Essential oil from leaves of Lantana canescens and L. lopez-palacii grown in Colombia

The chemical composition of the volatile compounds from the leaves of Lantana canescens Kunth (Verbenaceae) and L. lopez-palacii Moldenke grown in Colombia were analyzed by GC and GC/MS. One hundred and thirty-nine volatile compounds were identified in L. canescens, of which the major ones were beta-caryophyllene (13.5%), germacrene D (10.3%) and 1-octen-3-ol (8.4%). In the oil obtained from L. lopez-palacii, eighty-three compounds were identified, of which the most prominent were 1-octen-3-ol (24.4%) and beta-caryophyllene (15.2%). The in vitro antibacterial activity of the L. lopez-palacii essential oil was studied against three bacterial strains using the disc diffusion method. No antimicrobial activity was found against Escherichia coli, Enterobacter sakazakii and Listeria monocytogenes.     

Surface immobilization of fibronectin-derived PHSRN peptide on functionalized polymer films – Effects on fibroblast spreading

The Pro-His-Ser-Arg-Asn (PHSRN) sequence in fibronectin is a second cell-binding site that synergistically affects Arg-Gly-Asp (RGD). The PHSRN peptide also induces cell invasion and accelerates wound healing. We report on the surface immobilization of PHSRN by spontaneous adsorption on polysiloxane thin films which have different surface free energy characteristics. Low-surface energy (hydrophobic) polysiloxane and the corresponding high-surface energy (hydrophilic) surfaces obtained by UV–ozone treatments were used as adsorbing substrates. The peptide adsorption process was investigated by quartz crystal microbalance with dissipation monitoring and atomic force microscopy. Both adsorption kinetics and peptide rearrangement dynamics at the solid interface were significantly different on the surface-modified films compared to the untreated ones. Fibroblast cells cultures at short times and in a simplified environment, i.e., a medium-free solution, were prepared to distinguish interaction events at the interface between cell membrane and surface-immobilized peptide for the two cases. It turned out that the cell-adhesive effect of immobilized PHSRN was different for hydrophobic compared to hydrophilic ones. Early signatures of cell spreading were only observed on the hydrophilic substrates. These effects are explained in terms of different spatial arrangements of PHSRN molecules immobilized on the two types of surfaces.     

Sequential In Vitro Cyclization by Cytochrome P450 Enzymes of Glycopeptide Antibiotic Precursors Bearing the X‐Domain from Nonribosomal Peptide Biosynthesis

The biosynthesis of the glycopeptide antibiotics, which include vancomycin and teicoplanin, relies on the interplay between the peptide‐producing non‐ribosomal peptide synthetase (NRPS) and Cytochrome P450 enzymes (P450s) that catalyze side‐chain crosslinking of the peptide. We demonstrate that sequential in vitro P450‐catalyzed cyclization of peptide substrates is enabled by the use of an NRPS peptide carrier protein (PCP)‐X di‐domain as a P450 recruitment platform. This study reveals that whilst the precursor peptide sequence influences the installation of the second crosslink by the P450 OxyA_tei, activity is not restricted to the native teicoplanin peptide. Initial peptide cyclization is possible with teicoplanin and vancomycin OxyB homologues, and the latter displays excellent activity with all substrate combinations tested. By using non‐natural X‐domain substrates, bicyclization of hexapeptides was also shown, which demonstrates the utility of this method for the cyclization of varied peptide substrates in vitro.     

Investigating the electronic structure and bonding in uranyl compounds by combining NEXAFS spectroscopy and quantum chemistry

The nature of the reactivity of the "yl" oxygens has been a subject of constant interest for a long time in uranyl chemistry. Thus, the electron-donor ability of the equatorial ligands plays an important role in the nature of the uranyl U=O bond. In this paper, a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and both ground-state and time-dependent density functional theory (DFT) calculations have been used to examine the effect of equatorial plane ligation on the U=O bonding in two uranyl complexes: [UO(2)(py)(3)I(2)] and [UO(2)(CN)(5)][NEt(4)](3). By coupling experimental data and theory, spectral features observed in the oxygen K-edge NEXAFS spectra have been assigned. Despite the inert character of the U=O bond, we observe that the electron-donating or withdrawing character of the equatorial ligands has a measurable effect on features in the NEXAFS spectra of these species and thereby on the unoccupied molecular orbitals of {UO(2)}(2+).     

trans‐Chlorido(phenyl)bis(triphenylphosphine)nickel(II) and its 1:1 cocrystal with chloridobis(triphenylphosphine)nickel(I)

Two conformational polymorphs of trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II), [Ni(C₆H₅)Cl(C₁₈H₁₅P)₂], (1), viz. orange needle‐shaped crystals (form I) and brown prism‐shaped crystals (form II), were obtained under different crystallization conditions from a mixture of toluene and n‐hexane, and characterized by single‐crystal X‐ray diffraction at low temperature. These two forms were compared with that published previously [Zeller, Herdtweck & Strassner (2003). Eur. J. Inorg. Chem. pp. 1802–1806], characterized at room temperature. Additionally, blue–green prisms of a 1:1 cocrystal of complex (1) with chloridobis(triphenylphosphine)nickel(I), (2), viz.trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II)–chloridobis(triphenylphosphine)nickel(I) (1/1), [Ni(C₆H₅)Cl(C₁₈H₁₅P)₂]·[NiCl(C₁₈H₁₅P)₂], (3), were obtained concomitantly with form I. In forms I and II, as well as in the cocrystal, the overall crystal packings are determined by an energetic interplay between intramolecular torsions and weak intermolecular C—H...π and C—H...Cl interactions.     

From Mono‐ to Poly‐Substituted Frameworks: A Way of Tuning the Acidic Character of Cc?H in o‐Carborane Derivatives

The incorporation of iodine atoms onto the boron vertices of the o‐carborane framework causes, according to spectroscopic data, a uniform increase in the acidic character of the C_c? H (C_c= cluster carbon) vertices, whereas the incorporation of methyl groups onto the boron vertices of the o‐carborane framework reduces their acidity. Methyl groups when attached to boron are electron‐withdrawing in boron clusters, whereas iodine atoms bonded to boron act as electron donors. This has been proven on B‐methyl and B‐iodinated o‐carboranes with NMR spectroscopy measurements and DFT calculations of natural bond orbital (NBO) charges, which show a cumulative buildup of positive cluster‐only total charge (CTC) on B‐methyl o‐carboranes and a cumulative buildup of negative cluster‐only total charge for B‐iodinated o‐carboranes.     

Tunable Fluorophores Based on 2‐(N‐Arylimino)pyrrolyl Chelates of Diphenylboron: Synthesis,Structure, Photophysical Characterization,and Application in OLEDs

Reactions of 2‐(N‐arylimino)pyrroles (HNC₄H₃C(H)?N‐Ar) with triphenylboron (BPh₃) in boiling toluene afford the respective highly emissive N,N′‐boron chelate complexes, [BPh₂{κ²N,N′‐NC₄H₃C(H)?N‐Ar}] (Ar=C₆H₅ ( 12 ), 2,6‐Me₂‐C₆H₃ ( 13 ), 2,6‐iPr₂‐C₆H₃ ( 14 ), 4‐OMe‐C₆H₄ ( 15 ), 3,4‐Me₂‐C₆H₃ ( 16 ), 4‐F‐C₆H₄ ( 17 ), 4‐NO₂‐C₆H₄ ( 18 ), 4‐CN‐C₆H₄ ( 19 ), 3,4,5‐F₃‐C₆H₂ ( 20 ), and C₆F₅ ( 21 )) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N‐arylimino moieties. The complexes bearing electron‐withdrawing aniline substituents 17 – 20 show more intense (e.g., ?_f=0.71 for Ar=4‐CN‐C₆H₄ ( 19 ) in THF), higher‐energy (blue) fluorescent emission compared to those bearing electron‐donating substituents, for which the emission is redshifted at the expense of lower quantum yields (?_f=0.13 and 0.14 for Ar=4‐OMe‐C₆H₄ ( 15 ) and 3,4‐Me₂‐C₆H₃ ( 16 ), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6‐positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region (λ_max=410–465 nm) and a significant decrease in quantum yield (?_f=0.005, 0.023, and 0.20 for Ar=2,6‐Me₂‐C₆H₃ ( 13 ), 2,6‐iPr₂‐C₆H₃ ( 14 ), and C₆F₅ ( 21 ), respectively, in THF), even when electron‐withdrawing groups are also present. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance (ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light‐emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m^?2 being achieved for a green‐emitting device.     

Development of an ultra-high performance liquid chromatography analytical methodology for the profiling of olive (Olea europaea L.) pulp proteins

Ultra-high performance liquid chromatography (UHPLC) constitutes an interesting proposal to speed protein separations but it is almost not explored. In this work UHPLC is proposed, for the first time, to separate olive pulp proteins. An important difficulty in the analysis of proteins is related to their extraction. The difficulty in the extraction of proteins from the olive pulp is derived from its high content in lipids and phenolic compounds. Eight different methods for the extraction of pulp proteins were designed and evaluated. The optimized extraction procedure consisted of a cleaning step to remove interfering compounds, followed by the extraction of proteins with a Tris–HCl buffer containing sodium dodecyl sulphate (SDS) and dithiothreitol (DTT), precipitation of proteins with acetone, and solubilization in the Tris–HCl buffer. This methodology yielded the most successful isolation of pulp proteins and enabled the optimization of a UHPLC methodology for their separation. The method was applied to the profiling of olive pulp proteins from different olive cultivars observing in all cases a protein that had never been described before.     

Micellar electrokinetic chromatography estimation of size and composition of procyanidins after thiolysis with cysteine

This paper describes the characterization of procyanidin mixtures by acid depolymerization in the presence of cysteine (thiolysis with cysteine) and micellar electrokinetic chromatography (MEKC). Reversed-phase liquid chromatography (RP-HPLC) and MEKC were investigated for the separation of the major components of the depolymerized mixtures (catechins and their cysteinyl derivatives). The solutes could only be effectively separated using MEKC. Two background electrolytes (BGEs) are recommended: (i) 50 mM phosphate at pH 7, containing 40 mM sodium cholate (SC) and 10 mM sodium dodecyl sulfate (SDS); (ii) a BGE with the same composition but containing only 50 mM SDS. The MEKC procedures here reported, are cheap, reliable and fast, and their potential in the determination of the size and composition in procyanidin mixtures has been shown. The proposed MEKC methods were validated by comparison with our intralaboratory reference RP-HPLC method using cysteamine as thiol donor.     

Highly stable neutral and positively charged dicarbollide sandwich complexes

Novel sandwich metallacarboranes commo-[3,3'-Ni(8-SMe2-1,2-C2B9H10)2] (1), commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2]+ (2+), commo-[3,3'-Ru(8-SMe2-1,2-C2B9H10)2] (4) and commo-[3,3'-Fe(8-SMe2-1,2-C2B9H10)2] (5) have been prepared by reaction of [10-SMe2-7,8-nido-C2B9H10]- with NiCl2 x 6 H2O, CoCl2, [RuCl2(dmso)4] and [FeCl2(dppe)], respectively. Reduction of 2+ with metallic Zn leads to the neutral and isolable complex commo-[3,3'-Co(8-SMe2-1,2-C2B9H10)2] (3). Theoretical calculations using the ZINDO/1 semiempirical method show three energy minima for complexes 1-3 and 5 that agree with the presence of three different rotamers in solution at low temperature, while four relative energy minima have been found for 4. The calculated rotational energy barriers for complexes 1-5 have been found in the range 5.2+/-0.2 and 11.5+/-0.2 kcal mol(-1). These values are in agreement with the experimental data calculated for complexes 2+ and 5. Only one rotamer is found in the X-ray crystal structure of complexes 1-3, while two are observed for 4. Neutral complexes 1, 3 and 4 exhibit a gauche conformation, whereas a cisoid conformation is found for the 2+ ion. Rotamers evident from X-ray diffraction studies are in agreement with the global energy minimum calculated by the ZINDO/1 method. The electrochemical studies conducted on 1, 3, 4 and 5 support the proposal that the charge-compensated ligand [10-SMe2-7,8-nido-C2B9H10]- stabilises lower oxidation states in metals than the dianionic [7,8-nido-C2B9H11]2- and even the [C5H5]- ligands.