Mechanisms of isomerization and hydration reactions of typical β-diketone at the air-droplet interface

Acetylacetone (AcAc) is a typical class of β-diketones with broad industrial applications due to the property of the keto-enol isomers, but its isomerization and chemical reactions at the air-droplet interface are still unclear. Hence, using combined molecular dynamics and quantum chemistry methods, the heterogeneous chemistry of AcAc at the air-droplet interface was investigated, including the attraction of AcAc isomers by the droplets, the distribution of isomers at the air-droplet interface, and the hydration reactions of isomers at the air-droplet interface. The results reveal that the preferential orientation of two AcAc isomers (keto- and enol-AcAc) to accumulate and accommodate at the acidic air-droplet interface. The isomerization of two AcAc isomers at the acidic air-droplet interface is more favorable than that at the neutral air-droplet interface because the "water bridge" structure is destroyed by H3O+, especially for the isomerization from keto-AcAc to enol-AcAc. At the acidic air-droplet interface, the carbonyl or hydroxyl O-atoms of two AcAc isomers display an energetical preference to hydration. Keto-diol is the dominant products to accumulate at the air-droplet interface, and excessive keto-diol can enter the droplet interior to engage in the oligomerization. The photooxidation reaction of AcAc will increase the acidity of the air-droplet interface, which indirectly facilitate the uptake and formation of more keto-diol. Our results provide an insight into the heterogeneous chemistry of β-diketones and their influence on the environment.

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Acetylacetone effectively controlled the secondary metabolites of Microcystis aeruginosa under simulated sunlight irradiation

Inactivation of cyanobacterial cells and simultaneous control of secondary metabolites is of significant necessity for the treatment of cyanobacteria-laden water. Acetylacetone (AcAc) has been reported a specific algicide to inactivate Microcystis aeruginosa (M. aeruginosa) and an effective light activator to degrade pollutants. This study systematically investigated the photodegradation ability of AcAc under xenon (Xe) irradiation on the secondary metabolites of M. aeruginosa, mainly algal organic matter (AOM), especially toxic microcystin-LR (MC-LR). Results showed that AcAc outperformed H2O2 in destructing the protein-like substances, humic acid-like matters, aromatic proteins and fulvic-like substances of AOM. For MC-LR (250 µg/L), 0.05 mmol/L AcAc attained the same degradation efficiency (87.0%) as 0.1 mmol/L H2O2. The degradation mechanism of Xe/AcAc might involve photo-induced energy/electron transfer and formation of carbon center radicals. Alkaline conditions (pH > 9.0) were detrimental to the photoactivity of AcAc, corresponding to the observed degradation rate constant (k1 value) of MC-LR drastically decreasing to 0.0013 min-1 as solution pH exceeded 9.0. The PO43- and HCO3- ions had obvious inhibition effects, whereas NO3- slightly improved k1 value from 0.0277 min-1 to 0.0321 min-1. The presence of AOM did not significantly inhibit MC-LR degradation in Xe/AcAc system. In addition, the biological toxicity of MC-LR was greatly reduced after photoreaction. These results demonstrated that AcAc was an alternative algicidal agent to effectively inactivate algal cells and simultaneously control the secondary metabolites after cell lysis. Nevertheless, the concentration and irradiation conditions should be further optimized in practical application.

Multifunctional Cd-CP for fluorescence sensing of Cr(VI), MnO4-, acetylacetone and ascorbic acid in aqueous solutions

The development of multifunctional fluorescent chemosensors for the detection of multiple targets remains challenging but of great importance. In this paper, one novel coordination polymer (CP), denoted as [Cd₂(edda)(phen)₂]∙H₂O (compound 1, H₄edda = 5,5' (ethane-1,2-diylbis(oxy)) diisophthalic acid, phen = 1,10-phenanthroline) is successfully designed and prepared under hydrothermal conditions. Structural analysis indicates that compound 1 possesses a one-dimensional (1D) double chain structure, then self-assembles into a three-dimensional (3D) supramolecular framework via π…π interactions between phen molecules. Interestingly, compound 1 is found to be tolerant in wide range of acidic to alkaline aqueous solutions (pH = 2-13). Fluorescent spectral investigations reveal that compound 1 exhibits highly selective and sensitive fluorescence responses toward MnO₄^-, Cr(VI) ions, acetylacetone (acac) and ascorbic acid (AA) by fluorescence quenching in the aqueous phase. The detection limits are in the very low range, reaching μM level for the detection of MnO₄^-, Cr(VI) ions, nM for AA and ppm for acac detection. The distinguished multi-responsive performance suggests compound 1 to be a potential multifunctional probe. Furthermore, the possible quenching mechanisms have also been systematically investigated in this work.

A water-stable dual-responsive Cd-CP for fluorometric recognition of hypochlorite and acetylacetone in aqueous media

One novel cadmium(II)-coordination polymer [Cd₃L₂(datrz)(H₂O)₃] (CP 1) is controllably synthesized by surmising the astute combination of semi-rigid tricarboxylate acid 4-(2',3'-dicarboxylphenoxy) benzoic acid (H₃L) and auxiliary ligand 3,5-diamino-1,2,4-triazole (datrz). Structure analysis shows that CP 1 has a two-dimensional (2D) layer structure with a 5-nodal (4³) (4⁴·6²) (4⁵·6⁴·8) (4⁵·6) (4⁷·6⁶·8²) topology. Further investigations reveal that CP 1 shows superordinary water stability and good thermal stability. The fluorescent explorations suggest that the as-synthesized CP 1 could emit blue light centered at 485 nm, attributing to ligand-based emission. In terms of sensing investigations, CP 1 could act as a fluorescent sensor for detecting hypochlorite (ClO^-) and acetylacetone (acac) through fluorescence turn-off process in aqueous solution, and the detection limit could reach 0.18 μM and 0.056 μM, respectively. Further research reveals that it is more likely the N-H···O-Cl hydrogen bonds between -NH₂ groups of the triazole ligands and O atoms of ClO^- plays the key role in the system, which may serve as a bridge for the energy transfer, leading to fluorescence quenching of the chemosensor. While the photoinduced electron transfer (PET) combined with inner filter effect (IFT) should be responsible for the turn-off fluorescence of CP 1 triggered by acac.

Effects of a redox-active diketone on the photochemical transformation of roxarsone: Mechanisms and environmental implications

Organoarsenical antibiotics pose a severe threat to the environment and human health. In aquatic environment, dissolved organic matter (DOM)-mediated photochemical transformation is one of the main processes in the fate of organoarsenics. Dicarbonyl is a typical redox-active moiety in DOM. However, the knowledge on the photoconversion of organoarsenics by DOM, especially the contributions of dicarbonyl moieties is still limited. Here, we systematically investigated the photochemical transformation of three organoarsenics with the simplest β-diketone, acetylacetone (AcAc), as a model dicarbonyl moiety of DOM. The presence of AcAc significantly enhanced the photochemical conversion of roxarsone (ROX), whereas only minor effects were observed for 3-amino-4-hydroxyphenylarsonic acid (HAPA) and arsanilic acid (ASA), because the latter two (with an amino (-NH₂) group) are more photoactive than ROX (with a nitro (-NO₂) group). The results demonstrate that AcAc was a potent photo-activator and the reduction of -NO₂ to -NH₂ might be a rate-limiting step in the phototransformation of ROX. At a 1:1 M ratio of AcAc to ROX, the photochemical transformation rate of ROX was increased by 7 folds. In O₂-rich environment, singlet oxygen, peroxide radicals, and ·OH were the main reactive species that led to the breakage of the C-As bond in ROX and the oxidation of the released arsono group to arsenate, whereas the triplet-excited state of AcAc (³AcAc*) and carbon-centered radicals from the photolysis of AcAc dominated in the reductive transformation of ROX. In anoxic environment, 3-amino-4-hydroxyphenylarsonic acid was one of the main reductive transformation intermediates of ROX, whose photolysis rate was about 35 times that of ROX. The knowledge obtained here is of great significance to better understand the fate of organoarsenics in natural environment.

[Determination of acetylacetone in workplace air by solvent desorption-gas chromatography]

Objective: To establish a method for the determination of acetylacetone in the air of workplace by gas chromatography. Methods: In August 2020, acetylacetone in the air of workplace was collected by silica gel tube, eluted with methanol, separated and detected by gas chromatography with flame ionization detector. The detection limit and precision of the method were also analyzed. Results: The linear range of acetylacetone was 1.95-1950.60 μg/ml with the regression equation of y=0.815x-3.667, and the correlation coefficient was 0.99993. The limit of detection of the method was 0.18 μg/ml and the minimum detection concentration was 0.12 mg/m(3) (collected sample volume was 1.50 L). The within-run precisions were 1.08%-4.11% and the between-run precisions were 1.98%-2.80%. The desorption rates were 99.68%-100.45%. The sealed samples could be kept at least 15 days at room temperature without significant loss. Conclusion: The solvent desorption-gas chromatography method for the determination of acetylacetone has good precision, high sensitivity and simple operation, and is suitable for the determination of acetylacetone in the air of the workplace.

Peroxyl radicals from diketones enhanced the indirect photochemical transformation of carbamazepine: Kinetics, mechanisms, and products

In surface waters, photogenerated transients (e.g., hydroxyl radicals, carbonate radicals, singlet oxygen and the triplet states of dissolved organic matter) are known to play a role in the transformation of biorecalcitrant carbamazepine (CBZ). Small diketones, such as acetylacetone (AcAc) and butanedione (BD), are naturally abundant and have been proven to be effective precursors of carbon and oxygen centered radicals. However, the photochemical kinetics and mechanisms of coexisting diketones and CBZ are barely known. Herein, the effects of AcAc and BD on the photochemical conversion of CBZ were investigated compared with H₂O₂ which was the main ·OH precursor in the environment. An enhancing effect was observed for the degradation of CBZ by the addition of diketones. The enhancing effect of diketones was pH-dependent and much more significant than H₂O₂ under simulated solar irradiation. On the basis of the identification of transient species and the competition kinetic model, organic peroxyl radicals were found to play a dominant role in CBZ photodegradation, and the second-order rate constants of the reaction between CBZ and peroxyl radicals were determined to be approximately 10⁷-10⁸ M^-1s^-1. Furthermore, mutagenic acridine was found to be the major cumulative intermediate with a yield of > 30% in the presence of diketones, which might be an environmental concern. This work indicates that the coexistence of diketones and persistent organic pollutants might lead to some detrimental effects on aquatic environments if the water is exposed to sunlight.

A cholesterol benzoate RRS probe for the determination of trace ammonium ions

The measurement of NH₄⁺ has attracted considerable attention with the increase of NH₄⁺ emissions in sewage caused by human activities. So far, a variety of photometric and fluorescence methods for the detection of NH₄⁺ have been researched and summarized, but there is no report about the use of liquid crystals (LCs) cholesteryl benzoate (CB) as a resonance Rayleigh scattering (RRS) probe to determine ammonium ions. In the NaAc-HAc buffer solution with pH = 4.80, the yellow compounds 3,5 diacetyl-1,4 dihydrolutidine (DDL) generated by the reaction of NH₄⁺ with acetylacetone (AT) and formaldehyde (HCHO) act as the energy receiver and CB as the donor. Because the RRS spectrum of CB overlaps with the DDL absorption spectrum, resonance Rayleigh scattering energy transfer (RRS-ET) occurs. When the NH₄⁺ concentration increased, the generated DDL increased, and the RRS-ET also increased, so the RRS intensity of the system at 395 nm decreased. For this reason, a fast and sensitive CB RRS-ET method was established to apply to the detection of NH₄⁺ in water. The detection range was 1.00 × 10^-3 - 4.66 μg/mL, and the detection limit was 6.62 × 10^-3 μg/mL. Using this method to analyze and detect NH₄⁺ in environmental water samples, the precision and recovery rate were between 1.30-9.30% and 95.5-109.9%, respectively. Therefore, this method has the advantages of sensitivity and simplicity.

Regulation of Photosynthesis in Bloom-Forming Cyanobacteria with the Simplest β-Diketone

Selective inhibition of photosynthesis is a fundamental strategy to solve the global challenge caused by harmful cyanobacterial blooms. However, there is a lack of specificity of the currently used cyanocides, because most of them act on cyanobacteria by generating nontargeted oxidative stress. Here, for the first time, we find that the simplest β-diketone, acetylacetone, is a promising specific cyanocide, which acts on Microcystis aeruginosa through targeted binding on bound iron species in the photosynthetic electron transport chain, rather than by oxidizing the components of the photosynthetic apparatus. The targeted binding approach outperforms the general oxidation mechanism in terms of specificity and eco-safety. Given the essential role of photosynthesis in both natural and artificial systems, this finding not only provides a unique solution for the selective control of cyanobacteria but also sheds new light on the ways to modulate photosynthesis.

Key structural features that determine the selectivity of UV/acetylacetone for the degradation of aromatic pollutants when compared to UV/H2O2

Acetylacetone (AA) has proven to be a potent photo-activator for the decolorization of dyes. However, there is very limited information on the quantitative structure-activity relationship (QSAR) and the mechanisms of dye degradation by UV/AA. Herein, the photolysis of 65 aromatic compounds (dyes and dye precursors) was investigated at three pH values (4.0, 6.0, 9.0) by UV/AA and UV/H₂O₂. The obtained pseudo-first-order photodegradation rate constants (k₁) were processed using statistical analysis. The correlation between the k₁ values and the number of photons absorbed by AA, together with the observed pH effect, suggested that the protonated enol structure of AA plays a crucial role in the photodecolorization of dyes. According to quantum chemical computation, photo-induced direct electron transfer between the excited state of AA and the dye was the main mechanism in the UV/AA process. QSAR models demonstrated that the molecular size and stability were the key factors that determined the efficiency of UV/H₂O₂ for dye degradation. Statistically, the UV/AA process was target-selective and suffered less from the inner filter effect, which made it more effective than the UV/H₂O₂ process for dye degradation. The selectivity of the UV/AA process was mainly embodied in the substituent effects: dyes with hydroxyl groups in conjugated systems decomposed faster than those with nitro-substitution or ortho-substituted sulfonate groups. The results can be used for the selection of appropriate photochemical approaches for the treatment of dye-contaminated water.

Role of complexation in the photochemical reduction of chromate by acetylacetone

Organic ligands can alter the redox behavior of metal species through the generation of metal-ligand complexes. Photo-induced complexation between ligands and metals is an important, but under-appreciated, aspect of process. Acetylacetone (AA) is a good chelating agent due to keto-enol tautomerization. In the presence of AA, photoreduction of Cr(VI) is accelerated; however, it is unclear exactly how complexation is involved in UV/AA mediated Cr(VI) reduction. On the basis of spectral and kinetic analyses, this study shows that the formation of {Cr(VI)-AA}* complexes is the main mechanism of Cr(VI) reduction by UV/AA. Evidence for this includes (1) the formation rate constant of Cr(III)-AA complexes in the UV system was 2-3 orders of magnitude greater than that in the thermal system; (2) there was a linear relationship between the photons absorbed by AA and the reduction rate constants of Cr(VI); and (3) the reaction appeared initially zero-order in Cr(VI) and turned to first-order as the pool of available Cr(VI) ran out. The results presented here are not only important for the better understanding of the complexation effects in the reduction of Cr(VI), but also crucial for the possible application of the UV/AA process in many other scenarios.

Sludge reduction and cost saving in removal of Cu(II)-EDTA from electroplating wastewater by introducing a low dose of acetylacetone into the Fe(III)/UV/NaOH process

Cu(II)-EDTA is highly stable in a wide pH range (3.0∼12.0) and hard to be removed by the conventional precipitation method. Fe(III) displacement/UV photolysis/alkaline precipitation [Fe(III)/UV/NaOH] has been proposed as a promising method for the removal of Cu(II)-EDTA. Nevertheless, a high dose of Fe(III) is needed in this combined process, resulting in the production of a large amount of hazardous sludge. The photochemistry of Fe(III) is known to be ligand-dependent. Fe(III)-oxalate complexes are strongly photoactive. However, the addition of oxalic acid to the Fe(III)/UV/NaOH process was of little help. Acetylacetone (AA) is a good chelating ligand for many metals and has been proved as an efficient photo-activator. By introducing a low dose of AA ([AA]/[Cu] = 1.5) into the Fe(III)/UV/NaOH process, the Fe(III) dosage ([Fe]/[Cu]) was reduced from 10.4 to 3.2. As a result, the chemical cost was reduced from 13.9 to 7.6 kW h/m³. Meanwhile, the energy cost in the UV photolysis was reduced from 1066.5 to 752.4 kW h/m³. Most importantly, the sludge yields were reduced from 8.3 to 2.7 kg/m³ in a simulated wastewater and from 101.8 to 30.8 kg/m³ in a real electroplating wastewater. Such a sludge reduction is of great significance in mitigating the load of landfill.

Ligand effects on arsenite removal by zero-valent iron/O2: Dissolution, corrosion, oxidation and coprecipitation

Ligands may increase the yields of reactive oxygen species (ROS) in zero-valent iron (ZVI)/O₂ systems. To clarify the relationship between the properties of ligands and their effects on the oxidative removal of contaminants, five common ligands (formate, acetate, oxalate, ethylenediaminetetraacetic acid (EDTA), and phosphate) as well as acetylacetone (AA) were investigated with arsenite (As(III)) as the target contaminant at three initial pH values (3.0, 5.0, and 7.0). The addition of these ligands to the ZVI/O₂ system resulted in quite different effects on As(III) removal. EDTA enhanced the oxidation of As(III) to arsenate (As(V)) but inhibited the removal of As(V). Oxalate was the only ligand in this work that accelerated both the removal of As(III) and As(V). By analyzing the ligand effects from the four aspects: dissolution of surface iron (hydr)oxides, corrosion of ZVI, reaction with ROS, and interference with precipitation, the following properties of ligands were believed to be important: ability to provide dissociable protons, complexation ability with iron, and reactivity with ROS. The complexation ability is a double-edged sword. It could enhance the generation of ROS by reducing the reduction potential of the Fe(III)/Fe(II) redox couple, but also could inhibit the removal of arsenic by coprecipitation. The elucidated relationship between the key property parameters of ligands and their effects on the ZVI/O₂ system is helpful for the rational design of effective ZVI/ligand/O₂ systems.

Effects of acetylacetone on the thermal and photochemical conversion of benzoquinone in aqueous solution

Quinones are components of electron transport chains in photosynthesis and respiration. Acetylacetone (AA), structurally similar to benzoquinone (BQ) for the presence of two identical carbonyl groups, has been reported as a quinone-like electron shuttle. Both BQ and AA are important chemicals in the aquatic environment. However, little information is known about their interactions if co-existed. We found here that AA significantly enhanced the conversion of BQ. By analyzing the evolution of chemical concentration, solution pH, dissolved oxygen, and the final products, the interactions between AA and BQ were elucidated. The reactions between BQ and AA generated oxygen but ultimately led to the reduction of solution pH and dissolved oxygen. The reactions proceeded faster under indoor lighting condition than in the dark. The formation of semiquinone radicals is believed as the primary step. The secondary AA-derived radicals might be strongly oxidative or reductive, depending on the concentration of dissolved oxygen. Insoluble humus was generated in the mixture of BQ and AA. These results suggest that the presence of AA might interfere with photosynthesis and respiration through the interactions with quinones.

A rapid method to detect and estimate the activity of the enzyme, alcohol oxidase by the use of two chemical complexes - acetylacetone (3,5-diacetyl-1,4-dihydrolutidine) and acetylacetanilide (3,5-di-N-phenylacetyl-1,4-dihydrolutidine)

A rapid and sensitive method has been devised in order to detect and estimate the synthesis of the enzyme alcohol oxidase (AOX) by fungi, by way of the use of two chemical complexes, namely, acetylacetone (3,5-diacetyl-1,4-dihydrolutidine) and acetylacetanilide (3,5-di-N-phenylacetyl-1,4-dihydrolutidine). This method involves the use of the AOX enzyme that could specifically oxidize methanol, giving rise to equimolar equivalents each of formaldehyde (HCHO) and hydrogen peroxide (H₂O₂) as the end products. Further, the formaldehyde, thus produced was allowed to interact with the neutral solutions of acetylacetone and the ammonium salt, gradually developing a yellow color, owing to the synthesis and release of 3,5-diacetyl-1,4-dihydrolutidine (yellow product; λ = 420 nm; λ_ex/em = 390/470 nm) and the product, so generated was quantified spectrophotometrically by measureing its absorbance at 412 nm. In another set up, the amount of formaldehyde produced as a sequel to the oxidation of methanol by the AOX enzyme was determined by allowing it to react with the acetylacetanilide reagent, after which the volume of the fluorescent product - 3,5-di-N-phenylacetyl-1,4-dihydrolutidine (colorless product; λ_ex/em = 390/470 nm) that was generated was estimated by measuring its emission at 460 nm (excitation wavelength at 360 nm) in a spectrophotometer. Of the various substrates tested, a commercial source of the AOX enzyme appreciably oxidizes methanol, thereby generating formaldehyde, and further reacts with acetylacetone, to give rise to a bright yellow complex, displaying a maximum activity of 1402 U/mL. Determination of the AOX activity by the use of acetylacetone and acetylacetanilide could serve as a viable alternative to the conventional alcohol oxidase-peroxidase-2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (AOX-POD-ABTS) based method. In view of this, this method appears to be invaluable for application at the various food, pharmaceutical, fuel, biosensor, biorefinery, biopolymer, biomaterial, platform chemical, and biodiesel industries.

Advantages of titanium xerogel over titanium tetrachloride and polytitanium tetrachloride in coagulation: A mechanism analysis

Titanium xerogel coagulant (TXC) worked better than titanium tetrachloride (TC) and polytitanium chloride (PTC) in a wider pH/dose range for the removal of turbidity. However, the underlying mechanisms were not comprehensively understood. In this work, the better coagulation performance of TXC than TC and PTC was systematically elucidated from the following aspects: the physicochemical properties of the three coagulants, the removal of turbidity and organic matter, and the complexation reactions in coagulation. The results demonstrate that the merits of TXC were attributable to the following characteristics: (1) the higher surface charge density/total surface site concentration/isoelectric point of TXC hydrolysates, (2) the formation of TXC hydrolysates with a net-work structure, and (3) the strong binding affinity of TXC hydrolysates to organic matter caused by the bonded acetylacetone in the TXC framework. In short, the hydrolysis behavior of TXC significantly differed from both its precursor, TC, and the prehydrolyzed PTC. The difference in the hydrolysis of TXC was derived from the gelation process, which led to the polymerization of Ti in a way different from prehydrolyzation. The elucidation of the hydrolysis mechanisms is useful for the better application of Ti-based coagulants and may shed light on the preparation of other metal salts.

Acetylacetone as an efficient electron shuttle for concerted redox conversion of arsenite and nitrate in the opposite direction

The redox conversion of arsenite and nitrate has direct effects on their potential environment risks. Due to the similar reduction potentials, there are few technologies that can simultaneously oxidize arsenite and reduce nitrate in one process. Here, we demonstrate that a diketone-mediated photochemical process could efficiently do this. A combined experimental and theoretical investigation was conducted to elucidate the mechanisms behind the redox conversion in the UV/acetylacetone (AA) process. Our key finding is that UV irradiation significantly changed the redox potential of AA. The excited AA, ³(AA)*, acted as a semiquinone radical-like electron shuttle. For arsenite oxidation, the efficiency of ³(AA)* was 1-2 orders of magnitude higher than those of quinone-type electron shuttles, whereas the consumption of AA was 2-4 orders of magnitude less than those of benzonquinones. The oxidation of arsenite and reduction of nitrate could be both accelerated when they existed together in UV/AA process. The results indicate that small diketones are some neglected but potent electron shuttles of great application potential in regulating aquatic redox reactions with the combination of UV irradiation.

Sensitive inexpensive spectrophotometric and spectrofluorimetric analysis of ezogabine, levetiracetam and topiramate in tablet formulations using Hantzsch condensation reaction

Two highly sensitive, simple and selective spectrophotometric and spectrofluorimetric assays have been investigated for the analysis of ezogabine, levetiracetam and topiramate in their pure and in pharmaceutical dosage forms. The suggested methods depend on the condensation of the primary amino-groups in the three drugs with acetylacetone and formaldehyde according to Hantzsch reaction yielding highly fluorescent yellow colored dihydropyridine derivatives. The reaction products of ezogabine, levetiracetam and topiramate were measured spectrophotometrically at 418, 390 and 380nm or spectrofluorimetrically at λ_em/ex of 495/425nm, 490/415nm and 488/410nm, respectively. Various experimental conditions have been carefully studied to maximize the reaction yield. At the optimum reaction conditions, the calibration curves were rectilinear over the concentration ranges of 8-25, 60-180 and 80-200μg/mL spectrophotometrically and 0.02-0.2, 0.2-1.2 and 0.2-1.5μg/mL spectrofluorimetrically for ezogabine, levetiracetam and topiramate, respectively with good correlation coefficients. The suggested methods were applied successfully for the analysis of ezogabine, levetiracetam and topiramate in their commercial tablets with high percentage recoveries and negligible interference from various excipients in pharmaceutical dosage forms. The results were statistically analyzed and showed the absence of any significant difference between both developed and published methods. The procedures were validated and evaluated by the ICH guidelines revealing good reproducibility and accuracy. Therefore, the two proposed methods may be considered of high interest for practical and reliable analysis of ezogabine, levetiracetam and topiramate in pharmaceutical dosage forms.

Descriptors for Pentane-2,4-dione and Its Derivatives

We have used equations for partition coefficients of compounds from water and the gas phase to various solvents to obtain descriptors for pentane-2,4-dione and 21 of its derivatives. These descriptors can then be used to estimate further partition coefficients into a wide variety of solvents. The descriptors also yield information about the properties of pentane-2,4-dione and its derivatives. Pentane-2,4-dione and its alkyl derivatives are quite polar, with substantial hydrogen bond basicity but with no hydrogen bond acidity. In contrast 1,1,1-trifluoropentane-2,4-dione and hexafluoropentan-2,4-dione have significant hydrogen bond acidities.

Applicability of light sources and the inner filter effect in UV/acetylacetone and UV/H2O2 processes

Light source is a crucial factor in the application of a photochemical process, which determines the energy efficiency. The performances of acetylacetone (AA) in conversion of aqueous contaminants under irradiation with a low-pressure mercury lamp, a medium-pressure mercury lamp, a xenon lamp, and natural sunlight were investigated and compared with those of H₂O₂ as reference. In all cases, AA was superior to H₂O₂ in the degradation of Acid Orange 7. Using combinations of the different light sources with various cut-off and band-pass filters, the spectra responses of the absorbed photons in the UV/AA and UV/H₂O₂ processes were determined for two colored and two colorless compounds. The photonic efficiency (φ) of the two photochemical processes was found to be target-dependent. A calculation approach for the inner filter effect was developed by taking the obtained φ into account, which provides a more accurate indication of the reaction mechanisms.

Effects of acetylacetone on the photoconversion of pharmaceuticals in natural and pure waters

Acetylacetone (AcAc) has proven to be a potent photo-activator in the degradation of color compounds. The effects of AcAc on the photochemical conversion of five colorless pharmaceuticals were for the first time investigated in both pure and natural waters with the UV/H₂O₂ process as a reference. In most cases, AcAc played a similar role to H₂O₂. For example, AcAc accelerated the photodecomposition of carbamazepine, oxytetracycline, and tetracycline in pure water. Meanwhile, the toxicity of tetracyclines and carbamazepine were reduced to a similar extent to that in the UV/H₂O₂ process. However, AcAc worked in a way different from that of H₂O₂. Based on the degradation kinetics, solvent kinetic isotope effect, and the inhibiting effect of O₂, the underlying mechanisms for the degradation of pharmaceuticals in the UV/AcAc process were believed mainly to be direct energy transfer from excited AcAc to pharmaceuticals rather than reactive oxygen species-mediated reactions. In natural waters, dissolved organic matter (DOM) played a crucial role in the photoconversion of pharmaceuticals. The role of H₂O₂ became negligible due to the scavenging effects of DOM and inorganic ions. Interestingly, in natural waters, AcAc first accelerated the photodecomposition of pharmaceuticals and then led to a dramatic reduction with the depletion of dissolved oxygen. Considering the natural occurrence of diketones, the results here point out a possible pathway in the fate and transport of pharmaceuticals in aquatic ecosystems.

Ligand effects on nitrate reduction by zero-valent iron: Role of surface complexation

Surface passivation is a key limiting factor in the application of zero-valent iron (ZVI) for water remediation. Addition of ligands is a useful approach to overcome this issue. In this work, a small amount of acetylacetone (AA) (0.5 mM) was found highly efficient to enhance the reduction of nitrate by ZVI at near neutral conditions (pH 6.0) with the formation of considerable black coating on ZVI. At an initial nitrate concentration of 20 mg N/L, the pseudo first-order reduction rate constant of nitrate in the ZVI-AA-NO₃^- system was 0.0991 h^-1, which was 52 times higher than that in the ZVI-NO₃^- system. Under otherwise identical conditions, the other five ligands, including EDTA, formate, acetate, oxalate, and phosphate, had negligible effects. Based on the pK_a values of these ligands and the final species of iron, the ligand effects on nitrate reduction by ZVI were summarized from three aspects: (1) the ability to offer potentially dissociable protons from the ligands; (2) the complexation ability to eliminate iron (hydr)oxide precipitates from the surface of ZVI; and (3) the ability to lower down the redox potentials of iron species. The good performance of AA in these three aspects makes it advantage over the other ligands. A cycle test up to six runs demonstrates that AA could continuously take effect in the ZVI system. The results here point out the potential of AA as an effective ligand in ZVI system for enhanced contaminant transformation.

Fate and implication of acetylacetone in photochemical processes for water treatment

Acetylacetone (AA), due to the peculiar enol-keto structures, has attracted wide scientific interests. In terms of photo-decolorization, it works much more efficiently than the well-known H2O2. However, there is very limited information on the photochemistry of AA in aqueous solutions. Herein, the photolysis kinetics, quantum yield, mass balance, decomposition pathway, and bioavailability of AA during UV irradiation were systematically investigated. It seems that photophysical processes predominated over photochemical ones when AA was irradiated with UV light. Although the quantum yield of AA (0.116) was much lower than that of H2O2 (1.0), the stronger light absorption of AA and the better overlap of the AA absorption spectrum with the solar emission spectrum, as well as the direct energy/electron transfer mechanisms, ensured its high efficiency in photochemical processes. The main degradation products of AA in photochemical processes were similar to the metabolic products in bio-fermentation. Besides, the irradiated AA solution showed a high bioavailability to the cells in activated sludge. Therefore, the UV/AA process might be a promising pre-treatment approach for bio-treatment. The results provide new insights into the photochemical fate and implication of β-diketones in aqueous solutions.

Co-immobilization of laccase and mediator through a self-initiated one-pot process for enhanced conversion of malachite green

Laccase is a green biocatalyst. It works with molecular oxygen and produces water as the only by-product. However, its practical application is far less than satisfactory due to the low stability/poor reusability of free laccase and the potential secondary pollution caused by dissolved mediators. To address those bottlenecks in laccase-based catalysis, a novel biocatalyst (Immo-LMS) was fabricated by simultaneously immobilizing both laccase and a mediator (acetylacetone, abbreviated as AA) into a hydrogel through the laccase-AA initiated polymerization. This self-initiated immobilization process avoided the forced conformational change of laccase in the passive embedding to pre-existing carriers. Resulting from the effective cooperation of laccase and AA, the Immo-LMS had the highest substrate conversion quantity to malachite green, followed by the sole immobilized laccase and the immobilized laccase with an external mediator. Besides the improved activity, the Immo-LMS showed enhanced stability. The good performance of the Immo-LMS suggests that the co-immobilization of laccase and mediator through the self-initiated one-pot process was a promising strategy for the immobilization of laccase, which is expected to be helpful to cut down the running cost as well as the potential toxicity that come from mediators in the practical application of laccase.

Iron in non-hydroxyl radical mediated photochemical processes for dye degradation: Catalyst or inhibitor?

The acetylacetone (AA) mediated photochemical process has been proven as an efficient approach for decoloration. For azo dyes, the UV/AA process was several to more than ten times more efficient than the UV/H2O2 process. Iron is one of the most common elements on the earth. It is well known that iron can improve the UV/H2O2 process through thermal Fenton and photo-Fenton reactions. What will be the role of iron in the UV/AA process? Could iron-AA complexes act as photocatalysts in environmental remediation? To answer these questions, the photo-degradation of an azo dye, Acid Orange 7 (AO7), was conducted under the variant combinations of AA with iron species in both ionic (Fe2+, Fe3+) and complex (Fe(AA)3) forms. The pseudo-first-order decoloration rate constants of AO7 in these photochemical processes followed such an order: UV/Fe(II)/AA<UV/Fe(III)/AA<UV/Fe(AA)3<UV/AA. The results demonstrate that iron species, in either ionic or complex form, acts as an inhibitor rather than a catalyst in the UV/AA process. Based on spectroscopic analysis, the inner filter effect of iron and the competition between Fe(III) and AA for the complexation with AO7 were attributed to the inhibition effect of iron on the UV/AA process. The understanding of the role of iron provides insight into the practical application of the UV/AA process.

Photodegradation of Acid Orange 7 in a UV/acetylacetone process

Acetylacetone (AcAc) was employed as a photo-activator for the degradation of Acid Orange 7 (AO7) under UV irradiation. The feasibility of this process (named as UV/AcAc) was evaluated through comparison with the well-established UV/H2O2 process in terms of absorption spectrum and the biodegradability of the solutions. A complete decoloration of the AO7 solution could be fulfilled with AcAc at mM level. A self-acceleration phenomenon was observed for the UV/AcAc process. The pseudo first-order decoloration rate constant of AO7 in the UV/AcAc process was several times higher than that in the UV/H2O2 process, depending on the irradiation conditions. The BOD to COD ratio of the solutions increased from below 0.1 to above 0.3, along with a slight mineralization. Based on degradation product analysis, the possible pathways for AO7 degradation in the UV/AcAc process were proposed.