The periodic system and the idea of a chemical element: From Mendeleev to superheavy elements

Like other scientific concepts, the idea of a chemical element has changed considerably over time, since it was first established in the Enlightenment era. In Dmitri Mendeleev's construction of the periodic system, he distinguished between simple substances and elements as defined by their atomic weights. The foundation of the periodic system on the latter concept led to several challenges. For example, the system seemed unable to accommodate the radioactive substances eventually recognised as isotopes. Around 1920, elements were consequently redefined in terms of their atomic numbers, a nuclear property that could be determined by X‐ray spectroscopy. Although this understanding of an element has stood the test of time, new questions turned up relating to the concept of an element following the syntheses of transuranic elements since the early 1940s. These syntheses of very heavy elements have additionally led chemists and physicists to reconsider the criteria for the discovery of a new element. Recently, elements have been officially recognised on the sole ground that a small number of very heavy atomic nuclei were identified. The paper discusses how the notion of an element was modified during different periods of time, the reasons for the modifications, and the values ascribed to them in the communities of chemists and physicists.     

Nonribosomal Peptides Produced by Minimal and Engineered Synthetases with Terminal Reductase Domains

Nonribosomal peptide synthetases (NRPSs) use terminal reductase domains for 2-electron reduction of the enzyme-bound thioester releasing the generated peptides as C-terminal aldehydes. Herein, we reveal the biosynthesis of a pyrazine that originates from an aldehyde-generating minimal NRPS termed ATRed in entomopathogenic Xenorhabdus indica. Reductase domains were also investigated in terms of NRPS engineering and, although no general applicable approach was deduced, we show that they can indeed be used for the production of similar natural and unnatural pyrazinones.     

Exposure to virtual nature: the impact of different immersion levels on skin conductance level,heart rate,and perceived relaxation

Virtual Reality - It is generally accepted that natural environments reduce stress and improve mood. Since access to natural environments is sometimes limited, virtual natural environments,...     

Radiocesium in muscle tissue of reindeer and pike from northern Sweden before and after the Chernobyl accident. A retrospective study on tissue samples from the Swedish Environmental Specimen Bank.

After the Chernobyl accident in April 1986, considerable deposition of radionuclides occurred regionally in eastern, central and northwestern Sweden. Locally, the fallout of radiocesium exceeded the remainder from atmospheric nuclear weapons tests by several magnitudes. Since the end of the 1960s samples of organs from various plant and animal species, annually collected at different localities, have been preserved in the Swedish Environmental Specimen Bank (ESB). In this work samples from the ESB have been used for retrospective studies of radioactive pollution. The activities of Cs-134 and Cs-137 in muscle tissues from reindeer, Rangifer tarandus, and pike, Esox lucius, preserved in the ESB, were measured. The samples were collected annually; the reindeer at three localities in northern Sweden and the pike at one of them. In material collected prior to the Chernobyl accident, the levels of Cs-137 were 57-180 Bq/kg in reindeer and 14-24 Bq/kg in pike, fresh weight basis. These levels relate to earlier nuclear bomb tests. A significant decrease was found in pike during the pre-Chernobyl period (1971-86). In post-Chernobyl samples the burden of Cs-137 varied from amounts equal to the former levels in the northernmost locality and up to 80 times higher for the maximum values in the southernmost locality. The highest value recorded was 18,425 Bq/kg in reindeer. The geographic variations in reindeer from Chernobyl fallout were in accordance with the pattern of deposition estimated by aircraft surveys performed in May 1986. The ratio between 'new' and 'old' radiocesium burdens in pike, caught in 1987, approached the corresponding ratio for reindeer grazing in the precipitation area of the lake; 33 and 19, respectively.     

Dynamic-MFA examination of Chilean housing stock: long-term changes and earthquake damage

The dynamics and metabolism of the built environment are important for understanding the construction, renovation and demolition activities that characterize its long-term physical development. Previous research on building stock development is limited, particularly for developing countries. As one of the most seismically active countries in the world, Chile's built environment is constantly subjected to losses. This study included earthquake vulnerability and damage in a dynamic material flow analysis (MFA) of the Chilean housing stock. Stock and flows of residential floor area were modelled using population and life style parameters. Demolition was modelled assuming a constant demolition rate. By characterizing the building stock according to vulnerability classes and establishing a mass balance per class, the effects of different typology distributions on the overall damage to the stock caused by earthquakes could be assessed. Scenarios with different trends in typology distribution for new construction and renovation suggest that significant potential exists for reducing future earthquake damage in the Chilean housing stock. This is best achieved by gradually reducing the vulnerability of buildings to earthquakes. Legislation, building standards and financial instruments could be used to ensure such reductions in earthquake damage and thereby provide socio-economic benefits in the future.     

Comparative emission analysis of low-energy and zero-emission buildings

Different designs and concepts of low-energy and zero-emission buildings (ZEBs) are being introduced into the Norwegian market. This study analyses and compares the life cycle emissions of CO₂ equivalents (CO₂e) from eight different single-family houses in the Oslo climate. Included are four ZEBs: one active house, two passive houses, and a reference house (Norwegian building code of 2010). Monthly differences in CO₂e emissions are calculated for the seasonally sensitive Norwegian context for electricity generation and consumption. This is used to supplant the previous applied symmetric weighting approach for CO₂e/kWh factors for import and export of electricity for the ZEB cases. All the ZEBs have lower use-stage emissions compared with the other buildings or the reference case. Embodied impacts are found to be 60–75% for the analysed ZEB cases, confirming the importance of embodied impacts in Norwegian ZEBs. The lowest total emissions were from the smallest ZEB, emphasizing area efficiency. The highest emissions were from the reference case. By abandoning the symmetric approach, a new perspective was developed for assessing the performance of ZEBs within the Norwegian context. One of four ZEB cases managed to balance out its annual energy-related emissions.     

Rapid Determination of the Amino Acid Configuration of Xenotetrapeptide

An E. coli strain with deletions in five transaminases (ΔaspC ΔilvE ΔtyrB ΔavtA ΔybfQ) was constructed to be unable to degrade several amino acids. This strain was used as an expression host for the analysis of the amino acid configuration of nonribosomally synthesized peptides, including the novel peptide “xenotetrapeptide” from Xenorhabdus nematophila, by using a combination of labeling experiments and mass spectrometry. Additionally, the number of D ‐amino acids in the produced peptide was assigned following simple cultivation of the expression strain in D₂O.