The effect of co-initiator structure on photoinitiating efficiency of photoredox couples composed of quinoline[2,3-b]-1H-imidazo[1,2-a]pyridinium bromide and phenoxyacetic acid or N,N-dimethylaniline derivatives.

Summary  Two groups of electron donors (phenoxyacetic acid derivatives, PAADs, and the family of N,N-dimethylaniline derivatives DMADs) in combination with quinoline[2,3-b]-1H-imidazo[1,2-a]pyridinium bromide (QIPB) were applied as photoinitiator for free radical polymerization induced with UV emission of an argon-ion laser (351 and 361 nm). Analysis of the data obtained for the initial time of photoinitiated polymerization indicates that both, the rate of electron transfer process between QIPB and tested co-initiators as well as the structure of obtained free radical can affect the overall photoinitiation ability of tested photoredox pairs.     

Microwave photochemistry V: Low‐pressure batch and continuous‐flow microwave photoreactors with quartz mercury electrodeless discharge lamps. Photohydrolysis of mono‐chloroacetic acid

BACKGROUND: Low‐pressure batch and continuous‐flow microwave photoreactors were equipped with microwave powered quartz mercury electrodeless discharge lamps (Hg‐EDLs). Photohydrolysis of aqueous mono‐chloroacetic acid (MCAA) into hydroxyacetic acid and HCl was chosen as the model reaction to evaluate these photoreactors. The effects of operational parameters on the MCAA photolysis through a UV/MW process were investigated. RESULTS: Studies were carried out at relatively high MCAA concentration (0.1 mol L^?1). The photoreaction course was monitored by the pH change in the solution. The MCAA conversion was optimized as a result of a trade‐off between the thermal dependence of the photochemical quantum yield (which increases with increasing temperature) and the thermal dependence of the EDL light intensity of 254 nm line (which increases with decreasing temperature). The microwave photoreactors made it possible to study the temperature dependence of MCAA photohydrolysis. CONCLUSION: It was found that operational parameters (i.e. reaction temperature, quantum yield) had important effects on photoefficiency. Photohydrolysis of MCAA in the microwave photoreactors can be enhanced by the UV/MW system. The results of conversions (in 120 min) for the particular photoreactor set‐ups show that the best reaction conditions for MCAA photolysis were obtained in the low‐pressure batch microwave photoreactor (the conversion was 46% at 80 °C). Copyright © 2009 Society of Chemical Industry     

The Inhibition Effect of Photo-Cross-Linking between Probes in Photo-Induced Double Duplex Invasion DNA

Double duplex invasion (DDI) DNA is a useful antigene method that inhibits expression of genomic DNA. We succeeded in performing photoinduced-DDI (pDDI) using ultrafast photo-cross-linking. 5-Cyanouracil (^CNU) has been used in pDDI to inhibit photo-cross-linking between probes, but its importance has not been clarified. Therefore, in this study, we evaluated the effect of spacer (S) and d-spacer (dS) that exhibit photo-cross-linking ability similar to that of ^CNU. ^CNU exhibited the highest pDDI efficiency, and S, dS, and T were not very different. The photo-cross-linking inhibitory effect was better with S and dS than with thymidine (T). Conversely, the thermal stability was significantly lower with S and dS than with T. The results suggest that the pDDI efficiency is determined by the balance between the photo-cross-linking inhibitory effect and the thermal stability, which is the introduction efficiency for double-stranded DNA. Therefore, ^CNU, which has a photo-cross-linking inhibitory effect and a high T_m value, showed the highest inhibitory efficiency.     

Preparation of Janus-type superparamagnetic iron oxide nanoparticles modified with functionalized PCL/PHEMA via photopolymerization for dual drug delivery

In this study, superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by the coprecipitation of FeCl₂˙4H₂O and FeCl₃˙6H₂O and applied as a core for preparation of Janus nanoparticles. Accordingly, freshly modified methacrylated iron oxide nanoparticles were reacted with two functionalized polymers. Acrylated poly(ε-caprolactone) (PCL) and acrylated poly(2-hydroxyethyl methacrylate) (PHEMA) were synthesized via ring-opening and free-radical polymerization, respectively, and subsequent modification with acryloyl chloride. Acrylated PCL as the hydrophobic part and acrylated PHEMA as the hydrophilic domain were grafted on the surface of methacrylated iron oxide nanoparticles with two morphologies. Pickering emulsion and solution photopolymerization reactions were used to prepare nanoparticles with “Janus” and “mixed” morphologies, respectively. The products were characterized in each step using Fourier-transform infrared spectroscopy (FT-IR), Proton nuclear magnetic resonance (¹H-NMR), thermogravimetric analysis (TGA), dynamic light scaterring (DLS), transmission electron microscope (TEM), vibrating-sample magnetometer (VSM), energy dispersive X-ray (EDX), and ultraviolet–visible spectroscopy (UV-Vis). Quercetin and 5-FU (as two anticancer drugs) were loaded in the mentioned nanoparticles, and the drug loading capacity and encapsulation efficiency (EE) of these nanoparticles were calculated. in vitro release behavior at two pH values (5.8 and 7.4) and at 37°C demonstrated that morphology can affect the release profile. Finally, rat C6 cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay for drug-free and drug-loaded nanoparticles.     

Preparation of the flexible soybean oil-based material via [2 + 2] cycloaddition photo-polymerization

Polymers with high flexibility and high content renewable biomass materials have attracted particular attention. Plant-derived trans-cinnamic acid (CA) was introduced into the structure of epoxidized soybean oil to form trans-cinnamated epoxidized soybean oil (ESOCA). ESOCA with multi-cinnamate groups was cured via [2 + 2] cycloaddition photo-polymerization that with no need of photoinitiator, while acrylated epoxidized soybean oil (ESOAA) was photocured via free radical photopolymerization for comparison. The successful synthesis of ESOCA and ESOAA resin was proved by Fourier transform infrared, proton nuclear magnetic resonance, and gel permeation chromatography results. ESOCA is more environmentally friendly than ESOAA for that trans-CA volatility is much lower than acrylic acid during synthesis process. Notably, UV-cured ESOCA samples had a higher tensile strength at break and a 14.75 times elongation at break of that of UV-cured ESOAA samples, showing that [2 + 2] cycloaddition photo-polymerization is a good strategy to prepare flexible materials. Performances of ESOCA as coating on flexible PET film were also better than those of ESOAA, especially the flexibility, adhesion, and UV shielding performance. This study may open up a new way for design and synthesize flexible high performance polymer from renewable biomass materials.     

Photochromic films prepared by solid state processing of disentangled ultrahigh molecular weight polyethylene and photochromic dyes composites

Disentangled ultrahigh molecular weight polyethylene (DPE) is a special grade of polyethylene (molecular weight, >10⁶ Da) which can be processed by an environment friendly solid state process on counter rotating two roll mill (TRM) below the melt temperature of the polymer. This unique processing property of DPE was utilized to develop smart DPE photochromic films. Photochromic dye like 'Spirooxazine' or 'Spiropyran' has been mixed with DPE resin powder prior to film formation without altering the DPE properties. These films could change their optical appearances on exposure to UV-light of wavelength 365 nm and the color change phenomenon of the films could also be replicated by sunlight. The color change observed is found to be reversible, that is, films could return to colorless form either spontaneously in dark or by thermal stimuli. Such smart property was imparted to DPE even at very low concentration (2,000 ppm) of photochromic dyes. Spectrophotometric studies were used to measure the rate of forward reaction with UV radiation and the rate of backward reaction in dark. In fact, DPE powder and photochromic dye composite was used to produce the compression molded disc to understand the color change phenomena. Moreover, it was observed that the photo-degradation rate of dye, could be retarded ~30% by using amphoteric Zinc phthalate salt. TGA and DSC studies confirmed that the characteristics of DPE film remained almost unaltered even after with preparation of film photochromic dyes.     

Light‐Activated Reversible Imine Isomerization: Towards a Photochromic Protein Switch

Mutants of cellular retinoic acid‐binding protein II (CRABPII), engineered to bind all‐trans‐retinal as an iminium species, demonstrate photochromism upon irradiation with light at different wavelengths. UV light irradiation populates the cis‐imine geometry, which has a high pK_a, leading to protonation of the imine and subsequent “turn‐on” of color. Yellow light irradiation yields the trans‐imine isomer, which has a depressed pK_a, leading to loss of color because the imine is not protonated. The protein‐bound retinylidene chromophore undergoes photoinduced reversible interconversion between the colored and uncolored species, with excellent fatigue resistance.     

The effect of depth and duration of UV radiation on polypropylene modification via photoinitiation

Linear polypropylene (PP) was modified using UV radiation in the presence of 0.5 wt % of benzophenone photoinitiator to introduce long chain branching (LCB) to the PP backbone. Irradiation was carried out in the solid state and the temperature level was kept below 60°C. The effects of radiation duration and sample thickness on the extent of these branching modification reactions were investigated. Viscoelastic properties, molecular weight, molecular weight distribution, and gel content were determined and compared for runs having different sample thicknesses, irradiated for different times. Comparisons were also conducted with the parent PP and the PP mixed with photoinitiator. It was found that LCB decreased by increasing the thickness of the samples. Conversely, an increase in radiation duration resulted in enhanced LCB but also led to larger gel content in the samples. Based on all these measurements and observations, a mechanism was suggested to explain formation of long chain branches (LCBs) in PP in the solid state via photoinitiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41021.     

Thiol‐ene photofunctionalization of 1,4‐polymyrcene

1,4‐Polymyrcene was synthesized by anionic polymerization of β‐myrcene and was subjected to photochemical functionalization with various thiols (i.e. methyl thioglycolate, methyl 3‐mercaptopropionate, butyl 3‐mercaptopropionate, ethyl 2‐mercaptopropionate and 2‐methyl‐2‐propanethiol) using benzophenone/UV light as the radical source. The yield of thiol addition to the trisubstituted double bonds of 1,4‐polymyrcene decreased in the order 1° thiol (ca 95%) > 2° thiol (ca 80%) > 3° thiol (<5%), due to the reversibility of the thiol‐ene reaction. Remarkably, thiol addition to the side‐chain double bonds was 8 ? 10 times (1° thiol) or 24 times (2° thiol) faster than to the main‐chain double bonds, which can be explained by the different accessibility of the double bonds and steric hindrance. Despite the use of a 10‐fold excess of thiol with respect to myrcene units, the thiol‐ene addition was accompanied by chain coupling reactions, which in the extreme case of 3° thiol (or in the absence of thiol) resulted in the formation of insoluble crosslinked material. As an example, a methyl‐thioglycolate‐functionalized 1,4‐polymyrcene was saponified/crosslinked to give submicron polyelectrolyte particles in dilute alkaline solution. © 2018 Society of Chemical Industry