Amide Hydrolysis Research Articles

Enhanced degradation of iopamidol by peroxymonosulfate catalyzed by two pipe corrosion products (CuO and δ-MnO2)

Peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; also many organic micropollutants may be present in drinking water sources nowadays. However, pipe corrosion products (PCPs) may impact the reactions between a disinfectant and organic micropollutants in water distribution systems. This study investigated iopamidol (IPM) degradation by PMS under catalysis of two PCPs (i.e., CuO and δ-MnO2). The pseudo-first-order rate constant of IPM degradation in the CuO/PMS system (CuPS) was 3.7 times of that in the δ-MnO2/PMS system (MnPS), with values of 0.218 and 0.059 min−1, respectively. Sulfate radical (SO4−) was the major contributor to IPM degradation in the CuPS, while hydroxyl radical (HO) also played an important role in the MnPS. The radical yield ratio was 0.89 and 0.69 mol/mol in the CuPS and MnPS, respectively. The IPM degradation rate increased with increasing PMS dose, and reached a maximum with a PCP dose of 1.0 and 1.5 g L−1 in the CuPS and MnPS, respectively. The highest degradation efficiency was achieved at pH 7.0 in the two systems. The water matrix (i.e., natural organic matter, alkalinity and chloride) had detrimental effects on IPM degradation to different degrees. The majority of the iodine released from IPM was oxidized to iodate (IO3−) and a small fraction of the initial total organic iodine was transformed to iodoform (CHI3). The IPM degradation by PMS mainly proceeded through two pathways: (1) amide hydrolysis of side chain A, amino oxidation, and amide hydrolysis of side chains B and B′ in sequence; and (2) deiodination reactions.

O-Phthalaldehyde catalyzed hydrolysis of organophosphinic amides and other P([double bond, length as m-dash]O)-NH containing compounds.

Over 50 years ago, Jencks and Gilchrist showed that formaldehyde catalyses the hydrolysis of phosphoramidate through electrophilic activation, induced by covalent attachment to its nitrogen atom. Given our interest in the use of aldehydes as catalysts, this work was revisited to identify a superior catalyst, o-phthalaldehyde, which facilitates hydrolyses of various organophosphorus compounds bearing P([double bond, length as m-dash]O)-NH subunits under mild conditions. Interestingly, chemoselective hydrolysis of the P([double bond, length as m-dash]O)-N bonds could be accomplished in the presence of P([double bond, length as m-dash]O)-OR bonds.

Особенности нуклеофильного замещения нитрогруппы в 4-алкил-6-нитро-1,2,4-триазоло[5,1-c][1,2,4]триазинах

The nucleophilic substitution of the nitro group of 4-alkyl-6-nitro-4,7-dihydro-1,2,4-triazolo[5,1-c][1,2,4]triazine-7-ones on the example of interactionwith morpholine was studied. It is established that under the action of excess cycloalkylimine at room temperature the unusual easy disclosure of triazine cycle with the formation of sterically hindered hydrazones occurs which are the key intermediates for further transformations. The carrying of reaction at elevated temperatures leads to the formation of products of substitution of the nitro group with the amine and also with morpholyl hydrazones which are the products of hydrolysis of amides of hydrazones and subsequent decarboxylation. Thus, the nucleophilic substitution of the nitro group in the described triazolotriazines flows through the ANRORC mechanism.

Implementation of electrochemical elements for an alternative detection of ochratoxin A

Ochratoxin A (OTA) is a nephrotoxic metabolite, hepatotoxic and carcinogenic produced mainly by Aspergillus and Penicillium fungi. Usually, the mycotoxin analysed through the technique of high performance liquid chromatography. This method is expensive and takes a lot of time. Therefore, expected to automate a device of low cost, minimal instrumentation micropolarographic (MIMP) for the analysis. For this purpose, the right programming environment and the manufacturing of the software for the graphical user interface selected automation of the MIMP through the design and simulation of the circuit, imprint and assembled in a container with connection ports. Lastly, validation and analysis of Ochratoxin A by cyclic voltammetry from analogous MIMP, automatic MIMP and a potentiostat, in order to corroborate the registered data. This way, voltammetry analysis of coumarin is obtained and the simulation of the MIMP electric circuit. Therefore, this are the key data during the investigation, because the molecule of OTA can be monitored through an acid hydrolysis of amides, composed by a phenylalanine and coumaric acid group, generating the significant decrease in the costs and time of analysis.

Metabolite identification of bentysrepinine (Y101), a novel anti-HBV agent in rats using a five-step strategy based on a combined workflow with two different platforms of liquid chromatography-tandem mass spectrometry.

Bentysrepinine (Y101), a derivative of repensine (a compound isolated from Dichondrarepens Forst), is a novel phenyalanine dipeptide inhibiting DNA-HBV and cccDNA activities and is currently under development for the treatment of hepatitis B virus (HBV)-infected hepatitis. Our previous study implied that there might be an existence of extensive metabolism of Y101 in rats. Therefore, it is necessary to perform metabolic profiling study to further evaluate its safety and drug-like properties. In this study, the metabolism of Y101 in rats was investigated by a convincible five-step strategy to characterize metabolites in plasma and that excreted into urine, bile and feces. The five-step strategy was realized by using an combined workflow on two different MS platforms, including various scan modes of liquid chromatography with hybrid quadruple-linear ion trap mass spectrometry (LC-QTRAP-MS/MS) and various post-acquiring data mining tools of liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS). QTOF MS/MS was employed as a powerful complementary tool to enable high confidence of metabolites identification using its functions of accurate MS and MS/MS fragmentation. As a result, a total of 30 metabolites were detected, including 25 phase I and 5 phase II metabolites. Among them, four primary metabolites (M6-M9) were further identified by comparing with the authentic standards chemically synthesized. The possible metabolic pathways of Y101 in rats were proposed to be amide hydrolysis, monohydroxylation, dihydroxylation, N-oxidation, demethylation, methylation, glucosidation and glucuronidation. This is the first study of the metabolism of Y101 in rats. The five-step strategy was successfully used to systematically characterize metabolites of Y101 in rats, and it would be generally applied for metabolite identification of new drug candidate.

Enzymatic degradation of polyacrylamide in aqueous solution with peroxidase and H2O2

ABSTRACTPolyacrylamides are often used in water‐based hydraulic fracturing for natural gas and oil production. However, residual polymer remaining in the fractured rock can limit production. A novel approach for degrading partially hydrolyzed polyacrylamide (HPAM) was investigated using hydrogen peroxide and horseradish peroxidase (HRP). This sustainable HRP/H2O2 system degraded the polymer in solution, reducing its viscosity in both pure water and brine solutions. Molecular weight measurements confirmed that the viscosity reduction was due to a significant degradation of the polymer backbone and not primarily by other mechanisms such as amide hydrolysis or rearrangement, and so forth. The reduction in viscosity and molecular weight was first order with respect to H2O2 concentration. The kinetics of viscosity reduction and molecular weight are closely correlated which would allow the quicker and simpler viscosity method to help engineer future processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44560.

Effects of Surface Hydrophobicity on Functionalization of Oleic Acid on <i>Bombyx mori</i> Silkworm Cocoons

The objective of this study is to provide a method which allows introduction of functional groups onto silk cocoon surface. Plasma irradiation is straight-forward, relatively noninvasive and requires minimal chemical reaction steps to alter surface hydrophilicity of polymeric materials. Introduction of oleic acid on pristine and air-zero irradiated silkworm (Bombyx mori) cocoons was carried out via acid-catalyzed esterification. The reaction was confirmed by ATR-FTIR spectroscopy. Functionalization of oleic acids onto silkworm cocoons favors hydrophilic surface. In addition to the acid-catalyzed esterification, amide hydrolysis takes place as a side reaction. This reaction leads to formation of hydrophilic carboxylic acids and amines. The change in hydrophilic functionalities leads to an increase in cocoon wettability as confirmed by contact angle measurements.

Stepwise-activable multifunctional peptide-guided prodrug micelles for cancerous cells intracellular drug release

A novel type of stepwise-activable multifunctional peptide-guided prodrug micelles (MPPM) was fabricated for cancerous cells intracellular drug release. Deca-lysine sequence (K10), a type of cell-penetrating peptide, was synthesized and terminated with azido-glycine. Then a new kind of molecule, alkyne modified doxorubicin (DOX) connecting through disulfide bond (DOX-SS-alkyne), was synthesized. After coupling via Cu-catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry reaction, reduction-sensitive peptide-guided prodrug was obtained. Due to the amphiphilic property of the prodrug, it can assemble to form micelles. To prevent the nanocarriers from unspecific cellular uptake, the prodrug micelles were subsequently modified with 2,3-dimethyl maleic anhydride to obtain MPPM with a negatively charged outer shell. In vitro studies showed that MPPM could be shielded from cells under psychological environment. However, when arriving at mild acidic tumor site, the cell-penetrating capacity of MPPM would be activated by charge reversal of the micelles via hydrolysis of acid-labile β-carboxylic amides and regeneration of K10, which enabled efficient internalization of MPPM by tumor cells as well as following glutathione- and protease-induced drug release inside the cancerous cells. Furthermore, since the guide peptide sequences can be accurately designed and synthesized, it can be easily changed for various functions, such as targeting peptide, apoptotic peptide, even aptamers, only need to be terminated with azido-glycine. This method can be used as a template for reduction-sensitive peptide-guided prodrug for cancer therapy. A novel type of stepwise-activable multifunctional peptide-guided prodrug micelles (MPPM) was fabricated for selective drug delivery in cancerous cells. MPPM could be shielded from cells under psychological environment. However, when arriving at mild acidic tumor site, the cell-penetrating capacity of MPPM would be activated by charge reversal of the prodrug micelles via hydrolysis of acid-labile β-carboxylic amides and regeneration of K10. The cell-penetrating peptide, K10, would enable efficient internalization of MPPM by tumor cells, and the drug would be rapidly released induced by concentrated glutathione and numerous proteases inside the cancerous cells, resulting in the inhibited effect of the cells .

Stability study on an anti-cancer drug 4-(3,5-bis(2-chlorobenzylidene)-4-oxo-piperidine-1-yl)-4-oxo-2-butenoic acid (CLEFMA) using a stability-indicating HPLC method

CLEFMA, 4-(3,5-bis(2-chlorobenzylidene)-4-oxo-piperidine-1-yl)-4-oxo-2-butenoic acid, is a new chemical entity with anti-cancer and anti-inflammatory activities. Here, we report its stability in solution against stress conditions of exposure to acid/base, light, oxidant, high temperature, and plasma. The identity of the degradation products was ascertained by mass and proton nuclear magnetic resonance spectroscopy. To facilitate this study, we developed and validated a reverse phase high performance liquid chromatography method for detection of CLEFMA and its degradation. The method was linear over a range of 1–100µg/mL; the accuracy and precision were within acceptable limits; it was stability-indicating as it successfully separated cis-/trans-isomers of CLEFMA as well as its degradation product. The major degradation product was produced from amide hydrolysis at maleic acid functionality caused by an acidic buffer, oxidant (3% hydrogen peroxide), or temperature stress (40–60°C). The log k-pH profile showed that CLEFMA was most stable at neutral pH. In accelerated stability study we found that the shelf-life (T90%) of CLEFMA at 25°C and 4°C was 45 days and 220 days, respectively. Upon exposure to UV-light (365nm), the normally prevalent trans-CLEFMA attained cis-configuration. This isomerization also involved the maleic acid moiety. CLEFMA was stable in plasma from which it could be efficiently extracted by an acetonitrile precipitation method. These results indicate that CLEFMA is sensitive to hydrolytic cleavage at its maleic acid moiety, and it is recommended that its samples should be stored under refrigerated and light-free conditions, and under inert environment.

Tetracycline uptake and metabolism by vetiver grass (Chrysopogon zizanioides L. Nash).

Environmental contamination by antibiotics not only perturbs the ecological balance but also poses a risk to human health by promoting the development of multiantibiotic-resistant bacteria. This study focuses on identifying the biochemical pathways associated with tetracycline (TC) transformation/degradation in vetiver grass that has the potential to be used as a biological remediation system in TC-contaminated water sources. A hydroponic experimental setup was used with four initial TC concentrations (0, 5, 35, 75ppm), and TC uptake was monitored over a 30-day period. Results show that TC transformation in the media occurred during the first 5days, where a decrease in the parent compound and an increase in the concentration of the isomers such as epitetracycline (ETC) and anhyrotetracycline (ATC) occurred, and TC disappeared in 20days in tanks with vetiver grass. However, the isomers ETC and ATC remained in the control tanks for the duration of the trial. Transformation products of TC in plant tissue were analyzed by using ultra HPLC high-resolution Orbitrap mass spectrometery (HRMS/MS), which indicates amide hydrolysis of TC in vetiver roots. Metabolic profiling revealed that glyoxylate metabolism, TCA cycle, biosynthesis of secondary metabolites, tryptophan metabolism, and inositol phosphate metabolism were impacted in vetiver root by TC treatment.

Facilitating the Evolution of Esterase Activity from a Promiscuous Enzyme (Mhg) with Catalytic Functions of Amide Hydrolysis and Carboxylic Acid Perhydrolysis by Engineering the Substrate Entrance Tunnel.

Promiscuous enzymes can act as starting points in the evolution of novel catalytic activities, thus providing a molecular basis for the production of new biological functions. In this study, we identified a critical amino acid residue (Leu233) at the entry of the substrate tunnel of a promiscuous enzyme, Mhg. We found that substitution of this residue with smaller amino acids such as Gly, Ala, Ser, or Pro endowed the enzyme with novel esterase activity. Different amino acids at this site can facilitate different catalytic activities. These findings exhibited universal significance in this subset of α/β fold hydrolases, including Mhg. Furthermore, we demonstrate that engineering the entrance tunnel is an efficient strategy to evolve new enzyme catalytic capabilities. Our study has important implications for the regulation of enzyme catalytic promiscuity and development of protein engineering methodologies.

Understanding unconventional routes to impurities from drugs in hydrolytic conditions

Abstract: Introduction: Hydrolytic degradation is the most common cause of formation of impurities or degradation products in drugs during different stages of drug product development and/or shelf life of the drug/product. Degradation products formed by hydrolysis of ester, amide, urethane, sulfonamide, sulfonate and ether linkages, and of nitrile, hydroxyl and amino groups in drugs can be conveniently predicted and identified. Many drugs are known to degrade to such expected conventional hydrolytic degradation products, and the mechanisms of such degradations are also well known and reported. However, many drugs are reported to degrade under hydrolytic conditions to products, which cannot be justified by the conventional hydrolytic reactions. Objectives: Though structures of such unconventional hydrolytic products can be characterized through different spectral techniques, but there is a need to understand the mechanisms of such unconventional hydrolytic reactions in order to help in establishing intrinsic stability characteristics of a drug. Methodology: In the present review, we have studied and critically analysed all possible reports on hydrolytic degradation of various dugs to provide a thorough insight into unconventional routes of hydrolytic degradations of drugs. The various unconventional hydrolytic reactions found responsible for degradation of drugs are classified as oxidation, dehydrogenation, coupling/condensation, N-alkylation, C-C bond cleavage, C-N bond cleavage, dehalogenation, cyclization, decarboxylation and hydroxylation. Discussion: Varied types of reactions under hydrolytic conditions are triggered/controlled by the nature of substituent(s) across or around the susceptible bonds/groups. The mechanisms for such unconventional hydrolytic reactions have been discussed or proposed with support from the standard literature. The contents are expected to enable an analyst and a drug formulator to predict various possible as well as seemingly improbable hydrolytic degradation products of a drug well ahead of systematic forced degradation studies. Key words: Forced degradation, Impurities, Hydrolysis, Conventional, Unconventional, Mechanisms.

Antibacterial and Solubility Optimization of Thiomuracin A.

Synthetic studies of the antimicrobial secondary metabolite thiomuracin A (1) provided access to analogues in the Northern region (C2-C10). Selective hydrolysis of the C10 amide of lead compound 2 and subsequent derivatization led to novel carbon- and nitrogen-linked analogues (e.g., 3) which improved antibacterial potency across a panel of Gram-positive organisms. In addition, congeners with improved physicochemical properties were identified which proved efficacious in murine sepsis and hamster C. difficile models of disease. Optimal efficacy in the hamster model of C. difficile was achieved with compounds that possessed both potent antibacterial activity and high aqueous solubility.

Evaluation of the Ser-His Dipeptide, a Putative Catalyst of Amide and Ester Hydrolysis.

Efficient hydrolysis of amide bonds has long been a reaction of interest for organic chemists. The rate constants of proteases are unmatched by those of any synthetic catalyst. It has been proposed that a dipeptide containing serine and histidine is an effective catalyst of amide hydrolysis, based on an apparent ability to degrade a protein. The capacity of the Ser-His dipeptide to catalyze the hydrolysis of several discrete ester and amide substrates is investigated using previously described conditions. This dipeptide does not catalyze the hydrolysis of amide or unactivated ester groups in any of the substrates under the conditions evaluated.

Amides as thermo-sensitive tracers for investigating the thermal state of geothermal reservoirs

The application of thermo-sensitive tracers is a promising technique for evaluating the thermal state of geothermal reservoirs. To extend the compound spectrum for hydrolyzable compounds to reservoir temperatures between 100 and 200°C carboxamides were studied. The kinetic parameters of 17 self-synthesized amides were determined in hydrothermal batch and autoclave experiments. The influence of the molecular structure and the role of pH/pOH on hydrolysis kinetics were studied. Additionally, the thermal stabilities of the hydrolysis products were evaluated. The results demonstrate the high potential of tracers based on amide hydrolysis for use in medium enthalpy reservoirs.

Metabolism and Disposition of the Hepatitis C Protease Inhibitor Paritaprevir in Humans.

Paritaprevir (also known as ABT-450), a potent NS3-4A serine protease inhibitor [identified by AbbVie (North Chicago, IL) and Enanta Pharmaceuticals (Watertown, MA)] of the hepatitis C virus (HCV), has been developed in combination with ombitasvir and dasabuvir in a three-direct-acting antiviral agent (DAA) oral regimen for the treatment of patients infected with HCV genotype 1. This article describes the mass balance, metabolism, and disposition of paritaprevir in humans. After the administration of a single 200-mg oral dose of [(14)C]paritaprevir coadministered with 100 mg of ritonavir to four male healthy volunteers, the mean total percentage of the administered radioactive dose recovered was 96.5%, with recovery in individual subjects ranging from 96.0% to 96.9%. Radioactivity derived from [(14)C]paritaprevir was primarily eliminated in feces (87.8% of the dose). Radioactivity recovered in urine accounted for 8.8% of the dose. The biotransformation of paritaprevir in humans involves: 1) P450-mediated oxidation on the olefinic linker, the phenanthridine group, the methylpyrazinyl group, or combinations thereof; and 2) amide hydrolysis at the acyl cyclopropane-sulfonamide moiety and the pyrazine-2-carboxamide moiety. Paritaprevir was the major component in plasma [90.1% of total radioactivity in plasma, AUC from time 0 to 12 hours (AUC0-12hours) pool]. Five minor metabolites were identified in plasma, including the metabolites M2, M29, M3, M13, and M6; none of the metabolites accounted for greater than 10% of the total radioactivity. Paritaprevir was primarily eliminated through the biliary-fecal route followed by microflora-mediated sulfonamide hydrolysis to M29 as a major component in feces (approximately 60% of dose). In summary, the biotransformation and clearance pathways of paritaprevir were characterized, and the structures of metabolites in circulation and excreta were elucidated.

Metabolism and Disposition of Pan-Genotypic Inhibitor of Hepatitis C Virus NS5A Ombitasvir in Humans.

Ombitasvir (also known as ABT-267) is a potent inhibitor of hepatitis C virus (HCV) nonstructural protein 5A (NS5A), which has been developed in combination with paritaprevir/ritonavir and dasabuvir in a three direct-acting antiviral oral regimens for the treatment of patients infected with HCV genotype 1. This article describes the mass balance, metabolism, and disposition of ombitasvir in humans without coadministration of paritaprevir/ritonavir and dasabuvir. Following the administration of a single 25-mg oral dose of [(14)C]ombitasvir to four healthy male volunteers, the mean total percentage of the administered radioactive dose recovered was 92.1% over the 192-hour sample collection in the study. The recovery from the individual subjects ranged from 91.4 to 93.1%. Ombitasvir and corresponding metabolites were primarily eliminated in feces (90.2% of dose), mainly as unchanged parent drug (87.8% of dose), but minimally through renal excretion (1.9% of dose). Biotransformation of ombitasvir in human involves enzymatic amide hydrolysis to form M23 (dianiline), which is further metabolized through cytochrome P450-mediated oxidative metabolism (primarily by CYP2C8) at the tert-butyl group to generate oxidative and/or C-desmethyl metabolites. [(14)C]Ombitasvir, M23, M29, M36, and M37 are the main components in plasma, representing about 93% of total plasma radioactivity. The steady-state concentration measurement of ombitasvir metabolites by liquid chromatography-mass spectrometry analysis in human plasma following multiple doses of ombitasvir, in combination with paritaprevir/ritonavir and dasabuvir, confirmed that ombitasvir is the main component (51.9% of all measured drug-related components), whereas M29 (19.9%) and M36 (13.1%) are the major circulating metabolites. In summary, the study characterized ombitasvir metabolites in circulation, the metabolic pathways, and the elimination routes of the drug.

Explorations into Chemical Reactions and Biochemical Pathways.

A brief overview of the work in the research group of the present author on extracting knowledge from chemical reaction data is presented. Methods have been developed to calculate physicochemical effects at the reaction site. It is shown that these physicochemical effects can quite favourably be used to derive equations for the calculation of data on gas phase reactions and on reactions in solution such as aqueous acidity of alcohols or carboxylic acids or the hydrolysis of amides. Furthermore, it is shown that these physicochemical effects are quite effective for assigning reactions into reaction classes that correspond to chemical knowledge. Biochemical reactions constitute a particularly interesting and challenging task for increasing our understanding of living species. The BioPath.Database is a rich source of information on biochemical reactions and has been used for a variety of applications of chemical, biological, or medicinal interests. Thus, it was shown that biochemical reactions can be assigned by the physicochemical effects into classes that correspond to the classification of enzymes by the EC numbers. Furthermore, 3D models of reaction intermediates can be used for searching for novel enzyme inhibitors. It was shown in a combined application of chemoinformatics and bioinformatics that essential pathways of diseases can be uncovered. Furthermore, a study showed that bacterial flavor-forming pathways can be discovered.

Going Beyond Common Drug Metabolizing Enzymes: Case Studies of Biotransformation Involving Aldehyde Oxidase, -Glutamyl Transpeptidase, Cathepsin B, Flavin-Containing Monooxygenase, and ADP-Ribosyltransferase

The significant roles that cytochrome P450 (P450) and UDP-glucuronosyl transferase (UGT) enzymes play in drug discovery cannot be ignored, and these enzyme systems are commonly examined during drug optimization using liver microsomes or hepatocytes. At the same time, other drug-metabolizing enzymes have a role in the metabolism of drugs and can lead to challenges in drug optimization that could be mitigated if the contributions of these enzymes were better understood. We present examples (mostly from Genentech) of five different non-P450 and non-UGT enzymes that contribute to the metabolic clearance or bioactivation of drugs and drug candidates. Aldehyde oxidase mediates a unique amide hydrolysis of GDC-0834 (N-[3-[6-[4-[(2R)-1,4-dimethyl-3-oxopiperazin-2-yl]anilino]-4-methyl-5-oxopyrazin-2-yl]-2-methylphenyl]-4,5,6,7-tetrahydro-1-benzothiophene-2-carboxamide), leading to high clearance of the drug. Likewise, the rodent-specific ribose conjugation by ADP-ribosyltransferase leads to high clearance of an interleukin-2-inducible T-cell kinase inhibitor. Metabolic reactions by flavin-containing monooxygenases (FMO) are easily mistaken for P450-mediated metabolism such as oxidative defluorination of 4-fluoro-N-methylaniline by FMO. Gamma-glutamyl transpeptidase is involved in the initial hydrolysis of glutathione metabolites, leading to formation of proximate toxins and nephrotoxicity, as is observed with cisplatin in the clinic, or renal toxicity, as is observed with efavirenz in rodents. Finally, cathepsin B is a lysosomal enzyme that is highly expressed in human tumors and has been targeted to release potent cytotoxins, as in the case of brentuximab vedotin. These examples of non-P450- and non-UGT-mediated metabolism show that a more complete understanding of drug metabolizing enzymes allows for better insight into the fate of drugs and improved design strategies of molecules in drug discovery.

Multiscale characteristics dynamics of hydrochar from hydrothermal conversion of sewage sludge under sub- and near-critical water

Dewatered sewage sludge was upgraded to hydrochar using hydrothermal conversion in sub- and near-critical water. Three characteristic temperature regimes responsible for the upgrading were identified. Drastic hydrolysis of carbohydrates, amide II or secondary amines occurred at 200°C while noticeable decarboxylation initiated above 260°C. Elevated temperature improved porosity but did not induce higher surface area. Aliphatic C was mainly transformed to aromatic hydrocarbon rather than aromatic C–O in subcritical water, whereas COO/N–CO and aromatic C–O were decomposed to carbohydrate C at 380°C. Below 300°C, carbon functionalities in hydrochars were thermally stable and faster decomposition of N than C–(C,H) resulted in dramatic decline of N/C. Above 300°C, C–H was gradually polymerized to aromatic C–(C,H) which was considerably transformed to C–(O,N) and C–H at 380°C. CaO favored intense destruction of aromatic C–C/C–H, anomeric O–C–O, C–H and C–(O,N) functionalities but introduced more aromatic C–O and OC–O.