Amino Chemoassay Profiling of Aromatic Aldehydes-Unraveling Drivers of Their Skin Sensitization Potency.

Aromatic aldehydes are ubiquitous in humans' everyday life. As aldehydes, they can form imines (Schiff bases) with amino groups of skin proteins, leading to immune response-triggered allergic contact dermatitis. Many known aromatic aldehydes are considered as weak or nonsensitizers, but others like atranol and chloratranol, two components of the fragrance oak moss absolute, show strong sensitization potency. This large discrepancy in potency and, in particular, the underlying reaction mechanisms are only little understood so far. To reduce this knowledge gap, our chemoassay employing glycine-para-nitroanilide (Gly-pNA) as an amino model nucleophile was applied to 23 aromatic aldehydes. The determined Gly-pNA second-order rate constants for imine formation (k1 ≤ 2.85 L·mol-1·min-1) and the imine stability constant (K ≤ 333 L·mol-1) are on the lower end of the known amino reactivity scale for aldehydes, confirming many aromatic aldehydes as less potent sensitizers in line with animal and human data. The substantially higher sensitization potency of atranol and chloratranol, in turn, is reflected by their unique reaction chemistry profiles, inter alia, identifying them as cross-linkers able to form thermodynamically more stable epitopes with skin proteins (despite low formation kinetics, k1). The discussion further includes a comparison of experimentally determined k1 values with computed reactivity data (Taft σ*), the impact of the substitution pattern of the aryl ring on the reactivity with Gly-pNA, and analytically determined adduct patterns. Overall, this work provides new insights into the reaction of aromatic aldehydes with amino groups under aqueous conditions and fosters a better understanding of the chemistry underlying skin sensitization.

Baseline Narcosis for the Glass-Vial 96-h Growth Inhibition of the Nematode C. elegans and Its Use for Identifying Electrophilic and Pro-Electrophilic Toxicity.

The nematode Caenorhabditis elegans has been widely used as a model organism for assessing chemical toxicity. So far, however, a respective baseline narcosis reference has been lacking to predict narcosis-level toxicity and to identify excess-toxic compounds and associated mechanisms of action. Employing 22 organic narcotics that cover 7.2 units of their log Kow (octanol/water partition coefficient) from -1.20 to 6.03, a baseline narcosis model has been derived for a glass-vial 96-h growth inhibition test with C. elegans, both without and with correction for compound loss through volatilization and sorption. The resultant effective concentrations yielding 50% growth inhibition, EC50, vary by 6.4 log units from 5.04 · 10-1 to 1.90 · 10-7 mol/L (exposure-corrected). Application of the new model is illustrated through sensing the toxicity enhancement (Te) of four Michael-acceptor carbonyls driven by their reactive mode of action. Moreover, narcosis-level predicted vs experimental EC50 of two α,ß-unsaturated alcohols demonstrate the biotransformation capability of C. elegans regarding ADH (alcohol dehydrogenase). The discussion includes narcosis-level and excess-toxicity doses (critical body burdens) as well as chemical activities A50 (at the EC50) as compared to fish, daphnids, ciliates, bacteria, zebrafish embryo, and cell lines. Overall, the presently introduced model for predicting C. elegans baseline narcosis enables generating respective pre-test expectations, enriches experimental results by mechanistic information, and may complement 3Rs (reduce, refine, replace) test batteries through its ADH metabolic capacity.

Octanol/Air Partition Coefficient─A General-Purpose Fragment Model to Predict Log Koa from Molecular Structure.

The octanol/air partition coefficient Koa is important for assessing the bioconcentration of airborne xenobiotics in foliage and in air-breathing organisms. Moreover, Koa informs about compound partitioning to aerosols and indoor dust, and complements the octanol/water partition coefficient Kow and the air/water partition coefficient Kaw for multimedia fate modeling. Experimental log Koa at 25 °C has been collected from literature for 2161 compounds with molecular weights from 16 to 959 Da. The curated data set covers 18.2 log units (from -1.0 to 17.2). A newly developed fragment model for predicting log Koa from molecular structure outperforms COSMOtherm, EPI-Suite KOAWIN, OPERA, and linear solvation energy relationships (LSERs) regarding the root-mean-squared error (rms) and the maximum negative and positive errors (mne and mpe) (rms: 0.57 vs 0.86 vs 1.09 vs 1.19 vs 1.05-1.53, mne: -2.55 vs -3.95 vs -7.51 vs -7.54 vs (-5.63) - (-7.34), mpe: 2.91 vs 5.97 vs 7.54 vs 4.24 vs 6.89-10.2 log units). The prediction capability, statistical robustness, and sound mechanistic basis are demonstrated through initial separation into a training and prediction set (80:20%), mutual leave-50%-out validation, and target value scrambling in terms of temporarily wrong compound-Koa allocations. The new general-purpose model is implemented in a fully automatized form in the ChemProp software available to the public. Regarding Koa indirectly determined through Kow and Kaw, a new approach is developed to convert from wet to dry octanol, enabling higher consistency in experimental (and thus also predicted) Koa.

Henry's Law Constant─A General-Purpose Fragment Model to Predict Log Kaw from Molecular Structure.

Henry's law constant is important for assessing the environmental fate of organic compounds, including polar accumulation, indoor contamination, and the impact of airborne predominance on persistence. Moreover, it can be used in the context of alternative 3R bioassays to inform about the compound loss through volatilization as a confounding factor. For 2636 compounds, curated experimental log Kaw (air/water partition coefficient) data at 25° covering 23.6 orders of magnitude (from -18.6 to 5.0) have been collected from the literature. Subsequently, a new fragment model for predicting log Kaw from molecular structures has been developed. According to the root-mean-squared error (rms) and the maximum negative and positive errors (mne and mpe), this general-purpose model outperforms COSMOtherm, EPISuite HENRYWIN, OPERA, and LSER with calculated input parameters significantly (rms 0.50 vs 0.92 vs 1.25 vs 1.28 vs 1.38, mne -2.74 vs -6.78 vs -9.11 vs -6.24 vs -6.27, mpe 2.25 vs 6.22 vs 8.27 vs 11.5 vs 7.69 log units). Initial separation into a training and prediction set (80%:20%), mutual leave-50%-out validation, and target value scrambling (temporarily wrong compound-Kaw allocations) demonstrate the prediction capability, statistical robustness, and mechanistically sound basis of the fragment scheme. The new model is available to the public in fully computerized form through the ChemProp software, and can be combined with a separate existing model to extend the log Kaw prediction to temperatures different from 25 °C.

Insight into the Mechanism Underlying Dehalococcoides mccartyi Strain CBDB1-Mediated B12-Dependent Aromatic Reductive Dehalogenation.

Anaerobic bacteria transform aromatic halides through reductive dehalogenation. This dehalorespiration is catalyzed by the supernucleophilic coenzyme vitamin B12, cob(I)alamin, in reductive dehalogenases. So far, the underlying inner-sphere electron transfer (ET) mechanism has been discussed controversially. In the present study, all 36 chloro-, bromo-, and fluorobenzenes and full-size cobalamin are analyzed at the quantum chemical density functional theory level with respect to a wide range of theoretically possible inner-sphere ET mechanisms. The calculated reaction free energies within the framework of CoI···X (X = F, Cl, and Br) attack rule out most of the inner-sphere pathways. The only route with feasible energetics is a proton-coupled two-ET mechanism that involves a B12 side-chain tyrosine (modeled by phenol) as a proton donor. For 12 chlorobenzenes and 9 bromobenzenes with experimental data from Dehalococcoides mccartyi strain CBDB1, the newly proposed PC-TET mechanism successfully discriminates 16 of 17 active from 4 inactive substrates and correctly predicts the observed regiospecificity to 100%. Moreover, fluorobenzenes are predicted to be recalcitrant in agreement with experimental findings. Conceptually, based on the Bell-Evans-Polanyi principle, the computational approach provides novel mechanistic insights and may serve as a tool for predicting the energetic feasibility of reductive aromatic dehalogenation.

Mechanistic insight into the Dehalococcoides-mediated reductive dechlorination of polychlorinated biphenyls.

Microbial reductive dechlorination provides a green and highly desirable approach to address the pollution raised by the substantial legacies of polychlorinated biphenyls (PCBs) in soil, sediment, and underground water. It has been shown that the reaction event is catalyzed by supernucleophilic cob(I)alamin housed in reductive dehalogenases (RDases). However, the mechanism still remains elusive. Herein, we unravel the mechanism via quantum chemical calculations, considering a general model of RDase and the dechlorination regioselectivity of two representative PCB congeners, 234-236-CB and 2345-236-CB. The B12-catalzyed reductive dechlorination of PCBs starts with the formation of a reactant complex, followed by a proton-coupled two-electron transfer (PC-TET) and a subsequent single-electron transfer (SET). The PC-TET yields a cob(III)alamin-featured intermediate, which is quickly reduced by the latter SET fueled by significant energetic benefits (∼100 kcal mol-1). It rationalizes the exclusive detection and characterization of cob(I/II)alamins in RDase-mediated dehalogenation experiments. The determined mechanism successfully reproduces the experimental dechlorination regioselectivity and reactivity, as observed with Dehalococcoides mccartyi strain CG1.

Bottom-Up Synthesis of De-Functionalized and Dispersible Carbon Spheres as Colloidal Adsorbent.

Recent innovative adsorption technologies for water purification rely on micrometer-sized activated carbon (AC) for ultrafast adsorption or in situ remediation. In this study, the bottom-up synthesis of tailored activated carbon spheres (aCS) from sucrose as renewable feedstock is demonstrated. The synthesis is based on a hydrothermal carbonization step followed by a targeted thermal activation of the raw material. This preserves its excellent colloid properties, i.e., narrow particle size distribution around 1 µm, ideal spherical shape and excellent aqueous dispersibility. We investigated the ageing of the freshly synthesized, highly de-functionalized AC surface in air and aqueous media under conditions relevant to the practice. A slow but significant ageing due to hydrolysis and oxidation reactions was observed for all carbon samples, leading to an increase of the oxygen contents with storage time. In this study, a tailored aCS product was generated within a single pyrolysis step with 3 vol.-% H2O in N2 in order to obtain the desired pore diameters and surface properties. Adsorption characteristics, including sorption isotherms and kinetics, were investigated with monochlorobenzene (MCB) and perfluorooctanoic acid (PFOA) as adsorbates. The product showed high sorption affinities up to log (KD/[L/kg]) of 7.3 ± 0.1 for MCB and 6.2 ± 0.1 for PFOA, respectively.

Amino Reactivity of Glutardialdehyde and Monoaldehydes─Chemoassay Profile vs Skin Sensitization Potency.

Chemoassay profiling of organic electrophiles through the direct peptide reactivity assay has become an OECD-accepted nonanimal component in the REACH evaluation of potential skin sensitizers. For aldehydes forming imines (Schiff bases), however, existing chemoassays yielded inconclusive results, indicating issues with their NH2 sensitivity and the reversibility of the reaction. In the present study, a new kinetic chemoassay employing the N terminus of glycine-para-nitroanilide, Gly-pNA, as a model nucleophile for protein NH2 groups is introduced and applied to nine aliphatic monoaldehydes and glutardialdehyde (1,5-pentanedial) that have log Kow (octanol/water partition coefficient) values from 0.63 to 3.99. The Gly-pNA second-order rate constants k1 range from 8.56 to 150 L·mol-1·min-1 for the monoaldehydes. Interestingly, glutardialdehyde with a k1 of 17 731 L·mol-1·min-1 is 170-fold more reactive than its monoaldehyde counterpart pentanal. This can be rationalized by hydration or tautomerization of the dialdehyde to monoaldehydic forms, now facilitating Schiff base formation through an intramolecular H bond. Comparison with murine local lymph node assay data from the literature reveals that adduct stability in terms of reaction thermodynamics (K = k1/k-1pseudo) rather than formation kinetics (k1) governs the skin sensitization potency of Schiff-base-forming aldehydes. The discussion includes analytically determined adduct patterns, and the impact of α- and ß-carbon substitution as well as hydrophobicity on aldehyde reactivity.

Outer-sphere electron transfer does not underpin B12-dependent olefinic reductive dehalogenation in anaerobes.

Anaerobic microbial B12-dependent reductive dehalogenation may pave a way to remediate soil, sediment, and underground water contaminated with halogenated olefins. The chemical reaction is initiated by electron transfer (ET) from supernucleophilic cob(I)alamin (B12s). However, the inherent mechanism as outer-sphere or inner-sphere route is still under debate. To clarify the possibility of an outer-sphere pathway, we calculated free energy barriers of the initial steps of all outer-sphere ET routes by Marcus theory employing density functional theory (DFT). For 18 fluorinated, chlorinated, and brominated ethenes as representative olefins, 164 of 165 reactions with free energy barriers larger than 20 kcal mol-1 are not feasible under physiological dehalogenase conditions. Moreover, electronic structure analysis of perbromoethene with an outer-sphere free energy barrier of 18.2 kcal mol-1 reveals no ET initiation down to Co⋯Br and Co⋯C distances of 3.15 Å. The results demonstrate that the B12-catalyzed reductive dechlorination of olefins in microbes should proceed through an inner-sphere ET pathway.

Dehalococcoides-Mediated B12-Dependent Reductive Dehalogenation of Aromatics Does Not Proceed through Outer-Sphere Electron Transfer.

Several anaerobic bacteria can couple the reduction of aromatic halides to energy conservation. This organohalide respiration is catalyzed by enzymes containing cob(I)alamin, an activated supernucleophilic form of the coenzyme vitamin B12. However, the mechanism underlying the electron transfer (inner-sphere vs outer-sphere ET) still remains elusive. To clarify this issue, we selected 36 fluoro-, chloro-, and bromobenzenes as representative substrates and calculated their free-energy barriers at the quantum chemical density functional theory level, considering a wide range of theoretically possible outer-sphere ET mechanisms. Across all 336 reaction routes addressed, 334 routes involve free-energy barriers larger than 20 kcal/mol. For two reaction routes with highly brominated benzenes, free-energy barriers below 20 kcal/mol imply abiotic reduction as observed in experiments. Thus, microbial B12-dependent aromatic reductive dehalogenation does not proceed through an outer-sphere ET mechanism. Instead, the present study strongly suggests that microbe-catalyzed reductive dehalogenation of aromatic halides is governed by inner-sphere ET.

In Silico Finding of Key Interaction Mediated α3ß4 and α7 Nicotinic Acetylcholine Receptor Ligand Selectivity of Quinuclidine-Triazole Chemotype.

The selective binding of six (S)-quinuclidine-triazoles and their (R)-enantiomers to nicotinic acetylcholine receptor (nAChR) subtypes α3ß4 and α7, respectively, were analyzed by in silico docking to provide the insight into the molecular basis for the observed stereospecific subtype discrimination. Homology modeling followed by molecular docking and molecular dynamics (MD) simulations revealed that unique amino acid residues in the complementary subunits of the nAChR subtypes are involved in subtype-specific selectivity profiles. In the complementary ß4-subunit of the α3ß4 nAChR binding pocket, non-conserved AspB173 through a salt bridge was found to be the key determinant for the α3ß4 selectivity of the quinuclidine-triazole chemotype, explaining the 47-327-fold affinity of the (S)-enantiomers as compared to their (R)-enantiomer counterparts. Regarding the α7 nAChR subtype, the amino acids promoting a however significantly lower preference for the (R)-enantiomers were the conserved TyrA93, TrpA149 and TrpB55 residues. The non-conserved amino acid residue in the complementary subunit of nAChR subtypes appeared to play a significant role for the nAChR subtype-selective binding, particularly at the heteropentameric subtype, whereas the conserved amino acid residues in both principal and complementary subunits are essential for ligand potency and efficacy.

ERGO: Breaking Down the Wall between Human Health and Environmental Testing of Endocrine Disrupters.

ERGO (EndocRine Guideline Optimization) is the acronym of a European Union-funded research and innovation action, that aims to break down the wall between mammalian and non-mammalian vertebrate regulatory testing of endocrine disruptors (EDs), by identifying, developing and aligning thyroid-related biomarkers and endpoints (B/E) for the linkage of effects between vertebrate classes. To achieve this, an adverse outcome pathway (AOP) network covering various modes of thyroid hormone disruption (THD) in multiple vertebrate classes will be developed. The AOP development will be based on existing and new data from in vitro and in vivo experiments with fish, amphibians and mammals, using a battery of different THDs. This will provide the scientifically plausible and evidence-based foundation for the selection of B/E and assays in lower vertebrates, predictive of human health outcomes. These assays will be prioritized for validation at OECD (Organization for Economic Cooperation and Development) level. ERGO will re-think ED testing strategies from in silico methods to in vivo testing and develop, optimize and validate existing in vivo and early life-stage OECD guidelines, as well as new in vitro protocols for THD. This strategy will reduce requirements for animal testing by preventing duplication of testing in mammals and non-mammalian vertebrates and increase the screening capacity to enable more chemicals to be tested for ED properties.

Development of Novel Analogs of the Monocarboxylate Transporter Ligand FACH and Biological Validation of One Potential Radiotracer for Positron Emission Tomography (PET) Imaging.

Monocarboxylate transporters 1-4 (MCT1-4) are involved in several metabolism-related diseases, especially cancer, providing the chance to be considered as relevant targets for diagnosis and therapy. [18F]FACH was recently developed and showed very promising preclinical results as a potential positron emission tomography (PET) radiotracer for imaging of MCTs. Given that [18F]FACH did not show high blood-brain barrier permeability, the current work is aimed to investigate whether more lipophilic analogs of FACH could improve brain uptake for imaging of gliomas, while retaining binding to MCTs. The 2-fluoropyridinyl-substituted analogs 1 and 2 were synthesized and their MCT1 inhibition was estimated by [14C]lactate uptake assay on rat brain endothelial-4 (RBE4) cells. While compounds 1 and 2 showed lower MCT1 inhibitory potencies than FACH (IC50 = 11 nM) by factors of 11 and 25, respectively, 1 (IC50 = 118 nM) could still be a suitable PET candidate. Therefore, 1 was selected for radiosynthesis of [18F]1 and subsequent biological evaluation for imaging of the MCT expression in mouse brain. Regarding lipophilicity, the experimental log D7.4 result for [18F]1 agrees pretty well with its predicted value. In vivo and in vitro studies revealed high uptake of the new radiotracer in kidney and other peripheral MCT-expressing organs together with significant reduction by using specific MCT1 inhibitor α-cyano-4-hydroxycinnamic acid. Despite a higher lipophilicity of [18F]1 compared to [18F]FACH, the in vivo brain uptake of [18F]1 was in a similar range, which is reflected by calculated BBB permeabilities as well through similar transport rates by MCTs on RBE4 cells. Further investigation is needed to clarify the MCT-mediated transport mechanism of these radiotracers in brain.

Maternal phthalate exposure promotes allergic airway inflammation over 2 generations through epigenetic modifications.

BACKGROUND: Prenatal and early postnatal exposures to environmental factors are considered responsible for the increasing prevalence of allergic diseases. Although there is some evidence for allergy-promoting effects in children because of exposure to plasticizers, such as phthalates, findings of previous studies are inconsistent and lack mechanistic information. OBJECTIVE: We investigated the effect of maternal phthalate exposure on asthma development in subsequent generations and their underlying mechanisms, including epigenetic alterations. METHODS: Phthalate metabolites were measured within the prospective mother-child cohort Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk (LINA) and correlated with asthma development in the children. A murine transgenerational asthma model was used to identify involved pathways. RESULTS: In LINA maternal urinary concentrations of mono-n-butyl phthalate, a metabolite of butyl benzyl phthalate (BBP), were associated with an increased asthma risk in the children. Using a murine transgenerational asthma model, we demonstrate a direct effect of BBP on asthma severity in the offspring with a persistently increased airway inflammation up to the F2 generation. This disease-promoting effect was mediated by BBP-induced global DNA hypermethylation in CD4+ T cells of the offspring because treatment with a DNA-demethylating agent alleviated exacerbation of allergic airway inflammation. Thirteen transcriptionally downregulated genes linked to promoter or enhancer hypermethylation were identified. Among these, the GATA-3 repressor zinc finger protein 1 (Zfpm1) emerged as a potential mediator of the enhanced susceptibility for TH2-driven allergic asthma. CONCLUSION: These data provide strong evidence that maternal BBP exposure increases the risk for allergic airway inflammation in the offspring by modulating the expression of genes involved in TH2 differentiation through epigenetic alterations.

Interaction Mode and Regioselectivity in Vitamin B12-Dependent Dehalogenation of Aryl Halides by Dehalococcoides mccartyi Strain CBDB1.

The bacterium Dehalococcoides, strain CBDB1, transforms aromatic halides through reductive dehalogenation. So far, however, the structures of its vitamin B12-containing dehalogenases are unknown, hampering clarification of the catalytic mechanism and substrate specificity as basis for targeted remediation strategies. This study employs a quantum chemical donor-acceptor approach for the Co(I)-substrate electron transfer. Computational characterization of the substrate electron affinity at carbon-halogen bonds enables discriminating aromatic halides ready for dehalogenation by strain CBDB1 (active substrates) from nondehalogenated (inactive) counterparts with 92% accuracy, covering 86 of 93 bromobenzenes, chlorobenzenes, chlorophenols, chloroanilines, polychlorinated biphenyls, and dibenzo-p-dioxins. Moreover, experimental regioselectivity is predicted with 78% accuracy by a site-specific parameter encoding the overlap potential between the Co(I) HOMO (highest occupied molecular orbital) and the lowest-energy unoccupied sigma-symmetry substrate MO (σ*), and the observed dehalogenation pathways are rationalized with a success rate of 81%. Molecular orbital analysis reveals that the most reactive unoccupied sigma-symmetry orbital of carbon-attached halogen X (σC-X*) mediates its reductive cleavage. The discussion includes predictions for untested substrates, thus providing opportunities for targeted experimental investigations. Overall, the presently introduced orbital interaction model supports the view that with bacterial strain CBDB1, an inner-sphere electron transfer from the supernucleophile B12 Co(I) to the halogen substituent of the aromatic halide is likely to represent the rate-determining step of the reductive dehalogenation.

Computational Insight into the Activation Mechanism of Carcinogenic N'-Nitrosonornicotine (NNN) Catalyzed by Cytochrome P450.

Tobacco-specific N'-nitrosonornicotine (NNN), a genotoxic nitrosamine classified as Group 1 carcinogen, is also present in atmospheric particulate matter and has even been detected as a new disinfection byproduct in wastewaters. NNN generally requires metabolic activation by cytochrome P450 enzymes to exert its genotoxicity, but the respective biotransformation pathways have not been described in detail. In this work, we performed density functional theory (DFT) calculations to unravel possible NNN activation pathways including α-hydroxylation, ß-hydroxylation, pyridine N-oxidation, and norcotinine formation. The results reveal an initial rate-determining Hα-atom abstraction step for α-hydroxylation, followed by an unexpected kinetic competition between denitrosation and OH rebound, leading to ( iso-)myosmine as a detoxified product and α-hydroxyNNNs as the precursor of carcinogenic diazohydroxides, respectively. Further detoxification routes are given by ß-hydroxylation with relative high reaction barrier and N-oxidation with comparable barrier to the toxifying α-hydroxylation. Moreover, we show for the first time how norcotinine can be generated as a minor NNN metabolite that is formed from iso-myosmine through a unique porphyrin-assisted H atom 1,2-transfer mechanism. These results demonstrate that the carcinogenic potential of NNN is subject to a kinetic competition between activating and deactivating metabolic routes, and identify respective biomarkers to inform about the individual risk associated with NNN exposure.

Metabolic Mechanism of Aryl Phosphorus Flame Retardants by Cytochromes P450: A Combined Experimental and Computational Study on Triphenyl Phosphate.

Understanding metabolic mechanisms is critical and remains a difficult task in the risk assessment of emerging pollutants. Triphenyl phosphate (TPHP), a widely used aryl phosphorus flame retardant (aryl-PFR), has been frequently detected in the environment, and its major metabolite was considered as diphenyl phosphate (DPHP). However, knowledge of the mechanism for TPHP leading to DPHP and other metabolites is lacking. Our in vitro study shows that TPHP is metabolized into its diester metabolite DPHP and mono- and dihydroxylated metabolites by cytochromes P450 (CYP) in human liver microsomes, while CYP1A2 and CYP2E1 isoforms are mainly involved in such processes. Molecular docking gives the conformation for TPHP binding with the active species Compound I (an iron IV-oxo heme cation radical) in specific CYP isoforms, showing that the aromatic ring of TPHP is likely to undergo metabolism. Quantum chemical calculations have shown that the dominant reaction channel is the O-addition of Compound I onto the aromatic ring of TPHP, followed by a hydrogen-shuttle mechanism leading to ortho-hydroxy-TPHP as the main monohydroxylated metabolite; the subsequent H-abstraction-OH-rebound reaction acting on ortho-hydroxy-TPHP yields the meta- and ipso-position quinol intermediates, while the former of which can be metabolized into dihydroxy-TPHP by fast protonation, and the latter species needs to go through type-I ipso-substitution and fast protonation to be evolved into DPHP. We envision that the identified mechanisms may give inspiration for studying the metabolism of several other aryl-PFRs by CYP.

Glutathione Adduct Patterns of Michael-Acceptor Carbonyls.

Glutathione (GSH) has so far been considered to facilitate detoxification of soft organic electrophiles through covalent binding at its cysteine (Cys) thiol group, followed by stepwise catalyzed degradation and eventual elimination along the mercapturic acid pathway. Here we show that in contrast to expectation from HSAB theory, Michael-acceptor ketones, aldehydes and esters may form also single, double and triple adducts with GSH involving ß-carbon attack at the much harder N-terminus of the γ-glutamyl (Glu) unit of GSH. In particular, formation of the GSH-N single adduct contradicts the traditional view that S alkylation always forms the initial reaction of GSH with Michael-acceptor carbonyls. To this end, chemoassay analyses of the adduct formation of GSH with nine α,ß-unsaturated carbonyls employing high performance liquid chromatography and tandem mass spectrometry have been performed. Besides enriching the GSH adductome and potential biomarker applications, electrophilic N-terminus functionalization is likely to impair GSH homeostasis substantially through blocking the γ-glutamyl transferase catalysis of the first breakdown step of modified GSH, and thus its timely reconstitution. The discussion includes a comparison with cyclic adducts of GSH and furan metabolites as reported in literature, and quantum chemically calculated thermodynamics of hard-hard, hard-soft, and soft-soft adducts.

Anaerobic Dehalogenation of Chloroanilines by Dehalococcoides mccartyi Strain CBDB1 and Dehalobacter Strain 14DCB1 via Different Pathways as Related to Molecular Electronic Structure.

Dehalococcoides mccartyi strain CBDB1 and Dehalobacter strain 14DCB1 are organohalide-respiring microbes of the phyla Chloroflexi and Firmicutes, respectively. Here, we report the transformation of chloroanilines by these two bacterial strains via dissimilar dehalogenation pathways and discuss the underlying mechanism with quantum chemically calculated net atomic charges of the substrate Cl, H, and C atoms. Strain CBDB1 preferentially removed Cl doubly flanked by two Cl or by one Cl and NH2, whereas strain 14DCB1 preferentially dechlorinated Cl that has an ortho H. For the CBDB1-mediated dechlorination, comparative analysis with Hirshfeld charges shows that the least-negative Cl discriminates active from nonactive substrates in 14 out of 15 cases and may represent the preferred site of primary attack through cob(I)alamin. For the latter trend, three of seven active substrates provide strong evidence, with partial support from three of the remaining four substrates. Regarding strain 14DCB1, the most positive carbon-attached H atom discriminates active from nonactive chloroanilines in again 14 out of 15 cases. Here, regioselectivity is governed for 10 of the 11 active substrates by the most positive H attached to the highest-charge (most positive or least negative) aromatic C carrying the Cl to be removed. These findings suggest the aromatic ring H as primary site of attack through the supernucleophile Co(I), converting an initial H bond to a full electron transfer as start of the reductive dehalogenation. For both mechanisms, one- and two-electron transfer to Cl (strain CBDB1) or H (strain 14DCB1) are compatible with the presently available data. Computational chemistry research into reaction intermediates and pathways may further aid in understanding the bacterial reductive dehalogenation at the molecular level.

An Integrated Data-Driven Strategy for Safe-by-Design Nanoparticles: The FP7 MODERN Project.

The development and implementation of safe-by-design strategies is key for the safe development of future generations of nanotechnology enabled products. The safety testing of the huge variety of nanomaterials that can be synthetized is unfeasible due to time and cost constraints. Computational modeling facilitates the implementation of alternative testing strategies in a time and cost effective way. The development of predictive nanotoxicology models requires the use of high quality experimental data on the structure, physicochemical properties and bioactivity of nanomaterials. The FP7 Project MODERN has developed and evaluated the main components of a computational framework for the evaluation of the environmental and health impacts of nanoparticles. This chapter describes each of the elements of the framework including aspects related to data generation, management and integration; development of nanodescriptors; establishment of nanostructure-activity relationships; identification of nanoparticle categories; hazard ranking and risk assessment.