Hydrolysis of DNA model substrates catalyzed by metal-substituted Wells-Dawson polyoxometalates

In this study we report the first example of phosphoester bond hydrolysis in 4-nitrophenyl phosphate (NPP) and bis-4-nitrophenyl phosphate (BNPP), two commonly used DNA model substrates, promoted by metal-substituted polyoxometalates (POMs). Different transition metal and lanthanide ions were incorporated into the Wells-Dawson polyoxometalate framework and subsequently screened for their hydrolytic activity towards the cleavage of the phosphoester bonds in NPP and BNPP. From these complexes, the Zr(iv)-substituted POM showed the highest reactivity. At pD 7.2 and 50 °C a NPP hydrolysis rate constant of 7.71 × 10(-4) min(-1) (t(1/2) = 15 h) was calculated, representing a rate enhancement of nearly two orders of magnitude in comparison with the spontaneous hydrolysis of NPP. The catalytic (k(c) = 1.73 × 10(-3) min(-1)) and formation constant (K(f) = 520.02 M(-1)) for the NPP-Zr(iv)-POM complex were determined from kinetic experiments. The reaction proceeded faster in acidic conditions and (31)P NMR experiments showed that faster hydrolysis is proportional to the presence of the 1?:?1 monosubstituted Zr(iv)-POM at acidic pD values. The strong interaction of the 1?:?1 monosubstituted Zr(iv)-POM with the P-O bond of NPP was evidenced by the large chemical shift and the line broadening of the (31)P nucleus in NPP observed upon addition of the metal complex. Significantly, a ten-fold excess of NPP was fully hydrolyzed in the presence of the Zr(iv)-POM, proving the principles of catalysis. The NMR spectra did not show sign of any paramagnetic species, excluding an oxidative cleavage mechanism and suggesting purely hydrolytic cleavage.     

Two succinic acid derivatives of 2‐ethyl‐6‐methylpyridin‐3‐ol

Crystals of bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate–succinic acid (1/1), C₈H₁₂NO⁺·0.5C₄H₄O₄²⁻·0.5C₄H₆O₄, (I), and 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium hydrogen succinate, C₈H₁₂NO⁺·C₄H₅O₄⁻, (II), were obtained by reaction of 2‐ethyl‐6‐methylpyridin‐3‐ol with succinic acid. The succinate anion and succinic acid molecule in (I) are located about centres of inversion. Intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds are responsible for the formation of a three‐dimensional network in the crystal structure of (I) and a two‐dimensional network in the crystal structure of (II). Both structures are additionally stabilized by π–π interactions between symmetry‐related pyridine rings, forming a rod‐like cationic arrangement for (I) and cationic dimers for (II).     

Highly concentrated emulsified microemulsions as solvent-free plant protection formulations

Effective plant protection agents are readily available and well implemented in industry. However, delivery to the plant and application on the leaf are processes that still need to be optimized. Up to now plant protection formulations represent either emulsion or suspension concentrates that often contain environmentally harmful organic solvents and/or adjuvants. Emulsified microemulsions are hierarchically organized systems comprising emulsion droplets that confine a water-in-oil microemulsion. In the present contribution we show that emulsified microemulsions prepared from environmentally friendly components can be loaded with the plant-protection agent Fenpropimorph® up to 48 wt.% without organic solvent. The emulsion itself is highly concentrated, containing 60 wt.% of dispersed phase, and can be readily diluted with water for spraying in farming applications. Small-angle X-ray measurements reveal the existence of a water-in-Fenpropimorph® microemulsion confined inside the emulsion droplets. Dynamic light scattering shows that the emulsions prepared are monomodal, comprising droplet radii in the hundred nanometer range.     

Determination of Anthelmintic Pharmaceuticals in Wastewater by Solid-Phase Extraction and Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - The presented study describes the development, optimization, and validation of a method for the determination of four structurally...     

Influence of the Mobile-Phase Modifier on the Retention of Some para-Substituted Amides; Correlation with Compound Lipophilicity

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of para-substituted amides of α-phenylacetic, benzoic, propanoic, and 2,2-dimethylpropanoic acid...     

Tautomerism of 4-phenyl-2,4-dioxobutanoic acid. Insights from pH ramping NMR study and quantum chemical calculations

Aryldiketo acids (ADKs) exhibit the variety of biological activities, mainly due to large affinity toward divalent metal ions. Metal complexation ability of ADKs, as well as interactions with proteins, depend on tautomeric form present in solution. The main aim of this study was to fully explore the tautomeric preferences of 4-phenyl-2,4-dioxobutanoic acid (4PDA), as ADKs representative, in aqueous media at different pH values. 1D and 2D NMR spectroscopy in combination with quantum chemical calculations was applied in order to better understand the tautomeric preferences of 4PDA. The data in highly acidic media are especially interesting since there are no such findings in the literature due to low solubility of ADKs in molecular form. At low pH values, where 4PDA is unionized, the most abundant tautomeric form is enol with keto group closer to phenyl ring. At higher pH values, mixture of two 4PDA ionic forms coexists in solution. Their ratio calculated according to NMR data fits the values predicted using two experimentally determined pK _a values. Based on the complexity of ¹H NMR spectrum of monoanionic 4PDA form, coexistence of two stable rotamers was assumed. In an alkaline media, 4PDA is mostly present in dianionic form. As π-electrons of dianion are delocalized over an entire keto-enol moiety, spectral distinction between tautomers was not possible. Quantum chemical calculations were used to predict relative stability of tautomers. The predictions were in good accordance with experimental results only in case when explicit water molecule was included in calculations.     

Heterologous Expression,Biosynthetic Studies,and Ecological Function of the Selective Gq‐Signaling Inhibitor FR900359

The cyclic depsipeptide FR900359 (FR), isolated from the tropical plant Ardisia crenata, is a strong and selective inhibitor of Gq proteins, making it an indispensable pharmacological tool to study Gq‐related processes, as well as a promising drug candidate. Gq inhibition is a novel mode of action for defense chemicals and crucial for the ecological function of FR, as shown by in vivo experiments in mice, its affinity to insect Gq proteins, and insect toxicity studies. The uncultured endosymbiont of A. crenata was sequenced, revealing the FR nonribosomal peptide synthetase (frs) gene cluster. We here provide a detailed model of FR biosynthesis, supported by in vitro enzymatic and bioinformatic studies, and the novel analogue AC‐1, which demonstrates the flexibility of the FR starter condensation domains. Finally, expression of the frs genes in E. coli led to heterologous FR production in a cultivable, bacterial host for the first time.     

Adsorption of Dicarbollylcobaltate(III) Anion {(pi-(3)-1,2-B(9)C(2)H(11))(2)Co(III)(-)} at the Water/1,2-Dichloroethane Interface. Influence of Counterions' Nature

Interfacial tension has been used to study the adsorption at the water/1,2-dichloroethane interface of dicarbollylcobaltate(III) {(pi-(3)-1,2-B(9)C(2)H(11))(2)Co(III)(-)} of the monovalent and bivalent metals. At the limiting coverage, the area per dicarbollylcobaltate(III) anions in the monolayer found experimentally is equal to 95+/-8 ?(2). It can be assumed that the symmetry axis of the adsorbed anions is arranged parallel to the interface surface. By their effects on the surface activity of the dicarbollylcobaltate(III) anions, cations can be arranged in the following order: Mg(2+) approximately Ba(2+) approximately Pb(2+)>/=Li(+) approximately Na(+)>K(+)>NH(+)(4)>Rb(+)Tl(+) approximately Ag(+) approximately Cs(+). The parameters of Frumkin and the virial isotherms have been calculated. There is a rather strong repulsion among the adsorbed anions. To define the energy of the specific interaction between the anions and the adsorbed monolayer, the technique of E. Goddard et al. (J. Colloid Interface Sci. 24, 297 (1967)) was applied. Its application for two-phase systems permits us to define the parameters of the ion exchange reaction on the basis of measurements of interfacial tension. The ion exchange constants calculated by various methods have been compared. Copyright 2001 Academic Press.     

Optimization of artificial neural network for retention modeling in high-performance liquid chromatography

An artificial neural network (ANN) model for the prediction of retention times in high-performance liquid chromatography (HPLC) was developed and optimized. A three-layer feed-forward ANN has been used to model retention behavior of nine phenols as a function of mobile phase composition (methanol-acetic acid mobile phase). The number of hidden layer nodes, number of iteration steps and the number of experimental data points used for training set were optimized. By using a relatively small amount of experimental data (25 experimental data points in the training set), a very accurate prediction of the retention (percentage normalized differences between the predicted and the experimental data less than 0.6%) was obtained. It was shown that the prediction ability of ANN model linearly decreased with the reduction of number of experiments for the training data set. The results obtained demonstrate that ANN offers a straightforward way for retention modeling in isocratic HPLC separation of a complex mixture of compounds widely different in pK_a and log K_ow values.