Preparation and characterization of iron-chelating peptides from whey protein: An alternative approach for chemical iron fortification

Identification of calcium chelating peptides from peanut protein hydrolysate and absorption activity of peptide-calcium complex

BACKGROUND

Peanut peptides have good chelating ability with metal ions. However, there are few studies on the chelation mechanism of peanut peptides with calcium and absorption properties of peptide-calcium complex.

RESULTS

Peptides with high calcium chelating rate were isolated and purified from peanut protein hydrolysate (PPH), and the chelation rate of component F21 was higher (81.4 ± 0.8%). Six peptides were identified from component F21 by liquid chromatography-tandem mass spectrometry, and the frequency of acidic amino acids and arginine in the amino acid sequence was higher in all six peptides. Peanut peptide-calcium complex (PPH21-Ca) was prepared by selecting component F21 (PPH21). Ultraviolet analysis indicated that the chelate reaction occurred between peanut peptide and calcium ions. Fourier transform infrared analysis showed that the chelating sites were carboxyl and amino groups on the amino acid residues of peptides. Scanning electron microscopy revealed that the surface of peanut peptide had a smooth block structure, but the surface of the complex had a granular morphology. Caco-2 cell model tests revealed that the bioavailability of PPH21-Ca was 58.4 ± 0.5%, which was significantly higher than that of inorganic calcium at 37.0 ± 0.4%.

CONCLUSION

Peanut peptides can chelate calcium ions by carboxyl and amino groups, and the peptide-calcium complex had higher bioavailability. This study provides a theoretical basis for the development of new calcium supplement products that are absorbed easily. © 2024 Society of Chemical Industry.

Digestion and absorption characteristics of iron-chelating silver carp scale collagen peptide and insights into their chelation mechanism

Iron deficiency is widespread throughout the world, supplementing sufficient iron or improving the bioavailability of iron is the fundamental strategy to solve the problem of iron scarcity. Herein, we explored a new form of iron supplement, iron chelates of silver carp scales (SCSCP-Fe) were prepared from collagen peptide of silver carp scales (SCSCP) and FeCl2·4H2O, the effects of external environment and simulated gastrointestinal digestive environment on the stability of SCSCP-Fe and the structural changes of peptide iron chelates during digestion were investigated. The results of in vitro iron absorption promotion showed that the iron bioavailability of SCSCP-Fe was higher than that of FeSO4. Two potential high iron chelating peptides DTSGGYDEY (DY) and LQGSNEIEIR (LR) were screened and synthesized from the SCSCP sequence by molecular dynamics and LC-MS/MS techniques. The FTIR results displayed that the binding sites of DY and LR for Fe2+ were the carboxyl group, the amino group, and the nitrogen atom on the amide group on the peptide. ITC results indicated that the chelation reactions of DY and LR with Fe2+ were mainly dominated by electrostatic interactions, forming chelates in stoichiometric ratios of 1:2 and 1:1, respectively. Both DY and LR had a certain ability to promote iron absorption. The transport of DY-Fe chelate may be a combination of the three pathways: PepT1 vector pathway, cell bypass, and endocytosis, while LR-Fe chelate was dominated by bivalent metal ion transporters. This study is expected to provide theoretical reference and technical support for the high-value utilization of silver carp scales and the development of novel iron supplements.

Mineral-element-chelating activity of food-derived peptides: influencing factors and enhancement strategies

Mineral elements including calcium, iron, and zinc play crucial roles in human health. Their deficiency causes public health risk globally. Commercial mineral supplements have limitations; therefore, alternatives with better solubility, bioavailability, and safety are needed. Chelates of food-derived peptides and mineral elements exhibit advantages in terms of stability, absorption rate, and safety. However, low binding efficiency limits their application. Extensive studies have focused on understanding and enhancing the chelating activity of food-derived peptides with mineral elements. This includes obtaining peptides with high chelating activity, elucidating interaction mechanisms, optimizing chelation conditions, and developing techniques to enhance the chelating activity. This review provides a comprehensive theoretical basis for the development and utilization of food-derived peptide-mineral element chelates in the food industry. Efforts to address the challenge of low binding rates between peptides and mineral elements have yielded promising results. Optimization of peptide sources, enzymatic hydrolysis processes, and purification schemes have helped in obtaining peptides with high chelating activity. The understanding of interaction mechanisms has been enhanced through advanced separation techniques and molecular simulation calculations. Optimizing chelation process conditions, including pH and temperature, can help in achieving high binding rates. Methods including phosphorylation modification and ultrasonic treatment can enhance the chelating activity.

A novel antioxidant iron-chelating peptide from yak skin: analysis of the chelating mechanism and digestion stability in vitro

BACKGROUND

The global prevalence of iron deficiency has posed significant public health risks. Animal-derived collagen peptides have been recognized for their potent metal ion-chelating capabilities, which can greatly enhance the bioavailability of iron. Yak skins, typically discarded during production and processing, serve as a valuable resource. Based on yak skin collagen peptide (YSP), we have developed a novel iron-chelating peptide: yak skin collagen iron-chelating peptide (YSP-Fe).

RESULTS

The maximum level of iron chelation of YSP-Fe achieved was 42.72 ± 0.65 mg g-1. Structural analysis indicated that YSP-Fe was primarily formed from amino, carboxyl and carbonyl groups combined with ferrous ions. Through examination of the amino acid composition, molecular docking and peptide sequence identification, it was determined that Gly, Asp and Arg played crucial roles in the chelation of ferrous ions by YSP. Furthermore, YSP-Fe was more stable in simulated gastrointestinal digestion compared to FeSO4.

CONCLUSION

YSP-Fe demonstrated dual benefits of iron supplementation and antioxidant effects. These significant findings provide a foundation for the development of novel iron supplements and the effective utilization of yak skin as a valuable resource. © 2024 Society of Chemical Industry.

One-step high efficiency separation of prolyl endopeptidase from Aspergillus niger and its application

Prolyl endopeptidase from Aspergillus niger (An-PEP) is an enzyme that recognizes C-terminal peptide bonds of amino acid chains and cleaves them by hydrolysis. An aqueous two-phase system (ATPS) was used to separate An-PEP from fermentation broth. Through single factor experiments, the ATPS containing 16 % (w/w) PEG2000 and 15 % (w/w) (NH4)2SO4 at pH 6.0 obtained the recovery of 79.74 ± 0.16 % and the purification coefficient of 7.64 ± 0.08. It was then used to produce soy protein isolate peptide (SPIP) by hydrolysis of soy protein isolate (SPI), and SPIP-Ferrous chelate (SPIP-Fe) was prepared with SPIP and Fe2+. The chelation conditions were optimized by RSM, as the chelation time was 30 min, chelation temperature was 25 °C, SPIP mass to VC mass was two to one and pH was 6.0. The obtained chelation rate was 82.56 ± 2.30 %. The change in the structures and functional features of SPIP before and after chelation were investigated. The FTIR and UV-Vis results indicated that the chelation of Fe2+ and SPIP depended mainly on the formation of amide bonds. The fluorescence, SEM and amino acid composition analysis results indicated that Fe2+ could induce and stabilize the surface conformation and change the amino acid distribution on the surfaces of SPIP. The chelation of SPIP and Fe2+ resulted in the enhancement of radical scavenging activities and ACE inhibitory activities. This work provided a new perspective for the further development of peptide-Fe chelates for iron supplement.

Screening, separation and identification of metal-chelating peptides for nutritional, cosmetics and pharmaceutical applications

Metal-chelating peptides, which form metal-peptide coordination complexes with various metal ions, can be used as biofunctional ingredients notably to enhance human health and prevent diseases. This review aims to discuss recent insights into food-derived metal-chelating peptides, the strategies set up for their discovery, their study, and identification. After understanding the overall properties of metal-chelating peptides, their production from food-derived protein sources and their potential applications will be discussed, particularly in nutritional, cosmetics and pharmaceutical fields. In addition, the review provides an overview of the last decades of progress in discovering food-derived metal-chelating peptides, addressing several screening, separation and identification methodologies. Furthermore, it emphasizes the methods used to assess peptide-metal interaction, allowing for better understanding of chemical and thermodynamic parameters associated with the formation of peptide-metal coordination complexes, as well as the specific amino acid residues that play important roles in the metal ion coordination.

Effect of different iron ratios on interaction and thermodynamic stability of bound whey protein isolate

Whey protein isolates (WPI) are known to have mineral-binding capacity to promote iron absorption. The aim of this study was to investigate the effect of iron ratio on the conformational structure of iron-bound whey protein isolate (WPI-Fe) and its thermodynamic stability. It was shown that the iron to protein ratio affects both the iron binding capacity of WPI and the iron valence state on the surface of WPI-Fe complexes. As the iron content increases, aggregation between protein molecules occurs. In addition, WPI-Fe nanoparticles have thermodynamic stability and Fe2+ has a high affinity with WPI for spontaneous exothermic reactions. This study demonstrates that WPI-Fe complexes can be used to efficiently deliver high-quality iron source (Fe2+) for future iron supplements.

Preparation, characterization, and bioavailability evaluation of antioxidant phosvitin peptide-ferrous complex

BACKGROUND

Iron deficiency anemia (IDA) is one of the commonest global nutritional deficiency diseases, and the low bioavailability of iron is a key contributing factor. The peptide-iron complex could be used as a novel iron supplement to improve iron bioavailability.

RESULTS

In this study, antioxidant low molecular weight (<3 kDa) phosvitin peptide (named PP-4) was separated to prepare a phosvitin peptide-ferrous complex (named PP-4-Fe); then the structural conformation of PP-4-Fe was characterized and its bioavailability by in vitro digestion was evaluated. The results showed that PP-4 had good ferrous-binding activity with 96.14 ± 2.86 μg Fe2+ mg-1 , and had a strong antioxidant effect with 995.61 ± 79.75 μmol TE mg-1 in 2,2'-azinobis'3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 62.3 ± 3.95 μmol FeSO4 mg-1 in ferric ion reducing antioxidant power (FRAP). After ferrous binding, the FRAP activity of PP-4-Fe, enhanced by 1.8 times, formed a more ordered structure with an increase in α-helix and decrease in γ-random coil. The ferrous binding sites of PP-4 involved were the amino, carboxyl, imidazole, and phosphate groups. The PP-4-Fe complex displayed excellent gastrointestinal stability and antioxidant effects during digestion. The iron dialysis percentage of PP-4-Fe was 74.59% ± 0.68%, and increased to 81.10% ± 0.89% with the addition of 0.25 times vitamin C (VC). This indicated that PP-4-Fe displayed excellent bioavailability and VC in sufficient quantities had a synergistic effect on improving bioavailability.

CONCLUSIONS

This study demonstrated that antioxidant phosvitin peptide was an efficient delivery system to protect ferrous ions and suggested that the phosvitin peptide-ferrous complex has strong potential as a ferrous supplement. © 2023 Society of Chemical Industry.

Peptide composition analysis, structural characterization, and prediction of iron binding modes of small molecular weight peptides from mung bean

Iron supplementation is a proactive approach to limit instances of iron deficiency anemia. This study is based on the enzymatic hydrolysis and fractionation of mung bean proteins (MBPs) followed by the determination of the Fe2+ chelating activities of these peptide-containing fractions. MBP-Fe complex was generated using a chemical chelation method and subsequently characterized. Following Sephadex G15 separation of MBPs, one of the fractions containing 10 different peptides, demonstrated maximum Fe2+ chelating activity of 39.97 ± 0.07 μg/mg. The sequences of these peptides were determined using liquid chromatography-tandem mass spectrometry. The Fe2+ ion content of the MBP-Fe complex was determined using X-ray photoelectron spectroscopy and 80% of the iron was found to be in Fe2+ oxidation state. After iron chelation, there was an increase in the peptide's particle size, with an average value of 550.67 ± 0.70 nm. This increase in size was attributed to the contributions of the amino proline and glycine, which extended the peptides to form the MBP-Fe complex. Finally, molecular docking studies revealed that Fe2+ mainly bound to carboxy-oxygen of glutamate and aspartate residues of mung bean peptides to form MBP-Fe complex. This research could serve as a scientific foundation for the development of dietary iron supplements using plant-derived peptides.

A critical review of a typical research system for food-derived metal-chelating peptides: Production, characterization, identification, digestion, and absorption

In the past decade, food-derived metal-chelating peptides (MCPs) have attracted significant attention from researchers working towards the prevention of metal (viz., iron, zinc, and calcium) deficiency phenomenon by primarily inhibiting the precipitation of metals caused by the gastrointestinal environment and exogenous substances (including phytic and oxalic acids). However, for the improvement of limits of current knowledge foundations and future investigation directions of MCP or their derivatives, several review categories should be improved and emphasized. The species' uniqueness and differences in MCP productions highly contribute to the different values of chelating ability with particular metal ions, whereas comprehensive reviews of chelation characterization determined by various kinds of technique support different horizons for explaining the chelation and offer options for the selection of characterization methods. The reviews of chelation mechanism clearly demonstrate the involvement of potential groups and atoms in chelating metal ions. The discussions of digestive stability and absorption in various kinds of absorption model in vitro and in vivo as well as the theory of involved cellular absorption channels and pathways are systematically reviewed and highlighted compared with previous reports as well. Meanwhile, the chelation mechanism on the molecular docking level, the binding mechanism in amino acid identification level, the utilizations of everted rat gut sac model for absorption, and the involvement of cellular absorption channels and pathway are strongly recommended as novelty in this review. This review makes a novel contribution to the literature by the comprehensive prospects for the research and development of food-derived mineral supplements.

The Metschnikowia pulcherrima Clade as a Model for Assessing Inhibition of Candida spp. and the Toxicity of Its Metabolite, Pulcherrimin

Candidiasis is one of the most frequent infections worldwide. In this study, the antimicrobial properties of six strains belonging to the Metschnikowia pulcherrima clade were evaluated against twenty Candida and Candida-related Filobasidiella neoformans var. bacillispora (syn. Cryptococcus neoformans) of different origins, employing the agar cross method. The toxic effect of pulcherrimin, a red metabolite that is responsible for the antimicrobial activities of Metschnikowia spp., was evaluated in various experimental models. The results of agar tests showed that the selected M. pulcherrima strains inhibited the growth of the Candida and non-Candida strains. However, inhibition was dependent on the strain and the environment. The presence of peptone, sodium silicate, and a higher incubation temperature decreased the antifungal action of the M. pulcherrima strains. Pulcherrimin showed cytotoxic and antiproliferative activity, with oxidative stress in cells leading to apoptosis. More research is needed on the mechanism of action of pulcherrimin on somatic cells.

Metal-binding peptides and their potential to enhance the absorption and bioavailability of minerals

Minerals including calcium, iron, zinc, magnesium, and copper have several human nutritional functions due to their metabolic activities. Body tissues require sufficient levels of a variety of micronutrients to maintain their health. To achieve these micronutrient needs, dietary consumption must be adequate. Dietary proteins may regulate the biological functions of the body in addition to acting as nutrients. Some peptides encoded in the native protein sequences are primarily responsible for the absorption and bioavailability of minerals in physiological functions. Metal-binding peptides (MBPs) were discovered as potential agents for mineral supplements. Nevertheless, sufficient studies on how MBPs affect the biological functions of minerals are lacking. The hypothesis is that the absorption and bioavailability of minerals are significantly influenced by peptides, and these properties are further enhanced by the configuration and attribute of the metal-peptide complex. In this review, the production of MBPs is discussed using various key parameters such as the protein sources and amino acid residues, enzymatic hydrolysis, purification, sequencing and synthesis and in silico analysis of MBPs. The mechanisms of metal-peptide complexes as functional food ingredients are elucidated, including metal-peptide ratio, precursors and ligands, complexation reaction, absorbability and bioavailability. Finally, the characteristics and application of different metal-peptide complexes are also described.

Identification, in silico selection, and mechanism study of novel antioxidant peptides derived from the rice bran protein hydrolysates

The work aimed to assess the antioxidant ability and obtain a new antioxidant peptide from rice bran protein. Rice bran protein was hydrolyzed by Alcalase, Neutral, Pepsin, Chymotrypsin, and Trypsin, separately. Trypsin hydrolysate (T-RBPH) showed high Fe²⁺ chelating activity (IC₅₀, 2.271 ± 0.007 mg/mL), DPPH and hydroxyl radical scavenging ability (IC₅₀, 0.191 ± 0.006 and 1.038 ± 0.034 mg/mL). Moreover, T-RBPH could alleviate the H₂O₂-induced oxidative damage in Caco-2. The T-RBPH was purified and identified by UF, GF, FPLC, and LC-MS/MS. Finally, 9-amino acid peptide-AFDEGPWPK with low molecular weight (1045.48 Da), high antioxidant activity, good safety, and solubility was screened by in silico method and chemical oxidation determination, and its interaction with Keap1 was also demonstrated. The ORAC and DPPH radical scavenging ability of AFDEGPWPK were 44.16 ± 0.79 and 28.38 ± 0.14 μmol TE/mM. Moreover, the Molecular docking and Western blot (WB) results showed that AFDEGPWPK could enter the binding pocket in the Kelch domain and activate Keap1/Nrf2/HO-1 pathway.

Identification of a Novel Walnut Iron Chelating Peptide with Potential High Antioxidant Activity and Analysis of Its Possible Binding Sites

Peptide iron chelate is widely regarded as one of the best iron supplements for relieving iron deficiency. In this study, a new type of walnut peptide iron (WP-Fe) chelate was prepared using low molecular weight walnut peptides (WP) as raw materials. Under the conditions of this study, the chelation rate and iron content of the WP-Fe chelate were 71.87 ± 1.60% and 113.11 ± 2.52 mg/g, respectively. Fourier transform infrared spectroscopy (FTIR), zeta potential, amino acid composition, and other structural analysis showed that WP-Fe is formed by the combination of carboxyl, amino and carbonyl with Fe²⁺. The WP-Fe chelate exhibits a honeycomb-like bulk structure different from that of WP. In addition, we predicted and established the binding model of ferrous ion and WP by molecular docking technology. After chelation, the free radical scavenging ability of the WP-Fe chelate was significantly higher than that of the WP. Overall, the WP-Fe chelate has high iron-binding capacity and antioxidant activity. We believe that peptides from different sources also have better iron binding capacity, and peptide iron chelates are expected to become a promising source of iron supplement and antioxidant activities.

A new iron supplement: The chelate of pig skin collagen peptide and Fe2+ can treat iron-deficiency anemia by modulating intestinal flora

Introduction

Iron deficiency anemia (IDA) is one of the most common nutritional diseases encountered all over the world. Nowadays, oral iron supplementation is still the mainstay of IDA treatment.

Methods

In this study, a new iron nutritional supplement named pig skin collagen peptides ferrous chelates (PSCP-Fe) was prepared, and its structure was characterized by the scanning electron microscopy, sykam amino acid analyzer and Fourier transform infrared spectroscopy (FTIR). The anti-IDA activity of PSCP-Fe was evaluated in low-Fe²⁺ diet-induced IDA in rats. 16S amplicon sequencing technology was then used to reveal the mechanism of PSCP-Fe against IDA.

Results

The results of amino acid analysis and FTIR showed that aspartic acid (Asp), arginine (Arg), histidine (His), glutamic acid (Glu), cystine (Cys), and lysine (Lys) residued in PSCP chelated readily with Fe²⁺ through their functional groups. PSCP-Fe treated reversed the hematology-related indexes, such as red blood cells (RBC), hemoglobin (HGB), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentrate (MCHC), serum ferritin (SF), serum hepcidin (HEPC) and serum transferrin receptor (TFR). And its regulatory action was better than that of FeSO₄. Moreover, PSCP-Fe alleviated the hepatocyte apoptosis and necrosis, Fe²⁺ loss, and injury in IDA rats. In addition, PSCP-Fe could significantly retrace the disturbed profile of gut microbiota in IDA rats (p < 0.05) and significantly up-regulated the relative abundances of nine bacterial genus, including Lactobacillus, Alloprevotella, unclassified_of_Oscillospiraceae, and NK4A214_group (p < 0.05). It could also downgrade the relative abundances of Subdoligranulum and Coriobacteriaceae_UCG-002 (p < 0.05). The results of Spearman's correlation analysis and distance-based redundancy analysis (db-RDA) revealed that Subdoligranulum and Christensenellaceae_R-7_group may be potential microbial markers for effective PSCP-Fe action in the treatment of IDA.

Discussion

Overall, our results elucidate the interactions between gut bacteria and related cytokines and reveal the mechanisms underlying the anti-IDA effect of PSCP-Fe. They will thus provide a theoretical foundation for PSCP-Fe as a new iron nutritional supplement.

A Step for the Valorization of Spent Yeast through Production of Iron–Peptide Complexes—A Process Optimization Study

Given the importance of iron in human nutrition and the significance of waste and by-product valorisation in a circular economy environment, we investigated the effects of protein and iron concentration on the production yield of iron–peptide complexes from spent Saccharomyces cerevisiae. For this purpose, different amounts of protein and iron were used in the complexation process. The results have shown that higher concentrations, although permitting a faster and larger scale process, provide a significantly lower complexation yield, which deems the process less feasible. This is corroborated by fluorescence analysis, which shows a lower degree of complexation with higher protein concentration. In addition, varying the concentration of iron does not change the quality of formed complexes, as evidenced by Fourier transform infrared spectroscopy (FT-IR) analysis. The morphology of all samples was also evaluated using scanning electron microscopy (SEM). Therefore, further studies are needed to optimize the process and to evaluate the best conditions for an economically sound valorization process for iron–peptide complexes. Nonetheless, current results in the development of a new process for the valorisation of spent yeast, in the form of iron-peptide complexes, look promising.

Formulations with microencapsulated Fe–peptides improve in vitro bioaccessibility and bioavailability

The bioaccessibility and the bioavailability of iron complexed to peptides (active) in microparticles forms contained in dry beverages formulations were evaluated. The peptide-iron complexes microparticles were obtained by spray drying and added in three dry formulations (tangerine, strawberry, and chocolate flavors). The peptides isolated by iron ion affinity (IMAC-Fe III) had their biological activity predicted by BIOPEP® database and were evaluated by molecular coupling. The bioaccessibility was evaluated by solubility and dialysability and the bioavalability was assessed by Caco-2 cellular model. The proportion 10:1 of peptide-iron complexes presented higher rates of bioaccessibility (49%) and bioavailability (56%). The microparticle with peptide-iron complex showed greater solubility after digestion (39.1%), bioaccessibility (19.8%), and bioavailability (34.8%) than the ferrous sulfate salt (control) for the three assays (10.2%; 12.9%; 9.7%, respectively). Tangerine and strawberry formulations contributed to the iron absorption according to the results of bioaccessibility (36.2%, 30.0% respectively) and bioavailability (80.5%, 84.1%, respectively). The results showed that iron peptide complexation and microencapsulation process improve the bioaccessibility and bioavailability when incorporated into formulations.

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Iron solubility is increased in iron peptide complexes.

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In silico interaction between peptides > 5 KDa and ferric iron (Fe²⁺).

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Microparticle with Fe-peptides increase iron bioavailability after digestion.

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Microparticle formulations improve iron bioaccessibility and bioavailability.

Preparation of corn ACE inhibitory peptide-ferrous chelate by dual-frequency ultrasound and its structure and stability analyses

In order to improve iron chelating ability and retain the activity of functional peptide, corn peptide was chelated with iron to form corn ACE inhibitory peptide-ferrous chelate (CP-Fe) treated by dual-frequency ultrasound. Furthermore, the chelating mechanism was revealed by analyzing various structural changes, and the stability was further evaluated. Under this study condition, the iron-binding capacity of corn ACE inhibitory peptide (CP) and chelate yield reached 66.39% and 82.87%, respectively. Ultrasound-treated CP exhibited a high iron chelating ability, meanwhile, chelation reaction had no significant effect on the ACE inhibition activity (82.21%) of the peptide. CP-Fe was formed by binding the peptides amino, carbonyl and carboxyl groups with Fe2+ demonstrated by Ultra-violet spectroscopy, Fourier transform infrared characterization, X-ray diffraction, energy dispersion spectrum, zeta potential, amino acid composition and other multi-angle analyses. Moreover, ultrasound-treated CP-Fe chelate exhibited porous surface and uniform nanoparticle shape. Furthermore, ultrasound-treated CP-Fe chelate exhibited an excellent stability towards various pH (retention rate ≥ 95.47% at pH 6-10), temperatures (retention rate ≥ 85.10% at 25-70 °C), and gastrointestinal digestion (retention rate 79.18%). Overall, ultrasound-treated CP-Fe chelate possessed high iron-chelating ability, ACE inhibition activity and stability. This study provides a novel synthesis method of the iron-chelating corn ACE inhibitory peptide, which is promising to be applied as iron supplements with high efficiency, bioactivity, and stability.