Hydrolysis Of Acetate Research Articles

Mimic Carbonic Anhydrase Using Metal-Organic Frameworks for CO2 Capture and Conversion.

Carbonic anhydrase (CA) is a zinc-containing metalloprotein, in which the Zn active center plays the key role to transform CO2 into carbonate. Inspired by nature, herein we used metal-organic frameworks (MOFs) to mimic CA for CO2 conversion, on the basis of the structural similarity between the Zn coordination in MOFs and CA active center. The biomimetic activity of MOFs was investigated by detecting the hydrolysis of para-nitrophenyl acetate, which is a model reaction used to evaluate CA activity. The biomimetic materials (e.g., CFA-1) showed good catalytic activity, and excellent reusability, and solvent and thermal stability, which is very important for practical applications. In addition, ZIF-100 and CFA-1 were used to mimic CA to convert CO2 gas, and exhibited good efficiency on CO2 conversion compared with those of other porous materials (e.g., MCM-41, active carbon). This biomimetic study revealed a novel CO2 treatment method. Instead of simply using MOFs to absorb CO2, ZIF-100 and CFA-1 were used to mimic CA for in situ CO2 conversion, which provides a new prospect in the biological and industrial applications of MOFs.

Efficiency of Redispersible Polymer Powders in Mortars for Anchoring Application Based on Alkali Activated Portland Cements

Properties of dry mixes for anchoring application (increasing of mortars strength, adhesion, volume stability etc.) based on alkali activated Portland cement (AAPC) are influenced by different factors. One of them is application of chemical admixtures with different functionality. Adhesive properties are mainly achieved by redispersible polymer powders (RPP). The main problem in choice of RPP’s type is destruction of their molecules with ester links due to alkaline hydrolysis.The purpose of work was investigation of RPP’s molecular structure influence on properties of mortar for anchoring application based on AAPC and determination of the most effective.Efficiency of RPP based on copolymer of versatile acid ester was shown. The application of this RPP provides adhesion of 1.1 MPa and consistency of 190 mm. Positive effect of copolymer of ethylene and vinyl acetate was shown despite of partial destruction of RPP’s molecule as a result of alkaline hydrolysis of vinyl acetate at early terms of hardening. Negative effect of RPP is in decreasing of mortar strength. Thus this problem solving is decreasing of powder content to values which provide necessary physical-mechanical properties (strength, adhesion).

Comparative Study of Kinetics of Saponification of Ethyl Acetate by pH Method and Titration Method

The hydrolysis of ethyl acetate in presence of NaOH has been studied by pH method and by titration method. In the pH method the pH of the reaction mixture was recorded at various time intervals and the data was used to calculate the specific reaction rate constant of the reaction at room temperature (28°C). In the pH method, “alkaline error” correction was used to get the “true pH” of the reaction mixture and was used to calculate the specific reaction rate constant. In the titration method excess acetic acid was used to arrest the reaction. The pH method gave more reliable value of specific reaction rate constant of saponification of ethyl acetate than the titration method.

Functional Characterization of a New Antarctic Microbial Esterase EST112-2 and Its Use in the Preparation of Chiral Tertiary Alcohol (S)-Linalool

Chiral tertiary alcohols (TAs) are key building blocks for the synthesis of many crucial flavor compounds and pharmaceuticals. The two enantiomers of tertiary alcohol, linalool, differ in odor. So, sustainable strategies for the manufacture of optically pure TAs represented by linalool, are highly desirable. But the enzymatic synthesis of chiral tertian' alcohols through kinetic resolution was not easily achieved, possibly because of the steric hindrance from the chemical structures of tertiary alcohols. Herein, we identified and functionally characterized a new microbial esterase EST112-2 from the antarctic sediments and utilized esterase EST112-2 as a green biocatalyst in the synthesis of chiral tertiary alcohol (S)-linalool through asymmetric hydrolysis of racemic linalyl acetate. Parameters such as pH, temperature, co-solvents, substrate concentrations, enzyme loading and reaction time were optimized for the kinetic resolutions. Desired chiral product (S)-linalool was finally obtained with an enantiomeric excess of over 66% and a yield of over 72% after process optimization. The enantiomeric excess of (S)-linalool prepared by esterase EST112-2 was much higher than that from previous reports.

Enhanced catalytic activity and thermal stability of lipase bound to oxide nanosheets.

The present study reports the effects of binding of lipase, which is an inexpensive digestive enzyme (candida antarctica lipase) that catalyzes the hydrolysis reaction and is frequently utilized for artificial synthesis of a variety of organic molecules, to titanate nanosheets (TNSs) on their biocatalytic activities and stabilities under several lipase concentrations. TNSs were prepared through a hydrolysis reaction of titanium tetraisopropoxide (TTIP) with tetrabutylammonium hydroxide (TBAOH), resulting in formation of a colorless and transparent colloidal solution including TNSs with nanometric dimensions (hydrodynamic diameter: ca. 5.6 nm). TNSs were bound to lipase molecules through electrostatic interaction in an aqueous phase at an appropriate pH, forming inorganic-bio nanohybrids (lipase–TNSs). The enzymatic reaction rate for hydrolysis of p-nitrophenyl acetate (pNPA) catalyzed by the lipase–TNSs, especially in diluted lipase concentrations, was significantly improved more than 8 times as compared with free lipase. On the other hand, it was confirmed that heat tolerance of lipase was also improved by binding to TNSs. These results suggest that the novel lipase–TNSs proposed here have combined enhancements of the catalytic activity and the anti-denaturation stability of lipase.

Stereoselective synthesis of enantiomerically pure bowl-shaped hydroxytribenzotriquinacenes.

Enzyme-catalysed hydrolysis of the inherently chiral aryl acetate rac-11 bearing the bowl-shaped tribenzotriquinacene (TBTQ) core enables the stereoselective synthesis of the enantiomerically pure (M)-2-hydroxytribenzotriquinacene (M)-12. Starting from rac-11, for which two independent routes are described, the use of immobilised lipase CAL-A in buffered biphasic solution at pH 7 led to the TBTQ-phenol (M)-12 in 33% yield and with >99% ee on a preparative scale. Extended enzyme screening revealed that the use of CAL-B gives the same enantioselectivity. Furthermore, the chiroptical properties of the enantiomerically pure TBTQ-acetates (M)-11 and (P)-11, TBTQ-phenols (M)-12 and (P)-12 and the corresponding 2-hydroxy-3-iodotribenzotriquinacenes (M)-13 and (P)-13 are reported.

Transiently Thermoresponsive Acetal Polymers for Safe and Effective Administration of Amphotericin B as a Vaccine Adjuvant.

The quest for new potent and safe adjuvants with which to skew and boost the immune response of vaccines against intracellular pathogens and cancer has led to the discovery of a series of small molecules that can activate Toll-like receptors (TLRs). Whereas many small molecule TLR agonists cope with a problematic safety profile, amphotericin B (AmpB), a Food and Drug Administration approved antifungal drug, has recently been discovered to possess TLR-triggering activity. However, its poor aqueous solubility and cytotoxicity at elevated concentrations currently hampers its development as a vaccine adjuvant. We present a new class of transiently thermoresponsive polymers that, in their native state, have a phase-transition temperature below room temperature but gradually transform into fully soluble polymers through acetal hydrolysis at endosomal pH values. RAFT polymerization afforded well-defined block copolymers that self-assemble into micellar nanoparticles and efficiently encapsulate AmpB. Importantly, nanoencapsulation strongly reduced the cytotoxic effect of AmpB but maintained its TLR-triggering capacity. Studies in mice showed that AmpB-loaded nanoparticles can adjuvant an RSV vaccine candidate with almost equal potency as a highly immunogenic oil-in-water benchmark adjuvant.

Effect of fluid properties on ultrasound assisted liquid-liquid extraction in a microchannel

When immiscible liquids are subjected to an ultrasonic field, they form emulsions. This principle has been used to improve the mass transfer characteristics of a liquid-liquid extraction process in microreactor systems. The formation of emulsion and its characteristics are prominently dependent on the properties of the liquids used and this also holds true for emulsion brought about by ultrasound. This paper focuses on the properties of fluids that are reported to have an influence on the cavitation behaviour, namely viscosity, interfacial tension and vapour pressure. These properties were examined by changing the solvent of the organic phase in the hydrolysis of p-nitrophenyl acetate. The study is performed by comparing pairs of solvents that are different in one property but similar in the other two. The pairs selected are toluene – chlorobenzene for viscosity, toluene – methyl Isobutyl ketone for interfacial tension and methyl isobutyl ketone – 2-Methyl tetrahydrofuran for vapour pressure effects. A qualitative study was performed with a high-speed camera in flow to understand the emulsification initiation mechanisms and behaviours. These findings were further explored by performing the sonicated emulsion in a batch-sonicated reactor. The quantitative analysis of the fluid properties was evaluated and compared based on the relative percentage increase in yield upon sonication with respect to their individual silent conditions. The quantitative results were further supported by the quantification of the emulsion performed with an FBRM probe. The results indicate a two times improvement in yield with solvent of lower viscosity as 2 times more droplets were formed in the emulsion. Both the solvent systems with higher interfacial tension and vapour pressure had an improved yield of 1.4 times owing to larger number of droplets formed.

Optimization of process-specific catalytic packing in catalytic distillation process: A multi-scale strategy

A novel two-way coupling multi-scale model was proposed to investigate the catalytic distillation process. In the model, a microscopic model that focuses on the reactive performance of structure catalytic packing was used to calculate actual rate for catalytic distillation process, which is the basic parameter for process simulation. Furthermore, the traditional process simulation was used to provide proper boundary conditions for microscopic model. In order to validate the multi-scale model, heterogeneously catalyzed hydrolysis of methyl acetate was employed asa test system. The simulated final conversions of methyl acetate and catalyst layer efficiency factors were in good agreement with experimental results. The results indicated that as the equivalent diameter of catalyst layer decreases from 25.4mm to 8.1mm, the catalyst layer efficiency factor rises to 200% approximately. This study could provide a theoretical guide for the optimization of catalytic packing structure.

High Conversion of Methyl Acetate Hydrolysis in a Reactive Dividing Wall Column by Weakening the Self-Catalyzed Esterification Reaction

We show the superiority of reactive dividing wall column (RDWC) to the single reactive distillation (RD) column in improving the conversion of reactant, taking the hydrolysis of methyl acetate (MA) as example. It is difficult to achieve above 99% conversion for MA in a traditional reactive distillation column (TRDC) due to the existence of self-catalyzed methanol (MeOH)-acetic acid (HAc) esterification reaction in the column bottom. In this work, more than 99% conversion of MA hydrolysis was realized experimentally in an RDWC by separating MeOH from the hydrolysis mixture. The effects of several operation parameters on hydrolysis conversion were systematically investigated, including feedwater–MA mole ratio, heat duty, mole flow rate of feed MA, and vapor distribution. The simulation results by Aspen Plus showed that RDWC has several improvements in MA hydrolysis over TRDC, including lower energy consumption, lower water–MA mole ratio, and larger production capacity. With the increase in MA conversion, th...

Structural Insights on Recalcitrance during Hydrothermal Hemicellulose Extraction from Wood

Hydrothermal extraction of hemicelluloses from lignocellulosic biomass for conversion to renewable materials or fuels has captured attention. The extraction is however partial and some lignin is codissolved. Herein, we investigated the role of molecular structure in the recalcitrance. Wood meal of Spruce and Birch were subjected to pressurized hydrothermal extraction at 160 °C for 2 h, which extracted 68–75% of the hemicelluloses. 2D heteronuclear single quantum coherence (HSQC) NMR, HSQC-TOCSY, and 13C NMR were applied for structural studies of both extracts and residues. Subsequent to the known partial hydrolysis of native carbon-2 and carbon-3 acetates in hemicellulose, some acetylation of primary alcohols on hemicelluloses and lignin was observed. Lignin carbohydrate complexes (LCC) were detected in both the extracts and residues. In Spruce extracts, only the phenyl glycoside-type of LCC was detected. Birch extracts contained both the phenyl glycoside and benzyl ether-types. In the hydrothermal wood r...

Esterase EstK from Pseudomonas putida mt-2: An enantioselective acetylesterase with activity for deacetylation of xylan and poly(vinylacetate).

An extracellular esterase gene estK was identified in Pseudomonas putida mt-2 and overexpressed at high levels in Escherichia coli. The recombinant EstK enzyme was purified and characterized kinetically against p-nitrophenyl ester and other aryl-alkyl ester substrates and found to be selective for hydrolysis of acetyl ester substrates with high activity for p-nitrophenyl acetate (kcat 5.5 Sec-1 , KM 285 µM). Recombinant EstK was found to catalyze deacetylation of acetylated beech xylan, indicating a possible in vivo function for this enzyme, and partial deacetylation of a synthetic polymer (poly(vinylacetate)). EstK was found to catalyze enantioselective hydrolysis of racemic 1-phenylethyl acetate, generating 1R-phenylethanol with an enantiomeric excess of 80.4%.

Functional analysis of carboxylesterase in human induced pluripotent stem cell-derived enterocytes

Human carboxylesterase (CES) is a key esterase involved in the metabolism and biotransformation of drugs. Hydrolysis activity in the human small intestine is predominantly mediated by CES2A1 rather than CES1A. In drug development studies, Caco-2 cells are commonly used as a model to predict drug absorption in the human small intestine. However, the expression patterns of CES2A1 and CES1A in Caco-2 cells differ from those in the human small intestine. There are also species-specific differences in CES expression patterns between human and experimental animals. Furthermore, it is difficult to obtain primary human intestinal epithelial cells. Therefore, there is currently no system that can precisely predict features of drug absorption, such as CES-mediated metabolism, in the human intestine. To develop a novel system to evaluate intestinal pharmacokinetics, we analyzed CES expression and function in human induced pluripotent stem (iPS) cell-derived enterocytes. CES2A1 mRNA and protein levels in human iPS cell-derived enterocytes were comparable to Caco-2 cells, whereas CES1A levels were lower in human iPS cell-derived enterocytes compared with Caco-2 cells. p-nitrophenyl acetate hydrolysis in human iPS cell-derived enterocytes was significantly inhibited by the CES2A1-specific inhibitor telmisartan. Hydrolysis levels of the CES2A1-specific substrate aspirin were similar in human iPS cell-derived enterocytes and Caco-2 cells, whereas hydrolysis of the CES1A-specific substrate monoethylglycylxylidine was observed in Caco-2 cells but not in human iPS cell-derived enterocytes. These findings demonstrated that the expression and activity of CES isozymes in human iPS cell-derived enterocytes are more similar to the human small intestine compared with Caco-2 cells.

Spectroscopic studies on the interactions of bovine serum albumin in presence of silver nanorods

Abstract Due to the increasing usage of silver nanoparticles in biomedical applications, it becomes important to understand their interaction with biomolecules such as protein. In the present work, we have investigated the interaction of bovine serum albumin (BSA) with silver nanorods (SNRs) using different spectroscopic techniques. The interaction between BSA and SNRs can happen through non-covalent interactions like electrostatic and hydrophobic forces. Upon the interaction of SNRs with various concentrations of BSA, a small red-shift was found in the localized surface plasmon resonance (LSPR) peak of SNRs from UV–visible spectroscopic studies, indicating the adsorption of BSA on the surface of SNRs. The UV–visible absorption spectral studies confirmed the formation of a ground-state BSA-conjugated SNR system. The number of binding sites (n = 1.86) and binding constant (K = 8.719 × 104 L·mol− 1) were obtained to check the strength of conjugation of BSA in presence of different concentrations of SNRs from fluorescence quenching analysis. Further, DLS and zeta potential analyses proved significant binding of BSA towards the SNRs. The secondary structural changes in BSA in the presence of SNRs were obtained using circular dichroism (CD) spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The unfolding behavior of BSA and BSA-conjugated SNR complex were established using the surfactant, sodium dodecyl sulfate (SDS). Finally, the influence of SNRs in the hydrolysis of BSA was investigated by assaying the esterase activity. The esterase activity of BSA was determined by the hydrolysis of p-nitrophenyl acetate (p-NPA) to 4-nitrophenol.

Deceleration the hydrolysis reaction of ethyl acetate ester by β-cyclodextrin in basic medium: transition state analog

Electrical conductivity measurements were used to study the hydrolysis reaction of dilute aqueous solution of ethyl acetate with the presence β-cyclodextrin (β-CD) within a concentration range between 0.00 and 0.00750 M in basic medium at 25.0 °C. 0.00265 M of β-CD was chosen as typical concentration for studying the same reaction at different temperatures between 21.0 and 35.0 °C. Two different values of activation energy for the hydrolysis reaction of free ethyl acetate and ethyl acetate/β-CD complex were evaluated, and their values are 46.3 and 62.0 kJ mol−1 respectively. The standard Gibbs energy of activation (∆‡Go), standard enthalpy of activation (∆‡Ho), and standard entropy of activation (∆‡So) for the two different cases were evaluated. β-CD plays a notable role in retarding the rate of hydrolysis of ethyl acetate in basic medium.

Enhanced Catalytic Activity of α-Chymotrypsin in Cationic Surfactant Solutions: The Component Specificity Revisited.

Enhanced catalytic activity (super activity) of enzymes in the presence of surfactants is of key importance in "micellar enzymology"; such super activity is not very trivial, it is highly system specific, and the mechanism behind the activity enhancement is not always well apprehended. We report the catalytic activity of α-chymotrypsin (CHT) on ala-ala-phe-7-amido-4-methylcoumarin (AMC) in the presence of cationic surfactants of different hydrophobic chain lengths: dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB). It is observed that in comparison to buffer the catalytic activity of CHT is enhanced 5-fold in premicellar DTAB solutions, while negligible changes are observed in CTAB and OTAB. Activity decreases considerably in the post micellar concentration, specifically for the latter two surfactants. A similar trend is also obtained in another substrate 2-napthyal acetate hydrolysis. Such surfactant specific superactivity is intriguing. The protein's secondary and tertiary structures in the presence of these surfactants are determined using circular dichroism (CD) spectroscopy and it is found that both CTAB and OTAB perturb the protein structure significantly, especially in the post micellar concentrations. DTAB, on the other hand, does not produce noticeable changes in the protein structure. The various pairwise interactions present in the system have been underlined using both steady-state and time-resolved fluorescence spectroscopy. Assuming a three-step kinetics model, we determine the free energy changes of the reaction, and the observations have been discussed in the light of the various interactions among the components.

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels.

The effect of structural variations in acetal- and ketal-based linkers upon their degradation kinetics is studied through the design, synthesis, and study of six series of molecules, comprising a total of 18 different molecules. Through this systematic study, we show that the structural fine-tuning of the linkers allows access to variations in kinetics of degradation of more than 6 orders of magnitude. Hammett correlations show that the ρ value for the hydrolysis of benzylidene acetals is about -4.06, which is comparable to an SN1-like process. This shows that there is a strong, developing positive charge at the benzylic position in the transition state during the degradation of acetals. This positively charged transition state is consistent with the relative degradation rates of acetals vs ketals (correlated to stabilities of 1°, 2°, and 3° carboxonium ion type intermediates) and the observed effect of proximal electron-withdrawing groups upon the degradation rates. Following this, we studied whether the degradation kinetics study correlates with pH-sensitive variations in the host-guest characteristics of polymeric nanogels that contains these acetal or ketal moieties as cross-linking functionalities. Indeed, the trends observed in the small molecule degradation have clear correlations with the encapsulation stability of guest molecules within these polymeric nanogels. The implications of this fundamental study extend to a broad range of applications, well beyond the polymeric nanogel examples studied here.

Hydrophobic Lurylamine Modified Heteropoly Acid as an Efficient and Recyclable Catalyst for the Hydrolysis Reaction in Aqueous Solution under Microwave

A new modified phosphotungstic acid (HPW) catalyst (HPW-catal) was synthesized b y a simple mixing method under ambient atmosphere and evaluated for the hydrolysis of sucrose and ethyl acetate under microwave irradiation. The as-synthesized catalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy(FTIR), and NH3-TPD, which proved that HPW was sucessfully modified with lurylamine and the catalyst still remains the Keggin structure. Significantly, the HPW-catal showed excellent catalytic hydrolysis perforance for the sucrose and ethyl acetate under microwave irradiation. Both of the reactions were studied over other solid acid catalysts, such as AM-15 and ZSM-5. At mild tempretures, the sucrose and ethyl acetate could be hydrolyzed into corresponding products. The maximum glucose yield and alcohol could reach 100% and 95%, respectively. The HPW-catal can be recycled and reused. The HPW-catal will provides new ideas for the modifying of heteropoly acids.

A Bioinspired Dinickel(II) Hydrolase: Solvent Vapor-Induced Hydrolysis of Carboxyesters under Ambient Conditions.

From the perspective of synthetic metallohydrolases, a phenoxo-bridged dinickel(II) complex [NiII2(L)(H2O)2(CH3OH)][ClO4]·CH3OH (1) (H3L = 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N',N″-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol) has been synthesized and structurally characterized. The presence of a vacant coordination site and a weakly bound water molecule provides the scope for substrate binding to act as a metallohydrolase model. Ethyl acetate vapor diffusion at 298 K to a CH3CN/CH3OH solution of 1 results in the formation of a pentanuclear acetato-bridged complex [NiII5(H2L)2(μ3-OH)2(μ-O2CCH3)4][ClO4]2·CH3CO2C2H5 (2), demonstrating for the first time the metal-coordinated water-promoted hydrolysis of a carboxyester at room temperature. When the crystals of 1, moistened with a few drops of ethyl acetate, were kept for ethyl acetate vapor diffusion, it transforms into a monoacetato-bridged complex [NiII2(HL)(μ-O2CCH3)(H2O)2][ClO4]·4H2O (3). This kind of solvent (vapor)-induced single-crystal-to-single-crystal structural transformation concomitant with the hydrolysis of external substrate (ethyl acetate) is unprecedented. Reaction of H3L with 2 equiv of NiII(O2CCH3)2·4H2O, followed by the usual workup, and recrystallization from CH2Cl2 led to the isolation of [NiII2(H2L)(μ-O2CCH3)2][ClO4]·CH2Cl2·2H2O (4). Complex 4 is structurally different from 3, confirming that the reaction of NiII(O2CCH3)2·4H2O with H3L is a different phenomenon from the hydrolysis of ethyl acetate, promoted by NiII-coordinated water in 1. Complex 1 is also capable of hydrolyzing ethyl propionate to a propionato-bridged complex [NiII2(HL)(μ-O2CCH2CH3)(H2O)2][ClO4] (5). For the hydrolytic phenomena mentioned above, the coordinated ligand donor sites (phenolate and tertiary amine) provide a microenvironment around the dinickel(II) center to facilitate efficient stoichiometric hydrolysis of ethyl acetate and ethyl propionate under ambient conditions. Temperature-dependent magnetic studies of dimeric complexes 1, 4, and 5 reveal the presence of moderate antiferromagnetic coupling: J = -25.0(1) cm-1 for 1, J = -20.0(1) cm-1 for 4, and J = -18.80(8) cm-1 for 5. For pentanuclear complex 2, three types of magnetic-exchange interactions, two ferromagnetic (Ja = +16.02 cm-1, and Jb = +9.02 cm-1) and an antiferromagnetic (Jc = -49.7 cm-1), have been identified.

Trace water/amino-modified silica aerogel catalytic system in the one-pot sequential reaction of benzaldehyde dimethyl acetal and nitromethane

In this work, we demonstrate that solid-base such as amino-modified silica aerogel (SA-NH2) together with trace water showed excellent catalytic performance in one-pot sequential reaction of acid-catalyzed benzaldehyde dimethyl acetal hydrolysis and base-catalyzed Henry reaction which was usually catalyzed by acid-base bifunctional heterogeneous catalyst. The role of trace water in the reaction was discussed by batch control experiment. This SA-NH2/water catalytic system showed high reactant conversions (>99%) and main product selectivities (up to 99.4%). The trace water induced acid catalysis mechanism and a possible H+/-NH2 coexistence mechanism were given to explain the synergistic catalytic effect of solid-base and trace water.