Identification of the Schistosoma mansoni molecular target for the antimalarial drug artemether

Plasmodium falciparum and Schistosoma mansonii are the parasites responsible for most of the malaria and schistosomiasis cases in the world. Notwithstanding their many differences, the two agents have striking similarities in that they both are blood feeders and are targets of an overlapping set of drugs, including the well-known artemether molecule. Here we explore the possibility of using the known information about the mode of action of artemether in Plasmodium to identify the molecular target of the drug in Schistosoma and provide evidence that artemether binds to SmSERCA, a putative Ca2?-ATPase of Schistosoma . We also predict the putative binding mode of the molecule for both its Plasmodium and Schistosoma targets. Our analysis of the mode of binding of artemether to Ca2?-ATPases also provides an explanation for the apparent paradox that, although the molecule has no side effect in humans, it has been shown to possess antitumoral activity.     

Higher Differentiability of Solutions of Elliptic Systems with Sobolev Coefficients: The Case p = n = 2

We establish higher differentiability results for local solutions of elliptic systems of the type $$\text{div} A(x,Du)=0 $$ in a bounded open set in ?². The operator A(x, ξ) is assumed to be strictly monotone and Lipschitz continuous with respect to variable ξ. The novelty of the paper is that we allow discontinuous dependence with respect to the x-variable, through a suitable Sobolev function.     

Existence and multiplicity of weak solutions for elliptic Dirichlet problems with variable exponent

Under appropriate growth conditions on the nonlinearity, the existence of multiple solutions for nonlinear elliptic Dirichlet problems with variable exponent is established. The approach is based on variational methods. Some applications and examples illustrate the obtained results.     

Analysis of genomic methylation level using micellar electrokinetic chromatography with UV detection

Analytical methods for quantification of 5′‐methylcytosine in genomes are important tools to investigate epigenetic changes in gene expression during development, differentiation, aging, or cancer. Here, we report a novel genomic methylation content assay based on enzymatic hydrolysis of DNA and MEKC separation of 5′‐deoxyribonucleoside monophosphates (dNMP) using the cationic surfactant CTAB as pseudostationary phase. Calf Thymus DNA was used during method development to determine electrophoretic parameters and electrolyte composition for a complete separation between 2′‐deoxycytosine‐5′‐monophosphate and 2′‐deoxy‐5′‐methylcytosine 5′‐monophosphate (d5mCMP). Methylated and not methylated oligonucleotides were used to confirm the identity of each peak and evaluate analytical parameters of the method. The LOD of the method was found to be 12.5 pmol/μL for d5mCMP.     

Analysis of veterinary drug residues in cheese by ultra‐high‐performance LC coupled to triple quadrupole MS/MS

A simple, reliable, and fast multiresidue method has been developed for the determination of 17 veterinary drugs belonging to several families (macrolides, sulfonamides, and anthelmintics) in cheese at trace levels. Ultra‐high‐performance LC coupled to MS/MS has been used for the analysis of these compounds in less than 9 min. Veterinary drug residues have been extracted from cheese samples using a QuEChERS (quick, easy, cheap, effective, rugged, and safe)‐based extraction procedure without applying any further clean‐up step. Matrix‐matched calibration was used for quantification and recoveries were calculated at three concentration levels (10, 50, and 100 μg/kg). The obtained values ranged from 70 to 110% for the selected compounds except for tylosin and josamycin at 100 μg/kg (111.7 and 112.7%, respectively). Intra‐ and interday precision were also evaluated and RSDs were lower than 25% in all the cases. LOQs ranged from 0.3 μg/kg (for thiabendazole, oxfendazole, mebendazole, josamycin, and fenbendazole) to 10.5 μg/kg (abamectin), whereas decision limit and detection capability ranged from 2.3 (thiabendazole) to 11.3 (abamectin) and 4.2 (thiabendazole) to 14.3 μg/kg (abamectin), respectively. Finally, 13 samples were analyzed and traces of thiabendazole were detected in two different cheeses.     

Optimization of microwave‐assisted extraction of analgesic and anti‐inflammatory drugs from human plasma and urine using response surface experimental designs†

The performance of microwave‐assisted extraction and HPLC with photodiode array detection method for determination of six analgesic and anti‐inflammatory drugs from plasma and urine, is described, optimized, and validated. Several parameters affecting the extraction technique were optimized using experimental designs. A four‐factor (temperature, phosphate buffer pH 4.0 volume, extraction solvent volume, and time) hybrid experimental design was used for extraction optimization in plasma, and three‐factor (temperature, extraction solvent volume, and time) Doehlert design was chosen to extraction optimization in urine. The use of desirability functions revealed the optimal extraction conditions as follows: 67°C, 4 mL phosphate buffer pH 4.0, 12 mL of ethyl acetate and 9 min, for plasma and the same volume of buffer and ethyl acetate, 115°C and 4 min for urine. Limits of detection ranged from 4 to 45 ng/mL in plasma and from 8 to 85 ng/mL in urine. The reproducibility evaluated at two concentration levels was less than 6.5% for both specimens. The recoveries were from 89 to 99% for plasma and from 83 to 99% for urine. The proposed method was successfully applied in plasma and urine samples obtained from analgesic users.     

Cycloalkane and alicyclic heterocycle complexation by new switchable resorcin[4]arene-based container molecules: NMR and ITC binding studies

The synthesis and structural characterization of novel, "molecular basket"-type bridged cavitands is reported. The resorcin[4]arene-based container molecules feature well-defined cavities that bind a wide variety of cycloalkanes and alicyclic heterocycles. Association constants (K(a)) of the 1:1 inclusion complexes were determined by both (1)H NMR and isothermal titration calorimetry (ITC). The obtained K(a) values in mesitylene ranged from 1.7×10(2) M(-1) for cycloheptane up to 1.7×10(7) M(-1) for morpholine. Host-guest complexation by the molecular baskets is generally driven by dispersion interactions, C-H···π interactions of the guests with the aromatic walls of the cavity, and optimal cavity filling. Correlations between NMR-based structural data and binding affinities support that the complexed heterocyclic guests undergo additional polar C-O···C=O, N-H···π, and S···π interactions. The first crystal structure of a cavitand-based molecular basket is reported, providing precise information on the geometry and volume of the inner cavity in the solid state. Molecular dynamic (MD) simulations provided information on the size and conformational preorganization of the cavity in the presence of encapsulated guests. The strongest binding of heterocyclic guests, engaging in polar interactions with the host, was observed at a cavity filling volume of 63 ± 9%.     

Unprecedented 1,3-diaza[3]ferrocenophane scaffold as molecular probe for anions

The guanidine unit in the guise of 2-aminoimidazole in the new structural motif 2-arylamino-1,3-diaza[3]ferrocenophane 4 acts as a binding site for anions. The electrochemical behavior of this compound has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and was found to exhibit a quasi reversible oxidation peak, associated to the Fe(II)/Fe(III) redox couple (Ep = 440 mV), and a non-reversible oxidation wave (Ep = 817 mV), probably associated to the oxidation of the C═N unit present in the guanidine bridge. Recognition of AcO(-), PhCO(2)(-), F(-), Cl(-), and Br(-) anions by the free receptor and the less basic anions Br(-), Cl(-), and NO(3)(-) by its monoprotonated form takes place by unusual redox-ratiometric measurements and spectroscopic ((1)H NMR and UV-vis) changes.     

The phase coexistence method to obtain surface free energies and nucleation barriers: a brief review

ABSTRACT

A recently developed method where one analyses the finite size effects associated with liquid–solid phase equilibria including vapour–crystal coexistence is briefly reviewed. It is shown that the estimation of the chemical potential of the vapour surrounding the crystal as function of the crystal volume yields information on the bulk coexistence conditions, when an extrapolation to the thermodynamic limit is performed. Estimating the pressure of the fluid surrounding the crystal nucleus in the finite simulation box and the volume of this nucleus that coexists with the fluid in thermal equilibrium, an estimate for the total surface excess free energy can be obtained, which to a very good approximation is independent of the size of the simulation box. The free energy barrier against homogeneous nucleation of crystals thus can be estimated as a function of the nucleus volume. Monte Carlo simulations for the soft effective Asakura–Oosawa model of colloid-polymer mixtures which form face-centered cubic colloidal crystals are used to exemplify this method, computing the surface excess free energy of these crystals over a wide range of crystal volumes, without the need to characterise the non-spherical crystal shape. A possible extension of these concepts to heterogeneous nucleation is also briefly discussed.