Membrane Distillation (MD) is a thermal membrane process allowing for a theoretical 100% rejection of non-volatile compounds (i.e. ions, macromolecules, colloids, cells), whereas vapour molecules permeate through a micro-porous hydrophobic membrane due to a difference of vapour pressure established across the membrane-self. The effective driving force and, then, the vapour trans-membrane flux is affected by temperature polarization phenomena occurring in the boundary layers adjacent to the membrane. The temperature values at the membrane surface are usually difficult to measure and only recently some invasive techniques were adopted for this scope. The aim of this work was to introduce luminescent molecular probing as an innovative technology for non-invasive and in-situ monitoring of thermal polarization in MD. Tris(phenantroline)ruthenium(II) chloride (Ru(phen)3) was selected as temperature sensitive luminescent probe and immobilized in a flat poly(vinylidene fluoride) electrospun nanofibrous membrane (PVDF ENM). Experiments showed the key role of the Ru(phen)3 and Lithium Chloride (LiCl) in the preparation of homogeneous PVDF ENM due to their ionic nature that improved the electrical conductivity of the polymeric solution favouring the electrospinning. Furthermore, PVDF ENM showed a good performance in Direct Contact Membrane Distillation (DCMD) process. The immobilization of the molecular probe allowed to optically monitoring the membrane surface temperature during DCMD experiments. On the other hand, the employment of an IR-camera permitted the evaluation of the temperature of the bulk of liquid streams. Therefore, the combination of these two optical techniques enabled to evaluate, in a direct and non-invasive way, the thermal polarization along the membrane module during DCMD experiments.

In this work we show that, the combination of (i) high mechanical stability (provided by a PS matrix), (ii) high sensitivity and selectivity (provided by a two-dye system of Tris (1,10-phenanthroline)ruthenium(II) chloride hydrate (Ru(phen)(3)) and 7-Methoxy-4-methylcoumarin) and (iii) high reproducibility in the output signal/response, results in a membrane able for monitoring O-2 and temperature in membrane processes at laboratory and industrial scales.Due to the matched sensitivity of the developed ratiometric probe to oxygen and temperature a simple correction algorithm was implemented, which allows at overcoming the vulnerability of the ratiometric signal to the temperature, leading to a robust evaluation of the oxygen concentration.The impact of introducing this photochemical activity in membranes opens a new perspective for non-invasive monitoring of membrane processes (e.g. measurement of temperature in membrane distillation processes, oxygen measurement for monitoring of biofilm onset and development in reverse osmosis). (C) 2016 Elsevier B.V. All rights reserved.

In this work, tris(phenantroline)ruthenium(II) chloride (Ru(phen)3) was immobilized in silica nanoparticles prepared according to the Stöber method. Efforts were devoted on the optimization of the nano-thermometer in terms of size, polydispersity, intensity of the emission and temperature sensitivity. In particular, the immobilization of the luminophore in an external thin shell made of silica grown in a second step on bare silica nanoparticles allowed producing fluorescent monodisperse silica nanoparticles (420±20nm). A systematic study was addressed to maximize the intensity of the emission of the fluorescent nanoparticles by adjusting the concentration of Ru(phen)32+ in the shell from 0.2 to 24wt.%, whereas the thickness of the shell is affected by the amount of silica precursor employed. The luminescent activity of the doped nanoparticles was found to be sensitive to the temperature. In fact, the intensity of the emission linearly decreased by increasing the temperature from 20°C to 65°C. The thermoresponsive nanoparticles were functionalized with long aliphatic chains in order to obtain hydrophobic nanoparticles. The developed nanoparticles were immobilized via dip-coating procedure on the surface of hydrophobic porous membranes, such as Polyvinylidene fluoride (PVDF) prepared via Non-Solvent Induced Phase Separation (NIPS), providing local information about the membrane surface temperature.

An optical sensor for oxygen detection based on the immobilization of tris 1,10-phenanthroline ruthenium (Ru(phen)(3)) into polystyrene (PS) films was employed for monitoring the oxygen permeation through polymeric packaging films.7-Methoxy-4-methylcoumarin was selected as non-sensitive reference to oxygen and dispersed with the Ruthenium complex in order to develop a ratiometric sensor correcting the artifacts induced by operating conditions and improving the robustness of the sensor. The developed ratiometric sensor was successfully employed for the measurement of the oxygen permeation rate in an enclosed atmosphere (package) using polymeric films made of biaxially oriented polypropylene (BOPP) and polydimethyl siloxane (PDMS). It was observed that the oxygen concentration in the enclosed atmosphere increased from 0% to 21% in 3 h in the case of PDMS and from 0% to 3.6% in 24 h for BOPP. The concentration evolvement with time was well predicted by a solution-diffusion model and the final oxygen concentration in the packed atmosphere was confirmed by chromatographic measurements. According to these results, the ratiometric luminescent sensor is suitable for the development of smart packaging films allowing for continuous monitoring of oxygen concentration in-situ. (C) 2016 Elsevier Ltd. All rights reserved.

Molecularly imprinted polymers are simple and robust materials for the selective binding of analytes with affinities and selectivities similar to biological probes. A green supercritical CO2-assisted molecular imprinting protocol enabled the production of smart sensory particles, incorporating quantum dots, with molecular recognition to bisphenol A at very low concentrations (4 nM). The protocol uses amphibious vinyl-coated quantum dots and enables the design of sensors for a wide range of molecules through a simple, low cost and clean technology.

Laser Flash Photolysis was employed to measure the deprotonation and reprotonation rate constants of cyanidin 3-monoglucoside (kuromanin) in water/methanol mixtures. It was found that the deprotonation rate constant kd decreases with decreasing water content, reflecting the lack of free water molecules around kuromanin, which may accommodate and stabilize the outgoing protons. On the other hand, the reprotonation rate constant, kp, increases with the decrease in water concentration from a value of kp=2×1010lmol−1s−1 in water up to kp=6×1010lmol−1s−1 at 5.6M water concentration in the mixture. The higher value of kp at lower water concentrations reflects the fact that the proton is not freely escaping the solvation shell of the molecule. The deprotonation rate constant decreases with decreasing water content, reflecting the lack of free water molecules around kuromanin that can accommodate the outgoing protons. Overall, the acidity constant of the flavylium cation decreases with the decrease in water concentration from pKa values of 3.8 in water to approximately 4.8 in water-depleted media, thus shifting the equilibrium towards the red-coloured form, AH+, at low water contents.The presence, or lack, of water, will affect the colour shade (red to blue) of kuromanin. This is relevant for its role as an intrinsic food component and as a food pigment additive (E163).

Previous studies have reported the production of malformed virus-like-particles (VLP) in recombinant host systems. Here we computationally investigate the case of a large triple-layered rotavirus VLP (RLP). In vitro assembly, disassembly and reassembly data provides strong evidence of microscopic reversibility of RLP assembly. Light scattering experimental data also evidences a slow and reversible assembly untypical of kinetic traps, thus further strengthening the fidelity of a thermodynamically controlled assembly. In silico analysis further reveals that under favourable conditions particles distribution is dominated by structural subunits and completely built icosahedra, while other intermediates are present only at residual concentrations. Except for harshly unfavourable conditions, assembly yield is maximised when proteins are provided in the same VLP protein mass composition. The assembly yield decreases abruptly due to thermodynamic equilibrium when the VLP protein mass composition is not obeyed. The latter effect is more pronounced the higher the Gibbs free energy of subunit association is and the more complex the particle is. Overall this study shows that the correct formation of complex multi-layered VLPs is restricted to a narrow range of association energies and protein concentrations, thus the choice of the host system is critical for successful assembly. Likewise, the dynamic control of intracellular protein expression rates becomes very important to minimize wasted proteins.

We propose an experimental-based tool for dealing with fluorescence modulation close to nanoparticles for application in studies of fluorophores in the vicinity of gold nanoparticles (AuNPs), typically addressed via theoretical models. We performed a photophysical characterization of fluorophores in the vicinity of AuNPs, showing that correct ΦF determination suffers from a local pH effect, and address the observed radiative enhancement. Our approach is based on the experimental assurance that the reference fluorophores are in the same optical conditions as those of the AuNP–fluorophore conjugates. We demonstrate the relevance for introducing corrections for the inner filter effect and the reabsorption of the emitted light caused by AuNPs. The proposed approach could circumvent the need for theoretical based corrections and allow for more accurate determination of fluorescence emission in the vicinity of gold nanoparticles.

There are numerous reports of coumarin ester derivatives, in particular phosphate esters, as photocleavable cages in biological systems. Despite the comprehensive analysis of the photocleavage mechanism, studies of 4-methylcoumarin caged phosphates and/or nucleotides were always performed at constant pH. In this work, we present the study of the pH effect on the photochemistry of (7-diethylaminocoumarin-4-yl)methyl phosphate (DEACM-P). Fluorescence and photocleavage quantum yields, as well as the fluorescence decay times were measured as a function of the pH. It was found that the pH produces significant changes in the overall photochemical quantum yield of DEACM-P, and the observed changes are complementary to those obtained from the fluorescence quantum yield. Deprotonation of DEACM-HPO(4)(-) to yield DEACM-PO(4)(2-), produces a decrease in the photochemical quantum yield (from 0.0045 to 0.0003) and an increase in the fluorescence quantum yield (from 0.072 to 0.092). Moreover, from the analysis of the decay times, we have also found that hydroxyl ion is not only relevant, but it is mechanistically involved in the photoreaction of DEACM-HPO(4)(-).

We recently reported on the use of caged nucleotides to attain full control of enzymatic polymerization of RNA solely by light. In the absence of light no RNA formation was possible due to the efficient caging by the coumarin moiety; after irradiation, caged ATP was released with quantitative precision and RNA polymerization was resumed. As photolabile protecting group [7-(diethylamino)coumarin-4-yl]methyl] (DEACM) was used due to its high absorbance in the visible region of the spectrum, fast deprotection kinetics and absence of radical intermediates. However, the 7-diethylamino-4-hydroxymethylcoumarin photo-product (DEACM-OH) was shown to inhibit the transcription reaction for concentrations higher than 30μM [5]. This inhibition has been associated with poor water solubility, which is commonly dealt with via cumbersome chemical modifications of the protecting moiety. To overcome inhibition, we evaluated the use of molecular scavengers to sequester DEACM-OH formed after irradiation. Determination of association constants of coumarin with β-cyclodextrins allowed the assessment of its capability to remove free coumarin molecules from solution. The influence of β-cyclodextrin in transcription reaction was also assessed. Results show that β-cyclodextrin can be successfully used as scavenger as it increases the DEACM-OH threshold concentration for inhibition, amplifying the efficiency of light controlled in vitro transcription.

This work aims for determining the impact of different environmental conditions, such as pH, ionic strength (salt concentration) and the chemistry of the membrane surface (hydrophilic/hydrophobic character) on the structure of permeating proteins after ultrafiltration. In the permeation experiments reported in this paper, different solutions of a model protein - beta-lactoglobulin - at pH 3, 5 and 8 and salt concentrations of 1, 10 and 100 mM were processed with membranes of different molecular weight cut-off (10 and 30 kDa) and materials (regenerated cellulose-RC, and polyethersulfone-PES).The analysis of the structural alterations induced in the permeating molecules of P-lactoglobulin after ultrafiltration was performed using a methodology that combines the use of complementary fluorescence techniques: steady-state fluorescence and steady-state fluorescence anisotropy.From the results obtained it was concluded that permeation performed under pH values below the isoelectric point of beta-lactoglobulin, at high salt concentrations and using membranes with hydrophobic character allows for minimization of the impact of the membrane processing in the structure of beta-lactoglobulin. (C) 2007 Elsevier B.V. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

This work aims to identify of non-reversible structural changes induced in P-lactoglobulin by permeation through porous ultrafiltration membranes. The evaluation of these structural changes is performed using a fluorescence methodology, which combines the use of three different, complementary, fluorescence techniques: steady-state fluorescence, picosecond tirne-resolved fluorescence and steady-state fluorescence anisotropy. The identification of the nature of the structural changes induced upon permeation is possible through comparison of the fluorescence responses obtained for P-lactoglobulin solutions collected after permeation (permeates and retentates) with those induced by chemical (addition of Guanidine hydrochloride, GndHCl) and thermal denaturation of beta-lactoglobulin.The fluorescence approach used allowed to identify irreversible losses of structural integrity of beta-lactogglobulin in the permeates, while beta-lactoglobulin retentates seemed to be unaffected by the ultrafiltration process.The mechanisms that regulate the structural alterations of beta-lactoglobulm and the magnitude of these alterations depend on the protein to membrane pore size ratio, lambda, being more substantial at higher lambda(severe pore constriction). Under these conditions (permeation with a 10 kDa membrane) the structural changes induced in the proteins are dictated by the high shear stress at the membrane pore walls. The increase of the membrane cut-off (30 kDa membrane) induces a decrease in the magnitude of the shear stress and the effect of protein-membrane chemical interactions becomes noticeable. (c) 2007 Elsevier B.V. All rights reserved.

Changes in the molecular structure of horseradish peroxidase (HRP-4C) induced by membrane ultrafiltration, as well as its impact on the enzymatic activity, were monitored using three complementary fluorescence techniques: steady-state fluorescence, fluorescence anisotropy and picosecond time-resolved fluorescence. Ultrafiltration experiments were performed using membranes of polyethersulfone (PES) with 30 and 100 kDa and membranes of regenerated cellulose (RC) with 10 and 30 kDa.The results obtained clearly shows HRP-4C structural changes during ultrafiltration, which were essentially controlled by hydrophobic and electrostatic protein-membrane interactions. The structural changes observed depend on the affinity of the membrane material to ions, such as Fe3+ and Ca2+, which have a substantial structural and functional relevance to this enzyme. Additionally, it was found that the impact of the ultrafiltration process on the enzymatic activity was a direct consequence of the depletion of iron from the protein structure, causing irreversible structural alterations on HRP-4C, and thus inducing severe changes in its enzymatic activity. (c) 2006 Elsevier B.V. All rights reserved.

The outstanding solvatochromic properties of the complex Ru(bpy)(CN)42−, deriving from the ability of the nitrile goup to participate in H-bond interactions, were explored to develop a sensor for low concentrations of water on common organic aprotic solvents. In dry solvents, the maximum wavenumber of the low energy transition of Ru(bpy)(CN)42− presents linear correlations with the Kamlet–Taft solvent acidity parameter (slope=0.59±0.02, r>0.99) and Gutman acceptor number (slope=(1.7±0.1)×10−2, r>0.99). The slopes and regression coefficients of the correlations measure the sensitivity of the compound to H-bond donation by the solvent and confirm its high specificity towards the sensing of H-bond donating solvents, such as water. In acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dichloromethane and toluene, the sensor presents spectral changes that respond linearly to water concentrations in the range 5–70ppm and compete favorably with the widely spread Karl–Fisher method with a detection limit of ∼50ppm. The high sensitivity and the much simpler spectrophotometric titration, portends the use of this complex as an optical water sensor for determination of low water contents in organic solvents.