Twisted carotenoids do not support efficient intramolecular singlet fission in the orange carotenoid protein

Singlet exciton fission is the spin-allowed generation of two triplet electronic excited states from a singlet state. Intramolecular singlet fission has been suggested to occur on individual carotenoid molecules within protein complexes, provided the conjugated backbone is twisted out-of-plane. However, this hypothesis has only been forwarded in protein complexes containing multiple carotenoids and bacteriochlorophylls in close contact. To test the hypothesis on twisted carotenoids in a 'minimal' one-carotenoid system, we study the orange carotenoid protein (OCP). OCP exists in two forms: in its orange form (OCPo), the single bound carotenoid is twisted, whereas in its red form (OCPr), the carotenoid is planar. To enable room-temperature spectroscopy on canthaxanthin-binding OCPo and OCPr without laser-induced photoconversion, we trap them in trehalose glass. Using transient absorption spectroscopy, we show that there is no evidence of long-lived triplet generation through intramolecular singlet fission, despite the canthaxanthin twist in OCPo

Transforming U.S. agriculture with crushed rock for CO2_2 sequestration and increased production

Enhanced weathering (EW) is a promising modification to current agricultural practices that uses crushed silicate rocks to drive carbon dioxide removal (CDR). If widely adopted on farmlands, it could help achieve net-zero or negative emissions by 2050. We report detailed state-level analysis indicating EW deployed on agricultural land could sequester 0.23-0.38 Gt CO$_2$ yr$^{-1}$ and meet 36-60 % of U.S. technological CDR goals. Average CDR costs vary between state, being highest in the first decades before declining to a range of $\sim\$$100-150 tCO$_2{}^{-1}$ by 2050, including for three states (Iowa, Illinois, and Indiana) that contribute most to total national CDR. We identify multiple electoral swing states as being essential for scaling EW that are also key beneficiaries of the practice, indicating the need for strong bipartisan support of this technology. Assessment the geochemical capacity of rivers and oceans to carry dissolved EW products from soil drainage suggests EW provides secure long-term CO$_2$ removal on intergenerational time scales. We additionally forecast mitigation of ground-level ozone increases expected with future climate change, as an indirect benefit of EW, and consequent avoidance of yield reductions. Our assessment supports EW as a practical innovation for leveraging agriculture to enable positive action on climate change with adherence to federal environmental justice priorities. However, implementing a stage-gating framework as upscaling proceeds to safeguard against environmental and biodiversity concerns will be essential

Operationalizing marketable blue carbon

The global carbon sequestration and avoided emissions potentially achieved via blue carbon is high (∼3% of annual global greenhouse gas emissions); however, it is limited by multidisciplinary and interacting uncertainties spanning the social, governance, financial, and technological dimensions. We compiled a transdisciplinary team of experts to elucidate these challenges and identify a way forward. Key actions to enhance blue carbon as a natural climate solution include improving policy and legal arrangements to ensure equitable sharing of benefits; improving stewardship by incorporating indigenous knowledge and values; clarifying property rights; improving financial approaches and accounting tools to incorporate co-benefits; developing technological solutions for measuring blue carbon sequestration at low cost; and resolving knowledge gaps regarding blue carbon cycles. Implementing these actions and operationalizing blue carbon will achieve measurable changes to atmospheric greenhouse gas concentrations, provide multiple co-benefits, and address national obligations associated with international agreements

A thermostable protein matrix for spectroscopic analysis of organic semiconductors

Advances in protein design and engineering have yielded peptide assemblies with enhanced and non-native functionalities. Here, various molecular organic semiconductors (OSCs), with known excitonic up- and down-conversion properties, are attached to a de novo-designed protein, conferring entirely novel functions on the peptide scaffolds. The protein-OSC complexes form similarly sized, stable, water-soluble nanoparticles that are robust to cryogenic freezing and processing into the solid-state. The peptide matrix enables the formation of protein-OSC-trehalose glasses that fix the proteins in their folded states under oxygen-limited conditions. The encapsulation dramatically enhances the stability of protein-OSC complexes to photodamage, increasing the lifetime of the chromophores from several hours to more than 10 weeks under constant illumination. Comparison of the photophysical properties of astaxanthin aggregates in mixed-solvent systems and proteins shows that the peptide environment does not alter the underlying electronic processes of the incorporated materials, exemplified here by singlet exciton fission followed by separation into weakly bound, localized triplets. This adaptable protein-based approach lays the foundation for spectroscopic assessment of a broad range of molecular OSCs in aqueous solutions and the solid-state, circumventing the laborious procedure of identifying the experimental conditions necessary for aggregate generation or film formation. The non-native protein functions also raise the prospect of future biocompatible devices where peptide assemblies could complex with native and non-native systems to generate novel functional materials

The Availability Heuristic, Intuitive Cost-Benefit Analysis, and Climate Change

Because risks are on all sides of social situations, it is not possible to be “precautionary” in general. The availability heuristic ensures that some risks stand out as particularly salient, whatever their actual magnitude. Taken together with intuitive cost-benefit balancing, the availability heuristic helps to explain differences across groups, cultures, and even nations in the assessment of precautions to reduce the risks associated with climate change. There are complex links among availability, social processes for the spreading of information, and predispositions. If the United States is to take a stronger stand against climate change, it is likely to be a result of available incidents that seem to show that climate change produces serious and tangible harm

Time-resolved photophysics of orange carotenoid protein trapped in trehalose-sucrose glass films

This thesis presents studies on the photophysics of the orange carotenoid protein (OCP), a natural single-carotenoid-binding protein found in cyanobacteria, here binding canthaxanthin. We initially studied OCP to test a hypothesis forwarded in studies of light-harvesting complexes (LHCs) from purple photosynthetic bacteria. A protein-induced carotenoid twist in some LHCs putatively sensitises intramolecular singlet fission (SF), thus yielding the relatively long-lived (microsecond) triplet states observed. SF has promise in boosting solar photovoltaic efficiency, among other applications with a presently unmet requirement of microsecond triplet lifetimes. OCP is among the simplest systems for a direct test of the twist-induced intramolecular SF hypothesis. To prevent artefacts associated with its native photoprotective function involving a light-induced conformational change, we trap OCP in a trehalose-sucrose glass matrix, which we demonstrate yields identical initial photophysics to conventional buffer measurements. We found that OCP-twisted canthaxanthin does not yield the triplet population promised by the aforementioned studies. Indeed, a follow-up study inspired by this work (included as an appendix here) shows that SF in those LHCs proceeds on adjacent carotenoid and bacteriochlorophyll molecules, and significantly contributes to solar energy harvesting. We then tested a recent suggestion in the OCP literature that the light-induced photoconversion in OCP is triggered by a long-lived carotenoid singlet-like feature, dubbed S*. By examination of the pump wavelength dependence on the OCP photophysics in films and in buffer, we show that S* does not correlate with the photoconversion yield, ruling out S* as a sole trigger of the process. Dark-adapted OCP was found to have significant ground-state heterogeneity, with S* arising from it. We follow up with a hypothesis that the trigger is instead through a <1% yield of intersystem crossing triplets, though we lack a direct measurement, owing to difficulty in measuring the low yield of photoproducts

Doctoral Education, Danger and Risk Management

This paper examines how risk management is reworking the doctoral supervisor/candidate relationship. We argue that a larger and more diverse population of doctoral students means special challenges for universities worldwide in managing doctoral programs to optimize their productivity and minimize the risk of failure, costliness and/or litigation. An effect of this is that professional and personal relationships in universities, as in many other public and private institutions, are being reshaped in order to be more closely aligned with risk minimization policy directives and strategies. To understand what effects such reshaping is having on doctoral education, we bring together anthropological theorising of risk with pedagogical theorising of power and identity in education contexts. This theoretical cross-over between anthropology and education situates the pedagogic work of doctoral training within a culturally constituted order of professional care and risk management. We utilize this framework to interrogate ‘soft marking’ as a specific domain in which risk minimization is producing new relational identities for both supervisors and students involved in doctoral studies programs

A Thermostable Protein Matrix for Spectroscopic Analysis of Organic Semiconductors

Advances in protein design and engineering have yielded peptide assemblies with enhanced and non-native functionalities. Here, various molecular organic semiconductors (OSCs), with known excitonic up- and down-conversion properties, are attached to a de novo-designed protein, conferring entirely novel functions on the peptide scaffolds. The protein-OSC complexes form similarly sized, stable, water-soluble nanoparticles that are robust to cryogenic freezing and processing into the solid-state. The peptide matrix enables the formation of protein-OSC-trehalose glasses that fix the proteins in their folded states under oxygen-limited conditions. The encapsulation dramatically enhances the stability of protein-OSC complexes to photodamage, increasing the lifetime of the chromophores from several hours to more than 10 weeks under constant illumination. Comparison of the photophysical properties of astaxanthin aggregates in mixed-solvent systems and proteins shows that the peptide environment does not alter the underlying electronic processes of the incorporated materials, exemplified here by singlet exciton fission followed by separation into weakly bound, localized triplets. This adaptable protein-based approach lays the foundation for spectroscopic assessment of a broad range of molecular OSCs in aqueous solutions and the solid-state, circumventing the laborious procedure of identifying the experimental conditions necessary for aggregate generation or film formation. The non-native protein functions also raise the prospect of future biocompatible devices where peptide assemblies could complex with native and non-native systems to generate novel functional materials