The effects of cationic and zwitterionic micelles on the keto-enol interconversion of 2-phenylacetylfuran and 2-phenylacetylthiophene

The presence of micelles from cationic and zwitterionic surfactants increases the apparent acidity of either the keto and the enol forms of 2-phenylacetylfuran (2PAF) and 2-phenylacetylthiophene (2PAT). This effect can be attributed to the affinity of the surfactant micelles for the enolate of the two substrates. Although the equilibrium constants for keto-enol tautomerism of 2PAF and 2PAT, K_T=[enol]/[ketone]=pK_a^KH−pK_a^EH, do not change much, the presence of micelles provides an efficient method for producing appreciable quantities of the enolates under mild experimental conditions and in aqueous solutions. The obtained rate-profiles for the ketonisation reactions and the consistency of the kinetic rate constants over a wide range of ‘pH’ in several overlapping buffers indicate that the pH of the aqueous pseudophase (but not that at the micellar surface) can be controlled by buffers. Moreover, the increase of the acidity and the decrease of the ‘water’ rate of ketonisation of the enols of 2PAF and 2PAT upon addition of surfactants allow the uncovery of a metal ion catalysed pathway that cannot be observed in absence of surfactants.     

Long-term diffusive samplers for the indoor air quality evaluation

Three kinds of diffusion samplers, conceived to perform long-term samplings in indoor sites are illustrated in this work. Two of them, in part deriving from the previous "Analyst for VOC" device, extend the field of application up to the semi-volatile organic compounds (SVOC), PAHs and nicotine in particular. A third device, which employs a basic barium hydroxide solution as an absorbing medium, is proposed for the determination of carbon dioxide levels which indicate the air change quality in the indoor sites. Laboratory and field experiments, performed in order to assess the reliability of the proposed devices, are shown. A monthly monitoring campaign, performed at three private apartments in Rome and its outskirts highlights that the indoor pollution levels are a complex function of various concurrent and opposite factors, like external air pollution, internal sources, air change rate and sink effect of surfaces, which contribute to depletion phenomena through adsorption and/or decomposition processes.     

On the cycle index of point groups

In this brief work we express the cycle index of the molecular point groups as a function of a limited number of initial geometrical parameters. Such parameters are the number of elements composing the domain D of sites of substitutions in the molecule belonging to the point group G, and the numbers of sites of D lying on the symmetry elements for G.     

Flow injection system for hydrolysable tannin determination

A flow injection system was proposed to evaluate the transient product of a colorimetric reaction between hydrolysable tannin and potassium iodate (KIO₃) solution. The system optimization was accomplished by using statistical methods based on experimental design. Flow rate of KIO₃ solution, sample volume, carrier flow rate, and reaction coil were the selected factors for evaluation. On screening step, complete factorial 2⁴ was used and two levels for each selected factor were studied. For the optimization phase, a centered face composite design 2² + star was employed to evaluate sample volume and flow rate of KIO₃ solution, which were the factors identified in the screening phase as having more influence on the absorbance signal. After optimization, the proposed system was compared with batch determination. Some characteristics, such as analytical frequency, reagent consumption and chemical residues generation presented better results by the use of the proposed system if compared with batch method. The system presented good repeatability with standard deviation lower than 3%, for n = 10, linearity (R² = 0.9974) for tannic acid standard, analytical frequency of 15 injections h^− 1 and limit of quantification of 24 mg L^− 1 of tannic acid. Good results were obtained when the proposed system was applied to hydrolysable tannin determination in Stryphnodendron barbatimão, Eucalyptus citriodora and Phyllanthus niruri, samples of plants commonly used in popular medicine.     

Synthesis of new tren-based tris-macrocycles. Anion cluster assembling inside the cavity generated by a bowl-shaped receptor

The synthesis of three new tris-macrocycles, containing three [12]aneN(4) (L1), [12]aneN(3)O (L2), or [14]aneN(4) (L3) moieties appended to a tren unit, is reported. The crystal structure of the [(Na(ClO(4))(6)) subset L1(2)H(13)]Na(6)Cl(2)(ClO(4))(12) compound shows the anionic cluster [Na(ClO(4))(6)](5)(-) assembled inside the cavity defined by two bowl-shaped polyammonium receptors, held by multiple charge-charge and hydrogen bond interactions.     

New designs for inhibitors of the NF-κB: DNA binding

We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-^12,14 -prostaglandin J₂ (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs.     

Enantiomeric separation of acidic compounds of pharmaceutical interest by capillary electrochromatography employing glycopeptide antibiotic stationary phases

Enantiomeric separation of some selected acidic compounds of pharmaceutical interest belonging to the group of non-steroidal anti-inflammatory drugs were separated by capillary electrochromatography employing silica based glycopeptide antibiotic stationary phases, namely vancomycin or a teicoplanin derivatives (Hepta-Tyr). The vancomycin stationary phase allowed to achieve the chiral resolution of some racemic studied compounds only using mobile phases containing ammonium formate at a relatively low pH 2.5-3.5 and acetonitrile. Employing the teicoplanin derivative stationary phase, good enantiomeric resolution was achieved eluting with mobile phases containing sodium phosphate pH 6-acetonitrile. Enantiomers were moved to the detector because a relatively high reversed electroosmotic flow (due to the positive charge of the stationary phase) and to the electrophoretic mobility of analytes.     

Quantum mechanical calculations of NMR J coupling values in the determination of relative configuration in organic compounds

[structure: see text] An approach relying on quantum mechanical calculations of proton-proton and proton-carbon J coupling values is proposed as a tool for assigning the relative configuration on chiral organic compounds. The method is suitable for carbon frameworks containing several adjacent stereogenic centers and may allow significant advances in the extensive use of spin-spin couplings in structural elucidation.     

Conformational changes of the amyloid beta-peptide (1-40) adsorbed on solid surfaces

The conformational change of the 39-43 residues of the amyloid beta-peptide (Abeta) toward a beta-sheet enriched state promotes self-aggregation of the peptide molecules and constitutes the major peptide component of the amyloid plaques in Alzheimer patients. The crucial question behind the self-aggregation of Abeta is related to the different pathways the peptide may take after cleavage from the amyloid precursor proteins at cellular membranes. This work is aiming at determining the conformation of the Abeta (1-40) adsorbed on hydrophobic Teflon and hydrophilic silica particles, as model sorbent surfaces mimicking the apolar transmembrane environment and the polar, charged membrane surface, respectively. The mechanism by which the Abeta interacts with solid surfaces strongly depends on the hydrophobic/hydrophilic character of the particles. Hydrophobic and electrostatic interactions contribute differently in each case, causing a completely different conformational change of the adsorbed molecules on the two surfaces. When hydrophobic interactions between the peptide and the sorbent prevail, the adsorbed Abeta (1-40) mainly adopts an alpha-helix conformation due to H-bonding in the apolar part of the peptide that is oriented towards the surface. On the other hand, when the peptide adsorbs by electrostatic interactions beta-sheet formation is promoted due to intermolecular association between the apolar parts of the adsorbed peptide. Irrespective of the characteristics of the solid sorbent, crowding the surface results in intermolecular association between adsorbed molecules leading to a strong aggregation tendency of the Abeta (1-40). [Diagram: see text] CD spectra of Abeta (1-40) at pH 7: A) in solution ([Abeta]=0.2 mg.ml(-1)) freshly prepared (line) and after overnight incubation (symbols);B) on Teflon (Gamma=0.5 mg.m(-2)).