Asymmetric aziridine synthesis by aza-Darzens reaction of N-diphenylphosphinylimines with chiral enolates. Part 1: Formation of cis-aziridines

The aza-Darzens (‘ADZ’) reactions of N-diphenylphosphinyl (‘N-Dpp’) imines with chiral enolates derived from oxazolidinones and camphorsultam have been studied. Whilst oxazolidinone enolates reacted poorly in terms of aziridination, the use of the chiral enolate derived from both antipodes of N-bromoacetyl 2,10-camphorsultam, 2R-(5) and 2S-(5), with N-diphenylphosphinyl aryl and tert-butylimines proceeded in generally good yield to give, respectively, (2′R,3′R)- or (2′S,3′S)-cis-N-diphenylphosphinyl aziridinoyl sultams of high de.     

Theoretical Study of Screening Dependence of Aluminium Doped MgB_2

The screening dependence of superconducting state parameters(λ, μ*, T_c, and N_0V(1) of six alloys of aluminium doped Mg B2 systems are studied in the BCS–Eliashberg–Mc Millan framework by employing five forms of dielectric screening function, viz. random phase approximation(RPA), Harrison, Geldart and Vosko(GV), Hubbard and Overhauser in conjunction with Ashcroft's potential. It is observed that electron-phonon coupling strength λ and Coulomb pseudopotential μ*are quite sensitive to the form of dielectric screening, whereas transition temperature T_c, isotope effect exponent α and effective interaction strength N_0V(1 show weak dependence on the form of dielectric screening function. It is found that the RPA form of dielectric screening function yields the best results for transition temperature T_c for all alloys of the Mg-Al-B system. The results obtained using GV screening are much higher than the experimental results. This shows that all the four dielectric screenings used here almost describe superconductivity in all the alloys of the Mg-Al-B system, but the GV screening is not suitable for such an alloy system.     

Quantum discord with weak measurements

Weak measurements cause small change to quantum states, thereby opening up the possibility of new ways of manipulating and controlling quantum systems. We ask, can weak measurements reveal more quantum correlation in a composite quantum state? We prove that the weak measurement induced quantum discord, called as the “super quantum discord”, is always larger than the quantum discord captured by the strong measurement. Moreover, we prove the monotonicity of the super quantum discord as a function of the measurement strength and in the limit of strong projective measurement the super quantum discord becomes the normal quantum discord. We find that unlike the normal discord, for pure entangled states, the super quantum discord can exceed the quantum entanglement. Our results provide new insights on the nature of quantum correlation and suggest that the notion of quantum correlation is not only observer dependent but also depends on how weakly one perturbs the composite system. We illustrate the key results for pure as well as mixed entangled states.     

Nuclear Quadrupole Interactions in Nuclear Quadrupole Resonance Detection of Energetic and Controlled Materials: Theoretical Study

There has been a growing interest in nuclear quadrupole resonance (NQR) techniques useful for the detection of explosives and drugs in solid state systems. This paper uses the first-principles one-electron Hartree?CFock theoretical method to study the nuclear quadrupole interaction parameters e ² qQ and ?? for the ¹⁴N nuclei in the explosives RDX and ??-HMX as well as the drugs cocaine and heroin. It has been found in our earlier published investigations reviewed here that there is very good agreement for our calculated e ² qQ and ?? for ¹⁴N, for all these four systems, and experiment. We also present our unpublished theoretical results for cocaine with an HCl molecule attached. We successfully explain quantitatively the drastic decrease in e ² qQ in going to cocaine-HCl from cocaine-free base as well as the observed substantial increase in ?? and discuss the implications of these dramatic changes for NQR detection in general.     

Strategies to Overcome Oxygen Transfer Limitations During Hairy Root Cultivation of Azadiracta indica for Enhanced Azadirachtin Production

The vast untapped potential of hairy root cultures as a stable source of biologically active chemicals has focused the attention of scientific community toward its commercial exploitation. However, the major bottleneck remains its successful scale-up. Due to branching, the roots form an interlocked matrix that exhibits resistance to oxygen transfer. Thus, present work was undertaken to develop cultivation strategies like optimization of inlet gas composition (in terms of % (v/v) O₂ in air), air-flow rate and addition of oxygen vectors in the medium, to curb the oxygen transfer limitations during hairy root cultivation of Azadirachta indica for in vitro azadirachtin (a biopesticide) production. It was found that increasing the oxygen fraction in the inlet air (in the range, 20–100% (v/v) O₂ in air) increased the azadirachtin productivity by approximately threefold, to a maximum of 4.42 mg/L per day (at 100% (v/v) O₂ in air) with respect to 1.68 mg/L per day in control (air with no oxygen supplementation). Similarly, increasing the air-flow rate (in the range, 0.3–2 vvm) also increased the azadirachtin productivity to a maximum of 1.84 mg/L per day at 0.8 vvm of air-flow rate. On the contrary, addition of oxygen vectors (in the range, 1–4% (v/v); hydrogen peroxide, toluene, Tween 80, kerosene, silicone oil, and n-hexadecane), decreased the azadirachtin productivity with respect to control (1.76 mg/L per day).     

Development of a Mathematical Model for Growth and Oxygen Transfer in In Vitro Plant Hairy Root Cultivations

Genetically transformed, "Hairy roots" once developed can serve as a stable parent culture for in vitro production of plant secondary metabolites. However, the major bottleneck in the commercial exploitation of hairy roots remains its successful scale-up due to oxygen transfer limitation in three-dimensionally growing hairy root mass. Mass transfer resistances near the gas-liquid and liquid-solid boundary layer affect the oxygen delivery to the growing hairy roots. In addition, the diffusional mass transfer limitation due to increasing size of the root ball (matrix) with growth also plays a limiting role in the oxygen transfer rate. In the present study, a mathematical model is developed which describes the oxygen transfer kinetics in the growing Azadirachta indica hairy root matrix as a case study for offline simulation of process control strategies ensuring non-limiting concentrations of oxygen in the medium throughout the hairy root cultivation period. The unstructured model simulates the effect of oxygen transfer limitation in terms of efficiency factor (η) on specific growth rate (μ) of the hairy root biomass. The model is able to predict effectively the onset of oxygen transfer limitation in the inner core of the growing hairy root matrix such that the bulk oxygen concentration can be increased so as to prevent the subsequent inhibition in growth of the hairy root biomass due to oxygen transfer (diffusional) limitation.     

Gold-catalyzed synthesis of substituted 2-aminofurans via formal [4+1]-cycloadditions on 3-en-1-ynamides

Gold-catalyzed formal [4+1]-cycloadditions between 3-en-1-ynamides 1 and 8-methylquinoline oxide are reported. The success of this reaction relies on a hypothetic oxa-Nazarov cyclization on gold-stabilized allylic cations. Preliminary results on a new 1,2-difunctionalization of 3-en-1-ynamide are also reported.     

On weighted directed graphs

The study of a mixed graph and its Laplacian matrix have gained quite a bit of interest among the researchers. Mixed graphs are very important for the study of graph theory as they provide a setup where one can have directed and undirected edges in the graph. In this article we present a more general structure, namely the weighted directed graphs and supply appropriate generalizations of several existing results for mixed graphs related to singularity of the corresponding Laplacian matrix. We also prove many new combinatorial results relating the Laplacian matrix and the graph structure.     

Diorganotin(IV) complexes of polyaromatic azo‐azomethine ligand derived from salicylaldehyde and ortho‐aminophenol: Synthesis,characterization, and molecular structures

The diorganotin(IV) complexes of methyl 2‐{4‐hydroxy‐3‐[(2‐hydroxy‐phenylimino)‐methyl]‐phenylazo}‐benzoate (H2L) were obtained by the reaction of ortho‐aminophenol, R₂SnO (R = Me, ⁿBu, or Ph) and methyl 2‐[(E)‐(3‐formyl‐4‐hydroxy)diazenyl]benzoate (H2PL²) in ethanol, which led to diorganotin(IV) compounds of composition [Me₂SnL]₂ ( 1 ), ⁿBu₂SnL ( 2 ), and Ph₂SnL ( 3 ) in good yield. The ¹H, ¹³C, and ¹¹⁹Sn NMR, IR, the mass spectrometry along with elemental analyses allowed establishing the structure of ligand (H2L) and compounds 1–3 . In all the three cases, ¹¹⁹Sn chemical shifts are indicators of five‐coordinated Sn atoms in a solution state. The crystal structures of ligand H2L and complexes 1 and 2 were determined by a single crystal X‐ray diffraction study. In the solid state, the ligand H2L exists as a keto‐enamine tautomeric form. The molecular structure of complex 1 in the solid state shows a distorted octahedral geometry around a tin atom due to additional coordination with an oxygen atom from a neighboring molecule leading to a four‐membered ring with Sn‐O···Sn‐O intermolecular coordination, leading to a dimeric species. On the other hand, complex 2 is a monomer with trigonal bipyramidal geometry surrounding the tin atom. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:457–465, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21037