Opportunities and challenges with transitioning to non-lethal sampling of wild fish for microbiome research.

The microbial communities of fish are considered an integral part of maintaining the overall health and fitness of their host. Research has shown that resident microbes reside on various mucosal surfaces, such as the gills, skin, and gastrointestinal tract, and play a key role in various host functions, including digestion, immunity, and disease resistance. A second, more transient group of microbes reside in the digesta, or feces, and are primarily influenced by environmental factors such as the host diet. The vast majority of fish microbiome research currently uses lethal sampling to analyse any one of these mucosal and/or digesta microbial communities. The present paper discusses the various opportunities that non-lethal microbiome sampling offers, as well as some inherent challenges, with the ultimate goal of creating a sound argument for future researchers to transition to non-lethal sampling of wild fish in microbiome research. Doing so will reduce animal welfare and population impacts on fish while creating novel opportunities to link host microbial communities to an individual's behavior and survival across space and time (e.g., life-stages, seasons). Current lethal sampling efforts constrain our ability to understand the mechanistic ecological consequences of variation in microbiome communities in the wild. Transitioning to non-lethal sampling will open new frontiers in ecological and microbial research.

Tunable Photocatalytic Singlet Oxygen Generation by Metal-Organic Frameworks via Functionalization of Pyrene-Containing Linkers.

Metal-organic frameworks (MOFs) are highly versatile materials that have shown great promise in chemical warfare agent (CWA) adsorption and decontamination. Sulfur mustard has been one of the most prominently used CWAs over the last century; therefore, the development of effective detoxification strategies is of utmost importance. However, typical routes of detoxification are slow and/or result in the production of harmful byproducts. NU-1000 has previously shown promise as a "soft" oxidizer that can readily detoxify sulfur mustard and its simulant 2-chloroethyl ethyl sulfide (2-CEES) through the generation of singlet oxygen in the presence of either UV (396 nm) or blue (465 nm) light. Several variants of NU-1000 were synthesized (MOF-R, R = -Cl, -NO2, -CH3) with functional groups positioned either ortho or meta to the carboxylic acid on the linker. NU-1000-o-(Cl)4 and NU-1000-m-(Cl)4 showed significant enhancement of photooxidation of 2-CEES due to spin-orbit coupling, enhancing the intersystem crossing into the MOF triplet (T1) state. Furthermore, substitution of MOF linkers led to pyrene-phenyl rotation. Linkers with substituents in the ortho-position were shown to have smaller pyrene-phenyl torsion angles, leading to enhanced conjugation between the rings and a subsequent red shift in the absorption spectra. This red shift leads to enhanced reactivity of NU-1000-o-(Cl)4 under blue light conditions and gives perspective on making materials with enhanced reactivity utilizing visible light.

Whole-Genome Data from Curtobacterium flaccumfaciens pv. flaccumfaciens Strains Associated with Tan Spot of Mungbean and Soybean Reveal Diverse Plasmid Profiles.

Despite the substantial economic impact of Curtobacterium flaccumfaciens pv. flaccumfaciens on legume production worldwide, the genetic basis of its pathogenicity and potential host association is poorly understood. The production of high-quality reference genome assemblies of C. flaccumfaciens pv. flaccumfaciens strains associated with different hosts sheds light on the genetic basis of its pathogenic variability and host association. Moreover, the study of recent outbreaks of bacterial wilt and microevolution of the pathogen in Australia requires access to high-quality reference genomes that are sufficiently closely related to the population being studied within Australia. We provide the first genome assemblies of C. flaccumfaciens pv. flaccumfaciens strains associated with mungbean and soybean, which revealed high variability in their plasmid composition. The analysis of C. flaccumfaciens pv. flaccumfaciens genomes revealed an extensive suite of carbohydrate-active enzymes potentially associated with pathogenicity, including four carbohydrate esterases, 50 glycoside hydrolases, 23 glycosyl transferases, and a polysaccharide lyase. We also identified 11 serine peptidases, three of which were located within a linear plasmid, pCff119. These high-quality assemblies and annotations will provide a foundation for population genomics studies of C. flaccumfaciens pv. flaccumfaciens in Australia and for answering fundamental questions regarding pathogenicity factors and adaptation of C. flaccumfaciens pv. flaccumfaciens to various hosts worldwide and, at a broader scale, contribute to unraveling genomic features of gram-positive, xylem-inhabiting bacterial pathogens.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Research effort devoted to regulating and supporting ecosystem services by environmental scientists and economists.

The economic valuation of ecosystem services in part reflects the desire to use conventional economic tools (markets and economic instruments) to conserve ecosystem services. However, for regulating and supporting ecosystem services that depend on ecosystem structure and function, estimation of economic value requires estimates of the current level of underlying ecological functions first. This primary step is in principle, the job of environmental scientists, not economists. Here, we provide a coarse-level quantitative assessment of the relationship between the research effort expended by environmental scientists (on the biophysical values) and economists (on the monetary values) on 15 different regulating and supporting services in 32 ecosystem types using peer-reviewed article hits retrieved from bibliographic databases as a measure of research effort. We find a positive, moderately strong (r = 0.69) correlation between research efforts in the two domains, a result that, while encouraging, is likely to reflect serendipity rather than the deliberate design of integrated environmental science-economics research programs. Our results suggest that compared to environmental science research effort economic valuation is devoted to a smaller, less diverse set of ecosystem services but a broader, more diverse, set of ecosystem types. The two domains differed more with respect to the ecosystem services that are the major focus of research effort than they did with respect to the ecosystem types of principal research interest. For example, carbon sequestration, erosion regulation, and nutrient cycling receive more relative research effort in the environmental sciences; air quality regulation in economic valuations. For both domains, cultivated areas, wetlands, and urban/semi-urban ecosystem types received relatively large research effort, while arctic and mountain tundra, cave and subterranean, cryosphere, intertidal/littoral zone, and kelp forest ecosystem types received negligible research effort. We suggest ways and means by which the field of sustainability science may be improved by the design and implementation of a searchable database of environmental science and economic valuation literature as well as a global ecosystem service research network and repository that explicitly links research on the estimation and prediction of biophysical ecosystem functions with that of the social sciences and other knowledge systems. These suggestions would, at least in principle, facilitate a more efficient research agenda between economists and environmental scientists and aid management, regulatory and judicial decision-makers.

Solvent-Dependent Photophysics and Reactivity of Monomeric and Dimeric 4-Amino-1,8-Naphthalimides.

The solvent-dependent photophysics of two 4-amino-substituted 1,8-naphthalene imides (AIs) were studied using fluorescence spectroscopy and laser flash photolysis. The compounds were functionalized with water-soluble 2,2'(ethylenedioxy) diethylamine groups, yielding a monomer (AI3) and a dimer (AI4). The radiative and nonradiative singlet-state deactivation processes of AI3 and AI4 were quantified in 10 solvents and at different pH values. The fluorescence quantum yield for the AI4 dimer in water was more than 100× lower than in other solvents, or for the monomeric AI3. The enhanced nonradiative decay of aqueous solutions of dimeric AI4 is accompanied by biexponential decay kinetics, suggesting equilibration with a dark excited state. An oxygen-quenchable triplet state (T1) of AI3 was produced upon 416 nm excitation in both water and n-octanol. In water, the T1 state evolved into a long-lived transient that was unreactive toward oxygen or several electron donors. This species was not observed in n-octanol. The transient observed upon 416 nm excitation of AI4 in water was extremely weak. However, production of T1 in both AI3 and AI4 was evidenced by the photoinduced electron transfer to methyl viologen, albeit in low quantum yield (0.0503 and 0.00778 for AI3 and AI4, respectively). The photophysics and reactivity are consistent with the production of an intramolecular charge transfer (ICT) state that is stabilized in water. Significantly, this stabilization enhances nonradiative decay pathways, particularly in the AI4 dimer. The results indicate that the photochemistry of these compounds can be environmentally mediated, switching from radical- to triplet-initiated processes.

One Crop Disease, How Many Pathogens? Podosphaera xanthii and Erysiphe vignae sp. nov. Identified as the Two Species that Cause Powdery Mildew of Mungbean (Vigna radiata) and Black Gram (V. mungo) in Australia.

Powdery mildew is a significant threat to mungbean (Vigna radiata) and black gram (V. mungo) production across Australia and overseas. Although they have been present in Australia for at least six decades and are easily recognized in the field, the precise identification of the pathogens causing this disease has remained unclear. Our goal was to identify the powdery mildew species infecting mungbean, black gram, and wild mungbean (V. radiata ssp. sublobata) in Australia. The internal transcribed spacer (ITS) and large subunit sequences of the ribosomal DNA and/or morphology of 57 Australian specimens were examined. Mungbean and black gram were infected by two species: Podosphaera xanthii and a newly recognized taxon, Erysiphe vignae sp. nov. Wild mungbean was infected only with P. xanthii. Mungbean and black gram powdery mildew ITS sequences from China, India, and Taiwan revealed the presence of only P. xanthii on these crops despite controversial reports of an Erysiphe species on both crops in India. Sequence analyses indicated that the closest relative of E. vignae is E. diffusa, which infects soybean (Glycine max) and other plants. E. vignae did not infect soybean in cross-inoculation tests. In turn, E. diffusa from soybean infected black gram and provoked hypersensitive response in mungbean. The recognition of a second species, E. vignae, as another causal agent of mungbean and black gram powdery mildew in Australia may complicate plant breeding efforts and control of the disease with fungicide applications.

Formation and Reaction Kinetics of Biradicals and Triplet States in a Series of Carboxylated 1,4,5,8-Naphthalene Diimides.

The singlet-state deactivation products in a series of alkyl carboxylate substituted 1,4,5,8-naphthalene diimide (NDI) compounds were characterized using fluorescence and phosphorescence spectroscopies, as well as nanosecond laser flash photolysis. The reactive intermediates were quantified as a function of the number of methylenes in the alkyl linker. Rate constants for photoinduced electron transfer (PET) to the singlet excited state of the NDIs varied from 1.2 × 1010 to 4.9 × 1010 s-1. The yield of the long-lived amino ketyl radical ranged from 15% to 60% in compounds having 4 to 1 intervening methylenes between the NDI chromophore and the covalently attached carboxylic acid. A predominantly triplet state was observed upon direct excitation of the compound having the slowest PET. This T1 state of the NDIs was reductively quenched by DABCO electron donor. The amino ketyl radical was unreactive toward electron donors but was found to react with the hydrogen atom donor ß-mercaptoethanol. The compounds comprise a novel class of long-wavelength and strongly absorbing UV-activated chromophores that generate carbon-centered biradicals via direct 355 nm excitation in the absence of a cosensitizer.

Enzyme Modification and Oxidative Cross-linking Using Carboxylate-, Phenol- and Catechol-Conjugated 1,8-Naphthalimides.

The ground- and excited-state interactions of ß-alanine, tyrosine and l-dopa substituted 1,8 naphthalimides (NI-Ala, NI-Tyr and NI-Dopa) with lysozyme and mushroom tyrosinase were evaluated to understand the mechanism of oxidative modification. Photooxidative cross-linking of lysozyme was observed for all three conjugates. The yield was significantly reduced for NI-Tyr and NI-Dopa due to intramolecular electron transfer to the excited singlet state of the 1,8-naphthalimide. Incubation of NI-Tyr and NI-Dopa with mushroom tyrosinase resulted in an increased fluorescence from the naphthalimide, suggesting that the phenol and catechol portion of the conjugates are oxidized by the enzyme. This result demonstrates that the compounds bind in the active site of mushroom tyrosinase. The catalytic activity of mushroom tyrosinase to oxidize both tyrosine (monophenolase) and l-dopa (diphenolase) was modified by NI-Tyr and NI-Dopa. Monophenolase activity was inhibited, and the diphenolase activity was enhanced in the presence of these conjugates. Detailed Michaelis-Menten studies show that both Vmax and Km are modified, consistent with a mixed inhibition mechanism. Collectively, the results show that the compounds interact in the enzyme's active site, but also modify the distribution of the enzyme's oxidation states that are responsible for catalysis.

Plastic waste associated with disease on coral reefs.

Plastic waste can promote microbial colonization by pathogens implicated in outbreaks of disease in the ocean. We assessed the influence of plastic waste on disease risk in 124,000 reef-building corals from 159 reefs in the Asia-Pacific region. The likelihood of disease increases from 4% to 89% when corals are in contact with plastic. Structurally complex corals are eight times more likely to be affected by plastic, suggesting that microhabitats for reef-associated organisms and valuable fisheries will be disproportionately affected. Plastic levels on coral reefs correspond to estimates of terrestrial mismanaged plastic waste entering the ocean. We estimate that 11.1 billion plastic items are entangled on coral reefs across the Asia-Pacific and project this number to increase 40% by 2025. Plastic waste management is critical for reducing diseases that threaten ecosystem health and human livelihoods.

Angling into the Future: Ten Commandments for Recreational Fisheries Science, Management, and Stewardship in a Good Anthropocene.

A new geological epoch, the "Anthropocene", has been defined as the period in which humans have had substantial geological and ecological influence on the planet. A positive future for this epoch can be referred to as the "good Anthropocene" and would involve effective management strategies and changes in human behavior that promote the sustainability and restoration of ecosystems. Recreational fisheries hold significant social, cultural, and economic value and can generate many benefits when managed sustainably and thus be an integral part of a "good Anthropocene". Here, we list ten commandments to facilitate persistence and long-term sustainability of recreational fisheries in the "good Anthropocene". This list includes fostering aquatic stewardship, promoting education, using appropriate capture gear, adopting evidence-based management approaches, promoting the concept of resilience, obtaining and using effort data in management, embracing the ecosystem approach, engaging in multilevel collaboration, enhancing accessibility, and embracing optimism. When used singly, or simultaneously, these ten commandments will contribute to the harmonization of sustainable fish populations and angling practices, to create recreational fisheries' "bright spots".

Synthesis, characterization, and photophysical study of fluorescent N-substituted benzo[ghi]perylene "swallow tail" monoimides.

A set of N-substituted benzoperylene monoimide (BPI) fluorophores was synthesized and characterized structurally and photophysically. Condensation of benzo[ghi]perylene-1,2-dicarboxylic anhydride in the presence of "swallow tail" alkyl amines produced fluorophores that are soluble in a range of organic solvents, highly absorbing in the near-UV (ε(334) = 79,000 M(-1) cm(-1)), and fluorescent in the visible range. Photophysical behavior of the compounds was studied with steady-state and time-correlated single photon counting. The synthesized BPIs exhibit positive solvachromatic emission (λ(em) (hexane) = 469 nm; λ(em) (ethanol) = 550 nm) as a function of solvent polarity with little change in their excited-state lifetime (9.6-6.5 ns) and fluorescence quantum yield (0.27-0.44) over the polarity range studied. Solvachromatic shifts were analyzed using the Lippert-Mataga approach. In nonpolar hydrocarbon solvents evidence of dual emission from closely spaced (562 cm(-1)) S(1) and S(2) excited states is observed. Preliminary peak assignments for the anomalous S(2) emission are made.

Using complement coercion to understand the neural basis of semantic composition: evidence from an fMRI study.

Previous research regarding the neural basis of semantic composition has relied heavily on violation paradigms, which often compare implausible sentences that violate world knowledge to plausible sentences that do not violate world knowledge. This comparison is problematic as it may involve extralinguistic operations such as contextual repair and processes that ultimately lead to the rejection of an anomalous sentence, and these processes may not be part of the core language system. Also, it is unclear if violations of world knowledge actually affect the linguistic operations for semantic composition. Here, we compared two types of sentences that were grammatical, plausible, and acceptable and differed only in the number of semantic operations required for comprehension without the confound of implausible sentences. Specifically, we compared complement coercion sentences (the novelist began the book), which require an extra compositional operation to arrive at their meaning, to control sentences (the novelist wrote the book), which do not have this extra compositional operation, and found that the neural response to complement coercion sentences activated Brodmann's area 45 in the left inferior frontal gyrus more than control sentences. Furthermore, the processing of complement coercion recruited different brain regions than more traditional semantic and syntactic violations (the novelist astonished/write the book, respectively), suggesting that coercion processes are a part of the core of the language faculty but do not recruit the wider network of brain regions underlying semantic and syntactic violations.

Population-based study of ABCD2 score, carotid stenosis, and atrial fibrillation for early stroke prediction after transient ischemic attack: the North Dublin TIA study.

BACKGROUND AND PURPOSE: Transient ischemic attack (TIA) etiologic data and the ABCD(2) score may improve early stroke risk prediction, but studies are required in population-based cohorts. We investigated the external validity of the ABCD(2) score, carotid stenosis, and atrial fibrillation for prediction of early recurrent stroke after TIA. METHODS: Patients with TIA in the North Dublin city population (N=294 529) were ascertained by using overlapping hospital and community sources. The relations between individual ABCD(2) items, carotid stenosis, atrial fibrillation, and early stroke were examined. RESULTS: In confirmed TIA cases (n=443), carotid stenosis predicted 90-day stroke (hazard ratio=2.56; 95% CI, 1.27 to 5.15, P=0.003). Stroke risk rose with increasing grade of carotid stenosis, ranging from 5.4% (95% CI, 3.3% to 8.7%) with <50% stenosis to 17.2% (95% CI, 9.7% to 29.7%) with severe stenosis/occlusion (hazard ratio=3.3; 95% CI, 1.5 to 7.4, P=0.002). In confirmed TIA cases (n=443), the ABCD(2) score performed no better than chance for prediction of 90-day stroke (c-statistic=0.55; 95% CI, 0.45 to 0.64), largely related to the 24.2% (8/33) of patients who experienced a recurrence and had low ABCD(2) scores (0-3). However, in nonspecialist-suspected TIA cases (n=700), the predictive utility improved for stroke at 28 (c-statistic=0.61; 95% CI, 0.50 to 0.72) and 90 (c-statistic=0.61; 95% CI, 0.52 to 0.71) days. CONCLUSIONS: In a population-based TIA cohort, significant predictive information was provided by carotid stenosis. The ABCD(2) score had predictive utility in patients with TIA suspected by nonspecialists. Low scores occurred in several patients with stroke recurrences, suggesting that caution is needed before using the score in isolation.

Diagnostic usefulness of the ABCD2 score to distinguish transient ischemic attack and minor ischemic stroke from noncerebrovascular events: the North Dublin TIA Study.

BACKGROUND AND PURPOSE: Transient ischemic attack (TIA) diagnosis is frequently difficult in clinical practice. Noncerebrovascular symptoms are often misclassified as TIA by nonspecialist physicians. Clinical prediction rules such as ABCD(2) improve the identification of patients with TIA at high risk of early stroke. We hypothesized that the ABCD(2) score may partly improve risk stratification due to improved discrimination of true TIA and minor ischemic stroke (MIS) from noncerebrovascular events. METHODS: Consecutive patients with TIA were identified within a prospective population-based cohort study of stroke and TIA. The cohort was expanded by inclusion of patients with MIS and noncerebrovascular events referred to a daily TIA clinic serving the population. Diagnosis was assigned by a trained stroke physician independent of ABCD(2) score. RESULTS: Five hundred ninety-four patients were included (292 [49.2%] TIA, 45 [7.6%] MIS, and 257 [43.3%] noncerebrovascular). The mean ABCD(2) score showed a graded increase across diagnostic groups (MIS mean 4.8 [SD 1.4] versus TIA mean 3.9 [SD 1.5] versus noncerebrovascular mean 2.9 [SD 1.5]; P<0.00001). The ABCD(2) score discriminated well between noncerebrovascular and cerebrovascular events-TIA (c-statistic 0.68; 95% CI, 0.64 to 0.72), any vascular event (TIA+MIS; c-statistic 0.7; 95% CI, 0.66 to 0.74), and MIS (c-statistic 0.81; 95% CI, 0.75 to 0.87)-from noncerebrovascular events. Of ABCD(2) items, unilateral weakness (OR, 4.5; 95% CI, 3.1 to 6.6) and speech disturbance (OR, 2.5; 95% CI, 1.6, 4.1) were most likely overrepresented in TIA compared with noncerebrovascular groups. CONCLUSIONS: The ABCD(2) score had significant diagnostic usefulness for discrimination of true TIA and MIS from noncerebrovascular events, which may contribute to its predictive usefulness.

Sequence-dependent interactions of cationic naphthalimides and polynucleotides.

The binding interactions of three naphthalimide derivatives with heteropoly nucleic acids have been evaluated using fluorescence, absorption and circular dichroism spectroscopies. Mono- and bifunctionalized naphthalimides exhibit sequence-dependent variations in their affinity toward DNA. The heteropoly nucleic acids, [Poly(dA-dT)]2 and [Poly(dG-dC)]2, as well as calf thymus (CT) DNA, were used to understand the factors that govern binding strength and selectivity. Sequence selectivity was addressed by determining the binding constants as a function of polynucleotide composition according to the noncooperative McGhee-von Hippel binding model. Binding affinities toward [poly(dA-dT)](2) were the largest for spermine-substituted naphthalimides (Kb = 2-6 x 10(6) M(-1)). The association constants for complex formation between the cationic naphthalimides and [poly(dG-dC)]2 or CT DNA (58% A-T content) were 2-500 times smaller, depending on the naphthalimide-polynucleotide pair. The binding modes were also assessed using a combination of induced circular dichroism and salt effects to determine whether the naphthalimides associate with DNA through intercalative, electrostatic or groove-binding. The results show that the monofunctionalized spermine and pyridinium-substituted naphthalimides associate with DNA through electrostatic interactions. In contrast, intercalative interactions are predominant in the complex formed between the bifunctionalized spermine compound and all of the polynucleotides.

Ground-state interactions of spermine-substituted naphthalimides with mononucleotides.

Water soluble spermine, spermine-naphthalimide, and pyridinium-substituted 1,8-naphthalimide derivatives have been synthesized as nucleotide-specific binding agents. Both mono- and bifunctionalized spermine compounds were studied. The photophysical properties of each compound were studied by using time-resolved and steady-state fluorescence and absorption spectroscopies. The fluorescence decay of the mononaphthalimides was adequately fit to a single exponential decay, and in all cases, the lifetime (2.4 ns) was independent of the imide substitutent. In the case of the bisnaphthalimide, emission from both the monomer and ground-state dimer forms was observed. The fluorescence quantum yield of the monomer (0.03) was significantly smaller than that of the mononaphthalimides (0.27). The dimer emission was red-shifted relative to that of the monomer. The singlet-state lifetime of the dimer was found to be 20 ns. In all cases, only absorption from the triplet excited state was observed, indicating no evidence of a naphthalimide radical anion from dimer excitation. The ground-state interactions of the naphthalimides with four nucleotides were investigated. Nucleotide selectivity was evaluated by determining their individual binding constants (Keq). The association constants were measured by using absorption, time-resolved fluorescence, and combined time-resolved and steady-state fluorescence. The equilibrium binding constant was largest for association of the spermine-substituted mononaphthalimide with adenosine monophosphate (Keq=550 M-1) or guanosine monophosphate (Keq=440 M-1). The dimer form of the disubstituted spermine also showed binding constants in excess of 200 M-1 with the purine nucleotides. The association constant for binding of the pyridinium-substituted naphthalimide showed little dependence on the structure of the nucleotide.

Reactivities of carboxyalkyl-substituted 1,4,5,8-naphthalene diimides in aqueous solution.

A series of water-soluble 1,4,5,8-naphthalene diimide derivatives has been prepared and their redox and photophysical properties characterized. From laser flash photolysis studies, the triplet excited state of N,N'-bis[2-(N-pyridinium)ethyl]-1,4,5,8-naphthalene diimide (NDI-pyr) was found to undergo oxidative quenching with the electron donors DABCO, tyrosine, and tryptophan as expected from thermodynamics. Interestingly, the reactivities of naphthalene diimides (NDI) possessing alpha- and beta-carboxylic acid substituents (R = -CH2COO-, -C(CH3)2COO-, and -CH2CH2COO-) were strikingly different. In these compounds, the transient produced upon 355 nm excitation did not react with the electron donors. Instead, this transient reacted rapidly (k > 10(8)-10(9) M-1 s-1) with known electron acceptors, benzyl viologen and ferricyanide. The transient spectrum of the carboxyalkyl-substituted naphthalimides observed immediately after the laser pulse was nearly identical to the one-electron-reduced form of 1,4,5,8-naphthalene diimide (produced independently using the bis-pyridinium-substituted naphthaldiimide). From our studies, we conclude that the transient produced upon nanosecond laser flash photolysis of NDI-(CH2)nCOO- is the species produced upon intramolecular electron transfer from the carboxylate moiety to the singlet excited state of NDI. In separate experiments, we verified that the singlet excited state of NDI-pyr does, indeed, react intermolecularly with acetate, alanine, and glycine. The process is further substantiated using thermodynamic driving force calculations. The results offer new prospects of the efficient photochemical production of reactive carbon-centered radicals.