Potential therapeutic applications of microbial surface-activecompounds

Numerous investigations of microbial surface-active compounds or biosurfactants over the past two decades have led to the discovery of many interesting physicochemical and biological properties including antimicrobial, anti-biofilm and therapeutic among many other pharmaceutical and medical applications. Microbial control and inhibition strategies involving the use of antibiotics are becoming continually challenged due to the emergence of resistant strains mostly embedded within biofilm formations that are difficult to eradicate. Different aspects of antimicrobial and anti-biofilm control are becoming issues of increasing importance in clinical, hygiene, therapeutic and other applications. Biosurfactants research has resulted in increasing interest into their ability to inhibit microbial activity and disperse microbial biofilms in addition to being mostly nontoxic and stable at extremes conditions. Some biosurfactants are now in use in clinical, food and environmental fields, whilst others remain under investigation and development. The dispersal properties of biosurfactants have been shown to rival that of conventional inhibitory agents against bacterial, fungal and yeast biofilms as well as viral membrane structures. This presents them as potential candidates for future uses in new generations of antimicrobial agents or as adjuvants to other antibiotics and use as preservatives for microbial suppression and eradication strategies

Ab initio potential and variational transition state theory rate constant for H‐atom association with the diamond (111) surface

International audienceHigh‐level ab initio calculations were performed to determine accurate analytic potential energy functions for interactions a gas‐phase H‐atom has with H‐atoms attached to the diamond (111) surface and with C‐atom radical sites on this surface. The nonbonded potential between the gas‐phase H‐atom and H‐atoms attached to the surface was determined from coupled‐cluster ab initio calculations, including single, double, and perturbatively applied triple excitations [CCSD(T)], with the 6‐311++G(2df,p) basis set. The resulting nonbonded potential is nearly identical to that found previously from both theory and experiment for interactions between H‐atoms on different hydrocarbon molecules. In the ab initio calculations, a C‐atom radical site on the diamond surface is represented by a constrained tert‐butyl radical. Radial and small‐displacement angular potentials for a H‐atom interacting with this radical were determined from unrestricted quadratic configuration interaction calculations, with single, double and perturbatively applied triple excitations [UQCISD(T)], with the 6‐31G∗∗ basis set. UQCISD(T) calculations were performed on the H+CH3→CH4 reaction system with both the 6‐31G∗∗ and 6‐311++G(3df,3pd) basis sets to calibrate the accuracy of the 6‐31G∗∗ basis set results for the H‐atom plus constrained tert‐butyl radical. The above information was used to construct an analytic potential energy function for H‐atom association with a radical site on the (111) surface of diamond, which was then employed in a canonical variational transition state theory (CVTST) calculation of the association rate constant. The resulting rate constant is 1.8-2.1×1013 cm3 mol−1 s−1 for the 1000-2000 K temperature range. It is insensitive to the gas‐phase H‐atom/surface H‐atom nonbonded potential and the potential for the diamond lattice. The H+diamond (111) CVTST rate constant is used to estimate a rate constant of 4×1013 cm3 mol−1 s−1 for H+tert‐butyl association at 298 K. The UQCISD(T)/6‐31G∗ calculations give a H--C(CH3)3 bond dissociation energy which is only 1 kcal/mol lower than the experimental value

Heterogeneous Photochemistry of Agrochemicals at the Leaf Surface: A Case Study of Plant Activator Acibenzolar- S -methyl

International audienceThe photoreactivity of plant activator benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), commonly named acibenzolar-S-methyl, was studied on the surfaces of glass, paraffinic wax films, and apple leaves. Experiments were carried out in a solar simulator using pure and formulated BTH (BION). Surface photoproducts were identified using liquid chromatography coupled with electrospray ionization and high-resolution Orbitrap mass spectrometry, while volatile photoproducts were characterized using an online thermal desorption system coupled to a gas chromatography–mass spectrometry (GC–MS) system. Pure BTH degraded quickly on wax surfaces with a half-life of 5.0 ± 0.5 h, whereas photolysis of formulated BTH was 7 times slower (t1/2 = 36 ± 14 h). On the other hand, formulated BTH was found to photolyze quickly on detached apple leaves with a half-life of 2.8 h ± 0.4 h. This drastic difference in photoreactivity was attributed to the nature and spreading of the BTH deposit, as influenced by the surfactant and surface characteristics. Abiotic stress of irradiated apple leaf was also shown to produce OH radicals which might contribute to the enhanced photodegradability. Eight surface photoproducts were identified, whereas GC–MS analyses revealed the formation of gaseous dimethyl disulfide and methanethiol. The yield of dimethyl disulfide ranged between 1.5% and 12%, and a significant fraction of dimethyl disulfide produced was found to be absorbed by the leaf. This is the first study to report on the formation of volatile chemicals and OH radicals during agrochemical photolysis on plant surfaces. The developed experimental approach can provide valuable insights into the heterogeneous photoreactivity of sprayed agrochemicals and could help improve dissipation models

Photochemical transformation of the plant activator Acibenzolar-S-methyl in solution

Acibenzolar-S-methyl (BTH) is used to protect plants from pathogens by triggering Systemic Acquired Resistance. While this compound absorbs solar light strongly, little is known on its ability to undergo photodegradation and on the generated photoproducts. In the present work, we studied the photolysis of BTH dissolved in solvents of different polarities: n-heptane to mimic the hydrophobic surface of leaves and more polar solvents to simulate polar environmental compartments. We found that BTH is easily photodegraded in simulated solar light. The quantum yield of photolysis at 313 nm ranges from 0.048 to 0.092 depending on the solvent. LC-ESI-HRMS analyses in negative and positive modes revealed the presence of numerous photoproducts arising from two initial reaction pathways. As confirmed by DFT calculations, the main pathway involves the S-N bond cleavage followed by N-2 loss. The scission of the thioester bond with the generation of acyl and SCH3 radicals also takes place. Based on these findings, it can be predicted that BTH should undergo fast photodegradation once released in the environment and lead to numerous new compounds. (C) 2016 Elsevier B.V. All rights reserved

Photorelease of NOx from neonicotenoids : Environmental consequences and applications

International audienc

Sulfate radical induced degradation of beta 2-adrenoceptor agonists salbutamol and terbutaline: Phenoxyl radical dependent mechanisms

SSCI-VIDE+ATARI+LZO:CFE:JMCInternational audienceThe present study investigated the reactivity and oxidation mechanisms of salbutamol (SAL) and terbutaline (TBL), two typical β2-adrenoceptor agonists, towards sulfate radical (SO4−) by using photo-activated persulfate (PS). The reaction pathways and mechanisms were proposed based on products identification using high resolution HPLC-ESI-MS, laser flash photolysis (LFP) and molecular orbital calculations. The results indicated that SO4− was the dominant reactive species in the UV/PS process. The second-order rate constants of sulfate radical reaction with SAL and TBL were measured as (3.7 ± 0.3) × 109 and (4.2 ± 0.3) × 109 M−1 s−1 by LFP, respectively. For both SAL and TBL, phenoxyl radicals were found to play key roles in the orientation of the primary pathways. For SAL, a benzophenone derivative was generated by oxidation of the phenoxyl radical. However, in the case of TBL, the transformation of the phenoxyl radical into benzoquinone was impossible. Instead, the addition of OSO3H on the aromatic ring was the major pathway. The same reactivity pattern was observed in the case of TBL structural analogs resorcinol and 3,5-dihydroxybenzyl alcohol. Our results revealed that basic conditions inhibited the decomposition of SAL and TBL, while, increasing PS dose enhanced the degradation. The present work could help for a better understanding of the difference in oxidation reactivity of substituted phenols widely present in natural waters

Degradation of β2-adrenoceptor agonists salbutamol and terbutaline by UV-activated persulfate

SSCI-VIDE+ATARI+LZO:CFE:JMCInternational audienceThis work investigated the degradation reactivity and mechanisms of salbutamol (SAL) and terbutaline (TBL), two typical β2-adrenoceptor agonists by using persulfate (PS) activated bysimulated solar light. Our results indicated that UV/PS could remove these two target compounds efficiently, more than 94% of SAL and TBL could be decomposed within 2h. The quenching experiment suggested that SO4•− was the dominant reactive species in the oxidation process. The second-order rate constant of sulfate radical with SAL and TBL was calculated as (3.7 ± 0.3) × 109 and (4.2 ± 0.3) × 109 M-1 s-1 by using laser flasher photolysis (LFP), respectively. The results also revealed that basic conditions inhibited the decomposition of SAL and TBL, while, increasing PS dose enhanced the degradation. Reaction pathways and mechanisms were proposed based on products identification using high resolution HPLC-ESI-MS, LFP and molecular orbital calculations. For both of the target compounds, phenoxyl radicals were found to play key roles in the orientation of the primary pathways. For SAL, a benzophenone derivative was generated by oxidation of the phenoxyl radical. However, the transformation of the phenoxyl radical into benzoquinone was impossible for TBL. Instead, the addition of –OSO3H on the aromatic ring was the major pathway. The same reactivity pattern was observed in TBL structural analogs resorcinol and 3,5-dihydroxybenzyl alcohol. The present work indicated that UV/PS oxidation method could be a promising approach in the removal of β2-adrenoceptor agonists and related pharmaceuticals. Moreover, it could also help for a better understanding of the difference in oxidation reactivity of substituted phenols widely present in natural waters

Degradation of β2-adrenoceptor agonists salbutamol and terbutaline by UV-activated persulfate

SSCI-VIDE+ATARI+LZO:CFE:JMCInternational audienceThis work investigated the degradation reactivity and mechanisms of salbutamol (SAL) and terbutaline (TBL), two typical β2-adrenoceptor agonists by using persulfate (PS) activated bysimulated solar light. Our results indicated that UV/PS could remove these two target compounds efficiently, more than 94% of SAL and TBL could be decomposed within 2h. The quenching experiment suggested that SO4•− was the dominant reactive species in the oxidation process. The second-order rate constant of sulfate radical with SAL and TBL was calculated as (3.7 ± 0.3) × 109 and (4.2 ± 0.3) × 109 M-1 s-1 by using laser flasher photolysis (LFP), respectively. The results also revealed that basic conditions inhibited the decomposition of SAL and TBL, while, increasing PS dose enhanced the degradation. Reaction pathways and mechanisms were proposed based on products identification using high resolution HPLC-ESI-MS, LFP and molecular orbital calculations. For both of the target compounds, phenoxyl radicals were found to play key roles in the orientation of the primary pathways. For SAL, a benzophenone derivative was generated by oxidation of the phenoxyl radical. However, the transformation of the phenoxyl radical into benzoquinone was impossible for TBL. Instead, the addition of –OSO3H on the aromatic ring was the major pathway. The same reactivity pattern was observed in TBL structural analogs resorcinol and 3,5-dihydroxybenzyl alcohol. The present work indicated that UV/PS oxidation method could be a promising approach in the removal of β2-adrenoceptor agonists and related pharmaceuticals. Moreover, it could also help for a better understanding of the difference in oxidation reactivity of substituted phenols widely present in natural waters