Flow-based bioconjugation of coumarin phosphatidylethanolamine probes: Optimised synthesis and membrane molecular dynamics studies.

A series of phosphatidylethanolamine fluorescent probes head-labelled with 3-carboxycoumarin was prepared by an improved bioconjugation approach through continuous flow synthesis. The established procedure, supported by a design of experiment (DoE) set-up, resulted in a significant reduction in the reaction time compared to the conventional batch method, in addition to a minor yield increase. The characterization of these probes was enhanced by an in-depth molecular dynamics (MD) study of the behaviour of a representative probe of this family, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine labelled with 3-carboxycoumarin (POPE-COUM), in bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (SLPC) 2:1, mimicking the composition of the egg yolk lecithin membranes recently used experimentally by our group to study POPE-COUM as a biomarker of the oxidation state and integrity of large unilamellar vesicles (LUVs). The MD simulations revealed that the coumarin group is oriented towards the bilayer interior, leading to a relatively internal location, in agreement with what is observed in the nitrobenzoxadiazole fluorophore of commercial head-labelled NBD-PE probes. This behaviour is consistent with the previously stated hypothesis that POPE-COUM is entirely located within the LUVs structure. Hence, the delay on the oxidation of the probe in the oxygen radical absorbance capacity (ORAC) assays performed is related with the inaccessibility of the probe until alteration of the LUV structure occurs. Furthermore, our simulations show that POPE-COUM exerts very little global and local perturbation on the host bilayer, as evaluated by key properties of the unlabelled lipids. Together, our findings establish PE-COUM as suitable fluorescent lipid analogue probes.

Development of new 2-piperidinium-4-styrylcoumarin derivatives with large Stokes shifts as potential fluorescent labels for biomolecules.

A series of novel 2-piperidinium-4-styrylcoumarin derivatives, with large Stokes shifts and high fluorescence quantum yields, were synthesized using an efficient and low-cost synthetic strategy as potential fluorescent labels for biomolecules. Density functional theory and time-dependent density functional theory calculations were performed in order to rationalize the observed photophysical properties.

Ambipolar pentacyclic diamides with interesting electrochemical and optoelectronic properties.

Developing organic semiconductors for organic thin film transistors (OTFT) and optoelectronic applications is a challenge. We developed highly crystalline pentacyclic diimides (3) and (4) which showed good OTFT and OLED potential and energy gaps of 2.60 eV and 2.54 eV. They exhibited interesting photo and eletroluminescence activity. Both compounds showed good quantum yields (0.56 for (3) and 0.60 for (4)).

Interaction of Bile Salts With Lipid Bilayers: An Atomistic Molecular Dynamics Study.

Bile salts (BS) are biosurfactants crucial for emulsification and intestinal absorption of cholesterol and other hydrophobic compounds such as vitamins and fatty acids. Interaction of BS with lipid bilayers is important for understanding their effects on membranes properties. The latter have relevance in passive diffusion processes through intestinal epithelium such as reabsorption of BS, as well as their degree of toxicity to intestinal flora and their potential applications in drug delivery. In this work, we used molecular dynamics simulations to address at the atomic scale the interactions of cholate, deoxycholate, and chenodeoxycholate, as well as their glycine conjugates with POPC bilayers. In this set of BS, variation of three structural aspects was addressed, namely conjugation with glycine, number and position of hydroxyl substituents, and ionization state. From atomistic simulations, the location and orientation of BS inside the bilayer, and their specific interactions with water and host lipid, such as hydrogen bonding and ion-pair formation, were studied in detail. Membrane properties were also investigated to obtain information on the degree of perturbation induced by the different BS. The results are described and related to a recent experimental study (Coreta-Gomes et al., 2015). Differences in macroscopic membrane partition thermodynamics and translocation kinetics are rationalized in terms of the distinct structures and atomic-scale behavior of the bile salt species. In particular, the faster translocation of cholate is explained by its higher degree of local membrane perturbation. On the other hand, the relatively high partition of the polar glycine conjugates is related to the longer and more flexible side chain, which allows simultaneous efficient solvation of the ionized carboxylate and deep insertion of the ring system.

A photoswitchable "host-guest" approach for the selective enrichment of dimethoate from olive oil.

This work describes the development of a new selective photocontrollable molecularly imprinted-based sorbent for the selective enrichment/pre-concentration of dimethoate from spiked olive oil samples. To achieve this goal an improved molecularly imprinted strategy relying on the embedding of a functional monomer containing an azobenzene chromophore as light-responsive element, on the crosslinked tridimensional molecular imprinted network, has been assessed. To address the mechanisms underlying template recognition and uptake/release of the analyte from the functional imprinted material, computational studies using a quantum chemical approach, have been explored. This new functional sorbent provides a straightforward controllable uptake/release of the target template using light as the stimuli tool, which is highly advantageous due to light manipulation characteristics, such as superior clean, precision and remote controllable properties. In general, this work will contribute to the implementation of a photoswitchable analytical methodology that proves to be suitable for the selective isolation and further quantification of dimethoate from olive oil matrices at levels similar to the maximum residues limits imposed by the legislation. The limits of detection, calculated based on 3σ, was 1.6 mgL-1 and the limit of quantification, based on 10σ, was 5.2 mgL-1. The implemented sample preparation shows high reproducibility and recoveries (93.3 ±â€¯0.4%).

A magnetic controllable tool for the selective enrichment of dimethoate from olive oil samples: A responsive molecular imprinting-based approach.

Aiming to develop a straightforward magnetic-based sample preparation methodology for the selective extraction of dimethoate from olive oil, the synthesis of dimethoate-imprinted polymer on the surface of modified magnetic nanoparticles has been attempted. Molecular recognition assays have proven their suitability for the selective pre-concentration of dimethoate. Mechanistic basis for template selective recognition has been explored using a quantum chemical approach, providing new insights about the mechanisms underlying template recognition. Thus, a magnetic molecularly imprinted solid-phase extraction method was developed allowing the extraction of dimethoate from spiked olive oil samples, at levels similar to the maximum residue limits imposed by legislation, followed by the quantification of their levels by high-performance liquid chromatography with diode-array detection. Recoveries of 94.55% were obtained, with relative standard deviations lower than 0.53% (n = 3). The developed sample preparation technique enables a selective pre-concentration/enrichment of dimethoate from olive oil matrix with minimum handling and less solvent consumption.

Conformational Preference and Spectroscopical Characteristics of the Active Pharmaceutical Ingredient Levetiracetam.

The analysis of the possible conformers and the conformational change between solid and liquid states of a particular drug molecule are mandatory not only for describing reliably its spectroscopical properties but also for understanding the interaction with the receptor and its mechanism of action. Therefore, here we investigated the free-energy conformational landscape of levetiracetam (LEV) in gas phase as well as in water and ethanol, aiming to describe the 3-dimensional structure and energetic stability of its conformers. Twenty-two unique conformers were identified, and their energetic stability was determined at density functional theory B3LYP/6-31+G(2d,2p) level of theory. The 6 most stable monomers in water, within a relative free-energy window of 0.71 kcal mol-1 and clearly separated in energy from the remaining subset of 16 conformers, as well as the 3 most stable dimers were then used to compute the Boltzmann populations-averaged UV-Vis and NMR spectra of LEV. The conformational landscape in solution is distinctly different from that corresponding to gas phase, particularly due to the relative orientations of the butanamide group. Aiming to clarify the stability of the possible dimers of LEV, we also investigated computationally the structure of a set of 11 nonhydrated and hydrated homochiral hydrogen-bonded LEV dimers.

Adsorption of CO on the rutile TiO2(110) surface: a dispersion-corrected density functional theory study.

The geometry, energy and stretching frequency of carbon monoxide on the rutile TiO2(110) surface for coverages between 0.125 and 1.5 ML are investigated by means of density functional theory calculations. Four different approaches were considered, namely, the PBE exchange-correlation functional and the PBE-D2, vdW-DF and vdW-DF2 methods incorporating van der Waals dispersion interactions of different theoretical complexity and empiricism. It is found that upon the increase of the surface coverage, the adsorption becomes less favorable due to lateral destabilizing interactions between adsorbed molecules. The preferred geometry for CO changes from an upright configuration at 0.125 ML to tilted configurations at 1.5 ML and the tilting of the C-O axis from the surface normal increases with the increase of the surface coverage. At 1 ML, all computational approaches predict alternate tilted configurations which contradict the interpretation of recent experimental infrared reflection-absorption spectroscopic findings suggesting upright CO geometries. Encouragingly, a very good agreement between calculated and experimental shifts of the C-O stretching frequency of adsorbed CO at different coverages with respect to gaseous CO species was reached.

A Family of Styrylcoumarins: Synthesis, Spectroscopic, Photophysical and Photochemical Properties.

Keeping it in the family: A new family of 5-styrylcoumarins exhibit E-Z isomerization around the Cα Cß bond with large extinction coefficients, medium-lived excited states, and moderate fluorescence quantum yields. The alteration of these photophysical properties is also corroborated by computational studies.