Spectroscopic investigation of cyclodextrin monomers,derivatives, polymers and azo dyes (1)

Circular dichroism (CD) and visible spectra of inclusion compounds between Methyl Orange (MO) analogues and -, -, -cyclodextrin (cdx), 2,6-dimethyl-and 2,3,6-trimethyl--cdx, water soluble -, -, -cdx polymer products were investigated. In the CD-spectroscopic investigation, the complex with -cdx epichlorohydrin condensate showed a large amplitude and splitting of the induced ^* band. Fractions of glyceryl ether of less than 2000 and polymer of more than 10000 dalton molecular mass were separated. Complexes of above two fractions and MO showed the same splitting spectral pattern. Job's plots from visible spectra showed the formation of the 11 complex and CD-data suggested the co-existence of the 21 MO-cdx complex. This splitting pattern showed the reversal of the signs when -cdx-ethyleneglycol-bis(epoxypropyl) ether was used and disappeared when larger host molecules and azo dyes were used. The splitting was explained by exciton interaction.     

Efficient desulfurization of 2-thiopyrimidine nucleosides to the corresponding 4-pyrimidinone analogues using trans-2-(phenylsulfonyl)-3-phenyloxaziridine

A brief treatment of 2-thiopyrimidine nucleosides (s²U^∗) with trans-2-phenylsulfonyl-3-phenyloxaziridine (PSO) results in efficient substrate desulfurization leading to the corresponding 4-pyrimidinone analogues (H²U^∗). The key transformation proceeds through oxidation of the 2-thiocarbonyl group to a sulfur oxyacid derivative and subsequent elimination of sulfur dioxide. 4-Pyrimidinone 1-β-d-riboside (H²U) has been transformed into the respective phosphoramidite, a ready-to-use monomer for the introduction of a modified nucleoside into an oligonucleotide chain. Moreover, the effective desulfurization of the 2-thiouridine nucleotide could be achieved directly at the oligonucleotide level, by treatment of the TdA(s²U)dGdC oligonucleotide with PSO, as verified by MALDI-TOF mass spectrometry.     

Determination of fungicide residues in fruits by coupled-column liquid chromatography

Coupled-column liquid chromatography with fluorescence detection was applied to the determination of o-phenylphenol and bitertanol residues in orange and banana fruits. After extraction with a mixture of acetone, dichloromethane-petroleum ether, and ethyl acetate, an extract aliquot of 100 microL was injected directly without any additional clean-up into the chromatographic system using two reversed phase C18 coupled columns. The LC-LC approach allowed automated sample clean up of the vegetal extracts, leading to a simple and rapid analytical procedure, with limits of quantification between 0.01 and 0.05 mg kg(-1). Recovery experiments performed on orange and banana samples fortified at different concentrations (0.01 - 4 mg kg(-1)) gave average recoveries between 70 and 113% with relative standard deviations lower than 15%. The procedure developed was finally applied to orange and banana samples from different geographical locations and the results were confirmed by GC-MS.     

Application of main component fraction collection method for purification of compound libraries

In order to support high-throughput library purification, a novel UV triggered fraction collection method was developed in which a maximum-seeking-algorithm-driven, six-port valve collects the largest chromatographic peak. This straightforward strategy achieves the one sample-one fraction approach, thus resulting in a simpler and less error prone workup procedure. The effectiveness of this main component fraction collection method will be illustrated here by the results of the purification of compound libraries (altogether 6086 compounds, having an averaged success rate of 79.4%). Advanced applications, where the desired component differs from the main component, will also be discussed.     

Two-step upflow anaerobic sludge bed system for sewage treatment under subtropical conditions with posttreatment in waste stabilization ponds

A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.     

Wavelength dependence of the hyper Rayleigh scattering response from gold nanoparticles

The wavelength dependence of the quadratic hyperpolarizability of 11 nm diam gold nanoparticles, is reported as measured by hyper Rayleigh scattering. An important photoluminescence background underlying the hyper Rayleigh signal is observed, a contribution attributed to radiative electron-hole recombinations following multiphoton excitation favored by adsorbed organic compound like citrate on the surface of the nanoparticles. The absolute value of the quadratic hyperpolarizability of gold spherical nanoparticles is determined and a strong enhancement is observed for harmonic frequencies in resonance with the dipolar surface plasmon excitation. No contribution of the interband transition is observed. The absolute values reported, beta(C)=5.1x10(-26) esu at the second harmonic energy 2.39 eV, have been measured with femtosecond long laser pulse, and are 1 order of magnitude weaker that the one previously reported with nanosecond long pulses. This difference can be related to similar measurements performed on the second order hyperpolarizability of gold nanoparticles and may be attributed to different electronic relaxation regimes. Finally, the spectrum of the quadratic hyperpolarizability is compared to the theoretically expected one.     

Study of ab initio molecular data for inelastic and reactive collisions involving the H3+ quasimolecule

The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H3+ system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular structure of the triatomic. The method of Baer is employed to generate "diabatic" states and the residual nonadiabatic couplings are calculated. The ab initio results for these are markedly different from the corresponding DIM data, and show the need to consider the third PES.     

Simultaneous light emission from a mixture of dendrimer encapsulated chromophores: a model for single-layer multichromophoric organic light-emitting diodes

The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device.     

Conformation of glycomimetics in the free and protein-bound state: structural and binding features of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man

The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found.     

Spreading of viscous droplets on a non viscous liquid

Some polymer melts (of high viscosity ) can wet completely the surface of a non miscible, simple liquid. We discuss here the laws of spreading for a macroscopic droplet of this type, when the internal friction of the droplet dominates. We predict a droplet radius increasing liket ^1/4 wheret is the spreading time, or equivalently a droplet curvature decreasing liket ^–1. The droplet should be surrounded by a precursor film, which is not discussed in the present note.