Development and validation of an HPLC method for the quantitation of 1,3-dihydroxy-2-methylxanthone in biodegradable nanoparticles

A rapid and simple high-performance liquid chromatographic method for the analysis of 1,3-dihydroxy-2-methylxanthone (DHMXAN) in biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanosphere and nanocapsule formulations is developed and validated. The method does not require any complex sample extraction procedure. Chromatographic separation is made with a reversed-phase C18 column, using methanol-water (90:10, v/v) containing 1% (v/v) acetic acid as a mobile phase at a flow rate of 1 mL/min. Identification is made by UV detection at 237 nm. The isocratic system operates at ambient temperature and requires 7.5 min of chromatographic time. The developed method is statistically validated according to ICH guidelines and USP 29 for its specificity, linearity, accuracy, and precision. The assay method proposed in this study is specific for DHMXAN in the presence of nanosphere and nanocapsule excipients. Diode-array analyses confirm the purity of DHMXAN peak in stress conditions (> 99.0%). The method is shown to be linear (r > or = 0.999) over the concentration range of 0.25-3.0 microg/mL. Recovery ranges from 99.0% to 102.7% (RSD: 1.49%) and from 98.3% to 101.6% (RSD: 1.07%) for nanospheres and nanocapsules, respectively. Repeatability (intra-assay precision) and intermediate precision is acceptable with RSD values ranging from 0.6% to 1.9% and from 0.3% to 2.0%, respectively. The method is shown to be suitable for the evaluation of DHMXAN content entrapped in PLGA nanoparticles.     

Quantum monte carlo study of the energetics of small hydrogenated and fluoride lithium clusters

An investigation of the energetics of small lithium clusters doped either with a hydrogen or with a fluorine atom as a function of the number of lithium atoms using fixed‐node diffusion quantum Monte Carlo (DMC) simulation is reported. It is found that the binding energy (BE) for the doped clusters increases in absolute values leading to a more stable system than for the pure ones in excellent agreement with available experimental measurements. The BE increases for pure, remains almost constant for hydrogenated, and decreases rapidly toward the bulk lithium for the fluoride as a function of the number of lithium atoms in the clusters. The BE, dissociation energy as well as the second difference in energy display a pronounced odd–even oscillation with the number of lithium atoms. The electron correlation inverts the odd–even oscillation pattern for the doped in comparison with the pure clusters and has an impact of 29%–83% to the BE being higher in the pure cluster followed by the hydrogenated and then by the fluoride. The dissociation energy and the second difference in energy indicate that the doped cluster Li₃H is the most stable whereas among the pure ones the more stable are Li₂, Li₄, and Li₆. The electron correlation energy is crucial for the stabilization of Li₃H. © 2016 Wiley Periodicals, Inc.     

Ag Doped Titanium Dioxide Nanocomposite‐modified Glassy Carbon Electrode as Electrochemical Interface for Catechol Sensing

The electrochemical sensing of catechol (CC) on a glassy carbon electrode modified with the ionothermal assisted synthesis of Ag doped TiO₂ a nanoparticle has been successfully demonstrated for the first time.Ag doped TiO₂ nanoparticles composite modified glassy carbon electrode exhibits higher electrocatalytic activity towards oxidation of catechol than glassy carbon electrode itself. The modified electrode also exhibits high selectivity towards this analyte in the presence of some of the metal ions and some of the biological compounds. Linear ranges and the limit of detections with the above electrode are 1–15 µM and 0.0249 µM respectively. The optimized protocol has been utilized for monitoring the catechol in some of the natural samples like apple juice and green tea and in industrial effluents.     

Asymptotic stability and bifurcations of 3D piecewise smooth vector fields

The paper deals with the analysis of the behavior of a nonsmooth three-dimensional vector field around a typal singularity. We focus on a class of generic one-parameter families \({Z_{\lambda}}\) of Filippov systems and address the persistence problem for the asymptotic stability when the parameter varies near the bifurcation value \({\lambda = 0}\).     

Synthesis and cytotoxic activity of some 3-benzyl-5-arylidenefuran-2(5H)-ones

3-Benzyl-furan-2(5H)-one (2a) and 3-(4-bromobenzyl)-furan-2(5H)-one (2b) were treated with TBDMSOTf and converted into the corresponding tert-butyldimethyl-silylfuran ethers. These furans were further condensed with several aromatic aldehydes affording compounds 5-14 with general 3-benzyl-5-arylidene-furan-2(5H)-one structures in 31% to 98% yields. Such compounds are analogues of the naturally occurring nostoclide lactones, reported to present moderate cytotoxic activity. Compounds 5-14 were submitted to an in vitro bioassay against the HL-60, HCT-8, SF295 and MDA-MB-435 cancer cell lines using the MTT cytotoxicity assay.     

Simultaneous distillation-extraction of high-value volatile compounds from Cistus ladanifer L

The present paper describes a procedure to isolate volatiles from rock-rose (Cistus ladanifer L.) using simultaneous distillation-extraction (SDE). High-value volatile compounds (HVVC) were selected and the influence of the extraction conditions investigated. The effect of the solvent nature and extraction time on SDE efficiency was studied. The best performance was achieved with pentane in 1 h operation. The extraction efficiencies ranged from 65% to 85% and the repeatability varied between 4% and 6% (as a CV%).The C. ladanifer SDE extracts were analysed by headspace solid phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The HS-SPME sampling conditions such as fiber coating, temperature, ionic strength and exposure time were optimized. The best results were achieved with an 85 μm polyacrylate fiber for a 60 min headspace extraction at 40 °C with 20% (w/v) of NaCl. For optimized conditions the recovery was in average higher than 90% for all compounds and the intermediate precision ranged from 4 to 9% (as CV %). The volatiles α-pinene (22.2 mg g⁻¹ of extract), 2,2,6-trimethylcyclohexanone (6.1 mg g⁻¹ of extract), borneol (3.0 mg g⁻¹ of extract) and bornyl acetate (3.9 mg g⁻¹ of extract) were identified in the SDE extracts obtained from the fresh plant material.     

Thalidomide analogs from diamines: Synthesis and evaluation as inhibitors of TNF-alpha production

Fourteen thalidomide analogs bearing two phthalimido units were prepared in high yields (83-94%) by condensation of different diamines with phthalic or 3-nitrophthalic anhydride. An in vitro investigation of the compounds as inhibitors of the TNF-alpha production was performed. The inhibition was higher for compounds bearing amino and nitro groups and was modulated by increasing the size of the spacers between the phthalimide groups.     

Critical fluctuations of a binary fluid mixture confined in a porous medium

We have performed small angle neutron scattering experiments on the binary fluid mixture n-C₆H₁₄+n-C₈F₁₈ imbibed inside porous Vycor glass in the thermodynamic region corresponding to the bulk critical one. The resulting structure can be represented as the sum of a temperature dependent Lorentzian term and a term describing the interference between the porous matrix, a shell part richer in one component coating the glass surface, and a core part richer in the other component. We observe critical fluctuations extending over distances markedly larger than the mean pore size. Received 20 May 1999     

Theoretical characterization of the ground state of the alkaline-earth monocarbides: Ordering of the two lower-lying states of the BeC,MgC, and CaC molecules

The two lower-lying electronic states (³Σ⁻ and ⁵Σ⁻) of the BeC, MgC, and CaC molecules were investigated using restricted Hartree-Fock (RHF), generalized valence bond (GVB), and configuration interaction (CI) calculations to establish the relative ordering of those states as a function of the size of the alkaline-earth element. It is shown that as a result of the competition between bonding effects, which predominate for the ³Σ⁻ states, and exchange effects, which stabilize the ⁵Σ⁻ states, the ordering of these states can be reversed as we move from the Be to the Ca atom. For both the BeC and MgC molecules, the ground state was found to be a triplet X³Σ⁻ state, but for the CaC molecule, the high-spin X⁵Σ⁻ becomes more stable. © 1996 John Wiley & Sons, Inc.