Concentrated suspensions of Brownian beads in water: dynamic heterogeneities through a simple experimental technique

Concentrated suspensions of Brownian hard-spheres in water are an epitome for understanding the glassy dynamics of both soft materials and supercooled molecular liquids. From an experimental point of view, such systems are especially suited to perform particle tracking easily, and, therefore, are a benchmark for novel optical techniques, applicable when primary particles cannot be resolved. Differential variance analysis(DVA) is one such novel technique that simplifies significantly the characterization of structural relaxation processes of soft glassy materials, since it is directly applicable to digital image sequences of the sample. DVA succeeds in monitoring not only the average dynamics, but also its spatio-temporal fluctuations, known as dynamic heterogeneities. In this work, we study the dynamics of dense suspensions of Brownian beads in water, imaged through digital video-microscopy, by using both DVA and single-particle tracking. We focus on two commonly used signatures of dynamic heterogeneities: the dynamic susceptibility, χ_4, and the non-Gaussian parameter, α_2. By direct comparison of these two quantities,we are able to highlight similarities and differences. We do confirm that χ_4 and α_2 provide qualitatively similar information, but we find quantitative discrepancies in the scalings of characteristic time and length scale on approaching the glass transition.     

Degradation kinetic (D100) of lycopene during the thermal treatment of concentrated tomato paste

Heat treatments can cause degradation in tomatoes of lycopene which has important antioxidant effects. No information about decimal reduction time (D₁₀₀) of lycopene is available. D-value is the time required at a given temperature to reduce 90% of the molecule. This study for the first time determine the kinetic of lycopene thermal degradation. The content was measured at regular intervals of pasteurization using canned tomato paste to determinate D value. Microbiological analysis was carried out to verify product stability after packaging. Yeasts, molds and lactic acid bacteria were determined. The pasteurization time allowed to observe a loss of the red color. Lycopene content, after an increase at 8 min, decreased at 32 min of pasteurization. D₁₀₀ value was calculated at 75 min; a diminution of 90% in lycopene content in the concentrated tomato paste was observed. Microbiological analysis confirmed the stability of products after 8 min of pasteurization.     

Content of micronutrients,mineral and trace elements in some Mediterranean spontaneous edible herbs

Background

The analysis of mineral elements composition was determined in three wild edible herbs (Cichorium intybus L., Sonchus asper L. and Borago officinalis) collected in seven different sampling sites which were characterized by different pollution grade. The detection of mineral elements (Ca, K, Mg and Na), micronutrients (Cu, Fe, Li, Mn and Zn) and heavy metals (As, Cd, Hg, Ni and Pb) was performed.

Results

The results obtained show that in most cases a direct relationship appeared between the amount of elements and the sampling sites. The highest concentrations of heavy metals were found in samples grown in polluted soils. These evaluations showed that contaminants in plants may reflect the environmental state in which they develop.

Conclusion

The examined species are a good source of mineral elements and micronutrients, making them particularly adapt to integrate a well-balanced diet. The accumulation of heavy metals showed that contaminants in plants may reflect the environmental state in which they develop. Results showed high concentrations of heavy metals in samples taken in locations characterized by high human activity and in some samples from the local market, of which no one knows the collection area.

     

Fibrillation of β-lactoglobulin at low pH in the presence of a complexing anionic polysaccharide

The influence of electrostatic complexation with κ-carrageenan was tested on the fibrillation process of β-lactoglobulin at pH 2.0. Morphology and structural development were monitored through cross correlation dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Scattering indicated that noncomplexed β-lactoglobulin monomers aggregated to form fibrils after 15-90 min of heating at 90 °C. However, electrostatic protein-carrageenan complexes found in the unheated system were unchanged by the thermal process. Images and scattering results showed that carrageenan complexes slowed fibrillation kinetics, possibly through reduction in available monomer concentration. Complexes adhered to fibrils at ends and junctions in TEM images, indicating interactive affinity with the fibers, presumably as heterogeneous nucleation sites.     

Spray-dried oil powder with ultrahigh oil content

We report a new facile route to the production of solid oil powders with an oil weight content of as high as 90% or beyond. The proposed method starts from a standard protein-stabilized oil-in-water emulsion in which a protein monolayer absorbed at the oil-water interface is successively cross linked by a thermal treatment. The emulsion is then spray dried as for ordinary emulsions, however without the addition of hydrocolloids typically needed when spray drying liquid oil dispersions. This leads to a final solid oil powder in which the total mass is constituted of oil, proteins, and eventual buffer salts and in which the elasticity of the cross-linked protein monolayer is alone sufficient to stabilize the powder and to limit any oil leakage. To best illustrate the potential in food applications and to preserve the food-grade nature of the constituents, we have used thermal denaturation at 80 °C for 15 min to cross link a β-lactoglobulin-stabilized olive oil-in-water emulsion and to produce the corresponding solid oil powder. Because of the simplicity and flexibility of the proposed pathway, the present method can be used inexpensively to convert any type of hydrophobic liquid into the corresponding solid powder and is then particularly suitable for cosmetic, pharmaceutical, medical, biotechnological, and food applications.     

A Doppel α‐Helix Peptide Fragment Mimics the Copper(II) Interactions with the Whole Protein

The doppel protein (Dpl) is the first homologue of the prion protein (PrP^C) to be discovered; it is overexpressed in transgenic mice that lack the prion gene, resulting in neurotoxicity. The whole prion protein is able to inhibit Dpl neurotoxicity, and its N‐terminal domain is the determinant part of the protein function. This region represents the main copper(II) binding site of PrP^C. Dpl is able to bind at least one copper ion, and the specific metal‐binding site has been identified as the histidine residue at the beginning of the third helical region. However, a reliable characterization of copper(II) coordination features has not been reported. In a previous paper, we studied the copper(II) interaction with a peptide that encompasses only the loop region potentially involved in metal binding. Nevertheless, we did not find a complete match between the EPR spectroscopic parameters of the copper(II) complexes formed with the synthesized peptide and those reported for the copper(II) binding sites of the whole protein. Herein, the synthesis of the human Dpl peptide fragment hDpl(122–139) (Ac‐KPDNKLHQQVLWRLVQEL‐NH₂) and its copper(II) complex species are reported. This peptide encompasses the third α helix and part of the loop linking the second and the third helix of human doppel protein. The single‐point‐mutated peptide, hDpl(122–139)D124N, in which aspartate 124 replaces an asparagine residue, was also synthesized. This peptide was used to highlight the role of the carboxylate group on both the conformation preference of the Dpl fragment and its copper(II) coordination features. NMR spectroscopic measurements show that the hDpl(122–139) peptide fragment is in the prevailing α‐helix conformation. It is localized within the 127–137 amino acid residue region that represents a reliable conformational mimic of the related protein domain. A comparison with the single‐point‐mutated hDpl(122–139)D124N reveals the significant role played by the aspartic residue in addressing the peptide conformation towards a helical structure. It is further confirmed by CD measurements. Potentiometric titrations were carried out in aqueous solutions to obtain the stability constant values of the species formed by copper(II) with the hDpl peptides. Spectroscopic studies (EPR, NMR, CD, UV/Vis) were performed to characterize the coordination environments of the different metal complexes. The EPR parameters of the copper(II) complexes with hDpl(122–139) match those of the previously reported copper(II) binding sites of the whole hDpl. Addition of the copper(II) ion to the peptide fragment does not alter the helical conformation of hDpl(122–139), as shown by CD spectra in the far‐UV region. The aspartate‐driven preorganized secondary structure is not significantly modified by the involvement of Asp124 in the copper(II) complex species that form in the physiological pH range. To elaborate on the potential role of copper(II) in the recently reported interaction between the PrP^C and Dpl, the affinity of the copper(II) complexes towards the prion N terminus domain and the binding site of Dpl was reported.     

Copper(II) complex formation with a linear peptide encompassing the putative cell binding site of angiogenin

Angiogenin is one of the more potent angiogenic factors known, whose activity may be affected by the presence of copper ions. Copper(II) complexes with the peptides encompassing the putative endothelial cell binding domain of angiogenin, Ac-KNGNPHREN-NH(2) and Ac-PHREN-NH(2), have been characterized by potentiometric, UV-vis, CD and EPR spectroscopic methods. The coordination features of all the copper complex species derived by both peptides are practically the same, as predictable because of the presence of a proline residue within their aminoacidic sequence. In particular, Ac-PHREN-NH(2) is really the aminoacidic sequence involved in the binding to copper(II). Thermodynamic and spectroscopic evidence are given that side chain oxygen donor atom of glutamyl residue is involved in the copper binding up to physiological pH. EPR parameters suggest that the carboxylate group is still involved also in the predominant species [Cu(L)H(-2)], the metal coordination environment being probably formed by N(Im), 2N(-), H(2)O in equatorial plane and an oxygen atom from COO(-) in apical position, or vice versa, with the carboxylate oxygen atom in the copper coordination plane and the water molecule confined to one of the apical positions. Moreover, the comparison with the thermodynamic and spectroscopic results in the case of the copper(ii) complex species formed by the single point mutated peptide, Ac-PHRQN-NH(2), provides further evidence of the presence of carboxylate oxygen atom in the copper coordination sphere.     

A-priori bounds and asymptotics on the eigenvalues in bifurcation problems for perturbed self-adjoint operators

We prove upper and lower bounds on the eigenvalues and discuss their asymptotic behaviour (as the norm of the eigenvector tends to zero) in bifurcation problems from the line of trivial solutions, considering perturbations of linear self-adjoint operators in a Hilbert space. The proofs are based on the Lyapounov-Schmidt reduction. The results are applied to a class of semilinear elliptic operators in bounded domains of RN and in particular to Sturm-Liouville operators.     

Learning to signal: Analysis of a micro-level reinforcement model

We consider the following signaling game. Nature plays first from the set {1,2}$\{1,2\}$. Player 1 (the Sender) sees this and plays from the set {A,B}$\{A,B\}$. Player 2 (the Receiver) sees only Player 1’s play and plays from the set {1,2}$\{1,2\}$. Both players win if Player 2’s play equals Nature’s play and lose otherwise. Players are told whether they have won or lost, and the game is repeated. An urn scheme for learning coordination in this game is as follows. Each node of the decision tree for Players 1 and 2 contains an urn with balls of two colors for the two possible decisions. Players make decisions by drawing from the appropriate urns. After a win, each ball that was drawn is reinforced by adding another of the same color to the urn. A number of equilibria are possible for this game other than the optimal ones. However, we show that the urn scheme achieves asymptotically optimal coordination.     

One- and two-photon absorption and emission properties of a Zn(II) chemosensor

This paper presents the synthesis and two photon-induced absorption (TPA) properties of a functionalized distyrylbenzene (DSB) 1 containing a tetra-azacyclododecane (cyclen) receptor for Zn(II). The influence of Zn(II) on one- and two-photon absorption characteristics of 1 has been investigated in dimethyl sulfoxide. The experiments show that the TPA action spectrum of uncomplexed 1, at 750 nm employing nanosecond-long excitation pulses, is 5 times more intense than that of the complexed form. This moderate contrast between the bound and unbound species confirms, however, the potential of this design scheme for the development of molecular structures with enhanced sensitivity and contrast to be used as Zn(II) sensors through TPA-induced fluorescence microscopy.