Formation Of M1 Research Articles

Enantioselective N-Demethylation and Hydroxylation of Sibutramine in Human Liver Microsomes and Recombinant Cytochrome P-450 Isoforms

The enantioselective metabolism of sibutramine was examined using human liver microsomes (HLM) and recombinant cytochrome P-450 (CYP) isoforms. This drug is metabolized to N-mono-desmethyl- (M1) and N,N-di-desmethylsibutramine (M2), and subsequent hydroxylation results in hydroxyl M1 (HM1) and hydroxyl M2 (HM2). No significant difference was noted in formation of M1from sibutramine between R- and S-sibutramine in HLM. However, S-enantiomers of M1 and M2 were preferentially metabolized to M2, HM1, and HM2compared to R-enantiomers in HLM, and intrinsic clearance (Clint) ratios of S-enantiomers/R-enantiomers were 1.97, 4.83, and 9.94 for M2, HM1, and HM2, respectively. CYP3A4 and CYP3A5 were only involved in the formation of M1, whereas CYP2B6 and CYP2C19 were responsible for all metabolic reactions of sibutramine. CYP2C19 and CYP3A5 displayed catalytic preference for S-sibutramine to S-M1, whereas CYP2B6 and CYP3A4 showed little or no stereoselectivity in metabolism of sibutramine to M1. In the case of M2 formation, CYP2B6 metabolized S-M1 more rapidly than R-M1 with a Clint ratio of 2.14. However, CYP2C19 catalyzed less S-M1 than R-M1 and the Clint ratio of S-M1 to R-M1 was 0.65. The most significant enantioselectivity was observed in formation of HM1 from M1, and HM2 from M2. CYP2B6 and CYP2C19 exhibited preferential catalysis of formation of hydroxyl metabolites from S-enantiomers rather than R-enantiomers. These results indicate that S-sibutramine was more rapidly metabolized by CYP isoforms than R-sibutramine, and that enantioselective metabolism needs to be considered in drug interactions involving sibutramine and co-administered drugs.

Tramadol and o-desmethyl tramadol clearance maturation and disposition in humans: a pooled pharmacokinetic study.

We aimed to study the impact of size, maturation and cytochrome P450 2D6 (CYP2D6) genotype activity score as predictors of intravenous tramadol disposition. Tramadol and O-desmethyl tramadol (M1) observations in 295 human subjects (postmenstrual age 25 weeks to 84.8 years, weight 0.5-186 kg) were pooled. A population pharmacokinetic analysis was performed using a two-compartment model for tramadol and two additional M1 compartments. Covariate analysis included weight, age, sex, disease characteristics (healthy subject or patient) and CYP2D6 genotype activity. A sigmoid maturation model was used to describe age-related changes in tramadol clearance (CLPO), M1 formation clearance (CLPM) and M1 elimination clearance (CLMO). A phenotype-based mixture model was used to identify CLPM polymorphism. Differences in clearances were largely accounted for by maturation and size. The time to reach 50 % of adult clearance (TM50) values was used to describe maturation. CLPM (TM50 39.8 weeks) and CLPO (TM50 39.1 weeks) displayed fast maturation, while CLMO matured slower, similar to glomerular filtration rate (TM50 47 weeks). The phenotype-based mixture model identified a slow and a faster metabolizer group. Slow metabolizers comprised 9.8 % of subjects with 19.4 % of faster metabolizer CLPM. Low CYP2D6 genotype activity was associated with lower (25 %) than faster metabolizer CLPM, but only 32 % of those with low genotype activity were in the slow metabolizer group. Maturation and size are key predictors of variability. A two-group polymorphism was identified based on phenotypic M1 formation clearance. Maturation of tramadol elimination occurs early (50 % of adult value at term gestation).

Metabolite profiling of anhuienoside C by rat intestinal bacteria using the LC–MS metabolomic approach

1. Anhuienoside C (A-C) is the main active component of the saponin exact of “Di Wu”, an oral drug for rheumatism treatment in China. In this study, we aimed to elucidate the metabolic pathways of A-C by intestinal bacteria using the metabolomic approach.2. Four deglycosylated metabolites (M1, M2, M3 and M4) were identified after A-C (50 µM) was incubated with rat fecal lysate. Chemical structures of these metabolites were determined by high-resolution masses and nuclear magnetic resonance (NMR).3. A one-compartment pharmacokinetic model was used to describe the formation of bacterial metabolites at a dose of 10 µM A-C. The results revealed that formation of M1 and M2 was rapid, whereas formation of M3 was rather slow. Further, it was found that the metabolites were generated by successive cleavage of the glycosyl residues.4. This is the first report that A-C is subjected to efficient bacterial metabolism in the gut with M1 and M2 as main metabolites. Our study should be helpful for a better understanding of in vivo disposition of oral A-C.

Characterization of in vitro metabolites of TM‐2, a potential antitumor drug, in rat, dog and human liver microsomes using liquid chromatography/tandem mass spectrometry

TM-2 (13-(N-Boc-3-i-butylisoserinoyl-4,10-β-diacetoxy-2-α-benzoyloxy-5-β,20-epoxy-1,13-α-dihydroxy-9-oxo-19-norcyclopropa[g]tax-11-ene) is a novel semi-synthetic taxane derivative. Our previous study demonstrated that it is a promising taxane derivative. The in vitro comparative metabolic profile of a drug between animals and humans is a key issue that should be investigated at early stages of drug development to better select drug candidates. In this study, the in vitro metabolic pathways of TM-2 in rat, dog and human liver microsomes were established and compared. TM-2 was incubated with liver microsomes in the presence of NADPH. Two different types of mass spectrometers - a hybrid linear trap quadrupole orbitrap (LC/LTQ-Orbitrap) mass spectrometer and a triple-quadrupole tandem mass spectrometer (LC/QqQ) were employed to acquire structural information of TM-2 metabolites. Accurate mass measurement using LC/LTQ-Orbitrap was used to determine the accurate mass data and elemental compositions of metabolites thereby confirming the proposed structures of the metabolites. For the chemical inhibition study, selective P450 inhibitors were added to incubations to initially characterize the cytochrome P450 (CYP) enzymes involved in the metabolism of TM-2. A total of 12 components (M1-M12) were detected and identified as the metabolites of TM-2 in vitro. M1-M5 were formed by hydroxylation of the taxane ring or the lateral chain. Hydroxylated products can be further oxidized to the dihydroxylated metabolites M6-M10. M11 was a trihydroxylated metabolite. M12 was tentatively identified as a carboxylic acid derivative. The metabolism of TM-2 is much the same in all three species with some differences. The chemical inhibition study initially demonstrated that the formation of M2, the major metabolite of TM-2, is mainly mediated by CYP3A4. Hydroxylation is the major biotransformation of the TM-2 pathway in vitro. CYP3A4 may play a dominant role in the formation of M2 in liver microsomes. The knowledge of the metabolic pathways of TM-2 is important to support further research of TM-2.

Cytochrome p450-mediated metabolic activation of diosbulbin B.

Diosbulbin B (DIOB), a furan-containing diterpenoid lactone, is the most abundant component of Dioscorea bulbifera L. (DB), a traditional Chinese medicine herb. Administration of purified DIOB or DB extracts has been reported to cause liver injury in animals. The mechanisms of DIOB-induced hepatotoxicity remain unknown. The major objective of this study was to identify reactive metabolites of DIOB. A DIOB-derived cis-enedial was trapped by N-acetyl lysine (NAL) and glutathione (GSH) or N-acetyl cysteine (NAC) in rat and human liver microsomal incubation systems after exposure to DIOB. Four metabolites (M1-M4) associated with GSH were detected by liquid chromatography coupled to tandem mass spectrometry. Apparently, M1 was derived from both NAL and GSH. M2 and M3 resulted from the reaction of GSH without the involvement of NAL. Two molecules of GSH participated in the formation of M4. M2 and M3 were also detected in bile and urine of rats given DIOB. M5, a DIOB-derived NAC/NAL conjugate, was detected in microsomal incubations with DIOB fortified with NAC and NAL as trapping agents. Biomimetic M1-M5 were prepared by oxidation of DIOB with Oxone for metabolite identification. Microsomal incubation study demonstrated that ketoconazole inhibited the production of the enedial in a concentration-dependent manner, and CYP3A4 was found to be the enzyme responsible for the metabolic activation of DIOB. The metabolism study facilitates the understanding of the role of bioactivation of DIOB in its hepatotoxicity.

Formation and development of maxillary first molars with delayed eruption.

Cases of congenitally missing and delayed eruption of the maxillary first molar are rare. However, in recent years, we have experienced cases of suspected delayed eruption of or congenitally missing first molars. The purpose of this study was to analyze the formation of delayed erupted maxillary first molars (M1) (>2 standard deviations), which play important roles in occlusion, and normal eruption of the maxillary first molars (U6). The frequency of M1 among patients born between 1974 and 1994 in one institution with a clear total patient number and personal oral histories was 1.55 % [80 % bilateral eruption in 8 of 806 male patients (0.99 %) and 23 of 1195 female patients (1.92 %)]. To evaluate the formation and eruption of M1 according to Moorrees's tooth formation stages, panoramic X-ray films were obtained every year for 73 patients with M1 from 3 institutions (20 male and 53 female patients, total 131 M1s) without systematic histories or genetic disorders. The development/growth curve of M1 was fitted to both the logistic curve and U6 curve. The M1 development/growth curve was started behind with U6 curve; however, the straight part of the M1 curve exhibited steep inclination compared with the straight part of the U6 curve. The curve of the eruption pathway of M1 also exhibited a sigmoid S shape. These results indicate that the development and migration speed of M1 are faster than that of U6, excluding the delayed start point. These results may help orthodontists in treatment planning for patients with M1.

Chirality and polarity in the f-block borates M4[B16O26(OH)4(H2O)3Cl4] (M = Sm, Eu, Gd, Pu, Am, Cm, and Cf).

The reactions of trivalent lanthanides and actinides with molten boric acid in high chloride concentrations result in the formation of M4[B16O26(OH)4(H2O)3Cl4] (M = Sm, Eu, Gd, Pu, Am, Cm, Cf). This cubic structure type is remarkably complex and displays both chirality and polarity. The polymeric borate network forms helical features that are linked via two different types of nine-coordinate f-element environments. The f-f transitions are unusually intense and result in dark coloration of these compounds with actinides.

Interindividual variations in metabolism and pharmacokinetics of 3-(6-methylpyridine-3-yl-sulfanyl)-6-(4H-[1,2,4]triazole-3-yl-sulfanyl)-N-(1,3-thiazole-2-yl)-2-pyridine carboxamide, a glucokinase activator, in rats caused by the genetic polymorphism of CYP2D1.

3-(6-Methylpyridine-3-yl-sulfanyl)-6-(4H-[1,2,4]triazole-3-yl-sulfanyl)-N-(1,3-thiazole-2-yl)-2-pyridine carboxamide (Cpd-D) is a novel glucokinase activator that is being developed for the treatment of type 2 diabetes. Large interindividual variations were observed in the pharmacokinetics of Cpd-D in male Sprague-Dawley (SD) rats, which were subsequently divided into two phenotypes; >6-fold longer terminal-phase half-life and ∼10-fold larger AUC0-∞ values were observed in slow metabolizers (SM) than in fast metabolizers (FM) after the oral administration of Cpd-D. The thiohydantoic acid analog (M2) was the predominant metabolite detected in the urine, bile, and plasma after the oral administration of [(14)C]Cpd-D to the FM phenotypes of bile-duct cannulated SD rats. The liver microsomes prepared from FM phenotyped rats extensively formed M2 with the highest affinity (Km = 0.09 μM) and largest Vmax/Km value in primary metabolism, whereas those from SM phenotypes had little capacity to form M2. Of the rat cytochrome P450 isoforms tested, the formation of M2 was only catalyzed by recombinant CYP2D1. Sequence substitutions (418A/421C and 418G/421T) were detected in the CYP2D1 gene and were designated F and S alleles, respectively. The genotype-phenotype correlation analysis indicated that two S alleles were homozygous (S/S) in the SM phenotypes, whereas the FM phenotypes were either homozygous for the F-alleles (F/F) or heterozygous (F/S). These results indicated that the CYP2D1 polymorphism caused by nucleotide substitutions (418A/421C versus 418G/421T) was responsible for interindividual variations leading to the polymorphism in the major metabolism and pharmacokinetics of Cpd-D in male SD rats.

Metabolism of the hepatotoxic compound sophoraflavanone G in rat liver microsomes.

Our study aimed at investigating the metabolic characteristics of sophoraflavanone G (SFG), one of the hepatotoxic constituents of Sophora flavescens, in rat liver microsomes (RLMs). SFG was metabolized to 3 phase I metabolites, di-hydroxylated SFG (M1), mono-hydroxylated SFG (M2), dehydrogenated product of mono-hydroxylated SFG (M3) and 3 SFG glucuronides (M4, M5, and M6) by RLMs. The formation kinetics of M2 conformed to biphasic kinetics in RLMs. The formation kinetics of M4 and M5 best-fitted the Hill equation kinetics. Chemical inhibition studies found that CYP1A2 and CYP2E1 were the major enzymes responsible for the formation of M2, and the formation of M4 and M5 may be catalyzed by multiple UGT1A isoforms.

Cytochrome P450 3A-mediated metabolism of the topoisomerase I inhibitor 9-aminocamptothecin: Ιmpact on cancer therapy

The metabolism of 9-aminocamptothecin (9-AC) was investigated in human and rat liver microsomes. In both species 9-AC was almost exclusively biotransformed to dihydroxy-9-AC (M1) and monohydroxy-9-AC (M2). The enzymatic efficiencies of the formation of M1 and M2 (V(max)/K(m)) were 1.7- and 2.7‑fold higher in rat than in human liver microsomes indicating species-related differences in 9-AC hydroxylation. Incubation in the presence of human recombinant cytochrome P450 (CYP) enzymes demonstrated that the formation of M1 and M2 is mainly catalyzed by CYP3A4 and only to a minor extent by extrahepatic CYP1A1. The predominant role of CYP3A4 was further supported by a dramatic inhibition of metabolite formation in the presence of the CYP3A4 substrates troleandomycin and ketoconazole. Experiments conducted in isolated perfused rat livers further demonstrated that biliary excretion of 9-AC, M1 and M2 during 60 min of perfusion was pronounced and accounted for 17.7±2.59, 0.05±0.01 and 2.75±0.14% of total 9-AC applied to the liver, respectively. In summary, this study established that CYP3A-dependent hydroxylation is the main metabolic pathway for 9-AC in rat and human liver, which have to be taken into consideration during cancer therapy of patients.

Identification of metabolites of N-(5-benzoyl-2-(4-(2-methoxyphenyl)piperazin-1-yl)thiazol-4-yl)pivalamide including CYP3A4-mediated C-demethylation in human liver microsomes with high-resolution/high-accuracy tandem mass.

KRO-105714 [N-(5-benzoyl-2-(4-(2-methoxyphenyl)piperazin-1-yl)thiazol-4-yl)pivalamide] is a 2,4,5-trisubstituted 1,3-thiazole derivative that exerts anti-atopic dermatitis activity via robust suppression of the sphingosylphosphorylcholine receptor. This study used high-resolution/high-accuracy tandem mass spectroscopy (HRMS) and recombinant cDNA-expressed cytochrome P450 (P450) isoforms to identify the metabolic pathway and metabolites of KRO-105714 in human liver microsomes (HLMs) as therapeutic agents for inflammation. The incubation of KRO-105714 with pooled HLMs in the presence of NADPH generated four metabolites (M1-M4). The metabolites were identified using HRMS and confirmed using synthetic standards for M2 and M4. M1 and M2 were identified as monohydroxylated metabolites, and M3 and M4 were identified as O-demethyl KRO-105714 and C-demethyl KRO-105714, respectively. In the inhibition study with selective CYP3A4 inhibitors and incubation in recombinant cDNA-expressed P450 enzymes, all the metabolites of KRO-105714 were formed by CYP3A4 in HLMs. The CYP3A4-mediated formation of M4 from M2 was confirmed via incubation of M2 in HLMs. These results showed that the unusual C-demethylated metabolite M4 was generated from monohydroxyl metabolite M2 via a CYP3A4-mediated enzymatic reaction in HLMs.

The revised human liver cytochrome P450 "Pie": absolute protein quantification of CYP4F and CYP3A enzymes using targeted quantitative proteomics.

The CYP4F subfamily of enzymes has been identified recently to be involved in the metabolism of endogenous compounds (arachidonic acid and leukotriene B4), nutrients (vitamins K1 and E), and xenobiotics (pafuramidine and fingolimod). CYP4F2 and CYP4F3B are reported to be expressed in the human liver. However, absolute concentrations of these enzymes in human liver microsomes (HLMs) and their interindividual variability have yet to be determined because of the lack of specific antibodies. Here, an liquid chromatography with tandem mass spectrometry (LC-MS/MS)-based targeted quantitative proteomic approach was employed to determine the absolute protein concentrations of CYP4F2 and CYP4F3B compared with CYP3A in two panels of HLMs (n = 31). As a result, the human hepatic cytochrome P450 (P450) "pie" has been revised to include the contribution of CYP4F enzymes, which amounts to 15% of the total hepatic cytochrome P450 enzymes. CYP4F3B displayed low interindividual variability (3.3-fold) in the HLM panels whereas CYP4F2 displayed large variability (21-fold). However, CYP4F2 variability decreased to 3.4-fold if the two donors with the lowest expression were excluded. In contrast, CYP3A exhibited 29-fold interindividual variability in the same HLM panels. The proposed marker reaction for CYP4F enzymes pafuramidine/DB289 M1 formation did not correlate with CYP4F protein content, suggesting alternate metabolic pathways for DB289 M1 formation in HLMs. In conclusion, CYP4F enzymes are highly expressed in the human liver and their physiologic and pharmacologic roles warrant further investigation.

Complex Formation of Nickel(II) and Copper(II) with Barbituric Acid

Equilibrium studies have been carried out on complex formation of M2+ ions (M = Ni and Cu) with L = barbituric acid (BA) in aqueous solution at 25.0±0.1°C and with an ionic strength of I=0.10 M (KNO3) in aqueous medium. The basicity of the ligand was also assessed by the determination of the dissociation constants of the ligand. The experimental pH titration data were analyzed with the help of the BEST computer program in order to evaluate the stability constants of the various species formed. The stability constants of the binary systems decrease in the order of Cu(II) > Ni(II). Distribution diagrams for the species were drawn showing the concentrations of individual species as a function of pH by the SPE software program.

Hepatic Glucuronidation of Isoneochamaejasmin A from the Traditional Chinese MedicineStellera ChamaejasmeL. Root

Isoneochamaejasmin A (INCA), a biflavonoid, is one of main active ingredients in the dried root of Stellera chamaejasme L., a widely used traditional Chinese medicine. In the present study, we identified the glucuronidation metabolite of INCA and characterized the UDP glucuronosyltransferases (UGTs) responsible for INCA glucuronidation. 7-O-glucuronide (M1) and 4'-O-glucuronide (M2) were identified by incubation of INCA with human liver microsomes (HLMs) in the presence of UDP glucuronic acid, and their structures were confirmed by high-resolution mass spectrometry and nuclear magnetic resonance analyses. Although INCA is a single enantiomer molecule, its M1 metabolite showed two equal-size peaks on a πNAP stationary phase but only one peak on a C(18) stationary phase, indicating that the 7-/7''- and 4'-/4'''-hydroxyl groups of INCA were in different spatial configurations relative to each other. Among the recombinant human UGT isoform test and correlation analysis, UGT1A1, UGT1A3, and UGT1A9 were found to mediate M1 formation, whereas only UGT1A3 mediated M2 formation. Kinetic studies showed obvious species differences between human, mouse, rat, dog, and pig liver microsomes. UGT1A1, HLMs, and human intestinal microsomes, but not human kidney microsomes, exhibited substrate inhibition for the formation of M1. UGT1A1-mediated formation of M1 showed a 6- and 11-fold higher V(max) than did UGT1A3- and UGT1A9-mediated formation of M1, respectively. The results of the relative activity factor assay showed that UGT1A1 contributed approximately 75% in the formation of M1. These findings collectively indicate that UGT1A1 is the major enzyme in the formation of M1, whereas UGT1A3 is the major enzyme in the formation of M2.

Species Difference in Glucuronidation Formation Kinetics with a Selective mTOR Inhibitor

The mammalian target of rapamycin (mTOR) is a protein kinase that shows key involvement in age-related disease and promises to be a target for treatment of cancer. In the present study, the elimination of potent ATP-competitive mTOR inhibitor 3-(6-amino-2-methylpyrimidin-4-yl)-N-(1H-pyrazol-3-yl)imidazo[1,2-b]pyridazin-2-amine (compound 1) is studied in bile duct-cannulated rats, and the metabolism of compound 1 in liver microsomes is compared across species. Compound 1 was shown to undergo extensive N-glucuronidation in bile duct-catheterized rats. N-glucuronides were detected on positions N1 (M2) and N2 (M1) of the pyrazole moiety as well as on the primary amine (M3). All three N-glucuronide metabolites were detected in liver microsomes of the rat, dog, and human, while primary amine glucuronidation was not detected in cynomolgus monkey. In addition, N1- and N2-glucuronidation showed strong species selectivity in vitro, with rat, dog, and human favoring N2-glucuronidation and monkey favoring N1-glucuronide formation. Formation of M1 in monkey liver microsomes also followed sigmoidal kinetics, singling out monkey as unique among the species with regard to compound 1 N-glucuronidation. In this respect, monkeys might not always be the best animal model for N-glucuronidation of uridine diphosphate glucuronosyltransferase (UGT) 1A9 or UGT1A1 substrates in humans. The impact of N-glucuronidation of compound 1 could be more pronounced in higher species such as monkey and human, leading to high clearance in these species. While compound 1 shows promise as a candidate for investigating the impact of pan-mTOR inhibition in vivo, opportunities may exist through medicinal chemistry efforts to reduce metabolic liability with the goal of improving systemic exposure.

Prolyl‐isomerase Pin1 controls normal and cancer stem cells of the breast

Mammary epithelial stem cells are fundamental to maintain tissue integrity. Cancer stem cells (CSCs) are implicated in both treatment resistance and disease relapse, and the molecular bases of their malignant properties are still poorly understood. Here we show that both normal stem cells and CSCs of the breast are controlled by the prolyl-isomerase Pin1. Mechanistically, following interaction with Pin1, Notch1 and Notch4, key regulators of cell fate, escape from proteasomal degradation by their major ubiquitin-ligase Fbxw7α. Functionally, we show that Fbxw7α acts as an essential negative regulator of breast CSCs' expansion by restraining Notch activity, but the establishment of a Notch/Pin1 active circuitry opposes this effect, thus promoting breast CSCs self-renewal, tumor growth and metastasis in vivo. In human breast cancers, despite Fbxw7α expression, high levels of Pin1 sustain Notch signaling, which correlates with poor prognosis. Suppression of Pin1 holds promise in reverting aggressive phenotypes, through CSC exhaustion as well as recovered drug sensitivity carrying relevant implications for therapy of breast cancers.

Multiple Cytochrome P450 Isoforms Are Involved in the Generation of a Pharmacologically Active Thiol Metabolite, whereas Paraoxonase 1 and Carboxylesterase 1 Catalyze the Formation of a Thiol Metabolite Isomer from Ticlopidine

Ticlopidine is a first-generation thienopyridine antiplatelet drug that prevents adenosine 5'-diphosphate (ADP)-induced platelet aggregation. We identified the enzymes responsible for the two-step metabolic bioactivation of ticlopidine in human liver microsomes and plasma. Formation of 2-oxo-ticlopidine, an intermediate metabolite, was NADPH dependent and cytochrome P450 (CYP) 1A2, 2B6, 2C19, and 2D6 were involved in this reaction. Conversion of 2-oxo-ticlopidine to thiol metabolites was observed in both microsomes (M1 and M2) and plasma (M1). These two metabolites were considered as isomers, and mass spectral analysis suggested that M2 was a thiol metabolite bearing an exocyclic double bond, whereas M1 was an isomer in which the double bond was migrated to an endocyclic position in the piperidine ring. The conversion of 2-oxo-ticlopidine to M1 in plasma was significantly increased by the addition of 1 mM CaCl2. In contrast, the activity in microsomes was not changed in the presence of CaCl2. M1 formation in plasma was inhibited by EDTA but not by other esterase inhibitors, whereas this activity in microsomes was substantially inhibited by carboxylesterase (CES) inhibitors such as bis-(p-nitrophenyl)phosphate (BNPP), diisopropylphosphorofluoride (DFP), and clopidogrel. The conversion of 2-oxo-ticlopidine to M1 was further confirmed with recombinant paraoxonase 1 (PON1) and CES1. However, M2 was detected only in NADPH-dependent microsomal incubation, and multiple CYP isoforms were involved in M2 formation with highest contribution of CYP2B6. In vitro platelet aggregation assay demonstrated that M2 was pharmacologically active. These results collectively indicated that the formation of M2 was mediated by CYP isoforms whereas M1, an isomer of M2, was generated either by human PON1 in plasma or by CES1 in the human liver.

Chemical marker M2 (4-hydroxy-5-methyl-3(2H)-furanone) formation in egg white gel model for heating pattern determination of microwave-assisted pasteurization processing

Microwave-assisted pasteurization (MAP) is a potential thermal processing technology in which the non-uniform heating presents a challenge. This study evaluated the application of a chemical marker M2 (4-hydroxy-5-methyl-3(2H)-furanone) in an egg white gel model on the determination of possible heating patterns in prepackaged foods during MAP processing. The gel model samples were prepared by heating a homogeneous liquid egg white mixture (25% egg white, 1% D-ribose, 0.5% L-lysine) at 70°C for 30min. The chemical marker M2 formation was studied by heating the gel model samples in 75, 80, 85, 90, 95, and 100°C oil bath for 5, 10, 15, 20, and 30min. The marker yields were determined using high-performance liquid chromatography (HPLC). The color values of the heat-treated samples were measured using CIE L∗a∗b∗ and RGB models. The stability of M2 was evaluated at storage temperatures of 4 and 22°C for 1, 3, 5, and 9days. In order to validate the application of the new gel model system, the heating patterns of the gel models and marker yields of samples taken from 5 different locations of the MAP-processed gel models at 75 and 100°C were analyzed. Results showed that the M2 formation in egg white increased linearly with heat treatment time at 75–95°C, while a slight concavity was observed for samples treated at 100°C. Color parameters L∗ and G values were found to be significantly correlated with the heating temperatures. During storage, the M2 retention rate decreased with increasing time and temperature, while samples treated for longer times were more stable. Salt addition had no significant effect on the M2 yield within the studied time-temperature combination. The color change of egg white gel models due to different M2 yield after the MAP process could be clearly recognized using a computer vision method.

Specificity of the redox photoreaction of dimers of thiadicarbocyanine dyes

The primary steps of the redox reaction of dimers of the thiadicarbocyanine dye and its 5,5′-dichloro derivative in aqueous solutions were studied in the presence of 4-nitroacetophenone, ascorbic acid, or hydroquinone. In water the dye molecules (anion, M−) mainly exist as dimers M22−. The laser pulse irradiation (10 ns, 532 nm) results in the population of the lowest triplet level M22−, whose depletion occurs due to both intersystem crossing to the ground state and photoinduced transition to the highest triplet state of the dimer followed by photoionization. Photoionization at low intensities of a laser pulse proceeds via the one-quantum mechanism going to the two-quantum mechanism with an increase in the laser pulse intensity. The photooxidation of the dimer in the lowest triplet state with 4-nitroacetophenone results in the formation of unstable radical anion M2−· that spontaneously dissociates to monomer M− and radical M· of the dye. In the presence of electron donors (ascorbic acid, hydroquinone), the dimers in the triplet state are not photoreduced, but the electron donors reduce M2−· and M· to the dye dimer and monomer, respectively.

Tuning the ring-chain tautomerism of a tetrahydroquinazoline/Schiff base system with unexpected methanol oxidation

The ring-chain tautomerism of a tetrahydroquinazoline/Schiff base (H2Lring/H2Lchain) system can be controlled by metal coordination through varying ligand stoichiometry of the reaction H2L+M2+ [H2Lring: 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol; H2Lchain: N-{2-[(8-hydroxyquinolin-2-yl)methyleneamino]benzyl}-4-methylbenzenesulphonamide and M: Co2+ and Cd2+]. The ring tautomer H2Lring undergoes a ring-opening reaction upon formation of dinuclear complexes M2(Lchain)2, while Co2+ and Cd2+ stabilise the tetrahydroquinazoline ligand in their mononuclear complexes M(HLring)2. The detection of 3-tosyl-1,2,3,4-tetrahydroquinazoline on the methanolic mother liquors of Co2(Lchain)2 revealed the acid-catalysed hydrolysis of the Schiff base ligand and the cobalt-mediated aerobic oxidation of methanol to formaldehyde.