Sergio Kogikoski

Self-Assembly of Arg-Phe Nanostructures via the Solid-Vapor Phase Method

We report for the first time on the self-assembly of nanostructures composed exclusively of alternating positively charged and hydrophobic amino acids. A novel arginine/phenylalanine octapeptide, RF8, was synthesized. Because the low hydrophobicity of this sequence makes its spontaneous ordering through solution-based methods difficult, a recently proposed solid-vapor approach was used to obtain nanometric architectures on ITO/PET substrates. The formation of the nanostructures was investigated under different preparation conditions, specifically, under different gas-phase solvents (aniline, water, and dichloromethane), different peptide concentrations in the precursor solution, and different incubation times. The stability of the assemblies was experimentally studied by electron microscopy and thermogravimetric analysis coupled with mass spectrometry. The secondary structure was assessed by infrared and Raman spectroscopy, and the arrays were found to assume an antiparallel β-sheet conformation. FEG-SEM images clearly reveal the appearance of fibrillar structures that form extensive homogeneously distributed networks. A close relationship between the morphology and preparation parameters was found, and a concentration-triggered mechanism was suggested. Molecular dynamics simulations were performed to address the thermal stability and nature of intermolecular interactions of the putative assembly structure. Results obtained when water is considered as solvent shows that a stable lamellar structure is formed containing a thin layer of water in between the RF8 peptides that is stabilized by H-bonding.

Polycaprolactone fibers with self-assembled peptide micro/nanotubes: a practical route towards enhanced mechanical strength and drug delivery applications

Peptide-based scaffolds are a frontier research area in materials science with widespread impact in biomedical engineering. In this paper, we describe a hybrid material formulated through the conjugation of electrospun polycaprolactone (PCL) fibers and micro/nanotubes of l,l-diphenylalanine (FF-MNTs). Morphology and crystallinity of the composite matrices are investigated using a wide range of analytical techniques including electron microscopy, thermal analyses, X-ray diffraction and micro-tomography. Peptide assemblies are found to produce deep modifications on the microstructure of PCL fibers, impacting average diameters, crystallinity degree and porous size in the polymer network. These changes are correlated with mechanical properties of the resulting scaffolds, whose strength is found to exhibit a brittle-to-ductile transition upon increasing the amount of FF-MNTs and lead to enhanced Youngs moduli of polymer fibers. The PCL/FF-MNTs composites were tested for the drug delivery application of a lipophilic drug, benzocaine. In vitro permeation studies have shown that these polymer/peptide hybrids are able to produce a steady release of benzocaine over periods of up to ∼13 hours, much higher than commercially available gel formulations. Enzymatic tests have shown a significant increment in biodegradation rates in PCL/FF-MNTs hybrids containing higher peptide amounts, which exhibited almost 100% weight loss against only 10% found in pure PCL. Our findings indicate that using PCL/FF-MNTs materials is a simple route towards achieving enhanced mechanical strength of PCL networks that have the ability to promote controlled drug delivery from a completely biodegradable matrix.

Relaxation dynamics of deeply supercooled confined water in L,L-diphenylalanine micro/nanotubes

The temperature dependence (10-290 K) of the low-frequency (20-150 cm(-1)) Raman-active phonon modes of deeply supercooled confined water in L,L-diphenylalanine micro/nanotubes was analyzed. The isolated dynamics of a specific geometry of a water cluster (pentamer) in a supercooled confined regime was studied in detail. A fragile-to-strong transition at 204 K was observed and related to the crossing of the Widom line. Analysis of peptide vibrational modes coupled to water hydrogen bonds indicated that hydrogen bond fluctuations play an irrelevant role in this system. Our results are in agreement with the second critical point of water existence hypothesis.

SERS active self-assembled diphenylalanine micro/nanostructures: A combined experimental and theoretical investigation

Enhancing Raman signatures of molecules by self-assembled metal nanoparticles, nanolithography patterning, or by designing plasmonic nanostructures is widely used for detection of low abundance biological systems. Self-assembled peptide nanostructures provide a natural template for tethering Au and Ag nanoparticles due to its fractal surface. Here, we show the use of L,L-diphenylalanine micro-nanostructures (FF-MNSs) for the organization of Ag and Au nanoparticles (Nps) and its potential as surface-enhanced Raman scattering (SERS)-active substrates. The FF-MNSs undergo an irreversible phase transition from hexagonally packed (hex) micro-nanotubes to an orthorhombic (ort) structure at ∼150 °C. The metal Nps form chains on hex FF-MNSs as inferred from transmission electron microscopy images and a uniform non-aggregated distribution in the ort phase. The high luminescence from the ort FF-MNS phase precludes SERS measurements with AgNps. The calculated Raman spectra using density-functional theory shows a higher intensity from rhodamine 6G (R6G) molecule in the presence of an Ag atom bound to ort FF compared with hex FF. The SERS spectra obtained from R6G bound to FF-MNSs with AuNps clearly show a higher enhancement for the ort phase compared with hex FF, corroborating our theoretical calculations. Our results indicate that FF-MNSs both in the hex and ort phases can be used as substrates for the SERS analysis with different metal nanoparticles, opening up a novel class of optically active bio-based substrates.

Biosensors Based on Biological Nanostructures

The term biomaterials is attributed to the materials employed to medical applications, such as ceramic implants and biopolymer scaffolds, as well as a variety of composites (Hauser e Zhang, 2010). In recent decades, researchers of distinct subjects have gathered efforts in developing new biomaterials for applications in various branches of medicine. With the advent of molecular biology and biotechnology, and knowing that many of these biomaterials are not specific for medical applications, studies have been directed to directed towards to biological and biomimetic materials preparation biological and biomimetic materials (Sanchez, Arribart et al., 2005; He, Duan et al., 2008; Aizenberg e Fratzl, 2009). In this new class of materials, the peptide compounds appear as promising candidates to building blocks due to their easy preparation and physical and chemical stability (Cheng, Zhu et al., 2007). Thus, we can propose different peptide sequences and from their selforganization to obtain structures with different geometries (spherical, cylindrical, conical) and even nanotubes and/or nanofibers (Hirata, Fujimura et al., 2007) are obtained. Peptide nanomaterials form supramolecular structures which are interconnected by intermolecular interactions such as van der Waals forces, electrostatic, hydrophobic and hydrogen bonds, among others (Cheng, Zhu et al., 2007; Colombo, Soto et al., 2007). Due to these characteristics, crystal engineering of supramolecular architectures has rapidly expanded in recent years, mainly due to the possibility of intermolecular interactions, structural diversity and potential applications (Sanchez, Arribart et al., 2005; Cheng, Zhu et al., 2007; He, Duan et al., 2008; Aizenberg e Fratzl, 2009). This structural variety is possible due to the planning and construction of supramolecular architectures, as promising building blocks that allow the design of functional molecular materials that will display some sort of ownership of technological interest (Sanchez, Arribart et al., 2005; Cheng, Zhu et al., 2007; He, Duan et al., 2008; Aizenberg e Fratzl, 2009). The nanostructures obtained from biomolecules are attractive due to their biocompatibility, ability for molecular recognition and ease of chemical modification, important factors on various applications of interest. The functionalization of these materials have greatly

Insight into the Electro-Oxidation Mechanism of Glucose and Other Carbohydrates by CuO-Based Electrodes

In this work, a new hypothesis for the electrocatalytic behavior of CuO electrodes is presented. Different from the established mechanism, here we discuss why CuIII species do not participate in the oxidation mechanism of carbohydrates. We show that hydroxyl ion adsorption and the semiconductive properties of the material play a more significant role in this process. The relationship between the flat band potential and the potential that begin oxidation suggests that the concentration of vacancies in the charge region acts upon the reactivity of the adsorbed hydroxyl ions through a partial charge transfer reaction. In the presence of carbohydrate molecules, the electron transfer is facilitated and involves the transfer of electrons from the adsorbed hydroxyl ions to the CuO film. This mechanism is fundamentally relevant since it helps the understanding of several experimental misleads. The results can also lead to obtaining better catalysts, since improvements in the material should focus on enhancing the semiconductive properties rather than the CuII/CuIII redox transition. The results shed light on different aspects of carbohydrate molecules oxidation that could lead to novel applications and possibly a better description of other semiconductor mechanisms in electrocatalysis.

Nanostructured Antigen-Responsive Hydrogels Based on Peptides for Leishmaniasis Detection

Hydrogels based on peptide nanostructures are biological entities that can be applied in a wide range of applications, such as scaffolds for tissue engineering, drug delivery, and biosensors. The aim of this research was to study peptide hydrogels based on N-(9-fluorenylmethoxycarbonyl)L,L-diphenylalanine (Fmoc-FF) in two different media: water and phosphate buffer. These hydrogels were used for encapsulating Leishmania infantun chagasi soluble proteins. The structure of the matrices was investigated in detail through scanning and transmission electron microscopy, and small angle X-ray scattering (SAXS). The mechanical behavior of the hydrogels were assessed through rheology assays, demonstrating both the physical and chemical stability of the hydrogel scaffolds. The immunogenicity of immobilized antigens was studied using enzyme-linked immunosorbent assay (ELISA) detection after the reaction with positive and negative dog sera for Leishmania infantum chagasi. The hydrogel was efficient to encapsulate antigens, and can promote the development of novel devices that requires the storage of biomolecules under moist environmental conditions.