Chemical composition and repellent activity of essential oils of Tithonia diversifolia (Asteraceae) leaves against the bites of Anopheles coluzzii.

Tithonia diversifolia is widely used in African traditional medicine for the treatment of a large number of ailments and disorders, including malaria. In the present study, we evaluated the repellent activity of essential oils (EO) of this plant against Anopheles coluzzii, a major vector of malaria in Africa. Fresh leaves of T. diversifolia were used to extract EO, which were used to perform repellency assays in the laboratory and in the field using commercially available N,N-Diethyl-meta-toluamide (DEET) and Cymbopogon (C.) citratus EO as positive controls and vaseline as negative control. The repellency rates and durations of protection of the human volunteers involved were used as measures of repellent activity. Chemical composition of the T. diversifolia EO was established further by gas chromatography coupled with mass spectrometry. The moisture content and oil yield were 81% and 0.02% respectively. A total of 29 compounds in the T. diversifolia EO was identified, with D-limonene (20.1%), α-Copaene (10.3%) and o-Cymene (10.0%) as the most represented. In field studies, the mean time of protection against mosquito bites was significantly lower in T. diversifolia EO-treated volunteers compared to treatments with C. citratus EO (71 min versus 125 min, p = 0.04), but significantly higher when compared with the non-treated volunteers (71 min vs 0.5 min, p = 0.03). The same pattern was found in laboratory repellency assays against A. coluzzii. In contrast, repulsion rates were statistically similar between T. diversifolia EO and positive controls. In conclusion, the study suggests promising repellent potential of leaves of T. diversifolia EO against A. coluzzii.

Green-synthesized metal nanoparticles for mosquito control: A systematic review about their toxicity on non-target organisms.

Studies capturing the high efficiency of green-synthesized metal nanoparticles (NPs) in targeting mosquito vectors of the world's main infectious diseases suggest the NPs' possible utilization as bio-insecticides. However, it is necessary to confirm that these potential bio-insecticides are not harmful to non-target organisms that are often sympatric and natural enemies of the vectors of these diseases. In this systematic review, we comprehensively analyse the content of 56 publications focused on the potentially deleterious effects of NPs on these non-target organisms. Current research on biosynthesised NPs, characterization, and impact on mosquito vectors and non-target larvivorous organisms is reviewed and critically discussed. Finally, we pinpoint some major challenges that merit future investigation. Plants (87.5%) were mainly used for synthesizing NPs in the studies. NPs were found to be spherical or mainly spherical in shape with a large distribution size. In most of the included studies, NPs showed interesting mosquitocidal activity (LC50 < 50 ppm). Some plant families (e.g., Meliaceae, Poaceae, Lamiaceae) have produced NPs with a particularly high larvicidal and pupicidal activity (LC50 < 10 ppm). Regarding non-target organisms, most of the studies concluded that NPs were safe to them, with boosted predatory activity in NP-treated milieu. In contrast, some studies reported NP-elicited adverse effects (i.e., genotoxic, nuclear, and enzymatic effects) on these non-target organisms. This review outlines the promising mosquitocidal effects of biosynthesized NPs, recognizing that NPs' potential usage is currently limited by the harm NPs are thought pose to non-target organism. It is of utmost importance to investigate green NPs to determine whether laboratory findings have applications in the real world.

A systematic review on anti-malarial drug discovery and antiplasmodial potential of green synthesis mediated metal nanoparticles: overview, challenges and future perspectives.

BACKGROUND: The recent emergence in Southeast Asia of artemisinin resistance poses major threats to malaria control and elimination globally. Green nanotechnologies can constitute interesting tools for discovering anti-malarial medicines. This systematic review focused on the green synthesis of metal nanoparticles as potential source of new antiplasmodial drugs. METHODS: Seven electronic database were used following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. RESULTS: A total of 17 papers were included in the systematic review. 82.4% of the studies used plant leaves to produce nanoparticles (NPs) while three studies used microorganisms, including bacteria and fungi. Silver was the main metal precursor for the synthesis of NPs. The majority of studies obtained nanoparticles spherical in shape, with sizes ranging between 4 and 65 nm, and reported no or little cytotoxic effect of the NPs. Results based on 50% inhibitory concentration (IC50) varied between studies but, in general, could be divided into three NP categories; (i) those more effective than positive controls, (ii) those more effective than corresponding plant extracts and, (iii) those less effective than the positive controls or plant extracts. CONCLUSIONS: This study highlights the high antiplasmodial potential of green-synthesized metal nanoparticles thereby underscoring the possibility to find and develop new anti-malarial drugs based on green synthesis approaches. However, the review also highlights the need for extensive in vitro and in vivo studies to confirm their safety in humans and the elucidation of the mechanism of action.

Crystal structures of N'-amino-pyridine-2-carboximidamide and N'-{[1-(pyridin-2-yl)ethyl-idene]amino}-pyridine-2-carboximidamide.

The crystal structures of N'-amino-pyridine-2-carboximidamide (C6H8N4), 1, and N'-{[1-(pyridin-2-yl)ethyl-idene]amino}-pyridine-2-carboximidamide (C13H13N5), 2, are described. The non-H atoms in compound 1 are nearly planar (r.m.s. deviation from planarity = 0.0108 Å), while 2 is twisted about the central N-N bond by 17.8 (2)°. Both mol-ecules are linked by inter-molecular N-H⋯N hydrogen-bonding inter-actions; 1 forms a two-dimensional hydrogen-bonding network and for 2 the network is a one-dimensional chain. The bond lengths of these mol-ecules are similar to those in other literature reports of azine and di-imine systems.

Spectroscopic synthetic optimizations monitoring of silver nanoparticles formation from Megaphrynium macrostachyum leaf extract

ABSTRACT Nanobiotechnology is one of the most promising areas in modern nanoscience and technology. Metallic nanoparticles have found uses in many applications in different fields, such as catalysis, photonics, electronics, medicine and agriculture. Synthesized nanoparticles through chemical and physical methods are expensive and have low biocompatibility. In the present study, silver nanoparticles have been synthesized from Megaphrynium macrostachyum (Benth. & Hook. f.) Milne-Redh., Marantaceae, leaf extract. Megaphrynium macrostachyum is a plant with large leaves found in the rainforest of West and Central Africa. Synthetic optimizations following factors such as incubation time, temperature, pH, extract and silver ion concentration during silver formation are discussed. UV–visible spectra gave surface plasmon resonance for synthesized silver nanoparticles based Megaphrynium macrostachyum peaks at 400–450 nm. X-ray diffraction revealed the average size of pure crystallites composed from Ag and AgCl.

Crystal structure of an unknown solvate of bis-(tetra-n-butyl-ammonium) [N,N'-(4-tri-fluoro-methyl-1,2-phenyl-ene)bis-(oxamato)-κ(4) O,N,N',O']nickelate(II).

In the title compound, [N(C4H9)4]2[Ni(C11H3F3N2O6)] or [N(n-Bu)4]2[Ni(topbo)] [n-Bu = n-butyl and topbo = 4-tri-fluoro-methyl-1,2-phenyl-enebis(oxamate)], the Ni(2+) cation is coordinated by two deprotonated amido N atoms and two carboxyl-ate O atoms, setting up a slightly distorted square-planar coordination environment. The [Ni(topbo](2-) anion lies on a twofold rotation axis. Due to an incompatibility with the point-group symmetry of the complete mol-ecule, orientational disorder of the CF3 group is observed. The tetra-hedral ammonium cations and the anion are linked by weak inter-molecular C-H⋯O and C-H⋯F hydrogen-bonding inter-actions into a three-dimensional network. A region of electron density was treated with the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9-18] following unsuccessful attempts to model it as plausible solvent mol-ecule(s). The given chemical formula and other crystal data do not take into account the unknown solvent mol-ecule.

Magnetic superexchange interactions: trinuclear bis(oxamidato) versus bis(oxamato) type complexes.

The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me , Et , (n)Pr ) in good yields. Treatment of with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [(n)Bu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [(n)Bu4N]2[M(opboR2)] (M = Ni, R = Me , Et , (n)Pr ; M = Cu, R = Me , Et , (n)Pr ). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of , novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me , Et , (n)Pr ) could be obtained. Compounds have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of and have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted and (1%) in the host lattice of and (99%) (@ and @), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite (Cu)A and transferred (N)A hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)](2-) and [Cu(opbo(n)Pr2)](2-) complex fragments of and , respectively, could be determined. Additionally, as a single crystal ENDOR measurement of @ revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of were studied by susceptibility measurements versus temperature to give J values varying from -96 cm(-1) () over -104 cm(-1) () to -132 cm(-1) (). These three trinuclear Cu(II)-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of and , the geometries of the terminal [Cu(pmdta)](2+) fragments of determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.

1,4-Dihydro-benzo[g]quinoxaline-2,3-dione.

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