radioactive 125I-azidosalicylamidoethyl-1,3′-dithiopropyl group in a defined position within the primary structure, are described. The photoinduced cross-linking reaction of the toxin derivatives with membrane-bound receptor is investigated. The photoactivatable group located at position K25 reacts almost exclusively with the δ subunit of the receptor, whereas the K15 derivative reacts with the α and β subunits. The other derivatives did not react with the receptor to any significant extent. It is shown that, with respect to the receptor subunits, the cross-linking pattern depends on the length and chemical nature of the cross-linking group.

A new class of photoactivatable and cleavable derivatives of neurotoxin II from Naja naja oxiana. Synthesis, characterisation, and application for affinity labelling of the nicotinic acetylcholine receptor from Torpedo californica.

A new series of photoactivatable and cleavable derivatives of neurotoxin II from the cobra Naja naja oxiana is investigated which can be used for mapping the surface topology of the nicotinic acetylcholine receptor from Torpedo electric tissue. The preparation and characterisation of five toxin derivatives, each with a radioactive 125I-azidosalicylamidoethyl-1,3'-dithiopropyl group in a defined position within the primary structure, are described. The photoinduced cross-linking reaction of the toxin derivatives with membrane-bound receptor is investigated. The photoactivatable group located at position K25 reacts almost exclusively with the delta subunit of the receptor, whereas the K15 derivative reacts with the alpha and beta subunits. The other derivatives did not react with the receptor to any significant extent. It is shown that, with respect to the receptor subunits, the cross-linking pattern depends on the length and chemical nature of the cross-linking group.

Sequence-specific photo-induced cross-linking of the two strands of double-helical DNA by a psoralen covalently linked to a triple helix-forming oligonucleotide.

On the basis of the structure of DNA-psoralen bis adducts (formed by psoralen with two thymines on opposite strands), a psoralen-oligonucleotide conjugate was designed to photoinduce a cross-link between the two DNA strands at a specific sequence. Psoralen was attached via its C-5 position to a 5'-thiophosphate group of an 11-mer homopyrimidine oligonucleotide. The 11-mer binds to an 11-base-pair homopurine.homopyrimidine sequence of a DNA fragment, where it forms a triple helix. Upon near-UV-irradiation, the two strands of DNA are crosslinked at the TpA step present at the triplex-duplex junction. The reaction is specific for the homopurine.homopyrimidine DNA sequence and requires both oligonucleotide recognition of the DNA major groove and intercalation of psoralen at the triplex-duplex junction. The yield of the photo-induced cross-linking reaction is quite high (greater than 80%). Such psoralen-oligonucleotide conjugates are probes of sequence-specific triple-helix formation and could be used to selectively control gene expression or to induce site-directed mutations.

Photo-induced dimerization of anthracene phospholipids for the study of the lateral distribution of lipids in membranes.

It is shown that photo-induced cross-linking reaction between anthracene-labelled phospholipids can be used for studying, at a molecular level, their lateral distribution in bilayer structures. A simple and versatile method is proposed. It is based on the property of anthracene to form covalently bound dimers upon irradiation in the near ultraviolet (360 nm) and on the possibility of separating the lipid photo-dimers from the lipid monomers by thin-layer chromatography. Identification of the photo-dimers is easily achieved since, upon illumination at a shorter wavelength (250-280 nm), they partially dissociate to the native monomer molecules. The feasibility of the method was tested by checking the effects of cations (sodium, calcium) on the homogeneity of 1/1 mixtures of anthracene-phosphatidylcholine, i.e. 1-acyl-2-[9-(2-anthryl)-nonanoyl]-sn-glycero-3-phosphocholin e (Anthr-PC) with anthracene-phosphatidic acid (Anthr-PA) and with anthracene-phosphatidylglycerol (Anthr-PG) in the form of liposomes. These lipids were anthracene-labelled by acylation of their glycerol backbone at the sn-2 position with the synthetic 9-(2-anthryl)-nonanoic acid. Data presented indicate a good miscibility of these lipids in the presence of sodium. For each lipid mixture, the lipid heterodimers were clearly identified and, quantitatively, they dominated the lipid homodimers, as expected for a regular distribution of the lipids in the 1/1 mixture. Addition of calcium ions to the lipid suspensions did not alter the miscibility properties of Anthr-PC and Anthr-PG. In contrast, calcium triggered a clear-cut phase separation in the Anthr-PC/Anthr-PA mixture as, in this case, only traces of the heterodimer form of the lipids remained observable on the chromatogram. The three anthracene-phospholipids, pure or mixed together, exhibit a clear-cut gel-to-liquid phase transition which was detectable by fluorescence intensity measurements. The analysis of the corresponding phase-transition temperatures confirms, at a 'macroscopic' level, the effects of sodium and calcium on the mixing properties of the anthracene phospholipids which were revealed at a 'microscopic' level by the dimerization procedure.