Synthesis and lanthanide coordination properties of new 2,6-bis(N-tert-butylacetamide)pyridine and 2,6-bis(N-tert-butylacetamide)pyridine-N-oxide ligands

The compound 2,6-bis(N-tert-butylacetamide)pyridine (2) was obtained via a Ritter synthesis, and oxidation with oxone provided the title pyridine-N-oxide (3). The compounds were characterized by spectroscopic methods, and the molecular structure of the N-oxide was determined by single-crystal X-ray diffraction methods. The coordination chemistry with Eu(NO3)3 was examined by using 1:1 and 2:1 ligand/Eu ratios, and a single-crystal X-ray analysis for Eu(3)(NO3)3(H2O) was completed. The ligand 3 is found to chelate in a tridentate fashion on the Eu(III).     

Formation of a layered framework structure based upon 4-methyl-2,6-bis(methylphosphonic acid) phenol

The trifunctional ligands, [(HO)2P(O)CH2]2C6H2(R)OH, (5-H4)(R = CH3, Br) were prepared in good yield via an Arbusov reaction between P(OEt)3 and the respective 4-R-2,6-bis(chloromethyl)phenols followed by acidic aqueous hydrolysis and they were spectroscopically characterized by IR and NMR techniques. The ligand 5-H4-CH3 readily dissolves lanthanide hydroxide residues and it forms a crystalline complex from aqueous LaCl3 solutions. This complex was characterized by single crystal X-ray diffraction methods and found to adopt a complex 2-D lamellar network in the bc plane. The La(III) inner coordination sphere is seven coordinate formed by oxygen atoms from two water molecules and five phosphonate oxygen atoms from three different ligands. The phenolic oxygen atom is not involved in the ligand binding to La(III).     

Effect of Ligand Fields on the Reactivity of O2‐Activating Iron(II)‐Benzilate Complexes of Neutral N5 Donor Ligands

Three new iron(II)‐benzilate complexes [(N4Py)Fe^II(benzilate)]ClO₄ ( 1 ), [(N4Py^Me2)Fe^II(benzilate)]ClO₄ ( 2 ) and [(N4Py^Me4)Fe^II(benzilate)]ClO₄ ( 3 ) of neutral pentadentate nitrogen donor ligands have been isolated and characterized to study their dioxygen reactivity. Single‐crystal X‐ray structures reveal a mononuclear six‐coordinate iron(II) center in each case, where benzilate binds to the iron center in monodentate mode via one carboxylate oxygen. Introduction of methyl groups in the 6‐positions of the pyridine rings makes the N4Py^Me2 and N4Py^Me4 ligand fields weaker compared to that of the parent N4Py ligand. All the complexes ( 1 – 3 ) react with dioxygen to decarboxylate the coordinated benzilate to benzophenone quantitatively. The decarboxylation is faster for the complex of the more sterically hindered ligand and follows the order 3 > 2 > 1 . The complexes display oxygen atom transfer reactivity to thioanisole and also exhibit hydrogen atom transfer reactions with substrates containing weak C?H bonds. Based on interception studies with external substrates, labelling experiments and Hammett analysis, a nucleophilic iron(II)‐hydroperoxo species is proposed to form upon two‐electron reductive activation of dioxygen by each iron(II)‐benzilate complex. The nucleophilic oxidants are converted to the corresponding electrophilic iron(IV)‐oxo oxidant upon treatment with a protic acid. The high‐spin iron(II)‐benzilate complex with the weakest ligand field results in the formation of a more reactive iron‐oxygen oxidant.     

Characterization of corrugated feed horns at 216 and 300 GHz

We present measurements of the near-field beam profiles of two corrugated feed horns with center frequencies of 216 and 300 GHz. Both co-polar and cross-polar components of the electric field have been probed across the operation band of the horns. A full-wave numerical near-field transformation, based on a vector Kirchhoff integral, is implemented to transform the measured field to the horn aperture for a comparison with the ideal aperture field. From the overlap integral of the transformed and the ideal field, we conclude that the field radiated by these horns is the HE₁₁ mode, to a purity of better than 99%.     

Highly Selective and Catalytic Oxygenations of C−H and C=C Bonds by a Mononuclear Nonheme High‐Spin Iron(III)‐Alkylperoxo Species

The reactivity of a mononuclear high‐spin iron(III)‐alkylperoxo intermediate [Fe^III(t‐BuL^Urea)(OOCm)(OH₂)]²⁺( 2 ), generated from [Fe^II(t‐BuL^Urea)(H₂O)(OTf)](OTf) ( 1 ) [t‐BuL^Urea=1,1′‐(((pyridin‐2‐ylmethyl)azanediyl)bis(ethane‐2,1‐diyl))bis(3‐(tert‐butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C?H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C?H bonds of aliphatic substrates with high chemo‐ and stereoselectivity in the presence of 2,6‐lutidine. While 2 itself is a sluggish oxidant, 2,6‐lutidine assists the heterolytic O?O bond cleavage of the metal‐bound alkylperoxo, giving rise to a reactive metal‐based oxidant. The roles of the urea groups on the supporting ligand, and of the base, in directing the selective and catalytic oxygenation of hydrocarbon substrates by 2 are discussed.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.     

Nozzle and liquid effects on the spray modes in nanoelectrospray

Unforced nanoelectrospray can exhibit a number of stable spray modes. These include low frequency pulsations, high frequency pulsations, and a steady cone-jet. Experiments are reported here on such pulsations that have been observed in various salt loaded solutions of ethylene glycol, triethylene glycol and water. The spray current was monitored with 1 mus time resolution to show that spray regime characteristics depend on nozzle diameter and liquid conductivity. The frequency of pulsations was found to increase with both increased liquid conductivity and decreasing nozzle diameter. The charge ejected during a pulse is lower for smaller nozzles spraying higher conductivity liquids. Water solutions were observed undergoing high frequency pulsations, with these pulsations often occurring in lower frequency bursts. The frequencies of water pulsations were as high as 635 kHz but the charge ejected by each pulsation was an order of magnitude lower than that observed in triethylene glycol. An unforced electrospray of water was also identified as being in the steady cone-jet mode with a higher degree of confidence than previously. The values for stable pulsation frequency and charge ejected observed in ethylene glycol lay between those of TEG and water.