Alkaline‐Earth‐Catalysed Cross‐Dehydrocoupling of Amines and Hydrosilanes: Reactivity Trends,Scope and Mechanism

Alkaline‐earth (Ae=Ca, Sr, Ba) complexes are shown to catalyse the chemoselective cross‐dehydrocoupling (CDC) of amines and hydrosilanes. Key trends were delineated in the benchmark couplings of Ph₃SiH with pyrrolidine or tBuNH₂. Ae{E(SiMe₃)₂}₂ ? (THF)_x (E=N, CH; x=2–3) are more efficient than {N^N}Ae{E(SiMe₃)₂} ? (THF)_n (E=N, CH; n=1–2) complexes (where {N^N}^?={ArN(o‐C₆H₄)C(H)=NAr}^? with Ar=2,6‐iPr₂‐C₆H₃) bearing an iminoanilide ligand, and alkyl precatalysts are better than amido analogues. Turnover frequencies (TOFs) increase in the order Ca<Sr<Ba. Ba{CH(SiMe₃)₂}₂ ? (THF)₃ displays the best performance (TOF up to 3600 h^?1). The substrate scope (>30 products) includes diamines and di(hydrosilane)s. Kinetic analysis of the Ba‐promoted CDC of pyrrolidine and Ph₃SiH shows that 1) the kinetic law is rate=k[Ba]¹[amine]⁰[hydrosilane]¹, 2) electron‐withdrawing p‐substituents on the arylhydrosilane improve the reaction rate and 3) a maximal kinetic isotopic effect (k_SiH/k_SiD=4.7) is seen for Ph₃SiX (X=H, D). DFT calculations identified the prevailing mechanism; instead of an inaccessible σ‐bond‐breaking metathesis pathway, the CDC appears to follow a stepwise reaction path with N?Si bond‐forming nucleophilic attack of the catalytically competent Ba pyrrolide onto the incoming silane, followed by rate limiting hydrogen‐atom transfer to barium. The participation of a Ba silyl species is prevented energetically. The reactivity trend Ca<Sr<Ba results from greater accessibility of the metal centre and decreasing Ae?N_amide bond strength upon descending Group 2.     

Photodegradation of isotactic poly(1-butene): Multiscale characterization

The effect of photodegradation in isotactic poly(1-butene) (PB-1) have been investigated using rheology, differential scanning calorimetry and infrared spectroscopy. Two commercially available grades of PB-1 with different average molecular weight were chosen. Specimens prepared by compression moulding were UV irradiated in the interval from 0 to 70 h. UV-induced changes in molecular structure have been followed by evolution of rheological properties, thermal properties and degradation by-products. Thermal analysis showed significant changes in crystallization behaviour influencing morphology and resulting thermal properties. Moreover it has been confirmed that the degradation significantly retards the phase transformation. Rheological measurement has been found as an effective method for determination of early stages of photodegradation of PB-1.     

Cytotoxic effect of some pentacyclic triterpenes and hemisynthetic derivatives of stigmasterol

Two different oxidation reactions (PCC and KMnO₄) of stigmasterol gave three products, stigmasta-4,22-dien-3-one (1a), stigmasta-4,22-diene-3,6-dione (1b), and 3-O-acetyl-5β,6β-epoxystigmast-22-ene-3-ol (1c). The cytotoxic activities of hemisynthetic compounds, stigmasterol, and four pentacyclic triterpens 2–5 previously isolated from cultivated and wild Triumfetta cordifolia and identified were investigated against human fibrosarcoma cell line (HT1080). Most of the drugs showed moderate cytotoxic activity. It was also notice that the triterpene skeleton had a range of number of OH functions in which activity was observed. Spectroscopic analyses (¹H and ¹³ C NMR) and mass were used to elucidate the structure of hemisynthetic compounds.     

Design of a new oligotriazole peptide nucleic acid analogue (oT-PNA)

We describe in this Letter the synthesis of an original thymine azido-heterotrimer generated by Click Chemistry. This trimer has been obtained from an azido-thymidine and a new chloroethyl-propargylated PNA monomer analogue, after two azidation/click-reaction cycles. Conformational preferences of a rotameric intermediate have also been studied     

Bioinspired Synthesis of Well‐Ordered Layered Organic–Inorganic Nanohybrids: Mimicking the Natural Processing of Nacre by Mineralization of Block Copolymer Templates

The unique mechanical performance of nacre, the pearly internal layer of shells, is highly dependent on its complex morphology. Inspired by the structure of nacre, the fabrication of well‐ordered layered inorganic–organic nanohybrids is presented herein. This biomimetic approach includes the use of a block copolymer template, consisting of hydrophobic poly(vinylidene fluoride) (PVDF) lamellae covered with hydrophilic poly(methacrylic acid) (PMAA), to direct silica (SiO₂) mineralization. The resulting PVDF/PMAA/SiO₂ nanohybrid material resembles biogenic nacre with respect to its well‐ordered and layered nanostructure, alternating organic–inorganic phases, macromolecular template, and mild processing conditions.

     

Treatment of water-induced curvature of the DSC heat flow rate signal

In samples containing a volatile phase, quite often the evaporation of the volatile substance during heating causes appreciable curvature of the DSC heat flow rate signal as function of temperature, making it difficult to quantify thermal transitions and reorganization phenomena occurring in the same temperature range. This is the case for e.g. polyamide–water, polyamide–alcohol, and polypropylene–water systems, thus complicating the study of polymer crystallization, melting, and metastability by DSC. In this study, maleic anhydride-grafted polypropylene particles of sub-micrometer diameters dispersed in water are discussed. These samples show, upon cooling from the melt, different degrees of extra supercooling in crystallization and several phenomena in the subsequent heating, like reorganization of a crystalline phase into another one, perfecting of crystallites, and melting. All these phenomena are difficult to analyze quantitatively due to the mentioned curvature of the DSC trace. In this article two methods, the “Reference” and “Extrapolation from the melt” methods, are described to correct for the influence of evaporation on the DSC heat flow rate signal and for the baseline signal, enabling the discussion of the transitions by way of the excess heat flow rate as function of temperature.     

Kinetics of iron–copper sulphides oxidation in relation to protohistoric copper smelting

This article deals with one specific step of the copper extractive metallurgy process: the roasting of iron–copper sulphides. It aims at shedding light on an archaeological issue: the reconstruction of the copper extractive metallurgy processes during protohistory (IV^e–II^e millennium BC). Experimental simulations are performed at laboratory scale by modelizing the conditions of protohistoric furnaces. Kinetic of roasting is studied by thermogravimetry combined with the physico-chemical analysis of synthetic products. The influence of two parameters is studied: (i) the temperature (773, 973 and 1173 K) and (ii) the granularity of the roasted ores (1 mm and 100 μm). In each case, the chemical mechanism governing the oxidation of iron copper sulphide is proposed. Apart from one extreme case (∅ = 1 mm; T = 773 K), it is showed that kinetic is controlled by the transport of molecular oxygen (O₂) from the gas to the grain surface. Moreover, we prove that, in some cases where the diffusivity of gaseous oxygen is low, roasting can be accelerated by the presence of an oxide, which constitute an in-situ source of oxygen. Theses experiments support the hypothesis that such a technique could have allowed a roasting process where iron and sulfur were removed by the solid oxygen instead of the gaseous oxygen. These results allow to validate a one-step copper smelting process starting from sulphidic ores, and to identify the experimental parameters of this process.     

Longitudinal 3D Blood Flow Distribution Provided by Diffuse Correlation Tomography during Bone Healing in a Murine Fracture Model

Noninvasive monitoring of vascularization can potentially diagnose impaired bone healing earlier than current radiographic methods. In this study, a noncontact diffuse correlation tomography (DCT) technique was employed to measure longitudinal blood flow changes during bone healing in a murine femoral fracture model. The three-dimensional distribution of the relative blood flow was quantified from one day pre-fracture to 48 days post-fracture. For three mice, frequent DCT measurements were performed every other day for one week after fracture, and then weekly thereafter. A decrease in blood flow was observed in the bone fracture region at one day post-fracture, followed by a monotonic increase in blood flow beyond the pre-injury baseline until five to seven days post-fracture. For the remaining 12 mice, only weekly DCT measurements were performed. Data collected on a weekly basis show the blood flow for most mice was elevated above baseline during the first two post-fracture weeks, followed by a subsequent decrease. Torsional strength of the excised femurs was measured for all 15 mice after 7 weeks of healing. A metric based on the early blood flow changes shows a statistically significant difference between the high strength group and the low strength group.     

Taming the Reactivity of Phosphiranium Salts: Site-Selective C-Centered Ring Opening for Direct Synthesis of Phosphinoethylamines

Advances in the field of phosphorus chemistry are documented, by revealing the synthetic utility of previously underutilized quaternary phosphiranium salts (QPrS) as three-chain-atom electrophilic building blocks. Notably, control of their challenging C-centered electrophilicity is disclosed with an expedient synthesis of tertiary β-anilino phosphines as a proof-of-concept.