The application of vinylogous iminium salt derivatives to an efficient relay synthesis of the pyrrole containing alkaloids polycitone A and B

A new and efficient relay synthesis of the marine natural products polycitone A and B is described. The new strategy relies on the formation of 2,4-disubstituted pyrroles from a vinamidinium salt followed by electrophilic substitution at the 5-position of the pyrrole and Suzuki coupling at the 4-position to produce the tetrasubstituted heterocycle efficiently and with complete control of regiochemistry.     

Term isotope shift of high lying odd and even energy levels of Nd II

The isotope shifts of the odd and even parity energy levels of singly-ionised neodymium (Nd II) have been evaluated using the measurements carried out in more than 300 spectral lines of Nd II in the region 3290–5820 Å. Term shift, ΔT (¹⁴⁴Nd-¹⁵⁰Nd), is being reported for 23 low even and 15 high lying even parity levels of Nd II. ΔT for a level of 4f ³6s6p configuration and 8 even levels between 36892 and 43212 cm^-1 are being reported for the first time. ΔT values of 151 high lying odd parity levels are being reported and compared with some of the available earlier reported values. ΔT values of 47 odd parity levels are being reported for the first time, most of which are based on our isotope shift studies in UV region. The electronic configuration assignments to energy levels of Nd II by earlier workers are discussed on the basis of present ΔT values. Electronic configurations to some of the unclassified high lying odd levels have been suggested; the levels with ΔT (144–150) between 300mK and 380mK are assigned to 4f ³5d6s configuration whereas a level with ΔT value of 60mK to 4f46p configuration.     

Diastereoselective synthesis of diverse 3,2′-pyrrolidinyl bispirooxindoles via 1,3-dipolar cycloaddition reactions of azomethine ylides with exocyclic α,β-unsaturated ketones and in silico studies for prediction of bioactivity

A three-component highly regio- and diastereoselective 1,3-dipolar cycloaddition reaction between isatin, a series of primary amino acids (10 nos), and exocyclic α,β-unsaturated ketones was developed towards the synthesis of a small library of bispirooxindole (20 nos) at ambient temperature. The developed reaction afforded highly substituted 3,2′-pyrrolidine-bispirooxindole with two vicinal spiro-quaternary and four contiguous stereocenters from the cheap and abundant starting materials. The products were obtained with good to excellent yields (50–95%) and as a single diastereoisomer in the majority of the cases. Primary amino acids were served as amine component for the in-situ generation of azomethine ylides from isatin. Molecular docking studies were carried out to explore the synthesized bispirooxindoles as inhibitors of the epidermal growth factor receptor (EGFR). Two compounds exhibited excellent binding affinity towards EGFR receptor.     

The size dependence of micro-toughness in ductile fracture

Micro-toughness in ductile fracture is defined as the plastic work dissipated per unit fracture surface area in the material separation processes of void growth and coalescence. A micromechanics model for the estimation of the size dependence of micro-toughness in ductile fracture is presented. Size effects are incorporated in the model using the conventional mechanism-based strain gradient plasticity (CMSG) theory. A finite element model of an axisymmetric representative unit cell with an initial spherical void is used to validate model predictions. Two characteristic length scales emerge from the model. The initial void radius sets the scale for the initial spherical void growth. For the subsequent void coalescence, the scale is set by the width of the intervoid ligament. Energy dissipation in ductile fracture is found to be dominated by the mechanisms of coalescence, and the micro-toughness in ductile fracture is found to be size dependent for dimple sizes approximately one order of magnitude larger than the material length scale.     

Polarization properties of dipolelike defect modes in photonic crystal nanocavities

Far-field measurements of the in-plane polarization properties of spontaneous emission from optical nanocavities formed in two-dimensional photonic crystal slab waveguides are presented. A strong polarization signature, even subthreshold, is found for a pair of highly localized dipolelike resonant modes. This polarization signature is used to study the effects of symmetry lowering within the cavity.     

Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high-reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backward-propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward-propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.     

Synthesis of a Mn6 cluster and its self-assembly of an azido-bridged polymer

A rare micro6-oxo-centered Mn6 mixed-valent cluster (1) is prepared and used as a secondary building unit for the self-assembly of its azido-bridged polymeric analogue (2) in a systematic way with the retention of the Mn6 core of 1. Both complexes are characterized by X-ray single-crystal structure determination. The complex 1 was crystallized in a monoclinic system, space group P21, a=11.252(5) A, b=20.893(9) A, c=12.301(6) A, and beta=115.853(7) degrees, whereas the polymeric analogue 2 was crystallized in an orthorhombic system, space group P212121, a=13.1941(8) A, b=14.9897(9) A, and c=27.8746(14) A. Variable-temperature magnetic behavior showed the presence of strong antiferromagnetic interaction in both cases.