Preparative isolation and purification of alkannin/shikonin derivatives from natural products by high-speed counter-current chromatography

Alkannin and shikonin (A/S) and their derivatives have been found in the roots of several Boraginaceous species and are also produced through plant tissue cultures. The chiral compounds A/S are potent pharmaceutical substances with a wide spectrum of biological and pharmacological activities like wound healing, antimicrobial, anti-inflammatory, anticancer and antioxidant activity. High-speed counter-current chromatography (HSCCC) was applied for the first time to the separation, preparative isolation and purification of A/S and their esters from extracts of Alkanna tinctoria roots, as well as commercial samples. The constituents of HSCCC fractions and their purity were determined by high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS), since DAD cannot detect oligomeric A/S derivatives that are present in most of the samples containing the respective monomeric derivatives. The purity of HSCCC fractions was compared with the one of fractions isolated by column chromatography (CC) using as stationary phases silica gel and Sephadex LH-20. As shown, the purity of monomeric alkannin/shikonin was greater by HSCCC than CC separation of commercial A/S samples.     

The supramolecular chemistry of metal complexes with heavily substituted imidazoles as ligands: Cobalt(II) and zinc(II) complexes of 1-methyl-4,5-diphenylimidazole

An investigation of the M^II/X⁻/L [M^II = Co, Ni, Cu, Zn; X⁻ = Cl⁻, Br⁻, I⁻, NCS⁻, NO₃⁻, N₃⁻, CH₃COO⁻; L = 1-methyl-4,5-diphenylimidazole] general reaction system towards the detailed study of the intermolecular interactions utilized for controlling the supramolecular organization and the structural consequences on the structures produced has been initiated. Three representative complexes with the formulae [Co(NO₃)₂(L)₂] (1), [Zn(NO₃)₂(L)₂] (2) and [Co(NCS)₂(L)₂]·EtOH (3·EtOH) have been synthesized and characterized by spectroscopic methods and single-crystal X-ray analysis. Compounds 1 and 2 are isomorphous (tetragonal, I4₁cd) with their metal ions in a severely distorted octahedral Co/ZnN₂O₄ environment, while 3·EtOH crystallizes in P2₁/c with a tetrahedral CoN₄ coordination. The structural analysis of 1, 2 and 3·EtOH reveals a common mode of packing among neighbouring ligands (expressed through intramolecular π–π interactions between the 4,5-diphenylimidazole moieties), enhancing thus the rigidity and stability of the complexes. The bent coordination of the two isothiocyanates in 3 [Co–NCS angles of 173.8(2) and 160.8(2)°] seems to be caused by intermolecular hydrogen bonding and crystal packing effects.     

Humean Supervenience in the Light of Contemporary Science

It is shown that Lewis’ ontological doctrine of Humean supervenience incorporates at its foundation the so-called separability principle of classical physics. In view of the systematic violation of the latter within quantum mechanics, the claim that contemporary physical science may posit non-supervenient relations beyond the spatiotemporal ones is reinforced on a foundational basis concerning constraints on the state representation of physical systems. Depending on the mode of assignment of states to quantum systems — unit state vectors versus statistical density operators — we distinguish between strongly and weakly non-Humean, non-supervenient relations. It is demonstrated that in either case, the relations of quantum entanglement constitute prototypical examples of irreducible physical relations that do not supervene upon a spatiotemporal arrangement of Humean qualities, weakening, thereby, the thesis of Humean supervenience. In this respect, the status of Lewis’ recombination principle is examined, whereas his conception of lawhood is critically investigated. It is concluded that the assumption of ontological reductionism, as expressed in Lewis’ Humean doctrine, cannot be regarded as a reliable code of the nature of the physical world and its contents. It is proposed instead that due to the undeniable existence of non-supervenient relations, a metaphysic of relations of a moderate kind ought to be acknowledged as an indispensable part of our understanding of the natural world at a fundamental level.     

Low temperature electronic transport in sputter deposited a-IGZO films

We report on the electrical properties of a-IGZO thin films prepared by reactive sputtering. Without oxygen injection, dc resistivity measured at room temperature is ρ_300K = 1.22 × 10⁻³ Ωm. The lowest resistivity ρ_300K = 4.86 × 10⁻⁵ Ωm is obtained at a certain oxygen supply into the deposition process. Hall effect measurements of these films reveal a metallic-like behavior from mobility and carrier concentration vs. temperature in the range 15–300 K whereas films deposited without oxygen or for the highest oxygen flows behave as semiconductors. These enhanced electrical properties are connected to the oxygen vacancies and the local coordination structure around the In³⁺ cations.     

Pentanuclear complexes with unusual structural topologies from the initial use of two aliphatic amino-alcohol ligands in Fe chemistry

Five novel pentanuclear Fe(3+) clusters with the aliphatic amino-alcohol ligands 3-amino-1-propanol (Hap) and 2-(hydroxymethyl)piperidine (Hhmpip) [Fe(5)(μ(3)-Ο)(2)(L)(4)(O(2)CR)(7)] [L = ap(-), R = Ph (1); L = ap(-), R = C(CH(3))(3) (2); L = hmpip(-), R = Ph (3); L = hmpip(-), R = C(CH(3))(3) (4)] and [Fe(5)(μ(4)-Ο)(μ(3)-Ο)(O(2)CC(CH(3))(3))(8)(ap)(2)Cl(HO(2)CC(CH(3))(3))] (5) are reported. Compounds 1-4 were prepared from reactions of preformed trinuclear Fe(3+) clusters with the ligands in a molar ratio 1 : 5 in MeCN (1, 3, 4) or DMF (2), whereas compound 5 was prepared from the reaction of FeCl(3) with Hap in the presence of HO(2)CC(CH(3))(3) in a molar ratio 1 : 3 : 2 in MeCN. To the best of our knowledge, 1-5 are the first examples of Fe(3+) complexes with the ligands Hap and Hhmpip. The structures of 1-4 are composed of a quasi-planar [Fe(5)(μ(3)-O)(2)](11+) core which consists of two vertex-sharing [Fe(3)(μ(3)-O)](7+) triangles. The structure of 5 is based on the [Fe(5)(μ(4)-O)(μ(3)-O)](11+) core, in which the five Fe(3+) ions adopt a monocapped trigonal pyramidal topology. Variable-temperature magnetic susceptibility measurements on powdered microcrystalline samples of 1 and 5 revealed the existence of antiferromagnetic interactions which led to an S = 5/2 ground state. M?ssbauer spectroscopy studies on powdered microcrystalline samples of 1 and 5 confirmed that all iron ions of both complexes are in the Fe(3+) (S = 5/2) state. The variation of the ligand environment in the various iron sites was reflected in their different quadruple splitting parameters. At T < 50 K the M?ssbauer spectra indicated the onset of spin relaxation effects in the time scale of the technique (10(-7)-10(-8) s).     

Aspartyl methyl ester formation via aspartimide ring opening: a proposed modification of the protocols used in Boc- and Fmoc-based solid-phase peptide synthesis

Aspartimide formation is still an unresolved problem in the solid-phase peptide synthesis of aspartic acid-containing peptides, following either Boc- or Fmoc-based synthetic strategies. α-Aspartyl peptides of high purity can be obtained, despite aspartimide formation, by incorporating an additional step in the Boc- and Fmoc-based solid-phase peptide synthesis protocols, consisting of treatment of the peptide-resin with methanol in the presence of 2% DIEA (v/v) for 15 min immediately after completion of the peptide chain elongation.     

Reactions of 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) with yttrium(III) nitrate: preparation,X-ray crystal structures and spectroscopic characterization of the bis-bpy and bis-phen complexes

Y(NO₃)₃ · 5H₂O reacts with 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) to yield similar complexes of 1:2 yttrium:ligand stoichiometry. The crystal structures of the two complexes, namely, [Y(NO₃)₃(bpy)₂] (1) and [Y(NO₃)₃(phen)₂] (2), are reported. The three nitrate groups are O,O-bidentate and the organic ligands are also bidentate. In both structures the metal ion lies on a crystallographic two-fold axis. The stereochemistry about Y^III can be viewed as a sphenocorona. The new complexes were characterized by elemental analyses and spectroscopic (i.r., ¹H-n.m.r. and ¹³C-n.m.r.) techniques. The data are discussed in terms of the nature of bonding and known solid state structures.     

Glandulaurencianols A–C,brominated diterpenes from the red alga, Laurencia glandulifera and the sea hare, Aplysia punctata

Glandulaurencianols A and B were isolated from the organic extract of the red alga, Laurencia glandulifera, collected from the island of Crete in South Greece. Investigation of the mollusk, Aplysia punctata, collected from the coast of Nea Makri, Central Greece, resulted in the isolation of glandulaurencianols A and C. The structures of the new metabolites, as well as their relative configurations, were established on the basis of thorough analyses of their spectroscopic data.