Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ²‐N(PPh₂(BH₃))₂}Li(THF)₂] ( 2 ) and [{κ³‐N(PPh₂(BH₃))₂}₂M(THF)₂] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH₃ group in κ²‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ³‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described.     

One-pot multicomponent diastereoselective synthesis of novel dihydro-1H-furo[2,3-c]pyrazoles

An efficient method was developed for the diastereoselective synthesis of novel fused dihydro-1H-furo[2,3-c]pyrazole by a one-pot, four-component reaction of β-keto ester, hydrazine, aromatic aldehyde, and pyridinium ylide in the presence of triethylamine under microwave irradiation in solvent-free conditions in good yields. The merits of this cascade Knoevenagel condensation/Michael addition/cyclization sequence include its high atom economy, good yields, and efficiency of producing three new bonds (two C–C and one C–O) and two stereocenters in a single operation.     

Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al‐doped ZnO films

In this work, conductive atomic force microscopy is used to study the inhomogeneous surface electrical conductivity of Al‐doped ZnO thin films at a nanoscale dimension. To this end, Al‐doped ZnO films were deposited onto the soda lime glass substrates at substrate temperature (T_s) varying from 303 to 673 K in radio frequency magnetron sputtering. The obtained local surface electrical conductivity values are found to be influenced by their bulk electrical resistivity, surface topography and tip geometry. Further, the average (local) surface conductivity from the film surface is found to increase with increasing T_s from 303 to 623 K, beyond which they decrease until 673 K. Copyright © 2016 John Wiley & Sons, Ltd.     

Sufficient optimality conditions and duality theory for interval optimization problem

This paper addresses the duality theory of a nonlinear optimization model whose objective function and constraints are interval valued functions. Sufficient optimality conditions are obtained for the existence of an efficient solution. Three type dual problems are introduced. Relations between the primal and different dual problems are derived. These theoretical developments are illustrated through numerical example.     

Mass-spectrometric analysis of complex volatile and nonvolatile crude oil components: a challenge

Crude oil analysis has long been an inspiration for the development of analytical techniques. Especially mass spectrometry has flourished as a result of the challenge these extremely complex problems offer. Here an overview of different analytical methods is presented that shows different ways to analyze volatile and nonvolatile crude oil components. Focus has been placed on the use of mass spectrometry and especially the new developments that have been introduced using the emerging technique of Fourier transform ion cyclotron resonance mass spectrometry. These studies are examples of how far the development of analytical methods has come for the task of studying such complex problems.     

Formation of left-handed helices in hybrid peptide oligomers with cis beta-sugar amino acid and L-Ala as building blocks

Residue based control of specific helical folding is explored in hybrid peptide oligomers consisting of alternating L-Ala and cis-beta-furanoid sugar amino acid (FSAA) residues as building blocks; two series of these hybrid oligomers are designed, synthesized and extensively characterized by using NMR, CD, FT-IR and MD simulation studies; results show the co-existence of left-handed 11- and 14/15-helical conformations in these short oligomers of Boc-(alpha/beta) and Boc-(beta/alpha) series.     

Diversity-oriented synthetic approach to naturally abundant S-amino acid based benzannulated enantiomerically pure medium ring heterocyclic scaffolds employing inter- and intramolecular mitsunobu reactions

The diversity-oriented organic synthesis of enantiomerically pure benzannulated oxazepine, diazepine, thiazepine, oxazocine, and diazocine scaffolds is described from easily accessible naturally occurring S-amino acids as chiral synthons. Inter- and intramolecular Mitsunobu reactions for the formation of carbon-nitrogen, carbon-oxygen, and carbon-sulfur bonds have been used as key transformations to construct these biologically important privileged heterocycles. This is the first example where the Mitsunobu approach has been utilized for the construction of S-amino acid based seven- and eight-membered ring systems.     

pH‐Dependent Nitrotyrosine Formation in Ribonuclease A is Enhanced in the Presence of Polyethylene Glycol (PEG)

Protein nitration can occur as a result of peroxynitrite‐mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular medium can cause oxidative damage to biomolecules. The in vitro nitration of Ribonuclease A (RNase A) results in nitrotyrosine (NT) formation with a strong dependence on the pH of the medium. In order to mimic the cellular environment in this study, PN‐mediated RNase A nitration has been carried out in a crowded medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumor cell pH). The extent of nitration increases significantly when PN is added to RNase A in the presence of crowding agents PEG 400 and PEG 6000. PEG has been found to stabilize PN over a prolonged period, thereby increasing the degree of nitration. NT formation in RNase A also results in a significant loss in enzymatic activity.     

Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

This article deals with isomeric ruthenium complexes [Ru^III(L^R)₂(acac)] (S=1/2) involving unsymmetric β‐ketoiminates (AcNac) (L^R=R‐AcNac, R=H ( 1 ), Cl ( 2 ), OMe ( 3 ); acac=acetylacetonate) [R=para‐substituents (H, Cl, OMe) of N‐bearing aryl group]. The isomeric identities of the complexes, cct (cis‐cis‐trans, blue, a ), ctc (cis‐trans‐cis, green, b ) and ccc (cis‐cis‐cis_, pink, c ) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single‐crystal X‐ray structures and spectroscopic/electrochemical features. One‐electron reversible oxidation and reduction processes of 1 – 3 led to the electronic formulations of [Ru^III(L)(L ^? )(acac)]⁺ and [Ru^II(L)₂(acac)]^? for 1 ⁺‐ 3 ⁺ (S=1) and 1^? – 3^? (S=0), respectively. The triplet state of 1 ⁺‐ 3 ⁺ was corroborated by its forbidden weak half‐field signal near g≈4.0 at 4 K, revealing the non‐innocent feature of L. Interestingly, among the three isomeric forms ( a – c in 1 – 3 ), the ctc ( b in 2 b or 3 b ) isomer selectively underwent oxidative functionalization at the central β‐carbon (C?H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [Ru^II(L)(L ′ )(acac)] (L ′ =diketoimine) in 4 / 4′ . Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.