Anthraquinone Structure Research Articles

Exploration of novel 20S proteasome activators featuring anthraquinone structures and their application in hypoxic cardiomyocyte protection

Under hypoxic conditions, the accumulation of misfolded proteins primarily relies on the autonomous activity of 20S proteasome for degradation. The buildup of toxic proteins in cardiomyocyte contribute to various cardiovascular diseases. Therefore, enhancing the 20S proteasome degradation capacity and restoring protein homeostasis in myocardial cells with small molecule activators represent a promising therapeutic strategy for the treatment of ischemic cardiomyopathy. In this study, the lead compound 8016–8398 was identified through virtual screening, and subsequent structure optimization resulted in a series of highly potent 20S proteasome activators. Intracellular protein degradation assessment revealed that these compounds possessed abilities to alleviate endoplasmic reticulum stress, as demonstrated by the luciferase reporter system. Additionally, selected compound B-03 significantly enhanced the survival rate of hypoxic-damaged cardiomyocytes. Mechanistic investigations verified B-03 rescued hypoxic damaged cardiomyocyte through apoptosis inhibition and proliferation promotion.

Natural redox mediator anthraquinone aloe-emodin facilitated the in-situ mineralized γ-FeO(OH) membrane for the removal of tannic acid through photocatalytic-PMS activation

The growing utilization of Traditional Chinese Medicine (TCM) has resulted in an increase in wastewater. Herein, a new kind of organic-inorganic redox mediator membrane by immobilizing γ-FeO(OH) and aloe-emodin(AE) with the characteristic large π-conjugation anthraquinone structure on PVDF membrane was innovatively achieved. AE exhibiting both electron deficiency and redox activity possesses a co-catalyst role in degradation of tannic acid (TA), aiding in the separation of charge carriers through the sequential hydrogenation and dehydrogenation of AE. The removal rates of TA were 92.8 % in the tannic acid solution and 60.3 % in the simulated rhubarb wastewater by the AE-γ-FeO(OH) membrane under PMS+Vis conditions in 45 min. Also, they show a higher recovery of pure water flux and owning good fouling performance. Overall, this current work presents a novel approach for the design and preparation of organic-inorganic photocatalytic composite membrane using readily available natural products for the purification TCM wastewater.

Degradation of Anthraquinone dye wastewater by sodium percarbonate with CoO heterogeneous activation

AbstractBACKGROUNDAnthraquinone dyes have an anthraquinone structure as their nucleus, with one or more substituents forming different organic dyes. Anthraquinone dyes have a complex structure that allows them to exist stably in water environment, but also makes them more toxic than azo dyes. This results in varying degrees of harm to both humans and the environment as a result of residual dyes in the water or on the material’ surface. Sodium percarbonate (SPC) is a highly promising oxidant due to its green end product. Therefore, in this study, the catalytic performance and kinetic study of cobalt oxide (CoO) on SPC under different conditions were systematically investigated using RB19 as the target pollutant. The Box–Behnken Design (BBD) model was used to model the degradation of RB19 by CoO/SPC system, which gives the basis for practical application. The types of reactive oxygen species that effectively degrade RB19 and the potential degradation mechanism of the CoO/SPC system were revealed. At the same time, the CoO/SPC system was evaluated in terms of its practicality.RESULTSIn this work, the activation of SPC using CoO towards reactive blue 19 (RB19) degradation was explored. Experimental results showed that nearly 93.8% of RB19 could be removed within 30 min using 1 mmol L−1 SPC and 30 mg L−1 CoO. The three‐factor interaction effects of SPC concentration, CoO dosage and initial pH were investigated. The BBD model was set up to obtain the optimum working conditions of 1.039 mmol L−1 SPC, 33.35 mg L−1 CoO and the initial pH of 7.82, which gave a degradation rate of 95.372%. Additionally, it was confirmed that the solubility of Co2+ is consistently <150 μg L−1, meeting the emission standard (1 ppm). The presence of Cl−, NO3–, and HA had a similar profile, with a slight promoting effect in small amounts and an inhibitory effect when introduced in excess. The introduction of SO42– had a negligible effect on RB19 degradation, whereas the presence of HCO3− produced a slight inhibitory effect. Furthermore, the presence of PO43– showed a strong inhibitory effect. The CoO/SPC system is suitable for other organic dyes (32.7%–100%) and antibiotics (97.1–100%). Electron paramagnetic resonance (EPR) analysis and quenching experiments confirmed the presence and relative contribution of free radicals in the CoO/SPC system as CO3•‐ (88.12%) >O2•‐ (51.11%) >1O2 (37.21%) >•OH (5.27%) > SPC (3.33%) >CoO (0.09%). It has been confirmed that CoO activates SPC through electron transfer.CONCLUSIONThe present study describes a less time‐consuming, and more efficient method of treating anthraquinone dye wastewater that requires less oxidizer and catalyst, making it more economical. This proposes a straightforward, cost‐effective and efficient technique using SPC triggered by transition metal oxides. © 2024 Society of Chemical Industry (SCI).

Overview on natural dyes and their IR-spectra – Part I: Plant based dyes with naphthoquinone and anthraquinone structure

This is the first paper of a series of review articles reporting on natural dyes, their origin and infrared spectra (IR spectra). One aim of this review series is to compare IR spectra of natural dyes from different origin and discuss if this spectroscopic method can be used as versatile tool for the identification of natural dyes and their origin. This part I of the review series is related to four natural dyes based on the chemical structures of naphthoquinone and anthraquinone. Especially discussed are Lawson, juglone and alizarin, which are related to the natural products henna, walnut hull and madder root. Also, the natural dye based on alkanna root is investigated. Compared are the IR spectra of these natural dyes gained from different suppliers with the IR spectra of the pure chemical substances related to the natural dyes. A discussion with spectra from literature is supported. The aim of this review paper is to support infrared spectroscopic data of natural materials (natural dyes) to enable further material identification and also quality control supporting people working in the fields of fiber analytics or with production processes using natural dyes

Photocatalytic H2O2 production from resorcinol-formaldehyde resin spheres with anthraquinone structure

The production of hydrogen peroxide (H2O2) by photocatalytic oxygen reduction reaction (ORR) without sacrificial agents is a green method of great significance, in which the design of high-performance photocatalysts is its central task. This study reports a molecular-level structure design to introduce anthraquinone structure into the resin backbone through Schiff base reaction. In this design, 1,5-diaminoanthraquinone undergoes a Schiff base reaction with aldehyde groups through acid catalysis and is incorporated into the resin backbone (RF-DAAQ). The introduction of the carbonyl group in anthraquinone adjusts the ratio of D-A pairs in the resin, speeds up the separation speed of photogenerated electron holes, and makes it easier to absorb oxygen, further convert it into its intermediate product, and finally generate H2O2. The mechanism was explored by various characterization methods such as in situ diffuse reflectance fourier transform infrared spectroscopy (in situ DRIFTS) and DFT calculations. The RF-DAAQ-4 photocatalyst exhibits a H2O2 yield of 640.91 μM g-1h−1, which is 6 times higher than that of pristine RF and also shows a competitive advantage in many reported photocatalysts under similar reaction conditions. This work paves the way for designing molecular level catalyst for green synthetic H2O2 production.

2D redox-active COF with the anthraquinone structure for photocatalytic reduction of uranium

Photocatalysis can be an effective technology for the conversion of U(VI) to U(IV) because it is efficient, facile and free of secondary pollution. In this work, anthraquinone-functionalized covalent organic framework (DQTP) was fabricated by an irreversible tautomerization of 2,6-diaminoanthraquinone (DQ) and 2, 4, 6-triformylphloroglucinol (TP) in the β-ketoenamine structure. The resultant DQTP could be effectively used as a metal-free heterogeneous catalyst for the photoreduction of U(VI) (k = 0.00287 min−1). The pivotal role of anthraquinone moieties as the active sites for U(VI) reduction was evidenced, i.e., to promote charge separation and thus enhance photocatalytic activity, as well as the production of H2O2 followed by the formation of (UO2)O2·2H2O with U(VI) through in-situ reactions. Additionally, free radical capture experiments and spectrometry analysis were conducted to determine the synergistic reduction mechanism of photogenerated electrons, superoxide radicals and hydrogen peroxide. It was reassuring that this work could provide the research basis for the subsequent development of more practical metal-free photocatalysts for the purification of U(VI)-containing wastewater.

"Green" nZVI-Biochar as Fenton Catalyst: Perspective of Closing-the-Loop in Wastewater Treatment.

In the framework of wastewater treatment plants, sewage sludge can be directed to biochar production, which when coupled with an external iron source has the potential to be used as a carbon-iron composite material for treating various organic pollutants in advanced oxidation processes. In this research, "green" synthesized nano zero-valent iron (nZVI) supported on sewage sludge-based biochar (BC)-nZVI-BC was used in the Fenton process for the degradation of the recalcitrant organic molecule. In this way, the circular economy principles were supported within wastewater treatment with immediate loop closing; unlike previous papers, where only the water treatment was assessed, the authors proposed a new approach to wastewater treatment, combining solutions for both water and sludge. The following phases were implemented: synthesis and characterization of nano zero-valent iron supported on sewage sludge-based biochar (nZVI-BC); optimization of organic pollutant removal (Reactive Blue 4 as the model pollutant) by nZVI-BC in the Fenton process, using a Definitive Screening Design (DSD) model; reuse of the obtained Fenton sludge, as an additional catalytic material, under previously optimized conditions; and assessment of the exhausted Fenton sludge's ability to be used as a source of nutrients. nZVI-BC was used in the Fenton treatment for the degradation of Reactive Blue 4-a model substance containing a complex and stable anthraquinone structure. The DSD model proposes a high dye-removal efficiency of 95.02% under the following optimal conditions: [RB4] = 50 mg/L, [nZVI] = 200 mg/L, [H2O2] = 10 mM. pH correction was not performed (pH = 3.2). Afterwards, the remaining Fenton sludge, which was thermally treated (named FStreated), was applied as a heterogeneous catalyst under the same optimal conditions with a near-complete organic molecule degradation (99.56% ± 0.15). It could be clearly noticed that the cumulative amount of released nutrients significantly increased with the number of leaching experiments. The highest cumulative amounts of released K, Ca, Mg, Na, and P were therefore observed at the fifth leaching cycle (6.40, 1.66, 1.12, 0.62, 0.48 and 58.2 mg/g, respectively). According to the nutrient release and toxic metal content, FStreated proved to be viable for agricultural applications; these findings illustrated that the "green" synthesis of nZVI-BC not only provides innovative and efficient Fenton catalysts, but also constitutes a novel approach for the utilization of sewage sludge, supporting overall process sustainability.

An Extremely Stable, Highly Soluble Monosubstituted Anthraquinone for Aqueous Redox Flow Batteries

AbstractAn extremely stable, energy‐dense (53.6 Ah L−1, 2 m transferrable electrons), low crossover (permeability of <1 × 10−13 cm2 s−1 using Nafion 212 (Nafion is a trademark polymer from DuPont)), and potentially inexpensive anthraquinone with 2‐2‐propionate ether anthraquinone structure (abbreviated 2‐2PEAQ) is synthesized and extensively evaluated under practically relevant conditions for use in the negolyte of an aqueous redox flow battery. 2‐2PEAQ shows a high stability with a fade rate of 0.03–0.05% per day at different applied current densities, cut‐off voltage windows, and concentrations (0.1 and 1.0 m) in both a full cell paired with a ferro/ferricyanide posolyte as well as a symmetric cell. 2‐2PEAQ is further shown to have extreme long‐term stability, losing only ≈0.01% per day when an electrochemical rejuvenation strategy is employed. From post‐mortem analysis (nuclear magnetic resonance (NMR), liquid chromatography–mass spectrometry (LC‐MS), and cyclic voltammetry (CV)) two degradation mechanisms are deduced: side chain loss and anthrone formation. 2‐2PEAQ with the ether linkages attached on carbons non‐adjacent to the central ring is found to have three times lower fade rate compared to its isomer with ether linkages on the carbon adjacent to the central quinone ring. The present study introduces a viable negolyte candidate for grid‐scale aqueous organic redox flow batteries.

Antibacterial activities of anthraquinones: structure-activity relationships and action mechanisms.

With the increasing prevalence of untreatable infections caused by antibiotic-resistant bacteria, the discovery of new drugs from natural products has become a hot research topic. The antibacterial activity of anthraquinones widely distributed in traditional Chinese medicine has attracted much attention. Herein, the structure and activity relationships (SARs) of anthraquinones as bacteriostatic agents are reviewed and elucidated. The substituents of anthraquinone and its derivatives are closely related to their antibacterial activities. The stronger the polarity of anthraquinone substituents is, the more potent the antibacterial effects appear. The presence of hydroxyl groups is not necessary for the antibacterial activity of hydroxyanthraquinone derivatives. Substitution of di-isopentenyl groups can improve the antibacterial activity of anthraquinone derivatives. The rigid plane structure of anthraquinone lowers its water solubility and results in the reduced activity. Meanwhile, the antibacterial mechanisms of anthraquinone and its analogs are explored, mainly including biofilm formation inhibition, destruction of the cell wall, endotoxin inhibition, inhibition of nucleic acid and protein synthesis, and blockage of energy metabolism and other substances.

Highly efficient decontamination of tetracycline and pathogen by a natural product-derived Emodin/HAp photocatalyst

To address the water pollution induced by pharmaceuticals, especially antibiotics, and pathogens, natural product emodin, a traditional Chinese medicine with the characteristic large π-conjugation anthraquinone structure, was used to rationally develop a novel Emodin/HAp photocatalyst by integrating with a thermally stable and recyclable support material hydroxyapatite (HAp) through a simple preparation method. It was found that its photocatalytic activity to generate reactive oxygen species (ROS) was greatly improved due to the migration of photogenerated electrons and holes between emodin and HAp upon visible light irradiation. Thus, this Emodin/HAp photocatalyst not only quickly photodegraded tetracycline with 99.0% removal efficiency but also exhibited complete photodisinfection of pathogenic bacteria Staphylococcus aureus upon visible light irradiation. Therefore, this study offers a new route for the design and preparation of multifunctional photocatalysts using widely available natural products for environmental remediation.

Two anthraquinone compounds from the whole plants of Hedyotis corymbosa

Hedyotis corymbosa from the Rubiaceae family, widely distributed in tropical regions of Asia. Based on the traditional uses, researchers provided substantial scientific evidence revealing the beneficial impact of this plant highlighting its anticancer, hepatoprotective, antiulcer, antioxidant, anti-malarial, antibacterial and antifungal activities. This study aims to screen and identify anthraquinone from the methanol extract of whole plant H. corymbosa. The Anthraquinone was further fractionated and isolated using chromatographic techniques to obtain the purity of compounds. The anthraquinone structure was determined using spectroscopic analysis especially the Nuclear Magnetic Resonance (NMR) and Mass Spectrum (MS).

Targeted isolation of photoactive pigments from mushrooms yielded a highly potent new photosensitizer: 7,7\u2032-biphyscion

Pigments of fungi are a fertile ground of inspiration: they spread across various chemical backbones, absorption ranges, and bioactivities. However, basidiomycetes with strikingly colored fruiting bodies have never been explored as agents for photodynamic therapy (PDT), even though known photoactive compound classes (e.g., anthraquinones or alkaloids) are used as chemotaxonomic markers. In this study, we tested the hypothesis that the dyes of skin-heads (dermocyboid Cortinarii) can produce singlet oxygen under irradiation and thus are natural photosensitizers. Three photosensitizers based on anthraquinone structures were isolated and photopharmaceutical tests were conducted. For one of the three, i.e., (–)-7,7′-biphyscion (1), a promising photoyield and photocytotoxicity of EC50 = 0.064 µM against cancer cells (A549) was found under blue light irradiation (λexc = 468 nm, 9.3 J/cm2). The results of molecular biological methods, e.g., a viability assay and a cell cycle analysis, demonstrated the harmlessness of 1 in the dark and highlighted the apoptosis-inducing PDT potential under blue light irradiation. These results demonstrate for the first time that pigments of dermocyboid Cortinarii possess a so far undescribed activity, i.e., photoactivity, with significant potential for the field of PDT. The dimeric anthraquinone (–)-7,7′-biphyscion (1) was identified as a promising natural photosensitizer.

Self‐Delivering Supramolecular Nanofiber Based on Peptide‐Rhein Conjugate

A peptide‐drug conjugate (PDC) is a single molecule formed by one or more drug molecules that are conjugated with functional short peptides. Some specially designed PDC can construct self‐delivering supramolecular nanomedicine and improve the therapeutic effect. The design and synthesis of novel PDCs with unique assembly behavior are important for the drug delivery system. Rhein is a natural product extracted from rhubarb and has extensive pharmacological properties. In the present work, we successfully synthesized a novel PDC (VKVK‐rhein) based on rhein through solid‐phase synthesis technology and conventional coupling chemical methods. The anthraquinone structure of rhein and the structure of the short peptide (VKVK, Val‐Lys‐Val‐Lys) provided VKVK‐rhein with special assembly properties. VKVK‐rhein can be assembled into supramolecular nanofibers in water. The equilibrium solubility, oil‐water distribution coefficient, zeta potential, and cell viability of VKVK‐rhein were systematically studied. Our work lays a foundation for further biological application of rhein‐based PDCs.

Preparation and characterization of yellow waterborne polyurethane with 2,6-diaminoanthraquinone structure

Poly (2-methyl-1,3-propylene glycol-adipic acid) ester diol (PMA-1000), 2,2-dihydroxymethyl propionic acid (DMPA), toluene diisocyanate (TDI), 1,4-butanediol (BDO), 2,6-diaminoanthraquinone (DAAQ) were used as raw materials, triethylamine (TEA) as neutralizer, and yellow waterborne polyurethane dye (DAAQ-WPU) containing DAAQ was obtained after emulsification. The structure and properties of the product were characterized by infrared spectroscopy, fluorescence spectrophotometer, laser particle size analyzer, spectrophotometer and color fastness tester. The results show that, DAAQ anthraquinone structure is connected to the water-based polyurethane chain, DAAQ-WPU is synthesized, and its emulsion has purple fluorescence at 300–350 nm band. With the increase of DAAQ content, the particle size of DAAQ-WPU emulsion increases from 69.7 nm to 104.9 nm, the b* value of film increases from 10.4 to 45.39, and the yellow color deepens gradually. DAAQ-WPU has good color fastness to cotton cloth, and its color fastness to rubbing, water stain and soaping is 4–5 grade.

Anthraquinonoid pigments

AbstractColorants based on the anthraquinone structure are categorized as a subclass of carbonyl colorants. Anthraquinone textile dyes rank second in importance to azo dyes, especially within the vat dye application class. Vat dyes became of interest to the pigment industry because of their insolubility. This insolubility and generally excellent fastness properties inspired investigations into the selection of suitable established anthraquinonoid vat dyes for use as pigments after conversion to a physical form that is appropriate for their applications. Originally this proved difficult, but was eventually achieved following the development of appropriate conditioning after treatment processes. The structural chemistry of the various types of anthraquinonoid pigments in relation to their technical and coloristic performance is discussed. The chapter concludes with an illustrated description of the main synthetic routes and finally with a description of the principal applications of the individual commercial products. Anthraquinonoid pigments are generally regarded as high-performance products, suitable for highly demanding applications, although they tend to be expensive.

The optical and photo-electrochemical characterization of nano-ZnO particles and its application to degradation of Reactive Blue 19 under solar light

To assess its photocatalytic activity under sunlight, ZnO nano powder with crystallites sizes in the range (18–29 nm) was synthesized by decomposition from nitrate (ZnO-Nit) and acetate (ZnO-Ac) precursors by one-step calcinations. The powders were characterized by X-ray diffraction, transmission electron microscopy and Fourier-transform infrared spectroscopy. The optical band gap of ZnO-Ac, determined from the diffuse reflectance, was found to be 3.23 eV and the transition is directly allowed, due to the charge transfer O2−: 2p → Zn2+: 4s. The capacitance-potential (C−2 – E) characteristic plotted at pH ∼7 shows n type behaviour with a conductionband (−0.42 VSCE), made up of Zn2+: 4s orbital and positive of the O2/O2 level and a valence band (2.81 VSCE) deriving mostly from O2−: 2p orbital whose potential is less anodic than the OH/H2O level. So, ZnO was successfully used for the degradation of the Reactive Blue 19 (RB 19) a hazardous dye, by both radicals O2−and OH under solar light. Indeed, RB 19 is a vinylsulphone dye, difficult to eliminate by chemical oxidation because its anthraquinone structure is highly stabilized by resonance. The best photoactivity occurs over ZnO-Ac owing to its large active surface area (59 m2 g−1). The oxidation obeys a zero order kinetic with a rate constant of 7.3 × 10−3 mol L−1 min−1. The elaborated material showed an outstanding recyclability.

In Silico Investigation for the Design of Redox Based Molecular Switch

Molecular simulation based on density functional theory was performed on the structure of anthraquinone, pentacenequinone, heptacenequinone and their dianions. The HOMO–LUMO gap, excitation energy and absorption wavelength were calculated to examine the switching action of molecules via two electron OX/RED reaction. Drastic change has been found in HOMO–LUMO gap, excitation energy and absorption wavelength of neutral molecules and their dianions. It has been observed that these three poly-acenes based organic molecules are very auspicious for the design and manufacturing of redox-active molecular switches.

Donor–acceptor conjugates-functionalized aluminum phthalocyanines: Photophysical and nonlinear optical properties

Photoinduced electron transfer/energy transfer (PET/ET) plays a very important role in improving the nonlinear optical (NLO) response. AlPc-Aqn and HAlPc-Aqn with donor-acceptor (D-A) structure were prepared by grafting aluminum phthalocyanine (AlPc) and hyperbranched aluminum phthalocyanine (HAlPc) through anthraquinone axial covalent bonding. After the axial covalent connection, the formed D-A phthalocyanine materials enhance the PET/ET process between the phthalocyanine ring and the anthraquinone structure, which results in significant fluorescence quenching and effectively improves the material's NLO properties. The discrepancy of LUMO levels (ΔE) further confirms that both AlPc-Aqn and HAlPc-Aqn formed a D-A system. This effectively promotes the electron transfer between the anthraquinone and the phthalocyanine ring, performing enhanced NLO response. Furthermore, compared to AlPc-Aqn, the special three-dimensional structure of HAlPc-Aqn brings a more efficient PET/ET process and exhibits a larger nonlinear absorption coefficient.

Establishing GPCR Targets of hMAO Active Anthraquinones from Cassia obtusifolia Linn Seeds Using In Silico and In Vitro Methods.

The present study examines the effect of human monoamine oxidase active anthraquinones emodin, alaternin (=7-hydroxyemodin), aloe-emodin, and questin from Cassia obtusifolia Linn seeds in modulating human dopamine (hD1R, hD3R, and hD4R), serotonin (h5-HT1AR), and vasopressin (hV1AR) receptors that were predicted as prime targets from proteocheminformatics modeling via in vitro cell-based functional assays, and explores the possible mechanisms of action via in silico modeling. Emodin and alaternin showed a concentration-dependent agonist effect on hD3R with EC50 values of 21.85 ± 2.66 and 56.85 ± 4.59 μM, respectively. On hV1AR, emodin and alaternin showed an antagonist effect with IC50 values of 10.25 ± 1.97 and 11.51 ± 1.08 μM, respectively. Interestingly, questin and aloe-emodin did not have any observable effect on hV1AR. Only alaternin was effective in antagonizing h5-HT1AR (IC50: 84.23 ± 4.12 μM). In silico studies revealed that a hydroxyl group at C1, C3, and C8 and a methyl group at C6 of anthraquinone structure are essential for hD3R agonist and hV1AR antagonist effects, as well as for the H-bond interaction of 1-OH group with Ser192 at a proximity of 2.0 Å. Thus, based on in silico and in vitro results, hV1AR, hD3R, and h5-HT1AR appear to be prime targets of the tested anthraquinones.

Polylactide with improved optical property by introducing natural functional substance: Aloe-emodin

The PLA materials with improved optical property and derived from renewable resources were synthesized through ring-opening polymerization using natural aloe-emodin, having anthraquinone structure and alcoholic hydroxyl group, as initiator. The chemical bonding of the aloe-emodin unit on PLA backbone provided the PLA with the function of absorbing UV light and would avoid the migration of aloe-emodin during the lifetime of PLA materials. The chemical structure of the new PLA was confirmed by NMR and the content of aloe-emodin was evaluated by UV–Vis absorption spectra. By investigating the structural changes and the variation of average molecular weight (Mn) during the UV-irradiation test, it was found that the aloe-emodin unit could enhance the UV-stability of the polylactide. The molecular weight remained about 80% for aloe-emodin capped PLA after UV irradiation (PLA-E400), while it was only 50% for PLA-C400 without aloe-emodin. A small amount of aloe-emodin could enhance the UV block effect of PLA film. When covered with aloe-emodin functionalized PLA film, the optical damage rate of β-carotene decreased to one-fifth of that for the uncovered one. In addition, aloe-emodin showed little influence on the biodegradation of PLA.