Dehydration Mechanism Research Articles

Dehydration kinetics and mechanism of the stable isonicotinamide hydrate revealed by terahertz spectroscopy and DFT calculation

The dehydration behavior of pharmaceutical hydrates has a great influence on its physiochemical properties such as stability, dissolution rate and bioavailability. However, how the intermolecular interactions vary during dehydration process remains elusive. In this work, we employed terahertz time-domain spectroscopy (THz-TDS) to probe the low-frequency vibrations and the dehydration process of isonicotinamide hydrate I (INA-H I). Theoretical solid-state DFT calculation was conducted to reveal its mechanism. Vibrational modes which are responsible for the THz absorption peaks were decomposed for better understanding the characters of these low-frequency modes. The result suggests translational motion is the dominant component for water molecules in THz region. Evolution of the THz spectrum of INA-H I during dehydration provides direct evidence of the variations of crystal structure. Based on the THz measurements, a two-step kinetics mode including first-rate reaction and three-dimensional nuclei growth is proposed. And we figure that the low-frequency vibrations of water molecules are the origin of dehydration process of hydrate.

Characterization, Kinetic Using Deconvolution Techniques and Thermodynamic Study of Synthetic MgHPO4·3H2O

MgHPO4·3H2O was synthesized via a simple wet reaction and transformed to its final decomposed product, Mg2P2O7 at 873 K. The thermal properties, vibrational modes of block units, and solid phases of the synthetic compounds have been investigated by TG/DTG/DTA, FTIR, and XRD techniques. The temperature dependence of thermodynamic properties estimated from the DSC data occurred in two regions (before and after the dehydration reaction) indicating a characteristic of the prepared MgHPO4·3H2O sample. The dehydration reactions of 3.5 mol of water molecules in the structure overlapped in the temperature of 363–823 K and showed the phase transition at 921 K as revealed by TG/DTG/DTA. The deconvolution technique using the newly modified co-mathematical functions was used to separate the overlapped dehydration steps in the DTG curve, which obtained the three steps. Only the first and second steps were estimated using kinetic triplet parameters (Ea, A, and model), which indicate the single dehydration mechanism with the A1.25 model and the multi-step of a parallel mechanism with the A1.6 model, respectively. The data of kinetics and thermodynamics play key points in theoretical study, application development, and industrial production of magnesium phosphates as a theoretical basis.

Surgery assistance system for continuous resection of brain tumors-proposal of continuous tumor resection forceps, tumor cell separation, dehydration, and isolation mechanism

The tumor resection ratio must be improved due the increased possibility of recurrence or malignancy. The purpose of this study was to develop a system that includes forceps with a continuous suction function and flow cytometry to diagnose the malignancy of the tumor for safe, accurate, and effective surgery. A newly developed continuous tumor resection forceps consists of a triple pipe structure, which enables continuous suction of the tumor by integrating the reflux water and suction system. The forceps includes tip opening/closure detection switch to control the adsorption and suction strength when tip is opened and closed. To perform accurate tumor diagnosis using flow cytometry, a filtering mechanism was developed for dehydrating reflux water from continuous suction forceps. In addition, a cell isolation mechanism comprising a roller pump and shear force loading mechanism was also newly developed. By using a triple pipe structure, a significantly larger tumor collection ratio was observed compared to the previous double-pipe structure. By performing suction pressure control with the opening/closure detection switch, inaccurate suction can be prevented. By widening the filter area of dehydration mechanism, it was possible to improve the reflux water dehydration ratio. The most appropriate filter area was 85 mm2. By using a newly developed cell isolation mechanism, the processing time can be reduced to less than 1/10 of the original time, keeping the same cell isolation ratio, when compared to the existing pipetting method. Neurosurgery assistance system with continuous tumor resection forceps and a cell separation, dehydration and isolation mechanism was developed. An effective and safe tumor resection, accurate and fast diagnosis of malignancy can be achieved by using the current system.

Molecular Insights into Bifunctional Ambruticin DH3 for Substrate Specificity and Catalytic Mechanism.

Dehydratase (DH), a domain located at polyketide synthase (PKS) modules, commonly catalyzes the dehydration of β-hydroxy to an α,β-unsaturated acyl intermediate. As a unique bifunctional dehydratase, AmbDH3 (the DH domain of module 3 of the ambruticin PKS) is verified to be responsible for both dehydration and the following pyran-forming cyclization. Besides, in vitro studies showed that its catalytic efficiency varies with different chiral substrates. However, the detailed molecular mechanism of AmbDH3 remains unclear. In this work, the structural rationale for the substrate specificity (2R/2S- and 6R/6S-substrates) in AmbDH3 was elucidated and the complete reaction pathways including dehydration and cyclization were presented. Both MD simulations and binding free energy calculations indicated AmbDH3 had a stronger preference for 2R-substrates (2R6R-2, 2R6S-3) than 2S-substrates (2S6R-1), and residue H51 and G61 around the catalytic pocket were emphasized by forming stable hydrogen bonds with 2R-substrates. In addition, AmbDH3's mild tolerance at C6 was explained by comparison of substrate conformation and hydrogen bond network in 6S- and 6R-substrate systems. The QM/MM results supported a consecutive one-base dehydration and cyclization mechanism for 2R6S-3 substrate with the energy barrier of 25.2 kcal mol-1 and 24.5 kcal mol-1 , respectively. Our computational results uncover the substrate recognition and catalytic process of the first bifunctional dehydratase-cyclase AmbDH3, which will shed light on the application of multifunctional DH domains in PKSs for diverse natural product analogs and benefit the chemoenzymatic synthesis of stereoselective pyran-containing products.

Heat and let dye: Part II – Rapid heat‐fixing of blood traces

Blood-contaminated shoeprints and footmarks contain valuable operational information as they may bind an individual who stepped in the crime scene with the incident and not merely with the location. As determining the age of a bloodstain remains a challenge, while processing the scene, it is difficult to determine whether the blood is completely, or partially, dry. Thus, executing a dye staining protocol may wash these marks away as they might still be soluble. However, to meet this challenge, it is possible to fix blood marks using heat. This study aims to find a solution for floor surfaces covered by heavier blood traces (shoeprints and footmarks). For this purpose, a new pseudo-operating device was constructed for examining the blood-fixing process of both mentioned trace types. Two trials were performed with depletion marks. The results revealed that fully developed fresh and heavily blood deposits were obtained by heating to 200°C for 7.5min using the fixing device, followed by a staining protocol using amido black solution. The achieved sharp resolution of the examined bloody prints demonstrates that in certain cases the dehydration mechanism of heating is preferred over precipitating the proteins attributed to 5-sulfosalycilic acid; thus, reducing the risk of washing blood evidence while processing the crime scene.

Theoretical Substantiation of the Mechanism of Ultrasonic Dehydration of Materials Without a Phase Transition of Liquid Into Vapor

Theoretical Substantiation of the Mechanism of Ultrasonic Dehydration of Materials Without a Phase Transition of Liquid Into Vapor

Assembly Rules and Dehydration Mechanism of an Unconventional Hydrate: On the Complexity of the Hydrates of Creatine Phosphate Sodium

Unconventional hydrates with differently bound water molecules and related mazy intermolecular interaction networks need systematic investigation. The assembly rules, interaction analysis, and dehydration behavior can be dramatically more complicated when compared with those of common hydrates. In this work, creatine phosphate sodium (CPS) was selected as a model compound representing unconventional hydrates. The packing mode and the role of water molecules related to the dehydration mechanism were explored by the combination of experimental (diffraction, thermal, microscopy) and quantum chemistry computational (interplay visualization, binding energy calculation) methods. It was observed that in the structure of CPS heptahydrate and heminonahydrate, channel, isolated-site, and ion-associated water molecules exist simultaneously, constructing the framework via the coordination bond and hydrogen bond. The binding energy of some ion-coordinated water molecules is lower than that of hydrogen-bonded ones while that of some isolated-site water molecules is lower when compared with that of channel ones, which is counterintuitive. Moreover, the diverse types and locations of water molecules, complicated H2O···H2O interactions, and the trade-off between CPS···H2O and H2O···H2O lead to multistage, variable, and binding-energy-independent dehydration behavior. This work sheds light on the novel structure and variable dehydration mechanism of complicated hydrate systems and inspires the particularity and further investigation of unconventional hydrates.

Construction of bio-based ramie fabric/epoxy resin composites with high flame retardant and mechanical performances

The development of bio-based polymers will be beneficial to reducing carbon emissions. The biobased fiber-reinforced biobased epoxy resin can prepare fully-biobased polymer composites. However, their flame retardation will become a challenging issue. Here, fire-retardant ramie fabrics surface-modified by ammonium polyphosphate (APP) and polyethyleneimine were integrated into an epoxy system followed by fabricating high-performance composites. Notably, the epoxy resin composite with 8.9 % flame retardant displays a UL-94 V-0 rating. Besides, EP/(MF-2) exhibits a remarkably decreased peak of heat release rate (285 kW/m2) in contrast to pristine fabric-reinforced epoxy resin composite (608 kW/m2) from the cone calorimeter test. The improved flame-retardant performance follows the mechanism of the catalytic dehydration and charring effect by phosphorus-containing acids from the degradation of APP. Furthermore, flexural strength of EP/(MF-2) increases by 29 %, compared with neat EP, indicating obvious reinforcement of ramie fabric.

Biotransformation of bisphenol A in vivo and in vitro by laccase-producing Trametes hirsuta La-7: Kinetics, products, and mechanisms

Bisphenol A (BPA) is a ubiquitous endocrine disruptor that poses adverse human health risks. Herein, biotransformation kinetics, products, and mechanisms of BPA undergoing a laccase-producing Trametes hirsuta La-7 metabolism were for the first time reported. Strain La-7 could completely biotransform ≤0.5 mmol·L−1 BPA within 6 d in vivo. Notably, its extracellular crude laccase solution (ECLS) and intracellular homogenized mycelium (HM) only required 6 h to convert 85.71% and 84.24% of 0.5 mmol·L−1 BPA in vitro, respectively. The removal of BPA was noticeably hampered by adding a cytochrome P-450 inhibitor (piperonyl butoxide) in HM, disclosing that cytochrome P-450 monooxygenase participated in BPA oxidation and metabolism. BPA intermediates were elaborately identified by high-resolution mass spectrometry (HRMS) combined with 13C stable isotope ratios (BPA: 13C12-BPA = 0.25: 0.25, molar concentration). Based on the accurate molecular mass, isotope labeling difference, and relative intensity ratio of product peaks, 6 versatile metabolic mechanisms of BPA, including polymerization, hydroxylation, dehydration, bond cleavage, dehydrogenation, and carboxylation in vivo and in vitro, were confirmed. Germination index values revealed that inoculating strain La-7 in a BPA-contaminated medium presented no phytotoxicity to the germinated radish (Raphanus sativus L.) seeds. In vivo, Mg2+, Fe2+, Fe3+, and Mn2+ were conducive to BPA removal, but Cd2+ and Hg2+ significantly obstructed BPA elimination. Additionally, strain La-7 also exhibited high-efficiency metabolic ability toward estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2), with more than 96.13%, 96.65%, and 100% of E1, E2, and EE2 having been converted, respectively. Our findings provide an environmentally powerful laccase-producing fungus to decontaminate endocrine disruptor-contaminated water matrices by radical polymerization and oxidative decomposition.

PETpyrolysis and hydrolysis mechanism in the fixed pyrolyzer

AbstractIn the conventional polyethylene terephthalate (PET) pyrolysis process, the formation of char by excessive pyrolysis is mainly due to the dehydration mechanism, so water is considered an auxiliary agent that can effectively inhibit excessive pyrolysis. The preparation of terephthalic acid (TPA) by steam‐assisted pyrolysis of PET is an effective method to achieve closed‐loop recycling of waste PET. To ensure that the reaction is mild enough to reduce excessive cracking products such as char and benzoic acid and thus increase the yield of TPA, it is critical to reduce the reaction rate while maintaining a sufficient excess steam coefficient. Under the optimal operating conditions, when the temperature rise rate was 0.5 °C min−1and the excess steam coefficient was 150, the yield of TPA was 72.5 wt.%, and the purity was 85.5%. Noticeably, the steam‐assisted pyrolysis system is a heterogeneous reaction system whose reaction mechanism is different from the conventional hydrolysis and pyrolysis reactions and has a unique reaction path. The mechanistic study indicates that, in addition to the thermal cracking of PET molecules occurring in conventional pyrolysis, hydroxyl attack and transfer, and supplementation of benzene ring hydrogen also occur between water and intermediate molecules. Meanwhile, it has also been proven that the intermolecular hydrogen transfer between intermediate molecules and water molecules is the key to reduce the intensity of the reaction and inhibit the formation of char. This discovery illustrates the mechanism of the reaction between water and PET in the steam‐assisted pyrolysis process in the fixed pyrolyzer and justifies the distinction between it and the pyrolysis and hydrolysis processes of PET. It provides a theoretical basis for optimizing the pyrolysis process of PET, which is essential for the industrialization of TPA preparation from PET steam‐assisted pyrolysis.

Mechanisms of ethanol dehydration to ethylene on γ-Al2O3（100）and (110C): A combined DFT and KMC study

Periodic density function theory (DFT) and kinetic Monte Carlo (KMC) method are carried out to investigate ethanol dehydration to ethylene on γ-Al2O3 surface. Data on the adsorption energy, adsorption sites and heat of reaction of key species for the reaction of ethanol dehydration to ethylene on γ-Al2O3(100) , (110C) and (110D) surfaces were obtained by the DFT method. Subsequently, KMC simulations are performed with DFT results employed as database. The kinetics of ethanol dehydration from γ-Al2O3(100) surface to ethylene was studied by KMC. The effects of water-alcohol ratios on the reaction process were investigated. Under the process conditions of 750 K, 1 MPa, and water-ethanol ratio ratios in the range of 1 to 3, appropriate reducing the water-alcohol ratio can effectively inhibit carbon build-up without having a significant impact on the rate of ethylene production, providing a theoretical basis for extending catalyst life and reduce the industrial production cost.

A multi-faceted structural, thermodynamic, and spectroscopic approach for investigating ethanol dehydration over transition phase aluminas.

Understanding the role that the surface of a material plays in the mediation of a chemical reaction at the atomic level is paramount to the optimization and improvement of catalytic materials. While this area of research has matured over several decades, few techniques are sensitive enough to directly examine and differentiate the behavior of molecular adsorbates during the course of the chemical reaction with a substrate. In this study, a combined approach which involves structural characterization techniques, volumetric adsorption, temperature programmed desorption, and inelastic neutron scattering (INS) was used to investigate the mechanism of ethanol dehydration on the surface of transition phase aluminas. The alumina samples employed were extensively characterized using X-ray diffraction, solid-state 27Al nuclear magnetic resonance spectroscopy, and thermogravimetric analysis with differential scanning calorimetry. A high-precision volumetric adsorption apparatus was used to characterize the surface area and to controllably dose ethanol onto the surface of the aluminas. A modified temperature programmed desorption (TPD) method which samples the molecular composition of the vapor at discrete temperatures in a closed cell is described. INS results were used to confirm adsorption of ethanol on γ- and θ-alumina and show the reaction of ethanol and subsequent formation of ethylene as a function of temperature. The TPD and INS results affirm that the dehydration reaction and subsequent formation of ethylene on both γ- and θ-aluminas occur rapidly at 300 °C, though ethanol is still observed on θ-alumina indicating fewer active sites. These results demonstrate the value of a multi-faceted characterization approach, featuring INS, towards providing a detailed understanding of the ethanol dehydration mechanism on θ-alumina and further provide the basis for extending this approach to other systems in heterogeneous catalysis and areas where molecule-substrate interactions are poorly understood.

Dehydration mechanism of fructose to 5-hydroxymethylfurfural catalyzed by functionalized ionic liquids: a density functional theory study

The mechanism for the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF), catalyzed by functionalized ionic liquids (ILs), has been probed by DFT calculations.

A Measurement Method for the Pore Structure of Coal Slime Filter Cake

The accurate determination of the coal slime filter cake pore structure has always been a problem in the field of solid–liquid separation. An innovative measurement method for the pore structure of filter cake after filtration dehydration of coal slime water, including the preparation of coal slime filter cake, the solidification of the filter cake, and the preparation and measurement of test filter cake, was established in this paper. Epoxy resin and curing agent can ensure the strength of the filter cake, and red colorant can realize the accurate separation of coal particles and pores. The most suitable perfusate consists of epoxy resin, red colorant, and curing reagent, and the optimal ratio is 12:3:5. The application of the method to the study of the effect of filtration time on the coal slime filter cake pores shows that the modified method is effective. At the initial stage of filtration, intergranular pores formed by coarse particles are the main pores. With increasing filtration time, the macropores formed by the coarse particles are mainly filled with fine particles, and the pore size of the filter cake rapidly decreases. These measuring results and rules are accurate. This method can be conveniently used to study the microstructure of filter cake, pore channel regulation, filtration dehydration mechanisms, etc.

Mathematical modeling of convective drying of wheat gluten granules in suspended state: installation for process implementation

The purpose of the study is to solve a mathematical model for convective drying of wheat gluten granules in a suspended state and to develop a rational design of the apparatus for its implementation. In the course of the study, based on the analysis of the mechanism of convective dehydration of a granular product in a suspended state, a mathematical model of this process was constructed. This model was adapted to the study object and subject and its solution was carried out. Proceeding from the study of the advantages and disadvantages of well-known installations for drying gluten granulated products, a rational design of an installation for drying gluten granules is recommended. It should be noted that the proposed continuous-action installation, due to its design features, may be suitable not only for dehydration of the granulated semi-finished product under study, but also for drying similar products.

Grain filling leads to backflow of surplus water from the maize grain to the cob and plant via the xylem.

Rapid dehydration of maize grain is one of the main characteristics of cultivar selection for mechanical grain harvest; however, the dominant driving forces and mechanisms of grain dehydration before physiological maturity remain disputable and obscure. This study compared the grain moisture content and dehydration rate of coated treatment (no surface evaporation) and control grains. Meanwhile, the xylem-mobile dye was infused from stem and cob, and its movement was observed in cob, ear-stalk and stem xylem. The development dynamics of husk, grain and cob were analyzed to determine the mechanism of grain dehydration. The results showed that, from grain formation to 5-10 days before physiological maturity, the main driving force of grain dehydration of the early and middle-maturity maize cultivars was filling, followed by surface evaporation. In the dye movement experiment, the movement of the stem-infused xylem-mobile dye through the pedicel xylem was observed during but not after the grain formation period. Moreover, the cob-infused xylem-mobile dye moved to the ear- stalk and the stem via the xylem. There was a significantly positive correlation between grain filling rate and dehydration rate from grain formation to physiological maturity. According to these results, we proposed that in the grain dehydration phase driven by filling, the surplus water in the grain flows back to the cob via the pedicel xylem, of which some flowed back to the plant via the cob and ear- stalk xylem. This provides a new theoretical basis for selecting and breeding maize cultivars suitable for mechanical grain harvesting.

A multi-functional Ru Mo bimetallic catalyst for ultra-efficient C3 alcohols production from liquid phase hydrogenolysis of glycerol

Ru and Mo bimetallic catalysts supported on active carbon modified by phosphotungstic acid (PW) were designed and applied in glycerol hydrogenolysis reaction. The physicochemical properties of the catalysts were characterized and the presence of active sites was investigated from the perspective of the glycerol hydrogenolysis performance. The MoO x is highly selective for the C—O bond cleavage of glycerol molecules, which can reasonably regulate the strong C—C bond cleavage activity of Ru nanoparticles. By using sequential deposition of Ru and Mo supported on mesoporous PW-C, the characterization results show that the combination of isolated low-valence MoO x with metal Ru particles can form “MoO x -Ru-PW”, which provides highly catalytic activity toward C—O bond cleavage, selectively producing more C3 alcohols (mainly 1,2(3)-propanediol). The glycerol conversion of 1% Mo/Ru/PW-C catalyst was 59.6%, the selectivity of C3 alcohol was 96.1%, and the selectivity of propanediol (1,2(3)-propanediol) was 94.9%. It is noteworthy that the selectivity of 1,3-propanediol reached 20.7% when the PW was 21.07% (mass). This study provides experimental evidence for the tandem dehydration and hydrogenation mechanism of the multifunctional Mo/Ru/PW-C catalyst.

Kinetics of Acid-Catalyzed Dehydration of Alcohols in Mixed Solvent Modeled by Multiscale DFT/MD

Acid-catalyzed alcohol dehydration is a key reaction step in biomass upgrading, kinetics of which are significantly affected by mixed aqueous solvents. Computational modeling can provide fundamental understanding of solvation effects in catalysis, and ultimately a predictive tool for optimizing reactivity and selectivity. We introduce a multiscale method that combines density functional theory (DFT) with classical molecular dynamics (MD) to investigate the effect of mixed solvents (water with DMSO/GVL/MeCN) on the kinetics of acid-catalyzed dehydration of t-butanol and fructose. We determine the thermodynamically stable form of the excess proton (i.e., the catalyst) in mixed solvents. In water/GVL and water/MeCN mixtures, the excess proton resides on a water cluster (H5O2+). In water/DMSO, it forms a DMSO-H3O+ cluster in a bulk water/DMSO mixture, but appears as H5O2+ when close to an alcohol reactant. We model the E1 dehydration mechanism on t-butanol and fructose with DFT, and subsequently solvate each reaction intermediate and transition state with MD. Reaction free energy profiles for the elementary steps are mapped out at different solvent compositions. Our predictions compare well to results of Mellmer et al. Nature Catalysis 2018, 1, 199–207 and Nature Communications 2019, 10, 1–10, for both AIMD-measured reaction free energy profiles and experimental rate constants. By decoupling the gas-phase and solvation free energies, our calculation provides a clear interpretation of the solvation effects on an absolute free energy scale, and furthermore deconvolutes these effects into intuitive short-range electronic and longer range electrostatic interactions. Furthermore, our approach reveals solvent structuring around the reaction intermediates and the transition state. Our scalable DFT/MD approach provides a potentially powerful tool to predict reaction kinetics in condensed phases as well as detailed structural and energetic understanding of solvation effects in catalysis.

Kinetics and Mechanisms of Hydrothermal Dehydration of Cyclic 1,2- and 1,4-Diols.

Hydrothermal dehydration is an attractive method for deoxygenation and upgrading of biofuels because it requires no reagents or catalysts other than superheated water. Although mono-alcohols cleanly deoxygenate via dehydration under many conditions, polyols such as those derived from saccharides and related structures are known to be recalcitrant with respect to dehydration. Here, we describe detailed mechanistic and kinetic studies of hydrothermal dehydration of 1,2- and 1,4-cyclohexanediols as model compounds to investigate how interactions between the hydroxyls can control the reaction. The diols generally dehydrate more slowly and have more complex reaction pathways than simple cyclohexanol. Although hydrogen bonding between hydroxyls is an important feature of the diol reactions, hydrogen bonding on its own does not explain the reduced reactivity. Rather, it is the way that hydrogen bonding influences the balance between the E1 and E2 elimination mechanisms. We also describe the reaction pathways and follow-up secondary reactions for the slower-dehydrating diols.

Mechanism of Methanol Dehydration Catalyzed by Al8O12 Nodes Assisted by Linker Amine Groups of the Metal–Organic Framework CAU-1

Elucidation of catalytic sites and mechanisms of reactions on metal oxides is hindered by the complexity and heterogeneity of the surfaces. In contrast, the metal oxide cluster nodes of metal–organic frameworks (MOFs) have well-defined, essentially molecular structures that provide excellent platforms for understanding catalytic reactions in depth. We report an experimental and density functional theory (DFT) investigation of methanol dehydration on the Al8O12 nodes of the MOF CAU-1, presenting catalyst performance data obtained with vapor-phase methanol contacting MOF particles in a flow reactor at temperatures in the range of 180–250 °C. These data and infrared spectra of the MOF characterizing its reactivity with methanol and water show that the reactivities of node μ2-OH groups, influenced by the coordination environments of the node aluminum atoms, react with methanol to form catalytic sites incorporating methoxy ligands that bridge paired aluminum atoms, with the dehydration mechanism engaging nearby MOF linker amine groups that bond to methanol. DFT investigations of the mechanism suggest that the SN2-type methanol dehydration reaction is energetically favored to occur at MOF linker amine groups, which allow for a near-linear transition state (TS) geometry; in contrast, the central cavity of the Al8O12 node adsorbs methanol strongly but, because of geometric constraints, renders the TS for methanol dehydration energetically unfavorable.