Understanding the Mechanism of Action of Triazine-Phosphonate Derivatives as Flame Retardants for Cotton Fabric

Phosphoenolpyruvate mutase-catalyzed C-P bond formation: mechanistic ambiguities and opportunities

Phosphonates are produced across all domains of life and used widely in medicine and agriculture. Biosynthesis almost universally originates from the enzyme phosphoenolpyruvate mutase (Ppm), EC 5.4.2.9, which catalyzes O-P bond cleavage in phosphoenolpyruvate (PEP) and forms a high energy C-P bond in phosphonopyruvate (PnPy). Mechanistic scrutiny of this unusual intramolecular O-to-C phosphoryl transfer began with the discovery of Ppm in 1988 and concluded in 2008 with computational evidence supporting a concerted phosphoryl transfer via a dissociative metaphosphatelike transition state. This mechanism deviates from the standard 'in-line attack' paradigm for enzymatic phosphoryl transfer that typically involves a phosphoryl-enzyme intermediate, but definitive evidence is sparse. Here we review the experimental evidence leading to our current mechanistic understanding and highlight the roles of previously underappreciated conserved active site residues. We then identify remaining opportunities to evaluate overlooked residues and unexamined substrates/inhibitors.

An eco-friendly NP flame retardant for durable flame-retardant treatment of cotton fabric

A halogen-free, formaldehyde-free, efficient, durable, NP flame retardant, the ammonium salt of meglumine phosphoric ester acid (ASMPEA), was prepared. The Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹H NMR, ¹³C NMR, and ³¹P NMR) results indicated that ASMPEA was grafted onto cotton fibers by P-O-C covalent bonds. The LOI value of 30 wt% ASMPEA-treated cotton fabric was 40.2%, and after 50 laundering cycles (LCs), the LOI value decreased to 29.4%, indicating that the cotton fibers treated with ASMPEA were endowed with excellent durable flame retardancy. Thermogravimetry (TG), cone calorimetry, and vertical flammability test results showed that ASMPEA-treated cotton decomposed into phosphoric acid or polyphosphoric acid during combustion, which promoted the thermal degradation and charring of treated cotton fabrics and hindered the spread of flames. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectrometry (EDS) verified that ASMPEA infiltrated the cotton fiber without obviously affecting its surface morphology or crystal structure; however, the mechanical properties of the treated cotton fabric decreased slightly. These results confirm that ASMPEA achieved excellent durable flame retardancy when used to coat cotton fabric.

A highly efficient chemical approach to producing green phosphorylated cellulosic macromolecules

The introduction of phosphate groups into cellulosic fibers allows for the tuning of their fire resistance, chelating and metal-adhesion properties, enabling the development of flame-retardant adhesive and adsorbent materials. Toward that end, the major challenge is developing a novel efficient and environmentally friendly phosphorylation route that offers an alternative to existing methods, which can achieve the targeted properties. For this purpose, cellulosic fibers were chemically modified herein using solid-state phosphorylation with phosphoric acid and urea without causing substantial damage to the fibers. The morphological, physicochemical, structural and thermal characterisations were examined using FQA, SEM, EDX, FTIR, ¹³C/³¹P NMR, conductometric titration, zeta potential measurement and thermogravimetric analysis. All the characterisations converge towards a crosslinked polyanion structure, with about 20 wt% grafted phosphates, a nitrogen content of about 5 wt% and a very high charge density of 6608 mmol kg⁻¹. Phosphate groups are linked to cellulose through a P–O–C bond in the form of orthophosphate and pyrophosphates. Furthermore, thermal properties of the phosphorylated cellulosic fibers were investigated and a new degradation mechanism was proposed.

The introduction of phosphate groups into cellulosic fibers allows for the tuning of their fire resistance, chelating and metal-adhesion properties, enabling the development of flame-retardant adhesive and adsorbent materials.

Preparation of a novel flame retardant containing triazine groups and its application on cotton fabrics

A novel triazine-based flame retardant capable of reacting with natural cellulose fiber was successfully synthesized and used to improve the flame retardancy of cotton fabrics.

Insight into the Synthesis and Characterization of Organophosphorus-Based Bridged Triazine Compounds

In this article, we report the synthesis of 2,4,6-substituted s-triazine-based organophosphorus compounds via a two-step process, which enables their production in high yields, and with a high purity as solids. In the first step, a Michaelis–Arbuzov rearrangement of cyanuric chloride with triethyl phosphite afforded 2,4,6-trisdiethoxyphosphinyl-1,3,5-triazine (HEPT). Subsequently, the nucleophilic substitution reaction on the triazine carbon was achieved, owing to the electron-withdrawing ability of the phosphonate groups. This characteristic of HEPT facilitated its derivatization with bi-functional amines, producing novel P–C containing bridged triazine organophosphorus compounds. The molecular structures of all of the compounds were confirmed by NMR spectroscopy, CHN elemental analysis, and single crystal X-ray analysis. In the thermogravimetric analysis in an N₂ environment, >33% char formation was observed for the bridged compounds. The chemical composition analysis of the char obtained under the oxidative thermal decomposition of the bridged compounds confirmed the presence of phosphorus- and nitrogen-enriched species, which indicate their function in the condensed phase. Comparatively, the detection of HPO and H–C≡P in the gas phase during the pyrolysis of the bridged compounds can act as a source for PO^•, which is known for its gas phase flame inhibition reactions. The synergy of significant char formation and the generation of intermediates leading to PO^• during pyrolysis makes these molecules promising flame-retardant additives.

Phosphonate Biochemistry

Organophosphonic acids are unique as natural products in terms of stability and mimicry. The C-P bond that defines these compounds resists hydrolytic cleavage, while the phosphonyl group is a versatile mimic of transition-states, intermediates, and primary metabolites. This versatility may explain why a variety of organisms have extensively explored the use organophosphonic acids as bioactive secondary metabolites. Several of these compounds, such as fosfomycin and bialaphos, figure prominently in human health and agriculture. The enzyme reactions that create these molecules are an interesting mix of chemistry that has been adopted from primary metabolism as well as those with no chemical precedent. Additionally, the phosphonate moiety represents a source of inorganic phosphate to microorganisms that live in environments that lack this nutrient; thus, unusual enzyme reactions have also evolved to cleave the C-P bond. This review is a comprehensive summary of the occurrence and function of organophosphonic acids natural products along with the mechanisms of the enzymes that synthesize and catabolize these molecules.