Singlet-oxygen reactions sensitized on solid surfaces of lignin or titanium dioxide: Product studies from hindered secondary amines and from lipid peroxidation

2003 ◽  
Vol 81 (6) ◽  
pp. 457-467 ◽  
Author(s):  
L RC Barclay ◽  
M -C Basque ◽  
M R Vinqvist
Keyword(s):  
Titanium Dioxide ◽  
Free Radical ◽  
Methyl Linoleate ◽  
Singlet Oxygen ◽  
Lignin Content ◽  
Solid Dispersions ◽  
Secondary Amines ◽  
Type I ◽  
Organic Substrates ◽  
Type Ii

Product analyses and kinetic methods were used to determine the role of singlet oxygen in lignin-catalyzed oxidations of organic substrates. Method A used the ESR analysis of nitroxide radicals formed by singlet oxygen (Type II) on 2,2,6,6-tetramethylpiperidine, 1, or tetramethylpiperidone, 2. Method B used HPLC analysis of the 9- and 13-linoleate chain hydroperoxides formed on oxidation of methyl linoleate to distinguish free-radical peroxidation (Type I) from singlet-oxygen oxidation (Type II) on the basis of different cis,trans (kinetic) to trans,trans (thermodynamic) product ratios. Applications of method A to solid dispersions of lignin or titanium dioxide (TiO2, a known singlet-oxygen sensitizer) indicated singlet-oxygen reactions. In addition to the nitroxide triplet, irradiation of lignin produces a persistent broad signal in the solid attributed to phenoxyl radicals. Benzophenone and 3,5-di-tert-butyl-ortho-benzoquinone, 5, coated on silica gel were used as models to compare the effects of irradiating such compounds on the products and kinetics of methyl linoleate oxidation. Benzophenone acted as an initiator, giving free-radical peroxidation, whereas 5 or lignin coated with methyl linoleate acted as singlet-oxygen sensitizers, according to both product studies (method B) and the kinetic order in oxygen consumption during UV photolysis. Photolysis of phase-separated sensitizer (TiO2 or lignin) and substrate (methyl linoleate) resulted in typical singlet-oxygen products. These results indicate that singlet oxygen plays a significant role in the photo-yellowing of high-lignin-content wood pulps. Key words: lignin, singlet oxygen, mechanism, peroxidation, products.

scholarly journals Inorganic Salts and Antimicrobial Photodynamic Therapy: Mechanistic Conundrums?

Molecules ◽  
2018 ◽  
Vol 23 (12) ◽  
pp. 3190 ◽  
Author(s):  
Michael R. Hamblin ◽  
Heidi Abrahamse
Keyword(s):  
Electron Transfer ◽  
Titanium Dioxide ◽  
Singlet Oxygen ◽  
Potassium Thiocyanate ◽  
Molecular Iodine ◽  
Water Soluble ◽  
Inorganic Salts ◽  
Type I ◽  
Bacterial Cells ◽  
Type Ii

We have recently discovered that the photodynamic action of many different photosensitizers (PSs) can be dramatically potentiated by addition of a solution containing a range of different inorganic salts. Most of these studies have centered around antimicrobial photodynamic inactivation that kills Gram-negative and Gram-positive bacteria in suspension. Addition of non-toxic water-soluble salts during illumination can kill up to six additional logs of bacterial cells (one million-fold improvement). The PSs investigated range from those that undergo mainly Type I photochemical mechanisms (electron transfer to produce superoxide, hydrogen peroxide, and hydroxyl radicals), such as phenothiazinium dyes, fullerenes, and titanium dioxide, to those that are mainly Type II (energy transfer to produce singlet oxygen), such as porphyrins, and Rose Bengal. At one extreme of the salts is sodium azide, that quenches singlet oxygen but can produce azide radicals (presumed to be highly reactive) via electron transfer from photoexcited phenothiazinium dyes. Potassium iodide is oxidized to molecular iodine by both Type I and Type II PSs, but may also form reactive iodine species. Potassium bromide is oxidized to hypobromite, but only by titanium dioxide photocatalysis (Type I). Potassium thiocyanate appears to require a mixture of Type I and Type II photochemistry to first produce sulfite, that can then form the sulfur trioxide radical anion. Potassium selenocyanate can react with either Type I or Type II (or indeed with other oxidizing agents) to produce the semi-stable selenocyanogen (SCN)2. Finally, sodium nitrite may react with either Type I or Type II PSs to produce peroxynitrate (again, semi-stable) that can kill bacteria and nitrate tyrosine. Many of these salts (except azide) are non-toxic, and may be clinically applicable.

On the influence of secondary structure on the α-C→H bond dissociation energy of proline residues in proteins: a theoretical study

1998 ◽  
Vol 76 (7) ◽  
pp. 1042-1049 ◽  
Author(s):  
D A Block ◽  
D Yu ◽  
D A Armstrong ◽  
A Rauk
Keyword(s):  
Free Radical ◽  
Bond Dissociation Energy ◽  
Dissociation Energy ◽  
Type I ◽  
Structural Constraints ◽  
Type Ii ◽  
Isodesmic Reactions ◽  
Free Radical Damage ◽  
Bond Dissociation ◽  
Dissociation Energies

Ab initio computations (B3LYP/6-31G(D), coupled with isodesmic reactions) were used to predict αC→H bond dissociation energies (BDEs) for proline as a residue in a model peptide, intended to mimic the environment in proteins. The environment was further constrained to mimic common proline positions in turns of different types. The BDEs were found to be very dependent on the structural constraints imposed by the turn type, implying different structure-mediated susceptibilities to free radical damage to proline residues. Unnatural repair of proline (inversion of chirality) was found to be thermodynamically unfavourable. The predicted BDEs for the proline αC→H bond, in kJ mol-1, to an estimated accuracy of ±10 kJ mol-1 are as follows: fully optimized trans rotamer, 368.6; fully optimized cis rotamer, 357.7; ß turn type I, 380.7; ß turn type II, 397.8; ß turn type II', 385.4; ß turn type VIa, 374.0; ß turn type VIb, 355.0. Key words: proline, ß -turns, free radical, bond dissociation energy, molecular structure, oxidative damage.<

scholarly journals Influence of Polymer Charge on the Localization and Dark- and Photo-Induced Toxicity of a Potential Type I Photosensitizer in Cancer Cell Models

Molecules ◽  
2020 ◽  
Vol 25 (5) ◽  
pp. 1127 ◽  
Author(s):  
Mikael Lindgren ◽  
Odrun A. Gederaas ◽  
Monica Siksjø ◽  
Tom A. Hansen ◽  
Lena Chen ◽  
...  
Keyword(s):  
Cell Death ◽  
Singlet Oxygen ◽  
Deuterium Oxide ◽  
Current Trend ◽  
Chinese Hamster ◽  
Type I ◽  
Type Ii ◽  
Molecular Systems ◽  
Cell Compartments ◽  
Survival Studies

A current trend within photo-dynamic therapy (PDT) is the development of molecular systems targeting hypoxic tumors. Thus, type I PDT sensitizers could here overcome traditional type II molecular systems that rely on the photo-initiated production of toxic singlet oxygen. Here, we investigate the cell localization properties and toxicity of two polymeric anthracene-based fluorescent probes (neutral Ant-PHEA and cationic Ant-PIm). The cell death and DNA damage of Chinese hamster ovary cancer cells (CHO-K1) were characterized as combining PDT, cell survival studies (MTT-assay), and comet assay. Confocal microscopy was utilized on samples incubated together with either DRAQ5, Lyso Tracker Red, or Mito Tracker Deep Red in order to map the localization of the sensitizer into the nucleus and other cell compartments. While Ant-PHEA did not cause significant damage to the cell, Ant-PIm showed increased cell death upon illumination, at the cost of a significant dark toxicity. Both anthracene chromophores localized in cell compartments of the cytosol. Ant-PIm showed a markedly improved selectivity toward lysosomes and mitochondria, two important biological compartments for the cell’s survival. None of the two anthracene chromophores showed singlet oxygen formation upon excitation in solvents such as deuterium oxide or methanol. Conclusively, the significant photo-induced cell death that could be observed with Ant-PIm suggests a possible type I PDT mechanism rather than the usual type II mechanism.

Fluorescein-photosensitized Furan Oxidation in Methanolic and Reversed Micellar Solutions, Part II Kinetic Analysis

1980 ◽  
Vol 35 (1) ◽  
pp. 107-111 ◽  
Author(s):  
Norio Miyoshi ◽  
Giiti Tomita
Keyword(s):  
Singlet Oxygen ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Solvent Polarity ◽  
Radical Mechanism ◽  
Type I ◽  
Type Ii ◽  
Micellar Solutions ◽  
Alkyl Amines ◽  
Reaction Processes

Abstract The 1,3-diphenylisobenzofuran oxidation was investigated in methanolic and dodecyl-ammonium propionate reversed micellar solutions using fluorescein sodium as photosensitizer. The furan oxidation was caused by the singlet oxygen mechanism (Type II). Aniline enhanced remarkably the furan oxidation in methanolic solutions, but inhibited highly this oxidation in the reversed micellar solutions. This enhancement of the furan oxidation was considered to be brought about by the occurrence of a radical mechanism (Type I) besides Type II mechanism. No Type I reaction occurred in the micellar solutions. The rate constants concerning with both reaction processes were evaluated by kinetic analysis, employing various aryl-and alkyl-amines. The reaction mechanism of Type I and the quenching mechanism of singlet oxygen by amines were discussed from the relationship between the rate constants, and the ionization potential of amines and the solvent polarity.

Ground- and excited-state interactions of 2,7,12,17-tetraphenylporphycene with model target biomolecules for type-I photodynamic therapy

2009 ◽  
Vol 13 (01) ◽  
pp. 99-106 ◽  
Author(s):  
Noemí Rubio ◽  
Víctor Martínez-Junza ◽  
Jordi Estruga ◽  
José I. Borrell ◽  
Margarita Mora ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Photodynamic Therapy ◽  
Excited State ◽  
Singlet Oxygen ◽  
Cell Lines ◽  
Mechanism Of Action ◽  
Photophysical Properties ◽  
Type I ◽  
Type Ii ◽  
Hydrophobic Compound

Biosubstrate-sensitizer binding is one of the factors that enhances the type-I mechanism over the type-II in the whole photodynamic process. 2,7,12,17-Tetraphenylporphycene (TPPo), a second-generation photosensitizer, is a hydrophobic compound with good photophysical properties for photodynamic therapy applications that has proved its ability for the photoinactivation of different cell lines. Nevertheless, little is known about its mechanism of action. This paper focuses on the study of the interaction/binding of TPPo with different model biomolecules that may favor the type-I mechanism in the overall photodynamic process, including nucleosides, proteins, and phospholipids. Compared with more hydrophilic photosensitizers, it is concluded that TPPo is more likely to undergo type-II (singlet oxygen) than type-I (electron transfer) photodynamic processes in biological environments.

scholarly journals COMPARISON OF DEGRADATION CAPACITY OF OXIDATION AND PHOTOOXIDATION OF SULFIDE CATALYZED BY Zn(II) TETRASULFOPHTHALOCYANINE VÀ Co(II) TETRASULFOPHTHALOCYANINE

2009 ◽  
Vol 12 (7) ◽  
pp. 43-47
Author(s):  
Minh Thanh Le ◽  
Thao Thanh Phan ◽  
Tung Cao Thanh Pham ◽  
Tan Minh Phan
Keyword(s):  
Electron Transfer ◽  
Singlet Oxygen ◽  
Transfer Mechanism ◽  
Type I ◽  
Type Ii ◽  
Electron Transfer Mechanism ◽  
Catalytic Activities ◽  
Visible Irradiation

The oxidation and photooxidation of sulfide catalyzed by soluble phthalocynines were carried out. The results showed that both Zinc(II) Tetrasulfophthalocyanine (ZnTSPc) and Cobalt(II) Tetrasulfophthalocyanine (COTSPC) have catalytic activities in the oxidation of Sulfide. The degradation yiel minute under the light visible irradiation and in the dark were 96,61% and 71,11% respectively. Whereas, in case of CoTSPc during 40 minute, these were 98,10% and 96,30%, respectively. ZnTSPc demonstrates the photoactive property and catalyses the reaction via type II (singlet oxygen mechanism). COTSPc has not the photoactive property and catalyses the reaction via type I (electron transfer mechanism).

scholarly journals Analysis of Dynamic Efficacy Profile of Corneal Cross-Linking: Role of Oxygen and Rate Constants

2021 ◽  
Author(s):  
Jui-Teng Lin ◽  
Yi-Ze Lee
Keyword(s):  
Steady State ◽  
Singlet Oxygen ◽  
Uv Light ◽  
Scaling Law ◽  
Kinetic Equations ◽  
Type I ◽  
Type Ii ◽  
Steady State Condition ◽  
Time Profiles

Purpose:To explore (theoretically) the key parameters and their influence on the time profiles of photosensitizer (riboflavin), free radicals, singlet oxygen, oxygen and the efficacy of corneal collagen crosslinking (CXL)in both type-I and oxygen-mediated type-II mechanisms, specially the role of oxygen and the initiator regeneration. Methodology:Coupled kinetic equations are derived and numerically solved under the quasi-steady state condition for the 2-pathway mechanisms of CXL. The key parameters explored include (bI, V, Q', K, K',Q,P) and their influence on the time profiles of photosensitizer (riboflavin, C), radicals (R), singlet oxygen(S), oxygen (X) and efficacy (E), parameters of (K,K',Q) define the relative strength of type-I and type-II process. The oxygen depletion profile, X(t), and the associated singlet oxygen, S(t), depend on the parameters of V, Q' and the initial value of oxygen. The coupling strength given by (bI) governs almost all profiles, where b is an effective absorption parameter and I is the UV light intensity.Results:Our numerical method for CXL dynamic profiles demonstrated the following important features: (i) Type-I and type-II coexit in CXL, in the presence of oxygen. However, there is no type-II when oxygen is depleted or in a condition without oxygen. (ii) Type-I with bimolecular termination, the radical R(t) is a function of [K'(bIgC)]0.5, leading to the steady-state efficacy given by a scaling law of 1/(bI)0.5, in contract to that of type-II which is almost independent to the light intensity. (iii) The depletion rate (2 to 5 minutes) of X(t) is much faster than that of C(t) (10 to 20 minutes), (iv) Thepure type-II profile, has a transition point from straight line to saturating curve and matches the depletion point of singlet oxygen S(t). (v) Improved CXL efficacy of type-I and type-II may be achieved by external supply of photoinitiator (riboflavin) and oxygen, respectively.

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