Study of the Photochemical Properties and Conical Intersections of [2,2′‐Bipyridyl]‐3‐amine‐3′‐ol

The two isoelectronic bipyridyl derivatives [2,2′‐bipyridyl]‐3,3′‐diamine and [2,2′‐bipyridyl]‐3,3′‐diol are experimentally known to undergo very different excited‐state double‐proton‐transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. In a previous study, these differences were explained from a theoretical point of view, because of topographical features in the potential energy surface and the presence of conical intersections (CIs). Here, we analyze the photochemical properties of a new molecule, [2,2′‐bipyridyl]‐3‐amine‐3′‐ol [BP(OH)(NH₂)], which is, in fact, a hybrid of the former two. Our density functional theory (DFT), time‐dependent DFT (TDDFT), and complete active space self‐consistent field (CASSCF) calculations indicate that the double‐proton‐transfer process in the ground and first singlet π→π* excited state in BP(OH)(NH₂) presents features that are between those of their “parents”. The presence of two CIs and the role they may play in the actual photochemistry of BP(OH)(NH₂) and other bipyridyl derivatives are also discussed.     

Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions

New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu (III) complexes, Eu(PEP)₂Cl₃ and Eu(PEP)₂(NO₃)₃, are synthesized and characterized. The synthetic procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single crystals obtained. The compounds [Eu(PEP)₂Cl₃]·2CH₃CN and [Eu(PEP)₂(NO₃)₃]∙2CH₃CN crystalize in monoclinic space group P2_1/n and P2_1/c, respectively, with two acetonitrile solvent molecules. Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions in the inner coordination sphere, which allows exploring their influence on the stability, molecular and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition, molecular simulations are performed in order to explain the observed experimental behavior of the complexes. The discovered structure-properties relationships give insight on the role of the counter ions in the molecular design of new Eu (III) based luminescent materials.     

Enzymatic Hydrolysis of Soy Protein Isolates. DSC study

The aim of this work was to analyze the possible use of differential scanning calorimetry (DSC) as a method to study the process of protein modifications during enzymatic hydrolysis. Results of the enzymatic hydrolysis of soy protein showed significant differences in the values of maximum deflection temperature (T _p), heat of reaction (ΔH), and width at half peak height (ΔT _1/2), between DSC curves corresponding to the substrate, or zerotime of hydrolysis, and those of the hydrolysates obtained by the action of cucurbita and pomiferin enzymes. DSC curve changes mentioned were explained by the use of gel-filtration chromatography, denaturing electrophoresis and surface hydrophobicity of the hydrolysis products obtained at 30 min of reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Self-assembly of ligands designed for the building of a new type of [2 x 2] metallic grid. anion encapsulation and diffusion NMR spectroscopy

The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm), 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine (bpz(*)pm), 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Mebpzpm), and 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (ppdMe) were synthesized and were made to react with Cu(I) centers in the presence of different counteranions. Different [2 x 2] metallic grids were obtained. With ligands bpzpm, bpz*pm, and Mebpzpm, a new type of grid was obtained where the facing ligands were divergent and two counteranions (BF(4-) or PF(6-)) were hosted in the resulting cavities and exhibit C-H...F and anion...pi interactions in the solid state. The presence of methyl groups on the pyrazolyl rings induced several distortions in the structure. In complexes with the ligand ppdMe, there were found two groups of parallel ligands in the grid, and the cavities generated were smaller. The counteranions were situated outside the grid, and the facing ligands exhibited aromatic pi-pi stacking interactions. Anion-pi interactions involving the pyridazine ring were found. The behavior in solution of the new derivatives with a special emphasis on the cation-anion interactions was studied by UV-vis and NMR spectroscopy. Diffusion NMR experiments performed for some complexes allowed us to conclude that weak cation-anion interactions exist in solution, with the counteranions undergoing fast exchange on the diffusion time scale between the free and ion-paired states.     

Formation of polyelectrolyte multilayer architectures with embedded DMPC studied in situ by neutron reflectometry

The coupling of lipid molecules to polymer components in a planar biomimetic model membrane made of a lipid bilayer (dimyristoylphosphatidylcholine) supported by polyelectrolyte multilayers is studied. The polyelectrolyte support was prepared by layer-by-layer deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS). Two polymer sample terminations were considered: positively charged (PAH-terminated) and negatively charged (PSS-terminated). Neutron reflectometry studies showed that, whereas positively charged samples did not favor the deposition of lipid, negatively charged samples allowed the deposition of a lipid bilayer with a thickness of approximately 5 nm. In the latter case, formation of polyelectrolyte layers after the deposition of the lipid layer was also possible.     

Biocatalytic removal of nickel and vanadium from petroporphyrins and asphaltenes

Asphaltenes from a crude oil rich in heavy metals (Castilla crude oil) were fractionated and partially characterized. Biocatalytic modifications of these fractionated asphaltenes by three different hemoproteins: chloro-peroxidase (CPO), cytochrome C peroxidase (Cit-C), and lignin peroxi-dase (LPO) were evaluated in both aqueous buffer and organic solvents. The reactions were carried out in aqueous buffers, ternary systems of toluene: isopropanol: water, and aqueous-miscible organic solvent solutions with petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary systems and aqueous miscible-organic solvent systems than in the aqueous buffer systems. However, only the CPO-mediated reactions were effective in eliminating the Soret peak in both aqueous and organic solvent systems. The effects of CPO-mediated reactions on the release of the metals complexed with the porphyrins and asphaltenes were also determined. Chloroperoxidase was able to alter components in the heavy fractions of petroleum and remove 53 and 27% of total heavy metals (Ni and V, respectively) from petroporphyrin-rich fractions and asphaltenes     

Use of neural networks and diode-array detection to develop an isocratic HPLC method for the analysis of nitrophenol pesticides and related compounds

Summary We have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared the results with those obtained by application of response-surface methodology. These studies resulted in the selection the mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min⁻¹. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits, calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction on a C₁₈ cartridge.