A Single Terminal [NiII-OH] Catalyst for Direct Julia-Type Olefination and α-Alkylation Involving Sulfones and Alcohols.

A terminal [NiII-OH] complex 1, supported by triflamide-functionalized NHC ligands, showed divergent reactivity for the reaction of sulfone with alcohol, contingent on base concentration, temperature, and time. Julia-type olefination of alcohols with sulfones was achieved using one equiv. of base, whereas lowering base loading to 0.5 equiv. afforded α-alkylated sulfones. Besides excellent substrate scope and selectivity, biologically active stilbene derivatives DMU-212, pinosylvin, resveratrol, and piceatannol were synthesized in high yield under Julia-type olefination conditions. An extensive array of controlled experiments and DFT calculations provide valuable insight on the reaction pathway.

Circular current in a one-dimensional open quantum ring in the presence of magnetic field and spin-orbit interaction.

In an open quantum system having a channel in the form of loop geometry, the current inside the channel, namely circular current, and overall junction current, namely transport current, can be different. A quantum ring has doubly degenerate eigen energies due to periodic boundary condition that is broken in an asymmetric ring where the ring is asymmetrically connected to the external electrodes. Kramers' degeneracy and spin degeneracy can be lifted by considering non-zero magnetic field and spin-orbit interaction (SOI), respectively. Here, we find that symmetry breaking impacts the circular current conductance vs energy (E) spectra in addition to lifting the degeneracy. For charge and spin current conductances, the corresponding effects are not the same. Under symmetry-breaking they may remain symmetric or anti-symmetric or asymmetric aroundE = 0 whereas the transmission function (which is proportional to the junction current conductance) vs energy characteristic remains symmetric aroundE = 0. This study leads us to estimate the qualitative nature of the circular current and the choices of Fermi-energy/chemical potential to have a net non-zero current. As a result, we may manipulate the system to generate pure currents of charge, spin, or both, which is necessary for any spintronic and electronic applications.

Structural and chemical insights into the prebiotic property of hemicellulosic polysaccharide from Santalum album L.

Hemicellulose was extracted by alkali treatment of de-pectinated cell wall material of Santalum album L. (sandalwood) suspension culture cells. The physicochemical properties and prebiotic activities of a purified major fraction of Hemicellulose-B, termed as HB-I, were investigated. GC analysis of hydrolyzed and derivatized HB-I showed the presence of arabinose (~64 %), galactose (~16 %) and glucose (~16 %) as major monosaccharide units along with minor amount of rhamnose. Methylation and NMR studies on the purified polysaccharide revealed the presence of 6-ß-d-Glcp, ß-d-Galp, 3,5-α-l-Araf, α-l-Araf, 5-α-l-Araf, 2,3-α-l-Araf and, α-l-Rhap residues, from which a proposed structure of repeating units was established. The growth of probiotic Lactobacillus spp. strains L. acidophilus, L. casei, L. plantarum and L. rhamnosus was promoted while that of Escherichia coli was suppressed significantly in presence of HB-I. Our results highlight valorization of sandalwood biomass and explore the role of mixed α, ß-linked heteroglycan as a potential prebiotic molecule thus indicating the possibility of development of low-cost bioprocesses for production of functional food ingredients.

Hydroarylation of alkynes via dual ortho-C-H functionalization of diaryl amines on a dicopper(I,I) platform.

A pyridine and morpholine-functionalized dicopper(I,I)-NHC complex (1) features both terminal and bridging coordination modes of NHC within the same molecule, and catalyzes dual ortho-C-H functionalization of diaryl amines for the hydroarylation of alkynes. A bimetallic construct in catalyst 1 allows sequential activation of ortho-C-H bonds of two aryl units to furnish a wide variety of 9,10-dihydroacridine derivatives without the explicit use of a directing group.

Magneto-structural studies on a number of doubly end-on cyanate and azide bridged dinuclear nickel(ii) complexes with {N3O} donor Schiff base ligands.

Two new doubly µ 1,1-N3 bridged (1 and 3) and six new doubly µ 1,1-NCO bridged NiII complexes (2, 4-8) with six different N3O donor Schiff base ligands have been synthesized and magneto-structurally characterized. All these neutral complex molecules are isostructural and constitute edge sharing bioctahedral structures. Magnetic studies revealed that all these complexes exhibit ferromagnetic interaction through bridging pseudohalides with ferromagnetic coupling constant J being significantly higher for azide-bridged complexes than that of the cyanate analogues. This is consistent with the literature reported data and also the presence of polarizable π systems and two different N and O donor atoms in cyanate ion, rendering it a poor magnetic coupler in comparison to azide analogues. Although, the magneto-structurally characterized doubly µ 1,1-N3 bridged NiII complexes are abundant, only few such complexes with µ 1,1-bridging NCO- ions are reported in the literature. Remarkably, addition of these six new examples in this ever-growing series of doubly µ 1,1-NCO bridged systems gives us an opportunity to analyse the precise magneto-structural correlation in this system, showing a general trend in which the J value increases with an increase in bridging angles. Therefore, the high degree of structural and magnetic resemblances by inclusion of six new examples in this series is the major achievement of the present work. An elaborate DFT study was performed resulting in magneto-structural correlation showing that nature and value of the J-parameter is defined not only by Ni-Nb-Ni bond angles, but an important role is also played by the Ni1-Ni2-Nb-Xt dihedral angle (Nb and Xt are bridging N and terminal N or O atom of bridging ligands, respectively).

Electronic Coupling and Electrocatalysis in Redox Active Fused Iron Corroles.

Conjugated arrays composed of corrole macrocycles are increasingly more common, but their chemistry still lags behind that of their porphyrin counterparts. Here, we report on the insertion of iron(III) into a ß,ß-fused corrole dimer and on the electronic effects that this redox active metal center has on the already rich coordination chemistry of [H3tpfc] COT, where COT = cyclo-octatetraene and tpfc = tris(pentafluorophenyl)corrole. Synthetic manipulations were performed for the isolation and full characterization of both the 5-coordinate [FeIIItpfc(py)]2COT and 6-coordinate [FeIIItpfc(py)2]2COT, with one and two axial pyridine ligands per metal, respectively. X-Ray crystallography reveals a dome-shaped structure for [FeIIItpfc(py)]2COT and a perfectly planar geometry which (surprisingly at first) is also characterized by shorter Fe-N (corrole) and Fe-N (pyridine) distances. Computational investigations clarify that the structural phenomena are due to a change in the iron(III) spin state from intermediate (S = 3/2) to low (S = 1/2), and that both the 5- and 6-coordinated complexes are enthalpically favored. Yet, in contrast to iron(III) porphyrins, the formation enthalpy for the coordination of the first pyridine to Fe(III) corrole is more negative than that of the second pyridine coordination. Possible interactions between the two corrole subunits and the chelated iron ions were examined by UV-Vis spectroscopy, electrochemical techniques, and density functional theory (DFT). The large differences in the electronic spectra of the dimer relative to the monomer are concluded to be due to a reduced electronic gap, owing to the extensive electron delocalization through the fusing bridge. A cathodic sweep for the dimer discloses two redox processes, separated by 230 mV. The DFT self-consistent charge density for the neutral and cationic states (1- and 2-electron oxidized) reveals that the holes are localized on the macrocycle. A different picture emerges from the reduction process, where both the electrochemistry and the calculated charge density point toward two consecutive electron transfers with similar energetics, indicative of very weak electron communication between the two redox active iron(III) sites. The binuclear complex was determined to be a much better catalyst for the electrochemical hydrogen evolution reaction (HER) than the analogous mononuclear corrole.

Effect of spin-orbit interaction on circular current: pure spin current phenomena within a ring conductor.

A net circulating current may appear within a quantum ring under finite bias. We study the characteristic features of the circular current in the presence of Rashba spin-orbit interaction (RSOI). Both charge and spin currents appear within the ring. Whereas when the ring is symmetrically connected to the external leads, we can get a pure spin current at non-zero Fermi-energy. On the other hand, for asymmetric ring-to-leads configuration, at zero Fermi-energy, the spin current vanishes but a pure charge current flows within the ring. Tuning RSOI, we demonstrate a way to control the pure spin current externally. This new perspective of the generation of the pure spin circular current can open a new basis for the highly efficient, low energy cost spintronic devices.

Fucose-containing Abroma augusta mucilage hydrogel as a potential probiotic carrier with prebiotic function.

The mucilaginous polysaccharide from Abroma augusta stem was examined for its physicochemical, thermal, and functional behavior and explored as a carrier for probiotic bacteria. Composed of glucose, galactose, rhamnose, galactouronic acid and fucose, Abroma augusta mucilage (AAM) exhibited shear thinning behavior (following power law equation) and gel like characteristic (showing higher G' value than G″ value). AAM promoted the growth of probiotic strains with positive prebiotic scores of 0.5 ± 0.06 and 0.51 ± 0.05 for Lactobacillus acidophilus and Lactobacillus casei, respectively. Further, probiotic strains were embedded in the AAM matrix followed by freeze-drying with embedding efficiency of >95%. Viscoelastic properties were retained substantially in the rehydrated probiotic-embedded matrix. AAM could protect probiotic bacteria in simulated gastrointestinal conditions, at elevated (80 °C, 20 min) and at low (4 °C, 4 months) temperatures ensuring higher viabilities of embedded probiotic cells. Our findings established potential carrier capabilities of AAM polysaccharides for probiotic bacteria with thickening and prebiotic activity.

Engineering magnetoresistance: a new perspective.

A new proposal is given to achieve high degree of magnetoresistance (MR) in a magnetic quantum device where two magnetic layers are separated by a non-magnetic (NM) quasiperiodic layer that acts as a spacer. The NM spacer is chosen in the form of well-known Aubry-André or Harper (AAH) model which essentially gives the non-trivial features in MR due to its gaped spectrum and yields the opportunities of controlling MR selectively by tuning the AAH phase externally. We also explore the role of dephasing on magnetotransport to make the model more realistic. Finally, we illustrate the experimental possibilities of our proposed quantum system.

Externally controlled high degree of spin polarization and spin inversion in a conducting junction: Two new approaches.

We propose two new approaches for regulating spin polarization and spin inversion in a conducting junction within a tight-binding framework based on wave-guide theory. The system comprises a magnetic quantum ring with finite modulation in site potential is coupled to two non-magnetic electrodes. Due to close proximity an additional tunneling is established between the electrodes which regulates electronic transmission significantly. At the same time the phase associated with site potential, which can be tuned externally yields controlled transmission probabilities. Our results are valid for a wide range of parameter values which demonstrates the robustness of our proposition. We strongly believe that the proposed model can be realized in the laboratory.

Modulation of circular current and associated magnetic field in a molecular junction: A new approach.

A new proposal is given to control local magnetic field in a molecular junction. In presence of finite bias a net circular current is established in the molecular ring which induces a magnetic field at its centre. Allowing a direct coupling between two electrodes, due to their close proximity, and changing its strength we can regulate circular current as well as magnetic field for a wide range, without disturbing any other physical parameters. We strongly believe that our proposal is quite robust compared to existing approaches of controlling local magnetic field and can be verified experimentally.

Ligand centered radical pathway in catechol oxidase activity with a trinuclear zinc-based model: synthesis, structural characterization and luminescence properties.

A new trinuclear zinc(II) complex, [Zn3(L)(NCS)2](NO3)2·CH3OH·H2O (1), of a (N,O)-donor compartmental Schiff base ligand (H2L=N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol), has been synthesized in crystalline phase. The zinc(II) complex has been characterized by elemental analysis, IR spectroscopy, UV-Vis spectroscopy, powder X-ray diffraction study (PXRD), (1)H NMR, EI mass spectrometry and thermogravimetric analysis. PXRD revealed that 1 crystallizes in P-1 space group with a=9.218 Å, b=10.849 Å, c=18.339 Å, with unit cell volume is 2179.713(Å)(3). Fluorescence spectra in methanolic solution reflect that intensity of emission for 1 is much higher compared to H2L and both the compounds exhibit good fluorescence properties. The complex 1 exhibits significant catalytic activities of biological relevance, viz. catechol oxidase. In methanol, it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to corresponding quinone via formation of a dinuclear species as [Zn2(L)(3,5-DTBC)]. Electron Paramagnetic Resonance (EPR) experiment suggests generation of radicals in the presence of 3,5-DTBC and it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complex of redox-innocent Zn(II) ion.

Isolation and characterization of extracellular polysaccharide Thelebolan produced by a newly isolated psychrophilic Antarctic fungus Thelebolus.

The present investigation is on a newly isolated psychrophilic Antarctic filamentous Ascomycetous fungus that has been identified as Thelebolus sp. and given the designation of Thelebolus sp. IITKGP-BT12. The culture was primarily identified through morphological studies, and was further confirmed by 18S rRNA sequencing (GenBank Accession No. KC191572), which revealed its close relatedness with Thelebolus microsporus. The exopolysaccharide (EPS) produced (1.94 g L(-1)) by the fungus was isolated, purified and characterized as glucan having an average molecular mass of 5×10(5)Da. The structure of EPS was determined by gas chromatography with tandem mass spectrometry (GC-MS/MS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) studies ((1)H, (13)C and HSQC). NMR analysis indicated the presence of (1→3)-linked ß-d-glucan backbone with (1→6)-linked branches of ß-d-glucopyranosyl units. Antiproliferative activity of EPS was demonstrated in B16-F0 cells, with IC50 of 275.42 µg m L(-1). Flow cytometry analysis and DNA fragmentation studies revealed that the cytotoxic action of the EPS mediated apoptosis in cancer cells. This is the first ever report on bioactive EPS thelebolan from Thelebolus sp.