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2023 HCCE Symposium at Lake Tahoe

Keynote Speakers

Short Format Talks

Poster Session

Keynote Speakers

Jared Ali

Department of Entomology, Pennsylvania State University, State College, Pennsylvania

This talk’s focus will be on insect behaviour and chemical ecology of multi-trophic interactions.. This includes plant responses to belowground herbivory and beneficial organisms. It will look at trophic cascades and tradeoffs with above-belowground interactions, and the evolution of plant defense strategies.

Thomas Hoye

From paracaseolide A to ottelione A to the HDDA reaction.

On the value of persistence, details, and 'the little things'

Department of Chemistry, University of Minnesota, Minneapolis, Minnesota

I guide a research program broadly based in the field of organic chemistry. But do not fret if it has been a while since you have taken, thought about, or used your knowledge of organic chemistry. My goal in this presentation will be to offer you greater appreciation for the quote underlined at the end of this abstract.

Q.  What do the following three molecules have in common?


A.  In this presentation I will address that question from the context of the traits in the above subtitle.

"It has long been an axiom of mine that the little things are infinitely the most important."

Sir Arthur Conan Doyle (via Sherlock Holmes) in A Case of Identity (1892)

1. Diels-Alderase-free, bis-pericyclic, [4+2] dimerization in the biosynthesis of (±)-paracaseolide A. Wang, T.; Hoye, T. R. Nature Chem. 2015, 7, 641–645. (doi:10.1038/nchem.2281)

2. The hexadehydro-Diels–Alder reaction. Hoye, T. R.; Baire, B.; Niu, D.; Willoughby, P. H.; Woods, B. P. Nature 2012, 490, 208–212. (doi:10.1038/nature11518)

3. The domino hexadehydro-Diels–Alder reaction transforms polyynes to benzynes to naphthynes to anthracynes to tetracynes (and beyond?). Xiao, X.; Hoye, T. R. Nature Chem. 2018, 10, 838–844. (doi:10.1038/s41557-018-0075-y)

4. Hexadehydro-Diels−Alder reaction: Benzyne generation via cycloisomerization of tethered triynes. Fluegel, L. L.; Hoye, T. R. Chem. Rev. 2021, 121, 2413–2444. (doi: 10.1021/acs.chemrev.0c00825)

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Short Format Talks

Chasing variation: ecological approaches to natural product discovery

Casey S. Philbin

Hitchcock Center for Chemical Ecology, University of Nevada, Reno; Department of Chemistry, University of Nevada, Reno

Until recently, natural product (NP) discovery had been largely dismissed as a source of new drug leads, largely due to the consensus that all the “low-hanging fruit” had already been discovered, and that it was not worth the effort to isolate and characterize the remaining minor natural products. Unfortunately, with some exceptions, NP discovery in macro-organisms is largely still dependent on the “grind-and-find” approach which suffers from several assumptions: the highest concentration compounds (low-hanging fruit) are most likely drug leads, intraspecific phytochemical variation is low, and NP rediscovery is problematic. We propose that taking an ecological approach to NP discovery will yield previously overlooked, biologically active, high-quality drug-like NP lead compounds. Rather than chasing major compounds that are the most likely to have already been discovered or using reductive approaches such as activity-guided fractionation, ecological approaches presuppose that the most important chemicals have the highest variation – observed as phenotype-defining chemicals within populations or chemicals that co-varying with biotic or abiotic ecological factors. Natural products exhibiting such variation have inferred biological function within ecological systems, and by extension deserve status as lead compounds in a NP drug discovery program. This approach also generates added value to compound rediscovery in an ecological context: the occurrence of NPs across taxa is important to understanding multitrophic interactions and co-evolutionary processes. Here we demonstrate the multi-platform metabolomics approach for novel NP discovery implemented at the HCCE, driven by integrating variation in LC-MS and 1H NMR data across a common-garden chemical heritability experiment of a Piper sancti-felicis Trel. population collected in and around La Selva Biological Station in Costa Rica. This approach yielded several novel NPs representing unique phytochemical reactivity within small chemically-defined sub-populations found in the heritability experiment. The unique multi-omic approach undertaken by the HCCE and the statistical tools we have developed to integrate these data have facilitated this new NP-discovery approach.

Skin anti-microbial peptide profiles and seasonal disease dynamics in frog populations

Carolina Lambertini(1), Emily LeSage(2), Laura Reinert(2), Louise Rollins-Smith(2), Jamie Voyles(1)

(1)Department of Biology, University of Nevada, Reno; (2)Department of Biological Sciences, Vanderbilt University

Infectious disease results from a dynamic interaction among hosts, pathogens, and their shared environments. One of the most severe diseases ever recorded in wildlife is the amphibian disease known as chytridiomycosis. This disease exhibits strong intraannual variation in prevalence and intensity (i.e., pathogen load) in many different host species. Previously, seasonality in this system was thought to be solely driven by the thermal sensitivity of the pathogen. Seasonality in host immunity has not been thoroughly explored. We investigated a key component of the host innate (non-specific) immune system – the immunochemistry of anti-microbial peptides (AMPs) in skin secretions – in a recovering population of frogs in Panama. We found that total peptide quantity was higher in the dry season. However, some peptides were differentially expressed across season and may be involved in limiting infection in wild amphibians during the dry season. These findings suggest that host immunity, and the chemistry of skin secretions, are likely more important to seasonal disease dynamics that previously anticipated. Understanding these mechanisms is important to resolving long standing questions concerning seasonality in infectious disease systems.

How intra-population chemical diversity shapes specialist herbivore communities

Devon Picklum, Lora Robinson

Department of Biology, University of Nevada, Reno

Plants are the foundations of communities, interacting with a diversity of herbivores, pollinators, and higher trophic levels through complex networks of interactions. Plants use a broad array of physical and chemical traits to direct these interactions, which can have major fitness consequences. Variation in plant phenotypes is important to both the strength and quality of individual interactions and community structure more broadly. Herbivore community assembly is known to be shaped by heritable plant traits, including chemistry, and can vary across the landscape. However, much of the work investigating how plant defensive chemistry mediates interactions with herbivores has focused on single herbivore species or simple communities. Our understanding of how chemical diversity within natural plant populations shapes interactions with diverse herbivore communities via plant chemistry is less well understood. Here, we use a Great Basin specialist shrub Ericameria nauseosa (rubber rabbitbrush) and its diverse and variable community of gall forming insects (Cecidomyiidae and Tephritidae) to investigate whether intra-population patterns of plant chemical diversity influence diversity and abundance of specialist herbivores. Using GC-MS methods and a K-means cluster analysis we identified 6 shrub chemotypes within a large natural Rabbitbrush population in the Virginia Mountains, Nevada. To understand how herbivore communities vary with plant chemical diversity, gall species composition and abundance were quantified for twenty replicates from each chemotype. Further chemical analyses were used to investigate tissue-specific plant chemistry. Together these data provide a detailed picture of the importance of plant phenotypic variation in shaping specialist herbivore communities.

Herbivores disrupt clinal variation in plant phytochemical responses to water limitation

Aramee C. Diethelm, Elizabeth G. Pringle

Department of Biology, University of Nevada, Reno

Biotic and abiotic stressors can affect short-term changes in plant defensive traits. Plant trait responses, including secondary metabolites, are critical to survival and competitiveness under stressful conditions. Although trait responses to simultaneous stressors can be impacted by factors such as crosstalk in biochemical response pathways, resource availability, and evolutionary history, plant responses to concurrent abiotic and biotic stressors remain not well understood. In addition, geographical gradients in selective pressures may contribute to observed variations in secondary metabolite profiles among populations. In this study, we examined the combined effects of water limitation and herbivore damage on plant trait responses using narrowleaf milkweed, Asclepias fascicularis. Using seeds collected from a gradient of water availability and grown in a common garden, we found that water limitation increased the diversity of UV-absorbent secondary metabolites, while herbivory increased metabolite richness. Interestingly, however, plants experiencing both stressors exhibited minimal or no induced responses, resembling control plants more than plants that experienced a single stressor. Water availability at seed-source locations produced clinal patterns in the constitutive concentration flavonol glycosides, with mean values increased from wetter to drier sites, and the richness of pregnane glycosides, which was higher plants from wetter sites. Furthermore, plants from drier sites showed larger increases in phytochemical diversity than plants from wetter sites when experiencing water limitation in isolation. The addition of herbivore damage disrupted clinal patterns and weakened plant responses to water limitation.

Phytochemical disturbances during a spongy moth outbreak

Celso Oliveira(1), Amy Trowbridge(1), Phillip Townsend(1), Richard Lindroth(2), Margaret Marshall(1), Beckett Hills(1)

(1)Department of Forestry and Wildlife Ecology, University of Wisconsin-Madison; (2)Department of Entomology, University of Wisconsin-Madison

Phytochemical diversity plays a fundamental role in mediating plant-insect interactions and shaping the structure of forest ecosystems. Yet, invasive herbivore outbreaks can have a disruptive impact on this dynamic by affecting how trees allocate resources towards defenses, or by causing dramatic changes in tree defensive chemistry. With extreme climate events already being forecasted to impact tree health, repeated pest outbreaks may further push trees towards their biochemical limits and lead to intensified forest mortality. In this study we investigated the shifts in phytochemical profiles of aspen (Populous tremuloides) occurred during an event of mass defoliation by spongy moth (Lymantria dispar). Aspen produce two main classes of defensive compounds, namely, condensed tannins (CT) and phenolic glycosides (PG), the latter being considered the most effective against insect herbivores. Leveraging a common garden experimental plot of genetically and chemically diverse aspen trees, we quantified these two lines of defense through the growing season of 2021 and 2022, when the garden was impacted by repeated moth outbreaks. Data from the 2021 season show a dramatic increase of PGs following the outbreak, although the extent and swiftness of response was largely dependent on tree chemotype. Concomitantly, CT content was significantly reduced, suggesting a phytochemical tradeoff between these two classes of compounds resulting from intensified predation by spongy moth. Moreover, tree mortality by fungal pathogens was intensified following the outbreak, which might be an indirect consequence from this phytochemical disturbance in aspen.

Redox behavior and detailed structural analysis of cyanobacterial pigment scytonemin: implications in ultraviolet screening action

Tanzil Mahmud, Profulla Mondol, Christopher Barile, Christopher Jeffrey

Department of Chemistry, University of Nevada, Reno

The common cyanobacterial ultraviolet (UV) light-screening pigment scytonemin has been found in the organism in both oxidized and reduced form. This discovery was first reported over three decades ago; however, the redox behavior of this pigment and its implications in the UV-screening capabilities of the oxidized and reduced form of the pigment remains largely unexplored. We report the first electrochemical study on scytonemin employing cyclic voltammetry (CV) performed in an organic medium. Scytonemin shows an oxidation potential of 0.51 V and a reduction potential of 0.01 V at 200 mV/s scan rate. Cyclic voltammograms of the compound at varying scan rates suggest that oxidation is faster than the reduction process, validating similar claims made in the literature based on benchtop observations. Moreover, scytonemin showed reversible redox behavior throughout the duration of the repeated experiments. Randles–Ševčík analysis suggested that the redox events took place at the electrode interface without adsorption of the species on the electrode surface. These results suggest a highly reversible redox behavior of this molecule which might help explain the photostability of the pigment, its widespread occurrence in nature and the existence of several analogs in cyanobacteria. This study along with detailed structural studies of scytonemin and its analogs will be presented.

Toxic nectar and bee kombucha: chemistry mediates plant and pollinator interactions with microbes  

Rachel Lee Vanette

Department of Entomology and Nematology, University of California, Davis

Both flower and pollinators, including bees, frequently host bacteria and fungi. Sugar-rich environments like nectar and stored bee food can be degraded by microbial overgrowth, so plants and pollinators have evolved distinct strategies to either prevent or cultivate microbial growth. In this talk, I will present our group’s recent efforts where we couple chemical analyses of nectar and bee environments with microbial growth bioassays. In both systems, we document antimicrobial adaptations produced by plants and bees that reduce the growth of environmental microbes, as well as chemical signatures of microbes specialized to nectar or bee-associated environments.   

Poster Session

PharmEcology: drug discovery and pharmacological approaches to chemical ecology at the HCCE

Casey S. Philbin

Hitchcock Center for Chemical Ecology, University of Nevada, Reno; Department of Chemistry, University of Nevada, Reno

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.

How extreme fire events are affecting pinyon pine community structure

Chloe Collier-Allen(1), Christopher S. Jeffrey(2), Lee Dyer(1)

(1)Department of Biology, University of Nevada, Reno; (2)Department of Chemistry, University of Nevada, Reno

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)?

Photostability and excited-state features of vulpinic acid, a natural UV-screening compound

Derek C. Moore, Tanzil Mahmud, Christopher S. Jeffrey, Matthew J. Tucker

Department of Chemistry, University of Nevada, Reno

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.

Biomimetic total synthesis of scytonemin and its derivatives

Garrett Larson, Brittany George, Christopher Jeffrey

Department of Chemistry, University of Nevada, Reno

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.

Highly recyclable thermosets from dithioacetal polymers

Julian Rolsma, Lasith S. Kariyawasam, Ying Yang

Department of Chemistry, University of Nevada, Reno

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.

Investigating tetrodotoxin (TTX) sequestration in garter snakes (Thamnophis)

Kelly E. Robinson(1), Haley A. Moniz(1), Amber N. Stokes(2), Chris R. Feldman(1)

(1)Department of Biology, University of Nevada, Reno; (2)Department of Biology, California State University, Bakersfield

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.

Differential detoxification strategies in closely related herbivore species across a sharp ecotone

Lilly Whitehead(1), Casey Philbin(2,3), Lora Richards(1)

(1)Department of Biology, University of Nevada, Reno; (2)Hitchcock Center for Chemical Ecology, University of Nevada, Reno; (3)Department of Chemistry, University of Nevada, Reno

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.

Solvent-dependent photostability of lichen pigments (+)-usnic acid and anthrarufin

Nayeli Stopani-Humes, Tanzil Mahmud, Christopher Jeffrey

Department of Chemistry, University of Nevada, Reno

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.

Selective ammonia production from electrochemical nitrate reduction using Nafion-covered Cu electrodeposits

Profulla Mondol, Jashmeen K. Thind, and Christopher J. Barile

Department of Chemistry, University of Nevada, Reno

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.

Investigating local environment effects on intramolecular proton transfer dynamics in anthrarufin

Yingshi Feng, Christopher S. Jeffrey, Matthew J. Tucker

Department of Chemistry, University of Nevada, Reno

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.

Photochromic 2,2’-bipyridine sulfur trioxide complex

Cameron K. Locke, Connor Filbin, Christopher Mallon, Olajumoke Adeyiga, Samuel O. Odoh, Matthew Tucker, and Ying Yang

Department of Chemistry, University of Nevada, Reno

Photochromic bipyridines typically appear in the form of N, N’-disubstituted-bipyridines, known as viologens. Following irradiation with UV light, a viologen undergoes one-electron transfer to form a blue-colored radical cation. Many metal complexes with 2,2’-bipyridine ligands are also vibrantly colored due to the metal-to-ligand charge transfer. In this presentation, we will discuss another photo-responsive mechanism of metal-free 2,2’-bipyridine derivatives through photo-activated interactions with sulfur oxide and its applications in photo-switchable polymers. Through density functional theory (DFT) calculations, we found a local minimum conformation for the 2,2’-bipyridine-sulfur oxide complex which can be populated by photo-activation in the near-UV to the visible range. This conformation features a shorter N-S bond distance compared to the lowest energy structures, which destabilizes the HOMO and shortens the HOMO-LUMO gap to the visible portion. It represents a new class of molecular switches that can be adapted to various photo-responsive materials. Experimentally, the 2,2’-bipyridine derivatives synthesized in this study undergo a reversible color change from light yellow to magenta upon irradiation in UV to the visible light range with a new absorption peak at 550 nm. EPR spectroscopy did not show any detectable free radicals in the colored form, confirming a photochromic pathway that is different from viologens. The photochromism is reversible in solution and in polymers. Different from many photochromic systems, in polymers, the colored photoproduct can stay stable in the dark at room temperature. It then reverses back to the non-irradiated state by heating.

Metabolomics guided discovery of novel flavone-sesquiterpene conjugate raduladioxanolide from a chemical heritability experiment of Piper scintillans

Megan Burroughs(1), Casey S. Philbin(1,2), Lora A. Richards(3), Lee A. Dyer(3), Thomas L. Parchman(3), Christopher S. Jeffrey(1)

(1)Department of Chemistry, University of Nevada, Reno; (2)Hitchcock Center for Chemical Ecology, University of Nevada, Reno; (3)Department of Biology, University of Nevada, Reno

Mass spectrometry and 1H-NMR based metabolomic and genomic analysis of field collected parents and their offspring within a common garden experiment revealed 3-distinct genetically driven and highly heritable chemotypes in the tropical shrub species, P. scintillans (Piperaceae) in Costa Rica. Preparatory scale isolation of the key minor components of the chemotype with highest heritabilities was conducted using mass spectrometry guided prep-HPLC and preparatory thin layer chromatography. Determination of the targeted compound led to the discovery of a novel flavone-sesquiterpene conjugate, named raduladioxanolide, which was structurally characterized by NMR, CD, IR, and UV spectroscopy. The hypothesized biosynthetic precursors were isolated and supported the conjugation of flavone and a guaianolide sesquiterpene via a Diels-Alder cycloaddition reaction between an ortho-quinone of the flavone and a tri-substituted double bond of the sesquiterpene to produce raduladioxanolide. Other conjugates of this type have been identified using tandem mass spectrometry through observation of the neutral loss of the flavonoid moiety. Isolation efforts to characterize these related conjugates are currently underway. The approach leading to the discovery, the details of the structure determination, and our biosynthetic hypothesis of raduladioxanolide will be presented.

Electrochemical studies of the novel neolignan cabagranins, toward a total synthesis, and their implications in their biosynthesis

Zachary Ledvina(1), Celso Oliveira(2), Christopher Barile(1), Christopher S. Jeffrey(1)

(1)Department of Chemistry, University of Nevada, Reno; (2)Department of Entomology, University of Wisconsin, Madison

The generation of phytochemical diversity is essential to the maintenance of biodiversity and has been found to be an important variable driving plant-insect interactions. Recently, our group discovered a set of related neolignans and a novel neolignan-terpene conjugate from the tropical plant species P. cabagranum (Costa Rica). Consideration of the biosynthetic link between the isolated compounds led to the hypothesis that enone cabagranin C could be produced through a series of oxidative steps starting with eugenol. The formation of the terpene-neolignan conjugate could then be rationalized by reaction of the arylvinyl ketone with alpha-phellandrene, through an electrocatalytic Diels-Alder reaction. Our electrochemical studies starting from eugenol, the studies toward the biomimetic synthesis of cabagranin D, and the implications of the proposed redox neutral processes in the generation of phytochemical diversity will be presented.

Improved Performance of Positive-ion mode Free Radical-initiated Peptide Sequencing with para-TEMPO-Bz

Kemi E. Osho, Kim A. Wasik, Laina M. Geary, and Nicholas B. Borotto

Department of Chemistry, University of Nevada, Reno

Tandem mass spectrometry (MS/MS) is an analytical tool often employed for the fragmentation and sequencing of protein ions and the annotation of protein post-translational modification. Free radical-initiated peptide sequencing (FRIPS) is one such MS/MS technique and it generates sequence informative ions via collisionally-initiated radical chemistry. While FRIPS is highly effective at generating product ions when applied to cations, radical initiation competes directly with typical CID pathways. Our approach seeks to enhance the performance of FRIPS by leveraging a novel radical precursor, para-TEMPO-Bz. This approach is observed because when multiply charged cations of conjugated ACTH 1-14, β-amyloid 10-20, substance p, and melittin are collisionally activated a series of high abundance mass losses are observed which syphon ion abundance from the radically generated species. This loss of ion abundance reduces the sequence coverage generated by FRIPS fragmentation. In this work, it was hypothesized that these mass losses were instigated by the ortho-orientation of the radical precursor undergoing facile conversion into five- or six-membered intermediates and that the para-precursor would not undergo the same chemistry. To test this hypothesis, para-TEMPO-Bz was synthesized, conjugated to these peptides, and each conjugated peptide was collisionally activated. And indeed, the complete elimination of these undesired collisional processes was observed in some of the analyzed peptides and the significant increase in radical precursor ion abundance. Moreover, a significant increase was observed in the sequence coverage generated when the pTEMPO-Bz is utilized. From these results, p-TEMPO-Bz significantly improves the performance of positive-ion mode FRIPS and may be a suitable alternative to the currently utilized ortho-TEMPOBz-based FRIPS.

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