Investigations into the H-D Exchange of Malonganenone B

<p>H-D exchange at the formyl residue of the natural product malonganenone B was investigated. Models of the system were synthesised and displayed the same exchange. Kinetic studies, performed using NMR spectroscopy, found the exchange was first order with respect to base whilst displaying acid inhibition, in opposition to existing research. Cyclic species, including an N-heterocyclic carbene precursor, were formed that, in conjunction with the previous findings, suggested a carbene-based mechanism was in operation. Further synthetic studies were performed to demonstrate the existence of a carbene. With use of silver oxide, a fulvalene dimer and an organopalladium complex of this carbene were obtained, which provide further support towards a carbene-based mechanism being involved in the H-D exchange of malonganenone B.</p>

Investigations into the H-D Exchange of Malonganenone B

<p>H-D exchange at the formyl residue of the natural product malonganenone B was investigated. Models of the system were synthesised and displayed the same exchange. Kinetic studies, performed using NMR spectroscopy, found the exchange was first order with respect to base whilst displaying acid inhibition, in opposition to existing research. Cyclic species, including an N-heterocyclic carbene precursor, were formed that, in conjunction with the previous findings, suggested a carbene-based mechanism was in operation. Further synthetic studies were performed to demonstrate the existence of a carbene. With use of silver oxide, a fulvalene dimer and an organopalladium complex of this carbene were obtained, which provide further support towards a carbene-based mechanism being involved in the H-D exchange of malonganenone B.</p>

Effect of PbSO4-Oleate Coverage on Cesium Lead Halide Perovskite Quantum Dots to Control Halide Exchange Kinetics

The selective control of halide ion exchange in metal halide perovskite quantum dots (PQDs) plays an important role in determining their band gap and composition. In this study, CsPbX3 (X = Cl−, Br−, and I−) PQDs were self-assembled with PbSO4-oleate to form a peapod-like morphology to selectively control halide ion exchange. Considering the distinct absorption and bright luminescence characteristics of these PQDs, in situ UV-Vis. absorption and fluorescence spectroscopies were employed to monitor the time-dependent band gap and compositional changes of the PQDs. We determined that the halide exchange in the capped PQDs is hindered—unlike the rapid anion exchange in noncapped PQDs—by a reduction in the halide exchange kinetic rate depending on the extent of coverage of the PQDs. Thus, we tracked the halide ion exchange kinetics between CsPbBr3 and CsPbI3 PQDs, depending on the coverage, using in situ UV-Vis. absorption/photoluminescence spectroscopy. We regulated the halide exchange reaction rate by varying the capping reaction temperature of the PQDs. The capping hindered the halide exchange kinetics and increased the activation energy. These results will enable the development of white LEDs, photovoltaic cells, and photocatalysts with alternative structural designs based on the divalent composition of CsPbX3 PQDs.

The Money Paradox

Money has two key properties—accumulation (value) and liquidity (exchange), which results in what we define as “The Money Paradox”. In the language of Physics, money can be in either static (value, potential energy) or dynamic (exchange, kinetic energy) state, however the same money can’t be both static and dynamic at the same time because the states are mutually exclusive. In our paper we discuss the conditions under which money changes its state and how such transformations impact continuity (stability) of economics. Our goal is to identify the measures of continuity and thus sustainability of economic activity, as well as to help determine a point in time when new money must be infused into a financial system in order to maintain a continuous production and exchange of goods and services within an economic system without interruption, i.e., a financial crisis.

Estimates of mean residence times of phosphorus in commonly considered inorganic soil phosphorus pools

Quantification of turnover of inorganic soil phosphorus (P) pools is essential to improve our understanding of P cycling in soil–plant systems and improve representations of the P cycle in land surface models. Turnover can be quantified using mean residence time (MRT); however, to date there is little information on MRT of P in soil P pools. We introduce an approach to quantify MRT of P in sequentially extracted inorganic soil P pools using data from isotope exchange kinetic experiments. Our analyses of 53 soil samples from the literature showed that MRT of labile P (resin- and bicarbonate-extractable P) was on the order of minutes to hours for most soils, MRT in NaOH-extractable P (NaOH-P) was in the range of days to months, and MRT in HCl-extractable P (HCl-P) was on the order of years to millennia. Multiple-regression models were able to capture 54 %–63 % of the variability in MRT among samples and showed that land use was the most important predictor of MRT of P in labile and NaOH pools. MRT of P in HCl-P was strongly dependent on pH, as high-pH soils tended to have longer MRTs. This was interpreted to be related to the composition of HCl-P. Under high pH, HCl-P contains mostly apatite, with a low solubility, whereas under low-pH conditions, HCl-P may contain more exchangeable P forms. These results suggest that current land surface models underestimate the dynamics of inorganic soil P pools and could be improved by reducing model MRTs of the labile and NaOH-P pools, considering soil-type-dependent MRTs rather than universal exchange rates and allowing for two-way exchange between HCl-P and the soil solution.

Estimates of mean residence times of phosphorus in commonly-considered inorganic soil phosphorus pools

Quantification of turnover of inorganic soil phosphorus (P) pools is essential to improve our understanding of P cycling in soil-plant systems at different spatial scales. Turnover can be quantified using mean residence time (MRT), however, to date there is little information on MRT of P in soil P pools. We introduce an approach to quantify MRT of P in sequentially-extracted inorganic soil P pools using data from isotope exchange kinetic experiments. Our analyses of 53 soil samples from the literature showed that MRT of labile P (resin- and bicarbonate extractable P) was on the order of minutes to hours for most soils, MRT in NaOH-extractable P was in the range of days to months, and MRT in HCl-extractable P was on the order of years to millennia. Multiple regression models were able to capture 54–63 % of the variability in MRT among samples, and showed that land use was the most important predictor of MRT of P in labile and NaOH pools. MRT of P in HCl-P was strongly dependent on pH, as high pH soils tended to have longer MRTs. This was interpreted to be related to the composition of HCl-P. Under high pH, HCl-P contains mostly apatite, with a low solubility, whereas under low pH conditions, HCl-P may contain more exchangeable P forms. The estimates of MRT of P in inorganic pools improve our interpretation of soil P dynamics at the laboratory-, field- and ecosystem scale, and will also be useful to constrain P dynamics in global land surface models.

Printability study of metal ion crosslinked PEG-catechol based inks

Inspired by reversible networks present in nature, we have explored the printability of catechol functionalized polyethylene glycol (PEG) based inks with metal-coordination crosslinking. Material formulations containing Al3+, Fe3+ or V3+ as crosslinking ions were tested. The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the crosslinked materials were viable, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D (bio)printing, and enables straightforward adjustment of the printable formulation to meet application-specific needs.