Coordination Complexes and One-Step Assembly of Lignin for Versatile Nanocapsule Engineering

Abstract

Nanoencapsulation of active substances with controlled release in harmless matrices has been the subject of numerous scientific efforts mainly due to the significant biomedical potential of such endeavors. Lignin, the environmentally sustainable byproduct of the pulp and paper industry, contains a multitude of phenolic hydroxyl groups, some of which, are known to readily and strongly chelate with iron ions. In this effort we demonstrated that the concerted use of chelation chemistry, oil in water emulsion principles, and low energy sonication, offers a facile, one-pot strategy to assemble lignin nanocapsules (LNCs) of a controlled architecture. Under these conditions capsules are shown to rapidly assemble utilizing two driving forces, the π-stacking propensity of lignin and its metal chelating ability at alkaline pH. Detailed size exclusion chromatographic evidence validates that the formation of capsules is driven mainly by the enumerated physical interactions with no significant chemical modification of the lignin. The developed process was systematically optimized so as to create the foundations for the morphology and the yield of the capsules being modulated as a function of sonication time, power, and surface contact area. Both pure LNCs and Fe-LNCs were synthesized in high yields with size distributions varying from 0.3 to 6 μm and their release efficiencies were evaluated in detail. As anticipated, the complexation effects of the phenolic OH groups offered to the Fe-LNCs, increased stability, reduced shell thickness (allowing for greater loading efficiencies), and lower release kinetics, compared to LNCs.

Stimuli‐Responsive Tannin–FeIII Hybrid Microcapsules Demonstrated by the Active Release of an Anti‐Tuberculosis Agent

“…[30,31] In short, microscopy images were processed by using the image analysis software ImageJ combined with Excel-based analysis to obtain statistical key data, on the basis of the three qualitatively best images were chosen for the software-based ImageJ analysis. [30,31] In short, microscopy images were processed by using the image analysis software ImageJ combined with Excel-based analysis to obtain statistical key data, on the basis of the three qualitatively best images were chosen for the software-based ImageJ analysis.…”

“…[30,31] Spectra were obtained by using aS himadzu UV/Vis spectrophotometer UV 1800. [30,31] Spectra were obtained by using aS himadzu UV/Vis spectrophotometer UV 1800.…”

“…[30,31] In short, aliquots taken at designated time intervals (0, 30 min, 1, 2, 4, 8, and 24 h, 2, 3, 5, 7, 8, 9, and 10 d) by centrifuging the solution of coumarin 6-filled Fe-TMCs in PBS at 5000 rpm for 5min, whereby the intake amounts of coumarin 6i n the aqueous phase were isolated from the supernatant foam. [30,31] In short, aliquots taken at designated time intervals (0, 30 min, 1, 2, 4, 8, and 24 h, 2, 3, 5, 7, 8, 9, and 10 d) by centrifuging the solution of coumarin 6-filled Fe-TMCs in PBS at 5000 rpm for 5min, whereby the intake amounts of coumarin 6i n the aqueous phase were isolated from the supernatant foam.…”

“…[30] It wasd emonstrated that sonication of oil in water emulsions of different families of tannins are able to generate micro-and nanocapsules with varying degrees of stability.M ore specifically,o ligomeric condensed tannins were found to be able to form stable nanocapsules.U nfortunately, monomeric tannins such as epigallocatechin gallate (EGCG) or tannic acid( TA)g enerate unstablen anoemulsions and do not support the formation of stable micro-and nanocapsule preparations. [31] Recently,i tw as also reported that gallic acid-metal complexes are able to generate stable thin film coatingso ns pecific templates; am echanism that could eventually be used to generate ferric tannic acid capsules around as olid polystyrene core that neededt o be removed in THF after capsule formation. [31] Recently,i tw as also reported that gallic acid-metal complexes are able to generate stable thin film coatingso ns pecific templates; am echanism that could eventually be used to generate ferric tannic acid capsules around as olid polystyrene core that neededt o be removed in THF after capsule formation.…”

“…For example, iron in fact plays as ignificant role in severali nfections from mycobacteria, among them tuberculosis. [30,31,36,41] The presented capsules contemporarily exploit the high self-aggregating and metal complexing character of the tannins. [36] Aiming at an extension of possible fields of application of polyphenol-based delivery systems, [30,31,36] targeting the exploitation of various potentialt ransport and triggering mechanisms, as mallb ut representative library of novel hybrid ferric tannin capsules is presented in this study.T hey rely on coordination complexes betweenf erric ions and four selected examples of tanninsf rom various: Schinopsis balansae wood extract (Sb)a nd Acacia mearnsii bark extract (Am)a se xamples for condensed tannins, tannic acid (TA) as ah ydrolysable tannin, and purified green tea extract consistingo fe pigallocatechin-3-Ogallate (EGCG)t or epresent complex tannins.…”