In situ analysis of copper speciation during in vitro digestion: Differences between copper in drinking water and food.

In recent years, the safety of copper in drinking water has increasingly been questioned. Copper speciation is an important factor that affects its bioavailability and toxicity; thus, it is critical to investigate the speciation of copper that is ingested from food and drinking water during in vitro digestion. After digestion, water- and food-derived copper formed 60 ± 4% 0.1-1 kDa and 49 ± 6% 10-1,000 kDa copper complexes, respectively. Under simulated fasting drinking water conditions, up to 90 ± 2% 0.1-1 kDa copper complexes formed. In addition, using ion selective electrode analysis, water-derived copper was detected that contained higher Cu2+ concentrations after digestion than those of food-derived copper. These results indicate that water-derived copper forms smaller-sized species and exhibits higher Cu2+ concentrations during digestion than those of food-derived copper, thereby highlighting the importance of reassessing the safety limit for copper in drinking water.

The influence of gastrointestinal pH on speciation of copper in simulated digestive juice.

Speciation can provide knowledge about absorption, reactivity to binding sites, bioavailability, toxicity, and excretion of elements. In this study, the speciation of copper in different model solutions under the influence of gastrointestinal (GI) pH was studied by ion selective electrode (ISE) and inductively coupled plasma optical emission spectrometry (ICP OES). It was found that the electrode response (mV) against Cu2+ decreased with the increase in pH and dropped to the lowest point at pH 7.5 in all model solutions. When amino acids and organic acids were present, the ratio of filtered copper (0.45 µm, pH 7.5) was more than 90%. When casein was present, whey protein, pancreatin, and starch were added, and the ratio of filtered copper was 85.6 ± 0.3, 56.7 ± 8.8, 38.5 ± 5.1, and 1.0 ± 0.3%, respectively. When there is not enough organic ligand, excessive copper will form copper hydroxide precipitation with the increase in pH, but it got the highest electrode response (mV) against Cu2+. From this study, it can be concluded that the speciation of copper in GI tract is strongly influenced by the pH and the composition of food. When there are few ligands coexisting in the GI tract, the concentration of copper ion may be relatively high.

[Advances in polymer-based dendrimer-grafted chromatographic separation materials].

With the continuous developments in stationary phase preparation technology and materials science, numerous modification methods and new materials have been employed for the functional modification of the polymer stationary phases in solid-phase extraction, high performance liquid chromatography and ion chromatography. In particular, because of their unique structure and properties, poly(amidoamine) (PAMAM) dendrimers play an important role in improving the structure and performance of chromatographic separation materials. In this paper, the application of PAMAM to the modification of polymer-based chromatographic separation materials is reviewed, and further developments are prospected.

[Preparation of difunctional polymer-based cation exchangers and their application in ion chromatography].

Ion chromatography (IC) is one of the most important means for the separation and analysis of cationic compounds. Research on high-performance cation exchangers is of great significance for the advancement of modern IC techniques. Herein we proposed a newly developed modification method for polymer-based particles, based on thiol-radical-mediated polymerization. Specifically, acrylic acid and maleic anhydride were used as monomers and sodium 2-mercaptoethanesulfonate was used as the thiol modifier to prepare novel difunctional cation exchangers, functionalized with both carboxylic and sulfonic groups. With simple strong acid eluents, typical cations were well separated with good resolution. The retention behaviors of metal cations and organic amines on the cation exchangers were investigated using multiple chromatographic models. The good performances of the cation exchangers were also demonstrated by the gradient separation of ten cations within 24 min. The new method was easy to perform with high efficiency. Additionally, the cation exchange capacities of the cation exchangers were easily modulated by adjusting the initial content of the thiol modifier.

Effects of Organic Copper on Growth Performance and Oxidative Stress in Mice.

Copper (Cu) has been used as a feed additive for many years. However, high Cu amounts can cause oxidative stress and adversely affect animal performance. Such negative effects may depend on the amounts and forms of Cu. In the present study, the effects of inorganic Cu (CuSO4) and organic Cu (chelate-Cu) present in mice feed on daily growth rate and Cu deposition in the liver, kidneys, spleen, brain, and serum were assessed in addition to the oxidative stress levels in the liver and brain. Organic Cu at a concentration of 15 mg/kg significantly enhanced daily growth rate in mice, whereas Cu deposition in the livers was significantly lower than that in the inorganic Cu group. Glutathione peroxidase activity in the liver of the mice fed with organic Cu significantly improved, whereas malondialdehyde levels in the brain and liver were significantly lower than that in the inorganic Cu group. The different effects of organic Cu and inorganic Cu provide key evidence supporting the use of organic Cu in animal feeds.

Covalently grafted anion exchangers with linear epoxy-amine functionalities for high-performance ion chromatography.

Chemical constitution and construction of functional sites play a crucial part in the chromatographic behavior of stationary phases. We present novel polymeric anion exchangers covalently grafted with linear quaternary ammonium polyelectrolytes via simple one-step epoxy-amine polymerization. In separation of various anionic analytes, the newly developed anion exchangers showed high efficiency (e.g., >30,000 plates m-1 for chloride with hydroxide elution) and peculiar chromatographic behavior as compared to previously reported hyperbranched phases. By adopting different amines as the building unite of linear polyelectrolytes, the two types of model anion exchangers displayed segregated selectivity which in our opinion is associated with charge density, hydrophilicity and low cross-linking of the functionalities.

Hyperbranched anion exchangers prepared from thiol-ene modified polymeric substrates for suppressed ion chromatography.

The covalent modification of polymeric particles has been a challenge due to their chemical inertness. Herein we describe a facile and neat method via thiol-ene reaction to immobilize cysteamine/cysteine onto allylmethacrylate-divinylbenzene (AMA-DVB) and ethylvinylbenzene-divinylbenzene (EVB-DVB). The introduced functionalities were verified by elementary analysis and scanning electron microscope coupled with energy dispersive spectroscopy. This modification enabled the further grafting of hyperbranched condensation polymers (HBCPs), which converted the particles into anion exchangers. The anion exchangers demonstrated good separation with carbonate/bicarbonate eluents and hydroxide eluents for suppressed anion exchange chromatography. In the case of a 3-layered anion exchanger, simultaneous separation of nine model anions was achieved by isocratic elution in 17 min with efficiencies up to 16,100 plates m-1. High stability and dependable durability was exhibited in long-term tests.

Complex formation constant of ferric ion with Gly, Pro-Hyp and Gly-Pro-Hyp.

The complexes of protein hydrolysates with iron ions may provide one solution for treating iron deficiency because they can work as iron absorption promoters. The chelating ability of some protein hydrolyzates is the key for their iron absorption promotion. Collagen is the most abundant protein in the nature, and collagen peptides are reported to have the ability to promote iron absorption. Collagen's basic tri-peptide unit, i.e., glycine-proline-hydroxyproline (Gly-Pro-Hyp) and its digestion products, glycine (Gly) and proline-hydroxyproline (Pro-Hyp), have been studied against the ferric metal ion. The complexation abilities were determined potentiometrically at three different temperatures of 25 °C, 37 °C, and 40 °C. The ionic strength was maintained using 0.15 mol dm-3 NaCl. Potentiometric data were refined using Hyperquad 2008, and the species distributions were simulated using HySS2009. The complexes of [MA x H y ], with x = 1 to 3 and y = -4 to 2, were refined from three ligands at different temperatures and in the pH range from 2 to 11. The complex formation constant (log ß) indicated that the complex of Gly-Pro-Hyp was the most stable followed by Pro-Hyp and Gly complexes. Thermodynamic analysis revealed that the formation of the complexes of [MA x H y ], with x = 1 to 3 and y = 0, was spontaneous since the ΔG value was negative; this means that Gly, Pro-Hyp and Gly-Pro-Hyp have good iron chelating abilities and therefore, they can act as promising iron absorption promoters. The thermodynamic properties of these complexes were also studied, and the base for the usage of these complexes was provided.

Graphene-coated polymeric anion exchangers for ion chromatography.

Carbonaceous stationary phases have gained much attention for their peculiar selectivity and robustness. Herein we report the fabrication and application of a graphene-coated polymeric stationary phase for anion exchange chromatography. The graphene-coated particles were fabricated by a facile evaporation-reduction method. These hydrophilic particles were proven appropriate substrates for grafting of hyperbranched condensation polymers (HBCPs) to make pellicular anion exchangers. The new phase was characterized by zeta potentials, Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscope. Frontal displacement chromatography showed that the capacities of the anion exchangers were tuned by both graphene amount and HBCPs layer count. The chromatographic performance of graphene-coated anion exchangers was demonstrated with separation of inorganic anions, organic acids, carbohydrates and amino acids. Good reproducibility was obtained by consecutive injections, indicating high chemical stability of the coating.