Francesco Mantegazza

An extended Maxwell-Wagner theory for the electric birefringence of charged colloids

Recent frequency resolved electric birefringence experiments on dilute suspensions of charged, ellipsoidal particles reveal new relaxation features in the MHz frequency range. Such behavior can be explained in terms of surface transport processes. Here we develop a model for the electric polarizability of spheroidal particles by combining features of electrokinetic and Maxwell–Wagner theories. The model accurately depicts the high frequency features and relates them to the colloidal properties of the polyelectrolyte. Using the model, particle charge can be extracted from electric birefringence measurements.

Ions Transport and Adsorption Mechanisms in Porous Electrodes During Capacitive-Mixing Double Layer Expansion (CDLE)

A model of the electro-diffusion of ions in porous electrodes is applied to analyze the dynamics of capacitive-mixing extraction of energy from salinity gradients with carbon porous electrodes. The complex time-evolution of the cell voltage observed in experiments is satisfactorily described. The asymmetry on the duration of the solution-change steps performed in open circuit is found to be due to the nonlinear voltage–concentration relationship of the electric double layers and to a current that redistributes the counterions along the depth of the electrode leading to nonuniform charge and salt adsorption. The validated model is an essential tool for the design and optimization of renewable energy extraction by this technique.

New method based on capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) to monitor interaction between nanoparticles and the amyloid-β peptide.

A novel application of capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was proposed to efficiently detect and monitor the interaction between polymeric nanoparticles and the β-Amyloid peptide (Aβ(1-42)), a biomarker for Alzheimers Disease (AD), at concentrations close to physiological conditions. The CE-LIF method allowed the interaction between PEGylated poly(alkyl cyanoacrylate) nanoparticles (NPs) and the soluble Aβ(1-42) peptide monomers to be highlighted. These results were confirmed by surface plasmon resonance (SPR) and confocal laser scanning microscopy (CLSM). Whereas SPR showed an interaction between the NPs and the Aβ(1-42) peptide, CLSM allowed the formation of large aggregates/assemblies at high NP and peptide concentrations to be visualized. All these results suggested that these nanoparticles could bind the Aβ(1-42) peptide and influence its aggregation kinetics. Interestingly, the non-PEGylated poly(alkyl cyanoacrylate) NPs did not alter the aggregation kinetics of the Aβ(1-42) peptide, thus emphasizing the high level of discrimination of the CE-LIF method with respect to NPs.

Respiratory Electrodialysis. A Novel, Highly Efficient Extracorporeal CO2 Removal Technique

RATIONALE We developed an innovative, minimally invasive, highly efficient extracorporeal CO2 removal (ECCO2R) technique called respiratory electrodialysis (R-ED). OBJECTIVES To evaluate the efficacy of R-ED in controlling ventilation compared with conventional ECCO2R technology. METHODS Five mechanically ventilated swine were connected to a custom-made circuit optimized for R-ED, consisting of a hemofilter, a membrane lung, and an electrodialysis cell. Electrodialysis regionally modulates blood electrolyte concentration to convert bicarbonate to CO2 before entering the membrane lung, enhancing membrane lung CO2 extraction. All animals underwent three repeated experimental sequences, consisting of four steps: baseline (1 h), conventional ECCO2R (2 h), R-ED (2 h), and final NO-ECCO2R (1 h). Blood and gas flow were 250 ml/min and 10 L/min, respectively. Tidal volume was set at 8 ml/kg, and respiratory rate was adjusted to maintain arterial Pco2 at 50 mm Hg. MEASUREMENTS AND MAIN RESULTS During R-ED, chloride and H(+) concentration increased in blood entering the membrane lung, almost doubling CO2 extraction compared with ECCO2R (112 ± 6 vs. 64 ± 5 ml/min, P < 0.001). Compared with baseline, R-ED and ECCO2R reduced minute ventilation by 50% and 27%, respectively. Systemic arterial gas analyses remained stable during the experimental phases. No major complication occurred, but there was an increase in creatinine level. CONCLUSIONS In this first in vivo application, we proved electrodialysis feasible and effective in increasing membrane lung CO2 extraction. R-ED was more effective than conventional ECCO2R technology in controlling ventilation. Further studies are warranted to assess the safety profile of R-ED, especially regarding kidney function.

Atomic force microscopy study of DNA conformation in the presence of drugs

Binding of ligands to DNA gives rise to several relevant biological and biomedical effects. Here, through the use of atomic force microscopy (AFM), we studied the consequences of drug binding on the morphology of single DNA molecules. In particular, we quantitatively analyzed the effects of three different DNA-binding molecules (doxorubicin, ethidium bromide, and netropsin) that exert various pharmacologic and therapeutic effects. The results of this study show the consequences of intercalation and groove molecular binding on DNA conformation. These single-molecule measurements demonstrate morphological features that reflect the specific modes of drug–DNA interaction. This experimental approach may have implications in the design of therapeutically effective agents.

Magnetic tweezers measurements of the nanomechanical properties of DNA in the presence of drugs

Herein, we study the nanomechanical characteristics of single DNA molecules in the presence of DNA binders, including intercalating agents (ethidium bromide and doxorubicin), a minor groove binder (netropsin) and a typical alkylating damaging agent (cisplatin). We have used magnetic tweezers manipulation techniques, which allow us to measure the contour and persistence lengths together with the bending and torsional properties of DNA. For each drug, the specific variations of the nanomechanical properties induced in the DNA have been compared. We observed that the presence of drugs causes a specific variation in the DNA extension, a shift in the natural twist and a modification of bending dependence on the imposed twist. By introducing a naive model, we have justified an anomalous correlation of torsion data observed in the presence of intercalators. Finally, a data analysis criterion for discriminating between different molecular interactions among DNA and drugs has been suggested.

Electrokinetic properties of colloids of variable charge. III. Observation of a Maxwell–Wagner relaxation mechanism by high-frequency electric-birefringence spectroscopy

Frequency resolved electric birefringence measurements were made on dilute aqueous suspensions of charged, rodlike latex particles. Ionic amphiphile adsorption was used to vary the particle charge as described in the first paper of this series [J. Chem. Phys. 103, 8228 (1995)]. Using the high frequency part of the birefringence spectra, the electric polarizability is computed from the Kerr constant following the approach set out in the second paper of the series [J. Chem. Phys. 109, 6905 (1998)]. Then, the polarizability spectra were interpreted with our extended Maxwell–Wagner model [J. Chem. Phys. 113, 6974 (2000), preceding paper]. Theory and experiment are in good agreement. The procedure provides a new and simple way to extract the particle charge from birefringence data.

Magnetic tweezers measurements of the nanomechanical stability of DNA against denaturation at various conditions of pH and ionic strength

The opening of DNA double strands is extremely relevant to several biological functions, such as replication and transcription or binding of specific proteins. Such opening phenomenon is particularly sensitive to the aqueous solvent conditions in which the DNA molecule is dispersed, as it can be observed by considering the classical dependence of DNA melting temperature on pH and salt concentration. In the present work, we report a single-molecule study of the stability of DNA against denaturation when subjected to changes in solvent. We investigated the appearance of DNA instability under specific external applied force and imposed twist values, which was revealed by an increase in the temporal fluctuations in the DNA extension. These fluctuations occur in the presence of a continuous interval of equilibrium states, ranging from a plectonemic state to a state characterized by denaturation bubbles. In particular, we observe the fluctuations only around a characteristic force value. Moreover, this characteristic force is demonstrated to be notably sensitive to variations in the pH and ionic strength. Finally, an extension of a theoretical model of plectoneme formation is used to estimate the average denaturation energy, which is found to be linearly correlated to the melting temperature of the DNA double strands.

Transient Electric Birefringence Measurement of the Persistence Length of Sodium Polystyrene Sulfonate

The persistence length Lp of a flexible polyelectrolyte, sodium polystyrene sulfonate, is measured at very low concentration and ionic strength by transient electric birefringence. The data show that the persistence length reaches, at very low ionic strength, a limiting value which depends on the extended chain length L, but is much shorter than L. The results are not in agreement with the available theoretical predictions.

Electrokinetic properties of colloids of variable charge. I. Electrophoretic and electro‐optic characterization

We present an experimental study of the electrokinetic properties of a model colloidal system in which the number of ionizable sites per particle is controlled by exploiting the competitive adsorption between a ionic and a nonionic amphiphile. The adsorption of the nonionic amphiphile is monitored by light scattering. By measuring the electrophoretic mobility, we obtain the zeta‐potential ζ of the particles. We find that ζ is independent from the ionic strength and strongly dependent on the surface density of ionizable sites. This indicates that in our system we can separately control zeta potential and ionic strength. In the investigated range of ionic strength and particle concentration, the Kerr constant of the dispersion is found to be proportional to the particle concentration, and does not contain any significant collective effect.