Characterization of white wines from north-eastern Italy with surface-enhanced Raman spectroscopy.

In the present study, label-free SERS spectroscopy is applied as a useful analytical technique for white wine characterization. 180 samples of three white wines varieties from northeastern Italy, Sauvignon Blanc, Ribolla Gialla and Friulano, collected from three different Italian producers from 2016 vintage, have been analyzed using Ag citrate-reduced colloids and a portable Raman instrument with a 785 nm laser. A PCA of SERS spectra showed that discrimination between wines and wineries is possible. Main spectral differences are due to adenine, carboxylic acids and glutathione, with their ratio changing among different wine types and producers. A robust version of the Soft Independent Modelling of Class Analogy (SIMCA) method was used to model the class space of each wine and to perform the classification among the different categories, yielding overall efficiencies between 87 and 93%. These results are extremely encouraging and open the way to the application of this SERS protocol as a wine identification assay.

Electrophoretic characterization of gold nanoparticles functionalized with human serum albumin (HSA) and creatine.

The synthesis of composite nanoparticles consisting of a gold core coated with a human serum albumin (HSA)/creatine layer is described, and their possible application as novel drug carriers for brain delivery is discussed. In this paper, the effect of the concentration of creatine and HSA in the different formulations is studied by electrophoretic mobility measurements as a function of pH and ionic strength. Due to the permeable character of the coatings surrounding the gold cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed on the basis of three theoretical models of the electrokinetics of soft particles. As a result, information is obtained on both the surface potential and the charge density of the surrounding layer. The three models used reproduce properly the experimental behavior, although Duval and Ohshima's calculations appear to yield a more accurate fit of the data. It is shown that the albumin/nanogold particles absorb large amounts of creatine. In addition, the low surface charge and the albumin layer are expected to make it possible to deliver the particles through the blood-brain barrier.

Efficient synthesis and comparative studies of the arginine and Nomega,Nomega-dimethylarginine forms of the human nucleolin glycine/arginine rich domain.

The Gly- and Arg-rich C-terminal region of human nucleolin is a 61-residue long domain involved in a number of protein-protein and protein-nucleic acid interactions. This domain contains 10 aDma residues in the form of aDma-GG repeats interspersed with Phe residues. The exact role of Arg dimethylation is not known, partly because of the lack of efficient synthetic methods. This work describes an effective synthetic strategy, generally applicable to long RGG peptides, based on side-chain protected aDma and backbone protected dipeptide Fmoc-Gly-(Dmob)Gly-OH. This strategy allowed us to synthesize both the unmodified (N61Arg) and the dimethylated (N61aDma) peptides with high yield ( approximately 26%) and purity. As detected by NMR spectroscopy, N61Arg does not possess any stable secondary or tertiary structure in solution and N(omega),N(omega)-dimethylation of the guanidino group does not alter the overall conformational propensity of this peptide. While both peptides bind single-stranded nucleic acids with similar affinities (K(d) = 1.5 x 10(-7) M), they exhibit a different behaviour in ssDNA affinity chromatography consistent with the difference in pK(a) values. It has been previously shown that N61Arg inhibits HIV infection at the stage of HIV attachment to cells. This study demonstrates that Arg-dimethylated C-terminal domain lacks any inhibition activity, raising the question of whether nucleolin expressed on the cell-surface is indeed dimethylated.

Folding of epidermal growth factor-like repeats from human tenascin studied through a sequence frame-shift approach.

In order to investigate the factors that determine the correct folding of epidermal growth factor-like (EGF) repeats within a multidomain protein, we prepared a series of six peptides that, taken together, span the sequence of two EGF repeats of human tenascin, a large protein from the extracellular matrix. The peptides were selected by sliding a window of the average length of tenascin EGF repeats over the sequence of EGF repeats 13 and 14. We thus obtained six peptides, EGF-f1 to EGF-f6, that are 33 residues long, contain six cysteines each, and bear a partial overlap in the sequence. While EGF-f1 corresponds to the native EGF-14 repeat, the others are frame-shifted EGF repeats. We carried out the oxidative folding of these peptides in vitro, analyzed the reaction mixtures by acid trapping followed by LC-MS, and isolated some of the resulting products. The oxidative folding of the native EGF-14 peptide is fast, produces a single three-disulfide species with an EGF-like disulfide topology and a marked difference in the RP-HPLC retention time compared with the starting product. On the contrary, frame-shifted peptides fold more slowly and give mixtures of three-disulfide species displaying RP-HPLC retention times that are closer to those of the reduced peptides. In contrast to the native EGF-14, the three-disulfide products that could be isolated are mainly unstructured, as determined by CD and NMR spectroscopy. We conclude that both kinetics and thermodynamics drive the correct pairing of cysteines, and speculate about how cysteine mispairing could trigger disulfide reshuffling in vivo.