A beta based framework for (lower) bond risk premia.

We use a no-arbitrage essentially affine three-factor model to estimate term premia in US and German ten-year government bond yields. In line with the existing literature, we find that estimated premia have followed a downward trend since the 1980s: from 4.9 per cent in 1981 to 0.7 per cent in 2006 for the US bond and from 3.3 to 0.5 per cent for the German one. Subsequently, using an Error Correction Model (ECM) we prove that the decline is explained by a decrease in global output variability and an increase in the power of ten-year government bonds to diversify the investors’ portfolios. In addition, the ECM also forecasts both the US and the German term premia converging to around one percentage point over a five year horizon. Long-term return expectations for ten-year government bonds will have to incorporate bond risk premia that - while in line with average excess returns during the twentieth century - are significantly lower than average excess returns over the last two decades.Term structure model, bond risk premium, modern portfolio theory

Effect of ionic strength on intra-protein electron transfer reactions: The case study of charge recombination within the bacterial reaction center

It is a common believe that intra-protein electron transfer (ET) involving reactants and products that are overall electroneutral are not influenced by the ions of the surrounding solution. The results presented here show an electrostatic coupling between the ionic atmosphere surrounding a membrane protein (the reaction center (RC) from the photosynthetic bacterium Rhodobacter sphaeroides) and two very different intra-protein ET processes taking place within it. Specifically we have studied the effect of salt concentration on: i) the kinetics of the charge recombination between the reduced primary quinone acceptor QA- and the primary photoxidized donor P+; ii) the thermodynamic equilibrium (QA- ↔ QB-) for the ET between QA- and the secondary quinone acceptor QB. A distinctive point of this investigation is that reactants and products are overall electroneutral. The protein electrostatics has been described adopting the lowest level of complexity sufficient to grasp the experimental phenomenology and the impact of salt on the relative free energy level of reactants and products has been evaluated according to suitable thermodynamic cycles. The ionic strength effect was found to be independent on the ion nature for P+ QA- charge recombination where the leading electrostatic term was the dipole moment. In the case of the QA- ↔ QB- equilibrium, the relative stability of QA- and QB- was found to depend on the salt concentration in a fashion that is different for chaotropic and kosmotropic ions. In such a case both dipole moment and quadrupole moments of the RC must be considered

Wormlike reverse micelles in lecithin/bile salt/water mixtures in oil

Knowing the ability of water and bile salts to promote the reverse wormlike micelle growth in lecithin/water or lecithin/bile salt mixtures in oil, this work was aimed at elucidating the association properties of the three solutes lecithin, water and the bile salt (BS) sodium deoxycholate in cyclohexane. By systematically changing the fraction of the two additives (i.e.: water and BS) we could identify a region at low additive/lecithin molar ratios where stable wormlike micelle dispersions were formed. Small angle X-ray scattering and oscillatory rheology measurements demonstrated that the ability of bile salt and water to transform the originally spherical lecithin reverse micelles into wormlike micelles and thereby impart to the sample viscoelastic properties is preserved in the three-solute mixture. The results suggest that reverse micelle including both bile salt and water are formed in this system. Reasonably the two primers interact with the same region of the lecithin headgroups and are complementary in altering the packing parameter of the amphiphile to values suitable for the formation of cylindrical aggregates

Sensitive biosensors exploiting the minute changes in the capacitance of protein layers associated to the ligand recognition

Soft matter systems interfaced to an electronic device are presently one of the most challenging research activity that has relevance not only for fundamental studies but also for the development of highly performing bio-sensors. Layers of proteins anchored on solid surfaces have small capacitance that undergoes to only minute changes as the ligand–protein complex is formed. For properly designed systems, the protein layer represents smallest capacitance in a series of capacitors and as such dominates the overall capacitance. When such a protein layer is integrated in a Field Effect Transistor (FET) transduction is remarkably sensitive as the transistor output current is governed by the small changes due to ligand binding. These devices operate in aqueous solutions and are promising as portable sensors for point- of-care applications Two recent achievements will be illustrated: A) the sensitive and quantitative measurement of the weak interactions associated with the binding of neutral enantiomers to Odorant Binding Proteins (OBPs) [1]. immobilized to the gate of a bio-FET. Here the minute change in protein layer capacitance upon binding of S(-)-carvone and R(+)-carvone modulate the response of a water-gated OFET, allowing for chiral differential detection. The FET binding curves modelling provide information on the electrochemical free energies derived from the FET dissociation constants while the electrostatic component is isolated from the threshold voltage shifts. These can be combined with the chemical free energies gathered from the complex formation in solution, overall providing a comprehensive picture of the energy balances for a surface-bound pOBP-carvone complex undergoing chiral interactions. B) Hierarchically organized layers of phospholipids and proteins anchored on the surface of the semiconductor and acting as selective recognition elements independently form the solution ionic strength [2-3]. The charged moieties of the bound proteins along with the counter-ions form a layer that is analogous to an ionic gel. The fixed polyelectrolyte ions generate an electric field that confines the mobile counter-ions in the region of the fixed charges. Eventually a Donnan’s equilibrium is reached and the smallest capacitance in series is associated to the Donnan’s electrical double layer. The molecular recognition process (antigen/antibody in the present case) modify the charge density of the outermost layer and thus its capacitance. This capacitive tuning of the bio-FET response is virtually insensitive to the Debye’s length value and therefore is compatible with use of the transistor as sensor directly in biological fluids at high ionic strength . [1] M.Y. Mulla, E. Tuccori, M. Magliulo, G. Lattanzi, G. Palazzo, K. Persaud, L Torsi Capacitance-modulated transistor detects odorant binding protein chiral interactions Nat. Commun. 2015, 6, 6010 doi: 10.1038/ncomms7010 [2] M. Magliulo, A. Mallardi, M. Yusuf Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo, L Torsi Electrolyte-Gated Organic Field-Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer Adv. Mater. 2013, 25, 2090–2094 DOI: 10.1002/adma.201203587 [3]G. Palazzo, D. De Tullio, M. Magliulo, A. Mallardi, F. Intranovo, M.Y. Mulla, P. Favia, I. Vikholm-Lundin, L. Torsi Detection beyond the Debye’s length with an electrolyte gated organic field-effect transistor Adv. Mater. 2015, 27, 911-916. DOI: 10.1002/adma.2014035

An HLD framework for cationic ammonium surfactants

The Hydrophilic-Lipophilic Difference (HLD) model can be described by additive contributions accounting for the effect of the oil and surfactant nature, temperature, ionic strength, and so on. The first step to build an HLD framework for a surfactant class is to have Winsor III phase equilibria in a restricted range of formulation variables. In this respect, anionic and nonionic surfactants are well suited for an HLD study. On the contrary, it is difficult achieve for pure cationic surfactant Winsor III phase equilibria without the addition of alcohols and this has precluded the extension of the HLD to cationic surfactants. In the present contribution, we first propose a system based on a blend of single-tailed and double-tailed cationic surfactant to study the oil contribution, and then we afforded the determination of the surfactant contribution trough an experimental approach (the “HLD-titration”) that is especially tailored for systems displaying a wide range of existence of Winsor III phase equilibria. HLD-titration results confirmed the ionic strength contribution to HLD as a logarithmic function of salinity for cationic-based microemulsions similarly to anionic ones. However, the oil carbon number contribution is almost four-fold larger (k=0.70.1) with respect to anionic surfactants. A clearing point was observed in correspondence of the Winsor III phase equilibria under stirring. This approach allows us the determination of the so-called characteristic curvature (Cc), i.e. the term describing the surfactant nature contribution to the film curvature, of the cationic surfactant. Finally, the method was adopted to determine Cc values of 7 quaternary ammonium surfactants differing in the polar heads nature and further three amine oxide surfactant at pH=1 where they are protonated

Soft matter films interfaced to electronic devices: capacitance-modulated field effect transistors integrating protein layers

Soft matter systems interfaced to an electronic device are presently one of the most challenging research activity that has relevance not only for fundamental studies but also for the development of highly performing bio-sensors. Layers of proteins anchored on solid surfaces have small capacitance that undergoes to only minute changes as the ligand–protein complex is formed. For properly designed systems, the protein layer represents smallest capacitance in a series of capacitors and as such dominates the overall capacitance. When such a protein layer is integrated in a Field Effect Transistor (FET) transduction is remarkably sensitive as the transistor output current is governed by the small changes due to ligand binding. These devices operate in aqueous solutions and are promising as portable sensors for point-of-care applications Two recent achievements will be illustrated: A) the sensitive and quantitative measurement of the weak interactions associated with the binding of neutral enantiomers to Odorant Binding Proteins (OBPs) [1]. immobilized to the gate of a bio-FET. Here the minute change in protein layer capacitance upon binding of S(-)-carvone and R(+)-carvone modulate the response of a water-gated OFET, allowing for chiral differential detection. The FET binding curves modelling provide information on the electrochemical free energies derived from the FET dissociation constants while the electrostatic component is isolated from the threshold voltage shifts. These can be combined with the chemical free energies gathered from the complex formation in solution, overall providing a comprehensive picture of the energy balances for a surface-bound pOBP-carvone complex undergoing chiral interactions. B) Hierarchically organized layers of phospholipids and proteins anchored on the surface of the semiconductor and acting as selective recognition elements independently form the solution ionic strength [2-3]. The charged moieties of the bound proteins along with the counter-ions form a layer that is analogous to an ionic gel. The fixed polyelectrolyte ions generate an electric field that confines the mobile counter-ions in the region of the fixed charges. Eventually a Donnan’s equilibrium is reached and the smallest capacitance in series is associated to the Donnan’s electrical double layer. The molecular recognition process (antigen/antibody in the present case) modify the charge density of the outermost layer and thus its capacitance. This capacitive tuning of the bio-FET response is virtually insensitive to the Debye’s length value and therefore is compatible with use of the transistor as sensor directly in biological fluids at high ionic strength . [1] M.Y. Mulla, E. Tuccori, M. Magliulo, G. Lattanzi, G. Palazzo, K. Persaud, L Torsi Capacitance-modulated transistor detects odorant binding protein chiral interactions Nat. Commun. 2015, 6, 6010 doi: 10.1038/ncomms7010 [2] M. Magliulo, A. Mallardi, M. Yusuf Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo, L Torsi Electrolyte-Gated Organic Field-Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer Adv. Mater. 2013, 25, 2090–2094 DOI: 10.1002/adma.201203587 [3] G. Palazzo, D. De Tullio, M. Magliulo, A. Mallardi, F. Intranuovo, M.Y. Mulla, P. Favia, I. Vikholm-Lundin, L. Torsi Detection beyond the Debye’s length with an electrolyte gated organic field-effect transistor Adv. Mater. 2015, 27, 911-916. DOI: 10.1002/adma.201403541

Surfactant Interactions with Protein-Coated Surfaces: Comparison between Colloidal and Macroscopically Flat Surfaces

Surface interactions with polymers or proteins are extensively studied in a range of industrial and biomedical applications to control surface modification, cleaning, or biofilm formation. In this study we compare surfactant interactions with protein-coated silica surfaces differing in the degree of curvature (macroscopically flat and colloidal nanometric spheres). The interaction with a flat surface was probed by means of surface plasmon resonance (SPR) while dynamic light scattering (DLS) was used to study the interaction with colloidal SiO2 (radius 15 nm). First, the adsorption of bovine serum albumin (BSA) with both SiO2 surfaces to create a monolayer of coating protein was studied. Subsequently, the interaction of these BSA-coated surfaces with a non-ionic surfactant (a decanol ethoxylated with an average number of eight ethoxy groups) was investigated. A fair comparison between the results obtained by these two techniques on different geometries required the correction of SPR data for bound water and DLS results for particle curvature. Thus, the treated data have excellent quantitative agreement independently of the geometry of the surface suggesting the formation of multilayers of C10PEG over the protein coating. The results also show a marked different affinity of the surfactant towards BSA when the protein is deposited on a flat surface or individually dissolved in solution

A general approach to the encapsulation of glycoenzymes chains inside calcium alginate gel beads

In this work an enzyme encapsulation general approach, based on the use of calcium alginate hydrogels, is reported. Alginate gels are biodegradable and low cost and have been found to provide a good matrix for the entrapment of sensitive biomolecules. Alginate is an anionic polymer whose gelation occurs by an exchange of sodium ions from the polymer chains with multivalent cations, resulting in the formation of a three dimensional gel network. For gelation alginate is dripped into a calcium chloride solution. The cations diffuse from the continuous phase to the interior of the alginate droplets and form a gelled matrix. By means of this “external gelation method” beads with a diameter of few millimeters can be obtained (see figure 1). The entrapment of enzymes in alginate beads suffers some disadvantages, like as low enzyme loading efficiency with reduction of the immobilization yields and reusability, related to the enzyme leakage from the large beads pores (cut off of about 100 kDa). Please click Additional Files below to see the full abstract

On the stability of metal nanoparticles synthesized by laser ablation in liquids

Nanoparticles (NPs) synthesized through chemical routes are stabilized by a surface layer of capping agents. These molecules, beside avoid the infinite growth of the solid phase, impart steric or electrostatic repulsive inter- particle interactions. The technique known as “Laser ablation in liquid” (LAL) is an alternative technique to synthesize capping agents-free metal nanoparticles.1 LAL involves focused laser pulsed irradiation of a bulk metal target in a liquid and consist of four stages . Laser-matter interaction, plasma induction, cavitation bubble formation and particle release in solution. Strikingly, LAL leads to the formation of very stable “naked” NPs that are long standing for months. It is worth emphasizing that the stabilization of noble metal colloids in water is challenging because of the large Hamaker constant. Noble metal NPs prepared by LAL have a large negative zeta-potential and therefore their stability should be electrostatic in nature and it is due to the presence negative surface charges. The question is what is the origin of these surface charges? Common explanations for this phenomenon involve the presence of gold oxides and/or the anion adsorption.2, 3 However, the presence of oxidized gold species on the surface of NPs prepared in water has been recently questioned on the basis of XPS analysis.4 Very recently we have accumulated evidences that, in the case of gold NPs prepared by LAL, the metal oxidation and anion adsorptions have only a minor role on building the negative surface potential and we proposed that excess electrons formed within the plasma phase could charge the gold particles.5 The figure below describes an experiment that points in this direction: the addition of macroscopic metallic objects induce the loss of charge (as seen in the temporal evolution of the zeta-potential) and eventually NPs aggregation pnly the case of gold NP synthesized by LAL while it is ineffective in the case of NP synthesized by the classical Turkevitch chemical reduction of HAuCl4 reduction (see the picture of the cuvettes after 4 days). Please click Additional Files below to see the full abstract

Probing light-induced conformational transitions in bacterial photosynthetic reaction centers embedded in trehalose–water amorphous matrices

AbstractThe coupling between electron transfer and protein dynamics has been studied in photosynthetic reaction centers (RC) from Rhodobacter sphaeroides by embedding the protein into room temperature solid trehalose–water matrices. Electron transfer kinetics from the primary quinone acceptor (QA−) to the photoxidized donor (P+) were measured as a function of the duration of photoexcitation from 20 ns (laser flash) to more than 1 min. Decreasing the water content of the matrix down to ≈5×103 water molecules per RC causes a reversible four-times acceleration of P+QA− recombination after the laser pulse. By comparing the broadly distributed kinetics observed under these conditions with the ones measured in glycerol–water mixtures at cryogenic temperatures, we conclude that RC relaxation from the dark-adapted to the light-adapted state and thermal fluctuations among conformational substates are hindered in the room temperature matrix over the time scale of tens of milliseconds. When the duration of photoexcitation is increased from a few milliseconds to the second time scale, recombination kinetics of P+QA− slows down progressively and becomes less distributed, indicating that even in the driest matrices, during continuous illumination, the RC is gaining a limited conformational freedom that results in partial stabilization of P+QA−. This behavior is consistent with a tight structural and dynamical coupling between the protein surface and the trehalose–water matrix