Kinetics of the hydrolysis of synthetic substrates by horse urinary kallikrein and trypsin

The kinetic constants for horse urinary kallikrein and trypsin hydrolysis of BAEE, TAME, bradykinin methyl ester and bradykinyl-Ser-Val-Gin-Val-Ser were determined. The values of the ratio kcat/Km show that (1) kallikrein is catalytically less efficient than trypsin for all the substrates (2) the three esters are equally good substrates for trypsin while horse urinary kallikrein is 100-fold more effective on bradykinin methyl ester than on the other substrates (3) for both enzymes the ester of bradykinin is a better substrate than the tetradecapeptide.     

Ion exchange resins for gold cyanide extraction containing a piperazine functionality, 1. Synthesis and physico‐chemical properties

The synthesis of two types of metal‐chelating resins incorporating gold‐specific piperazine groups is described. PS‐PIP is a styrene‐divinylbenzene macroporous network. MC‐PIP is a (glycidyl methacrylate)‐co‐(ethylene dimethacrylate) network. The nominal functional group concentrations are 1.84 mmol/g for PS‐PIP and 1.14 mmol/g for MC‐PIP. The proton exchange capacity is 1.95 mmol/g for PS‐PIP and 0.91 mmol/g for MC‐PIP. Accurate titration curves were used to determine pK_a values (pK_H = 7.05 ± 0.12). XPS analyses of PS‐PIP resin were followed as a function of pH (cf. Fig. 8) demonstrating that the protonation of the amine is observable by a shift in binding energy of the N (1s) peak (±1.6 eV) moving from tertiary amine form (N (1s) 399.7 eV) to the protonated tertiary amine form (N (1s) 401.3 eV). Additionally, the presence of quaternary ammonium groups was detected at a N (1s) peak at 402.3 eV (cf. Fig. 9). Metal extraction from cyanide solutions, including Brazilian mine leach solution, showed considerable preference for gold (cf. Fig. 11–12). The piperazine resins extract gold via two mechanisms: (a) ligand substitution reactions at pH > 7.05 (pK_H(a)) or (b) anion exchange reactions via the quaternary ammonium groups at high pH values. Extraction profiles were S‐shaped (cf. Fig. 10) with 50% extraction ability at pH 8.0. Cyclic experiments involving extraction, elution, regeneration and recomplexation (cf. Tab. 6 and 7) showed the ability of MC‐PIP to perform consistently at high extraction efficiencies from pH 8.6.     

Ion Exchange Resins for Gold Cyanide Extraction Containing a Piperazine Functionality, 2. Study of the Gold Extraction Reaction

Ion exchange technology is offered as an alternative to activated carbon for gold cyanide recovery. A new type of ion‐exchange resin (PS‐PIP) incorporating a piperazine group, linked to a styrene‐divinylbenzene macroporous network, is described. The extraction of Au(CN)₂^– and other metal cyanides with the PS‐PIP resin involves three modes of metal extraction: the protonated secondary amine groups of the resin (at acidic pH conditions), the free amine groups of the resin (at neutral and basic pH values) and the small portion of the quaternary ammonium groups participate in the gold extraction mechanism. The gold cyanide extraction reaction on the polymeric piperazine was studied by a combination of metal extraction data, from batch experiments, and IR and XPS spectroscopic analysis of the metal loaded polymers. Extraction isotherms of gold cyanide show that gold binding is possible from 40–60 mg Au/g of resin in alkaline solutions, up to 150 mg Au/g of resin in acidic solutions. Efficient stripping of gold from the resin was achieved using ethanol/water solutions of sodium hydroxide, or 0.5 mol/l thiourea in sulfuric acid solutions.     

Biological nitrogen fixation in field-grown sorghum under different edaphoclimatic conditions is confirmed by N isotopic signatures

Nutrient Cycling in Agroecosystems - The association between sorghum and N2-fixing bacteria has been assessed only under limited conditions. We investigated biological nitrogen fixation (BNF) in...     

Overview of printing and coating techniques in the production of organic photovoltaic cells

The organic photovoltaic cell (OPV) is composed of multiple layers, and some printing and coating techniques are more suitable than others for a certain type of layer. This paper aims to characterize and compare the most relevant coating and printing techniques that can be used in the manufacture of OPVs. Extensive bibliographic research was carried out on articles published from 1998 to 2020 to identify various aspects OPV, such as the principle of operation, advantages, disadvantages, and which layers can be printed by each technique. The results show that the most used method for the processing of OPVs is spin-coating. In the studies found, rotation was used to coat the active layer, the electron transport layer, and the hole transport layer. The techniques of pad printing, casting, and meniscus are considered useful in the processing of the active layer. Regarding the deposition of the active layer, hole transport layer, electron transport layer, and anode, the rotogravure, crack matrix, spraying, and brushing techniques were satisfactory. Flexography has been used to form the active layer, electron transport layer, and anode. Screen printing, inkjet printing, and knife/blade coating were used in the processing of the active layer, hole transport layer, electron transport layer, anode, and cathode. All the double slot die coating, curtain coating, and slide coating allows simultaneous processing of multiple layers. Techniques compatible with roll-to-roll processing are more likely to be at the center of OPVs in the future, thus making solar photovoltaic technology more competitive.     

Laser sintering and influence of the Dy concentration on BaAl2O4:Eu2+, Dy3+ persistent luminescence ceramics

This work reports the effect of the Dy concentration on the persistence luminescence properties of Eu doped barium aluminate (BaAl₂O₄) laser-sintered ceramics. For this study, the ceramics were first sintered using the laser sintering technique, based on a CO₂ laser as the heating source, in an ambient atmosphere. The structural and morphology characteristics of the samples were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The laser-sintered ceramics presented are shown to be phase pure (single phased), and, for highest Dy concentration sample, a spurious Dy-rich phase at the grain boundary was observed. All samples exhibit the characteristic blue-green emission from the Eu²⁺ ion, due to the 4f⁶5d¹–4f⁷ transition (495 nm), even when they have been sintered in air. Finally, a clear dependence of the persistent luminescence intensity and decay time with the Dy concentration was verified.     

Effect of natural antioxidant combinations on lipid oxidation in cooked chicken meat during refrigerated storage

The effect of combinations of sage, oregano and honey on lipid oxidation in cooked chicken meat during refrigeration at 4°C for 96h was determined. Chicken samples (thigh and breast) were then separated into five groups: control; butylated hydroxytoluene; oregano+sage; oregano+sage+5%honey and oregano+sage+10%honey. Quantitative measurements of thiobarbituric acid reactive substances, conjugated dienes, hexanal, fatty acids, cholesterol and cholesterol oxides were used as indicators of lipid oxidation. Acceptability and preference were also evaluated. The effectiveness of the natural antioxidants for reducing the velocity of lipid oxidation in cooked chicken thigh and breast was demonstrated after 48 and 96h of refrigeration at 4°C. The treatments that presented the lowest hexanal values after 96h of refrigeration were oregano+sage+5%honey and oregano+sage+10%honey. Only traces of free cholesterol oxides were found (25-OH, 7-k, 7α-OH and 7β-OH). The natural antioxidants protected cooked chicken meat from oxidation processes and resulted in great acceptability.     

Improved Production of Cyclodextrins by Alkalophilic Bacilli Immobilized on Synthetic or Loofa Sponges

This study aimed to improve the production of β-cyclodextrin (β-CD) by microbial cells immobilized on synthetic or loofa sponges both with and without the use of alginate or chitosan. The most suitable matrix for the immobilization of Bacillus firmus strain 7B was synthetic sponge and for Bacillus sphaericus strain 41 was loofa sponge. After 330 days of storage, the β-CD production by Bacillus firmus and Bacillus sphaericus remained at around 41% and 49%, respectively, of initial levels. After 24 days of immobilization on loofa sponge, Bacillus sphaericus strain 41 achieved an improved operational stability, reaching 86.6 mM β-CD after 20 days of production, compared to only 32.8 mM of β-CD produced by free Bacillus sphaericus strain 41 cells. The expected increase in β-CD production by immobilized cells of Bacillus firmus strain 7B on synthetic sponge for 4 days was not statistically different to that for cells immobilized for 24 days. The application of this process on an industrial scale using loofa sponge, an inexpensive and renewable matrix, will allow the stable production of β-CD.