A density functional theory study on interactions in water-bridged dimeric complexes of lignin.

Lignin is the main plant cell wall component responsible for recalcitrance in the process of lignocellulosic biomass conversion into biofuels. The recalcitrance and insolubility of lignin in different reaction media are due in part to the hydrogen bonds and π interactions that hold syringyl (S) and guaiacyl (G) units together and promote the formation of stable water-bridged dimeric complexes (WBDCs): S⋯G and S⋯S, in native lignin. The current understanding of how each type of interaction influences the stability of these complexes within lignin native cell walls is still limited. Here, we found by DFT calculations that hydrogen bonding is more dominant than π-stacking interaction between aromatic rings of WBDCs. Although there is a stronger interaction of hydrogen bonds between subunits and water and higher π-stacking interaction in the S⋯S complex compared to the S⋯G complex, the former complex is less thermodynamically stable than the latter due to the entropic contribution coming from the methoxy substituents in the S-unit. Our results demonstrate that the methoxylation degree of lignin units does not significantly influence the structural geometries of WBDCs; if anything, an enhanced dispersion interaction between ring aromatics results in quasi-sandwich geometries as found in "coiled" lignin structures in the xylem tissue of wood. In the same way as that with ionic liquids, polar solvents can dissolve S-lignin by favorable interactions with the aliphatic hydroxyl group in the α-position as the key site or the aromatic hydroxyl group as the secondary site.

Dynamic Interfacial Trapping of Janus Nanorod Aggregates.

Taking advantage of both shape and chemical anisotropy on the same nanoparticle offers rich self-assembly possibilities for nanotechnology. Through dissipative particle dynamics calculations, in the present work, the directed assembly of Janus nanorod aggregates and their capability to assemble into metastable novel structures at an interfacial level have been assessed. Symmetric Janus rods become kinetically trapped and exhibit either parallel or antiparallel alignment with respect to their long axis (different compositions). This depends on several factors that have been mapped herein and that can be precisely tuned: Flory-Huggins interaction parameter χ between polymer phases; concentration; shear rate; and even aggregate shape. Ultimately, two different aggregate structures result from rod tumbling that are not observed under quiescent conditions: monolayer-like aggregates exhibiting trapped rods with antiparallel configuration; and stacked nanorod arrays similar to superlattice sheets. These different structures can be controlled by the likelihood with which tumbling Janus rods encounter other aggregate portions showing parallel alignment. Hence, the present study offers fundamental insight into relevant parameters that govern the directed assembly of Janus nanoparticles at an interfacial level. Novel applications may potentially derive from the resulting aggregate structures, such as peculiar displays and sensors.

Slip and momentum transfer mechanisms mediated by Janus rods at polymer interfaces.

As an incipient but preeminent technology for multiphase nanomaterials/fluids, exact compatibilizing mechanisms of Janus particles in polymer blends and the consequent morphology remain unknown. The contributions of Janus nanorods to slip suppression and momentum transfer across the interface have been explored through dissipative particle dynamics simulations under shear flow at unentangled polymer-polymer interfaces. Rods have been then grafted with flexible polymer chains to unveil interfacial structure-property relationships at a molecular level when compared with flexible diblock copolymer surfactants. When Janus rods are sparsely grafted with necessarily longer grafts, they favor a greater degree of graft interpenetration with polymer phases. This yields less effective momentum transfer that impacts droplet coalescence processes; dynamic heterogeneities at complex interfaces; and helps map their efficiency as compatibilizers.

Separation of praziquantel enantiomers using simulated moving bed chromatographic unit with performance designed for semipreparative applications.

Praziquantel (PZQ) composes a regular medicine available in a tablet form to fight schistosomiasis and just half of its mass is composed by the active principle (L-PZQ), the other half, D-PZQ, is frequently associated to a strong bitter taste. Moreover, optically pure L-PZQ derivatives could be used in studies about adult and juvenile worms' resistance. Nowadays, these studies use racemic PZQ (rac-PZQ) as starting point. The D-PZQ, which would be discarded, could be racemized, coming back as feed concentration in the process. The present work aims to get L-PZQ and D-PZQ with high optical purities (more than 97%) and productivity (more than 253 g kgads -1  day-1 ) towards semipreparative scale for researches involving L-PZQ, L-PZQ derivatives, and D-PZQ racemization. In order to achieve this goal, a built-in-house simulated moving bed chromatographic unit with the cellulose tris (3-chloro-4-methylphenylcarbamate) (Chiralcel OZ) as chiral stationary phase (CSP) was used to investigate different scenarios of separation according to a well-known design method called triangle theory. In all scenarios investigated, at least one of the outlet streams presented high optically purity for one of the enantiomers. Comparison with literature showed superior performance of our unit even at racemic mixture concentrations that were 10 times lower than the racemic concentrations found in literature.

Modeling and dynamic simulation of a two-stage pre-denitrification MBBR system under increasing organic loading rates.

Biofilm-based wastewater treatment systems have become attractive due to their numerous advantages when compared to other suspended growth processes. However, the mathematical modeling of these reactors is relatively complex, since it has to consider a wide range of phenomena to accurately describe the process behavior. This work deals with the modeling of a two-stage MBBR system run in pre-denitrification mode for the removal of organic matter and nitrogen from wastewater. The model development took into account diffusive phenomena and kinetics in a homogeneous biofilm composed of different bacterial functional groups (namely heterotrophs and nitrifiers). The thickness of the biofilm was treated as a variable, given that detachment of adhered biomass took place. The suspended biomass fraction was also considered to remove the pollutants by means of Monod-type kinetics associated with the activated sludge model. The dynamic behavior of the components involved in the system and their spatial distribution in the biofilm obtained from simulated data showed good agreement with those reported in the literature, demonstrating the reproducibility of the model and encouraging future applications in full-scale MBBR plants.

Improvement of enzymatic saccharification by simultaneous pulping of sugarcane bagasse and washing of its cellulose fibers in a batch reactor.

A modification of the conventional batch organosolv process is proposed in a way where the solid biomass remains inside a basket, physically separated from the liquid phase, with the vapor promoting the fractionation of the biomass and the extracted compounds and fragments being washed down to the liquid phase. The modified organosolv process applied to sugarcane bagasse (SB-M) delivers a rich cellulosic solid phase that after enzymatic hydrolysis leads to a hydrolyzed with approximately 100 g L-1 of glucose. At the same enzymatic hydrolysis conditions, the conventional organosolv process (SB-C) delivers a hydrolyzed with 80 g L-1 of glucose, while the autohydrolysis process (SB-A) leads to 55 g L-1 of glucose. These different results are related to the cellulose content: SB-M (70%), SB-C (57%), e SB-A (44%), as well the reduced lignin content in the SB-M. The novelty of this study is the confirmation that it is possible to degrade lignin from sugarcane bagasse and simultaneously remove its fragments from the cellulose fibers in a batch reactor containing an internal basket. This study describes a simple and rapid protocol for the isolation of the main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin), which may lead to the study of new catalysts for the chemical transformation of these components separately or simultaneously to the step of pretreatment.

Evaluation of the optimal performance of ModiCon and ModiCon+VariCol simulated moving bed variants.

The interest in the simulated moving bed (SMB) technology lies in its variants. Some of them that have a high potential to increase the performance in enantioseparations are the ModiCon and the ModiCon+VariCol. These variants are based on the modulation of feed concentration and a combination of feed concentration and length of zones modulations. The concept of the ModiCon process in the literature is that it can be applied only for systems described by nonlinear isotherms. However, there are no numerical or experimental studies that prove that. On the other hand, the hybrid operation of ModiCon+VariCol can be used in systems with a low number of columns due to the flexibility in the use of columns, but it has been little explored. In this work, the maximal performance of the ModiCon process was compared with the SMB process for a linear isotherm. Additionally, the ModiCon+VariCol process was evaluated in systems with a low number of columns. The enantioseparation of guaifenesin was considered as a case study. The result shows that the ModiCon process can also be applied with high performance in systems described by linear isotherms. In the evaluation of the ModiCon+VariCol process for unequal product purity, it was found that the hybrid operation with 3 columns showed a higher throughput and productivity than the SMB process with 6 columns. The productivity of the ModiCon+VariCol was more than three times higher than the conventional operation.

Recursive state and parameter estimation of COVID-19 circulating variants dynamics.

COVID-19 pandemic response with non-pharmaceutical interventions is an intrinsic control problem. Governments weigh social distancing policies to avoid overload in the health system without significant economic impact. The mutability of the SARS-CoV-2 virus, vaccination coverage, and mobility restriction measures change epidemic dynamics over time. A model-based control strategy requires reliable predictions to be efficient on a long-term basis. In this paper, a SEIR-based model is proposed considering dynamic feedback estimation. State and parameter estimations are performed on state estimators using augmented states. Three methods were implemented: constrained extended Kalman filter (CEKF), CEKF and smoother (CEKF & S), and moving horizon estimator (MHE). The parameters estimation was based on vaccine efficacy studies regarding transmissibility, severity of the disease, and lethality. Social distancing was assumed as a measured disturbance calculated using Google mobility data. Data from six federative units from Brazil were used to evaluate the proposed strategy. State and parameter estimations were performed from 1 October 2020 to 1 July 2021, during which Zeta and Gamma variants emerged. Simulation results showed that lethality increased between 11 and 30% for Zeta mutations and between 44 and 107% for Gamma mutations. In addition, transmissibility increased between 10 and 37% for the Zeta variant and between 43 and 119% for the Gamma variant. Furthermore, parameter estimation indicated temporal underreporting changes in hospitalized and deceased individuals. Overall, the estimation strategy showed to be suitable for dynamic feedback as simulation results presented an efficient detection and dynamic characterization of circulating variants.

Optimal performance comparison of the simulated moving bed process variants based on the modulation of the length of zones and the feed concentration.

The VariCol and ModiCon processes are two variants of the simulated moving bed (SMB) process, characterized by the modulation of the length of zones of the chromatographic column train and the feed concentration. These features give more flexibility than the conventional operation, leading to essential improvements in the separation and purification of mixtures. The optimal performance comparison of these two variants, the hybrid formed by their combination, and the conventional SMB process are scarce in the literature. This comparison helps discover new characteristics of each single and combined operation mode and creates guidelines to select the appropriate operation mode for possible real applications. In this work, the performance comparison of the ModiCon, VariCol, ModiCon+VariCol, and SMB processes is carried out in terms of maximal throughput for specific product purity values. Particular emphasis is placed on both the ModiCon and the hybrid ModiCon+VariCol processes characteristics. A strategy for combining and optimizing the ModiCon and the VariCol processes was determined. As a case study, the enantioseparation of guaifenesin was considered. In the ModiCon process, more than two modulation subintervals did not improve the performance in the separation. The optimal pattern, based on two subintervals, has zero feed concentration in the first subinterval and the maximal concentration in the second one. The best result for the hybrid operation (ModiCon+VariCol) was reached when the feed port moves simultaneously as the SMB process switching period. The optimal throughput of the ModiCon and the ModiCon+VariCol processes was almost doubled than that of the SMB process. These performances were based on larger zones I and II and not in zones II and III as occur with the SMB and VariCol process. The throughput in the hybrid operation increases more significantly than the ModiCon process when 5 columns were considered instead of 6. The hybrid operation could be more attractive for a system with a few numbers of columns.

One-step optimization strategy in the simulated moving bed process with asynchronous movement of ports: A VariCol case study.

The VariCol process is a variant of the conventional simulated moving bed (SMB) process, distinguished by the asynchronous shifting of the inlet and outlet ports of the chromatographic column train. This feature allows for a more flexible operation in column utilization and can also achieve higher separation performances. However, to take full benefit out of it, the operating parameters, such as the strategy for port switching, must be optimal. in this paper, a novel methodology for optimizing those parameters, based on a single NLP (non-linear programming), is proposed. The main advantage of this approach is that it significantly reduces the complexity of the original MINLP (mixed-integer non-linear programming) formulation currently discussed in the literature. The proposed optimization problem is built, considering that the average column configuration of three zones provides the necessary and sufficient information to describe the VariCol process. Several optimization scenarios for the enantioseparation of 1,1´-bi-2-naphthol and aminoglutethimide were considered to evaluate the proposed methodology and to compare the performance of VariCol and SMB processes. The results have shown that with the single NLP approach, it is possible to explore the optimal solution in all the VariCol process domains with less computational effort than other optimization strategies reported in the literature. That is a great advantage, especially in the context of real-time applications.

Simultaneous parameters identifiability and estimation of an E. coli metabolic network model.

This work proposes a procedure for simultaneous parameters identifiability and estimation in metabolic networks in order to overcome difficulties associated with lack of experimental data and large number of parameters, a common scenario in the modeling of such systems. As case study, the complex real problem of parameters identifiability of the Escherichia coli K-12 W3110 dynamic model was investigated, composed by 18 differential ordinary equations and 35 kinetic rates, containing 125 parameters. With the procedure, model fit was improved for most of the measured metabolites, achieving 58 parameters estimated, including 5 unknown initial conditions. The results indicate that simultaneous parameters identifiability and estimation approach in metabolic networks is appealing, since model fit to the most of measured metabolites was possible even when important measures of intracellular metabolites and good initial estimates of parameters are not available.

Determination of the external mass transfer coefficient and influence of mixing intensity in moving bed biofilm reactors for wastewater treatment.

In moving bed biofilm reactors (MBBR), the removal of pollutants from wastewater is due to the substrate consumption by bacteria attached on suspended carriers. As a biofilm process, the substrates are transported from the bulk phase to the biofilm passing through a mass transfer resistance layer. This study proposes a methodology to determine the external mass transfer coefficient and identify the influence of the mixing intensity on the conversion process in-situ in MBBR systems. The method allows the determination of the external mass transfer coefficient in the reactor, which is a major advantage when compared to the previous methods that require mimicking hydrodynamics of the reactor in a flow chamber or in a separate vessel. The proposed methodology was evaluated in an aerobic lab-scale system operating with COD removal and nitrification. The impact of the mixing intensity on the conversion rates for ammonium and COD was tested individually. When comparing the effect of mixing intensity on the removal rates of COD and ammonium, a higher apparent external mass transfer resistance was found for ammonium. For the used aeration intensities, the external mass transfer coefficient for ammonium oxidation was ranging from 0.68 to 13.50 m d(-1) and for COD removal 2.9 to 22.4 m d(-1). The lower coefficient range for ammonium oxidation is likely related to the location of nitrifiers deeper in the biofilm. The measurement of external mass transfer rates in MBBR will help in better design and evaluation of MBBR system-based technologies.

A growth kinetic model of Kluyveromyces marxianus cultures on cheese whey as substrate.

This work presents a multi-route, non-structured kinetic model for determination of microbial growth and substrate consumption in an experimental batch bioreactor in which beta-galactosidase is produced by Kluyveromyces marxianus growing on cheese whey. The main metabolic routes for lactose, and oxygen consumption, cell growth, and ethanol production are derived based on experimental data. When these individual rates are combined into a single growth rate, by rewriting the model equations, the model re-interpretation has a complexity similar to that of the usual variations of the Monod kinetic model, available in the literature. Furthermore, the proposed model is in good agreement with the experimental data for different growth temperatures, being acceptable for dynamic simulations, processes optimization, and implementations of model-based control technologies.