Correlation between oxygen consumption and photobleaching during in vitro photodynamic treatment with ATX-S10.Na(II) using pulsed light excitation: dependence of pulse repetition rate and irradiation time

We revealed that in ATX-S10.Na(II)(13,17-bis (1-carboxypropionyl) carbamoylethyl-8-etheny-2-hydroxy-3-hydroxyiminoethylidene-2,7,12,18-tetraethyl porphyrin sodium)-mediated photodynamic therapy using 667 nm nanosecond-pulsed light excitation at a peak intensity of 2.0 MW/cm(2), phototoxicity increased with decreasing pulse repetition rate in the range of 5-30 Hz for A549 cell cultures. To examine the relation between the reaction mechanism and measured phototoxicity, we carefully measured the kinetics of photochemical oxygen consumption and photobleaching during irradiation of ATX-S10.Na(II)-sensitized A549 monolayer cultures. Measurements of oxygen consumption with a microelectrode, which was performed just above the cells, showed that there was no significant difference between the magnitudes of decrease in oxygen at the three repetition rates at the same cumulative fluence. Loss of ATX-S10.Na(II) fluorescence intensity also exhibited little repetition rate dependence when compared at the same cumulative fluence. We investigated the correlation between oxygen consumption and photobleaching during irradiation and obtained "fluorescence-oxygen diagrams." The diagrams showed dynamic changes between oxygen-dependent and oxygen-independent photobleaching at the higher repetition rates of 10 and 30 Hz, whereas such change was not clearly seen over the whole irradiation time at 5 Hz. These results suggest that the reduced phototoxicity at high repetition rates might be due to an oxygen-independent reaction. We presumed that the change in the reaction mechanism was associated with the local concentrations of the photosensitizer and oxygen in cells during irradiation.     

Enhanced photopolymerization of dimethacrylates with ketones,amines, and iodonium salts: The CQ system

The kinetics and mechanism of the photopolymerization of dimethacrylates using three‐component initiation systems consisting of camphorquinone (CQ), diphenyliodonium hexafluorophosphate (Ph₂IPF₆), and either N,N,3,5‐tetramethylaniline (TMA) or N,N‐dimethylbenzylamine or triethylamine were studied by photo‐DSC and UV‐visible spectroscopy. The effect of monomer structure on the curing kinetics and photobleaching were also investigated. Photo‐DSC studies showed fivefold increases in polymerization rate when all three components were present and the kinetics followed the trend: CQ/amine/Ph₂IPF₆ ? CQ/amine > CQ/Ph₂IPF_6.. For both CQ/amine/Ph₂IPF₆ and CQ/amine systems, the CQ was rapidly photobleached during the photo‐DSC timescale but for the systems without amine there was an induction stage before CQ photobleaching was evident. Studies of the effect of monomer type on the photobleaching rate show that the photobleaching behavior was independent of monomer structure. Three photoinitiation mechanisms have been proposed. The reaction mechanism of the CQ/amine/Ph₂IPF₆ system involves the reduction of the excited CQ molecule by the amine to form ketyl and aminoalkyl radicals, followed by the irreversible oxidation of the amine, and to a lesser extent, the ketyl radical by the iodonium salt, to form an initiating radical. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

PHOTOCHROMIC PROPERTIES OF (E)-DICYCLOPROPYLMETHYLENE-(2,5-DIMETHYL-3-FURYLETHYLIDENE)-SUCCINIC ANHYDRIDE DOPED IN POLYSTYRENE THIN FILMS

Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures.Upon irradiation with UV light(366 nm),fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C.The later color was switched back to the original color when the films were irradiated with white light.The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at itsλ_(max) of 525 nm.The fir...     

樟脑酮/过氧化物复合体系引发丙烯酸酯可见光聚合反应

采用差热扫描方法（ＤＳＣ）研究了樟脑酮（ＣＱ）／过氧化物（ＰＯ）复合体系引发三缩乙二醇双甲基丙烯酸酯（ＴＥＧＤＭ）的可见光聚合．与ＣＱ单一引发体系相比,ＣＱ和ＰＯ组成的复合体系更为有效．实验结果指出,加入过氧化物,如ＤＣＰＯ和ＤＢＰＯ,使聚合速率显著增加,最大速率到达时间明显缩短,然而它们对应的过氧化氢化合物,如ＴＢＨＰ、ＣＭＨＰ却效果不佳,复合体系的增效作用表明,激发态ＣＱ通过能量传递机制,使过氧化物发生有效的光解生成活性自由基,同时发现在含氧的条件下聚合反应速率得到增加．     

Preparation and characterization of a water soluble methylated β‐cyclodextrin/camphorquinone complex

A water soluble methylated β‐cyclodextrin/camphorquinone (MCD/CQ) complex, based on methylated β‐cyclodextrin (MCD) and camphorquinone (CQ), was prepared and its structure was characterized by FTIR, ¹H‐NMR, and UV–vis spectra. The photopolymerization kinetics of MCD/CQ in the water soluble monomer system was studied by Real‐time Infrared spectroscopy (RT‐IR). Compared to the photopolymerization carried out under nearly identical conditions but without MCD, the polymerization rate and final conversion initiated by a CQ‐triethanolamine photoinitiator system were slightly lower. The effects of different MCD/CQ concentration, triethanolamine concentration, and light intensity were also studied. Copyright © 2009 John Wiley & Sons, Ltd.     

Fluorescence Photobleaching of ALA-induced Protoporphyrin IX during Photodynamic Therapy of Normal Hairless Mouse Skin: The Effect of Light Dose and Irradiance and the Resulting Biological Effect

The photobleaching of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was investigated during superficial photodynamic therapy (PDT) in normal skin of the SKH HRt hairless mouse. The effects of light dose and fluence rate on the dynamics and magnitude of photobleaching and on the corresponding PDT-induced dam-age were examined. The results show that the PDT damage cannot be predicted by the total light dose. Photo-bleaching was monitored over a wide range of initial PpIX fluorescence intensities. The rate of PpIX photo-bleaching is not a simple function of fluence rate but is dependent on the initial concentration of sensitizer. Also, at high fluence rates (50–150 mW/cm², 514 nm) oxygen depletion is shown to have a significant effect. The rate of photobleaching with respect to light dose and the corresponding PDT damage both increase with decreasing fluence rate. We therefore suggest that the definition of a bleaching dose as the light dose that causes a 1/e reduction in fluorescence signal is insufficient to describe the dynamics of photobleaching and PDT-induced dam-age. We have detected the formation of PpIX photoproducts during the initial period of irradiation that were themselves subsequently photobleached. In the absence of oxygen, PpIX and its photoproducts are not photo-bleached. We present a method of calculating a therapeutic dose delivered during superficial PDT that demonstrates a strong correlation with PDT damage.     

Effect of UV light scattering during photopolymerization on UV spectroscopy measurements

A photopolymerization reaction involving 2-hydroxyethylmethacrylate (HEMA), a hydroxytelechelic polybutadiene (HTPB) and 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as photoinitiator has been investigated by Real Time UV and Real Time IR spectroscopies. For this system, RTUV analyses are completely opposite to the expected curves, namely a decrease in the sample absorbance (photobleaching phenomenon). This apparent contradiction has been explained by a scattering phenomenon inside the sample, which can be linked to the formation of sub-structures that can create local fluctuations of refractive index during the polymerization. A four-flux theory, which takes into account the polymer absorption and scattering properties, has allowed us to describe the UV light intensity variation inside the sample.     

樟脑醌/乙二醇-3-吗啡啉基丙酸酯甲基丙烯酸酯引发牙科复合树脂的光聚合动力学研究

采用Photo-DSC研究了樟脑醌(CQ)/乙二醇-3-吗啡啉基丙酸酯甲基丙烯酸酯(EGMPM)可见光引发牙科复合树脂聚合的动力学过程.考察了CQ浓度、EGMPM浓度以及光强对牙科修复复合树脂光聚合动力学的影响.结果表明:增加引发体系的浓度和增加光强都可以增加反应速率和转化率;同时实验结果验证了Rp∝(I₀[CQ][EGMPM])^1/2的动力学关系.     

Competition between photobleaching and fluorescence increase of photosensitizing porphyrins and tetrasulphonated chloroaluminiumphthalocyanine

The time-dependent fluorescence changes of photosensitizing porphyrins and tetrasulphonated chloroaluminiumphthalocyanine (A1C1SPc) were measured at different intracellular sites using video-enhanced microscopy and image processing. To obtain variations in intracellular fluorescence intensity, different radiant exposures of a Kr+ laser-pumped dye laser were delivered via a 600 microns plastic-clad silica fibre connected to the microscope. During irradiation, competition between photobleaching and fluorescence increase of the different dyes was observed. The porphyrins normally showed photobleaching, which was dependent on the sensitizer and its specific accumulation within the cell. Photobleaching was less pronounced for hydrophilic uroporphyrin than for more hydrophobic dyes. In contrast with an almost exponential decrease in porphyrin fluorescence with increasing light dose, the fluorescence intensity of A1C1SPc significantly increased at the beginning of irradiation, and could be correlated with intracellular deaggregation.     

Polymerization of acrylamide and methacrylamide photoinitiated by azidopentamminecobalt(III) chloride

The kinetics of polymerization of acrylamide and methacrylamide, photoinitiated by azidopentamminecobalt(III) chloride in homogeneous aqueous acid medium was studied systematically. Monochromatic wavelengths 365, 405, and 435 mμ were employed for irradiation. Polymerization proceeded without any induction period, and the reaction was followed by measurements of rate of monomer disappearance (bromometrically), rate of complex disappearance (spectrophotometrically), and the chain lengths of the polymer formed (viscometrically). The dependences of the rate of polymerization on variables like light intensity, light absorption fraction by the complex, wavelength, monomer concentration, hydrogen ion concentration, nature of the acid used (HClO₄, HNO₃, and H₂SO₄), etc., were studied. The rate of polymerization of acrylamide depended on the unit power of monomer concentration and on the square root of light absorption fraction k_ε and light intensity I. The rate of methacrylamide polymerization was proportional to the unit power of monomer concentration and fractional powers of 0.25 and 0.30 of k_ε and I, respectively. A kinetic reaction scheme is proposed and discussed in the light of the experimental results, and it has been concluded that (1) the primary photochemical act is an electron transfer reaction from the azide ion to Co(III) in the complex, (2) initiation of polymerization is by azide radical, (3) termination is by mutual destruction of polymer radicals.     

OpticalIy Pumped Chemiluminescence of Indole-3-Acetic Acid

Optically pumped chemiluminescence of indole-3-acetic acid (IAA) was observed and studied. Rose Bengal (RB) was used as a photosensitizer. Long-lived chemiluminescence (CL) appeared after irradiation of the IAA/RB reaction mixture by monochromatic light at 550 nm (the maximum of RB absorption) or by visible light. The CL spectrum had a maximum at 480 nm. The kinetics of the CL decay were single exponential. Single-exponential kinetics were characterized by two experimentally measured values: initial CL intensity and exponential lifetime of the CL decay. We studied the influence of five parameters: (1) the rate of irradiation fluence, (2) the time of irradiation, (3) RIB concentration, (4) IAA concentration and (5) buffer pH on the initial CL intensity and the CL lifetime. Initial CL intensity was proportional to the rate of irradiation fluence and the concentration of RB. Saturation was observed in dependencies of initial CL intensity on the time of irradiation, the concentration of IAA and the buffer pH. The lifetime of the CL decay decreased with increasing pH and did not depend on the other four parameters. The mechanism explaining the experimental results was suggested and detailed kinetic analysis was performed to prove the proposed mechanism. Quantum yield of the CL and five rate constants that are involved in the mechanism were determined.     

Iodonium sulfonates as high‐performance coinitiators and additives for CQ‐based systems: Toward aromatic amine‐free photoinitiating systems

Iodonium sulfonates are proposed here as a new class of high‐performance coinitiators for camphorquinone (CQ)‐based systems for the polymerization of methacrylates under blue light irradiation. When combined with CQ, the new proposed coinitiators present excellent polymerization performances and are excellent candidates for the replacement of tertiary aromatic amines subjected to toxicological concerns in the well‐established CQ/amine photoinitiating system (PIS). Remarkably, good bleaching properties are obtained after polymerization. The use of the new PIS for dental adhesives is also investigated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1664–1669     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. IV. Dose rate and temperature dependences in the styrene–silica gel system

In order to elucidate the mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effects of dose rate and irradiation temperature were studied in detail. Monomer conversion increased with increasing dose rate and temperature. At the same conversion, the percent grafting increased with decreasing dose rate and also with increasing temperature. In general, GPC spectra of graft polymers and homopolymers showed two peaks; the ratio of the two peaks changed with dose rate and irradiation temperature. The dose-rate exponents of the polymerization rate of four peaks were different from each other. The activation energies of radical polymerization and cationic polymerization were about 2.6 kcal/mole and 0 kcal/mole, respectively. Based on the results obtained, a reaction mechansim is proposed.     

苯乙酮的TiO2光催化降解及其影响因素

在TiO2(Degussa P25)和波长大于350 nm的光作用下,水中苯乙酮(1×10-5～1×10-4mol／L)能发生光催化降解,生成邻羟基苯乙酮等中间产物.该降解过程遵循Langmuir-Hinshelwood动力学方程,降解速率随入射光强度的增强和溶液起始pH值的增大而增大,但反应温度的影响较小,其降解反应的表观活化能为4.2～6.4 KJ/mol.     

Photopolymerization of vinyl ether networks using an iodonium initiator—The role of photosensitizers

Photo‐differential scanning calorimetry (photo‐DSC) and UV‐visible spectrometry were used to investigate the photocuring kinetics of visible light initiated cationic photopolymerization of triethyleneglycol divinyl ether with a diphenyl iodonium salt and three photosensitizers, 1‐chloro‐4‐propoxy‐9H‐thioxanthen‐9‐one (CPTXO), acridine orange (AO), and camphorquinone (CQ). Although all photosensitizers were effective in causing photopolymerization, CPTXO and AO photo‐reacted during the irradiation; whereas CQ was not significantly consumed during the timescale of the photo‐DSC experiment. This difference in photo‐reactivity has not been reported previously, and indicates that the reaction of the iodonium ion with CPTXO and AO results in the formation of the photosensitizer radical cation, whereas the CQ mechanism involves the reduction of the CQ excited state to a ketyl radical by a H‐donor (monomer) followed by the oxidation of the ketyl radical by the iodonium salt and thus regeneration of the CQ. For the CPTXO and AO systems, the photopolymerization rate was retarded by a radical inhibitor but the CQ system was unaffected, which confirms that different mechanisms are involved. The cure rate was found to be proportional to the concentrations of CPTXO and CQ but appeared to follow an approximately square root dependence on the AO concentration. Mechanisms to explain these differences were presented. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5474–5487, 2009     

Effects of trivalent phosphorus compounds on vinyl polymerizations. II. Photopolymerization of acrylonitrile in the presence of triphenylphosphite

It was found that acrylonitrile is polymerized by UV irradiation in the presence of triphenylphosphite under conditions where acrylonitrile alone does not polymerize. The rate of polymerization was found to be proportional to the monomer concentration, the phosphite concentration, and the light intensity. It was thought that a donor-acceptor complex formed between triphenylphosphite and acrylonitrile absorbs light and initiates the radical polymerization.     

Monitoring in situ dosimetry and protoporphyrin IX fluorescence photobleaching in the normal rat esophagus during 5-aminolevulinic acid photodynamic therapy

Experimental therapies for Barrett's esophagus, such as 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT), aim to ablate the premalignant Barrett's epithelium. However, the reproducibility of the effects should be improved to optimize treatment. Accurate irradiation with light of a proper wavelength (633 nm), fluence and fluence rate has shown to be critical for successful ALA-PDT. Here, we have used in situ light dosimetry to adjust the fluence rate measured within the esophagus for individual animals and monitored protoporphyrin IX (PpIX) fluorescence photobleaching simultaneously. Rats were administered 200 mg kg-1 ALA (n = 14) or served as control (n = 7). Animals were irradiated with an in situ measured fluence rate of 75 mW cm-2 and a fluence of 54 J cm-2. However, this more accurate method of light dosimetry did not decrease the variation in tissue response. Large differences were also observed in the dynamics of PpIX fluorescence photobleaching in animals that received the same measured illumination parameters. We found that higher PpIX fluorescence photobleaching rates corresponded with more epithelial damage, whereas lower rates corresponded with no response. A two-phased decay in PpIX fluorescence could be identified in the response group, with a rapid initial phase followed by a slower rate of photobleaching. Non-responders did not show the rapid initial decay and had a significantly lower rate of photobleaching during the second phase of the decay (P = 0.012).     

INTENSITY DEPENDENCE OF FLUOROPHORE PHOTOBLEACHING BY A STEPPED-INTENSITY SLOW-BLEACH EXPERIMENT

Abstract— We describe a simple method for determination of the dependence of fluorophore photo-bleaching on the intensity of the incident light. A sample of fluorophore is illuminated uniformly with an intensity which is sufficient only to bleach a small fraction of the fluorophore during a fluorescence lifetime period. The long-term decay of fluorescence due to photobleaching is monitored before and after a stepped increase in the incident intensity. The order of the photobleaching reaction is determined by taking the ratio of the logarithms of the limiting values of the slope of the fluorescence bleaching curve and the absolute fluorescence change. The method is applied to fluorescein, bound to dextran or ovalbumin, in aqueous solution, and the order of the reaction in both cases is shown to be unity.     

Simultaneous in-situ monitoring of parallel polymerization reactions using light scattering; a new tool for high-throughput screening

A recently introduced technique, simultaneous multiple sample light scattering (SMSLS), was used to monitor parallel polymerization reactions in situ. SMSLS is designed for real-time, high-throughput screening and provides a time-dependent light scattering signature for each reaction, which contains both qualitative and semiquantitative information. Qualitatively, the signature immediately indicates whether the reaction occurs or not, whether there is an initial lag period, and how long the reaction takes until it stops. The signature also provides estimates of the reaction rate and weight average molecular mass M(w), and its shape can help identify mechanistic aspects, for example, controlled versus free radical polymerization, presence of impurities, etc. The method is inherently adapted to small sample volumes and requires no special sample preparation or postpolymerization characterization. The demonstration here involved the free radical polymerization of acrylamide under varying conditions and should be readily applicable to a wide variety of other reactions. Results were cross-checked with multi-detector gel permeation chromatography.