Stabilization of antiaromatic skeletons in oxidized biphenylene oligomers

Comunicación a congreso en forma de pósterThe importance of antiaromatic molecules in Chemistry and more recently in material science is rising. In the particular case of applications in electronics, the antiaromatic skeleton offers the favourable situation of high energy (i.e., strong destabilization) occupied molecular orbitals allowing to ease oxidation, doping or electron transfer to form conductive and photo-active substrates. Furthermore these systems show intriguing characteristics, such as paratropic ring current and π –bond localization, opposite the characteristics expected from aromaticity[1]. In this contribution, we will show new recently synthesized polycyclic compounds based on fused antiaromatic bis-phenylene which have resulted to be stable enough to be spectroscopically characterisable[2],[3]. We study two different isomer such as shown in Figure 1, either with linear arrangement of the rings or with angular disposition. The research is based on the study of neutral and oxidized species of the two molecules. Oxidation was carried out by electrochemistry and the generated species were analyzed by UV-Vis-NIR absorption spectroscopy. On the other hand, the redox forms were formed by chemical oxidation on which the Raman spectra were also obtained. All results are interpreted and guided theoretically through the use of DFT quantum chemical calculations. We conclude that oxidation generates the radical cation and the dication species which have completely different electronic and molecular structures which are in consonance with the varying degree of antiaromatic character. Stable cations and dications of antiaromatic molecules are scarce and therefore unexplored. We contribute to this knowledge by studying these in oligomers of biphenylene.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Oxidized Forms of Antiaromatic Oligomers of Biphenylene

Rsumen de la comunicaciónThe importance of antiaromatic molecules in Chemistry and more recently in material science is rising. In the particular case of applications in electronics, the antiaromatic skeleton offers the favorable situation of high energy (i.e., destabilized) occupied molecular orbitals allowing to ease oxidation, doping or electron transfer to form conductive and photo-active substrates.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Coral reef degradation is not correlated with local human population density

The global decline of reef-building corals is understood to be due to a combination of local and global stressors. However, many reef scientists assume that local factors predominate and that isolated reefs, far from human activities, are generally healthier and more resilient. Here we show that coral reef degradation is not correlated with human population density. This suggests that local factors such as fishing and pollution are having minimal effects or that their impacts are masked by global drivers such as ocean warming. Our results also suggest that the effects of local and global stressors are antagonistic, rather than synergistic as widely assumed. These findings indicate that local management alone cannot restore coral populations or increase the resilience of reefs to large-scale impacts. They also highlight the truly global reach of anthropogenic warming and the immediate need for drastic and sustained cuts in carbon emissions

Fish assemblages of Caribbean coral reefs: Effects of overfishing on coral communities under climate change

Coral reefs are threatened worldwide due to local stressors such as overfishing, pollution, and diseases outbreaks, as well as global impacts such as ocean warming. The persistence of this ecosystem will depend, in part, on addressing local impacts since humanity is failing to control climate change. However, we need a better understanding of how protection from local stressors decreases the susceptibility of reef corals to the effects of climate change across large-spatial scales. My dissertation research evaluates the effects of overfishing on coral reefs under local and global impacts to determine changes in ecological processes across geographical scales. First, as large predatory reef fishes have drastically declined due to fishing, I reconstructed natural baselines of predatory reef fish biomass in the absence of human activities accounting for environmental variability across Caribbean reefs. I found that baselines were variable and site specific; but that contemporary predatory fish biomass was 80-95% lower than the potential carrying capacity of most reef areas, even within marine reserves. Second, I examined the effect of current native predatory reef fishes on controlling the invasion of Pacific lionfish across the Caribbean. Native predators and lionfish abundance were not related, even when predatory capacity was relatively high within certain marine reserves. Third, as herbivorous fishes may facilitate coral recovery after warming events by controlling competitive macroalgae, I evaluated whether major benthic groups, such as hard corals, crustose coralline algae, and macroalgae, were associated with these fish assemblages across Caribbean and Pacific reefs. Although, macroalgae abundance was negatively related to herbivorous fishes across geographical regions, contemporary coral cover showed no association with herbivores abundance after a recent history of thermal stress. Finally, I analyzed the relationship between ~30 years of thermal stress anomalies and coral assemblages in the Caribbean and suggest that recent warming has partially promoted a shift in coral-community composition across the region that compromise reef functionality. My dissertation research highlights the complex interactions among functional groups in coral reefs, local stressors, and environmental variability across geographical scales, and provides novel insights to reevaluate conservation strategies for this ecosystem in a rapidly changing world.Doctor of Philosoph

Predatory fish depletion and recovery potential on Caribbean reefs

The natural, prehuman abundance of most large predators is unknown because of the lack of historical data and a limited understanding of the natural factors that control their populations. Determining the supportable predator biomass at a given location (that is, the predator carrying capacity) would help managers to optimize protection and would provide site-specific recovery goals. We assess the relationship between predatory reef fish biomass and several anthropogenic and environmental variables at 39 reefs across the Caribbean to (i) estimate their roles determining local predator biomass and (ii) determine site-specific recovery potential if fishing was eliminated. We show that predatory reef fish biomass tends to be higher in marine reserves but is strongly negatively related to human activities, especially coastal development. However, human activities and natural factors, including reef complexity and prey abundance, explain more than 50% of the spatial variation in predator biomass. Comparing site-specific predator carrying capacities to field observations, we infer that current predatory reef fish biomass is 60 to 90% lower than the potential supportable biomass in most sites, even within most marine reserves. We also found that the scope for recovery varies among reefs by at least an order of magnitude. This suggests that we could underestimate unfished biomass at sites that provide ideal conditions for predators or greatly overestimate that of seemingly predator-depleted sites that may have never supported large predator populations because of suboptimal environmental conditions

Invasive lionfish had no measurable effect on prey fish community structure across the Belizean Barrier Reef

Invasive lionfish are assumed to significantly affect Caribbean reef fish communities. However, evidence of lionfish effects on native reef fishes is based on uncontrolled observational studies or small-scale, unrepresentative experiments, with findings ranging from no effect to large effects on prey density and richness. Moreover, whether lionfish affect populations and communities of native reef fishes at larger, management-relevant scales is unknown. The purpose of this study was to assess the effects of lionfish on coral reef prey fish communities in a natural complex reef system. We quantified lionfish and the density, richness, and composition of native prey fishes (0–10 cm total length) at sixteen reefs along ∼250 km of the Belize Barrier Reef from 2009 to 2013. Lionfish invaded our study sites during this four-year longitudinal study, thus our sampling included fish community structure before and after our sites were invaded, i.e., we employed a modified BACI design. We found no evidence that lionfish measurably affected the density, richness, or composition of prey fishes. It is possible that higher lionfish densities are necessary to detect an effect of lionfish on prey populations at this relatively large spatial scale. Alternatively, negative effects of lionfish on prey could be small, essentially undetectable, and ecologically insignificant at our study sites. Other factors that influence the dynamics of reef fish populations including reef complexity, resource availability, recruitment, predation, and fishing could swamp any effects of lionfish on prey populations

Dynamic Electrochemistry of Anthanthrone.

In this investigation, we present a “nanographene” based on the low-cost commercially available 4,10-dibromoanthanthrone building block, where the anthanthrone core can be viewed as a fusion of two anthracene moieties with lateral functionalization. The chemical and physical properties of this molecule stand in sharp contrast with the present anthracene subunit. We have studied the dynamic electrochemistry from two derivates of anthanthrone where the research depends on the radical of peripheral phenyl groups. In this case, we compared the changes that produce a donor group and acceptor group respectively. In both cases, the neutral molecule has a butterfly shape due to the steric congestion between the protons at the peri position of the quinoidal anthanthrone core, which possess a nonplanar folded geometry, and the protons from the peripheral phenyl groups. However, when two electrons are subtracted, exist a core aromatization and planarization, this provides a stable flat shape. We show the existence of two conformational states through cyclic voltammetry, electrochemistry and variable temperature chemistry oxidation. We demonstrate the fast or slow equilibrium between both geometries depending on the radical of peripheral phenyl groups (donor or acceptor).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Native Predators Do Not Influence Invasion Success of Pacific Lionfish on Caribbean Reefs

Biotic resistance, the process by which new colonists are excluded from a community by predation from and/or competition with resident species, can prevent or limit species invasions. We examined whether biotic resistance by native predators on Caribbean coral reefs has influenced the invasion success of red lionfishes (Pterois volitans and Pterois miles), piscivores from the Indo-Pacific. Specifically, we surveyed the abundance (density and biomass) of lionfish and native predatory fishes that could interact with lionfish (either through predation or competition) on 71 reefs in three biogeographic regions of the Caribbean. We recorded protection status of the reefs, and abiotic variables including depth, habitat type, and wind/wave exposure at each site. We found no relationship between the density or biomass of lionfish and that of native predators. However, lionfish densities were significantly lower on windward sites, potentially because of habitat preferences, and in marine protected areas, most likely because of ongoing removal efforts by reserve managers. Our results suggest that interactions with native predators do not influence the colonization or post-establishment population density of invasive lionfish on Caribbean reefs

Re-examining the relationship between invasive lionfish and native grouper in the Caribbean

Biotic resistance is the idea that native species negatively affect the invasion success of introduced species, but whether this can occur at large spatial scales is poorly understood. Here we re-evaluated the hypothesis that native large-bodied grouper and other predators are controlling the abundance of exotic lionfish (Pterois volitans/miles) on Caribbean coral reefs. We assessed the relationship between the biomass of lionfish and native predators at 71 reefs in three biogeographic regions while taking into consideration several cofactors that may affect fish abundance, including among others, proxies for fishing pressure and habitat structural complexity. Our results indicate that the abundance of lionfish, large-bodied grouper and other predators were not negatively related. Lionfish abundance was instead controlled by several physical site characteristics, and possibly by culling. Taken together, our results suggest that managers cannot rely on current native grouper populations to control the lionfish invasion

Re-examining the relationship between invasive lionfish and native grouper in the Caribbean

Biotic resistance is the idea that native species negatively affect the invasion success of introduced species, but whether this can occur at large spatial scales is poorly understood. Here we re-evaluated the hypothesis that native large-bodied grouper and other predators are controlling the abundance of exotic lionfish (Pterois volitans/miles) on Caribbean coral reefs. We assessed the relationship between the biomass of lionfish and native predators at 71 reefs in three biogeographic regions while taking into consideration several cofactors that may affect fish abundance, including among others, proxies for fishing pressure and habitat structural complexity. Our results indicate that the abundance of lionfish, large-bodied grouper and other predators were not negatively related. Lionfish abundance was instead controlled by several physical site characteristics, and possibly by culling. Taken together, our results suggest that managers cannot rely on current native grouper populations to control the lionfish invasion