Minor Oxidation Products Research Articles

Minor Hydroxylated Triterpenoids Produced in Engineered Yeast by the Enzymes OSC and CYP716s from the Plant Enkianthus chinensis and Their Anti-Inflammatory and Hepatoprotective Activities.

Triterpenoids are a type of specialized metabolites that exhibit a wide range of biological activities. However, the availability of some minor triterpenoids in nature is limited, which has hindered our understanding of their pharmacological potential. To overcome this limitation, heterologous biosynthesis of triterpenoids in yeast has emerged as a promising and time-efficient production platform for obtaining these minor compounds. In this study, we analyzed the transcriptomic data of Enkianthus chinensis to identify one oxidosqualene cyclase (EcOSC) gene and four CYP716s. Through heterologous expression of these genes in yeast, nine natural pentacyclic triterpenoids, including three skeleton products (1-3) produced by one multifunctional OSC and six minor oxidation products (4-9) catalyzed by CYP716s, were obtained. Of note, we discovered that CYP716E60 could oxidize ursane-type and oleanane-type triterpenoids to produce 6β-OH derivatives, marking the first confirmed C-6β hydroxylation in an ursuane-type triterpenoid. Compound 9 showed moderate inhibitory activity against NO production and dose-dependently reduced IL-1β and IL-6 production at the transcriptional and protein levels. Compounds 1, 2, 8, and 9 exhibited moderate hepatoprotective activity with the survival rates of HepG2 cells from 61% to 68% at 10 μM.

Consequences of aging on ferromagnetic amorphous Fe75Si10B15 microwires for advanced inductive applications

Amorphous ferromagnetic microwires fabricated by water-quenching have been assessed to show favorable properties for next-generation high-frequency electric machines as compared to those of conventional amorphous magnetic alloys in sheet or ribbon form. Here, water-quenched amorphous Fe75Si10B15 microwires were subjected to a range of aging times of up to 5 years in the air at room temperature. While both newer and aged microwires are X-ray amorphous, the aged microwires do exhibit a slight degree of crystallinity, a lower initial susceptibility and a reduced enthalpy change for full devitrification. These small differences (typically < 5%) are attributed to the formation of minor surface oxidation products such as iron oxides and SiO2 which modify the surface strain state. The resultant stress couples to magnetostriction to promote the formation of radial magnetic domains that impair the magnetic reversal process. These results demonstrate that while amorphous ferromagnetic microwires are essentially stable against aging in the air, consideration of their surface state will be significant for advanced applications.

Techniques for the Analysis of Minor Lipid Oxidation Products Derived from Triacylglycerols: Epoxides, Alcohols, and Ketones.

Lipid oxidation can lead to flavor and safety issues in fat-containing foods. In order to measure the extent of lipid oxidation, hydroperoxides and their scission products are normally targeted for analytical purposes. In recent years, the formation of rarely monitored oxygenated products, including epoxides, alcohols, and ketones, has also raised concerns. These products are thought to form from alternative pathways that compete with chain scissions, and should not be neglected. In this review, a number of instrumental techniques and approaches to determine epoxides, alcohols, and ketones are discussed, with a focus on their selectivity and sensitivity in applications to food lipids and oils. Special attention is given to methods employing gas chromatography (GC), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance (NMR). For characterization purposes, GC-mass spectrometry (GC-MS) provides valuable information regarding the structures of individual oxygenated fatty acids, typically as methyl esters, isolated from oxygenated triacylglycerols (TAGs), while the use of liquid chromatography-MS (LC-MS) techniques allows analysis of intact oxygenated TAGs and offers information about the position of the oxygenated acyl chain on the glycerol backbone. For quantitative purposes, traditional chromatography methods have exhibited excellent sensitivity, while spectroscopic methods, including NMR, are superior to chromatography for their rapid analytical cycles. Future studies should focus on the development of a routine quantitative method that is both selective and sensitive.

Propylene glycol oxidation with tert-butyl hydroperoxide over Cr-containing metal-organic frameworks MIL-101 and MIL-100

Chromium-based metal-organic frameworks MIL-101 and MIL-100 catalyzed oxidation of propylene glycol (PG) using tert-butyl hydroperoxide (TBHP) as oxidant. The main oxidation product was hydroxyacetone (HA) while minor oxidation products were acetaldehyde and acetic acid. The best results (88% selectivity toward HA at ca. 10% PG conversion) were achieved over MIL-101 using acetonitrile as solvent. In water, CC bond cleavage products predominated. MIL-101 and MIL-100 revealed different behavior toward adsorption of PG from MeCN solution, which affected their catalytic performances. Additives of radical chain scavengers produced a strong rate-inhibiting effect whereas the presence of molecular oxygen accelerated the reaction, suggesting radical chain mechanism of the oxidation process. The oxidation of PG over MIL-101 at 50°C proceeded without leaching of the active metal into solution and the catalysis had the truly heterogeneous nature. The MIL-101 catalyst could be recycled without significant loss of activity and selectivity and preserved its structure during, at least three, catalytic cycles.

Heterogeneous Catalyzed Ozonation using Cu-Ni-Co Oxides for Degradation of Dichlorophenol

The ozone initiated oxidation of dichlorophenol (DCP) in aqueous medium, catalyzed by various loadings of Cu, Ni and Co oxides supported on γ-Al2O3 was studied, as function of ozonation time and pH. Ternary catalyst materials synthesized by a wet-impregnation were fully characterized. The XRD results showed metal oxides were well incorporated within the alumina phase. Microscope images illustrated that metal oxide particles are dispersed on the surface of the support. Dihydroxyfumaric acid and oxalic acid were, respectively, found to be major and minor oxidation products. The oxidation products were characterized by FT-IR, 1H NMR, and mass spectral data.

Effects of reactor pressure and inlet temperature on n‐butane/dimethyl ether oxidation and the formation pathways of the aromatic species

Oxidation of n‐butane/dimethyl ether (DME)/O2/Ar system was studied by chemical kinetic modeling in a tubular reactor operated adiabatically and at constant pressure. Effects of the reactor pressure on the formation of various major, minor, and trace oxidation products were investigated for two different pressures (1 and 5 atm) and at six different inlet temperature values (700, 800, 900, 1100, 1300, and 1500 K). The analysis was carried out for two different concentrations of dimethyl ether in the inlet fuel mixture (20 and 50 mol %). Higher pressure (5 atm) resulted in higher mole fractions of methane, vinylacetylene, and cyclopentadiene; and lower mole fractions of formaldehyde, acetylene, acetaldehyde, ethane, propargyl, and propane. The mole fractions of CO and CO2 were not affected considerably by the pressure change. The main formation routes of benzene were developed at two different inlet temperature values (1100 and 1300 K), and the main precursors participating in these routes were found to be propargyl, propene, and diacetylene. A skeletal mechanism was developed for the oxidation of n‐butane/DME mixture from the detailed mechanism by reduction of the elementary reactions by 79%, and it was tested for accuracy by comparison with the data from the literature. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 230–240, 2016

Synthesis and surface properties of polyamide-CuxSe composite thin films

A study of copper selenide (CuxSe) thin film deposition on PA 6 polymer surface via adsorption/diffusion method and the resulting surface properties is presented. A two stage process used to deposit these thin films involves (a) selenization in 0.1M K2SeS2O6 at pH 2.15 and 60°C followed by (b) treatment with 0.34M Cu(II) and 0.06M Cu(I) salt solution at 80°C. Resulting chemical and physical properties of CuxSe films were investigated using XRD, XPS, SEM and sheet resistivity measurements. XRD data showed a complex mixture of CuxSe phases with peaks due to the elemental Se present at longer exposures. Thin film bulk elemental composition varied with the exposure time whereas XPS analysis showed surface to be slightly copper enriched. Additionally, mostly CuSe bonds were observed on the surface with minor oxidation products. SEM crossectional analysis showed distinct CuxSe film formation on PA 6 surface with thickness of ∼1–5μm. Finally, it was found that sheet resistance of 150±10Ω/□ was achieved after 120min of selenization for all samples and remained constant after longer exposures.

Synthesis, X-ray Structure and Photo Chemistry of 2-(Methyl(1-Phenylvinyl)Carbamoyl)Phenyl Acetate

2-(Methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM), empirical formula C18H17NO3, crystallizes in the triclinic space group, P−1, with unit cell parameters a = 9.10870(10) A, b = 10.56940(10) A, c = 16.1340(2) A, α = 78.0590(10)°, β = 89.5080(10)°, γ = 86.6830(10)°, Z = 4. The 2-(methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM) molecule, upon irradiation of UV-light below 3,000 A, releases acetate group to give six membered cyclic lactam 1 as the major product. The quantum yield for the lactam 1 was found to be 0.053. An alternate conrotatory 6-pi electron photochemically allowed electrocyclic ring closure reaction also occurs upon irradiation to give a six-membered cyclic zwitterionic intermediate which retains acetate as leaving group. A [1,5]-H shift would then give the isomerized product 2. The quantum yield for the lactam 2 was found to be 0.026. A minor oxidation product lactam 3 that retains the leaving group also formed, likely from loss of a proton and tautomerization of enol. The loss of one hydrogen molecule is the driving force for revival of aromaticity in the minor product 3. The quantum yield for the lactam 3 was found to be 0.012. The low value of total quantum yield (0.091) for photocyclization of SM can be explained as the photoproducts absorb light in competition with the photoreactant. In this study, Synthesis, X-ray structure and photochemistry of 2-(methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM) is reported .

A product study of the isoprene+NO<sub>3</sub> reaction

Abstract. Oxidation of isoprene through reaction with NO3 radicals is a significant sink for isoprene that persists after dark. The main products of the reaction are multifunctional nitrates. These nitrates constitute a significant NOx sink in the nocturnal boundary layer and they likely play an important role in formation of secondary organic aerosol. Products of the isoprene+NO3 reaction will, in many locations, be abundant enough to affect nighttime radical chemistry and to persist into daytime where they may represent a source of NOx. Product formation in the isoprene + NO3 reaction was studied in a smog chamber at Purdue University. Isoprene nitrates and other hydrocarbon products were observed using Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and reactive nitrogen products were observed using Thermal Dissociation–Laser Induced Fluorescence (TD-LIF). The organic nitrate yield is found to be 65±12% of which the majority was nitrooxy carbonyls and the combined yield of methacrolein and methyl vinyl ketone (MACR+MVK) is found to be ∼10%. PTR-MS measurements of nitrooxy carbonyls and TD-LIF measurements of total organic nitrates agreed well. The PTR-MS also observed a series of minor oxidation products which were tentatively identified and their yields quantified These other oxidation products are used as additional constraints on the reaction mechanism.

Extracellular cross‐linking of maize arabinoxylans by oxidation of feruloyl esters to form oligoferuloyl esters and ether‐like bonds

Primary cell walls of grasses and cereals contain arabinoxylans with esterified ferulate side chains, which are proposed to cross-link the polysaccharides during maturation by undergoing oxidative coupling. However, the mechanisms and control of arabinoxylan cross-linking in vivo are unclear. Non-lignifying maize (Zea mays L.) cell cultures were incubated with l-[1-(3)H]arabinose or (E)-[U-(14)C]cinnamate (radiolabelling the pentosyl and feruloyl groups of endogenous arabinoxylans, respectively), or with exogenous feruloyl-[(3)H]arabinoxylans. The cross-linking rate of soluble extracellular arabinoxylans, monitored on Sepharose CL-2B, peaked suddenly and transiently, typically at approximately 9 days after subculture. This peak was not associated with appreciable changes in peroxidase activity, and was probably governed by fluctuations in H(2)O(2) and/or inhibitors. De-esterified arabinoxylans failed to cross-link, supporting a role for the feruloyl ester groups. The cross-links were stable in vivo. Some of them also withstood mild alkaline conditions, indicating that they were not (only) based on ester bonds; however, most were cleaved by 6 m NaOH, which is a property of p-hydroxybenzyl-sugar ether bonds. Cross-linking of [(14)C]feruloyl-arabinoxylans also occurred in vitro, in the presence of endogenous peroxidases plus exogenous H(2)O(2). During cross-linking, the feruloyl groups were oxidized, as shown by ultraviolet spectra and thin-layer chromatography. Esterified diferulates were minor oxidation products; major products were: (i) esterified oligoferulates, released by treatment with mild alkali; and (ii) phenolic components attached to polysaccharides via relatively alkali-stable (ether-like) bonds. Thus, feruloyl esters participate in polysaccharide cross-linking, but mainly by oligomerization rather than by dimerization. We propose that, after the oxidative coupling, strong p-hydroxybenzyl-polysaccharide ether bonds are formed via quinone-methide intermediates.

Primary Atmospheric Oxidation Mechanism for Toluene

The products of the primary OH-initiated oxidation of toluene were investigated using the turbulent flow chemical ionization mass spectrometry technique at temperatures ranging from 228 to 298 K. A major dienedial-producing pathway was detected for the first time for toluene oxidation, and glyoxal and methylglyoxal were found to be minor primary oxidation products. The results suggest that secondary oxidation processes involving dienedial and epoxide primary products are likely responsible for previous observations of glyoxal and methylglyoxal products from toluene oxidation. Because the dienedial-producing pathway is a null cycle for tropospheric ozone production and glyoxal and methylglyoxal are important secondary organic aerosol precursors, these new findings have important implications for the modeling of toluene oxidation in the atmosphere.

Peptide Ozonolysis: Product Structures and Relative Reactivities for Oxidation of Tyrosine and Histidine Residues

Angiotensin II (DRVYIHPF) and two analogs, (DRVYIAPA and DRVAIHPA), were used as model systems to study the ozonolysis of peptides containing tyrosine and histidine residues. The ESI mass spectrum of angiotensin II following exposure to ozone showed the formation of adducts containing one, three, and four oxygen atoms. CID and SID spectra of these adducts were consistent with formation of Tyr + O and His + 3O as expected from previous work with amino acids. However, several fragment ions observed in the CID and SID spectra suggested formation of a rather unexpected adduct, Tyr + 3O, and a small amount of the Phe + O adduct. These findings were confirmed by examining two angiotensin analogs. Exposure of DRVYIAPA to ozone resulted in the addition of either one or three oxygen atoms on Tyr, while DRVAIHPA showed only the addition of three oxygen atoms--all on His. Other noteworthy minor oxidation products were observed from these analogs including Tyr + 34 Da, His + 5 Da, His + 34 Da, and His + 82 Da. The reaction rates of the peptides with ozone were found to be similar: second-order rate coefficients are 274 +/- 3, 379 +/- 6, and 439 +/- 34 M(-1) s(-1) for DRVYIAPA, DRVAIHPA, and angiotensin II, respectively. The relative rates indicate (1) an isolated His residue has a slightly greater ozone reactivity than an isolated Tyr residue, and (2) the reaction rates of isolated residues are not additive when both residues are present in the same molecule.

Styrene Metabolism, Genotoxicity, and Potential Carcinogenicity

This report reviews styrene biotransformation, including minor metabolic routes, and relates metabolism to the genotoxic effects and possible styrene-related carcinogenicity. Styrene is shown to require metabolic activation in order to become notably genotoxic and styrene 7,8-oxide is shown to contribute quantitatively by far the most (in humans more than 95%) to the genotoxicity of styrene, while minor ring oxidation products are also shown to contribute to local toxicities, especially in the respiratory system. Individual susceptibility depending on metabolism polymorphisms and individual DNA repair capacity as well as the dependence of the nonlinearity of the dose-response relationships in the species in question and the consequences for risk evaluation are analyzd.

Active Control of Methanol Carbonylation Selectivity over Au/Carbon Anode by Electrochemical Potential

Electrochemical oxidative carbonylation of methanol was studied over Au supported carbon anode in CO. The major carbonylation products were dimethyl oxalate (DMO) and dimethyl carbonate (DMC). The minor oxidation products were dimethoxy methane (DMM) and methyl formate (MF) from methanol and CO(2). Influences of various reaction conditions were studied on carbonylation activities and selectivities. The selectivities to DMO and DMC can be controlled by the electrochemical potential. Electrocatalysis of Au/carbon anode was studied by cyclic voltammetry (CV), stoichiometric reactions among Au(3+), methanol, and CO, and UV-vis spectra. The Au/carbon anode was characterized by XRD, SEM, and BE images before and after the carbonylation. These experimental facts strongly suggest that transition of oxidation states of Au affects changing of the carbonylation selectivities to DMO and DMC. Au(0) is the active species for the selective DMO formation by direct electrochemical carbonylation at low potentials (<+1.2 V (Ag/AgCl)). On the other hand, Au(3+) is the active spices for the selective DMC formation by indirect electrochemical carbonylation through Au(3+)/Au(+) redox at high potentials (>+1.3 V).

Cobalt(III) Tetraazamacrocyclic Complexes with Pendant Amino Groups: Synthesis, Structure and Electrochemical Properties

AbstractTwo isomeric cis‐2,9‐bis(aminomethyl)‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (1 and 2) and two 2‐aminomethyl‐2‐methyl‐1,4,8,11‐tetraazacyclotetradecane (3 and 4) cobalt(III) complexes have been prepared and characterised. During the synthesis of 2 a minor oxidation product 5 was formed. The structures of 3, 4 and 5 have been determined by X‐ray crystallography, and the UV/Vis spectra of 1−5 have been analysed. The average Co−N distances in 1 and 2 have been estimated from the correlation between the average Co−N bond lengths and position of the maximum absorption for hexaamine complexes given in literature. The electrochemical behaviour of 1−5 in neutral and acidic solutions has been studied by cyclic voltammetry. In complexes displaying electronic maxima at higher energy, cobalt(III) was reduced at more negative potentials. Small differences in the conformation of ligand between 3 and 4 explain the different behaviour of these complexes in acidic solutions. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Mechanistic Study of CH3OH + O2 Photoredox Reaction in a FeAlPO4 Sieve by Time-Resolved FT-IR Spectroscopy

The mechanism of the ligand-to-metal charge transfer (LMCT) induced reaction of methanol and O2 at the gas−micropore interface of a FeAlPO4-5 sieve has been studied by time-resolved FT-IR spectroscopy. Measurements using the rapid-scan method revealed that the final products, HCO2-···Fe and H2O, emerge with a rise time of 4 s (250 K) by decomposition of the two-electron-transfer intermediate, HO2CH2OH. Intermediacy of hydroxymethylhydroperoxide was established by direct detection by step-scan FT-IR spectroscopy on the 500 microsecond time scale and by monitoring of its photodissociation products HCO2H + H2O on the millisecond and second time scale. Formaldehyde was observed as minor two-electron oxidation product. The fast rise of the HO2CH2OH intermediate strongly suggests that it is formed by direct coupling of HOO and CH2OH radicals. This constitutes the most conclusive evidence yet for the formation of a hydroperoxy radical and hydroxymethyl radical as the primary one-electron-transfer products of the...

Fourier Transform Infrared Study of the Performance of Nanostructured TiO2 Particles for the Photocatalytic Oxidation of Gaseous Toluene

Thermal and hydrothermal treatments have been applied to an amorphous TiO2 precursor for obtaining nanosized TiO2 particles (P11t and P11h, respectively) of different photocatalytic properties. The activity of these catalysts has been tested by performing the toluene oxidation in gas phase in a continuous photoreactor. A Fourier transform infrared (FTIR) investigation of the catalysts under conditions prevailing during the test photoreaction has also been carried out. The photoreactivity results showed that CO2 was the main oxidation product and benzaldehyde a stable intermediate. Anatase P11t photoactivity was similar to that observed for commercial photocatalysts, while anatase P11h presented a marked improvement. The FTIR study on these samples indicate that P11h has a higher number of hydrogen-bonded hydroxyl groups that are more stable under RT outgassing than P11t. The higher photoactivity of P11h is attributed to the participation of these hydrogen-bonded hydroxyls in the toluene conversion to CO2. FTIR spectra also suggest that benzaldehyde, the minor oxidation product, originates from toluene adsorbed on isolated hydroxyls. Benzaldehyde is more strongly adsorbed on P11h than on P11t; the presence of water vapor in the reacting mixture, however, facilitates its desorption and/or photooxidation.

Minor Strecker degradation products of phenylalanine and phenylglycine

Phenylalanine (Phe) was oxidized with either potassium peroxodisulfate or glyoxal. Volatile reaction products were isolated and analyzed by GC/FID and GC/MS. Nonvolatile products were derivatized with diazomethane and analyzed by the same methods. Under the experimental reaction conditions (equimolar ratio of reactants, 100 °C, 1 h), the decomposed amount of amino acid was 28% (glyoxal) and to 74% (peroxodisulfate), respectively. Sixteen volatile compounds having their origin in the amino acid molecule were detected and identified. The major compound was phenylacetaldehyde (208 mg/peroxodisulfate, 11 mg/glyoxal), followed by bibenzyl, benzaldehyde, and benzyl alcohol. Other products were present in concentrations lower then 0.1 mg. For comparison, the lower homologue of Phe, phenylglycine, was oxidized under the same conditions. Analogously, 21% (glyoxal) and 65% (peroxodisulfate) of this amino acid decomposed, predominantly to benzaldehyde (242 mg/peroxodisulfate, 95 mg/glyoxal). A minor decomposition product was benzoic acid (2.9 mg), other ten products arose at levels lower then 0.1 mg. The formation of minor oxidation products during Strecker degradation of amino acids suggests the importance of radical reactions. In systems comprising glyoxal, ten heterocyclic compounds arose as minor products (3-furancarbaldehyde, 5-methyl-2-furancarbaldehyde, 2-pyrrolcarbaldehyde, 3-phenylpyridine, pyrazine, methyl-, ethyl-, vinyl-, and 2-phenylethylpyrazine).

β-Carotene Is Converted Primarily to Retinoids in Rats In Vivo

beta-Carotene might be converted oxidatively to vitamin A- active products in animals by the following three possible routes: 1) central cleavage, 2) sequential excentric cleavage or 3) random cleavage. Central cleavage is strongly favored by stoichiometric studies with tissue homogenates in vitro. To examine the relative importance of these pathways in rats in vivo, an oral dose (5.6 micromol) of all-trans beta-carotene in oil was given to vitamin A-deficient (-A) and to vitamin A-sufficient (+A) adult female Sprague-Dawley rats. Serum and several tissues were analyzed before and 3 h after dosing. The primary products of beta-carotene found in the intestine, serum and liver were retinol, retinyl esters and retinoic acid. Two minor oxidation products of beta-carotene, namely, 5,6-epoxy-beta-carotene and a partially characterized hydroxy-beta-carotene, were present in the stomach and its contents as well as in intestinal preparations. In the intestine, including its contents, of -A rats, very minor amounts of 5,6-epoxyretinyl palmitate and of beta-apocarotenals (8', 10', 12', 14') were identified. The total amount of the beta-apocarotenoids, however, was <5% of the retinoids formed in the intestine from beta-carotene during the same period. Another beta-carotene derivative, with a spectrum similar to that of semi-beta-carotenone, citranaxanthin and beta-apo-6'-carotenal, was also found in the intestinal extract of a -A rat. beta-Apocarotenals, beta-apocarotenols, beta-apocarotenyl esters and beta-apocarotenoic acids were not detected in tissues of +A rats nor in other tissues of -A rats. These findings agree with the view that central cleavage is by far the major pathway for the formation of vitamin A from beta-carotene in healthy rats in vivo.

Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae.

Photodynamic treatment of the yeast Saccharomyces cerevisiae with the singlet oxygen sensitizer toluidine blue and visible light leads to rapid oxidation of ergosterol and accumulation of oxidized ergosterol derivatives in the plasma membrane. The predominant oxidation product accumulated was identified as 5alpha, 6alpha-epoxy-(22E)-ergosta-8,22-dien-3beta,7a lpha-diol (8-DED). 9(11)-dehydroergosterol (DHE) was identified as a minor oxidation product. In heat inactivated cells ergosterol is photooxidized to ergosterol epidioxide (EEP) and DHE. Disrupted cell preparations of S. cerevisiae convert EEP to 8-DED, and this activity is abolished in a boiled control indicating the presence of a membrane associated enzyme with an EEP isomerase activity. Yeast selectively mobilizes ergosterol from the intracellular sterol ester pool to replenish the level of free ergosterol in the plasma membrane during singlet oxygen oxidation. The following reaction pathway is proposed: singlet oxygen-mediated oxidation of ergosterol leads to mainly the formation of EEP, which is enzymatically rearranged to 8-DED. Ergosterol 7-hydroperoxide, a known minor product of the reaction of singlet oxygen with ergosterol, is formed at a much lower rate and decomposes to give DHE. Changes of physical properties of the plasma membrane are induced by depletion of ergosterol and accumulation of polar derivatives. Subsequent permeation of photosensitizer through the plasma membrane into the cell leads to events including impairment of mitochondrial function and cell inactivation.