Steric and electronic control of an ultrafast isomerization.

Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF3)2C2S2)(CO)(L)2, where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν(CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh3, P((p-Me)Ph)3, ((p-Cl)Ph)3, at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and in the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol-1. This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes

Animal Scavenging and Scattering and the Implications for Documenting the Deaths of Undocumented Border Crossers in the Sonoran Desert,

Since 1998, over 5500 people have died while attempting to cross the U.S.–Mexico border without authorization. These deaths have primarily occured in the Arizona desert. Despite the high volume of deaths, little experimental work has been conducted on Sonoran Desert taphonomy. In this study, pig carcasses were used as proxies for human remains and placed in different depositional contexts (i.e., direct sunlight and shade) that replicate typical sites of migrant death. Decomposition was documented through daily site visits, motion‐sensitive cameras and GIS mapping, while skeletal preservation was investigated through the collection of the remains and subsequent faunal analysis. Our results suggest that vultures and domestic dogs are underappreciated members of the Sonoran scavenging guild and may disperse skeletal remains and migrant possessions over 25 m from the site of death. The impact of scavengers and the desert environment on the decomposition process has significant implications for estimating death rates and identifying human remains along the Arizona/Mexico border.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110576/1/jfo12597.pd

Thermodynamic Strategies of Electrocatalyst Design for CO2 Reduction

The electrocatalytic reduction of CO2 represents a possible means of disrupting current petrochemical reliance by leveraging renewably-generated electricity to manufacture commodity chemicals and liquid fuels. Such an approach may enable economic feasibility of anthropogenic climate change mitigation by catalytic conversion of atmospheric CO2 to value-added products. However, many of the most active catalysts consist of rare metals whose cost renders them prohibitively expensive for scalability. Additionally, a wide distribution of reduction products is often possible and poor selectivity decreases overall efficiency and complicates downstream purification processes. Fundamental understanding of elementary steps involved in catalytic pathways may therefore allow for improved catalyst design from inexpensive, earth-abundant materials.One such elementary step consists of hydride transfer from a catalyst intermediate to CO2, yielding the two-electron reduction product, formate. The investigation, targeting, and tuning of the thermodynamics of such hydride intermediates to enable improved catalyst design represents the overarching aim of the work presented herein, which is underpinned by three distinct objectives. Firstly, a powerful scaling relationship is elucidated which relates the thermodynamic propensity of hydride transfer, hydricity (ΔG0H−), and the first reduction potential of the parent metal complex (E1/2(Mn+/(n-1)+)). This relationship not only establishes a mechanism for estimating hydricity based on E1/2(Mn+/(n-1)+) but also provides a platform for rationally targeting and tuning hydride intermediates for reactivity towards CO2 and proton sources.This scaling relationship is subsequently utilized to target and design reactive hydrides at nickel and the validity of the relationship is established. Installation of highly electron-donating ligand frameworks demonstrates successful tuning of hydricity at first-row metal complexes and additional thermodynamic arguments enable for the rational selection of mild conditions for both electrocatalytic hydrogen evolution at extremely low overpotentials and the complete suppression thereof.Finally, the electrocatalytic reactivity of these species with CO2 is described. While development of nickel-based CO2-to-formate catalysts using these methods is ultimately unsuccessful, this work provides insight on the utility and limitations of thermodynamic scaling relationships in catalyst design. Furthermore, the findings herein underscore the necessity of divergence from such scaling relationships and shed light on strategies by which that may be accomplished

Geoarchaeological evaluation of the soil profiles and collapsed Neolithic structures in Trenches XIX, XXII and XXIII at Drenovac, Serbia

Evaluative geoarchaeological investigations using thin section micromorphology, physical, geochemical and infrared spectroscopy analyses of the Neolithic structures in Trenches XIX, XXII and XXIII at Drenovac have revealed that the site was built on disturbed clay-enriched brown forest soils. The collapsed structures were highly burnt and appear to have been kept very clean and free from the buildup of settlement-derived rubbish material, both inside and outside the buildings. These promising results suggest that further systematic geoarchaeological investigations of the floor and ground surfaces inside and outside the structures will provide very valuable new information on the use of space and activity areas in this Neolithic settlement

Gourob

Dans le cadre de cette troisième campagne, le travail sur le terrain (pl. 1) a été réparti entre : Des travaux archéologiques dans les zones à l’est, dites du « fort » et de la « jetée », dans le palais, dans la zone des fours, dans les tombes au nord et à l’est du « fort » ainsi qu’à l’est de la zone des fours. Ils ont été complétés par une étude anthropologique sur les ossements provenant des sépultures. Travaux géoarchéologiques pour localiser l’ancien chenal du Nil à l’est du site. Travau..

Thermodynamic Strategies of Electrocatalyst Design for CO2 Reduction

The electrocatalytic reduction of CO2 represents a possible means of disrupting current petrochemical reliance by leveraging renewably-generated electricity to manufacture commodity chemicals and liquid fuels. Such an approach may enable economic feasibility of anthropogenic climate change mitigation by catalytic conversion of atmospheric CO2 to value-added products. However, many of the most active catalysts consist of rare metals whose cost renders them prohibitively expensive for scalability. Additionally, a wide distribution of reduction products is often possible and poor selectivity decreases overall efficiency and complicates downstream purification processes. Fundamental understanding of elementary steps involved in catalytic pathways may therefore allow for improved catalyst design from inexpensive, earth-abundant materials.One such elementary step consists of hydride transfer from a catalyst intermediate to CO2, yielding the two-electron reduction product, formate. The investigation, targeting, and tuning of the thermodynamics of such hydride intermediates to enable improved catalyst design represents the overarching aim of the work presented herein, which is underpinned by three distinct objectives. Firstly, a powerful scaling relationship is elucidated which relates the thermodynamic propensity of hydride transfer, hydricity (ΔG0H−), and the first reduction potential of the parent metal complex (E1/2(Mn+/(n-1)+)). This relationship not only establishes a mechanism for estimating hydricity based on E1/2(Mn+/(n-1)+) but also provides a platform for rationally targeting and tuning hydride intermediates for reactivity towards CO2 and proton sources.This scaling relationship is subsequently utilized to target and design reactive hydrides at nickel and the validity of the relationship is established. Installation of highly electron-donating ligand frameworks demonstrates successful tuning of hydricity at first-row metal complexes and additional thermodynamic arguments enable for the rational selection of mild conditions for both electrocatalytic hydrogen evolution at extremely low overpotentials and the complete suppression thereof.Finally, the electrocatalytic reactivity of these species with CO2 is described. While development of nickel-based CO2-to-formate catalysts using these methods is ultimately unsuccessful, this work provides insight on the utility and limitations of thermodynamic scaling relationships in catalyst design. Furthermore, the findings herein underscore the necessity of divergence from such scaling relationships and shed light on strategies by which that may be accomplished

Steric and electronic control of an ultrafast isomerization.

Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF3)2C2S2)(CO)(L)2, where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν(CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh3, P((p-Me)Ph)3, ((p-Cl)Ph)3, at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and in the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol-1. This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes

Nouvelles recherches sur le site de Gourob

Entre 1888 et 1920, le site de Gourob, à l’entrée sud du Fayoum, a fait l’objet de quatre campagnes de fouilles, ainsi que d’actions plus ponctuelles, qui ont permis de mettre au jour les principales composantes du Nouvel Empire, à savoir une ville, un « harem », des lieux d’artisanat, des nécropoles, ainsi qu’un « fort ». Le Gurob Harem Palace Project (mission anglo-danoise) a ensuite repris le travail sur le site jusqu’en 2015. Depuis 2016, Gourob est un chantier de l’Ifao et les résultats de la campagne 2017 sont ici présentés. L’une des principales nouvelles problématiques développées dans ce cadre est celle de la présence d’un port dans l’Antiquité, bien attesté dans la documentation textuelle. C’est en ce sens que des prospections géophysiques et géoarchéologiques ont été menées à l’est du site, avec des résultats particulièrement engageants. L’étude archéologique s’est quant à elle concentrée sur la zone au nord-est du palais-harem, qui n’avait pas fait l’objet de fouilles depuis 1920, et principalement sur un bâtiment appelé « fort » par les anciens fouilleurs, datant selon eux de la Première Période intermédiaire. Les sondages effectués dans les parties nord et est de cette structure ont permis de formuler des hypothèses préliminaires quant à sa fonction, sa datation et son lien avec la rampe qui coupe son flanc est. Ces observations demanderont à être vérifiées lors des prochaines saisons.Between 1888 and 1920, the site of Gurob, located at the south entrance of the Fayum area, was the subject of four campaigns of archaeological excavations, as well as some more specific actions. This led to the discovery of the main New Kingdom component, i.e. the town, a “harim,” an industrial area, several necropolises and a “fort.” The Gurob Harem Palace Project (British-Danish team) then carried out work between 2005 and 2015. Since 2016, Gurob is an IFAO fieldwork and the results of the campaign 2017 are presented herein. One of the main new issues developed within this framework is the presence of a harbor during Antiquity, well attested in the textual documentation. Geophysical and geoarchaeological surveys have been led in this sense along the eastern edge of the site, with particularly promising results. The archaeological study focused on the area north-east of the harim-palace, which has not been excavated since 1920, and mainly on a building called “fort” by the former excavators, who dated it back to the First Intermediate Period. The trench dug in the northern and eastern sectors of this structure allowed a preliminary hypothesis to be presented concerning its function, its dating and its link with the ramp cutting through its eastern side. These observations prompt verification during the next seasons

PAPER ANTHROPOLOGY Animal Scavenging and Scattering and the Implications for Documenting the Deaths of Undocumented Border Crossers in the Sonoran Desert

ABSTRACT: Since 1998, over 5500 people have died while attempting to cross the U.S.-Mexico border without authorization. These deaths have primarily occured in the Arizona desert. Despite the high volume of deaths, little experimental work has been conducted on Sonoran Desert taphonomy. In this study, pig carcasses were used as proxies for human remains and placed in different depositional contexts (i.e., direct sunlight and shade) that replicate typical sites of migrant death. Decomposition was documented through daily site visits, motion-sensitive cameras and GIS mapping, while skeletal preservation was investigated through the collection of the remains and subsequent faunal analysis. Our results suggest that vultures and domestic dogs are underappreciated members of the Sonoran scavenging guild and may disperse skeletal remains and migrant possessions over 25 m from the site of death. The impact of scavengers and the desert environment on the decomposition process has significant implications for estimating death rates and identifying human remains along the Arizona/Mexico border