François Eya’ane Meva

Unexplored vegetal green synthesis of silver nanoparticles: A preliminary study with Corchorus olitorus Linn and Ipomea batatas (L.) Lam

Antibacterial properties of silver ion are known from ancient times. The plant extract mediated synthesis of nanoparticles is gaining popularity due to green chemistry for the generation of nanosized materials. Corchorus olitorus Linn and Ipomea batatas (L.) Lam are world crops having leaves of high nutritional value. In the present work, Ag and AgCl nanoparticles were synthesized by incubating leaf aqueous extracts with silver nitrate salt, making them to react in the dark. Plasmon resonance bands, studied by ultraviolet spectroscopy, have been obtained. X-ray diffraction (XRD) revealed the average size of pure crystallites composed of Ag and AgCl. Optimization studies for the synthesis process highlight positive impact of pH, reaction time and reactants quantities. Key words: Silver, nanoparticles, Corchorus olitorus , Ipomea batatas , X-ray diffraction.

Natural Substances for the Synthesis of Silver Nanoparticles against Escherichia coli

The development of drug-resistant strains is rising and the search for new and novel ways of fighting new or reemerging microbes goes on. A hope of treating such multidrug-resistant infections came from plants mediated nanoparticles since nature is a generous source which provides a variety of chemical compounds that can be used for new drug discovery. Silver nanoparticles are reported to possess antiviral, antibacterial, antifungal, antiparasitic, larvicidal activity and anticancer properties. We reported green synthesis of silver nanoparticles mediated food plants Megaphrynium macrostachyum, Corchorus olitorus, Ricinodendron heudelotii, Gnetum bucholzianum, and Ipomoea batatas and their antibacterial efficacy against the Enterobacteriaceae Escherichia coli. The nature and size of the obtained nanoparticles are discussed as well as their Minimum Inhibitory Concentration (MIC) and the Minimum Bactericide Concentration (MBC) values considering their application in medical industry.

1,4-Dihydro­benzo[g]quinoxaline-2,3-dione

The title compound, C12H8N2O2, was prepared by the reaction of the diethyl ester of naphthalenebis(oxamate) with tert-BuNH2. The molecule is nearly planar, with an r.m.s. deviation of 0.017 Å from the plane through all 16 non-H atoms. In the crystal, a three-dimensional network is formed, composed of layers of molecules along the b- and c-axis directions, due to the formation of intermolecular N—H⋯O hydrogen bonds, as well as of chains along the a-axis direction due to parallel displaced sandwich-type π–π interactions with average distances between the interacting molecules in the range 3.35–3.40 Å.

Tuning the spin coherence time of Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes by advanced ESR pulse protocols

We have investigated with the pulsed ESR technique at X- and Q-band frequencies the coherence and relaxation of Cu spins S = 1/2 in single crystals of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opba)] (1%) in the host lattice of [n-Bu4N]2[Ni(opba)] (99%, opba = o-phenylenebis(oxamato)) and of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opbon-Pr2)] (1%) in the host lattice of [n-Bu4N]2[Ni(opbon-Pr2)] (99%, opbon-Pr2 = o-phenylenebis(N(propyl)oxamidato)). For that we have measured the electron spin dephasing time T m at different temperatures with the two-pulse primary echo and with the special Carr–Purcell–Meiboom–Gill (CPMG) multiple microwave pulse sequence. Application of the CPMG protocol has led to a substantial increase of the spin coherence lifetime in both complexes as compared to the primary echo results. It shows the efficiency of the suppression of the electron spin decoherence channel in the studied complexes arising due to spectral diffusion induced by a random modulation of the hyperfine interaction with the nuclear spins. We argue that this method can be used as a test for the relevance of the spectral diffusion for the electron spin decoherence. Our results have revealed a prominent role of the opba4– and opbon-Pr2 4– ligands for the dephasing of the Cu spins. The presence of additional 14N nuclei and protons in [Cu(opbon-Pr2)]2– as compared to [Cu(opba)]2– yields significantly shorter T m times. Such a detrimental effect of the opbon-Pr2 4− ligands has to be considered when discussing a potential application of the Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes as building blocks of more complex molecular structures in prototype spintronic devices. Furthermore, in our work we propose an improved CPMG pulse protocol that enables elimination of unwanted echoes that inevitably appear in the case of inhomogeneously broadened ESR spectra due to the selective excitation of electron spins.

Probing the magnetic superexchange couplings between terminal CuII ions in heterotrinuclear bis(oxamidato) type complexes

The reaction of one equivalent of [n-Bu4N]2[Ni(opboR2)] with two equivalents of [Cu(pmdta)(X)2] afforded the heterotrinuclear CuIINiIICuII containing bis(oxamidato) type complexes [Cu2Ni(opboR2)(pmdta)2]X2 (R = Me, X = NO3 – (1); R = Et, X = ClO4 – (2); R = n-Pr, X = NO3 – (3); opboR2 = o-phenylenebis(NR-substituted oxamidato); pmdta = N,N,N’,N”,N”-pentamethyldiethylenetriamine). The identities of the heterotrinuclear complexes 1–3 were established by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction studies, which revealed the cationic complex fragments [Cu2Ni(opboR2)(pmdta)2]2+ as not involved in any further intermolecular interactions. As a consequence thereof, the complexes 1–3 possess terminal paramagnetic [Cu(pmdta)]2+ fragments separated by [NiII(opboR2)]2– bridging units representing diamagnetic S Ni = 0 states. The magnetic field dependence of the magnetization M(H) of 1–3 at T = 1.8 K has been determined and is shown to be highly reproducible with the Brillouin function for an ideal paramagnetic spin = 1/2 system, verifying experimentally that no magnetic superexchange couplings exists between the terminal paramagnetic [Cu(pmdta)]2+ fragments. Susceptibility measurements versus temperature of 1–3 between 1.8–300 K were performed to reinforce the statement of the absence of magnetic superexchange couplings in these three heterotrinuclear complexes.

Crystal structure of an unknown solvate of bis­(tetra-n-butyl­ammonium) [N,N′-(4-tri­fluoro­methyl-1,2-phenyl­ene)bis­(oxamato)-κ4O,N,N′,O′]nickelate(II)

In the title compound, the Ni2+ cation is coordinated by two deprotonated amido N atoms and two carboxylate O atoms, setting up a square-planar coordination environment. The cations and the anion are linked by weak intra- and intermolecular C—H⋯O and C—H⋯F hydrogen bonds.