Quantitative Analysis of the Interactions of Metal Complexes and Amphiphilic Systems: Calorimetric, Spectroscopic and Theoretical Aspects

Metals and metal-based compounds have many implications in biological systems. They are involved in cellular functions, employed in the formation of metal-based drugs and present as pollutants in aqueous systems, with toxic effects for living organisms. Amphiphilic molecules also play important roles in the above bio-related fields as models of membranes, nanocarriers for drug delivery and bioremediating agents. Despite the interest in complex systems involving both metal species and surfactant aggregates, there is still insufficient knowledge regarding the quantitative aspects at the basis of their binding interactions, which are crucial for extensive comprehension of their behavior in solution. Only a few papers have reported quantitative analyses of the thermodynamic, kinetic, speciation and binding features of metal-based compounds and amphiphilic aggregates, and no literature review has yet addressed the quantitative study of these complexes. Here, we summarize and critically discuss the recent contributions to the quantitative investigation of the interactions of metal-based systems with assemblies made of amphiphilic molecules by calorimetric, spectrophotometric and computational techniques, emphasizing the unique picture and parameters that such an analytical approach may provide, to support a deep understanding and beneficial use of these systems for several applications.

Purification of proteins with native terminal sequences using a Ni(II)-cleavable C-terminal hexahistidine affinity tag

The role of the termini of protein sequences is often perturbed by remnant amino acids after the specific protease cleavage of the affinity tags and/or by the amino acids encoded by the plasmid at/around the restriction enzyme sites used to insert the genes. Here we describe a method for affinity purification of a metallonuclease with its precisely determined native termini. First, the gene encoding the target protein is inserted into a newly designed cloning site, which contains two self-eliminating BsmBI restriction enzyme sites. As a consequence, the engineered DNA code of Ni(II)-sensitive Ser-X-His-X motif is fused to the 3'-end of the inserted gene followed by the gene of an affinity tag for protein purification purpose. The C-terminal segment starting from Ser mentioned above is cleaved off from purified protein by a Ni(II)-induced protease-like action. The success of the purification and cleavage was confirmed by gel electrophoresis and mass spectrometry, while structural integrity of the purified protein was checked by circular dichroism spectroscopy. Our new protein expression DNA construct is an advantageous tool for protein purification, when the complete removal of affinity or other tags, without any remaining amino acid residue is essential. The described procedure can easily be generalized and combined with various affinity tags at the C-terminus for chromatographic applications.

Influence of Micellar Media on Extraction of Copper(II) from Sulphate and Chloride Solutions using an N,N′-Bis(salicylideneaminoethyl)amine Multidentate Schiff Base

The extraction properties of several organic ligands in micellar media have been investigated. In this paper, the extraction behavior of Schiff base ligand N,N′-bis(salicylideneaminoethyl)amine (H2SALDIEN) in the presence and absence of ionic surfactants in concentrated sulphate and chloride media has been studied. The physicochemical properties of H2SALDIEN, namely acidity, distribution, and extraction power were determined in pure water-chloroforme mixture (50 : 50) and in presence of sodium dodecyl sulphate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles and were compared. The best distribution of H2SALDIEN occurs at low acidity and at high concentrations of SDS. Conversely, in the case of CTAB the best distribution is observed at low concentrations of surfactant and at the lowest acidity. The recovery of copper(II) from highly concentrated sulphate and chloride solutions was shown to be exalted with synergistic SDS- and CTAB-H2SALDIEN micellar mixtures using solvent extraction technique. Generally, the synergistic extraction seems to be more pronounced in presence of SDS compared with CTAB in both chloride and sulphate media.

Ionic liquids as modulators of physicochemical properties and nanostructures of sodium dodecyl sulfate in aqueous solutions and potential application in pesticide microemulsions

The change of morphology of ILs/SDS aggregates with increased concentration of ILs.

Acid-responsive nanospheres from an asparagine-derived amphiphile

We describe the synthesis and self-assembly of an asparagine-derived amphiphile. The self-assembled systems formulated with the inclusion of cholesterol (0-50 mol%) show encapsulation for a hydrophobic model drug and rapidly disintegrate in response to mild acidic conditions.