Biomolecules with their important physical and chemical properties form a set with a lot of appeal for technological applications. Biomolecules and their mimetic structures can contribute to several technological processes due to their redox, catalytic, photochemical, and specific affinity properties. These properties can be used to generate electric current, as in fuel bio cells, capture solar energy to produce electricity and fuel, produce diagnostic biosensors, produce metallic nanoparticles, change material properties, among others. Here we present some works developed by our research groups that perfectly illustrate this diversity of applications.
Solid-state ionic conductor is an essential and critical part of electrochemical devices such as batteries and sensors. Nano-sized silver iodide (AgI) is the most promising ionic conductor due to its superionic conductivity at room temperature. In recent years, proteins have been used as organic templates to obtain high-performance solid-state ionic conductors as well as to extend their applications in a biosensor. Here, we report the unprecedented ultrafast synthesis of thermally stable protein-coated AgI nanoparticles (NPs) through the photo-irradiation method for solid-state electrolyte.
The synthesis was performed using a hyperthermostable bacterial β-glucosidase. The protein-coated AgI NPs with an approximate diameter of 13 nm showed that the controllable transition from the α- to β-/γ-phase was drastically suppressed down to 41 °C in the cooling process. After drying, the product represents a thermally stable organic-inorganic hybrid system with superionic conductivity. It is noteworthy that the superionic conductivity (σ ˜ 0.14 S/cm at 170 °C) of thermally stable protein-coated AgI NPs is maintained during several thermal cycles (25–170 °C). To our knowledge, this is the first report showing the diffusion of mobile Ag+ ions on the surface of the AgI NPs through a protein matrix. The facile synthesis method and high performance of the protein-coated AgI NPs may provide a latent application in the mass production of nanobatteries and other technological applications.
Pineapple crown is an important source of cellulose that is still going to waste because of the lack of knowledge about their economic uses. The isolation of cellulose nanocrystals (CNC) from pineapple crown leaf (PCL) wastes arises as an important alternative to use PCL wastes in high value-added applications, and has not been reported yet.
In this study, CNC were successfully extracted from PCL wastes using chemical treatments followed by acid hydrolysis using sulfuric acid.
FTIR results confirmed the removal of the non-cellulosic compounds of PCL through the mercerization and bleaching treatments.
SEM and AFM showed that the diameter of PCL fibers was reduced from 18 μm to 39 nm after the hydrolysis reaction, resulting in CNC with rod-like shape.
The obtained CNC showed cellulose I crystalline structure with high crystallinity index (73%).
The thermal degradation of CNC started at 124 °C, what was attributed to the presence of surface sulfate groups identified by elemental analysis.
The high hydrophilicity of CNC was verified by its high moisture content and absorption.
The results showed that the CNC isolated from PCL have interesting properties to be used in many liquid media applications, besides their use as reinforcement in nanocomposites.
Nowadays, cellulose nanostructures (CNS) have attracted considerable attention on the development of green bio-based and biodegradable materials. It has been occurred because this biopolymer is the most abundant and available biomaterial on the planet. Cellulose can be found in the form of nanoscale microfibrils in the plant cell wall (Cunha, Zhou, Larsson, & Berglund, 2014). Recently, the use of cellulose has been widely studied due to its sustainability, renewability characteristics, besides the low-cost and high-abundance. Furthermore, nanotechnology has attracted attention for development of advanced materials with properties such as high surface area, low density (i.e. low weight material for the volume occupied – generates lower transport costs and is lighter than non-polymeric materials) and high mechanical strength (Du et al., 2016).
In this study a homogeneous system for nanocellulose acetylation was investigated.
Cellulose nanostructures (CNS) were obtained from microcrystalline cellulose, and modification was conducted to increase hydrophobicity and physico-chemical properties of the nanoparticles. Sulfuric acid and hydrochloric acid were used for the isolation. The CNS were characterized with dynamic light scattering, zeta potential, atomic force microscopy, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, X-ray photoelectron spectrometry, degree of substitution (DS), X-ray diffraction (XRD), and thermogravimetric analysis. Nanostructures obtained with sulfuric acid showed lower particle sizes and lower thermal stability. After modification, the results indicated the substitution of OH groups in cellulose structure by acetyl groups. The XRD patter was considerably modified and it was verified that acetylation increased the thermal stability. Different methods were used to calculate the DS, and the differences between the methodologies were explained. The acetylated samples play an important role in the nanocomposites field, since the hydrophobic surface increase its applications.
The figure on the left shows the stability behavior of the suspensions, with time variation. For the H1 sample it was not possible to observe a significant change in the system, even after 6 h of follow-up, which is a high indication of the stability of the suspension. On the other hand, the H2 sample presents visual alteration with 10 min where the sample begins to agglomerate, demonstrating the low stability in aqueous suspension. This result corroborates the values of the zeta potential, where a greater potential (in modulus) was observed for the H1 sample and can be associated with the presence of sulfate groups and hydroxyl groups, for H1 and H2 respectively. The samples AC1 and AC2, despite the presence of acetyl groups, were still well dispersed in aqueous suspension for periods of up to 1 h, and above that period it is observed that the system begins to agglomerate and decant. This result corroborates the indicative that although it does not present electrostatic stability, the system presents a mechanism of steric stability by the presence of the acetyl groups, since the suspension was shown stable for low times.
On the right, the analysis shows AFM images of the obtained nanoparticles, which was used to evaluate in greater detail the structures formed. The action of both acids allowed the isolation of CNS with a very homogeneous morphology, and they have an elongated typical shape of cellulose nanofibers. Usually for the acid hydrolysis is observed the formation of cellulose nanocrystals, but it is also reported that under non-drastic reaction conditions it is possible to obtain nanofibers, as was the case (Corrêa, de Teixeira, Pessan, & Mattoso, 2010). It was observed that the samples H1 and H2 showed a L/D of 11.5 and 8.6 for H1 and H2, respectively. These values and the shape of nanofibers is consistent with the DLS result which presented values with great variation.
Prof. Wendel Alves’s research group, in partnership with Rheabiotech Ltda, has developed a biosensor that uses a chitosan-based polyamide-6 polymer blend to immobilize an L. infantum-specific antibody recognition peptide sequence (ACS Appl. Electron. Mater. 2019, DOI: 101021/acsaelm.9b00476).
The blend was chosen due to the excellent properties of chitosan (biocompatibility) and polyamide (mechanical properties), being used in the immobilization of biomolecules, which are incorporated by electrostatic entrapment, preserving their structure and therefore their bioactivity even when compared to materials that are already used for such function. The work was promising, where it was possible to detect concentrations of the order of 1 pg mL-1 (while the ELISA reached 1 ng mL-1), discriminating clearly and objectively human serum samples contaminated with visceral leishmaniasis and healthy humans.
Vibrational spectroscopy has been widely employed to unravel the physical-chemical properties of biological systems. Due to its high sensitivity to monitoring real time “in situ” changes, Raman spectroscopy has been successfully employed, e.g., in biomedicine, metabolomics, and biomedical engineering. The interpretation of Raman spectra in these cases is based on the isolated macromolecules constituent vibrational assignment. Due to this, probing the anharmonic or the mutual interactions among specific moieties/side chains is a challenge.
We present a complete vibrational modes calculation for connective tissue in the fingerprint region (800 – 1800 cm−1) using first-principles density functional theory. Our calculations accounted for the inherent complexity of the spectral features of this region and useful spectral markers for biological processes were unambiguously identified. Our results indicated that important spectral features correlated to molecular characteristics have been ignored in the current tissue spectral bands assignments. In particular, we found that the presence of confined water is mainly responsible for the observed spectral complexity.
In the present work a detailed vibrational modes assignment of a connective tissue based on the STmod is presented. To the best of our knowledge this is the first report on literature concerning complete vibrational assignment for a tissue. The vibrational calculations were performed on Cn (n – 8), C1s, D0, and D1 unit cells of STmod. The numeric subscript indicates the number of water molecules inside the unit cell. The “s” subscript related to the presence of external water solvating the C1 model. Starting from a hydrated collagen peptide each unit cell was obtained and calculations performed on periodic boundary conditions. The figure on the right shows the unit cell for C0, C1s, C2, and D0 structures.
New diagnostic tools based on photonic technology have been developed to achieve cancer treatment with favorable results. One of these tools is the optical biopsy. Optical biopsy refers to techniques where the light-tissue interaction is analyzed and the tissue state information is obtained both “in vivo” and “ex vivo”. Biological materials had been successfully characterized using these kinds of techniques. Vibrational spectroscopy, consisting of Raman scattering and Fourier-transform infrared (FTIR) techniques, are of particular interest due of their high sensitivity in the detection of biochemical and molecular changes in biological tissues [7–11].
In particular, the vibrational modes associated with important biochemical components of cells can be used as markers in the identification of metabolic alterations suffered by the cell during the carcinogenesis process.
In this paper, alterations in the amide (1500–1700 cm−1 ) spectral region probed by Fourier-transform infrared spectroscopy (FTIR) have been reported comparing tumor and normal tissues. The observed changes in the FTIR spectra of squamous cell carcinoma compared to normal tissues were analyzed by First-Principles Density Functional Theory vibrational calculations. Computational models for skin and prototype β-sheet model were employed. Computational models for the skin model (C0, C1, C4 and D1) and β sheet prototype were used.
Usually, bands in this range are assigned to the so-called Amide I, II, and III vibrations which provide pieces of information concerning peptide bonds and secondary structure (α-helix, β-sheet) of proteins. Proteins folding changes due to tumoral process are usually considered to qualitatively explain the observed differences between tumor and normal tissues. Our findings shown that predominates conjugated Amide I + Amide II, Amide V, methylene torsions, and ring side chains torsions and swings vibrations in this region. We also notice the lack of evidence concerning changes in the secondary structure of the β-sheet peptidic model to explain the spectral differences. In fact, we concluded that the proline amino acid has the main rule to explain the data in this region being it responsible for the strong coupling between vibrations instead of water.
There is a growing interest in exploiting the ability to synthesize gold nanoparticles (GNPs) of controlled size and shape mediated by amino acids and peptides. For many years, numerous synthetic strategies developed for the synthesis of GNPs have frequently required the use of harsh reagents for controlling the particle morphology. The search for eco-friendly conditions showed that peptides are an interesting alternative for reducing the environmental impacts during the synthesis of GNPs. Also, the capping of GNPs provided by peptides assures efficient delivery and biocompatibility that can contribute to the use of theranostic properties of these materials.8 Moreover, the functional groups available in the peptides, such as −SH and −NH2, allow a fine control of the synthesis for achieving the desired functionality for the material. Peptides provide templates that direct the growth and shape of the metal nanoparticles as well as their capping. Particularly, the presence of a cysteine residue in a peptide provides a mild reducing agent for biomineralization and an efficient anchor for the peptide on the GNP surface. Therefore, a peptide containing a cysteine residue is a promising compound for the controlled synthesis and capping of GNPs. The manipulation of the reaction conditions and a rational choice of the amino acids arrangement (bioinspired sequences) make feasible the specific directing of the GNP spatial growth assisted by peptides. Bioinspired peptides have been shown to be useful for the assembly and synthesis of gold nanostructures.
Alkaline peptides AAAXCX (X = lysine or arginine residues) were designed based on the conserved motif of the enzyme thioredoxin and used for the synthesis of gold nanoparticles (GNPs) in the pH range of 2–11. These peptides were compared with free cysteine, the counterpart acidic peptides AAAECE and γ-ECG (glutathione), and the neutral peptide AAAACA. The objective was to investigate the effect of the amino acids neighboring a cysteine residue on the pH-dependent synthesis of gold nanocrystals. Kohn–Sham density functional theory (KS-DFT) calculations indicated an increase in the reducing capacity of AAAKCK favored by the successive deprotonation of their ionizable groups at increasing pH values. Experimentally, it was observed that gold speciation and the peptide structure also have a strong influence on the synthesis and stabilization of GNPs. AAAKCK produced GNPs at room temperature, in the whole investigated pH range. By contrast, alkaline pH was the best condition for the synthesis of GNP assisted by the AAARCR peptide. The acidic peptides produced GNPs only in the presence of polyethylene glycol, and the synthesis using AAAECE and γ-ECG also required heating. The ionization state of AAAKCK had a strong influence on the preferential growth of the GNPs. Therefore, pH had a remarkable effect on the synthesis, kinetics, size, shape, and polydispersity of GNPs produced using AAAKCK. The AAAKCK peptide produced anisotropic decahedral and platelike nanocrystals at acidic pH values and spherical GNPs at alkaline pH values. Both alkaline peptides were also efficient capping agents for GNPs, but they produced a significant difference in the zeta potential, probably because of different orientations on the gold surface.
In an other study, poly(lactic acid) (PLA) and their blends with 5%/wt and 10%/wt thermoplastic starch (TPS) were submitted to degradation in simulated soil. To investigate the mechanisms involved in the degradation, we also submitted the samples to degradation by tert-butyl hydroperoxide, myoglobin, and peroxide-activated myoglobin. The samples were analyzed by Fourier-transformed infrared spectrometry (FTIR), scanning electronic microscopy (SEM), contact angle analysis, and mass loss measurement. The FTIR results indicated a weak interaction between the two components (PLA and starch) in the blend’s amorphous structure. However, the corresponding SEM images showed that TPA increased ridges and roughness at the material surface associated with an increase of wettability evidenced by contact angle analysis. Consistently, TPS favored degradation of the material both in the simulated soil and pro-oxidant model systems. In the simulated soil, the occurrence of TPS hydrolysis provided glucose, a biological fuel, that contributed to the growth of the microorganisms. The similar degradation patterns observed in mimetic pro-oxidant biological systems and soil suggest that oxidative reactions catalyzed by heme proteins from biological sources as well as the presence of peroxides and transition metal traces in the original materials have a significant contribution to PLA and PLA/TPS degradation. See the article in Biological Oxidative Mechanisms for Degradation of Poly(lactic acid) Blended with Thermoplastic Starch publicado em ACS Sustainable Chem. Eng. 2015.