Quantitative Recovery Research Articles

Optimization of pretreatment protocol for strontium-90 analysis in marine fish bone samples.

For systematic monitoring of radioactive nuclides in marine products, this study aimed at streamlining and simplifying the analysis method for the prominent radioisotope, strontium-90 (90Sr). The DGA chelate solid-phase extraction technique was employed for enhanced efficiency. The study focused on optimizing the necessary pretreatment procedures while minimizing the steps involving HNO3 leaching. This protocol enabled the quantitative recovery of strontium, and it facilitated a rapid analysis without the need for a time-consuming evaporation step and without waiting for secular equilibrium between 90Sr and its progeny to be reached. The method incorporating the optimized pretreatment protocol was applied to three diverse marine fish species and the accurate quantification of 90Sr at background levels in surface seawater was achieved. The method obtained concentrations in bone samples from these species that ranged from 0.036 to 0.120 mBq per kg-dry, and chemical yield values were notably high, ranging from 87.7% to 92.5%.

Single-shot quantitative differential phase contrast microscope using a single calcite beam displacer

This paper presents the development of a single-shot, partially spatially coherent quantitative differential phase contrast microscopy (Q-DPCM) system. The optical scheme comprises a polarizer, lenses, calcite beam displacer, and analyzer, which can be seamlessly integrated to an existing bright-field microscopy system, transforming it into a Q-DPCM system. It utilizes a partially spatially coherent light source, enabling single-shot quantitative differential phase recovery of the specimens with high spatial phase sensitivity. It generates highly sensitive quantitative differential phase images of the specimens along one direction, like a gradient light interference microscopy (GLIM) system, using only a single interferogram. First, we validated the differential phase measurement capability of the system through experiments on polystyrene spheres (diameter 5.2 µm) and HeLa cells. Next, the system is utilized to generate quantitative phase maps of human red blood cells using two orthogonal differential interferograms recorded at two orientations of the calcite beam displacer. Further, the Q-DPCM system is implemented for 1-h time-lapse live cell monitoring, revealing the dynamics of intracellular granules such as nucleolus and lipids in U2OS cells.

Improved Reductive Catalytic Fractionation of Lignocellulosic Biomass through the Application of a Recyclable Magnetic Catalyst.

The reductive catalytic fractionation (RCF) of second generation lignocellulosic biomass is an elegant one-pot process to obtain a highly delignified cellulose pulp, sugar-derived polyols, and depolymerized and stabilized lignin oils. However, the need of noble metal catalysts to prompt the reactions may impact the economic sustainability of the overall "lignin-first" biorefinery if the catalyst recovery and recyclability are not guaranteed. Herein, the use of a novel catalyst based on supported ruthenium over maghemite for the RCF of poplar sawdust is reported for the first time. This material allows us to obtain a pure cellulose pulp with a quantitative magnetic recovery efficiency after the first cycle. The obtained lignin oil is composed by a 12% yield in phenolic monomers (i.e., benzyl alcohol, 4-n-propylguaiacol, and 4-n-propylsyringol), together with dimers and trimers as confirmed by GPC analyses. The catalytic material was found to be stable and recyclable for three reaction cycles with only minor loss of RCF efficiency. On the other hand, the straightforward, lab-scale, magnetic recovery procedure needs to be further improved in the future to ensure quantitative recovery of the catalyst also after several RCF cycles.

Flakes and Nanoparticles from Waste Ru-Plated Fashion Items through Food Waste by-Products.

Ruthenium is relevant for a broad range of applications, including catalysis and electronics. Like other metals of the platinum group, ruthenium stands out as one of the rarest elements in the Earth's crust. The demand for Ru from the industry is putting pressure on its availability. Hence, its recovery from secondary sources is imperative. Fashion solid residues of the plating industry are an important waste stream for Ru. Within this context, we propose a novel approach to Ru recovery for its safe, sustainable, and economically affordable upcycling. The approach is based on peeling from waste metal wires by a green oxidizing agent, H2O2, in an environment acidic by lactic acid, a by-product of the food industry. Peeled flakes were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy for their structure and (surface) chemical composition and bonding. Inductively Coupled Plasma Optical Emission Spectroscopy shows the ultra-low concentration of noble metals in the leachate, thereby suggesting their quantitative recovery in their metallic state. Further, we observed the colloidal nature of the washing water of the peeled flakes. Therefore, we hypothesized the presence of nanoparticles in the washing water and went for their characterization.

Ultrasensitive SERS Detection of Five β-Blockers Achieved Using Chemometrics with a Two-Dimensional Substrate Formed by Large-Sized Ag@SiO2 Nanoparticles.

We report on a surface-enhanced Raman scattering (SERS) platform for the detection of five beta-blockers (β-blockers): atenolol, esmolol, labetalol, sotalol, and propranolol. Key to this platform was a two-dimensional substrate formed by self-assembling large Ag@SiO2 nanoparticles (Ag@SiO2 NPs) on a silicon wafer. The close arrangement of these large nanoparticles on the surface generated a strong and uniform electromagnetic field, which enhanced SERS signal intensity for the detection of small amounts of the target molecules. The intensities of characteristic peaks of the five β-blocker drugs increased linearly with the increase of their concentrations in the range of 10-5 to 10-8 mol/L. The detection limits were 10-10 mol/L for propranolol, 10-9 mol/L for atenolol, labetalol, and sotalol, and 10-8 mol/L for esmolol. Determination of these five β-blocker drugs added to human urine samples, using a portable Raman spectroscopy instrument, showed quantitative recovery (93-101%). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) of SERS spectral data improved the differentiation among these five β-blockers. This study highlights the potential of the developed SERS platform for rapid, on-site detection of illicit drugs and for antidoping screening.

Calixarene incorporated molecular imprinting on covalent organic framework for supramolecular recognition and specific extraction of citrinin

Specific recognition and selective extraction of mycotoxin in environmental and food matrixes is significant to guarantee public health. Covalent organic frameworks (COFs) are promising adsorbents with tailorable functionality, but their low binding affinity and poor selectivity hamper their wide application for selective extraction of trace mycotoxin from complex matrix. Herein, we report calixarene incorporated molecular imprinting on COF to prepare molecularly imprinted calix[4]arene-containing COF (MICOF-CX4) for supramolecular recognition and specific adsorption of citrinin. Calixarene with host-guest chemistry was used as a functional monomer, while amine units with different topologies and function groups were selected to regulate MICOF-CX4 to match with citrinin. The complementary shape and supramolecular interactions of MICOF-CX4 gave highly selective recognition for citrinin. Moreover, MICOF-CX4 with vast accessible surface and plentiful imprinting sites exhibited faster adsorption kinetics and 4-fold higher adsorption capacity for citrinin adsorption than no-imprinted COF-CX4. Combination of MICOF-CX4 based solid-phase extraction with high-performance liquid chromatography-mass spectrometry allowed interference free determination of trace citrinin in real samples with a low detection limit of 0.03 ng mL−1, good precision of 4.5 % and quantitative recovery of 88.2 %−101.4 %. The cooperative functions of calixarene and molecular imprinting make COF promising adsorbent for specific adsorption of trace targets in complex matrixes.

Cadmium oxide/calcium ferrite nanocomposite-based enhanced electrochemical sensing of metronidazole

The current study aimed to synthesize a cadmium oxide/calcium ferrite nanocomposite (CdO/CaFe2O4–NC) by sol–gel auto-combustion method, then applied on the surface of a glassy carbon electrode to fabricate a (CdO/CaFe2O4–NC/GCE) as a sensor for the electrochemical detection of metronidazole (MNZ). The characterization of synthesized CaFe2O4-NPs and CdO/CaFe2O4–NC was carried out through various analytical techniques, to confirm surface morphology, crystallite nature, average particle size, magnetic behavior, and stability. It is an effective electrochemical method for the detection of MNZ. The fabricated electrode was characterized by cyclic voltammetry, indicating its diffusion-controlled electron transfer behavior. Thus, CdO/CaFe2O4–NC/GCE was used to quantify MNZ using differential pulse voltammetry with a dynamic range of 0.05–130 µM (R2 = 0.0996) and LOD of 0.034 µM. The electrochemical method showed significant stability, sensitivity, and reproducibility (RSD < 4.00 %). The fabricated sensor was successfully applied to the contaminated water samples with quantitative recoveries up to 93.02 % by the spiking method.

Utility of an Archival Dried Blood Spot (DBS) Collection from HIV-Infected Individuals with and without Cancer in a Resource-Limited Setting.

The frequency of virus-associated cancers is growing worldwide, especially in resource-limited settings. One of the biggest challenges in cancer research among people living with HIV (PLWH) has been understanding how infection with both HIV and Kaposi sarcoma-associated herpesvirus (KSHV) promotes the pathogenesis of Kaposi sarcoma (KS), the most common cancer among PLWH worldwide and a significant public health problem in regions with high prevalence of HIV such as Sub-Saharan Africa (SSA). The AIDS and Cancer Specimen Resource (ACSR) provides samples for research, including dried blood spots (DBS) that were collected from large clinical epidemiology studies of KSHV and KS in PLWH conducted more than a decade ago in SSA. Here, we validated the quality of DNA derived from DBS samples from SSA studies and provided evidence of quantitative recovery of inflammatory cytokines using these DBS samples through comparison with paired frozen plasma. Significant differences in DNA, protein yields, and inflammatory biomarker levels were also observed between PLWH with/without KS. Establishing the fitness of DBS samples for studies of KS pathogenesis extends the number of projects that can be supported by these ACSR special collections and provides evidence that DBS collection for future KS research is a practical option in resource-limited settings.

Synthesis of magnetic multi-walled carbon nanotubes with layered double hydroxide (M-MWCNTs@MnAl-LDH) nanocomposite as an adsorbent for lead extraction

MnAl layered double hydroxide hybrid with magnetic-multiwalled carbon nanotubes was synthesized by a hydrothermal method and used for the extraction of Pb(II) (lead) from spices and water samples in the dispersive solid phase microextraction (dSPμE) technique using FAAS. The as-prepared adsorbent MMWCNTs@MnAl-LDH was characterized by XRD, FTIR, EDX, and SEM techniques. Various analytical parameters were optimized, including pH 8, adsorbent dosage of 5 mg, HNO3 eluent concentration of 1 mol L−1, eluent volume of 3 mL, eluent time of 60 s, and sample volume of 20 mL, for quantitative lead recoveries, with an LOD of 0.314 μg L−1, an LOQ of 1.048 μg L−1, and PF of 11.53. Under the optimized conditions, the linearity ranges from 0.5 to 500 μg L−1 (R2 = 0.9997). For the validation test of the established dSPμE procedure, Certified reference materials (CRMs) were used, yielding satisfactory recovery results ranging from 97.8 to 102.7 %. The method was applied to determine lead in turmeric, tap water, and industrial water samples.

Design and validation of a method for evaluating medical device cleanliness by recovering and quantifying residual proteins on stainless plates

We recently reported a method for recovering and quantifying residual proteins bound to surfaces of various medical instruments via thermal coagulation under neutral pH and room temperature. The method effectively recovered and solubilised coagulated proteins at high temperatures in dry and humid conditions, with a protein recovery rate of > 90%. This study validated the previous method by comparing residual protein recovery from test samples using a conventional extraction solution (1% SDS, [pH 11.0]) and proposed solution (1% SDS, 10 mM TCEP, and 10 mM HEPES [pH 7.0]). To mimic soiled medical equipment, pseudo-blood-contaminated stainless steel plates were prepared. Residual protein was recovered using conventional and proposed solutions under varying temperature and humidity conditions. Quantitative protein recovery limits were determined at nine facilities. Compared with the conventional solution, the proposed solution recovered proteins more effectively from samples processed at temperatures > 60 °C. However, low recovery rates were observed for samples processed at 95 °C, possibly owing to differences in protein adhesion due to sample and plate-surface properties. Our findings present a method for quantifying residual proteins on medical instruments exposed to high temperatures during use or disinfection. Further studies should standardise test soiling conditions, materials, and solutions to evaluate cleaning methods.

Fan assisted extraction and low pressure chromatographic system with a phenyl monolithic column for amperometric determination of volatile α-dicarbonyl compounds in coffee brews

In this work, a low pressure chromatographic system featuring a single 0.5 cm length phenyl monolithic column and an amperometric detector was developed to determine volatile ⍺-dicarbonyl compounds in coffee brews. The analytical strategy relied on the extraction of the volatile ⍺-dicarbonyl compounds and their derivatization with o-phenylenediamine, prior to the determination of the resulting quinoxaline derivative compounds in the designed chromatographic system. The studies of the mobile phase composition and electrochemical conditions are presented. The extraction of the volatile ⍺-dicarbonyl compounds was performed resourcing to a recent approach based on the fan assisted extraction system. This system performs the full evaporation technique and allowed the quantitative recovery (>85 %) of diacetyl and 2,3-pentanedione from the coffee brew based on the following experimental conditions: sample volume 30 µL, extraction period 15 min, acceptor solution (water, acetonitrile, 90:10, v/v) volume 400 µL, and sample temperature 50 °C. The developed method showed no matrix effect for different coffee brews and the quantification of the studied analytes can be performed through the external calibration method. Detection limits of 3.6 × 10−6 mol/L for diacetyl and 12.9 × 10−6 mol/L for 2,3-pentanedione were obtained. Sample analysis rate was of 5 h−1 and the acetonitrile consumption was of ca. 450 µL per chromatographic run.

Spectrophotometric Determination of Cobalt(II) by Natural Deep Eutectic Solvent (NADES) Air-Assisted Dispersive Liquid-Liquid Microextraction (AA-DLLME)

Cobalt is beneficial for human activity but has adverse effects when discharged in large quantities. Therefore, its precise and accurate quantification in samples is of importance. Here, a natural deep eutectic solvent (NADES), composed of camphor (H-bond acceptor) and menthol (H-bond donor), has been used for the preconcentration of Co(II) from water samples before determination by a spectrophotometer at 398 nm. The 8-hydroxyquinoline-Co(II) complex was transferred to the NADES using air-assisted dispersive liquid-liquid microextraction (AA-DLLME). The extraction efficiency was enhanced through fine tuning of various parameters, including pH, NADES volume, and quantity of dispersant. Similarly, the centrifugation rate and time, quantity of the complexing agent, matrix effects, and salt concentration were also evaluated. Under the optimized conditions, an enrichment factor of 37.5 and a preconcentration factor of 37.5 were obtained. The limits of detection (LOD) and quantification (LOQ) were 0.44 µg/L and 1.47 µg/L, respectively. For seven replicates of 50 µg/L Co(II), the relative standard deviation was 3.2%. The developed method was employed for the determination of Co(II) in water samples, with quantitative recovery values from 94.5 to 98.5%.

Magnetic solid phase extraction of methiocarb pesticide from food samples prior to HPLC analysis with magnetic activated carbon cloth/zinc aluminate (magnetic ACC@ZnAl2O4) composite

Methiocarb is a carbamate pesticide and is widely used due to its short lifetime but is a health concern due to its toxicity. To address this challenge, a novel nano-sorbent (zinc aluminate hybrid doped onto a magnetic activated carbon cloth (magnetic ACC@ZnAl2O4)) was synthesized. The characterization of the composite was done using FTIR spectroscopy, SEM, XRD, and EDX. The synthesized composite was then employed for the efficient extraction of methiocarb from food samples. Under the optimum conditions of (pH: 7.0, vortex time: 0.5 min, adsorbent dose: 5 mg, initial volume of sample: 50 mL, volume of eluent: 1.0 mL), quantitative recovery values of methiocarb in food samples were obtained (80–114%). This method impresses with its exceptional sensitivity, achieving incredibly low detection (LOD: 20 µg L−1) and quantification (LOQ: 67 µg L−1) limits for methiocarb. Its efficiency is equally impressive, with high values of preconcentration factor (PF: 50) and enhancement factor (EF: 49.4), ensuring accurate and reliable analysis with a low value of relative standard deviation (RSD: 4.8%). The method’s impressive selectivity, evident in its minimal interference from other pesticides, paves the way for reliable methiocarb analysis in food samples.

Novel Triton X-114 coated Fe3O4 magnetic nanoparticle adsorbent for Cd(II) and Co(II) ions preconcentration in honey samples using magnetic solid-phase extraction: Determination by ICP-OES

This work focuses on creating and studying the effectiveness of Fe3O4 nanoparticles coated with (3-aminopropyl)triethoxysilane (APTES) and polyethylene glycol tert-octylphenyl ether (TX-114), respectively, as adsorbent. Fe3O4@APTES@TX-114 adsorbent extracts heavy metal cations Cd2+ and Co2+ using a magnetic solid phase extraction technique. The synthesized magnetic nanoparticles (MNPs) were characterized by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and Thermogravimetric Analysis (TGA). After this stage, Cd2+ and Co2+ determinations were made with the ICP-OES device. The optimum conditions for recovering Cd2+ and Co2+ cations were pH 7, an adsorbent dosage of 2 g/L, and a contact time of 120 min. While the method was compatible with Langmuir and Freundlich isotherm models, the pseudo-second-order kinetic equation was more compatible than the pseudo-first-order. Acidic and basic media were investigated for the desorption of Cd2+ and Co2+ ions from the adsorbent. At the same time, maximum recovery was achieved for both cations at a concentration of 1.5 mol/L HCl, but no significant recovery was obtained in the NaOH medium. The common ion study observed that Cd2+ and Co2+ cations were recovered over 95 % in the presence of many cations and anions at different concentrations. The relative standard deviation (RSD), limit of quantification (LOQ), limit of detection (LOD), and enrichment factor (EF) were calculated as 1.40 %, 2.963 µg/L, 0.889 µg/L, 20.99 for Cd2+ and 3.05 %, 1.88 µg/L, 0.564 µg/L, 109.41 for Co2+, respectively. The magnetic solid phase extraction method realized quantitative recovery of Cd2+ and Co2+ cations in different honey samples. It was found that the heavy metal contents in honey samples from the Sakarya region are below permissible levels.

Hydrothermal conditioning of oleaginous yeast cells to enable recovery of lipids as potential drop-in fuel precursors

BackgroundLipids produced using oleaginous yeast cells are an emerging feedstock to manufacture commercially valuable oleochemicals ranging from pharmaceuticals to lipid-derived biofuels. Production of biofuels using oleaginous yeast is a multistep procedure that requires yeast cultivation and harvesting, lipid recovery, and conversion of the lipids to biofuels. The quantitative recovery of the total intracellular lipid from the yeast cells is a critical step during the development of a bioprocess. Their rigid cell walls often make them resistant to lysis. The existing methods include mechanical, chemical, biological and thermochemical lysis of yeast cell walls followed by solvent extraction. In this study, an aqueous thermal pretreatment was explored as a method for lysing the cell wall of the oleaginous yeast Rhodotorula toruloides for lipid recovery.ResultsHydrothermal pretreatment for 60 min at 121 °C with a dry cell weight of 7% (w/v) in the yeast slurry led to a recovery of 84.6 ± 3.2% (w/w) of the total lipids when extracted with organic solvents. The conventional sonication and acid-assisted thermal cell lysis led to a lipid recovery yield of 99.8 ± 0.03% (w/w) and 109.5 ± 1.9% (w/w), respectively. The fatty acid profiles of the hydrothermally pretreated cells and freeze-dried control were similar, suggesting that the thermal lysis of the cells did not degrade the lipids.ConclusionThis work demonstrates that hydrothermal pretreatment of yeast cell slurry at 121 °C for 60 min is a robust and sustainable method for cell conditioning to extract intracellular microbial lipids for biofuel production and provides a baseline for further scale-up and process integration.Graphical abstract

Quantitative recovery and regeneration of basic deep eutectic solvent for biomass treatment with industrialized membrane-based strategy

As a new type of ionic liquids, basic deep eutectic solvents have been reported as emerging medium for biorefinery, extraction, catalysis and so on. Quantitative recovery with recycling of basic DES was important for the scale utilization of biomass and the environmental conservation. An electrodialysis-based method was designed for divisionally regenerating basic DES choline chloride-monoethanol amine (ChCl-MEA) after pretreatment of wheat straw. Influence of primary process parameters on recovery of ChCl-MEA was studied and recovery economy of ChCl-MEA was analyzed. Recovery ratio of ChCl and MEA varied within 89.2 %-96.0 % and 93.3 %-97.9 %. Energy consumption of ChCl-MEA recovery changed within 4.2–29.4 kW·h/kg. Transport rate of basic DES ChCl-MEA altered in the range of 12.2–464.7 mmol/(m2·min). Process economy analysis proved that recovery cost of basic DES ChCl-MEA was less than 7 % (0.81–7.07 $/kg) of DES purchase cost. Insight brought by this study indicated a technically feasible and economical approach for basic DES recycling after biomass pretreatment.

Double pseudo-polymeric complexes of [Au(S2CNBu2)2][AgCl2] and [Au(S2CNHm)2]3[AgCl2][Ag0.59Au0.41Cl2]2: Preparation, supramolecular self-assembly, thermal behaviour and anti-mycobacterial activity

Pseudo-polymeric double complexes of [Au{S2CN(C4H9)2}2][AgCl2] (1) and [Au{S2CN(CH2)6}2]3[AgCl2][Ag0.59Au0.41Cl2]2 have been obtained and chemically identified using solution (1H, 13C{1H}) NMR and FT-IR spectroscopy. According to XRD analysis, it was established that both of the above crystalline compounds form complicated supramolecular architectures. Self-assembly and structural stabilization of these supramolecular formations are achieved due to numerous secondary interactions: Ag⋯S, Cl⋯S (in 1, 2) and Au⋯Cl, Au⋯S (in 2), which arose between the ionic structural units of the complexes. The combined manifestation of these interionic secondary interactions leads to the construction of two types of pseudo-polymeric chains of (⋯[Au(S2CNBu2)2]⋯[AgCl2]⋯)n (1) and (⋯[Au2(S2CNHm)4]⋯ [AgCl2]⋯)n (2). To study the thermal behaviour of the prepared compounds, the simultaneous thermal analysis (STA) technique was used, which allowed us to determine the conditions for the quantitative recovery of bound metals. Moreover, a high in vitro biological activity for each of the prepared gold(III)-silver(I) compounds against the non-pathogenic strain Mycolicibacterium smegmatis was experimentally revealed.

Developing a novel ultraselective and ultrasensitive label-free direct spectrofluorimetric nanobiosensor for direct highly fast field detection of explosive triacetone triperoxide

BackgroundDirect detection of the notorious explosive triacetone triperoxide (TATP) is very difficult because it lacks facile ionization and UV absorbance or fluorescence. Besides, the current indirect methods are time-consuming and need a pre-step for TATP cleavage to hydrogen peroxide. Moreover, they commonly show significant false-positive results in the presence of some camouflage which limits their field applications. Herein, for the first time, a novel label-free field-applicable spectrofluorimetric nanobiosensor was developed for direct TATP detection using a novel activated-protein protected gold nanocluster (ABSA-AuNCs; QY = 28.3 %) synthesized by a combined protein-assisted-ultrasonication procedure. ResultsThe ABSA-AuNCs revealed a fluorescence spectrum centered at 330.0 nm which was significantly quenched by TATP (binding constant = 154.06 M-1; ΔG = −12.5 kJ mol−1; E(%) = 88.5 %). This phenomenon was used as a basis for direct TATP quantification, providing a working range of 0.01–40.0 mg L−1 and a detection limit of 6.7 μg L−1 which is the lowest LOD provided for TATP detection up to now. A %RSD of 0.9 % and 1.56 % was obtained for repeatability and inter-day reproducibility, respectively. The selectivity was checked against a variety of camouflages, revealing ultra-selectivity. Several synthetic samples prepared by several camouflages and real samples (clay soil and real water media) were analyzed, revealing quantitative recoveries of TATP. SignificanceDuring the production of the notorious explosive TATP, it can be discharged into water and soil. This novel method eliminated the false-positive results of traditional methods and is applicable for direct quantitative detection of camouflaged TATP and its residues in real soil and water samples in a highly short response time (2 min). The camouflaged TATP analysis is important for tracking the terrorist attacks in field conditions and analysis of soil and water can provide a first indication of the location of the production site.

Effect of soil management on carbon stock and soil aggregation in an area of natural regeneration and surrounding systems in the Atlantic Forest biome

This study aimed to quantify total organic carbon (TOC), carbon of humic substances (HS), and their stocks and evaluate the soil structural stability of areas with different uses under sandy loam soil texture. Soil samples were collected from managed areas and a reference area: Permanent Pasture (PP), No-Till (NT), Private Natural Heritage Reserve in the process of natural regeneration (PNHR) and Native Forest (FN). Dry mass analysis, carbon stock quantification, chemical fractionation of soil organic matter and soil aggregation were carried out. The NF area had the highest deposition of litter mass (ML). The PP and NT areas had the highest bulk density (Bd). TOC and Stock-C contents were higher in PNHR, followed by NF, and stratification index (STRATI) was also higher in the regeneration area. The NT, PNHR, and NF areas had a higher proportion of carbon fulvic acid fraction (C-FA) than carbon humic acid fraction (C-HA), but the fraction with the highest representation in all areas was carbon humin fraction (C-HUM). The PP, PNHR, and NF areas obtained the best aggregate stability indicators, as well as a higher proportion of macroaggregates, with the NT area having low aggregate stability. Recovery of C contents was observed in recent years in the area of PNHR, leading to a greater storage of C, which shows a quantitative recovery of C in the soil in this area after four years of natural regeneration. Furthermore, the PP and NT areas present a lower capacity for C sequestration, mainly due to the management conditions. Keywords: aggregate stability, climate change, crop production, soil quality.

Mild Catalytic Degradation of Crystalline Polyethylene Units in a Solid State Assisted by Carboxylic Acid Groups.

Crystalline polyethylenes bearing carboxylic acid groups in the main chain were successfully degraded with a Ce catalyst and visible light. The reaction proceeds in a crystalline solid state without swelling in acetonitrile or water at a reaction temperature as low as 60 or 80 °C, employing dioxygen in air as the only stoichiometric reactant with nearly quantitative recovery of carbon atoms. Heterogeneous features of the reaction allowed us to reveal a dynamic morphological change of polymer crystals during the degradation.