Effect of organic matter on the in vitro photoeradication of Pseudomonas aeruginosa by means of a cationic tetraaryl-porphyrin

Photodynamic therapy is emerging as an antimicrobial alternative approach; the concomitant presence of a photosensitizer (PS), O(2) and visible light induces lethal oxidative damages to bacterial cells. Among Gram-negative bacteria, Pseudomonas aeruginosa seems to be one of the least susceptible to photodynamic treatment. In this study, we evaluated the influence of several experimental conditions on photoeradication of a planktonic culture of P. aeruginosa PAO1 by means of a tetracationic meso-arylsubstituted porphyrin (RM24). Our findings suggest that the photo-oxidative stress induced by RM24 is strictly correlated to the amount of PS bound to the cells that in turn decreases with the increasing concentrations of organic compounds in the medium. The photoeradication is dependent on PS concentrations, cellular density and light dose. RM24 was able to induce oxidative stress by means of singlet oxygen formation, although ROS formation cannot be ruled out. The standardized experimental conditions of the photospot test allowed us to evidence intraspecific PDT sensitivity differences among three strains of P. aeruginosa.     

Pyridinium/urea-based anion receptor: methine formation in the presence of basic anions

The influence of the positively charged N-methylpyridinium substituent on the anion binding tendencies of urea-based receptors has been investigated by comparing molecules 1 and 2. These receptors have been studied in acetonitrile, by performing UV-vis. and (1)H NMR titrations with several anions. UV-vis. titrations have also been performed in DMSO, MeOH and CHCl(3)/CH(3)CN mixture (1/1, v/v). In the case of 1, the presence of both H-donor and H-acceptor groups (urea and pyridine, respectively) favours aggregation and the formation of dimers in the solid state. In solution, this tendency to aggregate reduces affinity for anions with respect to the similar urea-based receptor 3. The methylation of the pyridyl group of 1 leads to the pyridinium-containing receptor 2. The pyridinium positive charge enhances the acidity of urea and increases anion affinity, as evidenced by the comparison of the binding constants. Both receptors (1-2) form stable adducts with all investigated anions. However, in the case of 2, the formation of 1?:?1 adducts with basic anions, such as acetate and fluoride, is followed by a proton transfer process. Quite interestingly, deprotonation does not involve the urea group, thus preserving the 1?:?1 adduct, as demonstrated by the (1)H NMR measurements. In particular, the proton transfer process takes place at the methylene group linking the pyridinium fragment to the receptor's skeleton. (1)H NMR studies indicate the formation of a stable neutral methine species, characterised by the loss of aromaticity by the pyridyl ring. These results open new perspectives in the field of anion recognition, as receptor 2 may by applied to the monitoring of both bound anion (through the urea unit) and excess anion in solution (through the development of the yellow methine species).     

Structural flexibility and role of vicinal 2-thienyl rings in 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)2Th2Pyz], its palladium(II) complex [(CN)2Th2Pyz(PdCl2)2], and the related pentametallic pyrazinoporphyrazines [(PdCl2)4Th8TPyzPzM] (M = Mg(II)(H2O), Zn(II))

The solid state and solution structure of 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)(2)Th(2)Pyz], and its Pd(II) derivative, [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, formed by reaction of [(CN)(2)Th(2)Pyz] with [(C(6)H(5)CN)(2)PdCl(2)] were characterized by X-ray, UV-visible, (1)H and (13)C NMR, and extended X-ray absorption fine structure (EXAFS) spectral measurements. The X-ray crystal structure of [(CN)(2)Th(2)Pyz] shows the presence of one thienyl ring positioned orthogonal to the rest of the molecule, with the two vicinal thienyl rings lying orthogonal to each other in a rare arrangement. NMR studies of [(CN)(2)Th(2)Pyz] in the solid state and in solutions of dimethylformamide or dimethyl sulfoxide confirm a nonequivalence of the thienyl rings in the solid state and also in solution. EXAFS results indicate that two distinct Pd(II) coordination sites are formed at the di(2-thienyl)pyrazino moiety of [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, with identical Pd-N(pyz) (2.03(3) ?) and Pd-Cl (2.36(3) ?) bond lengths but with different Pd-S1 (2.25(4) ?) and Pd-S2 (3.21(5) ?) bond distances in an overall asymmetric molecular framework. Density functional theory (DFT) and time-dependent DFT (TDDFT) theoretical studies also provide information about the structure and spectral behavior of the precursor and its metalated Pd(II) derivative. (1)H/(13)C NMR and UV-visible spectral measurements were also carried out on two heteropentametallic porphyrazine macrocycles which were prepared by a reaction of PdCl(2) with [Th(8)TPyzPzM] where Th(8)TPyzPz = tetrakis-2,3-[5,6-di-(2-thienyl)-pyrazino]porphyrazinato dianion and M = Mg(II)(H(2)O) or Zn(II). Spectroscopic data on the newly synthesized [(PdCl(2))(4)Th(8)TPyzPzM] compounds suggest that the binding of PdCl(2) involves coordination sites of the type S(2(th))PdCl(2) with the two thienyl rings of each di(2-thienyl)pyrazino fragment bound to Pd(II) in an equivalent manner ("th-th" coordination). This is similar to what was found for the corresponding octapyridinated analogues ("py-py" coordination).     

Unusual and unexpected reactivity of t-butyl dicarbonate (Boc2O) with alcohols in the presence of magnesium perchlorate. A new and general route to t-butyl ethers

[reaction: see text] A new mild method for protecting alcohols as t-butyl ethers is reported. The reaction proceeds with Mg(ClO4)2 and Boc2O and shows general applicability. The deprotection of t-butyl ethers has also been revisited. Preliminary results indicate the CeCl3 x 7H2O/NaI system is a very suitable catalyst for their removal.     

Thermodynamic study of heptane + secondary, tertiary and cyclic amines mixtures. Part IV. Excess and solvation enthalpies at 298.15 K

Partial molar enthalpies and excess enthalpies H^E of binary mixtures of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, and secondary (hetero)cyclic amines have been determined at 298.15 K by isothermal titration calorimetry in the whole composition range. All mixtures showed positive H^E values which decrease with increasing amine size in each category, and decrease in the order cyclic primary > cyclic secondary > linear primary [1] > secondary > tertiary when comparing amines of similar size in different categories. From partial molar enthalpies at infinite dilution and known enthalpies of vaporization, the solvation enthalpies have been calculated either for heptane in amines and for amines in heptane. These quantities, together with their cavitational and interactional terms obtained applying the scaled particle theory, are discussed to get insight into the types and relative strength of solute-solvent interactions and into their effects on molecular structure features such as branching and cyclization.     

Conformation of the tridimensional structure of 1,2,3,4,6-pentagalloyl-β-D-glucopyranose (PGG) by (1)H NMR, NOESY and theoretical study and membrane interaction in a simulated phospholipid bilayer: a first insight

1,2,3,4,6-Penta-O-galloyl-β-D-glucopyranose (PGG) is a polyphenolic compound found in substantial amounts in a number of medicinal herbs. We report (i) its conformational analysis by solution NMR and molecular dynamics calculation and (ii) theoretical study of its interaction with a model membrane bilayer. The galloyl groups B and E appear to play important roles in the interaction with the phospholipid bilayer.     

Application of nanosized zeolites in methanol conversion processes: A short review

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Recovery of pyridine from aqueous solution by membrane pervaporation

Three different membranes, based on poly(dimethylsiloxane) (PDMS), cation-exchange material and poly(vinyl alcohol) (PVA) respectively, were tudied for the separation of pyridine-water mixtures by pervaporation. The PDMS membrane was preferentially permeable to pyridine and the other two were selective towards water. Three membranes showed different permeation performance, allowing the application of the technique to the separation of feeds of different composition. The temperature profile of the permeability suggests that it is possible to carry out the operation at an elevated temperature in order to achieve high productivity. A combination of the three types of membranes was designed for the production of anhydrous pyridine from dilute pyridine aqueous solution by pervaporation.     

Monte Carlo simulation of water solvent with biomolecules: Serine and the corresponding zwitterion

Monte Carlo simulation results are reported for clusters consisting of 250 water molecules surrounding serine, both in the neutral form and in two zwitterionic conformers (in order to gain some insight into conformational effects). Calculations were carried out at 300 K and using two-body potentials obtained by means of quantum-mechanical calculations. The spatial dependence of the average interaction energies was investigated. The solvation structure was investigated by means of radial distribution functions and probability density maps, which showed a few water molecules directly solvating the hydrophilic groups and, beyond them, a more or less rich and complex hydrogen-bonded network of solvent molecules.