The growing interest in magnetic resonance imaging (MRI) for assessing regional lung function relies on the use of nuclear spin hyperpolarized gas as a contrast agent. The long gas‐phase lifetimes of hyperpolarized129Xe make this inhalable contrast agent acceptable for clinical research today despite limitations such as high cost, low throughput of production and challenges of129Xe imaging on clinical MRI scanners, which are normally equipped with proton detection only. We report on low‐cost and high‐throughput preparation of proton‐hyperpolarized diethyl ether, which can be potentially employed for pulmonary imaging with a nontoxic, simple, and sensitive overall strategy using proton detection commonly available on all clinical MRI scanners. Diethyl ether is hyperpolarized by pairwise parahydrogen addition to vinyl ethyl ether and characterized by1H NMR spectroscopy. Proton polarization levels exceeding 8 % are achieved at near complete chemical conversion within seconds, causing the activation of radio amplification by stimulated emission radiation (RASER) throughout detection. Although gas‐phase
Demonstration of parahydrogen‐induced polarization effects in hydrogenations catalyzed by heterogeneous catalysts instead of metal complexes in a homogeneous solution has opened an entirely new dimension for parahydrogen‐based research, demonstrating its applicability not only for the production of catalyst‐free hyperpolarized liquids and gases and long‐lived non‐equilibrium spin states for potential biomedical applications, but also for addressing challenges of modern fundamental and industrial catalysis including advanced mechanistic studies of catalytic reactions and operando NMR and MRI of reactors. This essay summarizes the progress achieved in this field by highlighting the research contributed to it by our colleague and friend Kirill V. Kovtunov whose scientific career ended unexpectedly and tragically at the age of 37. His role in this research was certainly crucial, further enhanced by a vast network of his contacts and collaborations at the national and international level.
more » « less- NSF-PAR ID:
- 10220692
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 22
- Issue:
- 8
- ISSN:
- 1439-4235
- Page Range / eLocation ID:
- p. 710-715
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract T 1relaxation of hyperpolarized diethyl ether (at partial pressure of 0.5 bar) is very efficient, withT 1of ca. 1.2 second, we demonstrate that, at low magnetic fields, the use of long‐lived singlet states created via pairwise parahydrogen addition extends the relaxation decay by approximately threefold, paving the way to bioimaging applications and beyond. -
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Abstract The para spin isomer of hydrogen gas possesses high nuclear spin order that can enhance the NMR signals of a variety of molecular species. Hydrogen is routinely enriched in the para spin state by lowering the gas temperature while flowing through a catalyst. Although parahydrogen enrichments approaching 100% are achievable near the H2liquefaction temperature of 20 K, many experimentalists operate at liquid nitrogen temperatures (77 K) due to the lower associated costs and overall simplicity of the parahydrogen generator. Parahydrogen that is generated at 77 K provides an enrichment value of ~51% of the para spin isomer; while useful, there are many applications that can benefit from low‐cost access to higher parahydrogen enrichments. Here, we introduce a method of improving parahydrogen enrichment values using a liquid nitrogen‐cooled generator that operates at temperatures less than 77 K. The boiling temperature of liquid nitrogen is lowered through internal evaporation into helium gas bubbles that are injected into the liquid. Changes to liquid nitrogen temperatures and parahydrogen enrichment values were monitored as a function of helium gas flow rate. The injected helium bubbles lowered the liquid nitrogen temperature to ~65.5 K, and parahydrogen enrichments of up to ~59% were achieved; this represents an ~16% improvement compared with the expected parahydrogen fraction at 77 K. This technique is simple to implement in standard liquid nitrogen‐cooled parahydrogen generators and may be of interest to a wide range of scientists that require a cost‐effective approach to improving parahydrogen enrichment values.
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Abstract Background Faculty Learning Communities (FLCs) and Faculty Online Learning Communities (FOLCs) are ways to support STEM faculty implementing research-based curricula. In these communities, faculty facilitators take on the role of sharing expertise and promoting discussion. However, as members gain more experience, their needs change from addressing logistical to pedagogical issues. Hence, facilitators need to change their practices in response. However, there is little research on the mechanisms of faculty facilitator change. In this article, we provide a case study of a specific STEM FOLC facilitator and demonstrate the usefulness of a teacher change model to investigate facilitator change.
Results Guided by our adaptation of the
Interconnected Model of Professional Growth (IMPG), we conducted interviews with FOLC facilitators, and selected a case facilitator who reported changes in facilitation goals and strategies over time. The model helped us identify specific areas of change and potential mechanisms for these changes. Using themes of change identified in the case facilitator interview, we developed coding schemes to analyze his FOLC meetings over a 2-year period. We found empirical evidence from multiple data sources, including FOLC meetings and facilitator reflections, that supported the change themes, including: changing his role as an “expert” by sharing his own expertise less and drawing on others’ expertise more frequently, changing his response to members’ comments by jumping in to answer less frequently and withholding his own responses more often to encourage member sharing, and a change in group discussions towards less logistical and more pedagogical conversations.Conclusions Our findings suggest that the IMPG can be fruitfully adapted to study facilitator change. A diagrammatic representation of the IMPG provides a description the types of change the case facilitator experienced and the factors that supported those changes. We discuss how the methodology used to analyze facilitator actions in FOLC group meetings may be useful to study other types of professional growth. Finally, because our analytical model allowed us to identify mechanisms of facilitator change, we describe the implications and provide suggestions to support facilitators in other faculty community groups.
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Abstract Side‐arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in‐vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous‐flow reactor, where separation from the solid catalysts is straightforward. Using a TiO2‐nanorod supported Rh catalyst, we demonstrate continuous‐flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube‐in‐tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl‐acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch‐mode technique of parahydrogen bubbling through a suspension of the same catalyst.
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Abstract Karl von Frisch, one of the leading zoologists of the twentieth century and co-founder of the Journal of Comparative Physiology A, has been frequently portrayed as an opponent of the Nazi regime because he, as a ‘quarter-Jew,’ faced the threat of forced retirement from his position as a professor at the University of Munich during the Third Reich. However, doubts about an active opposition role have surfaced in recent years. A litmus test for assessing the validity of this notion is provided by our discovery that four of the six core members of the anti-Nazi resistance group ‘White Rose’—Sophie Scholl, Hans Scholl, Christoph Probst, and Alexander Schmorell—were his students. When they were arrested, sentenced to death, and executed, he seemed to ignore this historic event, both during and after World War II—in line with his belief that resistance leads to self-destruction, and research can flourish only by ignoring what happens around oneself. On the other hand, this seemingly apolitical attitude did not prevent him from making use of politics when it served his interests. Such actions included his (pseudo-)scientific justification of forced sterilization of people suffering from hereditary disorders during the Third Reich and his praise of the Nazi government’s efforts to “keep races pure.” As unsettling as these and some other political views and actions of Karl von Frisch are, they enabled him to carry out several critical pieces of his research agenda during the Third Reich, which three decades later earned him a Nobel Prize.
