Does cation dehydration drive the binding of metal ions to polyelectrolytes in water? What we can learn from the behaviour of aluminium(III) and chromium(III)

Much stronger binding is seen in aqueous solutions between the anionic polyelectrolyte potassium poly(vinyl sulfate) and the substitution labile aluminium(III) than with the kinetically inert chromium(III). This strongly supports the idea that entropy driven water loss from the hydration sphere of the metal ion plays a major role in driving binding of the trivalent metal ion to the polyelectrolyte.

Gel network photodisruption: a new strategy for the codelivery of plasmid DNA and drugs

In the last 5 years, we have gained further insight on the physical/chemical field of DNA gels. Our expertise on the gel swelling behavior, compaction of DNA by cationic entities, as lipids and surfactants, as well as on the assembly structures of these complexes allow us for the development of novel systems to be used in a variety of biomedical applications. In our previous reports, the physicochemical characterization has been well-established, and now one can evolve to the challenge of using DNA-based carriers in the biological area. Moreover, a new plasmid DNA (pDNA) hydrogel that is porous, is able to swell in the presence of additives, is biocompatible and, thus, is suitable to be used therapeutically was prepared. Here, the dual release of pDNA and solutes with pharmaceutical interest was the main challenge, and thus, we report on the photodisruption of plasmid DNA (pDNA) gels cross-linked with ethylene glycol diglycidyl ether (EGDE) as a strategy for this simultaneous release. The disruption over time, after the irradiation of the gel with ultraviolet light (400 nm), was characterized through the cumulative plasmid DNA release, the evolution in dry weight, the extent of swelling, and also the variations in the gel mesh size. The controlled release of different molecular weight solutes from plasmid DNA gels was investigated, and the influence of both the hydrogel degradation and cross-linker density on the release kinetics were addressed. While the release of lysozyme follows a Fickian process, the release of bovine serum albumin (BSA) and fluoresceinisothiocyanato-dextran (FITC-dextran) is characteristic of a Super Case II release phenomena. In addition, the size of the three solutes partially influences the release behavior; polymer chain mobility and the degree of swelling also play a role. To gain a fundamental understanding of drug release profile from pDNA matrices, in vitro release studies were evaluated using several anti-inflammatory drugs. The quantification of the release mechanism indicates a Super Case II release profile, which can be related with the gel swelling degree. A correlation between the drug release trend and the drug hydrophobicity can be found, with more hydrophobic drugs showing a slower release rate. In brief, this new pDNA gel system is biocompatible, is degradable upon light irradiation, and allows for the controlled and sustained release of plasmid DNA and incorporated solutes. This codelivery of pDNA and drugs would find relevant clinical uses due to the possibility of gene and nongene therapy combination in order to improve the therapeutic efficiency.

(S)-glutamic acid on Ag(100): self-assembly in the nonzwitterionic form

The fundamental understanding of adsorption and self-organization of biological molecules at surfaces is of greatest importance for a huge variety of possible applications, ranging from molecular electronics to the study of biocompatible materials, hygiene, and biofouling. In spite of that, the characterization of the interactions of organic molecules of biological interest with surfaces is far from being complete. In the present paper we report on a combined microscopic (scanning tunneling microscopy (STM)) and spectroscopic (X-ray photoemission spectroscopy and high-resolution electron energy loss spectroscopy) study of glutamic acid (Glu) adsorption and self-assembly on Ag(100) at different temperature. STM allows one to determine the structures of the Glu layers, for which empirical models are proposed, while photoemission spectra exclude adsorption in the zwitterionic form, which is the most common especially for weakly interacting substrates.

Biomolecule-biomaterial interaction: a DFT-D study of glycine adsorption and self-assembly on hydroxylated Cr2O3 surfaces

The adsorption of glycine, the building block of amino acids, on hydroxylated (0001)-Cr2O3 model surfaces, representing the stainless steel passive film surface, was modeled by means of the GGA + U method. The roles of glycine coverage and surface termination (hydroxylated Cr- and O-terminated surfaces) on the adsorption mode and self-assembly properties were explored. The hydroxylated Cr-terminated Cr2O3 surface, which presents two types of (H)OH groups exhibiting different acidic character, is more reactive than the hydroxylated O-terminated surface, where one single type of OH group is present, for all adsorption modes and coverages considered. Outer sphere adsorption occurs in the zwitterion form, stabilized at low coverage through H-bond formation with coadsorbed water molecules, and at the monolayer coverage by glycine self-assembling. The OH substitution by glycinate is favored on the hydroxylated Cr-terminated surface and not on the O-terminated one. The inclusion of dispersion forces does not change the observed tendencies. An atomistic thermodynamics approach suggests that outer sphere adsorption is thermodynamically favored over inner sphere adsorption in the whole domain of glycine concentration. The obtained SAM's free energies of formation are rationalized in a model considering the balance between sublimation and solvation free energies, and extrapolated to other amino acids, to predict the SAMs formation above hydroxylated surfaces. It is found that hydrophobic AA tend to self-assemble at the surface, whereas hydrophilic ones do not.

Molecular dynamics of an embedded-charge model of lysozyme aqueous solutions

The onset of liquid-vapor separation in an interaction site model of a lysozyme aqueous solution is investigated by means of molecular dynamics (MD). Calculations are performed for a soft-core version of a potential early introduced by Carlsson et al. (J. Phys. Chem. B 2001, 105, 9040; 2001, 105, 12189.) whose liquid-vapor coexistence was studied by Rosch and Errington (J. Phys. Chem. B 2007, 111, 12591.); our modified model preserves the tailoring onto the experimental lysozyme solution properties embodied by those descriptions. We first show that the structural results obtained by Carlsson et al. at ambient conditions are quite well reproduced by our approach. Then, we cool the system along an isochoric path by monitoring the structural and dynamical properties at various temperatures. We thus show that a fluid-fluid separation takes place at a temperature 15% below the presumed binodal; in particular, we observe that density inhomogeneities develop rather early in the MD run and evolve over tens of nanoseconds into two dense aggregates that eventually merge, after approximately 100 ns more, into a single liquid phase separated from a vapor region by a well-defined planar interface. The densities of the two coexisting fluids are compatible with previous determinations of the binodal line. The connections of this work to the overall scenario of phase stability investigations in protein solutions, as well as possible developments based on the use of more refined models, are discussed.

Swelling properties of cross-linked DNA gels

This work represents our contribution to the field of physical chemistry of DNA gels, and concerns the synthesis and study of novel chemically cross-linked DNA gels. The use of covalent DNA gels is a very promising way to study DNA-cosolute interactions, as well as the dynamic behaviour of DNA and cationic compacting agents, like lipids, surfactants and polycations. Manipulating DNA in new ways, like DNA networks, allows a better understanding and characterization of DNA-cosolute complexes at the molecular level, and also allows us to follow the assembly structures of these complexes. The use of responsive polymer gels for targeted delivery of toxic and/or labile drugs has, during the past few years, shown to be a promising concept. The features found in the proposed system would find applications in a broader field of gel/drug interaction, for the development of controlled release and targeted delivery devices.

Self-assembly of (S)-glutamic acid on Ag(100): a combined LT-STM and ab initio investigation

Self-assembly of organic molecules at metal surfaces is of greatest importance in nanoscience; in fact, it opens new perspectives in the field of molecular electronics and in the study of biocompatible materials. Combining an experimental low-temperature scanning tunneling microscopy investigation with ab initio calculations, we succeeded to describe in detail (S)-glutamic acid adsorption on Ag(100) at T = 350 K. We find that (S)-glutamic acid organizes in a squared structure and, at variance with the majority of cases reported in literature, it adsorbs in the neutral form, 4.6 A above the surface plane. The interaction with the poorly reactive Ag substrate is only due to weak van der Waals forces, while H-bonds between carboxyl groups and the formation of a OCOH-OCOH-OCOH-OCOH cycle at the vertex of the squares are the main responsible for the self-assembly.

Diffusion of Hydrides in Palladium Nanoclusters. A Ring-Polymer Molecular Dynamics Study of Quantum Finite Size Effects

The diffusion kinetics of hydrogen in bulk palladium and in Pd nanoclusters containing up to 512 atoms has been theoretically investigated at 3% loading using ring-polymer molecular dynamics simulations. The electronic ground-state energy surfaces are modeled using an explicit many-body potential fitted to reproduce the properties of bulk palladium and palladium hydrides. The diffusion constant, calculated by integration of the velocity autocorrelation function, shows Arrhenius behavior with inverse temperature. In addition, both the prefactor and activation energy are found to exhibit approximately linear variations with inverse cluster radius for sizes exceeding 128 Pd atoms. Vibrational delocalization generally enhances diffusion, this effect being stronger in clusters than in bulk. An inherent structure analysis from the positions of the centroids was used to characterize the diffusion mechanisms. Quantum effects lead to not only a higher coordination of hydrogen atoms both in bulk (fcc) palladium and in clusters but also favor further softening of the outer layers.