Abstract  The primary and secondary free radical intermediates in the gamma radiolysis of poly(D,L-lactide-co-glycolide) (PLGA) and clonazepam loaded PLGA microspheres were investigated by matrix EPR spectroscopy in the temperature range 77-298 K. Drug-polymer interactions were found to be important leading to significant deviations of the G(radicals) from the additivity law. In particular, in the mixed system a stabilization of the polymer matrix with respect to the radiation damage was detected, witnessed by a decrease of the overall polymer radicals yield which is accompanied by an increase of the drug radicals yield. These effects have been attributed to the scavenging properties of the nitro group with respect to electrons and polymer radicals. It is conceivable that such conclusions be of general application for all pharmaceutical formulations containing drugs bearing nitro groups in their chemical structure. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract  5-[4-(2-Benzimidazolethiol)butoxyl]phenyl-10,15,20triphenylporphyrinatoiron(III) chloride, BzImPT(Ph) (PFeCl)-Cl-III, and its derivatives BzImPT(p-XC(6)H(4))-(PFeCl)-Cl-III(X = Me, OMe, Cl) were prepared and characterized by elemental analysis, H-1-n.m.r., i.r., u.v.-vis., mass spectra, e.s.r. and m.c.d. spectra. The hydroxylation of cyclohexane catalyzed by these complexes with molecular oxygen in the absence of added axial ligand was examined. The results indicated that these complexes had higher catalytic activity, due to the intermolecular coordination of the terminal groups to the iron centre which was indicated by their m.c.d. spectra. The effect of added reducing agent on the turnover numbers (TN) is discussed.

Abstract  Coordination properties between two new tailed porphyrin iron (III) complexes, 5-[o(-)(4-(1-imidazolyl)butoxyl)phenyl]-10, 15, 20-triphenylporphyrinatoiron (III) chloride {[Fe-III(ImTPP)]Cl} and 5-[p-(4-(3-pyridyloxyl)butoxyl]phenyl-10, 15, 20-triphenylporphyrinatoiron (III) chloride {[Fe-III(PyTPP)]Cl}, with nitrogenous ligands and the equilibrium constants for the addition of these ligands to [Fe-III P]Cl in chloroform were studied by spectral technique, Experimental results demonstrated that [Fe-III(PyTPP)]Cl, just similar to [Fe-III(TPP)]Cl, form 1:2 adducts with imidazole or pyridines, respectively, but [Fe-III(ImTPP)]Cl forms only 1:1 adducts with pyridines and form 1: 2 adduct with imidazole. The equilibrium constants for the addition of nitrogenous ligands to [Fe-III(ImTPP)]Cl are 10 similar to 10(3) times as big as those for [Fe-III(TPP)]Cl system. We believe that this result is from the fact that the axial coordination of these ligands to [ Fe-III(ImTPP)]Cl induces the coordination of terminal imidazole group with ferric iron in [Fe-III(ImTPP)]Cl and this kind of coordination mode strengthens the bonding between ferric ion in [Fe-III(ImTPP)]Cl and nitrogen atom in ligand. The novel coordination mode and its structure were identified by the experimental data from UV-vis, H-1 NMR and low-temperature EPR.

Abstract  Kinetic solvent effects on hydrogen abstractions involving C-H donors (dienes, ethers, alkylbenzenes) have been corroborated by experiment and theory (UB3LYP/6-311++G**, polarized continuum model). To single out the effect of solvent polarity, rate constants for scavenging of the cumyloxyl radical and fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene were obtained in binary aprotic mixtures of ethylacetate and acetonitrile. Polar solvents result in a selective stabilization of the reactants (see TOC graphic), which results in slower rate constants.

Abstract  Primary, secondary, and tertiary alkoxyl radicals add exo-selectively to the olefinic pi-bond in bicyclo[2.2.1]heptene to afford exo-2-alkoxybicyclo[2.2.1]kept-3-yl radicals, which are trapped with BrCCl3 preferentially from the endo face to furnish beta-bromohydrine ethers in 23-67% yield. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract  An amphiphilic derivative of carboxymethylchitosan (CMCS), (2-hydroxyl-3-butoxyl)propyl-CMCS (HBP-CMCS), was used as an organic additive in the precipitation process of calcium carbonate (CaCO3). HBP-CMCS molecules can interact with calcium ions, the functional groups of which act as active sites for the nucleation and crystallization of CaCO3. Simultaneously, HBP-CMCS molecule also functionalizes as a colloidal stabilizer to prohibit the sedimentation of the grown CaCO3 crystals, depending upon the molar ratio of the initial Ca2+ ions to the repeat units of HBP-CMCS molecules. The combination investigations of scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy on the precipitated CaCO3 crystals proved that concentrations of HBP-CMCS and Ca2+ exert great influence on the crystallization habit of CaCO3, such as the nucleation, growth, morphology, crystal form, etc. The formation of the peanut-shaped CaCO3 particles suggests the template effect of HBP-CMCS molecules on the aggregation behavior of CaCO3 nanocrystals.

Abstract  Using competitive methods, the rates of hydrogen-atom abstraction by a typical perfluoro-n-alkyl radical, n-C7F25; have been determined for a series of silane and stannane reductants including (n)Bu(3)Sn-H (2.03 X 10(8) M(-1) s(-1)), Et(3)Si-H (7.5 X 10(5)), (TMS)(2)SiMe-H (1.63 X 10(7)) and (TMS)(3)Si-H (5.1 X 10(7)), all of which exhibited substantial rate enhancements relative to their analogous reductions of hydrocarbon radicals. The reduction by PhSH is, in contrast, similar to 400-times slower than for hydrocarbon radicals. Transition state polar effects are invoked to rationalize the relative reactivity of perfluoro- versus hydrocarbon radicals in these hydrogen-transfer reactions. A Hammett study for H-atom transfer from arene thiols (rho+ = -0.56) provided further substantiation for this conclusion. A discussion of the relative reactivity of t-butoxyl and perfluoro-n-alkyl radicals is presented.

Abstract  Using a highly stable and excellently performed three-component photorefractive (PR) polymer composite, poly(N-vinylcarbazole):1-n-butoxyl-2,5-dimethyl-4-(4'-nitrophenylazo)benzene:2,4,7-trinitro-9-fluorenone optical image storage was demonstrated. The dark storage time was 5-7h. The PR response time was measured to be about 200 ms at an intensity of 1 W/cm(2) with an applied electric field of 84 V/mu m. A proof-of-principle experiment on real-time correction of distorted images based on phase conjugattion of four-wave mixing geometry was also carried out.

Abstract  Rate constants have been measured at 25 degrees C in 13 solvents (S) for abstraction of the phenolic hydrogen atom from alpha-tocopherol (TOH) by tert-butoxyl (BO.), k(TOH/BO)(S), and by 2,2-diphenyl-1-picrylhydrazyl (DPPH.), k(TOH/DO)(S), and in eight solvents for abstraction of the phenolic hydrogen atom from phenol by cumyloxyl, k(PhOH/CumO)(S), and DPPH., k(PhOH/DPPH)(S). Over the range of solvents examined k(TOH/BO)(S) and k(TOH/DPPH)(S) vary by a factor of Ca. 65, and k(PhOH/CumO)(S) and k(PhOH/DPPH)(S) vary by a factor of ca. 120. in accordance with a prediction(5) the kinetic solvent effect is essentially identical for the same substrate and is independent of the attacking radical. That is, for almost any pair of solvents, A and B (k(TOH/BO)(A)/k(TOH/BO)(B))/(k(TOH/DPPH)(A)/k(TOH/DPPH)(B)) approximate to 1.0. The same applies with phenol as the substrate. Exceptions to this 1:1 relationship occur when one of the reactions becomes partly diffusion-controlled and in the solvent tert-butyl alcohol in which DPPH. shows a larger reactivity than would be expected. The absolute magnitudes of the alkoxyl and DPPH rate constants in the same solvent differ by a factor of over 1 000 000 (10(6)) for alpha-tocopherol and by 10 000 000 000 (10(10)) for phenol! We have therefore confirmed, under extreme conditions, a new, unifying principle for free radical chemistry in solution.

Abstract  By using Fourier-Transform Infrared (FTIR) absorption spectroscopy, rate coefficients in the range of 10(-16) to 10(-14) cm(3) molecule(-1) s(-1) have been determined for the hydrogen atom abstraction reactions of several substrates including halogenated organic compounds and amines by t-butoxy radical generated from the uv photolysis of t-butyl nitrite in the gas phase. Arrhenius parameters for selected reactions have been measured in the temperature range 299-318 K. Transition states and activation barriers for such reactions have been computed with the help of GAUSSIAN 03 software and found to match very well with the experimental values. (c) 2006 Elsevier B.V. All rights reserved.

Abstract  Di(tert-butyl) trioxide in a solution of CFCl3 (Freon-11) at -23 degreesC exists in equilibrium with the tert-butoxyl and tert-butylperoxyl radicals virtually without irreversible decomposition. The above radicals decompose ozone to dioxygen with a high effective rate constant, which is proprotional to the square root of the (BuOOOBut)-O-t concentration. The kinetic scheme describing the found relationships was proposed.

Abstract  The ESR and ENDOR spectra and hyperfine coupling constants (hfi) of the tertiary butoxyl spin adduct of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) change markedly, but reversibly, with increase in temperature from 140 to 280 K, and the spectra can be cycled repeatedly between these temperature limits. The variation with temperature of the hfi of nitrogen, beta and gamma protons arises through a change in equilibrium concentrations of the planar and puckered conformers of the adduct pyrroline ring which are interconverting rapidly on the ESR time-scale (10(7) MHz). A simple mathematical model has been derived which successfully simulates the experimental temperature variation of the coupling constants, gives their values in the two conformers and estimates of 4.3 +/- 0.5 kJ mol(-1) for the energy difference between the conformers in three solvents. Accurate hfi measurements by ENDOR spectroscopy across a narrow temperature range (140-160K) corroborated ESR experiments and afforded the assignment of all magnetically inequivalent protons that have previously eluded observation. By using the di-tert-butyl tetroxide equilibrium, (ROOOORt)-R-t reversible arrow 2(t)ROO(.) as a clean source of tert-peroxyl radicals, it was shown that these radicals are not trapped singly by DMPO to give a peroxyl spin adduct but give an ESR-silent complex which decomposes at higher temperatures to the DMPO-OBut spin adduct. These studies highlight the problems of identifying the trapped radical from ESR spectra of spin adducts especially when the spectra are observed at only one temperature. Copyright (C) 2000 John Wiley & Sons, Ltd.

Abstract  Rate constants have been determined at 37-degrees-C for the ring opening of a variety of alkyl-substituted cyclopropylcarbinyl radical ''clocks'' by nitroxide radical trapping (NRT) using TEMPO. Relative yields of unrearranged and rearranged trialkylhydroxylamines were measured at various TEMPO concentrations, and these data were then combined with absolute rate constants for the reactions of structurally appropriate alkyl radicals with TEMPO as determined by laser flash photolysis. Cyclopropylcarbinyl radicals, including the bicyclo[2.1.0]pent-2-yl radical, were generated by H-atom abstraction from the parent hydrocarbon and, in a few cases, also from the appropriate diacyl peroxide. Twelve substrates yielded sixteen clock reactions because some cyclopropylcarbinyls can undergo two different ring-opening reactions. For six methyl-substituted cyclopropylcarbinyls rate constants ranged from 0.8 x 10(8) s-1 for 1-methylcyclopropylcarbinyl to 47 x 10(8) s-1 for pentamethylcyclopropylcarbinyl. Rate constants for the ring opening of cyclopropylcarbinyl, alpha-methyl- and alpha,alpha-dimethylcyclopropylcarbinyl are 1.2, 0.70, and 0.88 x 10(8) s-1, respectively. Rate constants for H-atom ion by tert-butoxyl from various positions in the 12 cyclopropane substrates relative to the rate of H-atom ion from cyclopentane have also been determined by using competitive NRT.

Abstract  Coherent anti-Stokes Raman scattering (CARS) microscopy is demonstrated to be a powerful imaging technique with chemical specificity for studying chemically amplified polymer photoresists. Samples of poly(tertbutyl oxycarbonyloxy styrene) (PTBOCST) resist imprinted by interferometric lithography with a pattern of lines/spaces of 400 nm/400 nm and 200 nm/200 nm were used to test CARS imaging capabilities. Chemical contrast in the image is obtained by probing the carbonyl stretching vibration of the tert-butoxyl carbonyl group of PTBOCST. The experimental images demonstrate high spatial resolution (approximate to270 nm) and strong signal, which allows short acquisition times. Advantages and limitations of CARS in comparison with other imaging techniques with chemical specificity, such as infrared near field scanning optical microscopy (IR NSOM), are discussed.

Abstract  Metabolic activation of peroxides and hydroperoxides to free radicals is associated with the tumor promoting activity of these compounds. tert-Butyl hydroperoxide (t-BOOH) metabolism has been extensively studied as a model of peroxide biotransformation. In vivo studies are limited, and the hemoglobin-thiyl radical was the only species thus far identified in the blood of treated rats. Here we further examine t-BOOH metabolism in vivo with regard to free radical and DNA adduct production. Spin-trapping experiments with phenyl-N-tert-butylnitrone (PBN) led to the detection of EPR signals in the blood, bile, and organic extracts of the liver and stomach of rats treated with t-BOOH. Analysis of these signals demonstrated that t-BOOH metabolism in vivo produces alkyl radicals, detected in the bile and organic extracts of liver and stomach, in addition to the previously identified hemoglobin-thiyl radical. To characterize the produced alkyl radicals, experiments were performed with (13)C-labeled t-BOOH and two spin traps, PBN and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). The latter was used because the EPR signals obtained with PBN were too weak to be unambiguous. Nevertheless, the EPR signals present in the bile of animals treated with (13)C-labeled t-BOOH and PBN or POBN were consistent with adducts of (13)C-labeled methyl radical and an unidentified alkyl radical. The latter is probably derived from lipids oxidized by the metabolically produced primary radicals, methyl and its precursor, tert-butoxyl. The presence of 8-methylguanine and 7-methylguanine in hydrolysates of DNA from liver and stomach of rats treated with t-BOOH was also examined. 8-Methylguanine, a typical product of methyl radical attack on DNA, was detectable in both the liver and stomach of treated rats. The results may be relevant to the understanding of the genotoxic properties of other peroxides, particularly of cumene hydroperoxide.

Abstract  Poly(ADP-ribose) polymerase (PARP)-1, an enzyme that catalyzes the attachment of ADP ribose to target proteins, acts as a component of enhancer/promoter regulatory complexes. In the present study, we show that pharmacologic inhibition of PARP-1 with 3,4-dihydro-5-[4-(I-piperidinyl)butoxyl]-1(2H)isoquinolinone (DPQ) results in a strong delay in tumor formation and in a dramatic reduction in tumor size and multiplicity during 7,12-dimethylbenz(a)anthracene plus 120-tetradecanoylphorbol-13-acetate-induced skin carcinogenesis. This observation was parallel with a reduction in the skin inflammatory infiltrate in DPQ-treated mice and tumor vasculogenesis. Inhibition of PARP also affected activator protein-1 (AP-1) activation but not nuclear factor-kappa B (NF-kappa B). Using cDNA expression array analysis, a substantial difference in key tumor-related gene expression was found between chemically induced mice treated or not with PARP inhibitor and also between wild-type and parp-.1 knockout mice. Most important differences were found in gene expression for Nfkbiz, S100a9, Hif-1 alpha, and other genes involved in carcinogenesis and inflammation. These results were corroborated by real-time PCR. Moreover, the transcriptional activity of hypoxia-inducible factor-lot (HIF-1 alpha) was compromised by PARP inhibition or in PARP-I-deficient cells, as measured by gene reporter assays and the expression of key target genes for HIF-1 alpha. Tumor vasculature was also strongly inhibited in PARP-1-deficient mice and by DPQ. In summary, this study shows that inhibition of PARP on itself is able to control tumor growth, and PARP inhibition or genetic deletion of PARP-1 prevents from tumor promotion through their ability to cooperate with the activation AP-1, NF-kappa B, and HIF-1 alpha.

Abstract  Although mechanisms of arsenic trioxide (As(2)O(3))-induced cell death have been studied extensively in hematologic cancers, those in solid cancers have yet to be clearly defined. In this study, we showed that the translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus is required for As(2)O(3)-induced cell death in human cervical cancer cells. We also showed that reactive oxygen species (ROS)-mediated poly(ADP-ribose) polymerase-1 (PARP-1) activation is necessary for AIF release from mitochondria. The treatment of human cervical cancer cells with As(2)O(3) induces dissipation of mitochondrial membrane potential (Deltapsi(m)), translocation of AIF from mitochondria to the nucleus, and subsequent cell death. Small interfering RNA targeting of AIF effectively protects cervical cancer cells against As(2)O(3)-induced cell death. As(2)O(3) also induces an increase of intracellular ROS level and a marked activation of PARP-1. N-acetyl-l-cystein, a thiol-containing antioxidant, completely blocks As(2)O(3)-induced PARP-1 activation, Deltapsi(m) loss, nuclear translocation of AIF from mitochondria, and the consequent cell death. Furthermore, pretreatment of 1,5-dihydroxyisoquinoline or 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone, PARP-1 inhibitors, effectively attenuates the loss of Deltapsi(m), AIF release, and cell death. These data support a notion that ROS-mediated PARP-1 activation signals AIF release from mitochondria, resulting in activation of a caspase-independent pathway of cell death in solid tumor cells by As(2)O(3) treatment.

Abstract  Nitric oxide (NO) induces cell proliferation or cell death, depending on the cell type involved, the isoform of nitric oxide synthase activated, and its cellular localisation. In neurons, the damaging effect of NO is usually attributed to the highly toxic peroxynitrite, formed by its reaction with superoxide. Peroxynitrite induces DNA damage and consequently the activation of poly (ADP-ribose) polymerase (PARP). This study set out to examine the contribution of peroxynitrite to the damage induced in cerebellar granule neurons (CGNs) by treatment with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), for short (6 h) or prolonged (24 h) exposures. The Alamar blue assay was used to quantify CGN viability, which was also assessed by morphological examination. SNAP (10 microM-1 mM) induced a concentration- and time-dependent reduction of CGN viability, with associated damage to cell bodies and neurite processes evident following 100 microM SNAP treatments. Damage from 6 h exposures was prevented by the presence of haemoglobin (a NO scavenger), uric acid (a peroxynitrite scavenger), melatonin (a non-specific antioxidant), and by cyclosporin A (a permeability transition pore blocker). It was reduced by the PARP-1 inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-isoquinolinone (DPQ), whilst superoxide dismutase (SOD) potentiated the effects. Following 24 h exposure to SNAP, damage was only partially blocked by haemoglobin, melatonin, cyclosporin A and DPQ, but was not affected by uric acid or SOD. The data suggest that short exposure to NO induces neuronal damage through peroxynitrite produced by its interaction with superoxide, whereas a longer exposure to NO can induce damage partly by a mechanism which is independent of peroxynitrite formation.

Abstract  Unreported methylated catechin and epicatechin derivatives 5 and 6 were synthesized by an oxa-Pictet-Spengler reaction. Catechin 5 shows the B and C rings coplanar because of the formation of a trans junction between the C ring and the newly generated six-term cycle D, in turn condensed to ring B. In contrast, epicatechin 6 presents a bent geometry due to the establishment of a cis junction between the C ring and the newly formed cycle D. The oxidation of compounds 5 and 6 in the presence of the Trametes villosa laccase/1-hydroxybenzotriazole (HBT) system was investigated under aerobic conditions in both a biphasic system and a reverse micelle. The unexpected different chemoselective oxidation at the benzylic position of catechin and epicatechin derivatives 5 and 6 has been rationalized using a molecular modelling approach. These results demonstrate that the Trametes villosa laccase/HBT system represents a useful tool to functionalize the C-2 or C-4 position of phenolic compounds depending on the structural features.

Abstract  When a p-polarized beam propagates through a high-performance photorefractive polymer composite, poly(N-vinylcarbazole:2,4,7-trinitro-9-fluorenone:1-n-butoxyl-2,5-dimethyl-4-(4'-nitrophenylazo)benzene, its transmission behavior is influenced by three effects: the electroabsorption, the photorefractive coupling with the reflected beam from the rear surface, and the amplified scattering. From the measurements on the incidence angle dependence as well as the applied-electric-field dependence of the three effects, some conclusions are obtained. At a small incidence angle with a low applied electric field, both the amplified scattering and the electroabsorption are small whereas the coupling between the incident beam and the reflected beam plays a principal role. At a large incidence angle or with a high poling electric field, the transmission is influenced mainly by the amplified scattering and the electroabsorption. A poling electric field asymmetric loss to the amplification scattering is also observed.

Abstract  Organic luminescent materials with aggregation-induced emission (AIE) characteristics have attracted much attention among the scientists in the fields of optoelectronic devices and fluorescence biotechnology. ATE materials overcomes the aggregation-caused quenching problem of traditional organic fluorescent compounds, which possess high fluorescence quantum efficiency in the aggregated states. Thanks to the great research effort of worldwide scientists, a large variety of AIE materials have been developed and the underlying mechanism has been rapidly explored. The deep understanding of the structure-property relationship of AIE compounds is still in an urgent demand for the design of new materials. In this work, based on the classical propeller-shaped AIEgen, tetraphenylethene (TPE), we designed and synthesized a series of electron donor/acceptor-containing alkynone derivatives with AIE feature such as cyano, nitro, butyl and butoxyl groups-substituted alkynone derivatives. Their chemical structures have been fully characterized by H-1 NMR, C-13 NMR, IR, and HRMS spectra, providing satisfactory analysis results. Their photophysical properties are systematically studied and the effect of substitution groups on the emission maximum, emission efficiency, as well as AIR property are discussed, respectively. Their emission maxima are located at 511 similar to 565 nm with the fluorescence quantum yields of up to 31% in the aggregated states in THF/water mixtures with high water content. The fluorescence intensity of the unsubstituted TPE-containing alkynone derivative in THF/H2O with phi(w)=90% water content is 157 times higher than that in THE solution. It is suggested that both electron-donating and electron-withdrawing substitution groups on the terminal phenyl ring decrease the emission efficiency of the the aggregated state and the introduction of nitro group dramatically quenches the emission while redshifts the emission maximum. Most importantly, the alkynone groups in these compounds can selectively coordinate with Pd2+ among a large variety of metal ions, which quench the emission of the nanoaggregates and possess high sensitivity towards Pd2+, demonstrating the potential application as an efficient Pd2+ fluorescent sensor.

Abstract  The quenching of the n,pi*-excitedazoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene by 19 heteroatom-containing electron and hydrogen donors, that is, amines, sulfides, ethers, and alcohols, was investigated in the gas phase. Deuterium isotope effects were measured for 9 selectively deuterated derivatives. The data support the involvement of an excited charge-transfer complex, that is, an exciplex, for tertiary amines and sulfides, and a competitive direct hydrogen transfer from the C-H bonds of ethers or from the N-H or O-H bonds of secondary and primary amines or alcohols. The recently observed "inverted" solvent effect for the fluorescence quenching of azoalkanes by amines and sulfides in solution is supported by the observed rate constants in the gas phase, which are substantially larger than those in solution. A more pronounced inverted solvent effect for the weaker electron-donating sulfides and a presumably faster exciplex deactivation result in a switch-over in absolute reactivity relative to tertiary amines in the gas phase. Most importantly, the kinetic data demonstrate that the reactivity of the strongly dipolar O-H and N-H bonds in photoinduced hydrogen abstraction reactions shows a larger decrease upon solvation than that of the less polar C-H bonds. The azoalkane data are compared with previous studies on quenching of n,pi*-triplet-excited ketones in the gas phase.

Abstract  A thermolysis mechanism with the concerted dissociation of two bonds, -OO- and -C-O-, and formation of carboxylic acid and two radicals (tert-butoxyl and acetyl) is suggested on the basis of kinetic measurements, studies of the decomposition products, and quantum-chemical modeling of the thermolysis of per oxides of the general formula (CH3)(3)C-OO-CH(CH3)OC(O)R. Concerted dissociation is proved by low thermolysis activation energies, negative activation entropies, the independence of the decomposition rate constant from medium viscosity, carboxylic acid formation (one mole per mole of reacted peroxide), and the special features of the structure of peroxides. The formation of the tert-butoxyl and acetyl radicals and carboxylic acid molecule is more favorable energetically than the other possible reaction directions.