Over the last ten years there has been a huge increase in development and applications of organocatalysis in which the catalyst acts as a nucleophile. Amidines and guanidines are often only thought ...of as strong organic bases however, a number of small molecules containing basic functional groups have been shown to act as efficient nucleophilic catalysts. This
tutorial review
highlights the use of amidine, guanidine, and related isothiourea catalysts in organic synthesis, as well as the evidence for the nucleophilic nature of these catalysts. The most common application of these catalysts to date has been in acyl transfer reactions, although the application of these catalysts towards other reactions is an increasing area of interest. In this respect, amidine and guanidine derived catalysts have been shown to be effective in catalysing aldol reactions, MoritaBaylisHillman reactions, conjugate additions, carbonylations, methylations, silylations, and brominations.
This tutorial review highlights the development and applications of amidine, isothiourea, and guanidine based nucleophilic catalysts for a range of reactions.
Summary
3-D X-ray micro-CT (XCT) is a non-destructive 3-D imaging method, increasingly used for a wide range of applications in Earth Science. An optimal XCT image-processing workflow is derived here ...for accurate quantification of porosity and absolute permeability of heterogeneous sandstone samples using an assessment of key image acquisition and processing parameters: image resolution, segmentation method, representative elementary volume (REV) size and fluid-simulation method. XCT image-based calculations obtained for heterogeneous sandstones are compared to two homogeneous standards (Berea sandstone and a sphere pack), as well as to the results from physical laboratory measurements. An optimal XCT methodology obtains porosity and permeability results within ±2 per cent and vary by one order of magnitude around the direct physical measurements, respectively, achieved by incorporating the clay fraction and cement matrix (porous, impermeable components) to the pore-phase for porosity calculations and into the solid-phase for permeability calculations. Two stokes-flow finite element modelling (FEM) simulation methods, using a voxelized grid (Avizo) and tetrahedral mesh (Comsol) produce comparable results, and similarly show that a lower resolution scan (∼5 µm) is unable to resolve the smallest intergranular pores, causing an underestimation of porosity by ∼3.5 per cent. Downsampling the image-resolution post-segmentation (numerical coarsening) and pore network modelling both allow achieving of a REV size, whilst significantly reducing fluid simulation memory requirements. For the heterogeneous sandstones, REV size for permeability (≥1 mm3) is larger than for porosity (≥0.5 mm3) due to tortuosity of the fluid paths. This highlights that porosity should not be used as a reference REV for permeability calculations. The findings suggest that distinct image processing workflows for porosity and permeability would significantly enhance the accurate quantification of the two properties from XCT.
1,5-Diazabicyclo4.3.0non-5-ene (DBN) has been shown to be an effective catalyst for the regioselective Friedel−Crafts C-acylation of pyrroles and indoles in high yields. A detailed mechanistic study ...implies that DBN is acting as a nucleophilic organocatalyst, with the X-ray crystal structure of a key N-acyl-amidine intermediate having been determined for the first time.
In 2014, the Association of American Medical Colleges (AAMC) published a list of 13 Core Entrustable Professional Activities for Entering Residency (Core EPAs) that medical school graduates might be ...expected to perform, without direct supervision, on the first day of residency. Soon after, the AAMC commissioned a five-year pilot with 10 medical schools across the United States, seeking to implement the Core EPA framework to improve the transition from undergraduate to graduate medical education.In this article, the pilot team presents the organizational structure and early results of collaborative efforts to provide guidance to other institutions planning to implement the Core EPA framework. They describe the aims, timeline, and organization of the pilot as well as findings to date regarding the concepts of entrustment, assessment, curriculum development, and faculty development. On the basis of their experiences over the first two years of the pilot, the authors offer a set of guiding principles for institutions intending to implement the Core EPA framework. They also discuss the impact of the pilot, its limitations, and next steps, as well as how the pilot team is engaging the broader medical education community. They encourage ongoing communication across institutions to capitalize on the expertise of educators to tackle challenges related to the implementation of this novel approach and to generate common national standards for entrustment. The Core EPA pilot aims to better prepare medical school graduates for their professional duties at the beginning of residency with the ultimate goal of improving patient care.
Formyloxyacetoxyphenylmethane is a stable, water-tolerant, N-formylating reagent for primary and secondary amines that can be used under solvent-free conditions at room temperature to prepare a range ...of N-formamides, N-formylanilines, N-formyl-α-amino acids, N-formylpeptides, and an isocyanide.
The new global biodiversity framework (GBF) being developed under the Convention on Biological Diversity must drive action to reverse the ongoing decline of the Earth's biodiversity. Explicit, ...measurable goals that specify the outcomes we want to achieve are needed to set the course for this action. However, the current draft goals and targets fail to set out these clear outcomes. We argue that distinct outcome goals for species, ecosystems, and genetic diversity are essential and should specify net outcomes required for each. Net outcome goals such as “no net loss” do, however, have a controversial history, and loose specification can lead to perverse outcomes. We outline seven general principles to underpin net outcome goal setting that minimize risk of such perverse outcomes. Finally, we recommend inclusion of statements of impact in action targets that support biodiversity goals, and we illustrate the importance of this with an example from the draft GBF action targets. These modifications would help reveal the specific contribution each action would make to achieving the outcome goals and provide clarity on whether the successful achievement of action targets would be adequate to achieve the outcome goals and, in turn, the 2050 vision: living in harmony with nature.
•Shortening in the Wharton Basin taken up on network of strike slip and reverse faults.•Fault motions detectable since 14 Ma, with acceleration and new faults since 7-9 Ma.•Shallow faulting defines a ...Riedel-shear system due to principal NNE sinistral slip.•The 2012 Intraplate earthquake rupture defines the principal displacement zone.
The equatorial eastern Indian Ocean hosts a diffuse plate boundary, where widespread deformation accommodates the relative motion between the Indian, Australian and Capricorn sub-plates. We integrate IODP Expedition 362 borehole data, which for the first time provides an accurate, ground-truthed chronostratigraphy of the sedimentary sequence east of the Ninety East Ridge (NER), with 2D seismic reflection profiles and multibeam bathymetry to assess the styles of faulting between the NER and the Sunda subduction zone, timing of activity and comparison with physical and rheological properties. We identify four distinct fault sets east of the NER in the northern Wharton Basin. N-S (350-010°) orientated faults, associated with the N-S fracture zones formed at the now extinct Wharton spreading centre, are still active and have been continuously active since at least 10 Ma. NNE- and WNW-trending fault fabrics develop between the fracture zones. The orientations and likely sense of displacement on these three sets of faults defines a Riedel shear system responding to ∼NNE-SSW left-lateral strike-slip activity at depth, demonstrated by the recent 2012 great intraplate earthquakes. We also find evidence of ∼NE-SW reverse faults, similar in style to E-W reverse faults observed west of the NER, where reverse faulting is more dominant. We show that the activity of this strike-slip system increased ca. 7-9 Ma, contemporaneous with reverse faulting and intraplate deformation west of the NER.
A high-resolution record of pollution is preserved in recent sediments from Windermere, the largest lake in the English Lake District. Data derived from X-ray core scanning (validated against ...wavelength dispersive X-ray fluorescence), radiochronological techniques (210Pb and 137Cs) and ultrahigh precision, double-spike mass spectrometry for lead isotopes are combined to decipher the anthropogenic inputs to the lake. The sediment record suggests that while most element concentrations have been stable, there has been a significant increase in lead, zinc, and copper concentrations since the 1930s. Lead isotope down-core variations identify three major contributory sources of anthropogenic (industrial) lead, comprising gasoline lead, coal combustion lead (most likely source is coal-fired steam ships), and lead derived from Carboniferous Pb–Zn mineralization (mining activities). Periods of metal workings do not correlate with peaks in heavy metals due to the trapping efficiency of up-system lakes in the catchment. Heavy metal increases could be due to flood-induced metal inwash after the cessation of mining and the weathering of bedrock in the catchment. The combination of sediment analysis techniques used provides new insights into the pollutant depositional history of Windermere and could be similarly applied to other lake systems to determine the timing and scale of anthropogenic inputs.
SUMMARY
Subsurface fluid escape structures are geological features which are commonly observed in sedimentary basins worldwide. Their identification and description have implications for various ...subsurface fluid flow applications, such as assuring integrity of overburden rocks to geological CO2 storage sites. In this study, we applied 3-D first-arrival traveltime tomography to a densely sampled wide-azimuth and wide-angle ocean bottom seismometer (OBS) data set collected over the Scanner Pockmark complex, a site of active gas venting in the North Sea. Seismic reflection data show a chimney structure underlying the Scanner Pockmark. The objective of this study was to characterize this chimney as a representative fluid escape structure in the North Sea. An area of 6$\times $6 km2 down to a depth of 2 km below sea level was investigated using a regularized tomography algorithm. In total, 182 069 manually picked traveltimes from 24 OBS were used. Our final velocity model contains compressional wave velocity perturbations ranging from −125 to +110 ms−1 relative to its average 1-D model and compares favourably with a coincident seismic reflection data set. The tomographic velocity model reveals that the chimney as observed in seismic reflection data is part of a larger complex fluid escape structure, and discriminates the genuine chimney from seismic artefacts. We find that part of the seeping gas migrates from a deep source, accumulates beneath the Crenulate Reflector unconformity at ∼250 m below seafloor (mbsf) before reaching the porous sediments of the Ling Bank and Coal Pit formation at <100 mbsf. In addition, the model shows that the venting gas at Scanner Pockmark is also being fed laterally through a narrow NW–SE shallow channel. Quantitative velocity analysis suggests a patchy gas saturation within the gas-charged sediments of the Ling Bank and the Coal Pit formations. Confined to the well-resolved regions, we estimate a base case average gas saturation of ∼9 per cent and in-situ gas volume of ∼1.64 $\times {10^6}\ {{\rm{m}}^3}$ across the Ling Bank and Coal Pit Fm. that can sustain the observed methane flux rate at the Scanner Pockmark for about 10 to 17 yr.
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