Adsorption of lanthanides on mordenite from nitrate medium

The adsorption of lanthanides (except for Pm) on mordenite was investigated under various solution conditions of nitrate ion concentrations ([NO*3]: 0.001-2 mol/dm3) and total lanthanide concentrations (0.0005 mol/dm3). Solutions of lanthanide nitrates were equilibrated with zeolite samples at 296 K. A concave tetrad effect was evident in the change of logK d values within the lanthanide series and an explanation by a comparison of covalence in Ln-O bonds existing in triple bond Al-O(1/3Ln)-Si species found in the zeolite phase and in Ln(H2O)3+x or Ln(NO3) n-3 n complexes formed in the aqueous phase is presented. The decreasing trend in C1 and C3 coefficients, which are the function of E1 and E3 Racah f-interelectron repulsion parameters, is evidence of the magnification of covalence in Ln-O bond in the series triple bond S-iO(1/3Ln)-Al triple bond 相似文献   

The case for the intermediacy of monomeric metaphosphate analogues during oxidation of H-phosphonothioate, H-phosphonodithioate, and H-phosphonoselenoate monoesters: mechanistic and synthetic studies

Studies on the reaction of H-phosphonothioate, H-phosphonodithioate, and H-phosphonoselenoate monoesters with iodine in the presence of a base led to identification of a unique oxidation pathway, which consists of the initial oxidation of the sulfur or selenium atom in these compounds, followed by oxidative elimination of hydrogen iodide to generate the corresponding metaphosphate analogues. The intermediacy of the latter species during oxidation of the investigated H-phosphonate monoester derivatives with iodine was supported by various diagnostic experiments. The scope and limitation of these oxidative transformations for the purpose of the synthesis of nucleoside phosphorothioate, nucleoside phosphorodithioate, and nucleoside phosphoroselenoate diesters was also investigated.     

The Role of Singlet Oxygen in Photoreactivity and Phototoxicity of Curcumin

Curcumin is a plant-derived yellow-orange compound widely used as a spice, dye and food additive. It is also believed to have therapeutic effects against different disorders. On the other hand, there are data showing its phototoxicity against bacteria, fungi and various mammalian cells. Since the mechanism of its phototoxic action is not fully understood, we investigated here the phototoxic potential of curcumin in liposomal model membranes and in HaCaT cells. First, detection of singlet oxygen (¹O₂) luminescence proved that curcumin generates ¹O₂ upon blue light irradiation in organic solvent and in liposomes. Then, HPLC-EC(Hg) measurements revealed that liposomal and cellular cholesterol is oxidized by ¹O₂ photogenerated by curcumin. Enrichment of liposome membranes with curcumin significantly increased the oxygen photo-consumption rate compared to the control liposomes as determined by EPR oximetry. Cytotoxicity measurements, mitochondrial membrane potential analyses and protein hydroperoxides detection confirmed strong phototoxic effects of curcumin in irradiated HaCaT cells. These data show that since curcumin is advertised as a valuable dietary supplement, or a component of cosmetics for topical use, caution should be recommended especially when skin is exposed to light.     

Conformational space of the Pseudosaccharin allyl ether 3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide in gas phase and in rare gas matrices

In this work, the conformational space of the pseudosaccharyl ether 3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide (ABID) has been studied by means of infrared spectroscopy and density functional theory (DFT) calculations. Five different low energy conformers (TSk, TC, GSk, GSk' and GC, with relative energies of 0.00, 1.97, 2.00, 3.82 and 6.02 kJ mol(-1), respectively) were found on the DFT(B3LYP)/6-311++G(3df,3pd) potential energy surface of the molecule, all of them differing in the conformation of the allyl substituent. According to the calculations, in the gaseous phase all conformers are significantly populated (TSk:TC:GSk:GSk':GC = 47%:16%:18%:12%:7%, at 350 K). In the cryogenic matrices, however, only the TSk and TC conformers exist due to isomerization from the higher energy gauche forms to the most stable trans isomers during deposition of the matrix (conformational cooling). The observed conformational cooling is in consonance with the low calculated energy barriers for the GSk --> TSk, GSk' --> TSk and GC --> TC isomerization processes. Results from annealing experiments in krypton matrix doubtlessly show that in this matrix the order of stability of the TSk and TC conformers is reversed, with the more planar TC form becoming the most stable conformer.     

Effect of temperature on n-tetradecane emulsion in the presence of phospholipid DPPC and enzyme lipase or phospholipase A2

Zeta potentials and effective diameters of n-tetradecane emulsions in 1 M ethanol were investigated in the presence of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) (1 mg/100 mL), Candida cylindracea lipase (CCL), and phospholipase PLA2 (1 mg/100 mL) at 20, 37, and 45 degrees C. The enzyme was added at the beginning of mechanical emulsion homogenization or 1 min before the end of stirring for 10 min at 10,000 rpm. It was found that DPPC decreases the negative zeta potentials at all three temperatures. The decrease was largest at 20 degrees C and smallest at 45 degrees C. The influence of the enzymes on the zeta potentials depended on the enzyme kind, time of its injection, and temperature. More negative values of the zeta potentials relative to n-C14H30/DPPC droplets were obtained if the lipase was present. Generally, the effective diameters correlate with the zeta potentials, i.e., lower zeta potential corresponds with bigger effective diameter. Possible reasons for the observed changes of the measured parameters are discussed.     

1H, 13C and 15N NMR studies on adducts formation of rhodium(II) tetraacylates with some azoles in CDCl3 solution

Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set.     

"Chemical ligation": a versatile method for nucleoside modification with boron clusters

A general approach to the synthesis of nucleoside conjugates containing carborane and metallocarborane complexes, based on Huisgen 1,3-dipolar cycloaddition ("chemical ligation"), is described. Boron-cluster-donors bearing terminal azide or ethynyl groups were prepared in the ring-opening reaction of dioxane-boron-cluster adducts and an azide anion or suitable alkynol-derived alcoholate nucleophile. Analogous derivatives bearing terminal sulfhydryl groups were also prepared. Nucleosides with various spacers containing terminal azide or ethynyl groups, located within nucleobases or sugar residues, were used as boron-cluster acceptors. The proposed methodology provides a convenient way to synthesize libraries of boron-cluster-modified nucleosides for various applications.     

Probing kinase activities by electrochemistry, contact-angle measurements, and molecular-force interactions

Three different methods to investigate the activity of a protein kinase (casein kinase, CK2) are described. The phosphorylation of the sequence-specific peptide (1) by CK2 was monitored by electrochemical impedance spectroscopy (EIS). Phosphorylation of the peptide monolayer assembled on a Au electrode yields a negatively charged surface that electrostatically repels the negatively charged redox label [Fe(CN)6]3-/4-, thus increasing the interfacial electron-transfer resistance. The phosphorylation process by CK2 is further amplified by the association of the anti-phosphorylated peptide antibody to the monolayer. Binding of the antibody insulates the electrode surface, thus increasing the interfacial electron-transfer resistance in the presence of the redox label. This method enabled the quantitative analysis of the concentration of CK2 with a detection limit of ten units. The second method employed involved contact-angle measurements. Although the peptide 1-functionalized electrode revealed a contact angle of 67.5 degrees , phosphorylation of the peptide yielded a surface with enhanced hydrophilicity, 36.8 degrees. The biocatalyzed cleavage of the phosphate units with alkaline phosphatase regenerates the hydrophobic peptide monolayer, contact angle 55.3 degrees . The third method to characterize the CK2 system involved chemical force measurements between the phosphorylated peptide monolayer associated with the Au surface and a Au tip functionalized with the anti-phosphorylated peptide antibody. Although no significant rupture forces existed between the modified tip and the 1-functionalized surface (6+/-2 pN), significant rupture forces (multiples of 120+/-20 pN) were observed between the phosphorylated monolayer-modified surface and the antibody-functionalized tip. This rupture force is attributed to the dissociation of a simple binding event between the phosphorylated peptide and the fluorescent antibody (Fab) binding region.     

Monitoring of NO2 in the ambient air with passive samplers before and after a road reconstruction event

Nitrogen dioxide (NO₂) concentrations were used to evaluate the air quality before and after the infrastructural change of an important traffic artery in Mortsel, Antwerp (Belgium). During the reconstruction works two pairs of traffic lanes were reduced to one in each direction. Two sampling campaigns were conducted: the first one before the works in 2003 and the second one in 2005, after the road works were finished. Sampling was performed on a weekly base with the use of passive diffusion tubes on the streets, and also indoors in nearby houses. The samples were analyzed by ion chromatography, from which data the NO₂ concentrations in air could be calculated. These results were compared with NO₂ values from the air monitoring station 42R801 of the Flemish Environment Agency in Borgerhout, Antwerp. On the base of different NO₂ concentrations, correlated well with the traffic density, sampling locations were classified into three groups as follows: 1) ‘heavily polluted’ (heavy traffic); 2) ‘moderately polluted’ (medium traffic); or 3) ‘less polluted’ (low traffic density). Sampling sites located further from the road works, enclosed to the group ‘less polluted’, showed the lowest NO₂ concentrations. The highest NO₂ level was found for the locations close to reconstruction works, which belonged to the group ‘heavily polluted’. The contribution of NO₂ was at the same level before and after the road works. During the first campaign it ranged from 30 ± 7 µg/m³ to 71 ± 11 µg/m³ and during the second sampling it was between 36 ± 17 µg/m³ and 73 ± 17 µg/m³. These modernization works had no impact on preventing the traffic-related pollutant as NO₂ and as a consequence no significant effect on the air quality in the studied region. It has been proven that the impact of traffic on the air quality is unmistakably high and simply reduction of the number of the traffic lanes, intended to discourage the traffic flow, had apparently no environmentally advantageous effect.     

Heterologous Production of Fungal Maleidrides Reveals the Cryptic Cyclization Involved in their Biosynthesis

Fungal maleidrides are an important family of bioactive secondary metabolites that consist of 7, 8, or 9‐membered carbocycles with one or two fused maleic anhydride moieties. The biosynthesis of byssochlamic acid (a nonadride) and agnestadride A (a heptadride) was investigated through gene disruption and heterologous expression experiments. The results reveal that the precursors for cyclization are formed by an iterative highly reducing fungal polyketide synthase supported by a hydrolase, together with two citrate‐processing enzymes. The enigmatic ring formation is catalyzed by two proteins with homology to ketosteroid isomerases, and assisted by two proteins with homology to phosphatidylethanolamine‐binding proteins.