Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization

Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.

Small shelly fossils and carbon isotopes from the early Cambrian (Stage 3-4) Mural Formation of western Laurentia

The extraordinary window of phosphatised and phosphatic Small Shelly Fossils (SSFs) during the early and middle Cambrian is an important testament to the radiation of biomineralising metazoans. While SSF are well known from most Cambrian palaeocontinents during this time interval, western Laurentia has relatively few SSF faunas. Here we describe a diverse SSF fauna from the early Cambrian (Stage 3-4) Mural Formation at three localities in Alberta and British Columbia, Canada, complemented by carbon isotope measurements to aid in a potential future bio-chemostratigraphic framework. The fauna expands the recorded SSF assemblage diversity in western Laurentia and includes several brachiopods, four bradoriids, three chancelloriids, two hyoliths, a tommotiid and a helcionellid mollusc as well as echinoderm ossicles and specimens of Microdictyon, Volborthella and Hyolithellus. New taxa include the tommotiid genus Canadiella gen. nov., the new bradoriid species Hipponicharion perforata sp. nov. and Pseudobeyrichona taurata sp. nov. Compared to contemporaneous faunas from western Laurentia, the fauna is relatively diverse, particularly in taxa with originally phosphatic shells, which appear to be associated with archaeocyathid buildups. This suggests that the generally low faunal diversity in western Laurentia may be at least partly a consequence of poor sampling of suitable archaeocyathan reef environments. In addition, the tommotiid Canadiella filigrana appears to be of biostratigraphic significance in Cambrian Stage 3 strata of western Laurentia and the unexpected high diversity of bradoriid arthropods in the fauna also suggests that this group may prove useful for biostratigraphic resolution in the region

Congenital Diaphragmatic hernia – a review

Congenital Diaphragmatic hernia (CDH) is a condition characterized by a defect in the diaphragm leading to protrusion of abdominal contents into the thoracic cavity interfering with normal development of the lungs. The defect may range from a small aperture in the posterior muscle rim to complete absence of diaphragm. The pathophysiology of CDH is a combination of lung hypoplasia and immaturity associated with persistent pulmonary hypertension of newborn (PPHN) and cardiac dysfunction. Prenatal assessment of lung to head ratio (LHR) and position of the liver by ultrasound are used to diagnose and predict outcomes. Delivery of infants with CDH is recommended close to term gestation. Immediate management at birth includes bowel decompression, avoidance of mask ventilation and endotracheal tube placement if required. The main focus of management includes gentle ventilation, hemodynamic monitoring and treatment of pulmonary hypertension followed by surgery. Although inhaled nitric oxide is not approved by FDA for the treatment of PPHN induced by CDH, it is commonly used. Extracorporeal membrane oxygenation (ECMO) is typically considered after failure of conventional medical management for infants ≥ 34 weeks’ gestation or with weight >2 kg with CDH and no associated major lethal anomalies. Multiple factors such as prematurity, associated abnormalities, severity of PPHN, type of repair and need for ECMO can affect the survival of an infant with CDH. With advances in the management of CDH, the overall survival has improved and has been reported to be 70-90% in non-ECMO infants and up to 50% in infants who undergo ECMO

Preterm infant gut microbial patterns related to the development of necrotizing enterocolitis

<p><b>Objectives:</b> To define gut microbial patterns in preterm infants with and without necrotizing enterocolitis (NEC) and to characterize clinical factors related to the composition of the preterm intestinal microbiome.</p> <p><b>Methods:</b> Fecal samples were collected at one-week intervals from infants with gestational ages <30 weeks at a single level IV neonatal intensive care unit. Using 16S rRNA gene sequencing, the composition and diversity of microbiota were determined in samples collected from five NEC infants and five matched controls. Hierarchical linear regression was used to identify clinical factors related to microbial diversity and specific bacterial signatures.</p> <p><b>Results:</b> Low levels of diversity were demonstrated in samples obtained from all preterm infants and antibiotic exposure further decreased diversity among both NEC cases and controls. Fecal microbial composition differed between NEC cases and controls, with a greater abundance of <i>Proteobacteria</i> and bacteria belonging to the class <i>Gammaproteobacteria</i> among NEC infants. Control infants demonstrated a greater abundance of bacteria belonging to the phylum <i>Firmicutes</i>.</p> <p><b>Conclusion:</b> These findings indicate that an association exists between intestinal <i>Proteobacteria</i> and NEC, and strengthens the notion that an overly exuberant response to Gram-negative products, particularly lipopolysaccharide, in the preterm intestine is involved in NEC pathogenesis. Cumulative exposure to antibiotics corresponded to a reduction in microbial diversity in both NEC cases and controls.</p

Microstructure of Crystallizable α‑Olefin Molecular Bottlebrushes: Isotactic and Atactic Poly(1-octadecene)

Isotactic and atactic poly­(1-octadecene) (iPOD and aPOD) have been synthesized by organometallic coordinative insertion polymerization of 1-octadecene. Analyzing X-ray and neutron scattering data of POD melts identifies their bottlebrush structures as flexible rods where the rod length is the extended backbone length and rod radius is the side chain coil dimension. Upon cooling, both iPOD and aPOD melts crystallize by fully extending their coiled side chains to form orthorhombic alkane crystals in iPOD and nematically ordered rotator alkane crystals in aPOD, as determined by X-ray scattering and Raman spectroscopy. Molecular dynamics simulations of isotactic and atactic 48-mers of 1-octadecene were applied to define and verify melt and crystalline structures and scattering peak assignments, respectively. Modeling suggests that side chains of both crystallized isotactic and atactic PODs align at 70° and 160° to the 4/1 spiral backbone of equal probability, at an average of 115°, and POD chains pack in an antiparallel pattern. Large wheat-sheaf structural assembly of fibril bundles can be observed in aPOD, which render high opacity to these samples. Each of those fibrils is made of several bottlebrush molecules packed into a hexagonal lattice. Faster crystallization observed in iPODs hinders the formation of large crystallites, which results in translucent samples