Complexes with ambidentate ligands derived from pyridine and pyrimidine-Part 1. Cyclic nickel(II) complexes

Summary In a series of hexacoordinated nickel(II) complexes, prepared from thio-, sulphinyl, and carbonyl derivatives of pyridine and pyrimidine, the endocyclic N-atom was always the preferred basic site; the sulphinyl O-atom was also a donor centre, forming 5-membered heterocycles, whereas the carbonyl O-atom did not bond to the metal. Alkylthio derivatives did not react, unlike thiolate anions, which form N, S-bonded 4-membered rings. On the other and 2,2-bis(pyridyl)ketone bonded exclusively through the N-atoms, forming 6-membered cycles.     

Malva sylvestris L. extract suppresses desferrioxamine‐induced PGE2 and PGD2 release in differentiated U937 cells: the development and validation of an LC‐MS/MS method for prostaglandin quantification

Malva sylvestris is a species used worldwide as an alternative to anti‐inflammatory therapies; however, its mechanism of action remains unknown. In this paper, the anti‐inflammatory effects of M. sylvestris alcoholic extracts were evaluated by measuring the pro‐inflammatory mediators PGE₂ and PGD₂ in desferrioxamine‐stimulated phorbol 12‐myristate 13‐acetate‐differentiated U937 cells. An HPLC‐DAD fingerprint of the M. sylvestris extract was performed and caffeic acid, ferulic acid and scopoletin were identified and quantified. An HPLC‐MS/MS method was developed and validated to separate and measure the prostaglandins. The lower limits of detection (~0.5 ng/mL for PGE₂ and PGD₂) and quantification (1.0 ng/mL for PGE₂ and PGD₂) indicated that the method is highly sensitive. The calibration curves showed excellent coefficients of correlation (r > 0.99) over the range of 1.0–500.0 ng/mL, and at different levels, the accuracy ranged from 96.4 to 106.4% with an RSD < 10.0% for the precision study. This method was successfully applied using U937‐d cells. A significant dose‐dependent reduction of PGE₂ and PGD₂ levels occurred using 10 µg/mL (10.74 ± 2.86 and 9.60 ± 6.89%) and 50 µg/mL of extract (48.37 ± 3.24 and 53.06 ± 6.15%), suggesting that the anti‐inflammatory mechanisms evoked by M. sylvestris may be related to modulation of these mediators. Copyright © 2014 John Wiley & Sons, Ltd.     

One‐pot Preparation,Spectroscopic and Structural Characterization of Mercury(II) Complexes of Bulky Diimines with Halides and Pseudohalides

The preparation and characterization of two novel HgCl₂ and Hg(SCN)₂ complexes with bis[N‐(2‐tert‐butylphenyl)imine]acenaphthene is here described. One‐pot reaction techniques were used, leading to high yields of 75 % and 81 %, respectively. The complexes were characterized by microanalysis, i.r. and ¹HNMR spectroscopy, and by single crystal X‐ray diffraction. The structures of the complexes present similar characteristics, the most outstanding being the formation of dimers via intermolecular interaction. Whereas the HgCl₂ complex shows a unidimensional network due to strong π–π interactions, its Hg(SCN)₂ counterpart displays a supramolecular arrangement resulting from non classical hydrogen bond formation.     

Drug resistance modulation in Staphylococcus aureus, a new biological activity for mesoionic hydrochloride compounds

Two salts of the mesoionic compounds 1,4-diphenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-thiol chloride (MC-1) and 4-phenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-phenylamine chloride (MC-2) were synthesized utilizing 1,4-diphenyl-thiosemicarbazide and 5-nitro-2-furoyl chloride as starting materials. Their structures were characterized by IR, 1H-NMR, 13C-NMR and elemental analysis. These compounds were analyzed for their influence on the effectiveness of norfloxacin, tetracycline, and erythromycin (standard antibiotics) against resistant strains of Staphylococcus aureus. MC-1 and MC-2, at sub-inhibitory concentrations of 16 μg/mL, favourably modulated the antibiotic activity of tetracycline by 16- and 32-fold, respectively (MIC), and that of erythromycin by 4-fold.     

A 119Sn Mössbauer Spectroscopic Investigation of Tin Complexes with Amidines

Several novel tin(IV) adducts of amidines, [SnClPh₃L], [SnCl₂Ph₂L] and [SnBr₄L] {L=N,N-diphenylacetamidine (Hdpac) or N,N-diphenylbenzamidine (Hdpba)}, were prepared and investigated by Mössbauer spectroscopy which was an important tool for the elucidation of bonding and structural features. The resulting Mössbauer data also led to the conclusion that the tin(IV) centre for the adduct [SnClPh₃L] is pentacoordinated in a trigonal bipyramidal arrangement and hexacoordinated for [SnCl₂Ph₂L] and [SnBr₄L] in a geometric patterns of an octahedral. The amidines act as monodentate ligands to the metal centre for the former and bidentate for the latter.     

Conformational behavior of cis-2-methoxy, cis-2-methylthio, and cis-2-methylselenocyclohexanol: a theoretical and experimental investigation

Studies on the conformational equilibria of 2-methoxy, 2-methylthio, and 2-methylselenocyclohexanol are reported. Dynamic NMR spectroscopy experiments at 203-210 K were performed, which provided the percentages of each conformer in equilibrium. Theoretical calculations using the B3LYP method and aug-cc-pvdz basis set were applied to determine the differences in energy between the conformers. The analysis of the potential energy surface of each conformer showed the presence of two rotamers. Natural bond orbital analysis provided an explanation of which factors are driving the rotamer and conformer preferences.     

On the Singular Effects in the Relativistic Landau Levels in Graphene with a Disclination

The effect of a pseudo Aharonov-Bohm (AB) magnetic field generated by a disclination on a two-dimensional electron gas in graphene is addressed in the continuum limit within the geometric approach. The influence of the coupling between the spinor fields and the singular conical curvature is investigated, which shows that singularities have pronounced impact in the Hall conductivity. Moreover, the degeneracy related to the Dirac valleys is broken for negative values of the angular momentum quantum numbers, l, includingl ≡ 0. In this case, a Hall plateau develops at the null filling factor. Obtaining the Hall conductivity by summing over the positive and the negative l's, the null Landau level is recovered and the plateau at the null filling factor disappears. In any case, the standard plateaus, which are seen in a flat graphene are not obtained with these curvature and singular effects.     

Di­bromo{N-[2-(di­phenyl­phosphino)­benzyl­idene]-2,6-diiso­propyl­aniline-κ2N,P}nickel

In the title compound, [NiBr₂(C₃₁H₃₂NP)], (I), the second reported example of a nickel–imino­phosphine N,P-chelate in which the Ni atom has tetrahedral coordination, the Ni coordination is distorted as a consequence of the N—Ni—P chelate bite angle of 91.07 (6)° compensated by the Br—­Ni—­Br angle of 126.385 (18)°. In (I) and its analogue, viz. dichloro{[2-(4-isobutyloxazol-2-yl)phenyl]diphenylphos­phine-N,P}nickel(II), the Ni—N and Ni—P distances are greater and the N—Ni—P ligand bite angles smaller than those observed in a series of related complexes with square-planar nickel.     

Modifications of Electron States,Magnetization, and Persistent Current in a Quantum Dot by Controlled Curvature

The thin‐layer quantization procedure is used to study the physical implications due to curvature effects on a quantum dot in the presence of an external magnetic field. Among the various physical implications due to the curvature of the system, the absence of the $m=0$ state is the most relevant one. This absence affects the Fermi energy and consequently the thermodynamic properties of the system. In the absence of magnetic fields, it is verified that the rotational symmetry in the lateral confinement is preserved in the electronic states of the system and its degeneracy concerning the harmonicity of the confining potential is broken. In the presence of a magnetic field, however, the energies of the electronic states in a quantum dot with curvature are greater than those obtained for a quantum dot in a flat space, and the profile of degeneracy changes when the field is varied. It is shown that the curvature of the surface modifies the number of subbands occupied in the Fermi energy. In the study of both magnetization and persistent currents, it is observed that Aharonov–Bohm‐type oscillations are present, whereas de Haas–van Alphen‐type oscillations are not well defined.