Photodynamic and Nail Penetration Enhancing Effects of Novel Multifunctional Photosensitizers Designed for The Treatment of Onychomycosis

Novel multifunctional photosensitizers (MFPSs), 5,10,15‐tris(4‐N‐methylpyridinium)‐20‐(4‐phenylthio)‐[21H,23H]‐porphine trichloride (PORTH) and 5,10,15‐tris(4‐N‐methylpyridinium)‐20‐(4‐(butyramido‐methylcysteinyl)‐hydroxyphenyl)‐[21H,23H]‐porphine trichloride (PORTHE), derived from 5,10,15‐Tris(4‐methylpyridinium)‐20‐phenyl‐[21H,23H]‐porphine trichloride (Sylsens B) and designed for treatment of onychomycosis were characterized and their functionality evaluated. MFPSs should function as nail penetration enhancer and as photosensitizer for photodynamic treatment (PDT) of onychomycosis. Spectrophotometry was used to characterize MFPSs with and without 532 nm continuous‐wave 5 mW cm^?2 laser light (± argon/mannitol/NaN₃). Nail penetration enhancement was screened (pH 5, pH 8) using water uptake in nails and fluorescence microscopy. PDT efficacy was tested (pH 5, ± argon/mannitol/NaN₃) in vitro with Trichophyton mentagrophytus microconida (532 nm, 5 mW cm^?2). A light‐dependent absorbance decrease and fluorescence increase were found, PORTH being less photostable. Argon and mannitol increased PORTH and PORTHE photostability; NaN₃ had no effect. PDT (0.6 J cm^?2, 2 μm ) showed 4.6 log kill for PORTH, 4.4 for Sylsens B and 3.2 for PORTHE (4.1 for 10 μm ). Argon increased PORTHE, but decreased PORTH PDT efficacy; NaN₃ increased PDT effect of both MFPSs whereas mannitol increased PDT effect of PORTHE only. Similar penetration enhancement effects were observed for PORTH (pH 5 and 8) and PORTHE (pH 8). PORTHE is more photostable, effective under low oxygen conditions and thus realistic candidate for onychomycosis PDT.     

Membrane‐Anchoring Photosensitizer with Aggregation‐Induced Emission Characteristics for Combating Multidrug‐Resistant Bacteria

Traditional photosensitizers (PSs) show reduced singlet oxygen (¹O₂) production and quenched fluorescence upon aggregation in aqueous media, which greatly affect their efficiency in photodynamic therapy (PDT). Meanwhile, non‐targeting PSs generally yield low efficiency in antibacterial performance due to their short lifetimes and small effective working radii. Herein, a water‐dispersible membrane anchor (TBD‐anchor) PS with aggregation‐induced emission is designed and synthesized to generate ¹O₂ on the bacterial membrane. TBD‐anchor showed efficient antibacterial performance towards both Gram‐negative (Escherichia coli) and Gram‐positive bacteria (Staphylococcus aureus). Over 99.8 % killing efficiency was obtained for methicillin‐resistant S. aureus (MRSA) when they were exposed to 0.8 μm of TBD‐anchor at a low white light dose (25 mW cm^?2) for 10 minutes. TBD‐anchor thus shows great promise as an effective antimicrobial agent to combat the menace of multidrug‐resistant bacteria.     

A Comparison of Dose Metrics to Predict Local Tumor Control for Photofrin‐mediated Photodynamic Therapy

This preclinical study examines light fluence, photodynamic therapy (PDT) dose and “apparent reacted singlet oxygen,” [¹O₂]_rx, to predict local control rate (LCR) for Photofrin‐mediated PDT of radiation‐induced fibrosarcoma (RIF) tumors. Mice bearing RIF tumors were treated with in‐air fluences (50–250 J cm^?2) and in‐air fluence rates (50–150 mW cm^?2) at Photofrin dosages of 5 and 15 mg kg^?1 and a drug‐light interval of 24 h using a 630‐nm, 1‐cm‐diameter collimated laser. A macroscopic model was used to calculate [¹O₂]_rx and PDT dose based on in vivo explicit dosimetry of the drug concentration, light fluence and tissue optical properties. PDT dose and [¹O₂]_rx were defined as a temporal integral of drug concentration and fluence rate, and singlet oxygen concentration consumed divided by the singlet oxygen lifetime, respectively. LCR was stratified for different dose metrics for 74 mice (66 + 8 control). Complete tumor control at 14 days was observed for [¹O₂]_rx ≥ 1.1 mm or PDT dose ≥1200 μm J cm^?2 but cannot be predicted with fluence alone. LCR increases with increasing [¹O₂]_rx and PDT dose but is not well correlated with fluence. Comparing dosimetric quantities, [¹O₂]_rx outperformed both PDT dose and fluence in predicting tumor response and correlating with LCR.     

Effect and Mechanism of a New Photodynamic Therapy with Glycoconjugated Fullerene

When irradiated, fullerene efficiently generates reactive oxygen species (ROS) and is an attractive photosensitizer for photodynamic therapy (PDT). Ideally, photosensitizers for PDT should be water-soluble and tumor-specific. Because cancer cells endocytose glucose more effectively than normal cells, the characteristics of fullerene as a photosensitizer were improved by combining it with glucose. The cytotoxicity of PDT was studied in several cancer cell lines cultured with C₆₀-(Glc)1 (d -glucose residue pendant fullerene) and C₆₀-(6Glc)1 (a maltohexaose residue pendant fullerene) subsequently irradiated with UVA₁. PDT alone induced significant cytotoxicity. In contrast, PDT with the glycoconjugated fullerene exhibited no significant cytotoxicity against normal fibroblasts, indicating that PDT with these compounds targeted cancer cells. To investigate whether the effects of PDT with glycoconjugated fullerene were because of the generation of singlet oxygen (¹O₂), NaN₃ was added to cancer cells during irradiation. NaN₃ extensively blocked PDT-induced apoptosis, suggesting that PDT-induced cell death was a result of the generation of ¹O₂. Finally, to investigate the effect of PDT in vivo, melanoma-bearing mice were injected intratumorally with C₆₀-(Glc)1 and irradiated with UVA₁. PDT with C₆₀-(Glc)1 suppressed tumor growth. These findings indicate that PDT with glycoconjugated fullerene exhibits tumor-specific cytotoxicity both in vivo and in vitro via the induction of ¹O₂.     

Self‐Amplified Photodynamic Therapy through the 1O2‐Mediated Internalization of Photosensitizers from a Ppa‐Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non‐selective release of photosensitizers still exist. Herein, we report a ¹O₂‐responsive block copolymer (POEGMA‐b‐P(MAA‐co‐VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (¹O₂) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The ¹O₂‐responsiveness of POEGMA‐b‐P(MAA‐co‐VSPpaMA) block copolymer enabled the realization of self‐amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.     

Studies on the Photodynamic Mechanism of Tetrapyrrole Compounds by Laser Flash Photolysis

Photodynamic therapy (PDT) is a promising new treatment technique which can potentially destroy unwanted and malignant tissues, such as those of cancer. The photodynamic mechanisms of three tetrapyrrole compounds: Mg‐purpurin‐18, tetra(meso‐chlorophenyl)porphyrin (m‐TCPP) and 2,7,12,18‐tetramethyl‐3,8‐di[(1‐isobutoxyl)‐ ethyl]‐13,17‐bis[3‐di(2‐chloroethyl)aminopropyl]porphyrin (TDBP) in acetonitrile were investigated by 355 nm laser flash photolysis. It was found that after laser flash photolysis (LFP), the excited states of TDBP and Mg‐purpurin‐18 could react with O₂ and ¹O₂ was produced, which proved that TDBP and Mg‐purpurin‐18 took effects through type II mechanism in PDT. This suggested that TDBP and Mg‐purpurin‐18 should be suitable for target tissues containing enough O₂. Mg‐purpurin‐18 has two extra absorptions at 550 and 700 nm, which means it has broad choices of laser wavelength in PDT. It was also found that m‐TCPP could be photoionized when excited with 355 nm laser under N₂‐saturated condition. It could also react with O₂ to produce reactive oxygen species such as superoxide and the peroxide anions, but not ¹O₂. These were known as the Type I mechanism. So m‐TCPP could be used even at low oxygen concentration or more polar environments with good behavior in PDT. From the above studies on the three different tetrapyrrole compounds it could be concluded that the structure of porphin ring takes a main role in PDT. And there was important impact on the photodynamic mechanism for the functional group directly connecting with porphin ring, while little influence for the functional group indirectly connecting with porphin ring. These will be of great value in the discovery of new PDT drugs.     

A Phototheranostic Strategy to Continuously Deliver Singlet Oxygen in the Dark and Hypoxic Tumor Microenvironment

Continuous irradiation during photodynamic therapy (PDT) inevitably induces tumor hypoxia, thereby weakening the PDT effect. In PDT‐induced hypoxia, providing singlet oxygen from stored chemical energy may enhance the cell‐killing effect and boost the therapeutic effect. Herein, we present a phototheranostic (DPPTPE@PEG‐Py NPs) prepared by using a 2‐pyridone‐based diblock polymer (PEG‐Py) to encapsulate a semiconducting, heavy‐atom‐free pyrrolopyrrolidone‐tetraphenylethylene (DPPTPE) with high singlet‐oxygen‐generation ability both in dichloromethane and water. The PEG‐Py can trap the ¹O₂ generated from DPPTPE under laser irradiation and form a stable intermediate of endoperoxide, which can then release ¹O₂ in the dark, hypoxic tumor microenvironment. Furthermore, fluorescence‐imaging‐guided phototherapy demonstrates that this phototheranostic could completely inhibit tumor growth with the help of laser irradiation.     

Gas‐phase chemistry of dihydromyrcenol with ozone and OH radical: Rate constants and products

A bimolecular rate constant, k_{OH + dihydromyrcenol}, of (38 ± 9) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 2,6‐dimethyl‐7‐octen‐2‐ol (dihydromyrcenol,) at 297 ± 3 K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, k, of approximately 2 × 10^?18 cm³ molecule^?1 s^?1 was determined by monitoring the decrease in ozone (O₃) concentration in an excess of dihydromyrcenol. To more clearly define part of dihydromyrcenol's indoor environment degradation mechanism, the products of the dihydromyrcenol + OH and dihydromyrcenol + O₃ reactions were also investigated. The positively identified dihydromyrcenol/OH and dihydromyrcenol/O₃ reaction products were acetone, 2‐methylpropanal (O?CHCH(CH₃)₂), 2‐methylbutanal (O?CHCH(CH₃)CH₂CH₃), ethanedial (glyoxal, HC(?O)C(?O)H), 2‐oxopropanal (methylglyoxal, CH₃C(?O)C(?O)H). The use of derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible dihydromyrcenol/OH and dihydromyrcenol/O₃ reaction mechanisms based on previously published volatile organic compound/OH and volatile organic compound/O₃ gas‐phase reaction mechanisms. © 2006 Wiley Periodicals, Inc. *

1 This article is a US Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 38: 451–463, 2006     

Membrane-Anchoring Photosensitizer with Aggregation-Induced Emission Characteristics for Combating Multidrug-Resistant Bacteria

Traditional photosensitizers (PSs) show reduced singlet oxygen (¹O₂) production and quenched fluorescence upon aggregation in aqueous media, which greatly affect their efficiency in photodynamic therapy (PDT). Meanwhile, non-targeting PSs generally yield low efficiency in antibacterial performance due to their short lifetimes and small effective working radii. Herein, a water-dispersible membrane anchor (TBD-anchor) PS with aggregation-induced emission is designed and synthesized to generate ¹O₂ on the bacterial membrane. TBD-anchor showed efficient antibacterial performance towards both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Over 99.8 % killing efficiency was obtained for methicillin-resistant S. aureus (MRSA) when they were exposed to 0.8 μm of TBD-anchor at a low white light dose (25 mW cm⁻²) for 10 minutes. TBD-anchor thus shows great promise as an effective antimicrobial agent to combat the menace of multidrug-resistant bacteria.     

Measuring the Physiologic Properties of Oral Lesions Receiving Fractionated Photodynamic Therapy

Photodynamic therapy (PDT) can treat superficial, early‐stage disease with minimal damage to underlying tissues and without cumulative dose‐limiting toxicity. Treatment efficacy is affected by disease physiologic properties, but these properties are not routinely measured. We assessed diffuse reflectance spectroscopy (DRS) for the noninvasive, contact measurement of tissue hemoglobin oxygen saturation (S_tO₂) and total hemoglobin concentration ([tHb]) in the premalignant or superficial microinvasive oral lesions of patients treated with 5‐aminolevulinic acid (ALA)‐PDT. Patients were enrolled on a Phase 1 study of ALA‐PDT that evaluated fluences of 50, 100, 150 or 200 J cm^?2 delivered at 100 mW cm^?2. To test the feasibility of incorporating DRS measurements within the illumination period, studies were performed in patients who received fractionated (two‐part) illumination that included a dark interval of 90–180 s. Using DRS, tissue oxygenation at different depths within the lesion could also be assessed. DRS could be performed concurrently with contact measurements of photosensitizer levels by fluorescence spectroscopy, but a separate noncontact fluorescence spectroscopy system provided continuous assessment of photobleaching during illumination to greater tissue depths. Results establish that the integration of DRS into PDT of early‐stage oral disease is feasible, and motivates further studies to evaluate its predictive and dosimetric value.     

Carbazole‐based conjugated polymer covalently coated Fe3O4 nanoparticle as efficient and reversible Hg2+ optical probe

A type of fluorescent–magnetic dual‐function nanocomposite, Fe₃O₄@SiO₂@P‐2, was successfully obtained by Cu⁺‐catalyzed click reaction between acetylene (C?C? H)‐substituted carbazole‐based conjugated polymer ( P‐2) and azide‐terminated silica‐coated magnetic iron oxide nanoparticles (Fe₃O₄@SiO₂–N₃). Optical and magnetization analyses indicate that Fe₃O₄@SiO₂@P‐2 exhibits stable fluorescence and rapid magnetic response. The fluorescence of Fe₃O₄@SiO₂@P‐2 was quenched significantly in the presence of I^? and gave a detection limit (DL) of ～8.85 × 10^?7 M. Given the high binding constant and matching ratio between Hg²⁺ and I^?, the fluorescence of Fe₃O₄@SiO₂@P‐2/I^? complex recovered efficiently with the addition of Hg²⁺. A DL of ～4.17 × 10^?7 M was obtained by this probing system. Recycling of Fe₃O₄@SiO₂@P‐2 probe was readily achieved by simple magnetic separation. Results indicate that Fe₃O₄@SiO₂@P‐2 can be used as an “on–off–on” fluorescent switchable and recyclable Hg²⁺ probe. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3636–3645     

Dual Metal Active Sites in an Ir1/FeOx Single‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir₁/FeO_x single‐atom catalysts. Water dissociates to OH* on the Ir₁ single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir₁ reacts with another adjacent O atom to produce CO₂, yielding an oxygen vacancy (O_vac). Then, the formation of H₂ becomes feasible due to migration of H from adsorbed OH* toward Ir₁ and its subsequent reaction with another H*. The interaction of Ir₁ and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe³⁺?O???Ir²⁺?O_vac to Fe²⁺?O_vac???Ir³⁺?O with the involvement of O_vac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir₁/FeO_x for sequential production of CO₂ and H₂.     

A Carbon Electrode Functionalized by a Tricopper Cluster Complex: Overcoming Overpotential and Production of Hydrogen Peroxide in the Oxygen Reduction Reaction

A study of the oxygen reduction reaction (ORR) on a screen printed carbon electrode surface mediated by the tricopper cluster complex Cu₃(7‐N‐Etppz(CH₂OH)) dispersed on electrochemically reduced carbon black, where 7‐N‐Etppz(CH₂OH) is the ligand 3,3′‐(6‐(hydroxymethyl)‐1,4‐diazepane‐1,4‐diyl)bis(1‐(4‐ethyl piperazin‐1‐yl)propan‐2‐ol), is described. Onset oxygen reduction potentials of about 0.92 V and about 0.77 V are observed at pH 13 and pH 7 vs. the reversible hydrogen electrode, which are comparable to the best values reported for any synthetic copper complex. Based on half‐wave potentials (E_1/2), the corresponding overpotentials are about 0.42 V and about 0.68 V, respectively. Kinetic studies indicate that the trinuclear copper catalyst can accomplish the 4 e^? reduction of O₂ efficiently and the ORR is accompanied by the production of only small amounts of H₂O₂. The involvement of the copper triad in the O₂ activation process is also verified.     

Dual Functioning Thieno‐Pyrrole Fused BODIPY Dyes for NIR Optical Imaging and Photodynamic Therapy: Singlet Oxygen Generation without Heavy Halogen Atom Assistance

We discovered a rare phenomenon wherein a thieno‐pyrrole fused BODIPY dye (SBDPiR690) generates singlet oxygen without heavy halogen atom substituents. SBDPiR690 generates both singlet oxygen and fluorescence. To our knowledge, this is the first example of such a finding. To establish a structure–photophysical property relationship, we prepared SBDPiR analogs with electron‐withdrawing groups at the para‐position of the phenyl groups. The electron‐withdrawing groups increased the HOMO–LUMO energy gap and singlet oxygen generation. Among the analogs, SBDPiR688, a CF₃ analog, had an excellent dual functionality of brightness (82290 m ^?1 cm^?1) and phototoxic power (99170 m ^?1 cm^?1) comparable to those of Pc 4, due to a high extinction coefficient (211 000 m ^?1 cm^?1) and balanced decay (Φ_flu=0.39 and Φ_Δ=0.47). The dual functionality of the lead compound SBDPiR690 was successfully applied to preclinical optical imaging and for PDT to effectively control a subcutaneous tumor.     

ESI‐MS studies of palladium (II) complexes with 1‐(p‐toluenesulfonyl)cytosine/cytosinato ligands

The mononuclear complex Pd(1‐TosC‐N3)₂Cl₂ (2) containing 1‐(p‐toluenesulfonyl)cytosine (1) as a ligand, as well as dinuclear complexes Pd₂(1‐TosC^?‐N3,N4)₄ (3) and Pd₂(1‐TosC^?‐N3,N4)₂DMSO₂Cl₂ (4) containing the ligand anion (1‐TosC^?), was mass analyzed by electrospray ionization ion trap MS/MS and high resolution MS. Complexes 3 and 4 were obtained by recrystallization of 2 from DMF and DMSO, respectively. The behavior of complex 2 in different solutions was monitored by electrospray ionization mass spectrometry (ESI‐MS). Under the applied ESI‐MS conditions, complex 2 in methanol reorganized itself dominantly as new complex 3 and the solvent did not coordinate the formed species. In H₂O/DMSO, CH₃CN/DMSO and CH₃OH/DMSO solutions, complex 2 formed several new species with solvent molecules involved in their structure, e.g. complex 4 was formed as the major product. The newly formed species were also examined by LC‐MS‐DAD, confirming the solvent induced reorganization and the solution instability of complex 2. Copyright © 2009 John Wiley & Sons, Ltd.     

Superoxide Stabilization and a Universal KO2 Growth Mechanism in Potassium–Oxygen Batteries

Rechargeable potassium–oxygen (K‐O₂) batteries promise to provide higher round‐trip efficiency and cycle life than other alkali–oxygen batteries with satisfactory gravimetric energy density (935 Wh kg^?1). Exploiting a strong electron‐donating solvent, for example, dimethyl sulfoxide (DMSO) strongly stabilizes the discharge product (KO₂), resulting in significant improvement in electrode kinetics and chemical/electrochemical reversibility. The first DMSO‐based K‐O₂ battery demonstrates a much higher energy efficiency and stability than the glyme‐based electrolyte. A universal KO₂ growth model is developed and it is demonstrated that the ideal solvent for K‐O₂ batteries should strongly stabilize superoxide (strong donor ability) to obtain high electrode kinetics and reversibility while providing fast oxygen diffusion to achieve high discharge capacity. This work elucidates key electrolyte properties that control the efficiency and reversibility of K‐O₂ batteries.     

Ketone photolysis in the presence of oxygen: A useful source of OH for flash photolysis kinetics experiments

Previous studies have shown a significant OH yield from the reaction of RCO radicals (generated from the photolysis of corresponding ketone) with oxygen below total pressures of 200 Torr. The potential of these reactions as a source of OH radicals for flash photolytic kinetic studies is investigated. The viability of the method was tested by measuring rate coefficients for the reaction of OH with ethanol using both acetone/O₂ mixtures and t‐butyl hydroperoxide photolysis. The results (with statistical errors at the 2σ level) are in excellent agreement with each other (k_EtOH(acetone) = (5.87 ± 0.34) × 10^?18 T² exp((515 ± 21)K/T) cm³ molecule^?1 s^?1 and k_EtOH (t‐butyl hydroperoxide) = (5.27 ± 0.34) × 10^?18 T² exp((557 ± 20)K/T) cm³ molecule^?1 s^?1) and with the IUPAC recommendation. The reaction of OH with methyl ethyl ketone (2‐butanone) has also been investigated using a similar technique. The results show a strong non‐Arrhenius temperature dependence, k = (3.84 ± 0.12) × 10^?24× T⁴ × exp((1038 ± 11)/t). The merits of the ketone/oxygen OH source are contrasted with other established precursors. A major advantage of the technique is the ability to cleanly generate OD without the potential for isotopic scrambling prior to photolysis. © 2008 Wiley Periodicals, Inc. 40: 504–514, 2008     

Highly Sensitive and Selective Fluorescence Probe for 2,4‐Dinitrophenylhydrazine Detection in Wastewater Using Water‐Soluble CdTe QDs

A simple, cheap, sensitive and selective probe for determination of DNPH in wastewater using thioglycolic acid (TGA)‐coated CdTe QDs (TGA‐QDs) as fluorescence probe has been established, and the properties of CdTe QDs were characterized by TEM, FT‐IR, DLS, XRD and zeta potentials. CdTe QDs fluorescence is highly efficiently quenched after adding DNPH on account of electron transfer effect, and the fluorescence quenching behavior of CdTe QDs interaction with DNPH is static quenching process. A good linear relationship is observed between the relative fluorescence intensity (F₀/F) and 0.06–10 ng mL^?1 of DNPH. As compared with some of reported methods, LOD of this method for analysis of DNPH (0.23 ng mL^?1) is the lowest. Masking agents of DDTC and NH₄OH can eliminate the interference of Cu²⁺, Ag⁺ and Hg²⁺. Hence, DNPH can be selectively and accurately detected and the established method was successfully used for detecting DNPH in wastewater with acceptable recovery of 90.6–102%.     

New technique for generating high concentrations of gaseous OH radicals in relative rate measurements

We have developed a technique for generating high concentrations of gaseous OH radicals in a reaction chamber. The technique, which involves the UV photolysis of O₃ in the presence of water vapor, was used in combination with the relative rate method to obtain rate constants for reactions of OH radicals with selected species. A key improvement of the technique is that an O₃/O₂ (3%) gas mixture is continuously introduced into the reaction chamber, during the UV irradiation period. An important feature is that a high concentration of OH radicals [(0.53–1.2) × 10¹¹ radicals cm^?3] can be produced during the irradiation in continuous, steady‐state experiment. Using the new technique in conjunction with the relative rate method, we obtained the rate constant for the reaction of CHF₃ (HFC‐23) with OH radicals, k₁. We obtained k₁(298 K) = (3.32 ± 0.20) × 10^?16 and determined the temperature dependence of k₁ to be (0.48 ± 0.13) × 10^?12 exp[?(2180 ± 100)/T] cm³ molecule^?1 s^?1 at 253–328 K using CHF₂CF₃ (HFC‐125) and CHF₂Cl (HCFC‐22) as reference compounds in CHF₃–reference–H₂O gas mixtures. The value of k₁ obtained in this study is in agreement with previous measurements of k₁. This result confirms that our technique for generating OH radicals is suitable for obtaining OH radical reaction rate constants of ～10^?16 cm³ molecule^?1 s^?1, provided the rate constants do not depend on pressure. In addition, it also needed to examine whether the reactions of sample and reference compound with O₃ interfere the measurement when selecting this technique. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 317–325, 2003     

Reaktivität von Koordinationsverbindungen,XXIII [1]. Bildung und Zerfall des Sauerstoffadduktes mit N,N′-Bis-(4-(5)-imidazolylmethyl)-äthylendiamin-kobalt (II)-Ionen

In aqueous solution N, N′-bis-(4-(5)-imidazolylmethyl)-ethylenediamine-cobalt (II) (CoIMEN²⁺) takes up molecular oxygen giving μ-dioxygen-μ-hydroxo-bis-[N, N′-bis-(4-(5)-imidazolylmethyl)-ethylenediamine]-dicobalt (II). (Co IMEN)₂ O₂ (OH)³⁺ is exceptionally stable against irreversible autoxydation to Co^III species. Its absorption spectrum is very similar to that of the known analogous complex (CoTRIEN)₂ O₂ (OH)³⁺. The kinetics of formation and dissociation of (CoIMEN)₂O₂(OH)³⁺ are studied by spectrophotometry and with an oxygen specific electrode. The rate of the forward reaction is described by v_f = [CoIMEN²⁺]² · [O₂] · (k₁ + k₂ · [OH^?]) with k₁ = 9 · 10⁴ M^?2 s^?1 and k₂ = 1 · 10¹²M^?3 S^?1, at 25° and I = 0,2. A mechanism including hydroxylated as well as nonhydroxylated intermediates is proposed. Dissociation is preceeded by protonation of the oxygen adduct. At pH 1–2 the rate of dissociation is independent of [H⁺] and follows first order kinetics: v_D = k₃ · [(CoIMEN)₂O₂(OH)³⁺] with k₃ = 2.15 · 10^?2 S^?1.