Headspace-single drop microextraction (HS-SDME) in combination with high-performance liquid chromatography (HPLC) to evaluate the content of alkyl- and methoxy-phenolic compounds in biomass smoke

The content of ten phenolic compounds present in four different biomass smoke materials: rock rose (Cistus monpelienisis), prickly pear (Opuntia ficus indica), pine needles (Pinus canariensis), and almonds skin (Prunus dulcis), have been evaluated. The sampling method mainly consisted of a trap alkaline solution to solubilize the phenols, and was optimized by an experimental design. Average sampling efficiencies of 78.1% and an average precision value of 10.6% (as relative standard deviation, RSD), were obtained for the selected group of phenols. The trapped phenolates were further analyzed by a headspace-single drop microextraction (HS-SDME) procedure, in combination with high-performance liquid chromatography (HPLC) with UV detection. The optimum variables for the HS-SDME method were: 1-decanol as extractant solvent, 3.5 μL of microdrop volume, 2 mL of sample volume, a pH value of 2, saturation of NaCl, an extraction temperature of 60 °C, and an extraction time of 25 min. The optimized HS-SDME method presented detection limits ranging from 0.35 to 5.8 μg mL⁻¹, RSD values ranging from 0.7 to 7.4%, and an average relative recovery (RR) of 99.8% and an average standard deviation of 5.2. The average content of phenolic compounds in the biomass materials studied were 70, 161, 206 and 252 mg kg⁻¹ of biomass for prickly pear, almonds skin, rock rose, and pine needles, respectively. The main components of the smokes were vanillin, phenol and methoxyphenols, in all smoking materials studied.     

Separation of secondary alcohols via enzymatic kinetic resolution using fatty esters as reusable acylating agents

A two consecutive step procedure for the resolution-separation of secondary alcohols employing ethyl tetradecanoate in the presence of lipase allowed the enzymatic kinetic resolution of two target molecules, 1-phenylethanol and 6-methylhept-5-en-2-ol. (S)-1-Phenylethanol was isolated in a yield of 47% with an ee of 94% and (R)-1-phenylethanol in a yield of 51% with an ee of 95%. (S)-6-Methylhept-5-en-2-ol was isolated in a yield 47% and an ee of 87% and (R)-6-methylhept-5-en-2-ol in a yield 49% and an ee of 90%.     

Electronic Effects of 11β Substituted 17β-Estradiol Derivatives and Instrumental Effects on the Relative Gas Phase Acidity

Numerous studies have highlighted the role of the proton donor characteristics of the phenol group of 17??-estradiol (E₂) in its association with the estrogen receptor alpha (ER??). Since the substitutions at position C₍₁₁₎ have been reported to modulate this association, we hypothesized that such substitutions may modify the phenol acidity. Hence, phenol gas-phase acidity of nine C₍₁₁₎-substituted E₂-derivatives were evaluated using the extended Cooks?? kinetic method, which is a method widely used to determine thermochemical properties by mass spectrometry. To enhance accuracy in data collection we recorded data from several instruments, including quadrupole ion trap, triple quadrupole, and hybrid QqTOF. Indeed, we report for the first time the use of the QqTOF instrument to provide a novel means to improve data accuracy by giving access to an intermediate effective temperature range. All experimental gas-phase acidity values were supported by theoretical calculations. Our results confirmed the ability of distant substituents at C₍₁₁₎ to modulate the phenol acidity through electrostatic interactions, electron withdrawing inductive effects, and mesomeric effects. However, no relationship was found between the phenol gas-phase acidity of investigated steroids and their binding affinity for ER?? assessed in solution. Thus, our results highlight that the intrinsic properties of the hormone do not influence sufficiently the stabilization of the hormone/ER?? complex. It is more likely that such stabilization would be more related to factors depending on the environment within the binding pocket such as hydrophobic, steric as well as direct intermolecular electrostatic effects between ER?? residues and the substituted steroidal estrogens.     

Ionic liquids as desorption solvents and memory effect suppressors in heterocyclic aromatic amines determination by SPME–HPLC fluorescence

The beneficial effects of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF₄) ionic liquid (IL) as mobile phase additive, desorption solvent, and memory effect suppressor in solid-phase microextraction (SPME)–high-performance liquid chromatography with fluorescence detection for the determination of six heterocyclic aromatic amines have been evaluated for the first time. Several chromatographic parameters have been evaluated in the presence or absence of IL or using triethylamine as the most common mobile phase additive, with a Nova-Pak® C18 stationary phase. This IL was found to be clearly superior to triethylamine for efficiency as well as peak shape enhancement and sensitivity increase. SPME was chosen because it is faster than conventional extraction techniques and allowed us to minimize the use of organic solvents. However, memory effect may become a problem when a high-sensitivity detector is used. The appropriate conditions for the desorption step and to eliminate the memory effect involving BMIm-BF₄ were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts.     

Traveling Wave Ion Mobility Mass Spectrometry and Ab Initio Calculations of Phosphoric Acid Clusters

Positive and negative ion electrospray mass spectra obtained from 50 mM phosphoric acid solutions presented a large number of phosphoric acid clusters: [(H₃PO₄)_n?+?zH] ^z+ or [(H₃PO₄)_n – zH] ^z– , with n up to 200 and z up to 4 for positively charged clusters, and n up to 270 and z up to 7 for negatively charged cluster ions. Ion mobility experiments allowed very explicit separation of the different charge states. Because of the increased pressures involved in ion mobility experiments, dissociation to smaller clusters was observed both in the trap and transfer areas. Voltages along the ion path could be optimized so as to minimize this effect, which can be directly associated with the cleavage of hydrogen bonds. Having excluded the ion mobility times that resulted from dissociated ions, each cluster ion appeared at a single drift time. These drift times showed a linear progression with the number of phosphoric atoms for cluster ions of the same charge state. Cross section calculations were carried out with MOBCAL on DFT optimized geometries with different hydrogen locations and with three types of atomic charges. DFT geometry optimizations yielded roughly spherical structures. Our results for nitrogen gas interaction cross sections showed that values were dependent on the atomic charges definition used in the MOBCAL calculation. This pinpointed the necessity to define a clear theoretical framework before any comparative interpretations can be attempted with uncharacterized compounds.

Acyl‐Chain Elongation Drives Ketosynthase Substrate Selectivity in trans‐Acyltransferase Polyketide Synthases

Type I modular polyketide synthases (PKSs), which are responsible for the biosynthesis of many biologically active agents, possess a ketosynthase (KS) domain within each module to catalyze chain elongation. Acylation of the KS active site Cys residue is followed by transfer to malonyl‐ACP to yield an extended β‐ketoacyl chain (ACP=acyl carrier protein). To date, the precise contribution of KS selectivity in controlling product fidelity has been unclear. Six KS domains from trans‐acyltransferase (trans‐AT) PKSs were subjected to a mass spectrometry based elongation assay, and higher substrate selectivity was identified for the elongating step than in preceding acylation. A close correspondence between the observed KS selectivity and that predicted by phylogenetic analysis was seen. These findings provide insights into the mechanism of KS selectivity in this important group of PKSs, can serve as guidance for engineering, and show that targeted mutagenesis can be used to expand the repertoire of acceptable substrates.     

Ionic liquid as an efficient promoting medium for two-phase nucleophilic displacement reactions

The use of the room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate as an efficient catalyst and solvent for several representative nucleophilic substitution reactions under aqueous-RTIL phase transfer conditions was explored. Recycling and reuse of the reaction medium was demonstrated for the azide formation.     

Gas‐phase doubly charged complexes of cyclic peptides with copper in +1, +2 and +3 formal oxidation states: formation,structures and electron capture dissociation

Copper complexes with a cyclic D‐His‐β‐Ala‐L‐His‐L‐Lys and all‐L‐His‐β‐Ala‐His‐Lys peptides were generated by electrospray which were doubly charged ions that had different formal oxidation states of Cu(I), Cu(II) and Cu(III) and different protonation states of the peptide ligands. Electron capture dissociation showed no substantial differences between the D‐His and L‐His complexes. All complexes underwent peptide cross‐ring cleavages upon electron capture. The modes of ring cleavage depended on the formal oxidation state of the Cu ion and peptide protonation. Density functional theory (DFT) calculations, using the B3LYP with an effective core potential at Cu and M06‐2X functionals, identified several precursor ion structures in which the Cu ion was threecoordinated to pentacoordinated by the His and Lys side‐chain groups and the peptide amide or enolimine groups. The electronic structure of the formally Cu(III) complexes pointed to an effective Cu(I) oxidation state with the other charge residing in the peptide ligand. The relative energies of isomeric complexes of the [Cu(c‐HAHK + H)]²⁺ and [Cu(c‐HAHK ? H)]²⁺ type with closed electronic shells followed similar orders when treated by the B3LYP and M06‐2X functionals. Large differences between relative energies calculated by these methods were obtained for open‐shell complexes of the [Cu(c‐HAHK)]²⁺ type. Charge reduction resulted in lowering the coordination numbers for some Cu complexes that depended on the singlet or triplet spin state being formed. For [Cu(c‐HAHK ? H)]²⁺ complexes, solution H/D exchange involved only the N–H protons, resulting in the exchange of up to seven protons, as established by ultra‐high mass resolution measurements. Contrasting the experiments, DFT calculations found the lowest energy structures for the gas‐phase ions that were deprotonated at the peptide C_α positions. Copyright © 2012 John Wiley & Sons, Ltd.     

A semiempirical conformational analysis of the 3-phenyl-1,2,3-oxathiazolidine 2-oxide

An extensive conformational search for the heterocyclic compound 3-phenyl-1,2,3-oxathiazolidine 2-oxide has been carried out using the semiempirical quantum-mechanical method PM3. All torsion angles were varied in the geometry optimization procedure which led to the prediction of four distinct conformers. Barriers to internal rotation leading to conformational interconversions were also calculated. The results of the present study indicate that this five-member ring substituted heterocyclic system may be expected to exist as a mixture of stable conformers rather than a unique molecular entity.     

Pyrocatechol-1-aldehyde salicyloylhydrazone as reagent for the spectrofluorimetric determination of zinc

Summary A procedure is developed for the Spectrofluorimetric determination of 10–800 ppb of zinc with pyrocatechol-1-aldehyde salicyloylhydrazone in a 60% (v/v) ethanol-water medium at apparent pH 6.7 (acetic-acetate buffer). _ex=400 nm, _em=530 nm. Interferences have been evaluated and the method applied to the determination of zinc in alloys and lubricating oils.

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Spektrofluorimetrische Bestimmung von Zink mit Brenzcatechin-1-aldehyd-salizyloylhydrazon

Zusammenfassung Zink bildet mit Brenzcatechin-1-aldehyd-salizyloylhydrazon ein gelbes, fluoreszierendes Chelat in Gegenwart von 60% Ethanol bei pH 6,7 (Essigsäure-Natriumacetat-Puffer); _ex=400 nm, _em=530 nm. Zwischen Intensität der Fluoreszenz und Zink-Konzentration besteht im Bereich von 10 bis 800 ppb Linearität. Das Verfahren wurde zur Bestimmung des Zinks in Legierungen und Schmierölen verwendet.