RESUMO
Poly(butylene succinate-co-furandicarboxylate) (PBSF) and poly(butylene adipate-co-furandicarboxylate) (PBAF) are novel furandicarboxylic acid-based biodegradable copolyesters with great potential to replace fossil-derived terephthalic acid-based copolyesters such as poly(butylene succinate-co-terephthalate) (PBST) and poly(butylene adipate-co-terephthalate) (PBAT). In this study, quantum chemistry techniques after molecular dynamics simulations are employed to investigate the degradation mechanism of PBSF and PBAF catalyzed by Candida antarctica lipase B (CALB). Computational analysis indicates that the catalytic reaction follows a four-step mechanism resembling the ping-pong bibi mechanism, with the initial two steps being acylation reactions and the subsequent two being hydrolysis reactions. Notably, the first step of the hydrolysis is identified as the rate-determining step. Moreover, by introducing single-point mutations to expand the substrate entrance tunnel, the catalytic distance of the first acylation step decreases. Additionally, energy barrier of the rate-determining step is decreased in the PBSF system by site-directed mutations on key residues increasing hydrophobicity of the enzyme's active site. This study unprecedently show the substrate binding pocket and hydrophobicity of the enzyme's active site have the potential to be engineered to enhance the degradation of copolyesters catalyzed by CALB.
Assuntos
Proteínas Fúngicas , Lipase , Poliésteres , Lipase/metabolismo , Lipase/química , Proteínas Fúngicas/metabolismo , Proteínas Fúngicas/química , Poliésteres/química , Poliésteres/metabolismo , Biodegradação Ambiental , Simulação de Dinâmica Molecular , Hidrólise , Modelos QuímicosRESUMO
Poly(butylene diglycolate-co-furandicarboxylate) (PBDF) is a newly developed biodegradable copolyester. Candida antarctica lipase B (CALB) has been identified as an effective catalyst for PBDF degradation. The mechanism is elucidated using a combination of molecular dynamics simulations and quantum chemistry approaches. The findings unveil a four-step catalytic reaction pathway. Furthermore, bond analysis, charge and interaction analysis are conducted to gain a more comprehensive understanding of the PBDF degradation process. Additionally, through the introduction of single-point mutations to crucial residues in CALB's active sites, two mutants, T138I and D134I, are discovered to exhibit improved catalytic efficiency. These significant findings contribute to the advancement of our comprehension concerning the molecular mechanism of underlying copolyesters degradation, while also presenting a novel approach for expediting the degradation rate by the CALB enzyme modification.
Assuntos
Proteínas Fúngicas , Lipase , Lipase/química , Proteínas Fúngicas/química , Simulação de Dinâmica Molecular , Domínio CatalíticoRESUMO
About 200 million tons of coal fly ash (CFA) is not effectively used in China every year. To enhance the utilization of biomass waste quinoa husk (QH) and solid waste CFA and reduce the preparation cost of superabsorbent resin (SAR), a low-cost, biodegradable modified quinoa husk-g-poly (acrylic acid)/coal fly ash superabsorbent resin (MQH-g-PAA/CFA SAR) was synthesized using modified quinoa husk (MQH), acrylic acid and CFA and used to improve the drought resistance and fertilizer conservation ability of soil. The surface morphology and performance of SAR were characterized by Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), which provided evidence for improving the properties of SAR by grafting MQH and adding CFA. In addition, the synthesis conditions were studied and optimized, together with the contents of initiator, crosslinker, MQH, and CFA to acrylic acid as well as the neutralization degree of acrylic acid. After optimization, the optimum water absorbency of SAR in deionized water, tap water, and physiological saline was 1302, 356, and 91 g/g respectively. The swelling and water-retention mechanisms of SARs were analyzed by a dynamic model and the results were in good agreement with the experimental data. In the soil experiment, the addition of SAR improved the drought resistance ability of soil, and reduced the leaching loss of fertilizer in the soil (from 49.5 % to 36.7 %). Therefore, this material exhibits significant potential in the field of agriculture and offers a novel approach with economic benefit for the utilization of MQH and CFA.
RESUMO
Hemoglobin is essential for carrying oxygen (O2) in the blood. However, its ability to bind excessively to carbon monoxide (CO) makes it susceptible to CO poisoning. To reduce the risk of CO poisoning, Cr-based heme and Ru-based heme were selected from among many transition metal-based hemes based on their characteristics of adsorption conformation, binding intensity, spin multiplicity, and electronic properties. The results showed that hemoglobin modified by Cr-based heme and Ru-based heme had strong anti-CO poisoning abilities. The Cr-based heme and Ru-based heme exhibited much stronger affinity for O2 (-190.67 kJ/mol and -143.18 kJ/mol, respectively) than Fe-based heme (-44.60 kJ/mol). Moreover, Cr-based heme and Ru-based heme exhibited much weaker affinity for CO (-121.50 kJ/mol and -120.88 kJ/mol, respectively) than their affinity for O2, suggesting that they were less likely to cause CO poisoning. The electronic structure analysis also supported this conclusion. Additionally, molecular dynamics analysis showed that hemoglobin modified by Cr-based heme and Ru-based heme was stable. Our findings offer a novel and effective strategy for enhancing the reconstructed hemoglobin's ability to bind O2 and reduce its potential for CO poisoning.