How does iron interact with sporopollenin exine capsules? An X-ray absorption study including microfocus XANES and XRF imaging

Abstract

Sporopollenin exine capsules (SECs) derived from plant spores and pollen grains have been proposed as adsorption, remediation and drug delivery agents. Despite many studies there is scant structural data available. This X-ray absorption investigation represents the first direct structural data on the interaction of metals with SECs and allows elucidation of their structure-property relationships. Fe K-edge XANES and EXAFS data have shown that the iron local environment in SECs (derived from Lycopodium clavatum) reacted with aqueous ferric chloride solutions is similar to that of ferrihydrite (FeOOH) and by implication ferritin. Fe Kα XRF micro-focus experiments show that there is a poor correlation between the iron distribution and the underlying SEC structure indicating that the SEC is coated in the FeOOH material. In contrast, the Fe Kα XRF micro-focus experiments on SECs reacted with aqueous ferrous chloride solutions show that there is a very high correlation between the iron distribution and the SEC structure, indicating a much more specific form of interaction of the iron with the SEC surface functional groups. Fe K-edge XANES and EXAFS data show that the Fe II can be easily oxidised to give a structure similar to, but not identical to that in the Fe III case, and that even if anaerobic conditions are used there is still partial oxidation to Fe III . CREATED USING THE RSC ARTICLE TEMPLATE (VER. 3.0) -SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS ARTICLE TYPE www.rsc.org/xxxxxx | XXXXXXXX 2 | Journal Name, [year], [vol], 00-00 ](ragweed with magnetite prepared from FeCl2 and FeCl3) have been proposed as a method for the removal of organic pollutants from aqueous media, 44 and those derived from Candida rugosa have shown excellent enatioselectivity. 45,46 Despite the large amount of work carried out on metal sorption and coordination to SECs there are very few reports on the nature of the interaction between the metal ions and the sporopollenin itself. It is important to understand how such conjugates are capable of fulfilling their roles to enable insights into new potential applications such as solid supports for metal catalysts. X-ray absorption spectroscopy (XAS) is able to probe the local structural environment around the element of interest. When carried out using micro-focus instrumentation it can provide both structural and chemical state imaging data from single exines. This approach has been used previously at the Fe K-edge to study geological [47][48][49][50][51] and soil samples, 52,53 archaeological specimens, 54-59 biological tissues [60][61][62][63][64][65][66][67][68] and cometary material. [69][70][71][72] Whilst there has been some X-ray absorption work on sporopollenin using the C K-edge (ca. 290 eV), which identified ketonic groups on the surface of the pollen grain and aliphatic carbon across the whole structure, 73 there appears to be no XAS experiments carried out at the metal K-edges in the literature. In this work we report an Fe K-edge XANES and EXAFS as well as an Fe Kα X-ray fluoresc...

Natural Sunflower Pollen as a Drug Delivery Vehicle

“…In recent years, the robust exine capsule, isolated from pollen grains and plant spores, has demonstrated strong potential as a delivery vehicle for the encapsulation of various materials including pharmaceutical drugs, vaccines, contrast agents, and oils . In the materials encapsulation strategies explored thus far, high‐purity exine capsules are required and obtained through vigorous and prolonged processing of pollen grains or spores under harsh conditions using organic solvents, acids and bases at elevated temperatures, or systematic exposure to numerous enzymes .…”

Lycopodium Spores: A Naturally Manufactured, Superrobust Biomaterial for Drug Delivery

“…These proven therapeutic benefi ts have led to the commercialization of L. clavatum based oral herbal formulations for the treatment of diverse health conditions such as anxiety, albuminuria, constipation, dysentery, gallstones, heartburn, hemorrhoids, impotence, indigestion, irritability, prostatitis, renal colic, and rheumatism. [ 8,[12][13][14][15] The therapeutic activity of these spore constituents is supported by bioassay-guided studies on L. clavatum indicating that a major component, a lycopodine alkaloid, is responsible for the anti-infl ammatory activity of the extract for wound-healing applications. [ 40 ] As other industrial applications, these spores have also been used as a dry powder in latex gloves and condom manufacturing.…”

“…[ 1 ] L. clavatum spores are used in traditional herbal medicine and have been shown to exhibit a wide range of therapeutic benefi ts including improved osteogenesis, [ 11 ] improved cognitive function, [ 12 ] treatment of gastrointestinal disorders, [ 8 ] hepatoprotective activity, [ 13 ] and antioxidative properties. [ 14 ] Recent studies have demonstrated the use of processed L. clavatum shells for encapsulation, [15][16][17][18][19] however, the production of L. clavatum sporopollenin capsules requires the prolonged processing of natural spores with harsh chemical treatments at elevated temperatures, so as to isolate the sporopollenin exine shell. [20][21][22][23][24] In many applications, this extensive processing may be unnecessary and potential therapeutic benefi ts may be lost.…”

2015 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry and their applications

“…Experiments were recorded at 13.5 keV with the incident X-ray beam focused using a pair of Kirkpatrick-Baez mirrors, and a Si (111) double-crystal monochromator. Another "rst" was claimed by Archibald et al 254 who showed how iron interacts with sporopollenin exine capsules. The authors were able to show that foliar applied zinc combined with an organic bio-stimulant increased the mobility of zinc within the sunower.…”