HCOOH disproportionation to MeOH promoted by molybdenum PNP complexes.

Molybdenum(0) complexes with aliphatic aminophosphine pincer ligands have been prepared which are competent for the disproportionation of formic acid, thus representing the first example so far reported of non-noble metal species to catalytically promote such transformation. In general, formic acid disproportionation allows for an alternative access to methyl formate and methanol from renewable resources. MeOH selectivity up to 30% with a TON of 57 could be achieved while operating at atmospheric pressure. Selectivity (37%) and catalyst performance (TON = 69) could be further enhanced when the reaction was performed under hydrogen pressure (60 bars). A plausible mechanism based on experimental evidence is proposed.

Correction: HCOOH disproportionation to MeOH promoted by molybdenum PNP complexes.

[This corrects the article DOI: 10.1039/D1SC04181A.].

Comparing the effects of climate and land use on surface water quality using future watershed scenarios.

Eutrophication of freshwaters occurs in watersheds with excessive pollution of phosphorus (P). Factors that affect P cycling and transport, including climate and land use, are changing rapidly and can have legacy effects, making future freshwater quality uncertain. Focusing on the Yahara Watershed (YW) of southern Wisconsin, USA, an intensive agricultural landscape, we explored the relative influence of land use and climate on three indicators of water quality over a span of 57 years (2014-2070). The indicators included watershed-averaged P yield from the land surface, direct drainage P loads to a lake, and average summertime lake P concentration. Using biophysical model simulations of future watershed scenarios, we found that climate exerted a stronger influence than land use on all three indicators, yet land use had an important role in influencing long term outcomes for each. Variations in P yield due to land use exceeded those due to climate in 36 of 57 years, whereas variations in load and lake total P concentration due to climate exceeded those due to land use in 54 of 57 years, and 52 of 57 years, respectively. The effect of land use was thus strongest for P yield off the landscape and attenuated in the stream and lake aquatic systems where the influence of weather variability was greater. Overall these findings underscore the dominant role of climate in driving inter-annual nutrient fluxes within the hydrologic network and suggest a challenge for land use to influence water quality within streams and lakes over timescales less than a decade. Over longer timescales, reducing applications of P throughout the watershed was an effective management strategy under all four climates investigated, even during decades with wetter conditions and more frequent extreme precipitation events.

Scenarios reveal pathways to sustain future ecosystem services in an agricultural landscape.

Sustaining food production, water quality, soil retention, flood, and climate regulation in agricultural landscapes is a pressing global challenge given accelerating environmental changes. Scenarios are stories about plausible futures, and scenarios can be integrated with biophysical simulation models to explore quantitatively how the future might unfold. However, few studies have incorporated a wide range of drivers (e.g., climate, land-use, management, population, human diet) in spatially explicit, process-based models to investigate spatial-temporal dynamics and relationships of a portfolio of ecosystem services. Here, we simulated nine ecosystem services (three provisioning and six regulating services) at 220 × 220 m from 2010 to 2070 under four contrasting scenarios in the 1,345-km2 Yahara Watershed (Wisconsin, USA) using Agro-IBIS, a dynamic model of terrestrial ecosystem processes, biogeochemistry, water, and energy balance. We asked (1) How does ecosystem service supply vary among alternative future scenarios? (2) Where on the landscape is the provision of ecosystem services most susceptible to future social-ecological changes? (3) Among alternative future scenarios, are relationships (i.e., trade-offs, synergies) among food production, water, and biogeochemical services consistent over time? Our results showed that food production varied substantially with future land-use choices and management, and its trade-offs with water quality and soil retention persisted under most scenarios. However, pathways to mitigate or even reverse such trade-offs through technological advances and sustainable agricultural practices were apparent. Consistent relationships among regulating services were identified across scenarios (e.g., trade-offs of freshwater supply vs. flood and climate regulation, and synergies among water quality, soil retention, and climate regulation), suggesting opportunities and challenges to sustaining these services. In particular, proactive land-use changes and management may buffer water quality against undesirable future climate changes, but changing climate may overwhelm management efforts to sustain freshwater supply and flood regulation. Spatially, changes in ecosystem services were heterogeneous across the landscape, underscoring the power of local actions and fine-scale management. Our research highlights the value of embracing spatial and temporal perspectives in managing ecosystem services and their complex interactions, and provides a system-level understanding for achieving sustainability of the food-water-climate nexus in agricultural landscapes.

Exploring multiple binding sites of an indoloquinoline in triple-helical DNA: a paradigm for DNA triplex-selective intercalators.

Employing NMR spectroscopic methods preferred binding sites of a triplex-selective indoloquinoline drug were examined with three DNA triplex targets. To directly derive and evaluate number and type of the different sites of interaction, studies were performed on short triple-helical constructs specifically labeled with 3-(15)N thymidine probes. The detection and assignment of several coexisting species was enabled through the observation of slow exchange on the chemical shift timescale between complexes and free triplex. In general, the 5'-triplex-duplex junction constitutes the most favorable intercalation site, in particular when flanked by a TAT base triad. NMR data also revealed two different orientations for the intercalating indoloquinoline drug. Binding affinity significantly decreases with a C(+)GC triad bordering the junction but junction binding is still preferred over intercalation between TAT base triads within the triplex stem. In addition to the intercalation between two uncharged TAT triplets, intercalation between a TAT and a 3'-terminal C(+)GC triplet was also observed, indicating a non-protonated third strand cytosine at the triplex end position.

Inter- and intrastrand DNA crosslinks by 2-fluoro-substituted pyrrolobenzodiazepine dimers: stability, stereochemistry and drug orientation.

A 2-fluoro-substituted pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimer with a 1,4-di-n-propyl piperazine linker was studied with respect to its binding and crosslinking capability towards double-helical DNA targets. Duplex thermal stabilizations upon drug binding as measured by UV melting experiments suggest that two guanine bases separated by four AT base pairs constitute the favorable binding site for the PBD dimer. Large stabilizations were observed for the self-complementary duplex d(AACAATTGTT)(2) as well as for the non-self-complementary duplex d(AAGAATTGTT)·d(AACAATTCTT) with both guanines located on the same strand. Formation of interstrand and intrastrand crosslinks by the covalent binding of both PBD moieties of the dimer to the exocyclic 2-amino group of the two guanine bases within the duplex minor groove was confirmed by NMR structural studies. In both the symmetric and non-symmetric DNA-PBD adducts the newly created stereogenic center at C11 of the tricyclic PBD subunits favors an S configuration. Different orientations of the PBD aromatic A-ring with respect to the covalently modified guanine as observed in the non-symmetric complex are shown to result in characteristic changes of PBD H11 and H11a proton chemical shifts. Based on a compilation of available NMR data on various PBD complexes, these differences may be used as valuable probes for the identification of PBD orientational preferences in DNA-PBD adducts.