Chelating Reagent Research Articles

Colorimetric and fluorescence detection of Pb2+ by fluorescein derivative

A simple and low cost method for rapid detection of Pb2+ was developed in this study using a simple fluorescent probe, biotin-4-fluorescein. The presence of Pb2+ induced the color change of fluorescein from yellow to pink which can be detected visually by naked eyes. The color change of biotin-4-fluorescein was not observed while testing with other metal ions, such as Fe3+, Cu2+, Ca2+, Co2+ and Cd2+, indicating the selectivity of fluorescein derivative with Pb2+. Moreover, the color change was observed at pH above 7.0, and the pink color got more intense when increasing pH. Adding EDTA, a chelating reagent, into the solution of biotin-4-fluorescein/Pb2+ resulted to the rebound of the color to the original color of free biotin-4-fluorescein. The fluorescence spectra of fluorescein decreased with increasing Pb2+concentration, and the quenching was enhanced at higher pH. The association constant (Ka) of 2.00 × 104 M−1 was calculated from the fluorescence spectra with the limit of detection (LOD) and the limit of quantitation (LOQ) of 1.38 × 10−5 M (2.86 ppm) and 4.61 × 10−5 M (9.55 ppm), respectively. Job’s plot analysis indicated 2:1 ratio of binding interaction. Pb2+ in untreated wastewater was quantified for 24.99 ppm using this method. This quick analysis can be beneficial for the application of lead detection in real sample solutions, such as wastewater from industrial factories.

An environmentally friendly depressant for magnesite and calcite flotation separation: Selective depression and adsorption mechanism

The similar crystal structures and chemical properties of magnesite and calcite make their effective separation through flotation challenging. This study explores the use of Glutamic acid diacetic acid tetrasodium salt (GLDA), a novel environmentally friendly chelating reagent, to enhance the flotation separation of magnesite and calcite. Flotation test results indicate that in a sodium oleate (NaOL) system, GLDA selectively inhibits the flotation of calcite. Under optimal conditions (slurry pH=9.20, GLDA 15 mg/L, and NaOL 140 mg/L), a flotation concentrate with an MgO grade of 46.21 %, CaO grade of 1.39 %, and an MgO recovery rate of 73.17 % was achieved. GLDA minimally affects the hydrophobicity of magnesite but significantly reduces the hydrophobicity of calcite. The selective inhibition mechanism of GLDA was investigated using zeta potential measurements, FTIR, and XPS analyses. Results show that GLDA selectively reacts with Ca sites on the calcite surface, adsorbing and covering it, thereby preventing NaOL from adsorbing on the calcite. Conversely, GLDA has a minor impact on the Mg sites on the magnesite surface, resulting in a negligible effect on NaOL adsorption by magnesite. Consequently, GLDA enhances the flotation separation efficiency of magnesite and calcite. The research results have potential for application in the purification of low-grade magnesite ore.

Exploring a facile preparation method for Co-Ni/MoS2-derived nanohybrid from wheat straw extract and its physicochemical properties.

This study presents a novel approach for the fabrication of a Co,Ni/MoS2-derived nanohybrid material using wheat straw extract. The facile synthesis method involves a sol-gel process, followed by calcination, showcasing the potential of agricultural waste as a sustainable reducing and chelating reagent. The as-prepared nanohybrid has been characterized using different techniques to analyse its physicochemical properties. X-ray diffraction analysis confirmed the successful synthesis of the nanohybrid material, identifying the presence of NiMoO4, CoSO4 and Mo17O47 as its components. Fourier-transform infrared spectroscopy differentiated the functional groups present in the wheat straw biomass and those in the nanohybrid material, highlighting the formation of metal-oxide and sulphide bonds. Scanning electron microscopy revealed a heterogeneous morphology with agglomerated structures and a grain size of around 70 nm in the nanohybrid. Energy-dispersive X-ray spectroscopy analysis shows the composition of elements with weight percentages of (Mo) 9.17%, (S) 6.21%, (Co) 12.48%, (Ni) 12.18% and (O) 50.46% contributing to its composition. Electrochemical analysis performed through cyclic voltammetry showcased the exceptional performance of the nanohybrid material as compared with MoS2, suggesting its possible applications for designing biosensors and related technologies. Thus, the research study presented herein underscores the efficient utilization of natural resources for the development of functional nanomaterials with promising applications in various fields. This study paves a way for manufacturing innovation along with advancement of novel synthesis method for sustainable nanomaterial for future technological developments.

Rapid synergistic cloud point extraction based on hydrophobic deep eutectic solvent combined with hydride generation atomic absorption spectrometry for determination of selenium in tea samples

Herein, hydrophobic deep eutectic solvents (HDESs) were created for the fast preconcentration of Se(IV) from tea samples at room temperature. A facile and rapid synergistic cloud point extraction (HDES-RS-CPE) procedure was used, followed by hydride generation atomic absorption spectrometry (HG-AAS). The selected synergistic DES included glycine and lauric acid (molar ratio 3:1). 2-hydroxy-5-p-tolylazobenzaldehyde (HTAB) and Triton X-114 were utilized as chelating reagent and non-ionic surfactant, respectively. The experimental parameters that impact extraction recovery were examined and optimized. The detection limit, quantification limit, preconcentration factor, and enhancement factor for Se(IV) under optimum circumstances were 0.02 μg L−1, 0.06 μg L−1, 125, and 149, respectively. The method exhibited analytical linearity in the range up to 700.0 μg L−1. The procedure was used effectively for the quantification of Se(IV) in tea and certified samples. Moreover, the National Environmental Method Index (NEMI), the analytical greenness scale for sample preparation (AGREEprep), and the Green Analytical Procedure Index (GAPI) criteria have been used to measure the greenness score of the extraction procedure. To further highlight the environmental friendliness of this method, a detailed evaluation has been performed.

Engineering Pseudomonas putida KT2440 for Dipicolinate Production via the Entner-Doudoroff Pathway.

Dipicolinic acid (DPA), a cyclic diacid, has garnered significant interest due to its potential applications in antimicrobial agents, antioxidants, chelating reagents, and polymer precursors. However, its natural bioproduction is limited since DPA is only accumulated in Bacillus and Clostridium species during sporulation. Thus, heterologous production by engineered strains is of paramount importance for developing a sustainable biological route for DPA production. Pseudomonas putida KT2440 has emerged as a promising host for the production of various chemicals thanks to its robustness, metabolic versatility, and genetic tractability. The dominant Entner-Doudoroff (ED) pathway for glucose metabolism in this strain offers an ideal route for DPA production due to the advantage of NADPH generation and the naturally balanced flux between glyceraldehyde-3-phosphate and pyruvate, which are both precursors for DPA synthesis. In this study, DPA production via the ED pathway was in silico designed in P. putida KT2440. The systematically engineered strain produced dipicolinate with a titer of 11.72 g/L from glucose in a 5 L fermentor. This approach not only provides a sustainable green route for DPA production but also expands our understanding of the metabolic potential of the ED pathway in P. putida KT2440.

New diarylplatinum complexes containing 4,5-diazafluoren-9-one; synthesis, characterization, X-ray crystallography structure investigation and oxidative addition reaction studies

The synthesis of a new diarylplatinum(II) complex containing 4,5-diazafluoren-9-one (DAFO) was reported using the reaction of [Pt(p-tolyl)2(S(CH3)2)2] and DAFO with one to one equivalent. The platinum(IV), [PtIMe(p-tolyl)2DAFO], was then formed through the oxidative addition (OA) of iodomethane and [Pt(p-tolyl)2DAFO]. In the synthesized complexes, the DAFO was coordinated to the metal center as a chelating reagent through the nitrogen atoms. Identifications of the compounds were achieved using various techniques such as proton NMR, UV–Vis, FT-IR, CHN analyses. Furthermore, the organoplatinum(II) structure, involving DAFO, has been identified using single crystal X-ray crystallography. The band of MLCT in the visible region of Pt(II) was decayed in the oxidative addition and producing Pt(IV) complex. This variation in the visible region was applied to calculate the activation parameters of the reaction. The excess amounts of iodomethane were utilized to make pseudo-first-order status. At different temperatures kobs, k2, entropy and enthalpy changes of activation were determined.

Dispersive Micro‐Solid Phase Extraction of Selected Metals in Water and Food Samples Followed by ICP‐OES Analysis: Method Development, Analysis of Real Samples and Greenness Evaluation

AbstractMultiwalled carbon nanotubes (MWCNTs) are well‐known adsorbents because of their high surface area, layered and hollow architecture, hydrophobicity, and multiple and easily accessible adsorption sites. In this study, MWCNTs were used for dispersive micro‐solid‐phase extraction of various metal chelates in environmental and food samples. Different parameters such as concentration of the chelating reagent, the sorbent dosage, the extraction time, the desorption time, and the strength of the eluent were suitably optimized. Under the optimum extraction conditions, the proposed method demonstrated a good linear working range for all the analytes, with correlation coefficients above 0.9915. The limit of detection ranged from 0.02 to 0.21 μg/L. The inter‐day and intra‐day relative standard deviations were less than 2.5 %. The proposed method was used for the determination of selected metals in tap water, drinking water, cucumber, and tomato samples. In the end, GAPI tool was used to evaluate the greenness of the method.

The enhanced flotation separation of magnesite and dolomite by introducing chelating reagent EDTA

In pulp environment, due to the migration and transformation of dissolved calcium ions, the surface properties of magnesite and dolomite tend to become similar, which in turn leads to difficulties in their flotation separation. In this paper, the chelating reagent EDTA is introduced to eliminate the adverse influence of calcium species and to restore the selectivity of magnesite-dolomite separation using sodium hexametaphosphate (SHMP) as depressant. Flotation experiments demonstrate that, in the presence of ethylenediaminetetraacetic acid (EDTA), the flotation recovery of magnesite increased by 22.14 % compared to using only the depressant SHMP. Zeta potential experiments combined with solution chemistry analysis indicate that the negatively charged hydrolysis species of EDTA can form soluble and stable chelates with positively charged Ca2+ and Ca(OH)+ species, effectively preventing the adsorption and transformation of calcium ions on the magnesite surface. Adsorption measurements directly confirm from a macroscopic perspective that the addition of EDTA reduces the adsorption of the depressant SHMP on the magnesite surface. X-ray photoelectron spectroscopy (XPS) measurements further confirm the phenomenon of calcium ion migration and transformation from the surface of magnesite to dolomite at the microscale, as well as the adsorption mechanisms of EDTA and SHMP on the surfaces of both minerals. Based on the experimental and analytical results, a flotation separation model of the system is established.

Recent Progress on Chelating Reagents in Flotation of Zinc Oxide Ores: A Review

Zinc oxide minerals (primarily smithsonite and hemimorphite) are important sources of Zn. Flotation is the most widely used method of enriching zinc oxide minerals for mineral processing. Chelating reagents have received extensive attention for the flotation of zinc oxide ores because of their high selectivity and stability. This paper systematically summarizes the selective separation performance and mechanisms of various chelating reagents as collectors, activators, and depressants in the flotation of zinc oxide ores. The types and mechanisms of chelating reagents in the flotation of zinc oxide ores are discussed, providing new ideas for the development of efficient flotation reagents for zinc oxide ores.

Simultaneous preconcentration and determination of trace metals in edible plants and water samples by a novel solvent bar microextraction using a meltblown layer of facemask as the extractant phase holder combined with FAAS

A new microextraction method as a facile, efficient, and safe intermediate sample preparation procedure was developed for simultaneous extraction and preconcentration of nickel (II), cobalt (II), and lead (II) in some vegetables and water samples. The new method uses a novel deep eutectic solvent as an extractant on the surface of a meltblown layer of a facemask with an iron wire inside of it. 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) was used as a chelating reagent. The concentrations of the enriched ions were measured using a flame atomic absorption spectrophotometer (FAAS). The introduced method underwent significant parameter optimization, which may influence the extraction process efficiency. Under the best situations, the calibration curve of the method showed excellent linearity over the concentration range 2–150 μg L−1, 3–150 μg L−1, and 7–500 μg L−1 have satisfactory coefficients of determination (R2 ≥ 0.998) for nickel (II), cobalt (II), and lead (II), respectively. Detection limits were within 0.61 – 2.30 μg L−1, and the relative standard deviation values were fewer than 2.6 % (n = 10). Experimental results indicated that the presented method has a high ability to cleanly and enrich metal ions in several samples, including natural water, dill, coriander, and spinach leaves, with limited solvent consumption and low operating costs.

Kynurenic acid mediates bacteria-algae consortium in resisting environmental cadmium toxicity.

Cadmium (Cd2+) is a toxic heavy metal in the environment, posing severe damage to animal health and drinking water safety. The bacteria-algae consortium remediates environmental Cd2+ pollution by secreting chelating reagents, but the molecular mechanisms remain elusive. Here, we showed that Cellulosimicrobium sp. SH8 isolated from a Cd2+-polluted lake could interact with Synechocystis sp. PCC6803, a model species of cyanobacteria, in strengthening Cd2+ toxicity resistance, while SH8 or PCC6803 alone barely immobilized Cd2+. In addition, the SH8-PCC6803 consortium, but not SH8 alone, could grow in a carbon-free medium, suggesting that autotrophic PCC6803 enabled the growth of heterotrophic SH8. Totally, 12 metabolites were significantly changed when SH8 was added to PCC6803 culture in the presence of Cd2+ (PCC6803/Cd2+). Among them, kynurenic acid was the only metabolite that precipitated Cd2+. Remarkably, adding kynurenic acid increased the growth of PCC6803/Cd2+ by 14.1 times. Consistently, the expressions of kynA, kynB, and kynT genes, known to be essential for kynurenic acid synthesis, were considerably increased when SH8 was added to PCC6803/Cd2+. Collectively, kynurenic acid secreted by SH8 mitigates Cd2+ toxicity for algae, and algae provide organic carbon for the growth of SH8, unveiling a critical link that mediates beneficial bacteria-algae interaction to resist Cd2+.

New solvent-free method for isolating ellagic acid from sulphite spent liquor

Ellagic acid (EA) is a plant polyphenol with wide potential in biomedical (e.g., anti-inflammatory, neuroprotective, and anti-melanogenic, among others) and technical applications such as copolymers, chelating reagents, ion-exchange resins and materials for electrochemical devices. Upon acid sulphite pulping of Eucalyptus wood, EA is partially dissolved in the spent liquor and adsorbed on the resulting pulp. In this work, a new solvent-free eco-friendly method for isolating EA from sulphite spent liquor and alkali extract of unbleached sulphite pulp is proposed. EA was recovered from sulphite pulping streams via crystallization from acidified solutions under preselected conditions (80 °C, 24 h, glass container and surface-to-volume ratio >1.0). The crystals obtained were washed with acidified water to reduce concomitants and increased EA purity from ca. 55–70% (w/w) to ca. 85–95% (w/w). The main contaminants of raw EA crystals were carbohydrates (ca. 15%), lignin (ca. 22%), lipophilic extractives (ca. 5%) and ash (ca. 3%). The obtained fractions were characterized by liquid and solid-state carbon nuclear magnetic resonance spectroscopy, mass spectrometry and wide-angle X-ray scattering, being the latter used to assess the crystalline structure. The purity of EA from sulphite spent liquor was much higher than that of the acidified alkaline extract of unbleached sulphite pulp obtained in the sulphite pulp purification step.

Contemporary Research and Developments in the Low-Toxic Chelating Reagents for the Extraction of Non-Ferrous and Noble Metals from Poor Polymetallic Ores and Processing Tailings

An urgent technological, economic and environmental task of mining and metallurgical enterprises is to involve poor, off-balance and hard-to-beneficiate ores in the technological process, as well as accumulated and current waste from mining and metallurgical industries. As the reserves of developed deposits are depleted, technogenic objects may become a priority, and in some cases the only, source of mineral raw materials. Mining wastes represent a large reserve of raw materials for the extraction of non-ferrous and precious metals, and at the same time, they are centers of local or regional environmental pollution. Stale waste re-processing may promote territorial cultivation and reduce the environmental burden. The conventional methods of poor ore and waste treatment do not fully provide for a sufficient separation degree of high metal extraction, and lead to significant valuable ore losses, while the quality of the obtained concentrates often does not meet the requirements for subsequent technological process. In this regard, the development of novel chelating agents with specific functional groups that can selectively adsorb on the mineral surface, change the contrast of chemical surface composition and improve the flotation properties of mineral complexes, is an innovative solution for increasing their flotation selectivity. Furthermore, the synthesis and application of novel flotation reagents may help to replace toxic reagents by ecologically friendly or less-toxic ones.

Subcellular redox responses reveal different Cu-dependent antioxidant defenses between mitochondria and cytosol.

Excess intracellular Cu perturbs cellular redox balance and thus causes diseases. However, the relationship between cellular redox status and Cu homeostasis and how such an interplay is coordinated within cellular compartments has not yet been well established. Using combined approaches of organelle-specific redox sensor Grx1-roGFP2 and non-targeted proteomics, we investigate the real-time Cu-dependent antioxidant defenses of mitochondria and cytosol in live HEK293 cells. The Cu-dependent real-time imaging experiments show that CuCl2 treatment results in increased oxidative stress in both cytosol and mitochondria. In contrast, subsequent excess Cu removal by bathocuproine sulfonate, a Cu chelating reagent, lowers oxidative stress in mitochondria but causes even higher oxidative stress in the cytosol. The proteomic data reveal that several mitochondrial proteins, but not cytosolic ones, undergo significant abundance change under Cu treatments. The proteomic analysis also shows that proteins with significant changes are related to mitochondrial oxidative phosphorylation and glutathione synthesis. The differences in redox behaviors and protein profiles in different cellular compartments reveal distinct mitochondrial and cytosolic response mechanisms upon Cu-induced oxidative stress. These findings provide insights into how redox and Cu homeostasis interplay by modulating specific protein expressions at the subcellular levels, shedding light on understanding the effects of Cu-induced redox misregulation on the diseases.

Ultrasonic-assisted dispersive liquid–liquid microextraction based on hydrophilic deep eutectic solvents: Application to lead and cadmium monitoring in water and food samples

A green and innovative ultrasonic-assisted dispersive liquid–liquid microextraction using hydrophilic deep eutectic solvents (UA-HDES-DLLME) was developed for the selective and simultaneous extraction and enrichment of Pb (II) and Cd (II) in water and food samples for flame atomic absorption spectrometry. Several natural deep eutectic solvents (NADES) were used for the preparation of six different HDES and methyl violet was used as chelating reagent. Effective parameters such as pH, sonication time, methyl violet amount, DES type, dispersive solvent types, etc were optimized. Relative standard deviation (RSD) and preconcentration factor (PF) were 4.0% and 80. Low limits of detection (LOD, 1.3 ng mL−1 for Pb (II) and 0.33 ng mL−1 for Cd (II)) and quantification (LOQ, 4.0 ng mL−1 for Pb (II) and 1.0 ng mL−1 for Cd (II)) were found. The method accuracy was confirmed with analyses of certified reference materials.

Determination of Vanadium(IV) and Vanadium(V) in Beverages by Two-Step Direct Immersion Single-Drop Microextraction with Graphite Furnace Atomic Absorption Spectrometry (GFAAS)

A novel two-step direct immersion single-drop microextraction (TS-DI-SDME) was reported for the sequential separation and enrichment of V(V) and V(IV) followed by graphite furnace atomic absorption spectrometry detection. Theonyltrifluoroacetone (HTTA) and chloroform were used as the chelating reagent and extraction solvent for TS-DI-SDME. In the first step, V(V)-HTTA complexes were separated and enriched in one organic solvent drop at pH 2.5, while V(IV) remained in the solution. Next, another organic solvent drop containing HTTA was immersed in the original solution after the extraction of V(V) for the enrichment of V(IV) at pH 4.5. This procedure avoids tedious and complicated pre-oxidation/pre-reduction operations, which may cause contamination and error. Under the optimized conditions, the limits of detection were equal to 3.1 and 2.6 ng L−1 for V(IV) and V(V) with relative standard deviation values of 4.9 and 5.8%, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was successfully utilized for the determination of V(IV) and V(V) in beverages. To validate this approach, a water-certified reference material was analyzed with satisfactory results.

Direct immersion dual-drop microextraction for simultaneous separation and enrichment of Cr(III) and Cr(IV) in food samples prior to graphite furnace atomic absorption spectrometry detection

Non-chromatographic speciation methods generally involve speciation conversion, which may cause sample contamination, analysis errors and tedious operations. In this work, a direct immersion dual-drop microextraction (DIDDME) was firstly developed for separation and preconcentration of Cr(III) and Cr(VI). In DIDDME, two organic drops on needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent for reacting with a specific species. Thus, Cr(III) and Cr(VI) were selectively extracted into different drops. This method afforded detection limits of 3.0 and 4.1 ng/L, quantification limitof 10 ng/L and 14 ng/L, linear range of 0.01–30 ng mL−1 and enrichment factors of 354-fold and 326-fold for Cr(III) and Cr(VI), respectively. Precisions like repeatability and reproducibility were assessed by calculating relative standard deviations, which were lower than 5.4 % and 6.9 %, respectively. This procedure was used successfully for quantification of Cr(III) and Cr(VI) in food samples.

A novel separation and preconcentration methodology based on direct immersion dual-drop microextraction for speciation of inorganic chromium in environmental water samples

In this study, for the first time, a novel separation and preconcentration method of direct immersion dual-drop microextraction (DIDDME) was proposed for the species of inorganic chromium (Cr(III) and Cr(VI)) followed by graphite furnace atomic absorption spectrometry detection. The methodology is based on that two organic drops hold on the needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent, which can react with a specific species under the same pH value. Therefore, Cr(III) and Cr(VI) can be selectively extracted into different drops. This procedure did not require tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may lead to the risk of sample contamination and analysis errors. Main parameters influencing separation, preconcentration and identification of the target species were investigated. An enrichment factor of 400-fold was obtained for Cr(III) and Cr(VI). Under the optimized conditions, detection limits for this method were 1.1 ng L−1 and 1.4 ng L−1 for Cr(III) and Cr(VI) with relative standard deviations of 5.1 and 6.3%, respectively. This procedure was applied for the separation, preconcentration and determination of Cr(III) and Cr(VI) in environmental water samples and certified reference materials with satisfactory results. Recoveries of spiked experiments ranged from 86.0 to 112%.

Applications of polyaniline-impregnated silica gel-based nanocomposites in wastewater treatment as an efficient adsorbent of some important organic dyes

AbstractDue to a recent lack of clean water as a result of an increasing water demand, new wastewater solutions are required. Many researchers have looked into the removal of organic dyes from wastewater, with adsorption being an easy and effective method for removing organic and inorganic contaminants from contaminated water. Conjugated modified polymers, primarily polyaniline (Pani), have been widely used in the wastewater treatment because of their unique properties, such as easy synthesis, tunable morphology, porous structure, good electrorheological property, biodegradability, and nontoxic nature. Modified surface polymers are more reactive for the removal of dyes from wastewater and have outstanding dye removal capabilities in the wastewater treatment. This review article elaborates on wastewater treatment by utilizing silica gel-impregnated polyaniline nanocomposites as adsorbents. The use of polyaniline-modified silica gel in dye migration behavior to the most suited system for the resolution of co-existing dyes is referred to as the separation of organic dyes from their mixtures. Adsorption of important organic dyes to optimize conditions for efficient organic dye removal and comparison with another commercially available adsorbent. Chemical modification with the introduction of acidic or basic surface functionality could increase cationic and anionic chemical adsorption, as well as charged organic species such as dyes. The carrier is thus obtained with a chelating reagent on the surface of a silica gel after impregnation with polyaniline.

Characterization of a Novel Esterase Est33 From an Antarctic Bacterium: A Representative of a New Esterase Family.

Studies of microorganisms from extreme environments can sometimes reveal novel proteins with unique properties. Here, we identified a novel esterase gene (Est33) from an Antarctic bacterium. The protein was expressed and purified for biochemical characterizations. Site-mutation variants including S94A, D205A, and H233A were constructed to explore the structure–function relationship of the catalytic triad of Est33, and we found mutating Ser94, Asp205, and His233 residues lead to a complete loss of enzyme activity. In addition, the catalytic Ser94 located in a conserved pentapeptide motif GVSWG. Phylogenetic analysis showed that Est33 and its closely related homologs belonged to an independent group apart from other known family members, indicating that Est33 represented a new family of esterase. The Est33 enzyme was found to be a cold-active esterase retaining 25%–100% activity from 10°C to 30°C and to have optimal catalytic activity toward p-nitrophenol acetate (30°C and pH7.5). The serine modifying reagent phenylmethylsulfonyl fluoride inhibited the activity of Est33 by 77.34%, while thiol reagents such as dithiol threitol (DTT) activated the enzyme by 3-fold. Metal chelating reagents EDTA had no effects, indicating that Est33 is not a metalloenzyme. Collectively, these results indicate that Est33 constitutes the first member of a novel esterase family XXI that has been identified.