The mechanism of iron binding processes in erionite fibres

Our plain-English summary of The mechanism of iron binding processes in erionite fibres, by A. Pacella, C. Cremisini, E. Nardi, et al (Scientific Reports, 2017).

The study

• Authors: A. Pacella, C. Cremisini, E. Nardi, M.R. Montereali, I. Pettiti, P. Ballirano
• Journal: Scientific Reports
• Published: 2017;7(1):1319
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Fibrous erionite-Na from Rome (Oregon, USA) was K-exchanged and characterized from the structural point of view. In addition, the modifications experienced after contact with a Fe(II) source were investigated for evaluating if the large potassium ions, blocking off nearly all the erionite cavity openings, might prevent the Fe(II) binding process, which is currently assumed to be one of the reasons of the toxicity of erionite. The K-exchanged sample had a 95% reduction of the BET surface area indicating that it behaves as a mesoporous material. Exchanged K is segregated at K2 and at OW sites commonly occupied by H2O. The latter K cations provide a relevant contribution to the reduction of the surface area. Surprisingly, despite the collapse of its surface area the sample preserves the tendency to bind Fe(II). Therefore, yet in the case of a peculiar and potentially hostile structural environment the Fe(II) ion-exchange process has essentially the same kinetics observed in a typical erionite sample. This is a clear evidence of the very limited effect of the chemical composition of erionite on the Fe(II) binding process and reasonably it does not play a significant role in its toxicity.

In plain English

This was a laboratory study of erionite, a fibrous zeolite mineral, using fibres of erionite-Na from Rome, Oregon, USA. The authors asked whether loading the fibres with large potassium ions, which block the mineral's internal cavities, would stop the fibres from taking up iron in its Fe(II) form. The authors described Fe(II) binding as currently assumed to be one of the reasons for erionite's toxicity. The fibres were treated with a concentrated potassium chloride solution and then placed in an iron chloride solution. The potassium treatment raised the potassium content from 2.5 to 5.91 atoms per formula unit. The measured surface area collapsed to about 12 square metres per gram, compared with 252 reported earlier for the untreated material. Even so, the potassium-treated fibres bound 290 nanomoles of iron per milligram, comparable to the 291 found earlier for untreated erionite-Na. The iron was taken up mostly in exchange for potassium. The authors concluded that the fibres' chemical composition has a very limited effect on iron binding, and hypothesized that it does not play a significant role in toxicity. The experiments used mineral samples only.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment: chemical and structural characterization of potassium-exchanged erionite fibres before and after contact with an Fe(II) (ferrous chloride) solution
• Who was studied: Mineral sample, not people or animals: fibrous erionite-Na from Rome, Oregon, USA, previously characterized by the same research group; about 5 g of raw sample was enriched
• Exposure: Erionite fibres were first K-exchanged in a concentrated potassium chloride (KCl) solution. Then 25 mg of the K-exchanged fibres were suspended in 25 mL of a 500 µM ferrous chloride (FeCl2) solution for 1 hour at 37 °C. Experiments were done in triplicate.
• Main results:
  • After the KCl treatment, potassium content of the fibres rose from 2.5 (3) to 5.91 (9) atoms per formula unit and sodium fell from 3.8 (3) to 1.41 (10), so the sample was classified as erionite-K
  • The BET surface area of the K-exchanged samples collapsed to about 12 square metres per gram, against 252 (5) square metres per gram reported earlier for the untreated erionite-Na
  • The K-exchanged fibres bound 290 (13) nmol/mg of iron from the 500 µM FeCl2 solution
  • This was comparable to the 291 (1) nmol/mg found in an earlier study (Ballirano et al.) for untreated erionite-Na in the same solution
  • During iron loading the K-exchanged fibres released a net 445 (33) nmol/mg of potassium, indicating iron was taken up mainly by exchange with potassium
  • Within the crystal structure, iron was attributed to a specific cavity site called Ca3
  • After iron loading, the BET surface area rose to 73.7 (17) square metres per gram, still below the untreated sample
  • When the iron-loaded sample was further heated under vacuum at 200 °C, its surface area rose to 308 (7) square metres per gram
• The authors' conclusion: The authors concluded that, although potassium blocked nearly all the cavities, erionite-K kept its capacity to bind Fe(II). They saw this as evidence of a very limited effect of the fibres' chemical composition on Fe(II) binding, and hypothesized that chemical composition does not play a significant role in inducing toxicity.
• Limitations the authors state:
  • Sodium results from the two analytical methods disagreed (SEM-EDS versus ICP). The authors attributed this to sodium moving in the outer layer of the fibres during micro-analysis, and suggested sodium may have been underestimated by SEM-EDS.

Topics

Medical terms in this study, explained in our Lexicon: erionite, Cation.

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