The pincer platform provides increased stability and often a rigid coordination mode in transition metal complexes that allows for the incorporation of reactive functional groups in the coordination ...sphere of a metal. Classical coordination patterns in pincer‐type complexes were established over the past decades, involving a preferred set of binding sites. In the current review, we discuss pincer‐type ligands with remarkable bonding situations and reactivity patterns, which are beyond the privileged ligand systems frequently used in homogeneous catalysis and bond activation reactions. This includes ligands with ligating atoms based on metalloid elements, π‐systems as well as different kinds of metallo‐ligands. We categorize the discussed pincer‐type ligands herein according to the covalent bond classification and distinguish between metallo‐ligands and ligands, which are based on nonmetal and metalloid elements.
The platform of pincer‐type ligands can be used to utilize uncommon binding sites, leading to unprecedented reactivity patterns and applications in homogeneous catalysis. Herein we analyze binding sites in complexes with pincer‐type motifs that are not typically used in “classic” coordination chemistry with pincer ligands and discuss their reactivity patterns.
The emergence of low-cost, user-friendly and very compact air pollution platforms enable observations at high spatial resolution in near-real-time and provide new opportunities to simultaneously ...enhance existing monitoring systems, as well as engage citizens in active environmental monitoring. This provides a whole new set of capabilities in the assessment of human exposure to air pollution. However, the data generated by these platforms are often of questionable quality.
We have conducted an exhaustive evaluation of 24 identical units of a commercial low-cost sensor platform against CEN (European Standardization Organization) reference analyzers, evaluating their measurement capability over time and a range of environmental conditions. Our results show that their performance varies spatially and temporally, as it depends on the atmospheric composition and the meteorological conditions. Our results show that the performance varies from unit to unit, which makes it necessary to examine the data quality of each node before its use.
In general, guidance is lacking on how to test such sensor nodes and ensure adequate performance prior to marketing these platforms. We have implemented and tested diverse metrics in order to assess if the sensor can be employed for applications that require high accuracy (i.e., to meet the Data Quality Objectives defined in air quality legislation, epidemiological studies) or lower accuracy (i.e., to represent the pollution level on a coarse scale, for purposes such as awareness raising).
Data quality is a pertinent concern, especially in citizen science applications, where citizens are collecting and interpreting the data. In general, while low-cost platforms present low accuracy for regulatory or health purposes they can provide relative and aggregated information about the observed air quality.
•We find challenges associated with sensor robustness and measurement repeatability.•Field performance evaluation under diverse environmental conditions is necessary.•We show low-cost sensors are not ready for applications that require high accuracy.•Low-cost sensors can provide coarse information about the observed air quality.
The recent emergence of low-cost microsensors measuring various air pollutants has significant potential for carrying out high-resolution mapping of air quality in the urban environment. However, the ...data obtained by such sensors are generally less reliable than that from standard equipment and they are subject to significant data gaps in both space and time. In order to overcome this issue, we present here a data fusion method based on geostatistics that allows for merging observations of air quality from a network of low-cost sensors with spatial information from an urban-scale air quality model. The performance of the methodology is evaluated for nitrogen dioxide in Oslo, Norway, using both simulated datasets and real-world measurements from a low-cost sensor network for January 2016. The results indicate that the method is capable of producing realistic hourly concentration fields of urban nitrogen dioxide that inherit the spatial patterns from the model and adjust the prior values using the information from the sensor network. The accuracy of the data fusion method is dependent on various factors including the total number of observations, their spatial distribution, their uncertainty (both in terms of systematic biases and random errors), as well as the ability of the model to provide realistic spatial patterns of urban air pollution. A validation against official data from air quality monitoring stations equipped with reference instrumentation indicates that the data fusion method is capable of reproducing city-wide averaged official values with an R2 of 0.89 and a root mean squared error of 14.3 μg m−3. It is further capable of reproducing the typical daily cycles of nitrogen dioxide. Overall, the results indicate that the method provides a robust way of extracting useful information from uncertain sensor data using only a time-invariant model dataset and the knowledge contained within an entire sensor network.
•A method is presented to map urban air quality in real time with low-cost sensors.•The method merges low-cost sensor data with time-invariant model output.•Resulting maps exhibit realistic spatial patterns of urban air pollution.•Comparison against station data shows good replication of temporal daily cycle.•Validation indicates an R2 value of 0.89 against reference observations.
A DNA origami rotary ratchet motor Pumm, Anna-Katharina; Engelen, Wouter; Kopperger, Enzo ...
Nature (London),
07/2022, Letnik:
607, Številka:
7919
Journal Article
Recenzirano
Odprti dostop
Abstract
To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient ...temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry
1–5
. Ratcheting is thought to underpin the function of many natural biological motors, such as the F
1
F
0
-ATPase
6–8
, and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref.
3
) and also in artificial molecular motors created by organic chemical synthesis
9–12
. DNA nanotechnology
13
has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems
14–17
, which can adopt different configurations, for example, triggered by strand-displacement reactions
18,19
or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins
20–26
. This previous work and considering low-Reynolds-number dynamics and inherent stochasticity
27,28
led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F
1
F
0
-ATPase.
The first example of a catalytic Michael addition reaction of non-activated aliphatic nitriles to α,β-unsaturated carbonyl compounds under mild, neutral conditions is reported. A new de-aromatized ...pyridine-based PNP pincer complex of the Earth-abundant, first-row transition metal manganese serves as the catalyst. The reaction tolerates a variety of nitriles and Michael acceptors with different steric features and acceptor strengths. Mechanistic investigations including temperature-dependent NMR spectroscopy and DFT calculations reveal that the cooperative activation of alkyl nitriles, which leads to the generation of metalated nitrile nucleophile species (α-cyano carbanion analogues), is a key step of the mechanism. The metal center is not directly involved in the catalytic bond formation but rather serves, cooperatively with the ligand, as a template for the substrate activation. This approach of “template catalysis” expands the scope of potential donors for conjugate addition reactions.
The very low-cost Nova particulate matter (PM) sensor SDS011 has recently drawn attention for its use for measuring PM mass concentration, which is frequently used as an indicator of air quality. ...However, this sensor has not been thoroughly evaluated in real-world conditions and its data quality is not well documented. In this study, three SDS011 sensors were evaluated by co-locating them at an official, air quality monitoring station equipped with reference-equivalent instrumentation in Oslo, Norway. The sensors’ measurement results for PM2.5 were compared with data generated from the air quality monitoring station over almost a four-month period. Five performance aspects of the sensors were examined: operational data coverage, linearity of response and accuracy, inter-sensor variability, dependence on relative humidity (RH) and temperature (T), and potential improvement of sensor accuracy, by data calibration using a machine-learning method. The results of the study are: (i) the three sensors provide quite similar results, with inter-sensor correlations exhibiting R values higher than 0.97; (ii) all three sensors demonstrate quite high linearity against officially measured concentrations of PM2.5, with R2 values ranging from 0.55 to 0.71; (iii) high RH (over 80%) negatively affected the sensor response; (iv) data calibration using only the RH and T recorded directly at the three sensors increased the R2 value from 0.71 to 0.80, 068 to 0.79, and 0.55 to 0.76. The results demonstrate the general feasibility of using these low cost SDS011 sensors for indicative PM2.5 monitoring under certain environmental conditions. Within these constraints, they further indicate that there is potential for deploying large networks of such devices, due to the sensors’ relative accuracy, size and cost. This opens up a wide variety of applications, such as high-resolution air quality mapping and personalized air quality information services. However, it should be noted that the sensors exhibit often very high relative errors for hourly values and that there is a high potential of abusing these types of sensors if they are applied outside the manufacturer-provided specifications particularly regarding relative humidity. Furthermore, our analysis covers only a relatively short time period and it is desirable to carry out longer-term studies covering a wider range of meteorological conditions.
Organic light-emitting diodes (OLEDs) are revolutionizing display applications. In this aspect, luminescent complexes of precious metals such as iridium, platinum, or ruthenium still playing a ...significant role. Emissive compounds of earth-abundant copper with equivalent performance are desired for practical, large-scale applications such as solid-state lighting and displays. Copper(I)-based emitters are well-known to suffer from weak spin–orbit coupling and a high reorganization energy upon photoexcitation. Here we report a cationic organo-copper cluster Cu4(PCP)3+ (PCP = 2,6-(PPh2)2C6H3) that features suppressed nonradiative decays, giving rise to a robust narrow-band green luminophore with a photoluminescent (PL) efficiency up to 93%. PL decay kinetics corroborated by DFT calculations reveal a complex emission mechanism involving contributions of both thermally activated delayed fluorescence and phosphorescence. This robust compound was solution-processed into a thin film in prototype OLEDs with external quantum efficiency up to 11% and a narrow emission bandwidth (65 nm fwhm).
The development of an efficient catalytic process that mimics the enzymatic function of alcohol dehydrogenase is critical for using biomass alcohols for both the production of H2 as a chemical energy ...carrier and fine chemicals under waste-free conditions. Dehydrogenation of alcohol-water mixtures into their corresponding acids with molecular hydrogen as the sole by-product from the reaction can be catalysed by a ruthenium complex with a chelating bis(olefin) diazadiene ligand. This complex, K(dme)2Ru(H)(trop2dad), stores up to two equivalents of hydrogen intramolecularly, and catalyses the production of H2 from alcohols in the presence of water and a base under homogeneous conditions. The conversion of a MeOH-H2O mixture proceeds selectively to CO2/H2 gas formation under neutral conditions, thereby allowing the use of the entire hydrogen content (12% by weight). Isolation and characterization of the ruthenium complexes from these reactions suggested a mechanistic scenario in which the trop2dad ligand behaves as a chemically 'non-innocent' co-operative ligand.
The increased availability of commercially-available low-cost air quality sensors combined with increased interest in their use by citizen scientists, community groups, and professionals is resulting ...in rapid adoption, despite data quality concerns. We have characterized three out-the-box PM sensor systems under different environmental conditions, using field colocation against reference equipment. The sensor systems integrate Plantower 5003, Sensirion SPS30 and Alphasense OCP-N3 PM sensors. The first two use photometry as a measuring technique, while the third one is an optical particle counter. For the performance evaluation, we co-located 3 units of each manufacturer and compared the results against optical (FIDAS) and gravimetric (KFG) methods for a period of 7 weeks (28 August to 19 October 2020). During the period from 2nd and 5th October, unusually high PM concentrations were observed due to a long-range transport episode. The results show that the highest correlations between the sensor systems and the optical reference are observed for PM1, with coefficients of determination above 0.9, followed by PM2.5. All the sensor units struggle to correctly measure PM10, and the coefficients of determination vary between 0.45 and 0.64. This behavior is also corroborated when using the gravimetric method, where correlations are significantly higher for PM2.5 than for PM10, especially for the sensor systems based on photometry. During the long range transport event the performance of the photometric sensors was heavily affected, and PM10 was largely underestimated. The sensor systems evaluated in this study had good agreement with the reference instrumentation for PM1 and PM2.5; however, they struggled to correctly measure PM10. The sensors also showed a decrease in accuracy when the ambient size distribution was different from the one for which the manufacturer had calibrated the sensor, and during weather conditions with high relative humidity. When interpreting and communicating air quality data measured using low-cost sensor systems, it is important to consider such limitations in order not to risk misinterpretation of the resulting data.
Localized electron spins can couple magnetically via the Ruderman-Kittel-Kasuya-Yosida interaction even if their wave functions lack direct overlap. Theory predicts that spin-orbit scattering leads ...to a Dzyaloshinskii-Moriya type enhancement of this indirect exchange interaction, giving rise to chiral exchange terms. Here we present a combined spin-polarized scanning tunneling microscopy, angle-resolved photoemission, and density functional theory study of MnO
chains on Ir(100). Whereas we find antiferromagnetic Mn-Mn coupling along the chain, the inter-chain coupling across the non-magnetic Ir substrate turns out to be chiral with a 120° rotation between adjacent MnO
chains. Calculations reveal that the Dzyaloshinskii-Moriya interaction results in spin spirals with a periodicity in agreement with experiment. Our findings confirm the existence of indirect chiral magnetic exchange, potentially giving rise to exotic phenomena, such as chiral spin-liquid states in spin ice systems or the emergence of new quasiparticles.
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