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Porous silica-based materials are attractive for biomedical applications due to their biocompatibility and biodegradable character. In addition, inorganic supports such as porous silicon are being developed due to integrated circuit chip compatibility and tunable properties leading to a wide range of multidisciplinary applications. In this contribution, biosilica extracted from a rarely studied plant material (Equisetum Myriochaetum), its conversion to silicon and the potential for both materials to be used as supports for enzyme immobilization are investigated. E. myriochaetum was subject to conventional acid digestion to extract biogenic silica with a% yield remarkably higher (up to 3 times) than for other Equisetum sp. (i.e. E. Arvense). The surface area of the isolated silica was ∼400 m 2 /g, suitable for biotechnological applications. Biogenic silicon was obtained by magnesiothermic reduction. The materials were characterized by SEM-EDX, XRD, FT-IR, ICP-OES, TGA and BET analysis and did not contain significant levels of class 1 heavy elements (such as Pb, Cd, Hg and As). Two commercial peroxidases, horseradish peroxidase (HRP) and Coprinus cinereus peroxidase (CiP) were immobilized onto the biogenic materials using three different functionalization routes: (A) carbodiimide, (B) amine + glutaraldehyde and (C) amine + carbodiimide. Although both biogenic silica and porous silicon could be used as supports differences in behaviour were observed for the two enzymes. For HRP, loading onto biogenic silica via the glutaraldehyde immobilization technique (route B) was most effective. The loading of CiP showed a much higher peroxidase activity onto porous silicon than silica functionalized by the carbodiimide method (route A). From the properties of the extracted materials obtained from Equisetum Myriochaetum and the immobilization results observed, these materials appear to be promising for industrial and biomedical applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Silica is the second most abundant biomineral being exceeded in nature only by biogenic CaCO3. Many land plants (such as rice, cereals, cucumber, etc.) deposit silica in significant amounts to reinforce their tissues and as a systematic response to pathogen attack. One of the most ancient species of living vascular plants, Equisetum arvense is also able to take up and accumulate silica in all parts of the plant. Numerous methods have been developed for elimination of the organic material and/or metal ions present in plant material to isolate biogenic silica. However, depending on the chemical and/or physical treatment applied to branch or stem from Equisetum arvense; other mineral forms such glass-type materials (i.e. CaSiO3), salts (i.e. KCl) or luminescent materials can also be isolated from the plant material. In the current contribution, we show the chemical and/or thermal routes that lead to the formation of a number of different mineral types in addition to biogenic silica.

This contribution provides the first detailed chemical evidence for the association of 'Si' with soluble carbohydrate and proteinaceous components of Equisetum arvense cell walls. For Equisetum telmateia and E. arvense, the presence of intrasilica organics trapped within phytolithic silica deposits and organics packaged within silica coated particles on the outside of spores have previously been identified. The current paper shows that 'Si' is also found intimately associated with cell wall polymers that can be released using mild extraction procedures (CDTA and Na(2)CO(3)/NaBH(4)) that do not solubilise the mineral phase. The isolates comprise both protein and carbohydrate components with increases in 'Si' (up to slightly more than 1% by weight) being particularly linked to increased levels of protein within the extracts. The general composition of the cell wall isolates associated with 'Si' was very different to that previously found for intrasilica and spore related material with much lower levels of charged amino acids, particularly basic amino acids being detected. The range of monosaccharides detected was much wider than for the other silicified materials investigated. It is possible that 'Si' in some form could act to crosslink the cell wall polymers thereby providing a modest improvement in rigidity/stability of the cell wall against biotic and abiotic stresses. This study demonstrates that distinct differences are to be found between extra- and intrasilica organics in the cell wall of E. arvense.

The use of high pH anion exchange chromatography combined with pulsed amperometric detection has been established as an effective and sensitive method for the separation, detection and quantification of monosaccharides from a wide range of sources. However, careful examination of the separation conditions required is necessary to ensure that a complete monosaccharide profile can be determined from structures such as the plant cell wall which is a complex network of both neutral and charged polysaccharides. This study has investigated the optimal conditions required for the analysis of such a challenging mixture, including both the stationary and mobile phase minimising co-elution and reducing method complexity. The preferred methods have been used to successfully identify and quantify the monosaccharide components of a selected extract from the plant cell wall of the primitive higher plant Equisetum arvense.

Equisetum species are primitive vascular plants that benefit from the biogenesis of silica bio-organic inclusions in their tissues and participate in the annual biosilica turnover in local eco-systems. As means of Equisetum reproduction and propagation, spores are expected to reflect the evolutionary adaptation of the plants to the climatic conditions at different times of the year. Combining methods of Raman and scanning electron microscopy and assisted with density functional theory, we conducted material spatial-spectral correlations to characterize the distribution of biopolymers and silica based structural elements that contribute to the bio-mineral content of the elater. The elater tip has underlying skeletal-like structural elements where cellulose fibers provide strength and flexibility, both of which are necessary for locomotion. The surface of the elater tips is rich with less ordered pectin like polysaccharide and shows a ridged, folded character. At the surface we observe silica of amorphous, colloidal form in nearly spherical structures where the silica is only a few layers thick. We propose the observed expansion of elater tips upon germination and the form of silica including encapsulated biopolymers are designed for ready dispersion, release of the polysaccharide-arginine rich content and to facilitate silica uptake to the developing plant. This behavior would help to condition local soil chemistry to facilitate competitive rooting potential and stem propagation. [ABSTRACT FROM AUTHOR]