Mass Spectrometric Characterization of 2-Amino-1-methyl-6-phenylimidazo[4,5-<i>b</i>]pyridine <i>N</i>-Oxidized Metabolites Bound at Cys³⁴ of Human Serum Albumin

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic aromatic amine that is formed during the cooking of meats and poultry. PhIP is a carcinogen in rodents and a potential human carcinogen. Several short-term biomarkers of PhIP have been established for human biomonitoring, but validated long-term biomarkers of the biologically effective dose of PhIP remain to be developed. Metabolites of PhIP have been reported to covalently bind to human serum albumin (SA), which is the most abundant protein in plasma; however, the chemical structures of PhIP-SA adducts are unknown. Cysteine34 is one of 35 conserved Cys residues in SA across species. Thirty-four of these Cys are involved in 17 disulfide bonds. The single unpaired Cys34 residue in SA is well-known to react with carcinogenic metabolites and toxic electrophiles. 2-Nitro-1-methyl-6-phenylimidazo[4,5-b]pyridine (NO2-PhIP), 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (HONH-PhIP), and 2-nitroso-1-methyl-6-phenylimidazo[4,5-b]pyridine (NO-PhIP), three genotoxic metabolites of PhIP, were reacted with purified human SA or human plasma, and the SA adduction products, following enzymatic digestion, were separated by ultra performance liquid chromatography and characterized with a linear quadrupole ion trap mass spectrometer. The major adduct of NO2-PhIP was formed at the Cys34 of SA with bond formation occurring between the sulfhydryl group of Cys and the C-2 imidazole atom of PhIP. The major adducts formed between SA and HNOH-PhIP or NO-PhIP were identified as acid-labile sulfinamide linkages at Cys34. These PhIP-SA adducts represent a measure of bioactivation of PhIP and may serve as long-term biomarkers of the biologically effective dose of PhIP

Capturing Labile Sulfenamide and Sulfinamide Serum Albumin Adducts of Carcinogenic Arylamines by Chemical Oxidation

Aromatic amines and heterocyclic aromatic amines (HAAs) are a class of structurally related carcinogens that are formed during the combustion of tobacco or during the high temperature cooking of meats. These procarcinogens undergo metabolic activation by N-oxidation of the exocyclic amine group to produce N-hydroxylated metabolites, which are critical intermediates implicated in toxicity and DNA damage. The arylhydroxylamines and their oxidized arylnitroso derivatives can also react with cysteine (Cys) residues of glutathione or proteins to form, respectively, sulfenamide and sulfinamide adducts. However, sulfur–nitrogen linked adducted proteins are often difficult to detect because they are unstable and undergo hydrolysis during proteolytic digestion. Synthetic N-oxidized intermediates of 2-amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (PhIP), a carcinogenic HAA produced in cooked meats, and 4-aminobiphenyl, a carcinogenic aromatic amine present in tobacco smoke, were reacted with human serum albumin (SA) and formed labile sulfenamide or sulfinamide adducts at the Cys³⁴ residue. Oxidation of the carcinogen-modified SA with <i>m</i>-chloroperoxybenzoic acid (<i>m</i>-CPBA) produced the arylsulfonamide adducts, which were stable to heat and the chemical reduction conditions employed to denature SA. The sulfonamide adducts of PhIP and 4-ABP were identified, by liquid chromatography/mass spectrometry, in proteolytic digests of denatured SA. Thus, selective oxidation of arylamine-modified SA produces stable arylsulfonamide-SA adducts, which may serve as biomarkers of these tobacco and dietary carcinogens

Integrated Process of Coke-Oven Gas Tri-Reforming and Coal Gasification to Methanol with High Carbon Utilization and Energy Efficiency

The hydrogen to carbon (H/C) ratio of coal gasified gas in the range 0.2–1.0, far less than the desired value for the coal to methanol process. Therefore, a water gas shift unit is needed to raise the H/C ratio, which results in a great deal of CO₂ emission and carbon resource waste. At the same time, there is 7 × 10¹⁰ m³ coke-oven gas (COG) produced in coke plants annually in China. The hydrogen-rich COG consists of 60% hydrogen and 26% methane. However, a massive amount of COG is utilized as fuel or discharged directly into the air, which makes a waste of precious hydrogen resources and causes serious environmental pollution. This paper proposes an integrated process of coke-oven gas and coal gasification to methanol, in which a tri-reforming reaction is used to convert methane and CO₂ to syngas. The carbon utilization and energy efficiency of the new process increase about 25% and 10%, whereas CO₂ emission declines by 44% in comparison to the conventional coal to methanol process

Correction to Mapping Serum Albumin Adducts of the Food-Borne Carcinogen 2‑Amino-1-methyl-6-phenylimidazo[4,5‑<i>b</i>]pyridine by Data-Dependent Tandem Mass Spectrometry

Correction to Mapping Serum Albumin Adducts of the Food-Borne Carcinogen 2‑Amino-1-methyl-6-phenylimidazo[4,5‑b]pyridine by Data-Dependent Tandem Mass Spectrometr

Mapping Serum Albumin Adducts of the Food-Borne Carcinogen 2‑Amino-1-methyl-6-phenylimidazo[4,5‑<i>b</i>]pyridine by Data-Dependent Tandem Mass Spectrometry

2-Amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (PhIP) is a heterocyclic aromatic amine that is formed during the cooking of meats. PhIP is a potential human carcinogen: it undergoes metabolic activation to form electrophilic metabolites that bind to DNA and proteins, including serum albumin (SA). The structures of PhIP-SA adducts formed in vivo are unknown and require elucidation before PhIP protein adducts can be implemented as biomarkers in human studies. We previously examined the reaction of genotoxic N-oxidized metabolites of PhIP with human SA in vitro and identified covalent adducts formed at cysteine³⁴ (Cys³⁴); however, other adduction products were thought to occur. We have now identified adducts of PhIP formed at multiple sites of SA reacted with isotopic mixtures of electrophilic metabolites of PhIP and 2-amino-1-methyl-6-[²H₅]-phenylimidazo­[4,5-<i>b</i>]­pyridine ([²H₅]-PhIP). The metabolites used for study were 2-nitro-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (NO₂-PhIP), 2-hydroxyamino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (HONH-PhIP), or <i>N</i>-acetyloxy-2-amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (<i>N</i>-acetoxy-PhIP). Following proteolytic digestion, PhIP-adducted peptides were separated by ultra performance liquid chromatography and characterized by ion trap mass spectrometry, employing isotopic data-dependent scanning. Analysis of the tryptic or tryptic/chymotryptic digests of SA modified with NO₂-PhIP revealed that adduction occurred at Cys³⁴, Lys¹⁹⁵, Lys¹⁹⁹, Lys³⁵¹, Lys⁵⁴¹, Tyr¹³⁸, Tyr¹⁵⁰, Tyr⁴⁰¹, and Tyr⁴¹¹, whereas the only site of HONH-PhIP adduction was detected at Cys³⁴. <i>N</i>-Acetoxy-PhIP, a penultimate metabolite of PhIP that reacts with DNA to form covalent adducts, did not appear to form stable adducts with SA; instead, PhIP and 2-amino-1-methyl-6-(5-hydroxy)-phenylimidazo­[4,5-<i>b</i>]­pyridine, an aqueous reaction product of the proposed nitrenium ion of PhIP, were recovered during the proteolysis of <i>N</i>-acetoxy-PhIP-modified SA. Some of these SA adduction products of PhIP may be implemented in molecular epidemiology studies to assess the role of well-done cooked meat, PhIP, and the risk of cancer

Mass Spectrometric Characterization of Human Serum Albumin Adducts Formed with N‑Oxidized Metabolites of 2‑Amino-1-methylphenylimidazo[4,5‑<i>b</i>]pyridine in Human Plasma and Hepatocytes

2-Amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (PhIP), a carcinogenic heterocyclic aromatic amine formed in cooked meats, is metabolically activated to electrophilic intermediates that form covalent adducts with DNA and protein. We previously identified an adduct of PhIP formed at the Cys³⁴ residue of human serum albumin following reaction of albumin with the genotoxic metabolite 2-hydroxyamino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (HONH-PhIP). The major adducted peptide recovered from a tryptic/chymotryptic digest was identified as the missed-cleavage peptide LQQC*^[SO₂PhIP]PFEDHVK, a [cysteine-S-yl-PhIP]-S-dioxide linked adduct. In this investigation, we have characterized the albumin adduction products of <i>N</i>-sulfooxy-2-amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (<i>N</i>-sulfooxy-PhIP), which is thought to be a major genotoxic metabolite of PhIP formed <i>in vivo</i>. Targeted and data-dependent scanning methods showed that <i>N</i>-sulfooxy-PhIP adducted to the Cys³⁴ of albumin in human plasma to form LQ­QC*^[SO₂PhIP]PF­E­D­H­VK at levels that were 8–10-fold greater than the adduct levels formed with <i>N</i>-(acetyloxy)-2-amino-1-methyl-6-phenylimidazo­[4,5-<i>b</i>]­pyridine (<i>N</i>-acetoxy-PhIP) or HONH-PhIP. We also discovered that <i>N</i>-sulfooxy-PhIP forms an adduct at the sole tryptophan (Trp²¹⁴) residue of albumin in the sequence AW*^[PhIP]A­VAR. However, stable adducts of PhIP with albumin were not detected in human hepatocytes. Instead, PhIP and 2-amino-1-methyl-6-(5-hydroxy)­phenylimidazo­[4,5-<i>b</i>]­pyridine (5-HO-PhIP), a solvolysis product of the proposed nitrenium ion of PhIP, were recovered during the proteolysis, suggesting a labile sulfenamide linkage had formed between an N-oxidized intermediate of PhIP and Cys³⁴ of albumin. A stable adduct was formed at the Tyr⁴¹¹ residue of albumin in hepatocytes and identified as a deaminated product of PhIP, Y^{*[desaminoPhIP]}TK, where the 4-HO-tyrosine group bound to the C-2 imidazole atom of PhIP

Relationship between Energetic Performance and Clustering Effects on Incremental Nitramine Groups: A Theoretical Perspective

Nitramine compounds are typical high-energy-density materials (HEDMs) and are widely used as explosives because of their superior explosive performance over conventional energetic materials. In this work, the thermal properties of 1-nitropiperidine (NPIP), 1,4-dinitropiperazine (DNP), and 1,3,5-trinitro-1,3,5-triazinane (RDX) were investigated from quantum mechanics (QM) and reactive force field (ReaxFF) molecular dynamics simulations. We found that the bond dissociation energy of the N–NO2 bond, heat of formation, released energy, produced fragments, and oxygen balance are closely related to the incremental nitramine group. The nitramine group has a significant effect on the energetic performance of these nitramine compounds. In addition, the increase of the nitramine group will improve thermal decomposition activity, promote the generation of small molecules, and restrain the formation of carbon clusters. We hope that this work can shed new light on the design of energetic materials

FeCo Alloy Nanoparticles Supported on Co–N–C Cubes Derived from Imidazolate Frameworks as a Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

Recently, metal–organic frameworks (MOFs) have emerged as attractive precursors to prepare electrocatalysts for the oxygen reduction reaction and oxygen evolution reaction (ORR and OER). Herein, the FeCo alloy nanoparticles supported on Co–N–C (FeCo/Co–N–C) as an efficient catalyst were obtained through high-temperature pyrolysis. The regulation of the electronic structure of the catalyst by Fe doping, coupled with the strong interaction between the FeCo nanoalloy and N-doped amorphous carbon, leads to the formation of Fe–N and Co–N bonds, which, in turn, create a multitude of active centers. Accordingly, optimized FeCo/Co–N–C exhibits excellent ORR/OER activity with a potential difference of 0.75 V, even close to commercial Pt/C + RuO2 (0.74 V). Furthermore, as an air electrode in a rechargeable liquid zinc–air battery, the catalyst exhibits a superior power density (188 mW cm–2) and high cyclic stability. The flexible batteries exhibit good stability and power a small electronic watch

Table_1_Integrative analysis of sensory evaluation and non-targeted metabolomics to unravel tobacco leaf metabolites associated with sensory quality of heated tobacco.xlsx

IntroductionHeated tobacco (Nicotiana tabacum L.) products are heating tobacco plug at a temperature of 350°C and produce different emissions in aerosol and sensory perceptions of tobacco leaf compared with combustible tobacco. Previous study assessed different tobacco varieties in heated tobacco for sensory quality and analyzed the links between sensory scores of the final products and certain chemical classes in tobacco leaf. However, contribution of individual metabolites to sensory quality of heated tobacco remains largely open for investigation.MethodsIn present study, five tobacco varieties were evaluated as heated tobacco for sensory quality by an expert panel and the volatile and non-volatile metabolites were analyzed by non-targeted metabolomics profiling.ResultsThe five tobacco varieties had distinct sensory qualities and can be classified into higher and lower sensory rating classes. Principle component analysis and hierarchical cluster analysis showed that leaf volatile and non-volatile metabolome annotated were grouped and clustered by sensory ratings of heated tobacco. Orthogonal projections to latent structures discriminant analysis followed by variable importance in projection and fold-change analysis revealed 13 volatiles and 345 non-volatiles able to discriminate the tobacco varieties with higher and lower sensory ratings. Some compounds such as β-damascenone, scopoletin, chlorogenic acids, neochlorogenic acids, and flavonol glycosyl derivatives had strong contribution to the prediction of sensory quality of heated tobacco. Several lyso-phosphatidylcholine and lyso-phosphatidylethanolamine lipid species, and reducing and non-reducing sugar molecules were also positively related to sensory quality.DiscussionTaken together, these discriminating volatile and non-volatile metabolites support the role of leaf metabolites in affecting the sensory quality of heated tobacco and provide new information on the types of leaf metabolites that can be used to predict applicability of tobacco varieties for heated tobacco products.</p

DataSheet_1_Integrative analysis of sensory evaluation and non-targeted metabolomics to unravel tobacco leaf metabolites associated with sensory quality of heated tobacco.docx

IntroductionHeated tobacco (Nicotiana tabacum L.) products are heating tobacco plug at a temperature of 350°C and produce different emissions in aerosol and sensory perceptions of tobacco leaf compared with combustible tobacco. Previous study assessed different tobacco varieties in heated tobacco for sensory quality and analyzed the links between sensory scores of the final products and certain chemical classes in tobacco leaf. However, contribution of individual metabolites to sensory quality of heated tobacco remains largely open for investigation.MethodsIn present study, five tobacco varieties were evaluated as heated tobacco for sensory quality by an expert panel and the volatile and non-volatile metabolites were analyzed by non-targeted metabolomics profiling.ResultsThe five tobacco varieties had distinct sensory qualities and can be classified into higher and lower sensory rating classes. Principle component analysis and hierarchical cluster analysis showed that leaf volatile and non-volatile metabolome annotated were grouped and clustered by sensory ratings of heated tobacco. Orthogonal projections to latent structures discriminant analysis followed by variable importance in projection and fold-change analysis revealed 13 volatiles and 345 non-volatiles able to discriminate the tobacco varieties with higher and lower sensory ratings. Some compounds such as β-damascenone, scopoletin, chlorogenic acids, neochlorogenic acids, and flavonol glycosyl derivatives had strong contribution to the prediction of sensory quality of heated tobacco. Several lyso-phosphatidylcholine and lyso-phosphatidylethanolamine lipid species, and reducing and non-reducing sugar molecules were also positively related to sensory quality.DiscussionTaken together, these discriminating volatile and non-volatile metabolites support the role of leaf metabolites in affecting the sensory quality of heated tobacco and provide new information on the types of leaf metabolites that can be used to predict applicability of tobacco varieties for heated tobacco products.</p