Authors:Önder İdil, İkbal Macit, Özge Kaygusuz and Cihan Darcan
In this study, the survival time of wild type E. coli W3110 and 11 mutants was analysed with a plate count method in methylene blue added or control groups under daylight fluoroscence illumination (4950 lux) at different pH values (5.0, 6.0, 7.0, and 8.0) in phosphate buffer. As a result, while the number of bacteria did not decrease under photooxidative stress at pH 5.0 and 6.0 during a 6-hour incubation, the wild type and all mutants decreased more than 2 log. at pH 8.0, and approximately one log. at pH 7.0. It was determined that a 2 log decrease in wild type E. coli takes 3.7 h according to t99 value at pH 8, these values were 2.39 h in the katE mutant, 2.64 h in the soxR mutant, 2.67 h in the oxyR mutant, 2.71 h in the sodB mutant, 3 h in the btuE mutant, 3.38 h in the zwf mutant and 3.40 h in the soxS mutant, respectively (p < 0.05). The roles of these genes were proved with complement tests. Finally, it is found that the effectiveness of photooxidative stress is in direct relation with pH, and the katE, soxR, oxyR, sodB, btuE, zwf, and soxS genes are important for the protection against this stress.
Authors:Zine Eddine Hamami, Laurent Vanoye, Pascal Fongarland, Claude de Bellefon and Alain Favre-Reguillon
An efficient and metal-free method for the oxidation of aldehydes to the corresponding carboxylic acids has been developed. In a simple continuous-flow photochemical reactor, the use of camphorquinone (CQ) irradiated with a white light-emitting diode (LED) source enhanced the autoxidation of aldehydes. Under 5 bar of oxygen, visible light, and 0.3 mol% of CQ, the rate of oxidation was increased from 6 times with 2-ethylhexanal to 30 times for n-nonanal. The large interfacial area generated by a segmented flow apparatus associated with radicals formed by photooxidation of CQ ensures metal-free high throughput of carboxylic acids under safe conditions.
Authors:Yanxiang Liu, Xujie Lu, Feng Wu and Nansheng Deng
The adsorption and photodegradation behavior of tetracycline (TC), chloramphenicol (CAP) and sulfamethoxazole (SMX) in clay mineral dispersion was investigated in this work. Only TC showed significant adsorption to natural montmorillonite and rectorite, whereas CAP and SMX adsorbed to natural montmorillonite, kaolinite and rectorite to a much lower extent. The adsorption equilibrium constants (L/kg) of TC to natural montmorillonite were 332 and 108 at pH 3.0 and 7.0, respectively. The kinetic rate constant kapp (min−1) for the removal of CAP in the presence of different clay minerals follows the sequence: montmorillonite KSF (1.6 × 10−2) > rectorite (4.6 × 10−3) > natural montmorillonite (3.8 × 10−3) > kaolinite (2.8 × 10−3). Removal of SMX follows the same sequence. Oxalate significantly promotes the removal of CAP and SMX in montmorillonite KSF dispersion, while penicillamine (PEN) and β-cyclodextrin retard the diminution. After 3 h of irradiation in 5 g/L KSF dispersion, the total organic carbon was reduced by 72 and 39% for CAP and SMX, respectively.
Authors:Jana Výchopňová, R. Čermák, M. Obadal, V. Verney and Sophie Commereuc
The work deals with crystallization of photodegraded polypropylene containing various amounts of β-nucleating agent based
on N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide. Compression-moulded samples were irradiated by UV-light, melted and subsequently
non-isothermally crystallized. The results showed that the crystallization temperature decreased with increasing irradiation
time. The irradiation caused the splitting of crystallization exotherms into two peaks indicating two crystallization mechanisms.
The presence of β-nucleating agent in the material suppressed the peak splitting; the higher was the amount of nucleating
agent in the sample, the later was the splitting observed.
Line-broadening due to paramagnetic relaxation was observed in Mössbauer spectra of Eu2+ in glassy frozen solutions; such broadening may be used as an indicator of the state of dispersion of europium. It was demonstrated by the Mössbauer technique that Eu2+ was oxidized to Eu3+ by photoirradiation at >300 nm and that this oxidation reaction was induced by photoexcitation of the 320-nm band of Eu2+.
Many works have been devoted to the photo-oxidation of polyolefins but numerous questions remain. The aim of this paper is to constitute a complementary source of informations leading to the radiation oxidation mechanism of these polymers which could explain the chain scission process the basis of the alteration of mechanical and physical properties of polyolefins. It can be seen from our results that the hydroperoxides and the ketones are primary products of the reaction. A new secondary reaction efficiently leading to the alteration of mechanical properties has been proposed.
The potential effect of combined salicylic acid and fish flour to improve plant tolerance to salt stress was investigated. This pre-treatment improved the growth of wheat seedlings under salinity when compared to control (untreated wheat seedlings). Moreover, combined pre-treatment improved significantly phenylalanine ammonia lyase (PAL) and peroxidase (POD) enzyme activities, also phenolic-flavonoid content in the shoots of salt stressed seedlings. One of the most important consequences of increase in salt stress is the oxidative tissue damage. In our study, salt stress increased lipid peroxidation levels (LPO) and also the loss of chlorophylls levels during stress might also be related to photo-oxidation resulting from oxidative stress. Whereas phenylalanine ammonia-lyase (PAL) activities of wheat shoots increased by a 2.1-fold under salt stress, the activities of shoots grown from seeds primed with salicylic acid and fish flour (SA + FF) increased by a 4-fold for 0.05 mM SA + FF, 4.8- fold for 0.1 mM SA + FF and 3.7-fold for 2.5 mM SA + FF combined pre-treatment under salt stress. Also, the combined salicylic acid + fish flour primed seedlings showed higher content of the scopoletin, and salicylic, syringic, vanilic and gallic acids under both salt and nonsalinity stress conditions.
Authors:Mahdi Hajimohammadi, Farzad Bahadoran, Saied Davarani and Nasser Safari
Photooxidation of cyclooctene by molecular oxygen in the presence of tetraphenyl porphyrin (H2TPP), tetramesityle porphyrin (H2TMP), tetrakis dichlorophenyl porphyrin (H2TDCPP) and ClFeTMP, ClFeTPP, tetrakis pentaflouro phenyl porphyrin iron chloride (ClFeTPFPP), ClFeTDCPP, ClMnTPP, ClMnTPFPP,
ZnTDCPP, ClMnTDCPP, ClCoTDCPP, ClCoTPP and ZnTPP as sensitizers has been studied. 98% cyclooctene conversion with 97% selectivity
toward cyclooctene oxide was obtained by H2TDCPP and ZnTDCPP sensitizers. The effect of electron-donating and withdrawing groups on the porphyrin macrocycle ring showed
that non-metalled porphyrins with electron-withdrawing groups have higher reactivity (H2TDCPP > H2TPP > H2TMP). The order of reactivity for metalloporphyrins is Zn > Mn > Fe > Co for the same porphyrin ligand. A turnover number
(TON) up to 6,000 with selectivity up to 95% was obtained by ClMnTDCPP. In free-base porphyrins and Zn porphyrins, singlet
oxygen production is the major route for oxidation, whereas in Mn and Fe porphyrins, two parallel pathways for oxidation products
Authors:Danna Zhou, Wenyu Huang, Feng Wu, Chaoqun Han and Yin Chen
This study of photodegradation of the antibiotic chloromycetin (Cm) in aqueous solution by direct and indirect photolysis
included photolysis under UV-C light (λ = 254 nm) and photo-oxidation under UV–vis light (λ ≥ 365 nm) in the presence of iron
and humic acid. The factors affecting Cm degradation were studied and are described in detail, including initial pH, ionic
strength and initial concentrations of iron and humic acid. Results showed that a degradation efficiency up to 90% was achieved
by direct photolysis of Cm at pH 5–7 and the calculated quantum yield was 0.084. Higher salt content (NaCl, 0.01–0.5 M) was
found to benefit direct photolysis. Indirect photolysis of Cm in the presence of iron(III) formed OH• radicals at pH ~ 3. Under UV–vis light, increased pH resulted in a significant decrease in the efficiency of indirect photolysis.
Direct and indirect photolysis reactions both followed a pseudo first-order kinetic law. Humic acid tended to inhibit the
photodegradation of Cm under the conditions of this work, implying that photosensitization of humic acid did not play any
role in the photodegradation.