Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited

Water activity and its relationship with interactions stabilising lamellar stacks of mixed lipid bilayers in their fluid state are investigated by means of osmotic pressure measurements coupled with small-angle x-ray scattering. The (electrically-neutral) bilayers are composed of a mixture in various proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. For highly dehydrated samples the osmotic pressure profile always exhibits the "classical" exponential decay as hydration increases but, depending on Simulsol to lecithin ratio, it becomes either of the "bound" or "unbound" types for more water-swollen systems. A simple thermodynamic model is used for interpreting the results without resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European Physical Journal

Self-assembled gold nanoparticles and amphiphile peptides: a colorimetric probe for copper(ii) ion detection

Morphological, spectroscopic and scattering studies of the self-assembly and aggregation process of hybrids containing gold nanoparticles (AuNPs) and the amyloid peptides [RF]4 and P[RF]4 (where R = arginine; F = phenylalanine; P = proline) in aqueous solution were performed. Two methodologies were tested for the AuNP nucleation, using sodium borohydride (NaBH4) or epigallocatechin gallate (EGCG) as a reducing agent. This led to remarkable distinct modes of assembly, AuNP decorated fibrils with NaBH4 reduction or isolated AuNPs with EGCG reduction. For both methodologies, the presence of spherical AuNPs was observed by plasmonic resonance bands in absorption spectra at ∼520 nm. Zeta potential measurements confirmed stable systems, with a similar aggregation state. Circular dichroism spectra revealed an antiparallel β-sheet conformation of the peptides. The transmission electron microscopy (TEM) images showed the coexistence of nanometer fibers and globular nanoparticles with 20 nm size. The small-angle X-ray scattering (SAXS) results show that the NaBH4 systems presented large cylindrical structures, while with increasing P[RF]4 content, a decrease in radius was observed. However, the EGCG-AuNPs were characterized by spherical particles, with a radius of 10–20 nm. Also, the colorimetric efficiency of the hybrids in the capture of Cu2+ ions in solution was monitored. Raman spectroscopy data confirmed the conformation/structure of self-assembled samples. Moreover, there are indications for a surface-enhanced Raman spectroscopy (SERS) effect for Cu2+ sites. The set of results indicates that these systems could act as a promising sensitive metal concentration probes

Hierarchical Self-Assembly of Peptides and its Applications in Bionanotechnology

Self-assembled structures obtained from organic molecules have shown great potential for applications in a wide range of domains. In this context, short peptides prove to be a particularly versatile class of organic building blocks for self-assembled materials. These species afford the biocompatibility and polymorphic richness typical of proteins while allowing synthetic availability and robustness typical of smaller molecules. At the nano-to-mesoscale, the architectures obtained from peptide units exhibit stability and a large variety of morphologies, the most common of which are nanotubes, nanoribbons, and nanowires. This review describes the formation of peptide-based self-assembled structures triggered by different stimuli (e.g., ionic strength, pH, and polarity), and the interactions that drive the assembling processes. It is surveyed how judicious molecular design is exploited to impart favourable assembling properties to afford systems with desired characteristics. A large body of literature provides the experimental and in silico data to predict self-assembly in a given peptide system and obtain different supramolecular organizations for applications in a wide range of fields, from transport to sensing, from catalysis to drug delivery and tissue regeneration

Amyloid formation by short peptides in the presence of dipalmitoylphosphatidylcholine membranes

The aggregation of two short peptides, [RF] and [RF]4 (where R = arginine and F = phenylalanine), at dipalmitoylphosphatidylcholine (DPPC) model membranes was investigated at the air–water interface using the Langmuir technique and vesicles in aqueous solutions. The molar ratio of the peptide and lipid components was varied to provide insights into the peptide–membrane interactions, which might be related to their cytotoxicity. Both peptides exhibited affinity to the DPPC membrane interface and rapidly adopted β-sheet-rich structures upon adsorption onto the surface of the zwitterionic membrane. Results from adsorption isotherm and small-angle X-ray scattering experiments showed changes in the structural and thermodynamic parameters of the membrane with increasing peptide concentration. Using atomic force microscopy, we showed the appearance of pores through the bilayer membranes and peptide aggregation at different interfaces, suggesting that the hydrophobic residues might have an effect on both pore size and layer structure, facilitating the membrane disruption and leading to different cytotoxicity effects

Interaction between glyphosate pesticide and amphiphilic peptides for colorimetric analysis

The large-scale use of glyphosate pesticides in food production has attracted attention due to environmental damage and toxicity risks. Several regulatory authorities have established safe limits or concentrations of these pesticides in water and various food products consumed daily. The irreversible inhibition of acetylcholinesterase (AChE) activity is one of the strategies used for pesticide detection. Herein, we found that lipopeptide sequences can act as biomimetic microenvironments of the AChE, showing higher catalytic activities than natural enzymes in an aqueous solution, based on IC50 values. These biomolecules contain in the hydrophilic part the amino acids L-proline (P), L-arginine (R), L-tryptophan (W), and L-glycine (G), covalently linked to a hydrophobic part formed by one or two long aliphatic chains. The obtained materials are referred to as compounds 1 and 2, respectively. According to fluorescence assays, the system composed only by 2 is more hydrophobic than the other composed only by 1. The circular dichroism (CD) data present a significant difference in the ellipsometry values, likely related to distinct conformations assumed by the proline residue in the lipopeptides' supramolecular structure in solution. The morphological aspect was further characterized using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-TEM), which showed the compounds 1 and 2 self-assembly into cylindrical and planar core-shell structures, respectively. The mimetic AchE behavior of lipopeptides was confirmed by Ellman’s hydrolysis reaction, where the proline content of the peptides acts as nucleophilic scavengers of organophosphate pesticides. Moreover, the isothermal titration calorimetry (ITC) experiments revealed that host-guest interactions in both systems were dominated by enthalpically-driven thermodynamics. The UV-Vis kinetic experiments were performed to assess the inhibition of the lipopeptide catalytic activity and the IC50 values, where we found that the detection limit correlated with the increase in hydrophobicity of the lipopeptides, implying the micellization process to be more favorable

A biophysical study of DNA condensation mediated by histones and protamines

The compaction of long DNA strands into confined spaces such as the nuclei of eukaryotic cells is an essential phenomenon towards the emergence of elaborated forms of life. Histones and protamines are the major nucleoproteins involved in this task participating in the formation of chromatin in somatic and germinative cells, respectively. In addition to a fundamental understanding of critical biological processes, DNA condensation also holds strong potential in biotechnology. Herein, we investigate the mesoscale structure of complexes formed between DNA and histones or protamines. A sophisticated set of biophysical methods encompassing steady-state fluorimetry, small-angle X-ray scattering and infrared nano spectroscopy was used to unveil both the self-assembly and molecular interactions of these complexes. We explored the fluorescence of a molecular rotor, thioflavin T, to investigate the accessibility of ligands in the inter-base environment of DNA strands. AFM-based infrared spectroscopy was used for the first time to probe the vibrational signature of individual DNA/nucleoprotein nano assemblies and disclose secondary-structure features. Our results show that protamines form highly compact structures in which DNA folding hinders access to the inter-base spacing. These assemblies exhibit diversified secondary-structure conformations, with the presence of -sheets stabilizing the packing. In contrast, histone-based complexes are characterized by fibrillar nano assemblies exhibiting larger inter strands separations and access to guest molecules that intercalate between bases. The findings presented here may help the understanding of DNA condensation mediated by these two major nucleoproteins and may assist the optimization of gene vehicles based on these promising nano assemblies.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP, 19/20907-

Desenvolvimento do olhar e do contato ocular em lactentes de zero a quatro meses de idade The development of looking behavior and eye-contact in breast feeding children aged between 0 and 4 months

OBJETIVOS: investigar o desenvolvimento do contato ocular e do comportamento visual de bebês entre zero e quatro meses. MÉTODOS: dezessete bebês típicos foram filmados mensalmente por 30 minutos, sendo transcritas 11 categorias de observação do olhar, quantificadas e tratadas estatisticamente através dos testes de Friedman (&#945; = 0,050) e dos Postos Sinalizados de Wilcoxon (&#945; de Bonferroni = 0,010). RESULTADOS: houve diferenças estatisticamente significantes nas frequências das categorias: "olhar para os olhos da mãe" (p<0,001), "olhar para o rosto da mãe" (p<0,001), "olhar para objeto" (p<0,001), "olhar para a pesquisadora" (p<0,001), "olhar para o ambiente de forma ativa" (p<0,001), "olhar para o ambiente de forma passiva" (p<0,001), "olhar para o próprio corpo" (p=0,001) e "olhos fechados" (p=0,005). Detectou-se o contato ocular na terceira semana de vida (64,7%) e comprovou-se sua evolução nos cinco primeiros meses (p=0,010 em 50% dos intervalos entre coletas). CONCLUSÕES: o contato ocular pode ser detectado desde o período neonatal e se desenvolve nos primeiros meses de vida. A frequência do contato ocular do bebê com sua mãe aumenta longitudinal-mente nos primeiros quatro meses. Existem outros focos de olhar do bebê fundamentais no início do desenvolvimento extrauterino além dos olhos de sua mãe.<br>OBJECTIVES: to investigate the development of eye-contact and visual behavior in babies aged between 0 and 4 months. METHODS: sixteen normal babies were filmed monthly for 30 minutes, and 11 eleven visual behavior categories observed and transcribed. These were then quantified and treated statistically using the Friedman test (&#945; = 0.050) and Wilcoxon's Signed Rank test (Bonferroni's &#945; = 0,010). RESULTS: there were statistical differences in frequency between the various categories: "looking mother in the eye" (p<0.001), "looking mother in the face" (p<0.001), "looking at an object" (p<0.001), "looking at the researcher" (p<0.001), "actively looking at the surroundings" (p<0.001), "passively looking at the surroundings" (p<0.001), "looking at own body" (p=0.001) and "eyes closed" (p=0.005). Eye-contact was detected in the third week of life in 64.7% and developed during the first five months of life (p=0.010 in 50% of the intervals between data collection). CONCLUSIONS: eye-contact can be detected from the neonatal period onwards and develops over the first few months of life. The frequency of the baby's eye-contact with its mother increases longitudinally in the first four months. Other focuses of attention, apart from the mother's eyes, are also fundamental during the early stages of development outside the womb

Formulation matters! A spectroscopic and molecular dynamics investigation on the peptide CIGB552 as itself and in its therapeutical formulation

Synthetic therapeutic peptides (STP) are intensively studied as new-generation drugs, characterized by high purity, biocompatibility, selectivity and stereochemical control. However, most of the studies are focussed on the bioactivity of STP without considering how the formulation actually used for therapy administration could alter the physico-chemical properties of the active principle. The aggregation properties of a 20-mer STP (Ac-His-Ala-Arg-Ile-Lys-D-Pro-Thr-Phe-Arg-Arg-D-Leu-Lys-Trp-Lys-Tyr-Lys-Gly-Lys-Phe-Trp-NH2), showing antitumor activity, were investigated by optical spectroscopy and atomic force microscopy imaging, as itself (CIGB552) and in its therapeutic formulation (CIGB552TF). It has found that the therapeutic formulation deeply affects the aggregation properties of the investigated peptide and the morphology of the aggregates formed on mica by deposition of CIGB552 and CIGB552TF millimolar solutions. Molecular dynamics simulations studied the first steps of CIGB552 aggregation under physiological ionic strength conditions (NaCl 150 mM), showing that peptide oligomers, from dimers to tetramers, are preferentially formed in this environment. Interestingly, cell viability assays performed on H-460 cell lines indicate a major antiproliferative activity of the peptide in its therapeutic formulation with respect to the peptide aqueous solution