Energy transfer between singlet (1Delta(g)) and triplet (3Sigma(g)-) molecular oxygen in aqueous solution

We clearly demonstrate the occurrence of energy transfer between 18O2 (1Deltag) and 16O2 in the ground state (3Sigmag-) with subsequent conversion of the latter species into its singlet excited state (1Deltag) in aqueous solution. This was inferred from the results of incubation experiments involving DHPN18O2 as a chemical generator of 18O2 (1Deltag) and the water-soluble disodium salt of anthracene (EAS) used as a chemical trap of singlet oxygen. The products of the reaction were accurately analyzed by HPLC-ESI-MS.     

Photodynamic studies and photoinactivation of Escherichia coli using meso-substituted cationic porphyrin derivatives with asymmetric charge distribution

The photodynamic activities of novel asymmetrically meso-substituted cationic porphyrins, 5,10-di(4-methylphenyl)-15,20-di(4-trimethylammoniumphenyl)porphyrin iodide 1 and 5-(4-trifluorophenyl)-10,15,20-tris(4-trimethylammoniumphenyl)porphyrin iodide 2 and its metal complex with Pd(II) 3, have been investigated in both homogeneous medium bearing photooxidizable substrates and in vitro on a typical gram-negative bacterium Escherichia coli. The amphiphilic character of porphyrin 2 was increased by the presence of a high-lipophilic trifluoromethyl group and its photophysical properties changed by forming a complex with Pd(II). Absorption and fluorescence spectroscopic studies were compared in different media. Fluorescence quantum yields (phi(F)) of 0.16 for 1 in tetrahydrofuran and 0.08 for 2 in N, N-dimethylformamide (DMF) were calculated, whereas no significant emission was detected for Pd(II) porphyrin 3. The singlet molecular oxygen, O(2)((1)Delta(g)), production was evaluated using 9,10-dimethylanthracene in DMF yielding relative values of 1, 0.55 and 0.47 for porphyrins 3, 2 and 1, respectively. A faster decomposition of l-tryptophan was obtained using Pd(II) porphyrin 3 as sensitizer with respect to the free-base porphyrins 1 and 2. In biological medium, the behavior of cationic porphyrins 1-3 were compared with that of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin 4, which was used as a noncationic sensitizer. These porphyrins are rapidly bound to E. coli cells in 5 min and the amount of cell-bound sensitizer is not appreciably changed incubating the cultures for longer times. The recovered porphyrin 2 after one washing step reaches a value of approximately 2.9 nmol/10(6) cells and this amount remains high even after three washes, indicating that this sensitizer is tightly bound to cells. Photosensitized inactivation of E. coli was analyzed using cells without and with one washing step. In both cases, a higher photoinactivation of cells was found for tricationic porphyrin 2 and 3, causing a approximately 5.5 log (99.999%) decrease of cell survival, when treated with 10 microM of sensitizer. Under these conditions, a lower effect was found for porphyrin 1 (approximately 4 log) whereas sensitizer 4 did not produce appreciable photodamage. The results were also confirmed by growth delay experiments. These studies show that the amphiphilic tricationic porphyrin 2 and 3 bearing a trifluoromethyl group can be a promising model for phototherapeutic agents with potential applications in inactivation of bacteria by photodynamic therapy.     

Synthesis and X-ray structures of dinitrato-bis[2-(2′-thienyl)-1-(2′-thienylmethyl)benzimidazole]copper(II) and dichloro-bis-[2-(2′-thienyl)-benzimidazole]copper(II)-ethanol

Summary The reactions of Cu(NO₃)₂ · 3 H₂O with 2- (2-thienyl)-1-(2-thienylmethyl)benzimidazole (L) and of CuCl₂ · 2H₂O with 2-(2-thienyl)benzimidazole (L) have been carried out. The crystal structure of two isolated complexes,(1) and(2), have been determined by single-crystal x-ray diffraction methods. Crystals of(1) are monoclinic, space groupP2₁ /c, witha=9.884(4),b=9.892(4),c=18.732(8) Å, =114.89(2)°,Z=2;R=0.068 for 1909 observed reflections. Crystals of (2) are orthorhombic, space groupPbcn, witha=14.835(1),b=8.193(1),c=20.493(1) Å,Z=4;R=0.086 for 415 observed reflections. In the complex (1) the copper co-ordination is tetragonal (compressed octahedral) and involves a nitrogen atom of the organic ligand [Cu-N 1.970(6) Å] and two oxygen atoms of the nitrate group [Cu-O 2.318(7) and 2.246(9) Å] which appears to coordinate nearly symmetrically to the metal; however it has unusually large thermal motion which suggests a fluxional behaviour. In the complex (2) the co-ordination is square planar and involves an imidazole nitrogen [Cu-N 1.95(3) Å] and a chlorine atom [Cu-Cl 2.27(1) Å]. A long interaction Cu-S=3.37(2) Å completes the co-ordination polyhedron to a very elongated distorted tetragonal bipyramid. In both compounds a thiophene ring is disordered.     

Dolbeault Cohomology for G2-Manifolds

Cocalibrated G₂-manifolds are seven-dimensional Riemannian manifolds with a distinguished 3-form which is coclosed. For such a manifold M, S. Salamon in Riemannian Geometry and Holonomy Groups (Longman, 1989) defined a differential complex related with the G₂-structure of M.In this paper we study the cohomology of this complex;it is treated as an analogue of a Dolbeault cohomologyof complex manifolds. For compact G₂-manifoldswhose holonomy group is a subgroup of G₂ special propertiesare proved. The cohomology of any cocalibrated G₂-nilmanifold \K is also studied.     

Serine versus threonine glycosylation: the methyl group causes a drastic alteration on the carbohydrate orientation and on the surrounding water shell

Different behavior has been observed for the psi torsion angle of the glycosidic linkages of D-GalNAc-Ser and D-GalNAc-Thr motifs, allowing the carbohydrate moiety to adopt a completely different orientation. In addition, the fact that the water pockets found in alpha-D-GalNAc-Thr differ from those obtained for its serine analogue could be related to the different capability that the two model glycopeptides have to structure the surrounding water. This fact could have important biological inferences (i.e., antifreeze activity).     

Organometal additions to alpha-iminoesters: N-alkylation via umpolung

Alpha-iminoesters are useful precursors to substituted alpha-amino acid derivatives and are utilized in a number of organic transformations. As a consequence of the adjacent ester functionality, these imines are more reactive relative to other types of imines. While a significant body of work has focused on nucleophilic additions to the imine carbon (C-alkylation), a second pathway that involves nucleophilic reaction at the nitrogen (N-alkylation) is much less explored. This tutorial review highlights work that has exploited this unusual alpha-iminoester reactivity mode.     

On MDS convolutional codes over $${\mathbb {Z}}_{p^{r}}$$

Maximum distance separable (MDS) convolutional codes are characterized through the property that the free distance meets the generalized Singleton bound. The existence of free MDS convolutional codes over \({\mathbb {Z}}_{p^{r}}\) was recently discovered in Oued and Sole (IEEE Trans Inf Theory 59(11):7305–7313, 2013) via the Hensel lift of a cyclic code. In this paper we further investigate this important class of convolutional codes over \({\mathbb {Z}}_{p^{r}}\) from a new perspective. We introduce the notions of p-standard form and r-optimal parameters to derive a novel upper bound of Singleton type on the free distance. Moreover, we present a constructive method for building general (non necessarily free) MDS convolutional codes over \({\mathbb {Z}}_{p^{r}}\) for any given set of parameters.