Reversible Metal Ion/Complex Binding to Chitin Controlled by Ligand, Redox, and Photochemical Reactions and Active Movement of Chitin on Aquatic Arthropods

Abstract

There is strong adsorption of metal ions and their complexes to chitin, which depends on both the oxidation and complexation states of many of the said elements (whereas others display chemical reactions detectable via electrochemical methods while being retained by chitin); thus, ad- and desorption at ambient water concentrations (often in the nMol/L range) are controlled by the presence and photochemical properties (concerning Eu and probably U and Ag) of mainly biogenic organic matter (both DOC and POC, and DON). With chitin forming the outer hull of mobile organisms (animals), this biopolymer is expected to take part in metal distribution in aquatic (limnetic and riverine) ecosystems. Having studied the attachment of many different elements to both crayfish and grafted (marine shrimp) chitin, with the highest accumulations observed in Bi, V, Ni, and LREEs, one should consider secondary biochemical transformations which take place at different water and sediment levels. After chitin had been embedded into sediment, methanogenesis (which requires Ni), Bi, and Sb biomethylations and photodesorption in the illuminated water column will occur if there are appropriate organics, causing the vertical separation of Eu from other REEs, at least during the daytime. Eutrophication will enhance both the production and especially the photooxidation rates of organics in water because phosphorylated sugars and lipids are formed quantitatively within min P, which enter water and undergo Eu-mediated photooxidation much more readily. Another biopolymer, gelatin, acts as an inert matrix-enhancing organic photooxidation product via Eu, producing chemical waves, indicating autocatalysis upon light impact. From the redox-related photodesorption of metal analytes from chitin, both sensors and devices for (light-assisted) electrochemical energy conversion are being developed by our workgroup. The electrochemical determination of adsorption thermodynamics on chitin is thus directly linked to its applications in environmental monitoring and technology.

Metal Ions, Element Speciation Forms Retained on Wet Chitin: Quantitative Aspects of Adsorption and Implications for Biomonitoring and Environmental Technology

“…The exact procedure of calculating expected partition factors from empirical data on water/chitin concentrations and a, b values for the respective ions are described elsewhere [13], so they should not be fully repeated here to avoid self-plagiarism. Chitin samples obtained by either exposing grafted chitin (from Pandalus borealis) or representing parts of crayfish (Faxonius limosus) cover are treated with a defined amount of a solution of 15 g LiClO 4 in 100 mL dimethylformamide (DMF; 0.5 mL of solution/cm 2 of surface).…”

“…Previous work on chitin application dealt with either metal ion removal from wastewater [1,2], including anthropogenic radionuclides [3,4], or strived to outline an alternative to older methods of biomonitoring [5,6]. While the latter gave strong evidence for the response of chitin adsorption amounts to diffusion gradients in sediment [5,7,8], a formally rigorous treatment of partition factors PF aiming at their first-principles calculation and prediction still was missing. For a proper understanding, one should use all the available information from the performance of different chitin sorts at the same spot to extract thermodynamic information rather than trying to fit data to one or another of different empirical adsorption isotherms (without using electrochemical data proving pieces of information on adsorption to chitin previously [8].…”

“…While the latter gave strong evidence for the response of chitin adsorption amounts to diffusion gradients in sediment [5,7,8], a formally rigorous treatment of partition factors PF aiming at their first-principles calculation and prediction still was missing. For a proper understanding, one should use all the available information from the performance of different chitin sorts at the same spot to extract thermodynamic information rather than trying to fit data to one or another of different empirical adsorption isotherms (without using electrochemical data proving pieces of information on adsorption to chitin previously [8]. Differences among metal ions in terms of binding to chitin from water samples cover a range of typical environmental concentrations.…”

“…Since we deal with mesoscopic (plankton, cell walls of bacteria) to macroscopic (lichens, arthropods, mosses, larger animals or fungi) test organisms and the environment to be measured has dimensions of meters or more, the Schrödinger equation to predict the chance to encounter the analyte or some other molecule, ion at the organism or chitin surface rather than somewhere else in the "box" ( [9], and Figure 1) can be replaced with a simple partition function from empirical thermodynamics. Fitting to classical adsorption isotherms is not wise except for a few cases (mainly adsorption of Hg atoms from vapor Metabolic transformations may increase adsorption because the adsorbed chemical species is constantly removed from equilibrium (cp.…”

“…This function can be integrated to obtain theoretical partition factors (see [13] and Section 2). If there is metabolism, measured partition factors should be higher.…”