Açaí (Euterpe oleracea Mart.) Seed Extracts from Different Varieties: A Source of Proanthocyanidins and Eco-Friendly Corrosion Inhibition Activity

Euterpe oleracea Mart. (Arecaceae) is an endogenous palm tree from the Amazon region. Its seeds correspond to 85% of the fruit’s weight, a primary solid residue generated from pulp production, the accumulation of which represents a potential source of pollution and environmental problems. As such, this work aimed to quantify and determine the phytochemical composition of E. oleracea Mart. seeds from purple, white, and BRS-Pará açaí varieties using established analytical methods and also to evaluate it as an eco-friendly corrosion inhibitor. The proanthocyanidin quantification (n-butanol/hydrochloric acid assay) between varieties was 6.4–22.4 (w/w)/dry matter. Extract characterization showed that all varieties are composed of B-type procyanidin with a high mean degree of polymerization (mDP ≥ 10) by different analytical methodologies to ensure the results. The purple açaí extract, which presented 22.4% (w/w) proanthocyanidins/dry matter, was tested against corrosion of carbon steel AISI 1020 in neutral pH. The crude extract (1.0 g/L) was effective in controlling corrosion on the metal surface for 24 h. Our results demonstrated that the extracts rich in polymeric procyanidins obtained from industrial açaí waste could be used to inhibit carbon steel AISI 1020 in neutral pH as an abundant, inexpensive, and green source of corrosion inhibitor.     

Structure and radiation properties of dislocations arising during oxygen precipitate growth in silicon

The structural and radiation properties of defects formed during oxygen precipitation in Czochralski-grown silicon (Cz-Si) has been investigated by the methods of transmission electron microscopy (TEM) and photoluminescence (PL). It has been shown that the spectral intensity of dislocation-related luminescence (DL) is considerably redistributed as precipitates grow. A comparison of the concentration of different types defects with the DL integral intensity has shown that the secondary defects, namely, dislocations punched out of precipitates, make a main contribution to DL. In this case, the spectral distribution and integral intensity of DL are related to the extension of dislocation loops. The results show the capability of optimization of the dislocation-generation process to increase the intensity of the D1 line for its use in optoelectronics.     

Electrochemical concept of scanning tunnel microscopy and scanning tunnel spectroscopy

The history of investigation, development and application of electrochemical scanning tunneling microscopy (ESTM) are reviewed.     

Piezoelectric Current Generation in Wurtzite GaAs Nanowires

Generation of electric current is observed when GaAs nanowires with wurtzite crystal structure are bent by the probe of an atomic force microscope. The current originates from a piezo active phase in the nanowires due to the piezoelectric effect. Increasing of the piezo‐potential in bent nanowires enhances tunneling through the probe–nanowire Schottky barrier due to the thermionic field emission. Laser illumination amplifies short‐circuit current pulses by two orders of magnitude from 9 pA to 1 nA due to the piezo‐phototronic effect. Utilization of such piezo‐phototronic effect in GaAs nanowires is a solution to accelerate the efficiency of hybrid energy sources “piezoelectric nanogenerator ? solar cell” comprised of III–V nanowires.     

Hydrogen's isotopic exchange reaction in the C‐methyl sides in the medicinal agent xymedon: NMR spectroscopy and ab initio calculations

The kinetics of intramolecular and intermolecular exchange processes in xymedon (1‐(2‐hydroxyethyl)‐4,6‐dimethyl‐1,2‐dihydropyrimidin‐2‐one, a regeneratory, wound‐healing drug) and its analogue were investigated in the solution. Hydrogen's mobility was detected in the C‐methyl sides of these compounds. This mobility was monitored via NMR in the hydrogen/deuterium exchange reaction in water. Two models were proposed as explanations for this hydrogen‐deuterium exchange. According to the main model, the key intermediates of these reactions are low‐energy tautomers of xymedon in which the N³ is protonated following which one proton leaves either 6‐Me or 4‐Me and thus its hybridization is changed. This hydrogen‐to‐deuterium exchange reaction is much faster under acidic conditions although it also occurs in alkaline conditions. Methylation via MeOTs or MeI leads to products with a quaternized ring N³ atom in which a hydrogen‐to‐deuterium exchange reaction also takes place, although the rates of the 6‐Me and 4‐Me hydrogens exchange are reversed. According to density functional theory calculations, the presence of methyl groups at the C⁴/C⁶ positions and of the C═O fragment is crucial to remarkably lower the energies of these “rare” tautomers. The exact position of the C═O in heterocycle is also very important in the tautomers' relative stability.     

Photo-crystallization in a-Se imaging targets: Raman studies of competing effects

Photo-induced crystallization of a-Se is investigated by Raman spectroscopy as a function of temperature (250–340 K) and exposure time in thin-film structures used as targets in high-gain avalanche rushing photoconductor (HARP) video cameras. The Stokes-to-Antistokes ratio is monitored to obtain the local temperature T_loc at the laser spot; fluxes (632 nm) of 17 and 10 W/cm² are used. We find a rich temperature behavior that reflects the competition of changes in viscosity and strain, and defines four distinct regimes. No photo-crystallization is seen for T_loc below 260 K, nor in a 15 K range around T_g ～ 310 K. For T_loc in the regime 260–302 K the initial rate of crystal growth after onset of photo-crystallization is temperature independent, whereas for T_loc > 318 K the growth rate is thermally enhanced. Our results are in qualitative accord with a theory by Stephens treating the effects of local strain on the secondary growth of crystalline nuclei in a-Se. We conclude that the observed growth rate between 260 and 302 K is driven by local strain, and that relaxation of this strain near T_g suppresses crystal growth until thermally assisted processes accelerate the photo-crystallization at higher temperatures.     

Complexation of Scandium upon Its Extraction with Solutions of N-(2-Hydroxy-5-nonylbenzyl)-β,β-dihydroxyethylamine in Octanol

Complexation of scandium upon its extraction with N-(2-hydroxy-5-nonylbenzyl)-,-dihydroxyethylamine in octanol from chloride solutions (ScCl₃ + HCl) at pH 3.90–4.60 was studied. The extractant and scandium extract were investigated using IR spectroscopy. The composition of the extractable complex was determined, and an equation for scandium extraction was suggested.     

1-alkyl 3,5-diallyl isocyanurates as synthetic building blocks for sulfur-containing macroheterocycles

2-Sulfanylethanol was added to readily available 1-alkyl 3,5-diallyl isocyanurates to obtain 1-alkyl 3,5-bis[3-(2-hydroxyethylsulfanyl)propyl] isocyanurates. Treatment of the products with thionyl chloride gave 1-alkyl 3,5-bis[3-(2-chloroethylsulfanyl)propyl] isocyanurates whose reaction with thiourea followed by hydrolysis resulted in preparation 1-alkyl 3,5-bis[3-(2-sulfanylethylsulfanyl)propyl] isocyanurates. Oxiative cyclization of the latter gave macrocyclic disulfides in 56–75% yields. The composition and structure of the macrocyclic disulfides were established on the basis of the elemental and X-ray diffraction analyses, ¹H and ¹³C NMR and IR spectra, as well as MALDI-TOF and electron impact mass spectra.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1368–1376.Original Russian Text Copyright © 2004 by Fattakhov, Shulaeva, Saifina, Efremov, Rizvanov, Soloveva, Nafikova, Azancheev, Gubaidullin, Litvinov, Reznik.This revised version was published online in April 2005 with a corrected cover date.     

Dispersion of magnetic excitations in optimally doped superconducting YBa2Cu3O6.95

Detailed neutron scattering measurements of YBa2Cu3O6.95 found that the resonance peak and incommensurate magnetic scattering induced by superconductivity represent the same physical phenomenon: two dispersive branches that converge near 41 meV and the in-plane wave vector q(AF)=(pi/a,pi/a) to form the resonance peak. One branch has a circular symmetry around q(AF) and quadratic downward dispersion from approximately 41 meV to the spin gap of 33+/-1 meV. The other, of lower intensity, disperses from approximately 41 meV to at least 55 meV. Our results exclude a quartet of vertical incommensurate rods in q-omega space expected from spin waves produced by dynamical charge stripes as an origin of the observed incommensurate scattering in optimally doped YBCO.