Structure-activity relationships of 4-N-substituted ferroquine analogues: Time to re-evaluate the mechanism of action of ferroquine

A series of five new alkyl 4-N-substituted analogues of ferroquine (FQ, SR97193) were designed, synthesized, and characterized. The antimalarial activity of the compounds was measured against twelve strains of Plasmodiumfalciparum. The compounds were more active than chloroquine (CQ) against all the CQ-resistant clones. For a better understanding of their mechanism of action, their physicochemical properties (lipophilicity and basicity) and their action on the inhibition of β-hematin formation were evaluated. The importance of the intramolecular hydrogen bond in neutral FQ in the antimalarial activity was probed, compared to the methyl analogue 1.Results of additional physicochemical measurements suggested new insights into the mechanism of action of FQ in sharp contrast with CQ. We complement here our understanding on the mechanism of action of FQ with the process of catalysis-mediated hemozoin formation at the interface between vacuolar content and membrane lipids.     

A 32 vertex polyhedron via supramolecular assembly of silanedithiolate silanolate units

A high yield synthesis of the first silanedithiolate silanolate is reported which spontaneously assembles forming an inorganic rugby ball shaped 32 vertex polyhedral cluster stabilized by sterically demanding 2,6-dimesitylphenyl substituents and two LiCl units.     

Field-theoretic methods in strongly-coupled models of general gauge mediation

An often-exploited feature of the operator product expansion (OPE) is that it incorporates a splitting of ultraviolet and infrared physics. In this paper we use this feature of the OPE to perform simple, approximate computations of soft masses in gauge-mediated supersymmetry breaking. The approximation amounts to truncating the OPEs for hidden-sector current–current operator products. Our method yields visible-sector superpartner spectra in terms of vacuum expectation values of a few hidden-sector IR elementary fields. We manage to obtain reasonable approximations to soft masses, even when the hidden sector is strongly coupled. We demonstrate our techniques in several examples, including a new framework where supersymmetry breaking arises both from a hidden sector and dynamically. Our results suggest that strongly-coupled models of supersymmetry breaking are naturally split.     

Inclusive photon and π0 production inK + p interactions at 70 GeV/c

Inclusive and semi-inclusive cross sections and distributions of γ's and π⁰'s inK ⁺ p interactions at 70 GeV/c are presented. The results are compared to other experiments and to the Lund model for low-p _T hadron collisions.     

Preparation and magnetic characterization of Co2-W strontium hexaferrites doped with Ni and La

The formation and magnetic properties of new Ni- and La-substituted SrCo₂-W hexaferrites were investigated. Fabrication of single phase samples required undertaking composition and sintering conditions optimization. This process confirmed the production of W hexaferrites from intermediate cubic and hexagonal ferrite phases and additionally proved the enhancement of final purity by the excessive hexagonal component. Furthermore, according to the X-ray diffraction analysis, pure Ni- or La-doped compounds were formed in most cases, which actually necessitated more intense heat treatment (1225–1250 °C). Yet, magnetic measurements interestingly reveal that substances with low substitution possess high saturation magnetization (～72–75 Am²/kg) and unexpectedly lower coercivity (～28–46 Oe), compared to the undoped one. This behavior is attributed to the chemistry of both substitutions, inducing the magnetic order variation and the anisotropy transition from in-plane to axial. Thus, a scarcely elaborated transient compositional region with planar anisotropy and strong magnetization is discerned, highlighting the potential of these soft ferrites.     

π‐Stacking Modulates the Luminescence of [(dppz)Ni(Mes)Br] (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine,Mes = 2,4,6‐trimethylphenyl)

The red colour of the novel organonickel complex [(dppz)Ni(Mes)Br] (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine, Mes = 2,4,6‐trimethylphenyl) originates from long‐wavelength MLCT/L′LCT charge transfer bands. However, luminescence in dilute solution comes presumably from the ³π‐π* (phenazine) excited state. The red‐shifted emission exhibited in concentrated solutions is assigned to dimers. In the solid state emission is quenched. The crystal structure reveals two different types of π‐π stacking along the crystallographic a axis.     

Reduction pathway of end-on terminally coordinated dinitrogen. V. N-N bond cleavage in Mo/W hydrazidium complexes with diphosphine coligands. Comparison with triamidoamine systems

N-N cleavage of the dialkylhydrazido complex [W(dppe)2(NNC5H10)] (B(W)) upon treatment with acid, leading to the nitrido/imido complex and piperidine, is investigated experimentally and theoretically. In acetonitrile and at room temperature, B(W) reacts orders of magnitude more rapidly with HNEt3BPh4 than its Mo analogue, [Mo(dppe)2(NNC5H10)] (B(Mo)). A stopped-flow experiment performed for the reaction of B(W) with HNEt3BPh4 in propionitrile at -70 degrees C indicates that protonation of B(W) is completed within the dead time of the stopped-flow apparatus, leading to the primary protonated intermediate B(W)H+. Propionitrile coordination to this species proceeds with a rate constant k(obs(1)) of 1.5 +/- 0.4 s(-1), generating intermediate RCN-B(W)H+ (R = Et) that rapidly adds a further proton at Nbeta and then mediates N-N bond splitting in a slower reaction (k(obs(2)) = 0.35 +/- 0.08 s(-1), 6 equiv of acid). k(obs(1)) and k(obs(2)) are found to be independent of the acid concentration. The experimentally observed reactivities of B(Mo) or B(W) with acids in nitrile solvents are reproduced by DFT calculations. In particular, geometry optimization of models of solvent-coordinated, Nbeta-protonated intermediates is found to lead spontaneously to separation into the nitrido/imido complexes and piperidine/piperidinium, corresponding to activationless heterolytic N-N bond cleavage processes. Moreover, DFT indicates a spontaneous cleavage of nonsolvated B(W) protonated at Nbeta. In the second part of this article, a theoretical analysis of the N-N cleavage reaction in the Mo(III) triamidoamine complex [HIPTN3N]Mo(N2) is presented (HIPTN3N = hexaisopropylterphenyltriamidoamine). To this end, DFT calculations of the Mo(III)N2)triamidoamine complex and its protonated and reduced derivatives are performed. Calculated structural and spectroscopic parameters are compared to available experimental data. N-N cleavage most likely proceeds by one-electron reduction of the Mo(V) hydrazidium intermediate [HIPTN3N]Mo(NNH3)+, which is predicted to have an extremely elongated N-N bond. From an electronic-structure point of view, this reaction is analogous to that of Mo/W hydrazidium complexes with diphos coligands. The general implications of these results with respect to synthetic N2 fixation are discussed.     

Comparative study of different types of graphenes as electrocatalysts for ascorbic acid

A comparative study regarding the electrocatalytic activity of graphene oxide (GO), chemically-reduced graphene oxide (crGO) and graphene produced by direct liquid exfoliation (dG) is presented. Sensors were developed by modifying glassy carbon (GC) electrodes with GO, crGO and dG and ascorbic acid was used as a pilot analyte. GC/GO electrodes offer substantially lower oxidation overpotential, up to 350 mV, compared with GC/crGO, GC/dG and unmodified GC electrodes. In addition, the different carbon-to-oxygen atomic ratios in GO, as it occurs depending on the synthetic route, were found to have a remarkable effect on the performance of the sensors. Reduction of GO was achieved by immersing the modified electrodes into a stirred solution of NaBH₄ for 10 min at room temperature. This process was used alternatively of the time consuming and laborious process of hydrazine, and its effectiveness was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Analytical utility of the sensors is demonstrated.     

LiB12PC, the first boron-rich metal boride with phosphorus--synthesis, crystal structure, hardness, spectroscopic investigations

We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB₁₂PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB₁₂PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Å and Z=4. Brown LiB₁₂P_0.89C_1.11 is very similar, but with a lower P content. Red single crystals of LiB₁₂P_1.13C_0.87 have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B₁₂ icosahedra connected by exohedral B? B bonds and P? P, P? C or C? C units. Li atoms are located in interstitials. The structure is closely related to MgB₇, LiB₁₃C₂ and ScB₁₃C. LiB₁₂PC fulfils the electron counting rules of Wade and also Longuet‐Higgins. Measurements of Vickers micro‐hardness (H_V=27 GPa) revealed that LiB₁₂PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra.