Carbamate Hydrolysis Research Articles

Effect of water on CO2 absorption by a novel anhydrous biphasic absorbent: Phase change behavior, absorption performance, reaction heat, and absorption mechanism

The ionic liquids (ILs)-based biphasic absorbents are viewed as promising substitutes for CO2 capture due to their remarkable CO2 absorption performance, excellent stability and low energy requirement for regeneration. Further decreasing the regeneration heat requirement can be achieved by utilizing ILs-based anhydrous biphasic absorbents, whose solid CO2-rich phase contained small volume and low specific heat capacity. Given the high hygroscopicity of ILs and the water present in the flue gas, comprehending the effect of water is crucial for post-combustion carbon capture using ILs-based anhydrous biphasic absorbents. In this work, the effect of water on CO2 absorption by an anhydrous biphasic absorbent, tetramethylammonium glycinate ([N1111][Gly])/ethanol, was studied. The experimental results demonstrated that the CO2 loading and absorption rate were decreased in the presence of water, but the CO2 desorption efficiency was enhanced. Besides, the presence of water slightly reduced the reaction heat of CO2 absorption by [N1111][Gly]/ethanol to 69.48 kJ/mol CO2, which was 20% lower than that of monoethanolamine (MEA) absorbent. Furthermore, the 13C NMR results indicated that the primary CO2-product was bicarbonate in the presence of water rather than carbamate. There were three possible pathways for bicarbonate generation: zwitterion hydrolysis, carbamate hydrolysis, and base-catalyzed CO2 hydration. Water and ethanol competed to react with carbamate. When a large amount of water was present (≥70 wt%), the reaction of ethanol with the carbamate hardly occurred.

Energy-efficient non-aqueous biphasic solvent for carbon capture: Absorption mechanism, phase evolution process, and non-corrosiveness

High latent heat and corrosivity related to H2O inhibit the application of aqueous biphasic absorbents for CO2 capture. An energy-efficient non-aqueous biphasic solvent DETA-EG-PMDETA (D-E-P) was developed with EG-assisted CO2 absorption, interesting phase-transition behavior, and non-corrosiveness. EG could increase the absorption capacity through direct alcoholysis of carbamate and the complex reaction among EG, DETA, and CO2. When EG:PMDETA = 3.5:6.5, the CO2 saturated loading was as high as 2.02 mol/mol. Unlike common biphasic solvents, flue gas saturated-absorbent presented a denser CO2-rich phase with larger CO2 loading (6.01 mol/L) and smaller volume (26.7%), and more convenient homogeneous desorption, whereas the pure CO2-saturated absorbent exhibited an EG-diluted CO2-rich phase (4.34 mol/L, 43.5%) and heterogeneous desorption. Benefiting from low vapor pressure, vaporization enthalpy, and heat capacity of EG, and greatly reduced regeneration volume, the Qlatent (0.0208 GJ/t CO2) and Qsen (0.12797 GJ/t CO2) were considerably decreased, resulting in a regeneration energy of 1.87 GJ/t CO2. It's significantly lower than 30 wt% MEA and other aqueous biphasic absorbents. In addition, because the carbamate hydrolysis and CO2 hydration could not take place in non-aqueous absorbent, the content of H+ was considerably limited, leading to a non-corrosive feature, and the corrosion rate was only 3.70 E−3 mm/a.

Theoretical Assessment of Carbon Dioxide Reactivity in Methylpiperidines: A Conformational Investigation.

In this work, the possible mechanisms for the reactions of CO2 with various positional isomers of methylpiperidines (MPs) (N-MP, 2-MP, 3-MP, and 4-MP) including the effect of aqueous solvation have been explored using quantum chemical methods. The major pathways investigated for CO2 capture in aqueous amines are carbamate formation, its hydrolysis, and the bicarbonate formation (CO2 + H2O + MP) reaction. The calculations indicate that an axial orientation for the methyl group and an equatorial for the COO- group could be energetically ideal in the carbamate product of MPs. The proton abstraction step in the carbamate pathway is almost barrierless for the zwitterion-amine route, while a much higher energy barrier is observed for the zwitterion-H2O route. During carbamate hydrolysis, the addition of even two explicit water molecules does not exhibit any notable effect on the already high energy barrier associated with this reaction. This indicates that bicarbonate formation is less likely to occur via carbamate hydrolysis. The calculations suggest that, although the carbamate pathway is kinetically favored, the MP carbamate could still be a minor product, especially for sterically hindered conformations, and the bicarbonate pathway should be predominant in aqueous MPs.

Urethanasen für die enzymatische Hydrolyse niedermolekularer Carbamate und das Recycling von Polyurethanen

AbstractEnzymatischer Abbau und Recycling können die Umweltbelastung durch Plastik reduzieren. Trotz jahrzehntelanger Forschung wurde bisher nicht über Enzyme für die effiziente Hydrolyse von Polyurethanen berichtet. Während die Hydrolyse von Esterbindungen in Polyester‐Polyurethanen durch Cutinasen bekannt ist, blieben die Urethanbindungen in Polyether‐Polyurethanen für biokatalytische Hydrolyse bislang unzugänglich. Wir berichten hier über die Entdeckung von Urethanasen in einer Metagenombibliothek, erstellt aus einer Bodenprobe, welche Polyurethanabfall für viele Jahre ausgesetzt war. Wir demonstrieren weiterhin die Anwendung einer Urethanase in einem chemo‐enzymatischen Prozess zum Polyurethan‐Recycling. Diese Urethanase hydrolysiert niedermolekulare Dicarbamate, welche aus der chemischen Glykolyse von Polyether‐Polyurethanschaum entstehen, was diese Strategie breit anwendbar auf diverse Polyether‐Polyurethan Abfälle macht.

Urethanases for the Enzymatic Hydrolysis of Low Molecular Weight Carbamates and the Recycling of Polyurethanes.

Enzymatic degradation and recycling can reduce the environmental impact of plastics. Despite decades of research, no enzymes for the efficient hydrolysis of polyurethanes have been reported. Whereas the hydrolysis of the ester bonds in polyester-polyurethanes by cutinases is known, the urethane bonds in polyether-polyurethanes have remained inaccessible to biocatalytic hydrolysis. Here we report the discovery of urethanases from a metagenome library constructed from soil that had been exposed to polyurethane waste for many years. We then demonstrate the use of a urethanase in a chemoenzymatic process for polyurethane foam recycling. The urethanase hydrolyses low molecular weight dicarbamates resulting from chemical glycolysis of polyether-polyurethane foam, making this strategy broadly applicable to diverse polyether-polyurethane wastes.

Thermochemical model for evaluating CO2 regeneration energy for amine absorbents

We present a thermochemical model for evaluating CO2 regeneration energies for aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP), and 2-(isopropylamino)ethanol (IPAE). The regeneration heat consists of the reaction heat, the sensible heat, and the vaporization heat. We calculated the reaction heat using a thermochemical model. We calculated the concentrations of all chemical species present in the CO2 absorption state at 40 °C and the CO2 release state at 120 °C. We calculated the reaction heat by summing enthalpies of associated reactions and reacted molar quantities derived from the concentration changes between the absorption and release states. For sterically hindered amines AMP and IPAE, the contribution of the protonation reaction to the reaction heat is large, whereas the contributions of protonation and carbamate hydrolysis are large for MEA and DEA. In the regeneration heat, the sensible heat is much larger than the reaction and vaporization heats.

Carbon Dioxide Chemical Absorption Using Diamines with Different Types of Active Centers

The present research analyzes chemical solvents based on the use of diamines (Ethylenediamine-EDA, 1,2-Dimethylethylenediamine-DMEDA and Tetramethylethylenediamine-TMEDA) for carbon dioxide absorption, taking into account the type of amino centers in the molecules. The presence and type of radicals can affect amine solubility in water, reaction mechanism, reaction kinetics, etc. Diamines have been considered interesting candidates for carbon dioxide chemical absorption, observing a high influence of the molecule structure. The present work analyzes a series of solvents based on diamines with the same chain length between amino centers, but different types of radicals. This study shows an important variability in the behavior of these solvents. EDA-based solvents have shown high absorption rates and stability, but carbamate hydrolysis is relatively low, avoiding an increase in carbon dioxide loading.

Stereoselective Synthesis of Nojirimycin α-C-Glycosides from a Bicyclic Acyliminium Intermediate: A Convenient Entry to N,C-Biantennary Glycomimetics.

A simple and efficient method for the stereoselective synthesis of nojirimycin α-C-glycoside derivatives has been developed using a bicyclic carbamate-type sp2-iminosugar, whose preparation on a gram scale has been optimized, as the starting material. sp2-iminosugar O-glycosides or anomeric esters serve as excellent precursors of acyliminium cations, which can add nucleophiles, including C-nucleophiles. The stereochemical outcome of the reaction is governed by stereoelectronic effects, affording the target α-anomer with total stereoselectivity. Thus, the judicious combination of C-allylation, carbamate hydrolysis, cross-metathesis, and hydrogenation reactions provides a very convenient entry to iminosugar α-C-glycosides, which have been transformed into N,C-biantennary derivatives by reductive amination or thiourea-forming reactions. The thiourea adducts undergo intramolecular cyclization to bicyclic iminooxazolidine iminosugar α-C-glycosides upon acid treatment, broadening the opportunities for molecular diversity. A preliminary evaluation against a panel of commercial glycosidases validates the approach for finely tuning the inhibitory profile of glycomimetics.

Molecular and functional characterization of three novel carboxylesterases in the detoxification of permethrin in the mosquito, Culex quinquefasciatus.

Carboxylesterases (CarEs) belong to a super family of multifunctional enzymes associated with the degradation of endogenous and exogenous compounds. Many insect CarEs are known to play important roles in catalyzing the hydrolysis of organophosphates (OPs), carbamates, and synthetic pyrethroids (SPs). The elevation of esterase activity through gene amplification and overexpression of estα2 and estβ2 genes contributes to the development of resistance to OP insecticides in the mosquito Culex quinquefasciatus. Three additional CarE genes are upregulated in permethrin-resistant Cx. quinquefasciatus according to an RNA-seq analysis, but their function remains unknown. In this study, we, for the first time, characterized the function of these three novel genes using in vitro protein expression, an insecticide metabolism study and molecular docking analysis. All three CarE genes were significantly overexpressed in resistant mosquito larvae, but not adults, compared to susceptible strain. No gene copy differences in these three genes were found in the mosquitoes tested. In vitro high-performance liquid chromatography (HPLC) revealed that CPIJ018231, CPIJ018232, and CPIJ018233 metabolized 30.4% ± 2.9%, 34.7% ± 6.8%, and 23.2% ± 2.2% of the permethrin, respectively. No mutations in resistant strains might significantly affect their CarE hydrolysis ability. A docking analysis further confirmed that these three CarEs from resistant strain all potentially metabolize permethrin. Taken together, these three carboxylesterase genes could play important roles in the development of permethrin resistance in Cx. quinquefasciatus larvae through transcriptional overexpression, metabolism, and detoxification.

Multistage Chemical Recycling of Polyurethanes and Dicarbamates: A Glycolysis–Hydrolysis Demonstration

The use of polyurethanes and, therefore, the quantity of its scrap are increasing. Considering the thermoset characteristic of most polyurethanes, the most circular recycling method is by means of chemical depolymerization, for which glycolysis is finding its way into the industry. The main goal of polyurethane glycolysis is to recover the polyols used, but only limited attempts were made toward recovering the aromatic dicarbamate residues and derivates from the used isocyanates. By the split-phase glycolysis method, the recovered polyols form a top-layer phase and the bottom layer contain transreacted carbamates, excess glycol, amines, urea, and other side products. The hydrolysis of carbamates results in amines and CO2 as the main products. Consequently, the carbamates in the bottom layer of polyurethane split-phase glycolysis can also be hydrolyzed in a separate process, generating amines, which can serve as feedstock for isocyanate production to complete the polyurethane material cycle. In this paper, the full recycling of polyurethanes is reviewed and experimentally studied. As a matter of demonstration, combined glycolysis and hydrolysis led to an amine production yield of about 30% for model systems. With this result, we show the high potential for further research by future optimization of reaction conditions and catalysis.

13C NMR study on carbamate hydrolysis reactions in aqueous amine/CO2 solutions

Carbamates of primary or secondary amines play a central role in amine CO2 absorbents. The equilibrium constant of a carbamate hydrolysis reaction, Kch, is important for evaluating the performance of absorbents. However, few Kch values have been reported to date. We determined the Kch values of normal amines, such as monoethanolamine (MEA), diethanolamine (DEA), and hindered amines, such as 2-amino-2-methyl-1-propanol (AMP) and 2-(isopropylamino)ethanol (IPAE), using a method involving a combination of 13C NMR spectroscopy and a chemical equilibrium analysis. The Gibbs energy changes derived from Kch for AMP and IPAE at 25 °C were negative, whereas those for normal amines, MEA and DEA, were positive. These properties are characteristic of hindered amines. We determined the standard enthalpy and entropy changes of the carbamate hydrolysis reactions from the temperature dependence of the equilibrium constant. The equilibrium constants and standard enthalpies obtained using the present method will be valuable for evaluating the performance of amine CO2 absorbents.

Aspergillus oryzae acetamidase catalyzes degradation of ethyl carbamate

Urethanase (EC 3.5.1.75) catalyzes the hydrolysis of ethyl carbamate (EC) to ethanol, carbon dioxide, and ammonia. From our recent study, we expected that an acetamidase encoded by amdS of Aspergillus oryzae may catalyze the degradation of EC because it is homologous with a Candida parapsilosis urethanase (CPUTNase) recently identified. Urethanase is a prospective candidate to reduce EC in alcoholic beverages, but knowledge of this enzyme is very limited. Recombinant AmdS was expressed to study its enzymatic properties. Purified AmdS was identified as a homo-tetramer consisting of four 60kDa units and exhibited urethanase activity. In a 20% ethanol solution, AmdS had 65% activity compared with a solution without ethanol. Residual activity after 18h indicated that AmdS was stable in 0%-40% ethanol solutions. The optimum temperature of AmdS was 40°C. This enzyme showed urethanase activity at pH 6.4-9.6 and exhibited its highest activity at pH 9.6. The Km value of AmdS for EC was 8.2mM, similar to the Km value (7.6mM) of CPUTNase. AmdS showed activity not only for EC and acetamide but also other amide compounds. In this study, we investigated the enzymatic properties of AmdS that was identified as acetamidase and showed that an amidase can be an enzymatic candidate that degrades EC.

Highly Selective Butyrylcholinesterase Inhibitors with Tunable Duration of Action by Chemical Modification of Transferable Carbamate Units Exhibit Pronounced Neuroprotective Effect in an Alzheimer's Disease Mouse Model.

In this study, the carbamate structure of pseudo-irreversible butyrylcholinesterase (BChE) inhibitors was optimized with regard to a longer binding to the enzyme. A set of compounds bearing different heterocycles (e.g., morpholine, tetrahydroisoquinoline, benzimidazole, piperidine) and alkylene spacers (2 to 10 methylene groups between carbamate and heterocycle) in the carbamate residue was synthesized and characterized in vitro for their binding affinity, binding kinetics, and carbamate hydrolysis. These novel BChE inhibitors are highly selective for hBChE over human acetycholinesterase (hAChE), yielding short-, medium-, and long-acting nanomolar hBChE inhibitors (with a half-life of the carbamoylated enzyme ranging from 1 to 28 h). The inhibitors show neuroprotective properties in a murine hippocampal cell line and a pharmacological mouse model of Alzheimer's disease (AD), suggesting a significant benefit of BChE inhibition for a disease-modifying treatment of AD.

Investigation on the inclusion of 1-(2-aminoethyl) piperazine as a promoter on the equilibrium CO2 solubility of aqueous 2-amino-2-methyl-1-propanol

The present work demonstrates the experimental and theoretical study of equilibrium CO2 solubility in a potential absorbent, aqueous 1-(2-aminoethyl) piperazine (AEP) and its blend with 2-amino-2-methyl-2-propanol (AMP). The measurements have been conducted at 303.2 to 323.2 K and within the CO2 partial pressure range of 2 to 250 kPa. The experimental data are modeled using modified Kent-Eisenberg (KE) equilibrium model for all the concentration range. Carbamate hydrolysis and AEP deprotonation constants are expressed as a function of pressure, temperature and amine concentration from the modified KE model. The developed model is used to predict the equilibrium liquid phase speciation in the CO2 loaded amine solution. An artificial neural network (ANN) model is also developed to predict the CO2 solubility in the understudy solvent system. The feed forward ANN model provides very good prediction with respect to the experimental solubility data having an average absolute deviation (% AAD) of 0.16. Qualitative 13C NMR and FTIR-ATR analysis have been performed for CO2 loaded solvent to understand the reaction scheme and identify the various important reaction products. Further, physicochemical properties such as density and viscosity of both the binary and ternary solvent system were also determined and correlated using Redlich-Kister and Grunberg-Nissan models.

Carbaryl Photochemical Degradation on Soil Model Surfaces

The phototransformation of carbaryl was investigated upon solar light exposure on three surfaces, silica, kaolin and sand, as soil models. By excitation with a Suntest set up at the surface of the three solid supports, the degradation of carbaryl followed first-order kinetics with a rate constant of 0.10 h−1. By using the Kubelka Munk model, the quantum yield disappearance at the surface of kaolin was evaluated to 2.4 × 10−3. Such a value is roughly one order of magnitude higher than that obtained in aqueous solutions. The results indicated that the particle size and the specific surface area of the various models have significant effects. The photo-oxidative properties as well as the byproduct elucidation by liquid chromatography combined with diode arrays (LC-DAD) and liquid chromatography coupled mass spectrometry (LC-MS) analyses allowed us to propose the degradation mechanism pathways. The main products were 1-naphtol and 2-hydroxy-1,4-naphthoquinone, which arise from a photo-oxidation process together with products from photo-Fries, photo-ejection and methyl carbamate hydrolysis. The toxicity tests clearly showed a significant decrease of the toxicity in the early stages of the irradiation. This clearly shows that the generated products are less toxic than the parent compound.

The Impact of Carboxylesterases in Drug Metabolism and Pharmacokinetics.

Background: Carboxylesterases (CES) play a critical role in catalyzing hydrolysis of esters, amides, carbamates and thioesters, as well as bioconverting prodrugs and soft drugs. The unique tissue distribution of CES enzymes provides great opportunities to design prodrugs or soft drugs for tissue targeting. Marked species differences in CES tissue distribution and catalytic activity are particularly challenging in human translation.Methods: Review and summarization of CES fundamentals and applications in drug discovery and development.Results: Human CES1 is one of the most highly expressed drug metabolizing enzymes in the liver, while human intestine only expresses CES2. CES enzymes have moderate to high inter-individual variability and exhibit low to no expression in the fetus, but increase substantially during the first few months of life. The CES genes are highly polymorphic and some CES ge-netic variants show significant influence on metabolism and clinical outcome of certain drugs. Monkeys appear to be more predictive of human pharmacokinetics for CES substrates than other species. Low risk of clinical drug-drug interaction is anticipated for CES, although they should not be overlooked, particularly interaction with alcohols. CES enzymes are moderately inducible through a number of transcription factors and can be repressed by inflammatory cy-tokines.Conclusion: Although significant advances have been made in our understanding of CESs, in vitro - in vivo extrapolation of clearance is still in its infancy and further exploration is needed. In vitro and in vivo tools are continuously being developed to characterize CES substrates and inhibitors

Biodegradation of pyraclostrobin by two microbial communities from Hawaiian soils and metabolic mechanism

Pyraclostrobin has been widely and long-termly applicated to agricultural fields. The removal of pyraclostrobin from ecological environment has received wide attention. In this study, using sequential enrichments with pyraclostrobin as a sole carbon source, two microbial communities (HI2 and HI6) capable of catabolizing pyraclostrobin were obtained from Hawaiian soils. The microfloras analysis indicated that only Proteobacteria and Bacteroides could survive in HI2-soil after acclimatization, whereas the number of Proteobacteria in HI6-soil accounted for more than 99%. The percentages of Pseudomonas in the HI2 and HI6 microfloras were 69.3% and 59.3%, respectively. More than 99% of pyraclostrobin (C0 = 100 mg L−1) was degraded by the HI2 and HI6 microorganisms within five days. A unique metabolite was identified by high performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS/MS). A metabolic pathway involving carbamate hydrolysis was proposed. The tertiary amine group of pyraclostrobin was hydrolyzed to primary amine group with the decarboxylation, which facilitated pyraclostrobin detoxification because carboxylester was an important functional group. The metabolic mechanism suggested that Pseudomonas expressing carboxylesterase might be able to degrade carbamate chemicals. Therefore, Pseudomonas might be an ideal candidate for expression and cloning of carbamate-degrading gene in genomics studies. The current study would have important implications in detoxification and bioremediation of carbamates through the CN bond cleavage of methyl carbamate.

CO2 absorption using aqueous potassium lysinate solutions: Vapor – liquid equilibrium data and modelling

The solubility of CO2 in aqueous potassium lysinate (LysK) solutions was measured in a stirred reactor at temperatures from 298 to 353K, for 9.0, 17.4, 25.3, 33.1 and 41.2mass% LysK and CO2 partial pressures up to 110kPa. The vapor-liquid equilibrium (VLE) data were interpreted using the modified Kent-Eisenberg model. The apparent equilibrium constants of carbamate hydrolysis and amino acid deprotonation were correlated as a function of temperature, CO2 loading (expressed as mole CO2 per mole LysK) and LysK concentration to fit the experimental solubility data. The proposed model satisfactorily predicted the VLE data for the H2O-LysK-CO2 system, especially at moderate to high CO2 loading, with an average absolute deviation within 3.2%. Liquid species in the CO2-loaded LysK solutions were also qualitatively characterized by 13C NMR experiments.

Synthesis and Reactivity of 5-Substituted Furfuryl Carbamates via Oxanorbornadienes.

Furfuryl carbamates are labile and require care to be accessed by activating furfuryl alcohols. An alternative oxanorbornadiene (OND)-based strategy is presented for the preparation of 5-R-substituted furfuryl carbamates via the reactions of amines with intermediate OND carbonates. The resulting OND carbamates, which are stable for several months, undergo thiol mediated retro-Diels-Alder reaction to deliver the desired furfuryl carbamates in a single flask. Conditions for the selective hydrolysis of furfuryl carbamates in the presence of tert-butyloxycarbonyl (Boc) groups were identified, and it was shown that furfuryl carbamates can be used as a prodrug handle.

Experimental study of CO2 absorption in aqueous cholinium-based ionic liquids

CO2 removal (or separation) is the key step for biogas upgrading. This research aims to investigate aqueous solutions of amino acid ionic liquids to achieve effective CO2 separation. In this work, three cholinium-based amino acid ionic liquids ([Cho][AA]s) (i.e. cholinium glycinate ([Cho][Gly]), cholinium alaninate ([Cho][Ala]) and cholinium prolinate ([Cho][Pro])) were synthesized and characterized. The effect of water on the viscosity, CO2 absorption loading (m and α) and apparent absorption rate constant was systematically studied. The CO2 absorption mechanism in the aqueous solution of [Cho][Gly] was explored by 13C Nuclear Magnetic Resonance (NMR). The results demonstrate that the absorption loading (m) and viscosity increase with increasing IL concentration, while the apparent absorption rate constant decreases. The absorption loading decreased with increasing temperature. The CO2 absorption mechanism in the aqueous [Cho][Gly] solution started with the chemical reaction to form carbamate at low absorption loading (α), and followed by the hydrolysis of carbamate and CO2 hydration reaction at high absorption loading (α). Moreover, the aqueous solution with 5 wt % [Cho][Gly] showed the highest regeneration efficiency, and the absorption and regeneration performance of the aqueous solution of [Cho][Gly] was compared with commercial CO2 absorbents with promising results.