A macrocyclic ligand as receptor and Zn(II)-complex receptor for anions in water: binding properties and crystal structures

Binding properties of 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ(5,8),Δ(14,17)-diene ligand L towards Zn(II) and anions, such as the halide series and inorganic oxoanions (phosphate (Pi), sulfate, pyrophosphate (PPi), and others), were investigated in aqueous solution; in addition, the Zn(II)/L system was tested as a metal-ion-based receptor for the halide series. Ligand L is a cryptand receptor incorporating two squaramide functions in an over-structured chain that connects two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base. It binds Zn(II) to form mononuclear species in which the metal ion, coordinated by the Me(2)[12]aneN(4) moiety, lodges inside the three-dimensional cavity. Zn(II)-containing species are able to bind chloride and fluoride at the physiologically important pH value of 7.4; the anion is coordinated to the metal center but the squaramide units play the key role in stabilizing the anion through a hydrogen-bonding network; two crystal structures reported here clearly show this aspect. Free L is able to bind fluoride, chloride, bromide, sulfate, Pi, and PPi in aqueous solution. The halides are bound at acidic pH, whereas the oxoanions are bound in a wide range of pH values ranging from acidic to basic. The cryptand cavity, abundant in hydrogen-bonding sites at all pH values, allows excellent selectivity towards Pi to be achieved mainly at physiological pH 7.4. By joining amine and squaramide moieties and using this preorganized topology, it was possible, with preservation of the solubility of the receptor, to achieve a very wide pH range in which oxoanions can be bound. The good selectivity towards Pi allows its discrimination in a manner not easily obtainable with nonmetallic systems in aqueous environment.     

A simple HPLC-DAD method for determination of adapalene in topical gel formulation

A simple stability indicating high-performance liquid chromatography method for the analysis of adapalene in pharmaceutical gel formulation is developed and validated. An isocratic separation is performed using a Merck RP-8 (150 mm × 4.6 mm i.d., particle size 5 m) column and a mixture of acetonitrile water (67:33, v/v, pH adjusted to 2.5 with phosphoric acid) as the mobile phase. The detection is achieved with a photodiode array detector at 321 nm. The specificity of the method is verified by subjecting both the reference substance and the pharmaceutical form to hydrolytic, oxidative, photolytic, and thermal stress conditions. There is no interference from the excipients of the formulation on the determination of adapalene in gel. The response is linear over the concentration range of 8.0-16.0 μg/mL (r > 0.999) with a limit of detection and quantification of 0.04 and 0.14 μg/mL, respectively. The mean recovery is 100.8%. The RSD values for the intra- and inter-day precision studies are < 1.2%. The method is validated by reaching satisfactory results for linearity, selectivity, specificity, precision, accuracy, robustness, and system suitability.     

Electrochemical Behavior of a Glassy Carbon Electrode Chemically Modified with Nickel Pentacyanonitrosylferrate in Presence of Sulfur Compounds

The glassy carbon electrode was modified with a nickel pentacyanonitrosylferrate film by electrodeposition of Ni and subsequent derivatization with NaPCNF. The film was characterized by XPS and electrochemical methods. Cyclic voltammetry of the NiPCNF onto the GC shows a redox couple (Fe^III/Fe^II) with E°′ of 538 mV (I_pa/I_pc around 1) and ΔE_p of 93 mV in 0.5 mol L^?1 KNO₃, with a diffusion‐controlled process. There was a decrease of anodic peak currents of the film in the presence of sulfide and 2‐propanethiol due to a precipitation reaction on the film surface by nucleophilic attack.     

Gas phase charged aggregates of bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions: first evidence of AOT solvated aggregates

Assembling and chelating properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) towards divalent metal ions have been investigated in the gas phase by electrospray ionization mass spectrometry. A variety of positively charged monometallated and mixed metal aggregates are formed. Interestingly, several ions contain solvent (MeOH, H(2)O) molecules and constitute the most abundant AOT cationic aggregates not containing sodium. These species are the first example of solvated AOT-metal ion aggregates in the gas phase. By increasing the surfactant aggregation number, the abundance of solvated species becomes lower than that of unsolvated ones. Decompositions of ionic species have been studied by tandem mass spectrometry, and their stability has been determined through energy resolved mass spectrometry. In contrast with positively charged AOT-alkaline metal ion aggregates, whose decompositions are dominated by the loss of individual surfactant molecules, AOTNa-divalent ion aggregates mainly dissociate through the cleavage of the AOT H(2)C-O bond followed by further intramolecular fragmentations. This finding, that is consistent with an enhanced chelation of divalent ions with AOT(-) head groups, has been taken as an indication that such aggregates are characterized by a reverse micelle-like organization with a ionic core formed by the metal cations interacting with the negatively charged surfactant polar heads, whereas the surfactant alkyl chains point outside.     

Effects of the net charge on abundance and stability of supramolecular surfactant aggregates in gas phase

Self-assembling of amphiphilic molecules under electrospray ionization (ESI) conditions is characterized by quite unexpected phenomenology. The noticeable differences with respect to the condensed phase are attributable to the absence of the surfactant-solvent interactions, the presence of net charge in the aggregates, and the strong deviation from equilibrium conditions. Aiming to investigate the effects of the net charge on abundance and stability of supramolecular surfactant aggregates, positively and negatively charged aggregates of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium methane sulfonate (MetS), butane sulfonate (ButS) and octane sulfonate (OctS) have been studied by ESI mass spectrometry, energy resolved mass spectrometry and density functional theory calculations. The negatively charged aggregates are found to be less stable than their positive counterparts. The results are consistent with a self-assembling pattern dominated by electrostatic interactions involving the counterions and head groups of the investigated amphiphilic compounds while the alkyl chains point outwards, protecting the aggregates from unlimited growth processes.     

Carbonyl oxides reactions from geraniol-trans-(3,7-dimethylocta-2,6-dien-1-ol), 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis: kinetics and mechanisms

A density functional theory (DFT) study of the mechanisms of carbonyl oxide reactions from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis is presented. The geometries, energies, and harmonic vibrational frequencies of each stationary point were determined by B3LYP/6-31(d,p) and BH&HLYP/cc-pVDZ methods. According to the calculations, the ozonolysis reactions are initiated by the formation of van der Waals (VDW) complexes to yield primary ozonides, which rapidly open to carbonyl oxide compounds. These carbonyl oxide compounds react to form dioxanes and hydroperoxides. The hydroperoxides react by isomerization to form stable products. Glyoxal and methyl-glyoxal have been identified as the final product from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis. Our results are in good agreement with the experimental studies.     

Simultaneous detection and quantification of parecoxib and valdecoxib in canine plasma by HPLC with spectrofluorimetric detection: development and validation of a new methodology

Parecoxib is the injectable prodrug of valdecoxib, a cicloxygenase-2 selective drug, currently used in human medicine. Recent studies have suggested both its excellent clinical effectiveness and wide safety profile. The aim of the present study was to develop and validate a new high-performance liquid chromatography (HPLC) with spectrofluorimetric detection method to quantify parecoxib and valdecoxib in canine plasma. Several parameters both in the extraction and the detection method were evaluated. The applicability of the method was determined by administering parecoxib to one dog: the protocol provided the expected pharmacokinetic results. The final mobile phase was acetonitrile: AcONH₄ (10 mM; pH 5.0) 55:45, v/v, with a flow rate of 0.4 mL min⁻¹, and excitation and emission wavelengths of 265 and 375 nm, respectively. The analytical column was a reverse-phase C18 ODS2 3-μm particle size. Protein precipitation in acidic medium followed by two successive liquid–liquid steps was carried out. The best extraction solvent was cyclohexane:Et₂O (3:2, v/v) that gave recoveries ranging from 81.1% to 89.1% and from 94.8% to 103.6% for parecoxib and valdecoxib, respectively. The limits of quantification were 25 and 10 ng mL⁻¹ for parecoxib and valdecoxib, respectively. The chromatographic runs were specific with no interfering peaks at the retention times of the analytes, as confirmed by HPLC–mass spectrometry experiments. The other validation parameters were in agreement with the European Medicines Evaluation Agency and International Conference on Harmonisation guidelines. In conclusion, this method (extraction, separation and applied techniques) is simple and effective. This is the first time that use of a HPLC with spectrofluorimetric detection technique to simultaneously detect parecoxib and valdecoxib in plasma has been reported. This technique may have applications for pharmacokinetic studies.     

Efficient organic monoliths prepared by γ-radiation induced polymerization in the evaluation of histone deacetylase inhibitors by capillary(nano)-high performance liquid chromatography and ion trap mass spectrometry

New monolithic HPLC columns were prepared by γ-radiation-triggered polymerization of hexyl methacrylate and ethylene glycol dimethacrylate monomers in the presence of porogenic solvents. Polymerization was carried out directly within capillary (250-200 μm I.D.) and nano (100-75 μm I.D.) fused-silica tubes yielding highly efficient columns for cap(nano)-LC applications. The columns were applied in the complete separation of core (H2A, H2B, H3, and H4) and linker (H1) histones under gradient elution with UV and/or electrospray ionization (ESI) ion trap mass spectrometry (MS) detections. Large selectivity towards H1, H2A-1, H2A-2, H2B, H3-1, H3-2 and H4 histones and complete separation were obtained within 8 min time windows, using fast gradients and very high linear flow velocities, up to 11 mm/s for high throughput applications. The method developed was the basis of a simple and efficient protocol for the evaluation of post-translational modifications (PTMs) of histones from NCI-H460 human non-small-cell lung cancer (NSCLC) and HCT-116 human colorectal carcinoma cells. The study was extended to monitoring the level of histone acetylation after inhibition of Histone DeACetylase (HDAC) enzymes with suberoylanilide hydroxamic acid (SAHA), the first HDAC inhibitor approved by the FDA for cancer therapy. Attractive features of our cap(nano)-LC/MS approach are the short analysis time, the minute amount of sample required to complete the whole procedure and the stability of the polymethacrylate-based columns. A lab-made software package ClustMass was ad hoc developed and used to elaborate deconvoluted mass spectral data (aligning, averaging, clustering) and calculate the potency of HDAC inhibitors, expressed through a Relative half maximal Inhibitory Concentration parameter, namely R_IC(50) and an averaged acetylation degree.     

A one-pot azido reductive tandem mono-N-alkylation employing dialkylboron triflates: online ESI-MS mechanistic investigation

An efficient one-pot reductive tandem mono-N-alkylation of both aromatic and aliphatic azides using dialkylboron triflates as alkylating agents has been examined under standardized reaction conditions. This methodology after optimization has been employed toward the syntheses of various secondary alkyl as well as aryl amines, including the synthesis of N10-butylated pyrrolo[2,1-c][1,4]benzodiazepine-5,11-diones via in situ azido reductive-cyclization process. This protocol is particularly attractive to provide an environmentally benign and practical method for mono-N-alkylation from organic azides without the use of toxic catalysts or corrosive alkylating agents. In addition, the mechanistic aspects have been investigated and the intermediates associated with this selective transformation have been intercepted and characterized by online monitoring of the reaction by ESI-MS/MS.