Biological Oxidative Mechanisms for Degradation of Poly(lactic acid) Blended with Thermoplastic Starch

In the present 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 <i>tert</i>-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

pH-Dependent Synthesis of Anisotropic Gold Nanostructures by Bioinspired Cysteine-Containing Peptides

In the present study, 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

Intermediate Tyrosyl Radical and Amyloid Structure in Peroxide-Activated Cytoglobin.

We characterized the peroxidase mechanism of recombinant rat brain cytoglobin (Cygb) challenged by hydrogen peroxide, tert-butylhydroperoxide and by cumene hydroperoxide. The peroxidase mechanism of Cygb is similar to that of myoglobin. Cygb challenged by hydrogen peroxide is converted to a Fe4+ oxoferryl π cation, which is converted to Fe4+ oxoferryl and tyrosyl radical detected by direct continuous wave-electron paramagnetic resonance and by 3,5-dibromo-4-nitrosobenzene sulfonate spin trapping. When organic peroxides are used as substrates at initial reaction times, and given an excess of peroxide present, the EPR signals of the corresponding peroxyl radicals precede those of the direct tyrosyl radical. This result is consistent with the use of peroxide as a reducing agent for the recycling of Cygb high-valence species. Furthermore, we found that the Cygb oxidation by peroxides leads to the formation of amyloid fibrils. This result suggests that Cygb possibly participates in the development of degenerative diseases; our findings also support the possible biological role of Cygb related to peroxidase activity

Facile Gram-Scale Synthesis of NiO Nanoflowers for Highly Selective and Sensitive Electrocatalytic Detection of Hydrazine

The design and development of efficient and electrocatalytic sensitive nickel oxide nanomaterials have attracted attention as they are considered cost-effective, stable, and abundant electrocatalytic sensors. However, although innumerable electrocatalysts have been reported, their large-scale production with the same activity and sensitivity remains challenging. In this study, we report a simple protocol for the gram-scale synthesis of uniform NiO nanoflowers (approximately 1.75 g) via a hydrothermal method for highly selective and sensitive electrocatalytic detection of hydrazine. The resultant material was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For the production of the modified electrode, NiO nanoflowers were dispersed in Nafion and drop-cast onto the surface of a glassy carbon electrode (NiO NF/GCE). By cyclic voltammetry, it was possible to observe the excellent performance of the modified electrode toward hydrazine oxidation in alkaline media, providing an oxidation overpotential of only +0.08 V vs Ag/AgCl. In these conditions, the peak current response increased linearly with hydrazine concentration ranging from 0.99 to 98.13 μmol L–1. The electrocatalytic sensor showed a high sensitivity value of 0.10866 μA L μmol–1. The limits of detection and quantification were 0.026 and 0.0898 μmol L–1, respectively. Considering these results, NiO nanoflowers can be regarded as promising surfaces for the electrochemical determination of hydrazine, providing interesting features to explore in the electrocatalytic sensor field

Interatoma of rat Cygb with hydrogen peroxide.

<p>The network shows, in each node, a protein predicted to have functional links with Cygb and hydrogen peroxide. Inside the figure the abbreviations are SOD1 (superoxide dismutase [Cu-Zn]), Hmox2 (heme oxygenase 2 [HO-2]), Mb (myoglobin), Mpo (myeloperoxidase), cat (catalase), Cygb (cytoglobin), Prdx1 (peroxyredoxin-1), Prdx5 (peroxyredoxin-5) and Srxn1 (Ab2-390). In the figure light green, cyan and magenta lines correspond, respectively, to textmining, databases and experiments supporting the relationship among the proteins and hydrogen peroxide.</p

Changes in the EA spectrum of Cygb during the reaction with hydrogen peroxide.

<p>A) Bleaching of Soret and Q bands of EA spectra of Cygb in the course of the reaction with hydrogen peroxide. The black line represents the EA spectrum of resting Cygb, red, green and blue lines corresponds to the spectra obtained at 30, 60 and 200 s after addition of hydrogen peroxide and indicated by the arrows. B) Normalized spectra of Cygb resting form and 200 s after hydrogen peroxide addition. C) Differential spectra of Cygb obtained 30 and 200 s after the addition of hydrogen peroxide The experiments of EA spectroscopy were performed using 65 μmol.L^-1 Cygb and 0.1 cm optical length. When present, the concentration of peroxide was 650 μmol.L^-1. These results are representative of three independent replicates.</p

Spectroscopic characteristics of Cygb.

<p>The upper panel shows the EA spectrum of Cygb and the respective inset the corresponding far-UV CD spectrum. The lower panel shows the CD (light gray line) and the MCD spectra of Cygb obtained by addition and subtraction of the original spectra obtained at positive and negative magnetic fields. MCD is shown at increasing magnetic fields and the respective inset shows the linear increase of Soret band intensity promoted by increasing the magnetic field. The experiments of EA spectroscopy were performed with 65 μmol.L^-1 Cygb using 0.1 cm optical length. The experiments of CD and MCD were performed using 20 μmol.L^-1 protein solution in 20 mmol.L^-1 phosphate buffer, pH 7.4. These results are representative of three independent replicates.</p

Formation of Cygb amyloid structure after challenge by peroxides.

<p>A), B) and C) show, respectively the epifluorescence images of Cygb control, control plus GSH and challenged by hydrogen peroxide obtained immediately (left panels) 24 h (right panels) after incubation and staining by thioflavine-T. For the low-vacuum SEM experiments, it was used 7 μmol.L^-1 cygb solution with 70 μmol.L^-1 peroxide solutions. For the epifluorescence experiments 70 μmol.L^-1 protein solution was incubated for 1 h with 700 μmol.L^-1 peroxide solution in the presence of thioflavin-T. For FTIR measurements, 7 μmol.L^-1 protein solution was incubated with 70 μmol.L^-1 peroxide solutions for 1 h. The results are representative of three independent experiments.</p

Changes in the EPR spectrum of resting Cygb during the reaction with hydrogen peroxide.

<p>The spectra marked as a, b and c were obtained at 30, 60 and 210 s after the addition of hydrogen peroxide. The inset shows a zoom in the spectra of the free radical produced concomitantly with the formation of high valence species. For EPR experiments, the protein concentration was of 1.2 mmol.L^-1and when present, the peroxide concentration was of 12 mmol.L^-1. These results are representative of three independent replicates.</p