Simple HPLC‐UV for the quantification of a new leishmanicidal candidate (E)‐1‐4(trifluoromethyl) benzylidene)‐5‐(2‐4‐dichlorozoyl) carbonylhydrazine (LASSBio‐1736) in rat plasma for pharmacokinetics assessment

In this study, a sensitive HPLC‐UV assay was developed and validated for the determination of LASSBio‐1736 in rat plasma with sodium diclofenac as internal standard (IS). Liquid–liquid extraction using acetonitrile was employed to extract LASSBio‐1736 and IS from 100 μL of plasma previously basified with NaOH 0.1 M. Chromatographic separation was carried on Waters Spherisorb^®S5 ODS2 C₁₈ column (150 × 4.6 mm, 5 μm) using an isocratic mobile phase composed by water with triethylamine 0.3% (pH 4), methanol and acetonitrile grade (45:15:40, v/v/v) at a flow rate of 1 mL/min. Both LASSBio‐1736 and IS were eluted at 4.2 and 5 min, respectively, with a total run time of 8 min only. The lower limit of quantification was 0.2 μg/mL and linearity between 0.2 and 4 μg/mL was obtained, with an R² > 0.99. The accuracy of the method was >90.5%. The relative standard deviations intra and interday were <6.19 and <7.83%, respectively. The method showed the sensitivity, linearity, precision, accuracy and selectivity required to quantify LASSBio‐1736 in preclinical pharmacokinetic studies according to the criteria established by the US Food and Drug Administration and European Medicines Agency. Copyright © 2016 John Wiley & Sons, Ltd.     

Ferroxidase Activity in Eukaryotic Ferritin is Controlled by Accessory‐Iron‐Binding Sites in the Catalytic Cavity

Ferritins are iron‐storage nanocage proteins that catalyze the oxidation of Fe²⁺ to Fe³⁺ at ferroxidase sites. By a combination of structural and spectroscopic techniques, Asp140, together with previously identified Glu57 and Glu136, is demonstrated to be an essential residue to promote the iron oxidation at the ferroxidase site. However, the presence of these three carboxylate moieties in close proximity to the catalytic centers is not essential to achieve binding of the Fe²⁺ substrate to the diferric ferroxidase sites with the same coordination geometries as in the wild‐type cages.     

On the Ambiphilic Reactivity of Geometrically Constrained Phosphorus(III) and Arsenic(III) Compounds: Insights into Their Interaction with Ionic Substrates

The ambiphilic nature of geometrically constrained Group 15 complexes bearing the N,N‐bis(3,5‐di‐tert‐butyl‐2‐phenolate)amide pincer ligand (ONO^3?) is explored. Despite their differing reactivity towards nucleophilic substrates with polarised element–hydrogen bonds (e.g., NH₃), both the phosphorus(III), P(ONO) ( 1 a ), and arsenic(III), As(ONO) ( 1 b ), compounds exhibit similar reactivity towards charged nucleophiles and electrophiles. Reactions of 1 a and 1 b with KOtBu or KNPh₂ afford anionic complexes in which the nucleophilic anion associates with the pnictogen centre ([(tBuO)Pn(ONO)]^? (Pn=P ( 2 a ), As ( 2 b )) and [(Ph₂N)Pn(ONO)]^? (Pn=P ( 3 a ), As ( 3 b )). Compound 2 a can subsequently be reacted with a proton source or benzylbromide to afford the phosphorus(V) compounds (tBuO)HP(ONO) ( 4 a ) and (tBuO)BzP(ONO) ( 5 a ), respectively, whereas analogous arsenic(V) compounds are inaccessible. Electrophilic substrates, such as HOTf and MeOTf, preferentially associate with the nitrogen atom of the ligand backbone of both 1 a and 1 b , giving rise to cationic species that can be rationalised as either ammonium salts or as amine‐stabilised phosphenium or arsenium complexes ([Pn{ON(H)O}]⁺ (Pn=P ( 6 a ), As ( 6 b )) and [Pn{ON(Me)O}]⁺ (Pn=P ( 7 a ), As ( 7 b )). Reaction of 1 a with an acid bearing a nucleophilic counteranion (such as HCl) gives rise to a phosphorus(V) compound HPCl(ONO) ( 8 a ), whereas the analogous reaction with 1 b results in the addition of HCl across one of the As?O bonds to afford ClAs{(H)ONO} ( 8 b ). Functionalisation at both the pnictogen centre and the ligand backbone is also possible by reaction of 7 a / 7 b with KOtBu, which affords the neutral species (tBuO)Pn{ON(Me)O} (Pn=P ( 9 a ), As ( 9 b )). The ambiphilic reactivity of these geometrically constrained complexes allows some insight into the mechanism of reactivity of 1 a towards small molecules, such as ammonia and water.     

Spin-orbit ab initio investigation of the ultraviolet photolysis of diiodomethane.

The UV photodissociation (<5 eV) of diiodomethane (CH(2)I(2)) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH(2)I(2) and CH(2)I--I lead to geminate-radical products, CH(2)I (.)+I((2)P(3/2)) or CH(2)I (.)+ I*((2)P(1/2)). The recombination process from CH(2)I--I to CH(2)I(2) is explained by an isomerization process and a secondary photodissociation reaction of CH(2)I--I. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH(2)I--I species.     

Ionization and tautomerization of 2-nitrocyclohexanone in aqueous solution

The keto-enol tautomerism of 2-nitrocyclohexanone (2-NCH) was studied in aqueous solution under different experimental conditions. Ketonization rate constants were measured spectrophotometrically at 25 degrees C at an ionic strength of 0.4 mol dm-3 (NaCl) in diluted hydrochloric acid, in diluted sodium hydroxide, and in several buffers by using NaHSO3 as the scavenger of the keto form. A value of pK(a)(EH) = 4.78 for the enol form was obtained from the rate-pH profile of the reaction. A value of pK(a)(KH) = 5.97 for the keto form was directly obtained from the UV-vis spectra of 2-NCH recorded at different pHs. The equilibrium constant for the keto-enol tautomerism, pK(T) = -log([enol]/[ketone]) = 1.19, was obtained by combining the two pKa values (pK(T) = pK(a)(KH) - pK(a)(EH)). A comparison of these results with the corresponding values (Keefe, J. R.; Kresge, A. J. In The Chemistry of Enols; Rappoport, Z., Ed.; Wiley & Sons: New York, 1990; pp 399-480) for cyclohexanone shows the dramatic effects of an alpha-nitro substituent on the keto-enol acidities and the tautomerization constant of alicyclic ketones. Rates and equilibria were discussed in the light of the Br?nsted equation, the principle of nonperfect synchronization, and the Marcus theory. It turns out that, on passing from nitroalkanes to nitroketones, the resonance contribution to pKa and deprotonation rate decreases, being overwhelmed by steric and inductive effects.     

Determination of biogenic amines in alcoholic beverages by ion chromatography with suppressed conductivity detection and integrated pulsed amperometric detection

The determination of biogenic amines in alcoholic beverages is important to assess the potential risks associated with the consumption of high concentrations of these compounds. In addition, product storage conditions and the length of storage can cause the formation of biogenic amines that reduce product quality. We report a new method using cation-exchange chromatography with either suppressed conductivity, integrated pulsed amperometry, UV, or a combination of these detection techniques to determine biogenic amines in alcoholic beverages. The main objective was to provide a direct comparison between IPAD and suppressed conductivity detection for determining biogenic amines in alcoholic beverages. Suppressed conductivity is the simplest detection approach for determining putrescine, cadaverine, histamine, agmatine, phenylethylamine, spermidine, and spermine with good sensitivity (0.004-0.08 mg/l) and was used to evaluate the influence of storage time and conditions on the evolution of biogenic amines in alcoholic beverages. Integrated pulsed amperometric detection (IPAD) detects more biogenic amines than suppressed conductivity detection, enabling the detection of dopamine, tyramine, and serotonin. Tyramine was simultaneously determined by UV detection and IPAD to provide confirmation and ensure the accuracy of the analytical results. The linearity of biogenic amine responses was within 0.1-20 mg/l and peak area precisions were 0.24-4.97% for IPAD, suppressed conductivity-IPAD, and UV detection. The sensitivity for the 10 biogenic amines using the 3 detection techniques varied considerably from 0.004-1.1 mg/l and recoveries were within 85-122%.     

Protolytic behavior of hydroxylated Pyrex glass surfaces in NaCl media

Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass-water interface was investigated by acid-base titration (glass electrode) at 25 degrees C and at the ionic strengths 0.010, 0.030, 0.10, 1.0, and 3.0 mol dm(-3). The pH values ranged from 2 to 7. The Pyrex samples had a specific surface area of 19.2x10(3) m(2)kg(-1) and a porous structure (pores 2.4 nm thick, 280 nm long). The reactions were found to be extremely slow but showed good reversibility. The potentiometric data, due to the small effect of ionic strength on the equilibria, were fitted with a simple nonelectrostatic model based on strong specific interactions of medium ions with deprotonated silanol, >SiO(-), and boranol, >BO(-), as well as with protonated sites. The acid-base properties are described by the reactions and equilibrium constants at the infinite dilution reference state: >SiONa + H(+) <==> >SiOHNa(+), logbeta110Si=3.1+/-0.2; >SiONa + 2H(+) + Cl(-) <==> >SiOH(2)Cl + Na(+), logbeta201Si=6.75+/-0.15; >SiONa + H(+) <==> >SiOH + Na(+), logbeta100Si=1.8+/-0.2, >BONa + H(+) <==>BOH + Na(+), logbeta100B=6.4+/-0.2; >BONa + H(+) <==> >BOHNa(+), logbeta110B=6.6+/-0.2; >BONa + 2H(+) <==> >BOH(+)(2) + Na(+), logbeta200B=11.56+/-0.15.     

Glycine- and sarcosine-based models of vanadate-dependent haloperoxidases in sulfoxygenation reactions

Reaction of R-styreneoxide with glycine-tert-butylester yielded amino alcohols of the general formula NR1R2R3, where R1 = CH2COOtBu and R2 = R3 = 2-phenyl-2-hydroxyethyl (H2LA); R2 = 2-phenyl-2-hydroxyethyl and R3 = 1-phenyl-2-hydroxyethyl (H2LB); R2 = H and R3 = 2-phenyl-2-hydroxyethyl (HLC); and R2 = H and R3 = 1-phenyl-2-hydroxyethyl (HLD). The corresponding reaction with sarcosine-tert-butylester and subsequent hydrolysis provided the zwitterion +NH(CH3){CH2CHPh(OH)}(CH2CO2-), HLE* (asterisk refers to unprotected carboxylate). Reaction of these ligands with VO(OiPr)3 in CH2Cl2 gave the oxovanadium(V) complexes [VOL(OiPr)2] and [VOL2(OiPr)] (for LC and LD) or, when reacted in the presence of MeOH, [VOL'(OMe)], where L' represents the methyl ester of LA, LB, and LE. The crystal and molecular structures of R-HLC, S-HLD, R,S-HLE* x H2O, and lambda-[VO(R,S-LB')OMe] have been determined. The complex [VOLB'(OMe)] contains vanadium in a distorted trigonal-bipyramidal array (tau = 0.72), the oxo group in the equatorial plane, and methoxide and N in the apical positions, and thus, it structurally models the active center of vanadate-dependent haloperoxidases. The structure and the bonding parameters, including a particularly long d(V-N) of 2.562 A, are backed up by DFT calculations. The isolated oxovanadium(V) complexes and the in situ systems L + VO(OiPr)3 catalyze the oxidation, by cumylhydroperoxide HO2R', of prochiral sulfides (MeSPh, MeSp-Tol, PhSBn) to chiral sulfoxides plus some sulfone. The best results with respect to enantioselectivity (enantiomeric excess (ee) = 38%) were obtained with the system VO(OiPr)3/LA, and the best selectivity with respect to sulfoxide (100%) was obtained with [VOLA(OiPr)]. The reaction with the hexacoordinated [VO(OMe)(HOMe)LD*] was very slow. Oxidation of PhSBn is faster than that of MeSPh and MeSpTol. Turn-over numbers are up to 60 mol of sulfoxide mol-1 of catalyst h-1 (-20 degrees C). The unspectacular ee apparently is a consequence of flexibility of the active catalyst in solution, as shown by the 51V NMR of the catalysts [VOL(OR)] and the oxo-peroxo intermediates [VOL(O2R')]. As shown by DFT calculations, the peroxo ligand coordinates in the tilted end-on fashion in the axial or equatorial position (energy difference = 17.6 kJ/mol).