Late-Stage Hydrocarbon Conjugation and Cyclisation in Synthetic Peptides and Proteins

The conventional S-alkylation of cysteine relies upon using activated electrophiles. Here we demonstrate high-yielding and selective S-alkylation and S-lipidation of cysteines in unprotected synthetic peptides and proteins by using weak electrophiles and a Zn²⁺ promoter. Linear or branched iodoalkanes can S-alkylate cysteine in an unprotected 38-residue Myc peptide fragment and in a 91-residue miniprotein Omomyc, thus highlighting selective late-stage synthetic modifications. Metal-assisted cysteine alkylation is also effective for incorporating dehydroalanine into unprotected peptides and for peptide cyclisation via aliphatic thioether crosslinks, including customising macrocycles to stabilise helical peptides for enhanced uptake and delivery to proteins inside cells. Chemoselective and efficient late-stage Zn²⁺-promoted cysteine alkylation in unprotected peptides and proteins promises many useful applications.     

Response of Corn Seedlings (Zea mays L.) to Different Concentrations of Nitrogen in Absence and Presence of Silicon

Silicon - Corn plants are highly demanding of nitrogen and the application of silicon has been studied because it minimizes stress from different natures, and for the better utilization of some...     

Nanocomposite powders of hydroxyapatite-graphene oxide for biological applications

The repair of bone fractures is a clinical challenge for patients with impaired healing, such as osteoporosis. Currently, different strategies have been developed to design new biomaterials, enhancing their interactions with biological systems and conducting the cellular behavior in the desired direction to help fracture healing. In the present work, hydroxyapatite-graphene oxide (HA-GO) nanocomposites were produced and the morphological and physicochemical influences of the addition of 0.5 wt%, 1.0 wt% and 1.5 wt% of GO to HA were observed. FEG-SEM and TEM analyses of HA-GO nanocomposites showed HA nanoparticles adhered to the surface of the GO sheets, suggesting an effective method to form nanostructured graphene-based biomaterials. As confirmation, physicochemical analyses by Raman, FTIR and TGA demonstrated a strong affinity between HA and GO, according to the increase of concentration from 0.5 wt% to 1.5 wt% GO in the HA-GO nanocomposites. Also, in order to evaluate the HA-GO nanocomposites behavior under biological microenvironment, in vitro bioactivity and indirect cytotoxicity tests were performed. FEG-SEM analyses confirmed the positive results for the bioactivity properties of HA-GO nanocomposite and indirect cytotoxicity demonstrated that even with a decrease in the hDPSCs viability and proliferation, when increasing to 1.5 wt% of GO concentration, high level of cell viability was exhibited by HA-GO nanocomposites. These biological results suggested the 0.5 wt% HA-GO nanocomposite as a potential bioactive bone graft and a promising biomaterial for bone tissue regeneration, when compared to the pure HA.     

Microwave hybrid fast sintering of red clay ceramics

This work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X-ray fluorescence, loss on ignition (LOI), X-ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre-sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X-ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.     

Structural,electronic paramagnetic resonance and magnetic properties of praseodymium-doped rare earth CeO2 semiconductors

In this work, praseodymium (Pr) doped cerium oxide (CeO₂) was prepared using the microwave-assisted hydrothermal method (MAH) and the properties were investigated by X-ray diffraction analysis (XRD), Raman spectroscopy, Field Emission Gun Scanning Electron Microscope (FEG-SEM), BET method, Photoluminescence spectroscopy (PL), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet–visible spectroscopy (UV–Vis), Electron paramagnetic resonance spectroscopy (EPR) and Magnetometry. The results showed that increasing the Pr-doping promotes a structural disorder due to increased oxygen vacancies. XRD confirmed a cubic structure without deleterious phases with modifications in the structure caused by alteration in the cerium oxidation state as well as changes in the crystallite size and strain obtained by Wellinson-Hall method. Raman spectroscopy shows that changing the Pr content results in samples with different defect densities at short range. FEG-SEM showed that the nanocrystals are agglomerated with small particles tend to aggregate spontaneously to decrease the surface energy. BET method showed that the Pr doping results in a gain of specific surface area. PL indicated that Pr³⁺ leads to distinct emissions; red emission associated to oxygen vacancies located near the conduction band (shallow defects), green emission associated to electron-hole recombination and orange emission associated to shallow defects and electron-hole recombination. FTIR indicated the complete process of nucleation with no other phase. UV–Vis showed the transitions between oxygen 2p, cerium 4f and praseodymium 4f states. The EPR signal shows events occurring around 344 mT. These events can be related due the presence of paramagnetic elements containing unpaired electrons, such as Ce (III), which is indicative of cerium reduction caused by Pr ions, as evidenced by Rietveld data. Regardless of the Pr concentration used in this research, the magnetic measurements show a superparamagnetic system below the blocking temperature of ~20 K and a paramagnetic system above this temperature, which indicates no significant changes in the average size of the nanoparticles. Surface area, crystallite size and the temperature are important parameters, which control the magnetic properties of such N-type semiconductors.     

Effect of height on the corrosion of steel and galvanized steel in nontropical coastal marine environments

In this study, the behavior of carbon steel and galvanized steel in nontropical coastal marine environments was evaluated. Evaluation was carried out with specimens with dimensions of 10 cm × 10 cm × 0.3 cm. These specimens were exposed to four testing stations (Iquique, Mejillones, Los Vilos, and San Vicente), where racks were installed both at ground level (ground), as well as in the upper zone of electrical transmission towers (tower). In each station, 24 specimens of A36 carbon steel and galvanized steel were placed (12 each). The corrosivity of the environment was measured using the ISO 9223, 9225, and 9226 standards. The specimens were evaluated on-site, monthly, through visual inspection and photographic record. Once withdrawn, the corrosion rate was determined and the corrosion products were analyzed through Raman and Fourier-transform infrared. The results show that, in all cases, the corrosion rate is greater in the tower than on the ground. However, even though the Los Vilos station is located farther from the sea (3,500 vs. ≈500 m), the corrosion rate of steel in the tower is the highest. This is caused by the generation of HCl from the transformation of lepidocrocite into goethite, in the presence of low chloride content, which acidifies the steel/corrosion product interface. In the case of galvanized steel, the corrosion rate is a function of the chloride content in the atmosphere, obtaining an excellent correlation between both parameters.