Reactive organoallyl species generated from aryl halides and allene: allylation of α,β-unsaturated aldehydes and cyclic ketones employing Pd/In transmetallation processes

Allylation of α,β-unsaturated aldehydes and cyclic ketones promoted by Pd/In transmetallation processes has been studied. The unsaturated aldehydes underwent regioselective 1,2-addition to afford secondary homoally alcohols. The reactions have been performed using Pd(OAc)₂/PPh₃ as catalytic system and metallic indium affording the products in good yields. The same transformation with unsaturated ketones proved to be less efficient, while saturated cyclic ketones delivered generally excellent yields in the presence of CuI. In these latter processes the presence of a distal heteroatom influences the reaction rate.     

Proton and protonic entities in solid heteropoly compounds: An ab initio calculation of the environmental effect on the ion

Systematic experimental investigations of heteropoly compounds, particularly their structure and activity, led to the conclusion that most of their characteristics are governed by the presence of protons and protonic entities. Special attention has been paid to two forms of 12-tungstophosphoric acid: hexahydrate (WPA-6) and dehydrated phase (WPA-0). It was postulated that in WPA-6 dynamic equilibrium of protonic entities exists, and that dehydrated phase is stabilized by protons. To confirm the role of the “free protons” or “proton gas” derived on the basis of thermal, structural and spectroscopic experimental studies, we carried out also ab initio calculations on a number of systems containing ion. We were not able to perform direct calculations on the real systems investigated experimentally since the structure of heteropoly compounds is too complex. However, it has been found that ion in WPA-6 definitely is not planar and the results obtained indirectly support the postulated dynamic equilibrium, i.e. possibility of existing of free protons.     

The Biochemical Mechanisms of Antimicrobial Photodynamic Therapy†

The unbridled dissemination of multidrug-resistant pathogens is a major threat to global health and urgently demands novel therapeutic alternatives. Antimicrobial photodynamic therapy (aPDT) has been developed as a promising approach to treat localized infections regardless of drug resistance profile or taxonomy. Even though this technique has been known for more than a century, discussions and speculations regarding the biochemical mechanisms of microbial inactivation have never reached a consensus on what is the primary cause of cell death. Since photochemically generated oxidants promote ubiquitous reactions with various biomolecules, researchers simply assumed that all cellular structures are equally damaged. In this study, biochemical, molecular, biological and advanced microscopy techniques were employed to investigate whether protein, membrane or DNA damage correlates better with dose-dependent microbial inactivation kinetics. We showed that although mild membrane permeabilization and late DNA damage occur, no correlation with inactivation kinetics was found. On the other hand, protein degradation was analyzed by three different methods and showed a dose-dependent trend that matches microbial inactivation kinetics. Our results provide a deeper mechanistic understanding of aPDT that can guide the scientific community toward the development of optimized photosensitizing drugs and also rationally propose synergistic combinations with antimicrobial chemotherapy.     

Concentration as the switch for chiral recognition in biomembrane models

Chiral recognition was observed in a biomembrane model. Micellar aggregates formed by enantiopure N-alkyl-N,N-dimethyl-N-(1-phenyl)ethylammonium bromide were in fact able to convert the racemic mixture of bilirubin-IXalpha into an enantiomerically enriched mixture. The stereochemical preference and the extent of enantiomeric enrichment depend on the length of the hydrophobic portion of the surfactant and on the concentration conditions, and changes in the stereochemical bias are reversible.     

Role of the hydrophobic effect in the transfer of chirality from molecules to complex systems: from chiral surfactants to porphyrin/surfactant aggregates

The interaction between the achiral sulfonated porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, H 2TPPS 4 (4-), and two chiral cationic surfactants has been studied by optical absorption, fluorescence, and circular dichroism (CD) spectroscopies. At surfactant concentrations above the critical micellar concentration (cmc) the porphyrin is included in the micellar aggregates, but it is CD silent. Below the cmc at a definite porphyrin/surfactant stoichiometry the formation of heteroaggregates with transfer of chirality to the porphyrin chromophore occurs. The preferred surfactant/porphyrin stoichiometry is 3:1, which suggests a structure driven by electrostatic and hydrophobic interactions between porphyrin and surfactant and dipolar and ionic interactions with the water solution. At surfactant concentrations above the cmc, depending on the protocol of preparation of the samples, the formation of the two kinds of aggregates can be observed, reversible for the simple surfactant micelles incorporating the porphyrin, but irreversible for the heteroaggregates.     

TG-DTA-FTIR analysis and isoconversional reaction profiles for thermal and thermo-oxidative degradation processes in black chokeberry (<Emphasis Type="Italic">Aroniamelanocarpa</Emphasis>)

The thermal and thermo-oxidative processes in Aroniamelanocarpa (black chokeberry) were investigated using combined thermo-analytical (TG-DTA) and spectroscopic (FTIR) experimental techniques. Isoconversional analysis revealed that the process in an inert (argon) atmosphere was probably governed by chlorogenic acid degradation, where autocatalysis (described by the empirical ?esták-Berggren model) might occur due to water already present in the early stages of the process through hydrolysis. Thermal degradation is described by the intrinsic kinetic parameters, where the degradation rate increases proportionally with an increase in the heating rate. Under oxidative conditions, the process was found to be primarily driven by neochlorogenic acid degradation. The thermo-oxidative degradation of Aroniamelanocarpa fresh samples can be described by two competitive reactions, where it was established that a cyanidin-3-glucosylrutinoside degradation made a significant contribution to a comprehensive kinetics. This study showed the targeting of the neochlorogenic acid in Aroniamelanocarpa fresh samples to have a strong hydrogen-donating activity, thereby rendering it capable of very efficiently entrapping the peroxy radicals. Current research has demonstrated that the relative contribution of the two competitive reactions to the overall process is highly dependent on the heating rate of the system under consideration.     

Asymptotic Behavior of the Fourth Painlevé Transcendents in the Space of Initial Values

We study the asymptotic behavior of solutions of the fourth Painlevé equation as the independent variable goes to infinity in its space of (complex) initial values, which is a generalization of phase space described by Okamoto. We show that the limit set of each solution is compact and connected and, moreover, that any solution that is not rational has an infinite number of poles and infinite number of zeros.     

Certification of methylmercury content in two fresh-frozen reference materials: SRM 1947 Lake Michigan fish tissue and SRM 1974b organics in mussel tissue (Mytilus edulis)

This paper describes the development of two independent analytical methods for the extraction and quantification of methylmercury from marine biota. The procedures involve microwave extraction, followed by derivatization and either headspace solid-phase microextraction (SPME) with a polydimethylsiloxane (PDMS)-coated silica fiber or back-extraction into iso-octane. The identification and quantification of the extracted compounds is carried out by capillary gas chromatography/mass spectrometric (GC/MS) and inductively coupled plasma mass spectrometric (GC/ICP-MS) detection. Both methods were validated for the determination of methylmercury (MeHg) concentrations in a variety of biological standard reference materials (SRMs) including fresh-frozen tissue homogenates of SRM 1946 Lake Superior fish tissue and SRM 1974a organics in mussel tissue (Mytilus edulis) and then applied to the certification effort of SRM 1947 Lake Michigan fish tissue and SRM 1974b organics in mussel tissue (Mytilus edulis). While past certifications of methylmercury in tissue SRMs have been based on two independent methods from the National Institute of Standards and Technology (NIST) and participating laboratories, the methods described within provide improved protocols and will allow future certification efforts to be based on at least two independent analytical methods within NIST.     

Solution equilibria between aluminum(III) ion and some fluoroquinolone family members. Spectroscopic and potentiometric study

Complex formation between aluminum(III) ion and fluoroquinolone antibacterials-either moxifloxacin (4th generation antibiotic) or fleroxacin (2nd generation antibiotic) were studied in aqueous solutions without and in the presence of sodium dodecylsulfate (SDS). The investigations were performed by glass electrode potentiometric (ionic medium: 0.1 mol/dm(3) LiCl, 298 K), UV spectrophotometric, multinuclear (1H and 13C) magnetic resonance and ESI-MS measurements. The experimental data were consistent with the formation of Al(HL)L2+, Al(HL)3+ AlL2+, Al(OH)L+ and Al(OH)2L complexes in the pH interval ca. 3-8 and up to 5 : 1 ligand to metal mole ratio with range of Al3+ concentrations between ca. 0.025 to 1.0 mmol/dm3. The binary complex, AlL2+ is fairly stable (log beta(1,0,1) ca. 11.0) and its stability increases in the presence of SDS. At higher concentration ratios of ligands to aluminum, up to 5 : 1, the complex Al(HL)L2+ is formed with rather high overall stability constant (log beta(1,1,2) ca. 24.0). The ESI-MS data generally, confirmed the derived model, and the formation of the complex with ligand to metal ratio 2 : 1. NMR measurements indicate that both ligands utilize 4-carbonyl and carboxyl oxygens as donor atoms. The presence of surface active substance, SDS, favors the formation of the complex in which the ligand is protonated, i.e. Al(HL) and its maximum formation is shifted toward milder acidic region (pH ca. 4). The aluminum-quinolone complexes may affect the bio-distribution of both, quinolone and/or aluminum ion upon concomitant ingestion of aluminum-based antacids or phosphate binders and fluoroquinolones.     

Sample preparation methods in the analysis of pesticide residues in baby food with subsequent chromatographic determination

Pesticides are widely utilized at various stages of cultivation and during postharvest storage to protect plants against a range of pests and/or to provide quality preservation. Reliable confirmatory methods are required to monitor pesticide residues in baby foods and to ensure the safety of baby food supply. This review covers methods in which pesticide residues have been determined in baby food by the use of a wide range of chromatographic techniques after various sample preparation steps. The main attention is paid to the evaluation and improvement of sample extraction and clean-up methods (liquid extraction, solid-phase extraction (SPE), dispersive SPE (DSPE), microextraction procedures, matrix solid-phase dispersion (MSPD) and supercritical fluid extraction (SFE)) considering low concentration levels of pesticide residues in baby food resulting from stringent European Union (EU) legislation. Instrumental aspects together with the matrix effects significantly contributing to the most important parameters considered in pesticide residues analysis of baby food--limits of detection (LODs) and limits of quantification (LOQs) were included within the scope of this overview. Paper involves also monitoring studies.