Coccolithophoriden und Ozeanversauerung: Von monoklonalen zu Mehr-Arten Systemen

The human induced global climate change has severe consequences for the marine systems. Oceans have absorbed 50% of anthropogenic carbon dioxide emissions, consequently, attenuating global atmospheric warming. However, once entering the oceans, CO2 loses its inert characteristics. By the reaction with water it forms carbonic acid resulting in the phenomenon latterly referred to as ocean acidification. In the last two centuries, with the beginning of the industrial revolution, the global mean surface pH was already reduced by 0.1 units. Within the next 90 years the acidity level is believed to drop by another 0.35 units. Based on a simple causality a given atmospheric partial pressure of CO2 can easily be transferred into surface ocean carbon chemistry. Nevertheless, implications for the marine biota caused by increasing ocean acidification are complex and difficult to assess. Although the effects of rising pCO2 have been shown on single species of corals, pteropods, foraminifera, diverse phytoplankton species and larvae of echinoderms and fishes, research is far from understanding correlations between single species response and ecosystem functioning. Based on the importance as the most prominent pelagic calcifier and their hypothesised functioning as carbon export ballast, coccolithophores are among the best evaluated species with respect to ocean acidification. Calcification and photosynthesis has turned out to be sensitive to future conditions, however, with highly variable responses among species and species strains. For most analysed species calcification declined with rising pCO2, also the production of organic matter usually decreased, but turned out to rise for Gephyrocapsa oceanica. Surprisingly, the species Coccolithus braarudii appeared to be insensitive to an elevation of pCO2 from 380 µatm to 750 µatm. Based on this intriguing picture of coccolithophore response to ocean acidification this dissertation was concerned with the following questions: Does the insensitivity of C. braarudii to ocean acidification hold true for higher CO2 concentrations and what is the reason for the different sensitivities of various species? Does the total population carbon accumulation in the stationary phase reveal what could have been expected from the physiological ocean acidification response while undergoing exponential growth and are these results, gathered in the stationary phase dependent on the applied nutrient ratio? Higher diversity is known to positively affect stability and resistance of ecosystems. Is it possible to extrapolate single species responses to ocean acidification to multi-species responses? The study presented in chapter I affirms the insensitivity of C. braarudii for a pCO2 range up to 800 µatm. Further increases to values of 2500 µatm, however, revealed a decrease in calcification. The biomass production by photosynthesis, showed an optimum at 1600 µatm pCO2. An optimum response has been observed earlier for the coccolithophore Calcidiscus leptoporus, however, for calcification. Based on these findings, an increase in dissolved inorganic carbon, i.e. increase in the substrate for calcification and photosynthesis was discussed as to be an advantage in the first place. At a certain CO2 concentration the linked reduction in pH might negatively affect physiological processes and antagonise the positive effects of increasing substrate. For these reasons, the variable sensitivities of coccolithophores might not arise from different intracellular mechanisms but rather different optima for CO2, 〖"HCO" 〗_3^- and H+. Studies on coccolithophores in the exponential growth phase and their response to ocean acidification have proven to be useful to analyse underlying physiological mechanisms. Additional experiments concerning total population carbon accumulation in the stationary phase might allow for first estimates on ecosystem functioning of single species populations with respect to ocean acidification. Chapter II describes an experiment, allowing Emiliania huxleyi and Gephyrocapsa oceanica to deplete nutrients and stay for three days in the stationary phase. Under the stress of phosphate limitation and three different ocean acidification scenarios cells revealed an increase in cell size in the stationary phase. This increase was attenuated with rising pCO2. Also the accumulations of calcite and organic carbon on a population level showed pronounced responses to increasing ocean acidification. These responses, however, were significantly dependent on the nutrient ratio the cells had to face. The biomass decrease for Emiliania huxleyi and increase for Gephyrocapsa oceanica as well as the decrease in calcite of both species were more pronounced for cells growing under a high N:P ratio compared to cells facing a Redfield ratio. This was contrary to the response on a population level. Due to changing nutrient uptake the more sensitive “High N:P” treatments were able to produce more cells with rising pCO2, resulting in an attenuated calcite and biomass accumulation decrease. Based on these results, estimations of the future influence of coccolithophores on both atmospheric pCO2 feedback and carbon export should take the affects of nutrient limitation on cell physiology stronger into consideration. Despite their relevance for the physiological mechanisms of coccolithophores, hitherto published studies are far from assessing whole ecosystem functioning with respect to ocean acidification. Diversity is known to have positive effects on ecosystem stability and resistance, nevertheless, community interactions of coccolithophores and their collective response to rising pCO2 were so far neglected. To gain first indications of the potential community interaction of coccolithophores, the experiment presented in chapter III allows three species, namely G. oceanica, E. huxleyi and C. braarudii to grow alone and within a community. Under the stress of nutrient limitation and three different pCO2 single species cultures revealed a decrease in the population calcite and biomass accumulation. In contrary, the multiple species approach showed no significant variation in photosynthesis and calcification. This suggests a higher resilience caused by community interactions. This dissertation underlines the importance of single species approaches to understand the underlying physiological processes with respect to ocean acidification. But it also shows our ignorance of marine ecosystem resilience and therefore, suggests that it might not be appropriate to extrapolate the changes in calcification rates of single species to ocean acidification onto a global scale. In near future it needs further experiments to evaluate the role of diversity and nutrient ratios as a positive factor for resilience and resistance of coccolithophore ecosystems.Der vom Menschen induzierte Klimawandel hat nicht nur eine Temperaturerhöhung der Atmosphäre und der Ozeane zur Folge. Wenn vielfach in den Medien bereits von dem „anderen CO2-Problem“ gesprochen wird, dann ist die Rede von der Ozeanversauerung. Zwar ist Kohlendioxid in der Atmosphäre inert, reagiert allerdings mit Wasser zu Kohlensäure und führt somit in den Ozeanen zu einer Erniedrigung des pH-Wertes. Bis heute haben die Weltmeere 50% der vom Menschen verursachten Kohlendioxidemissionen aus fossilen Brennstoffen aufgenommen. Dies hat auf der einen Seite zu verringerten Anstieg der atmosphärischen CO2-Konzentrationen geführt, andererseits wurde dadurch in den letzten 100 Jahren der globale Mittelwert des Oberflächen-pH-Wertes bereits um 0,1 Einheiten gesenkt. In diesem Jahrhundert könnte dieser Wert bei weiterschreitenden Emissionen um weitere 0,35 Einheiten sinken. So einfach die Meereschemie bei bekannten atmosphärischen CO2-Konzentrationen zu berechnen ist, so schwer ist es, die vielschichtigen möglichen biologischen Konsequenzen der Versauerung abzuschätzen und zu beurteilen. Vielfach konnten Auswirkungen auf die Biologie von Phytoplankton, Echinodermen- und Fischlarven, Pteropoden und Korallen gezeigt werden, dennoch ist die Wissenschaft noch weit davon entfernt, Zusammenhänge, die über die Reaktion von einzelnen Arten hinausgehen, zu verstehen und zu beurteilen. Ein besonderes Augenmerk lag in den vergangen Jahren auf den Coccolithophoriden. Diese kalzifizierenden Einzeller produzieren neben den Flügelschnecken und Foraminiferen 50% des ozeanischen Kalks und spielen somit eine wichtige Rolle in der Ballast-Hypothese. In dieser Theorie wird der Export von organischer Materie maßgeblich von Mineralien getriebenen. Zwar spielen Coccolithophoriden in Bezug auf die globale ozeanische Primärproduktion neben anderen Phytoplankton Arten, wie z. B. den Diatomeen, nur eine untergeordnete Rolle; sie sind dennoch die einzigen Primärproduzenten, die mit ihrer Kalzifizierung direkt die Pufferkapazität der Ozeane beeinflussen. Bisherige Studien konnten zeigen, dass sowohl die Kalzifizierung als auch die Photosynthese von verschiedenen Coccolithophoriden durch die Ozeanversauerung beeinflusst werden. Allerdings zeigte sich zwischen den verschiedenen Arten, aber auch zwischen verschiedenen Stämmen derselben Art, Unterschiede in der Sensitivität. Insbesondere die Produktion von partikulärem organischem Kohlenstoff durch die Photosynthese zeigte sich bei einigen Arten durch Ozeanversauerung stimuliert, bei anderen wiederum gehemmt. Bei bis dato einer einzigen Art, Coccolithus braarudii, zeigte eine Erhöhung des pCO2 von 380 auf 750 µatm keinerlei Auswirkungen auf die beiden Prozesse Photosynthese und Kalzifizierung. Auf Grund dieser Ergebnisse beschäftigt sich die vorliegende Dissertation mit folgenden drei Fragen: Bestätigt sich die gezeigte Insensibilität von C. braarudii auf Ozeanversauerung auch bei höheren pCO2-Werten und was ist der Grund für die unterschiedlichen Sensibilitäten verschiedener Arten? Die bisherigen Ergebnisse zu den Effekten der Ozeanversauerung auf Coccolithophoriden wurden weitestgehend in der exponentiellen Wachstumsphase der Zellen erzielt. Zeigen Coccolithophoriden dieselben Reaktionen, wenn sie sich in der stationären Phase befinden und hat das Verhältnis der Nährstoffe vor der Limitation Auswirkungen auf die Ergebnisse? Aus früheren Studien ist bekannt, dass erhöhte Diversität von Ökosystemen zu einer erhöhten Stabilität und Resistenz gegenüber Stress führt. Daraus ergibt sich die Frage, ob Mehr-Arten-Systeme die Ergebnisse liefern, die aus Einzelkulturen zu erwarten wären? In Kapitel I dieser Dissertation konnte die Insensibilität von C. braarudii für CO2-Partialdrücke bis 800 µatm bestätigt werden. Wurden die Partialdrücke allerdings auf Werte bis 2500µatm erhöht, konnte auch bei dieser Art eine Reduktion der Kalzifizierung beobachtet werden. Die Biomasse-Produktion offenbarte ein Optimum für pCO2, dabei konnte bis etwa 1600 µatm ein Anstieg, für höhere CO2-Konzentrationen ein Abfall der Produktion verzeichnet werden. Schon bei Calcidiscus leptoporus wurde ein Optimum-Verlauf in Bezug auf Ozeanversauerung beobachtet, allerdings für die Kalzifizierung. Es wird daher diskutiert, dass der Anstieg im gelösten anorganischen Kohlenstoff und die damit verbundene Erhöhung des Substrats für Photosynthese und Kalzifizierung sich in erster Linie als Vorteil auswirken könnten. Ab einer gewissen CO2-Konzentration könnte sich die damit verknüpfte Reduktion des pH-Wertes als negativ herausstellen, wodurch Photosynthese und Kalzifizierung negativ beeinflusst werden könnten. Demzufolge wären die unterschiedlichen Reaktionen verschiedener Arten nicht auf unterschiedliche intrazelluläre Mechanismen zurück zu führen. Vielmehr könnten unterschiedliche Optima für CO2, 〖"HCO" 〗_3^- und H+ der Grund für die verschiedenen Reaktionen auf Ozeanversauerung sein. Ozeanversauerungsstudien an Coccolithophoriden in ihrer exponentiellen Wachstumsphase geben Einblicke in deren Physiologie und erlauben Vergleiche zwischen den Arten. Für eine Abschätzung der Folgen von Ozeanversauerung auf die gesamte Ökosystemleistung einer Population bringen Versauerungsstudien zu Coccolithophoriden in der stationären Phase zusätzliche Erkenntnisse. In Kapitel II wurden den Arten Emiliania huxleyi und Gephyrocapsa oceanica die Möglichkeit gegeben, ihre Nährstoffe aufzubrauchen und drei Tage in der stationären Phase zu verweilen. Dabei wurde die Größenzunahme der Zellen unter Phosphatlimitierung durch den CO2-Partialdruck gehemmt. Die Reaktionen von Kalzifizierung und Photosynthese auf zunehmende Ozeanversauerung waren allerdings abhängig von den Nährstoffverhältnissen, denen die Arten ausgesetzt wurden. Zellen, die unter einem „Hoch N:P“-Nährstoffverhältnis gewachsen waren, zeigten auf die Versauerung deutlich ausgeprägtere Reaktionen in der Akkumulation von organischen und anorganischem Kohlenstoff, als solche Zellen, die einem Redfield-Verhältnis ausgesetzt wurden. Bezogen auf die Akkumulation von Kohlenstoff auf Populationsebenen, zeigte sich genau das entgegengesetzte Bild. Die empfindlicheren Zellen der „Hoch N:P“-Ansätze konnten auf Grund einer veränderten Nährstoffnutzung deutlich mehr Zellen bei erhöhtem CO2 produzieren, wodurch sich die abfallenden Trends der Biomasse- und Kalk-Akkumulation auf Zellebene fast (Kalk) oder ganz (Biomasse) ausglichen. Für eine Beurteilung des zukünftigen Einflusses von Coccolithophoriden auf den atmosphärischen pCO2 und ihre Funktion in den Kohlenstoffexport-Mechanismen sollten daher die Auswirkungen der Nährstofflimitierung auf die Zellphysiologie stärker berücksichtigt werden. Die meisten bisherigen Studien sind trotz ihrer Bedeutung für die Erforschung der physiologischen Mechanismen von Coccolithophoriden noch weit von der Beurteilung ganzer Ökosysteme entfernt. Bis dato wurden Gemeinschaftsinteraktionen für die Beurteilung der Ozeanversauerung völlig außen vor gelassen. Dabei ist bekannt, dass sich eine erhöhte Diversität positiv auf die Ökosystemleistung und -stabilität auswirkt. Um einen ersten Eindruck zu erlangen, wurden daher in einem Experiment, beschrieben in Kapitel III, drei verschiedene Arten einzeln und als Gemeinschaft dem Stress der Ozeanversauerung ausgesetzt. Die Kalk- und Biomasse-Anteile, die jede Zelle in der stationären Phase aufbaute, verhielten sich unter Einfluss der Versauerung dabei in den Einzelkulturen so, wie man es aus früheren Studien vermuten würde. Alle drei Arten reduzierten ihren Kalkanteil, die Organik hingegen stieg für G. oceanica an und blieb unverändert für E. huxleyi und C. braarudii. Auf der Ebene der Population wurde sowohl die Organik als auch der Kalk pro Liter negativ durch eine Versauerung beeinflusst. Die Gesamtleistung der Gemeinschaft hingegen zeigte sich von der Versauerung unbeeinträchtigt. Weder in der Kalzifizierung, noch in der Photosynthese gab es wesentliche Unterschiede zwischen den verschiedenen pCO2-Ansätzen. Damit deutet sich an, dass Mehr-Arten-Systeme widerstandsfähiger gegenüber dem Stress der Ozeanversauerung sein könnten. Die Auswirkungen der Ozeanversauerung auf die Ökosysteme dieser Ozeane sind noch in keinster Weise verstanden. Diese Dissertation unterstreicht die Bedeutung von Experimenten an einzelnen Arten, um deren physiologische Effekte besser zu verstehen. Sie zeigt aber auch auf, dass es wahrscheinlich nicht angebracht ist, die Effektstärke aus diesen Experimenten auf die globale Kalzifizierung zu extrapolieren. Es müssen in der nahen Zukunft weitere Experimente durchgeführt werden, um die Funktion der Diversität als Stresspuffer besser verstehen zu können

Evidence for a Ru4+^{4+} Kondo Lattice in LaCu3_3Ru4_4O12_{12}

Rare $d$-electron derived heavy-fermion properties of the solid-solution series LaCu$_3$Ru$_x$Ti$_{4-x}$O$_{12}$ were studied for $1 \leq x \leq 4$ by resistivity, susceptibility, specific-heat measurements, and magnetic-resonance techniques. The pure ruthenate ($x = 4$) is a heavy-fermion metal characterized by a resistivity proportional to $T^2$ at low temperatures $T$. The coherent Kondo lattice formed by the localized Ru 4$d$ electrons is screened by the conduction electrons leading to strongly enhanced effective electron masses. By increasing titanium substitution the Kondo lattice becomes diluted resulting in single-ion Kondo properties like in the paradigm $4f$-based heavy-fermion compound Ce$_x$La$_{1-x}$Cu$_{2.05}$Si$_2$ [M. Ocko {\em et al.}, Phys. Rev. B \textbf{64}, 195106 (2001)]. In LaCu$_3$Ru$_x$Ti$_{4-x}$O$_{12}$ the heavy-fermion behavior finally breaks down on crossing the metal-to-insulator transition close to $x = 2$.Comment: 9 pages, 8 figure

New Advances in the Treatment of Metastatic Pancreatic Cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) is characterised by an extremely poor overall survival (OS) compared to other solid tumours. As the incidence of the disease is rising and the treatment options are limited, PDAC is projected to be the 2nd leading cause of cancer-related deaths in the United States by 2030. A majority of patients are not eligible for curative resection at the time of diagnosis, and those that are resected will often relapse within the first few years after surgery. Summary: Until recently, the nucleoside analogue gemcitabine has been the standard of care for patients with non-resectable PDAC with only marginal effects on OS. In 2011, the gemcitabine-free FOLFIRINOX regimen (folinic acid, fluorouracil, irinotecan and oxaliplatin) showed a significant survival advantage for patients with metastatic PDAC in a phase III trial. In 2013, the Metastatic Pancreatic Adenocarcinoma Trial phase III trial with nano-formulated albumin-bound paclitaxel (nab-paclitaxel) in combination with gemcitabine also resulted in a significant survival extension compared to gemcitabine monotherapy. However, both intensified therapy regimens show a broad spectrum of side effects and patients need to be carefully selected for the most appropriate protocol. Key Message: In this study, recent advances in the chemotherapeutic options available to treat metastatic PDAC and their implications for today's treatment choices are reviewed

Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO2_2

We report crystal structure and magnetic behavior of the triangular antiferromagnet KYbO$_2$, the A-site substituted version of the quantum spin liquid candidate NaYbO$_2$. The replacement of Na by K introduces an anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice expansion. Compared to NaYbO$_2$, both Curie-Weiss temperature and saturation field are reduced by about 20% as the result of the increased Yb--O--Yb angles, whereas the $g$-tensor of Yb$^{3+}$ becomes isotropic with $g=3.08(3)$. Field-dependent magnetization shows the plateau at 1/2 of the saturated value and suggests the formation of the up-up-up-down field-induced order in the triangular AYbO$_2$ oxides (A = alkali metal), in contrast to the isostructural selenides that exhibit the 1/3 plateau and the up-up-down field-induced order

Evidence for electronically-driven ferroelectricity in the family of strongly correlated dimerized BEDT-TTF molecular conductors

By applying measurements of the dielectric constants and relative length changes to the dimerized molecular conductor $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl, we provide evidence for order-disorder type electronic ferroelectricity which is driven by charge order within the (BEDT-TTF)$_2$ dimers and stabilized by a coupling to the anions. According to our density functional theory calculations, this material is characterized by a moderate strength of dimerization. This system thus bridges the gap between strongly dimerized materials, often approximated as dimer-Mott systems at 1/2 filling, and non- or weakly dimerized systems at 1/4 filling exhibiting charge order. Our results indicate that intra-dimer charge degrees of freedom are of particular importance in correlated $\kappa$-(BEDT-TTF)$_2$X salts and can create novel states, such as electronically-driven multiferroicity or charge-order-induced quasi-1D spin liquids.Comment: 6 pages, 4 figures + Supplementary Information (8 pages, 8 figures

Real-World Clinical Practice of Intensified Chemotherapies for Metastatic Pancreatic Cancer: Results from a Pan-European Questionnaire Study

Introduction: Recently, FOLFIRINOX and gemcitabine + nab-paclitaxel have been introduced as a novel intensified chemotherapy regimen for patients with metastasized pancreatic cancer. This study aims to analyze the real-world clinical practice with FOLFIRINOX and gemcitabine + nab-paclitaxel across Europe. Methods: Invitations to participate in an anonymous web-based questionnaire were sent via e-mail to 5,420 doctors in 19 European countries through the network of national gastroenterological, oncological, surgical and pancreatic societies as well as the European Pancreatic Club. The questionnaire consisted of 20 questions, 14 regarding the use of intensified chemotherapy, 4 regarding demographics of the participants, and 1 to verify the active involvement in the management of metastatic pancreatic cancer. Results: Two hundred and thirteen responses were received and 153 entries were valid for analysis. Of those, 63.4% came from an academic institution, 51% were oncologists, and 52% treated more than 25 cases per year. A majority of responses (71%) were from Italy (40%), Germany (23%), and Spain (8%). As first-line therapy, 11% used gemcitabine +/- erlotinib, 42% used FOLFIRINOX, and 47% used gemcitabine + nab-paclitaxel. Of the intensified regimens, both were applied to equal parts, but the likelihood of protocol deviation was higher when using FOLFIRINOX (p < 0.01). FOLFIRINOX was considered more toxic than gemcitabine + nab-paclitaxel (neutropenia 88 vs. 68%; polyneuropathy 42 vs. 41%; rapid deterioration 42 vs. 31%). FOLFIRINOX was rated to achieve longer survival with an acceptable quality of life (52 vs. 44%). Moreover, 57% of participants thought that gemcitabine + nab-paclitaxel should be the backbone for further clinical trials in pancreatic cancer. Conclusion: Intensified chemotherapy is widely used in pancreatic cancer patients in Europe following its recent clinical approval. Interestingly, nab-paclitaxel and FOLFIRINOX were used at comparable frequency although the latter had to be de-escalated more often

Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide

Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO2), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO2 perturbation study in Kongsfjorden on the west coast of Spitsbergen (Norway), in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO2 levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured as high in comparison to low CO2 during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO2 effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO2 effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO2-related shifts in nutrient flow into different phytoplankton groups (mainly dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO2.publishedVersio

From genotypes to organisms: State-of-the-art and perspectives of a cornerstone in evolutionary dynamics

Understanding how genotypes map onto phenotypes, fitness, and eventually organisms is arguably the next major missing piece in a fully predictive theory of evolution. We refer to this generally as the problem of the genotype-phenotype map. Though we are still far from achieving a complete picture of these relationships, our current understanding of simpler questions, such as the structure induced in the space of genotypes by sequences mapped to molecular structures, has revealed important facts that deeply affect the dynamical description of evolutionary processes. Empirical evidence supporting the fundamental relevance of features such as phenotypic bias is mounting as well, while the synthesis of conceptual and experimental progress leads to questioning current assumptions on the nature of evolutionary dynamics-cancer progression models or synthetic biology approaches being notable examples. This work delves into a critical and constructive attitude in our current knowledge of how genotypes map onto molecular phenotypes and organismal functions, and discusses theoretical and empirical avenues to broaden and improve this comprehension. As a final goal, this community should aim at deriving an updated picture of evolutionary processes soundly relying on the structural properties of genotype spaces, as revealed by modern techniques of molecular and functional analysis.Comment: 111 pages, 11 figures uses elsarticle latex clas

Magnetization and specific heat of the dimer system CuTe2O5

We report on magnetization and specific heat measurements on single-crystalline CuTe2O5. The experimental data are directly compared to theoretical results for two different spin structures, namely an alternating spin-chain and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B 77, 224437 (2008)]. While the analysis of the specific heat does not allow to distinguish between the two models, the magnetization data is in good agreement with the 2D coupled dimer model.Comment: 5 pages, 3 figure

Spin-state dependent pressure responsiveness of Fe(<scp>ii</scp>)-based triazolate metal–organic frameworks

Fe(II)-containing Metal–Organic Frameworks (MOFs) that exhibit temperature-induced spin-crossover (SCO) are candidate materials in the field of sensing, barocalorics, and data storage. Their responsiveness towards pressure is therefore of practical importance and is related to their longevity and processibility. The impact of Fe(II) spin-state on the pressure responsiveness of MOFs is yet unexplored. Here we report the synthesis of two new Fe(II)-based MOFs, i.e. Fe(cta)2 ((cta)− = 1,4,5,6-tetrahydrocyclopenta[d][1,2,3]triazolate) and Fe(mta)2 ((mta)− = methyl[1,2,3]triazolate), which are both in high-spin at room temperature. Together with the isostructural MOF Fe(ta)2 ((ta)− = [1,2,3]triazolate), which is in its low-spin state at room temperature, we apply these as model systems to show how spin-state controls their mechanical properties. As a proxy, we use their bulk modulus, which was obtained via high-pressure powder X-ray diffraction experiments. We find that an interplay of spin-state, steric effects, void fraction, and absence of available distortion modes dictates their pressure-induced structural distortions. Our results show for the first time the role of spin-state on the pressure-induced structural deformations in MOFs and bring us a step closer to estimating the effect of pressure as a stimulus on MOFs a priori