Amidoxime-derived rice husk as biocatalyst and scavenger for organophosphate neutralization and removal.

Organophosphates are a worldwide threat because of their presence in agrochemicals and chemical warfare. Situations of misuse, apprehensions of prohibited chemicals (e.g. pesticides), undesired stockpiles and chemical attacks require effective measures for neutralization and removal. Herein, a green approach is shown by functionalizing the agricultural waste rice husk with amidoximes leading to heterogeneous catalysts that were applied in the degradation/scavenging of toxic organophosphates. In aqueous medium, the waste-derived catalyst was efficient in the catalytic neutralization of a phosphotriester (increments up to 1 × 104-fold), while allying important features: selective, recyclable and lead to less toxic products. Curiously, the amidoximated rice husk behaved as a scavenger in the aprotic polar solvents MeCN and acetone by covalently bonding to the phosphoryl moiety. Upon addition of water, this bond is broken and the phosphoryl liberated (hydrolyzed) to the aqueous medium. Thus, the scavenging process is reversible and can be used to remove toxic organophosphates. 31P nuclear magnetic resonance spectroscopy was crucial for confirming the overall mechanisms involved. In summary, a sustainable material was synthetized from a waste source and employed as catalyst and scavenger for eliminating threatening organophosphates. This is promising for assuring chemical security such as in chemical emergencies.

Waste-derived biocatalysts for pesticide degradation.

A green approach to produce a cellulose-derived biocatalyst containing hydroxamic acids targeted for the neutralization of toxic organophosphates is shown. The cellulose source, rice husk, is among the largest agricultural waste worldwide and can be strategically functionalized, broadening its sustainable application. Herein, rice husk was oxidized in different degrees, leading to carboxylic acid-based colloidal and solid samples. These were functionalized with hydroxamic acids via amide bonds and fully characterized. The hydroxamic acid derived biocatalysts were evaluated in the cleavage of toxic organophosphates, including the pesticide Paraoxon. Catalytic increments reached up to 107-fold compared to non-catalyzed reactions. Most impressively, the materials showed P atom-selectivity and recyclability features. This guarantees only one reaction pathway that leads to less toxic products, hereby, detoxifies. Overall, highly sustainable catalysts are presented, that benefits from waste source, its green functionalization and is successfully employed for the promotion of chemical security of threatening organophosphates. To the best of our knowledge, this is the first report of a hydroxamate-derived rice husk (selectively modified at the C6 of cellulose) and its application in organophosphates reaction.

pKa determination of graphene-like materials: Validating chemical functionalization.

We report a novel pKa determination for different graphene-like samples: graphene oxide (GO), reduced GO (rGO), graphene nanoribbons (GNR), oxidized GNR (GONR), thiol- and imidazole-functionalized GO (GOSH and GOIMZ, respectively) and thiol-functionalized GONR (GONRSH). Using the specialized computational program BEST7 for treating titration curves, pKas for different functional groups were discriminated (confirmed by infrared spectra) and their composition quantified. Overall, three equilibria were distinguished, two relative to carboxylic acids exhibiting different acidic degrees (pKa1∼4.0 and pKa2∼6.0) and one relative to alcohols (pKa4∼10.0). Upon functionalization on carboxylate sites, thiol (pKa(GOSH/GONRSH)=6.7) and imidazole (pKa(GOIMZ)=6.6) moieties were discerned, followed by a decrease of their carboxylate percentage (compared to the precursors), thus allowing determining the degree of functionalization (48% and 36% of thiol content for GOSH and GONRSH respectively, and 29% of imidazole for GOIMZ). The proposed method is innovative and simpler when compared to the traditional tools usually employed to quantify chemical functionalization.

An ionically tagged water-soluble artificial enzyme promotes the dephosphorylation reaction with nitroimidazole: enhanced ionic liquid effect and mechanism.

In this paper, we describe a novel synthesized ionically tagged water-soluble artificial enzyme (PI) that can efficiently cleave phosphate esters, with enhanced an ionic liquid effect through cooperative effects for the substrate activation and further nucleophilic reaction. The dephosphorylation reaction with PI was evaluated in the presence and absence of 2-methyl-4(5)-nitroimidazole, showing impressive rate enhancements of up to 2 × 10(6)-fold, ascribed to the imidazolide species known as excellent nucleophiles, and formed favorably at lower pH values in the presence of PI.

A tailored biocatalyst achieved by the rational anchoring of imidazole groups on a natural polymer: furnishing a potential artificial nuclease by sustainable materials engineering.

Foreseeing the development of artificial enzymes by sustainable materials engineering, we rationally anchored reactive imidazole groups on gum arabic, a natural biocompatible polymer. The tailored biocatalyst GAIMZ demonstrated catalytic activity (>10(5)-fold) in dephosphorylation reactions with recyclable features and was effective in cleaving plasmid DNA, comprising a potential artificial nuclease.

Functionalized graphene oxide as a nanocatalyst in dephosphorylation reactions: pursuing artificial enzymes.

The present study reports for the first time the use of a thiol-functionalized graphene oxide nanocatalyst with impressive activity (>10(5)-fold) in dephosphorylation reactions. The innovative and recyclable nanocatalyst has potential in designing artificial enzymes with targeted multifunctionalities and in detoxification of organophosphorus agents.