PharmEcology is an approach to chemical ecology inspired by natural products chemistry, drug discovery and pharmacology – all key aspects of drug discovery and development in the pharmaceutical industry. Part of the HCCE’s mission is to train the next generation of scientists in the skills necessary to succeed in the pharmaceutical industry and other industries that work at the interface of chemical-biological interactions. One way in which we fulfill this mission is by taking pharmaceutical approaches to studying ecological systems. Key techniques used in drug discovery and development are being applied by HCCE researchers (many of which are supported by metabolomics and proteomics analyses through the HCCE), such as: in vitro biological assays and xenobiotic transformations, target identification and characterization, as well as in vivo studies of toxicity, efficacy, and pharmacokinetics. In addition to the benefits of applying pharmaceutical approaches to ecology, ecological approaches have opened new avenues for discovering natural products whose ecological activity may portend further applications as drugs or other bioactive molecules. Novel chemical transformations discovered through chemical ecology research have also led to the discovery of privileged scaffolds which can serve as linchpins of chemical diversity – leading to the development of new techniques for developing diversity-targeted organic syntheses. This presentation describes the traditional drug discovery pipeline and the various ways in which HCCE activities interact with each stage of that pipeline.

The growing incidence and intensity of fires in the western United States is having drastic effects on ecosystems in the region as well as human communities. Fire is an important part of the landscape, but the recent trend towards higher intensity fires is leading to rapid alterations of biotic ecosystems and human activities within those ecosystems. Pinyon-juniper communities are abundant throughout the Great Basin and are affected by the increasing intensity of fires. The increase in the invasive species, Bromus tectorum (cheat grass) contributes to the increased acreage and intensity of these fires. Little is known about overall changes in phytochemical diversity, which is the richness and relative abundance of specialized metabolites in leaves, after fire. However, terpene levels in surviving pinyon pine needles can change significantly after very intense fires due to increased temperatures. Pinyon tissue terpene complexity and concentration can control insect herbivore populations. Partly in response to fires, there have been concerted initiatives to remove pinyon pine and juniper species to reduce fuel load. In addition to potentially contributing to declines in insects associated with pinyons, removing these key species has contributed to an increase in soil erosion, since pine root systems keep rocky hillslope soils intact. I plan to quantify the interactions between high intensity fires and arthropod populations by collecting arthropods and pinyon pine needles in plots across a historical burn gradient to address this general question: Has fire exposure caused changes in phytochemical diversity of Pinus monophyla (single-leaf pinyon, one of Nevada’s state trees)?

Environments that are subjected to significant amounts of ultraviolet radiation, such as the surface of Earth prior to the formation of the ozone layer and the current surface of Mars, are inhospitable to most organisms. However, certain species of lichens have been uncovered that are able to survive in areas with elevated UV exposure. We hypothesize that photoprotective compounds found within the upper cortex of these lichens interact with other compounds, including a polysaccharide sheath, to effectively dissipate the energy from absorbed UV light. Several spectroscopic techniques were utilized to evaluate the photostability and excited-state features of one of these natural products, vulpinic acid, isolated from wolf lichen. This compound was investigated under environmental conditions mimicking those found in nature and its spectral response was compared to the isolated form. Significant increases in photostability were observed in vulpinic acid when it was in environments rich with hydrogen bonding potential, and features of the transient absorption spectrum differed from those of the isolated compound. This suggests that intermolecular interactions between UV-absorbing compounds and other localized compounds within the organism are responsible for protecting lichens from harmful wavelengths of light.

Scytonemin is implicated as one of the key components that is proposed to have permitted life on early Earth prior to the formation of the mature ozone layer. The biosynthesis operon of scytonemin has been estimated to have originated between 2.1-2.6 billion years ago, a time where high incidence UV radiation was present on Earth’s surface. Our group recently became interested in the photophysical properties of this sheath localized pigment that allows it to effectively thermalize UV radiation. Access to this pigment from biologic material is cumbersome and low yielding, producing only ca. 1 mg per Kg of dry tissue as a mixture of reduced and oxidized analogs of the pigment and limit the extent of the ultrafast photophysical studies that can be conducted. To overcome the shortage of material from natural sources and support the full extent of photophysical studies, our group pursued the total synthesis of scytonemin. Our studies toward a concise and scalable total synthesis of scytonemin will be presented.

Thermoset polymers are widely used in consumer plastics for their durability and stability, but prove to be an undeniable issue regarding sustainability. This issue with consumer thermosets has prompted the creation of new classes of polymers: Covalently Adaptable Networks (CANs). These materials act as thermosets at low temperatures, giving comparable durability and stability to existing thermosets, but at higher temperatures they can flow under mechanical load like thermoplastics, enabling them to be reprocessed and given new purpose without sacrificing the quality of the material. Another interesting quality of this class of materials is the possibility of reclaiming the material through depolymerization. The resulting monomers could then be collected and repolymerized without sacrificing the quality of the polymer. With this in mind, we have developed an efficient monomer-polymer recycling system using crosslinked polydithioacetal (PDTA). Pristine PDTAs can be synthesized from 3,4,5-trimethoxybenzaldehyde and alkyl dithiols, with teraphthalaldehyde introduced as a crosslinker in an acid catalyzed reaction. The system can undergo depolymerizability via ring-closing depolymerization into macrocycles. These macrocycles can then be repolymerized via entropy-driven ring-opening polymerization, all done with only the catalyst still present from the initial polymerization. The crosslinked networks also showed a penchant for thermal reprocessing enabled by acid catalyzed dithioacetal exchanges. As the system is mechanically reprocessed, the tensile characteristics improve with each cycle, a trend that is present in both the strictly mechanically reprocessed films as well as mechanical reprocessing of repolymerized macrocycles. This demonstrates PDTA as a viable foundation for the design and development of recyclable polymers critical to moving towards a sustainable future.

Coevolutionary systems are ideal for studying adaptations because reciprocal selection between interacting partners can lead to arms-races of escalating adaptation and counter-adaptation. Pacific newts (Taricha) employ tetrodotoxin (TTX) as a powerful anti-predator defense. Despite this nearly impenetrable chemical defense, Thamnophis (garter snakes) from several populations in western North America prey on newts. These TTX-resistant snakes possess mutant sodium channels, which reduces the ability of TTX to bind to these proteins. Although these snakes can consume TTX-laden newts with relative ease, TTX is still present in the snake’s body after they successfully consume a newt, meaning the snakes need to be able to deal with TTX beyond their sodium channel resistance. We hypothesized that Thamnophis are capable of TTX sequestration which aids in their resistance as well as their detoxification. We tested this hypothesis by examining differences in TTX sequestration between TTX-resistant and TTX-sensitive snakes from three species (T. sirtalis, T. couchii, T. atratus) and in contrast to two outgroup species (T. elegans and Pituophis catenifer). Specifically, we quantified the TTX concentrations and rates of elimination of TTX from various tissues (heart, liver, kidney, muscle) across four time points (24 hrs, 72 hrs, 9 days and 18 days) following exposure to TTX. We found that TTX in T. sirtalis, T. couchii, T. atratus have longer half-lives than T. elegans and P. catenifer. Additionally, we found that TTX remains in the liver and the heart of snakes much longer than it does in their muscle or kidney. Our results suggest species involved in coevolution with newts (T. sirtalis, T. couchii, T. atratus) are capable of sequestering TTX and may gain some protection from their own predators by retaining TTX in their body.

Herbivores face a continual challenge of balancing their nutritional needs with the toxicity that they encounter in their diets. Plants produce toxic phytochemicals to defend against herbivores, while herbivores have evolved methods of detoxifying these chemicals. One such method is the use of cytochrome P450 enzymes (CYPs), many of which are found in the liver. While there has been much study of CYPs in model systems, there has been little research on CYPs in wild systems. The woodrat species Neotoma lepida and N. bryanti live across a sharp ecotone in which they encounter plants with vastly different chemistry. N. lepida, more of a specialist, prefers the cyanogenic glycoside-containing Prunus fasciculata, while N. bryanti, more of a generalist, has a more varied diet including a large proportion of the anthraquinone-containing Frangula californica. We investigated woodrat CYP activity to ask the following questions: 1) What is the role of CYPs in detoxifying specialized diets in N. lepida and N. bryanti? 2) How does CYP detoxification ability limit diet switching in N. lepida and N. bryanti? To answer these questions, we performed feeding trials and developed an in vitro assay to isolate liver CYPs and test their activity on plant extracts as well as individual compounds, using LCMS-TOF to compare post-assay chemistry. Here we found that N. lepida showed a limited ability to detoxify anthraquinones using CYPs compared to N. bryanti, indicating that CYP detoxification ability limits their ability to eat the anthraquinone-containing F. californica. However, neither woodrat species appears to use CYPs as a major method of detoxification of cyanogenic glycosides, which prompts further investigation into other detoxification pathways. In conclusion, this study suggests that CYP detoxification enzymes play an integral role in maintaining the species boundary between N. lepida and N. bryanti at their hybrid zone by limiting their capacity to switch diets. Additionally, the development of this assay can lead to future studies of CYPs in other wild systems.

Lichen pigments, like parietin and usnic acid, have long been proposed to function as sunscreens to protect the organisms from exposure to UV radiation. However, the photostability of these molecules and the photophysical studies is not well understood. Our interest in the ability of UV protective pigments to dissipate UV radiation has motivated our mechanistic studies of these lichen and cyanobacterial derived systems. Here we report our preliminary photostability studies of (+)-usnic acid (UA) and anthrarufin (AR), two lichen derived UV absorbing pigments. Studies were completed in protic and aprotic solvents to test the behavior of the compounds in different solvents. Photodegradation of AR was monitored by ultraviolet-visible (UV-Vis) spectroscopy, and that of UA was monitored by UV-Vis and circular dichroism (CD) spectroscopy. The anthrarufin photoproduct was able to absorb UV-C and absorb more intensely in the UV-C region after 3-day recovery post-irradiation. The CD signal of UA was lost after a period of irradiation without significant loss of UV absorption. A direct comparison was made between (+)-usnic acid and anthrarufin using the decay constant as well as the same pigment in different solvents. These results help us better understand how the structural differences between the photoactive pigments interact with UV radiation and implicate different modes of UV dissipation between these families of lichen pigments.

Though Haber-Bosch process to produce ammonia (NH3) in industrial scale is very popular technology, it is an energy intensive process and produces 1-2% carbon-dioxide (CO2). Electrocatalytic NH3 production from electrochemical NO3- reduction could be a promising alternative of Haber-Bosch process. Although Nafion is commonly employed as a separator in two-compartment electrochemical cells and as a binder in catalyst inks, in this project, we use Nafion as an overlayer on top of Cu electrodeposits to enhance NH3 selectivity. Faradaic efficiencies for NH3 and NO2- generation were evaluated as a function of electrodeposit morphology with and without the Nafion layer. These studies reveal that the combination of Cu (220) faces in the electrodeposits and activation of a NO intermediate by Nafion enables NH3 production with a high Faradaic efficiency of (97.0 ± 0.3)%. This optimized architecture also exhibits the fastest rate of NH3 production among the catalysts studied even after normalizing for its rough electrochemical active surface area. In addition to voltammetry, the electrocatalysts were characterized using a variety of techniques including atomic force microscopy, scanning electron microscopy, X-ray diffraction, and water contact angle measurements. Insights garnered about the parameters needed for selective NH3 production will inform future research on non-precious metal NO3- reduction catalysts.

Energy flow in small molecules is pivotal to the survival of many organisms. For example, UV screening compounds can dissipate large amounts of UV radiation to avoid apoptosis. The mechanisms for energy dissipation involve hydrogen bonding, proton transfer, conformational motions, and dumping into the vibrational manifold. Anthrarufin is a compound with a well-established pathway of energy flow. It undergoes either a single or dual intramolecular proton transfer. The dependence of proton transfer on local environments is still far from understood. In this work, we found the time constant of anthrarufin photodegradation increased in polar solvents. Ultrafast transient absorption will allow us to assess the excited state dynamics of proton transfer and vibrational relaxation to uncover the mechanisms within different environmental conditions.