Search

The n-octanol/water partition coefficient (log P) is an important parameter to characterize the overall hydrophobicity of organic compounds. Reversed-phase liquid chromatography (RPLC) has been recommended as an effective method for the indirect determination of log P by the Organization for Economic Cooperation and Development (OECD). Using RPLC, most studies focus on the determination of log P or the apparent n-octanol/water partition coefficient (log D) of neutral compounds and weakly ionized compounds. However, the experimental log P or log D values of strongly ionized compounds have rarely been reported. In our previous work, the experimental log D of strongly ionized compounds could be determined well by ion-pair reversed-phase liquid chromatography (IP-RPLC) on an octadecyl-poly(vinyl alcohol) column using the log D-log kw-IP model established by different types of model compounds. However, the universality of this strategy for different chromatographic columns has yet to be verified. In this study, the retention behavior of neutral compounds, phenolic acids, carboxylic acids, sulfonic acids, and some amphoteric compounds was systematically investigated on a silica-based C18 column (150 mm×4.6 mm, 5 μm) via ion-suppressed RPLC (IS-RPLC) and IP-RPLC, respectively. In the IS-RPLC mode, methanol and 20 mmol/L ammonium dihydrogen phosphate buffer (pH 7.0) were used as the mobile phase to perform isocratic elution at different methanol ratios. The log kw values of the test compounds were obtained using the linear solvent strength (LSS) model. Neutral compounds, weakly ionized phenolic acids and benzene carboxylic acids were then used as model compounds to establish the log D-log kw-IS model. The quantitative structure-retention relationship (QSRR) model, including structure-related descriptors like the charge (ne) and Abraham solvation parameters (A and B), exhibited much better correlation than the unary linear regression model between log D and log kw-IS. The log D7.0 (log D under pH 7.0) values of 19 ionized compounds were then determined by the model; the determined compounds were used as model compounds and validation compounds in IP-RPLC. In the IP-RPLC mode, besides methanol and ammonium dihydrogen phosphate buffer, the mobile phase also contained tetrabutylammonium bromide, as an ion-pair reagent. The retention behaviors of all tested compounds conformed well with the LSS model even under IP-RPLC, with a log k-φ linear correlation coefficient (R2) greater than 0.99. The log D-log kw-IP model was then established using 62 compounds as a mixed model set, including neutral, weakly ionized, and strongly ionized compounds. Similarly, by introducing ne, A, and B, the log D-log kw-IP model showed good linearity, with R2 greater than 0.94. Comparing the log D-log kw-IP model established on the silica-based C18 column in this work with that established on a poly(vinyl alcohol)-based C18 column in our previous work, ne, A, and B contributed more to the model in this work, indicating there was a greater secondary effect on the silica-based column. To confirm the reliability of the log D-log kw-IP model, three different types of acidic compounds were used as validation compounds. The predicted log D of the three ionic compounds was very similar to that determined by the shake-flask method (SFM)/slow stirring method (SSM) or IS-RPLC method in this work, confirming the reliability of the model. Based on the above results, the log D7.0 values of eight strongly ionized compounds were predicted by IP-RPLC. The findings suggested that IP-RPLC is a promising method to predict the experimental log D of strongly ionized compounds, and that the conventional silica-based C18 column offers more flexible options in log D determination.

Liquid-liquid phase separation (LLPS) is involved in both physiological and pathological processes. The intrinsically disordered protein Tau and its K18 construct can undergo LLPS in a distinct temperature-dependent manner, and the LLPS of Tau protein can initiate Tau aggregation. However, the underlying mechanism driving Tau LLPS remains largely elusive. To understand the temperature-dependent LLPS behavior of Tau at the monomeric level, we explored the conformational ensemble of Tau at different temperatures by performing all-atom replica-exchange molecular dynamic simulation on K18 monomer with an accumulated simulation time of 26.4 μs. Our simulation demonstrates that the compactness, β-structure propensity, and intramolecular interaction of K18 monomer exhibit nonlinear temperature-dependent behavior. 295DNIKHV300/326GNIHHK331/337VEVKSE342 make significant contributions to the temperature dependence of the β propensity of K18 monomer, while the two fibril-nucleating cores display relatively high β propensity at all temperatures. At a specific temperature, K18 monomer adopts the most collapsed state with exposed sites for both persistent and transient interactions. Given that more collapsed polypeptide chains were reported to be more prone to phase separate, our results suggest that K18 monomer inherently possesses conformational characteristics favoring LLPS. Our simulation predicts the importance of 295DNIKHV300/326GNIHHK331/337VEVKSE342 to the temperature-dependent conformational properties of K18, which is corroborated by CD spectra, turbidity assays, and DIC microscopy. Taken together, we offer a computational and experimental approach to comprehend the structural basis for LLPS by amyloidal building blocks.

Our simulations reveal that two enantiomeric catechins display a better disruptive effect on Aβ42 protofibril than their stereoisomer epicatechin. Unexpectedly, we find that catechins adopt both collapsed and extended states, while epicatechin populates only an extended state. Their different protofibril-disruptive effects are mostly attributed to the steric effect caused by the conformational differences.

Abnormal aggregation of proteins into pathological amyloid fibrils is implicated in a wide range of devastating human neurodegenerative diseases. Intracellular fibrillary inclusions formed by Tau protein are characterized as the hallmark of tauopathies, including Alzheimer's disease and frontotemporal dementia. Heparin has been often used to trigger Tau aggregation in in vitro studies. However, the conformational changes induced by heparin and the underlying mechanism of promotion of Tau aggregation by heparin are not well understood. Structural characterization of Tau oligomers in the early stage of fibrillation is of great importance but remains challenging due to their dynamic and heterogeneous nature. R3, the third microtubule-binding repeat of Tau, contains the fibril-nucleating core (PHF6) and is crucial for Tau aggregation. In this study, utilizing extensive all-atom replica-exchange molecular dynamic simulations, we explored the conformational ensembles of R3 monomer/dimer in the absence and presence of heparin. Our results show that without heparin, both monomeric and dimeric R3 preferentially adopt collapsed β-sheet-containing conformations and PHF6 plays an important role in the formation of interchain β-sheet structures, while in the presence of heparin, R3 can populate relatively extended disordered states where chain dimension is similar to that of R3 in Tau filaments. Through electrostatic, hydrogen-bonding and hydrophobic interactions, heparin has a preference for interacting with residues V306/Q307/K317/K321/H329/H330/K331 which distribute throughout the entire sequence of R3, in turn acting as a template to extend R3 conformations. More importantly, heparin alters intramolecular/intermolecular interaction patterns of R3 and increases the intermolecular contact regions. Our results suggest that heparin remodels the conformations of R3 towards fibril-prone structures by increasing chain dimension and intermolecular contact regions, which may shed light on the atomic mechanism of heparin-induced amyloid fibrillization of Tau protein.

Ion-pair reversed-phase liquid chromatography (IP-RPLC) enhances separation by adding ion-pair reagents to the mobile phase, thereby improving the retention of oppositely charged solutes. IP-RPLC is primarily used for the separation and analysis of strongly ionized compounds. In IP-RPLC, researchers often focus more on the influence of the counter-ion type and concentration, buffer salt concentration and pH, and column temperature, on the retention behavior of solutes. However, the effects of the buffer salt type and non-counter ions in ion-pair reagents on the retention behavior of solutes have rarely been investigated. Accordingly, in this work, the effects of buffer salt types and non-counter ions on the retention behavior of strongly ionized compounds were investigated by IP-RPLC using 14 sulfonic acid compounds as model compounds. Experiments were performed using a silica-based C18 column with methanol as the organic modifier. In the first type of experiment, tetrabutylammonium bromide was kept unchanged as the ion-pair reagent in the mobile phase, and ammonium dihydrogen phosphate, ammonium chloride, and ammonium acetate were used as buffer salts, respectively. The retention factor (k) was obtained at different methanol ratios, and linear solvent strength (LSS) models were established to determine the log kw (logarithm of retention factors of solutes when 100% aqueous phases were used as the mobile phase) and S (intercept of the LSS model) values of each solute. All solutes exhibited the highest log kw with the ammonium chloride buffer system; most compounds also exhibited the highest S values with this system, except for 1,5-naphthalenedisulfonic acid, 4-methylbenzenesulfonic acid, 5-amino-2-nanphthalenesulfonic acid, and 4-hydroxybenzenesulfonic acid. However, the chromatographic hydrophobic indices (CHIs, log kw/S) of the solutes with different buffer salts were approximately equal. In the second type of experiment, ammonium dihydrogen phosphate was kept unchanged as the buffer salt in the mobile phase, and tetrabutylammonium bromide, tetrabutylammonium dihydrogen phosphate, tetrabutylammonium hydrogen sulfate, tetrabutylammonium nitrate, and tetrabutylammonium acetate were used as ion-pair reagents, respectively. Almost all solutes exhibited the highest S with the tetrabutylammonium acetate system, indicating that weakly ionized anions (such as acetate ions) in ion-pair reagents will improve the S values of sulfonic acid compounds. Interestingly, the CHIs of the solutes were almost the same for solutes with different non-counter ions. These results suggest that both, the buffer salt types and non-counter ions, influence the log kw and S values of sulfonic acid compounds. Comparison of the retention behavior of solutes with different mobile phases suggested ion-pair mechanisms as well as dynamic ion-exchange mechanisms plays role in the IP-RPLC retention of sulfonic acid compounds. In addition, with all the experimental mobile phases, the apparent n-octanol/water partition coefficient (log D) presented a good linear correlation with log kw, S, and CHI, respectively, by the introduction of structure-related descriptors such as charge (ne), Abraham solvation parameters (A and B), and the polar surface area (PSA). Considering the differences in the log kw and S values obtained with different buffer salts and non-counter ions, the CHIs were relatively stable; therefore, the CHI is more suitable for establishing a quantitative structure-retention relationship (QSRR) model in IP-RPLC, compared to log kw and S.

Among the diverse toxic components produced by cyanobacteria, microcystins (MCs) are one of the most toxic and notorious cyanotoxin groups. Besides their potent hepatotoxicity, MCs have been revealed to induce potential reproductive toxicity in various animal studies. However, little is still known regarding the distribution of MCs in the reproductive organ, which could directly affect reproductive cells. In order to respond to this question, an acute study was conducted in adult medaka fish (model animal) gavaged with 10 µg.g-1 body weight of pure MC-LR. The histological and immunohistochemical examinations reveal an intense distribution of MC-LR within hepatocytes along with a severe liver lesion in the toxin-treated female and male fish. Besides being accumulated in the hepatocytes, MC-LR was also found in the connective tissue of the ovary and the testis, as well as in oocytes and degenerative spermatocyte-like structures. Both liver and gonad play important roles in the reproductive process of oviparous vertebrates. This observation constitutes the first observation of the presence of MC-LR in the reproductive cell of a vertebrate model with in vivo study. Our results, which provide intracellular localization of MC-LR in the gonad, advance our understanding of the potential reproductive toxicity of MC-LR in fish.

The expression changes of CD2-associated protein (CD2AP) can lead to kidney diseases with proteinuria, including nephrotic syndrome (NS). A recent study reported that miRNAs may be important transcriptional regulators. In this study, we found increased expression of miR-939-5p and decreased expression of CD2AP in the peripheral blood of patients with NS. However, miR-939-5p did not show a regulatory effect on the 3'-untranslated region of CD2AP. The expression levels of specific protein 1 and adenovirus E2 promoter-binding factor 1, important transcription regulators in the promoter region of CD2AP, were also not affected by microRNA (miR)-939-5p. We confirmed that miR-939-5p is in the nucleus by fluorescent in situ hybridization and cytoplasmic separation polymerase chain reaction. The promoter plasmid and miR-939-5p were cotransfected into HEK-293 cells, and the luciferase reporter gene assay was used to analyze the promoter activity. We found that miR-939-5p binds to a specific sequence in the CD2AP promoter. miR-939-5p was confirmed to reduce the recruitment of RNA polymerase II to the CD2AP promoter region by chromatin immunoprecipitation. These findings improve our understanding of the mechanism of miR-939-5p in NS and provide potential molecular therapeutic targets for NS.

Mercapto- and amino-functionalized magnetic nanoparticles, Fe3O4@SiO2@MPTMS (SMNPs-MPTMS) and Fe3O4@SiO2@APTES (SMNPs-APTES), have been applied as magnetic solid-phase extraction (MSPE) sorbents to directly extract arsenite (As(III)) and arsenate (As(V)) respectively, followed by inductively coupled plasma-mass spectrometry (ICP-MS) detection. Various MSPE parameters were optimized including dose of magnetic adsorbent, pH of sample solution, loading and elution conditions of analytes, adsorption capacity and reusability of SMNPs-MPTMS and SMNPs-APTES for As(III) and As(V) respectively. Under the optimized MSPE conditions, this combined scheme possesses excellent selectivity and strong anti-interference ability without any oxidation or reduction prior to capture of these two species. It is found that with a 25-fold enrichment factor, the limits of detection of As(III) and As(V) were 23.5 and 10.5 ng L−1, respectively. To verify the reliability of the proposed protocol, a certified reference material of environmental water was analyzed, and the results for inorganic arsenic species were in close agreement with the certified values. The applicability of the combination strategy for speciation analysis of inorganic arsenic was evaluated in spiked tap, river, lake and rain water samples. Good recoveries of 89%–96% and 90%–102% were achieved for As(III) and As(V), respectively, with the relative standard deviation ranges of 3.2%–8.0% and 2.5%–7.6%. Through the characterization of functionalized magnetic nanoparticles and the optimization of MSPE experiment, it is confirmed that the existence of mercapto and amino groups on SMNPs-MPTMS and SMNPs-APTES sorbents are responsible for the extraction of As(III) and As(V), respectively, via coordination and electrostatic interactions.

Novel core shell structured magnetic covalent organic frameworks were synthesized at room temperature and first applied in water samples for the enrichment of trace polybrominated diphenyl ethers (PBDEs) through magnetic solid-phase extraction. The prepared materials were characterized through transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer and X-ray photoelectron spectroscopy. During adsorption, the parameters affecting extraction and desorption efficiency were further optimized. Combined gas chromatography and mass spectrometry (GC/MS) revealed that high enrichment factors (275–292), low limits of detection (0.12–0.38 ng·L−1), wide linear ranges (0.5–1000 ng·L−1), and good reproducibility (intra-day 1.40%–4.31% and inter-day 5.14%–9.12%) were obtained under optimal conditions. The method successfully detected PBDEs in different water samples.

In this work, the correlations between retention behavior and lipophilicity of a large set of hydrophilic neutral and ionic analytes were studied based on three hydrophilic interaction liquid chromatography (HILIC) stationary phases, including zwitterionic, crosslinked diol and triazole stationary phases. It was found that HILIC, due to the diversity of retention mechanism, is a more complex chromatography separation mode than reversed-phase liquid chromatography (RPLC) which has been widely accepted for lipophilicity assessment. Because electrostatic interactions contributed to the overall retention of the charged solutes on all three stationary phases, ion-strength of the mobile phase kept the same during the whole experiment. After the correlations between retention factor log k and water volume fraction Φ were investigated, the mixed retention model was revealed to be more suitable for HILIC retention behavior than other single models including partitioning and adsorption model. Moreover, in order to bridge the relationship between HILIC log k and lipophilicity parameter log D, net charge ne and Abraham solvation parameter were introduced in the quantitative structure-retention relationship (QSRR) model. Although the correlation coefficients between log D and log k were still moderate, the significant improvement in correlation has made HILIC a potential choice as the complement of RPLC for log D measurement.

The amyloid deposits of human islet amyloid polypeptide (hIAPP) are found in type 2 diabetes patients. hIAPP monomer is intrinsically disordered in solution, whereas it can form amyloid fibrils both in vivo and in vitro. Extensive evidence suggests that hIAPP causes the disruption of cellular membrane, and further induces cytotoxicity and the death of islet β-cells in pancreas. The presence of membrane also accelerates the hIAPP fibril formation. hIAPP oligomers and protofibrils in the early stage of aggregation were reported to be the most cytotoxic, disrupting the membrane integrity and giving rise to the pathological process. The detailed molecular mechanisms of hIAPP-membrane interactions and membrane disruption are complex and remain mostly unknown. Here in this review, we focus on recent computational studies that investigated the interactions of full length and fragmentary hIAPP monomers, oligomers and protofibrils with anionic, zwitterionic and mixed anionic-zwitterionic lipid bilayers. We mainly discuss the binding orientation of monomers at membrane surface, the conformational ensemble and the oligomerization of hIAPP inside membranes, the effect of lipid composition on hIAPP oligomers/protofibrils-membrane interactions, and the hIAPP-induced membrane perturbation. This review provides mechanistic insights into the interactions between hIAPP and lipid bilayers with different lipid composition at an atomistic level, which is helpful to understand the hIAPP cytotoxicity mediated by membrane. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.

Aconitum carmichaelii has long been used as a traditional Chinese medicine, and its processed lateral roots are known commonly as fuzi. Aconitine-type C19-diterpenoid alkaloids accumulating in the lateral roots are some of the main toxicants of this species, yet their biosynthesis remains largely unresolved. As a first step towards understanding the biosynthesis of aconitine-type C19-diterpenoid alkaloids, we performed de novo transcriptome assembly and analysis of rootstocks and leaf tissues of Aconitum carmichaelii by next-generation sequencing. A total of 525 unigene candidates were identified as involved in the formation of C19-diterpenoid alkaloids, including those encoding enzymes in the early steps of diterpenoid alkaloids scaffold biosynthetic pathway, such as ent-copalyl diphosphate synthases, ent-kaurene synthases, kaurene oxidases, cyclases, and key aminotransferases. Furthermore, candidates responsible for decorating of diterpenoid alkaloid skeletons were discovered from transcriptome sequencing of fuzi, such as monooxygenases, methyltransferase, and BAHD acyltransferases. In addition, 645 differentially expressed genes encoding transcription factors potentially related to diterpenoid alkaloids accumulation underground were documented. Subsequent modular domain structure phylogenetics and differential expression analysis led to the identification of BAHD acyltransferases possibly involved in the formation of acetyl and benzoyl esters of diterpenoid alkaloids, associated with the acute toxicity of fuzi. The transcriptome data provide the foundation for future research into the molecular basis for aconitine-type C19-diterpenoid alkaloids biosynthesis in A. carmichaelii.

In this work, retention behaviors of oligonucleotides and double-stranded deoxyribonucleic acids (dsDNAs) have been investigated in ion-pair reversed-phase liquid chromatography (IP-RPLC). We demonstrated that classic linear solvent strength (LSS) model is applicable for describing isocratic retention of oligonucleotides and dsDNAs, which indicated that nucleic acids share the similar retention mechanism as other common small molecules in IP-RPLC. The separation of nucleic acids in IP-RPLC is driven by both hydrophobic and electrostatic interactions. We defined the parameter lnkw/S obtained from LSS model in IP-RPLC as chromatographic hydrophobic and electrostatic interaction index (CHEI). CHEI of a nucleic acid has been revealed to correlate well with its gradient retention time. Notably, we proposed a strategy for retention prediction based on CHEI and base sequence information of nucleic acids. Corresponding to base locus, each base sequence is converted to a featured locus vector consisting of zeros and ones. CHEI prediction models were established by support vector regression (SVR) algorithm with locus vectors. Predicted CHEI values have been applied to predict retention times under desired gradient elution runs. This protocol is easy to grasp and worth pursuing further development for more precise retention prediction performance of nucleic acids in IP-RPLC.

Polymorphism is inherent for G-quadruplexes (G4s), and the different structural forms are important for the participation in different biological functions of telomeres. A lot of progress has been made in the exploration of G4 polymorphism. However, quick separation and reliable assessment methods for different conformations of G4 are still very few. In this work, the polymorphism of three sequences d[(G3T)3G3], d[(G3C)3G3] and d[(G3T)4] annealed in six different solutions were investigated by means of reversed-phase high performance liquid chromatography (RP-HPLC), liquid chromatography-mass spectrometry (LC-MS), fluorescence spectroscopy, circular dichroism spectroscopy, together with native-polyacrylamide gel electrophoresis. Different G4 conformations of these three sequences can be separated clearly by RP-HPLC, and further characterized by on-line LC-MS analysis. It is revealed that high-order structures other than intramolecular quadruplexes were favored for d[(G3T)3G3] and d[(G3C)3G3] under the annealing conditions. However, flanking loop impeded d[(G3T)4] to form higher-order structures than dimer. In addition, the nature and concentration of cation, as well as the annealing solution component, all have decent influence on the stability and relative ratios of various G4 building blocks. Based on the above findings, RP-HPLC and LC-MS combined with spectroscopic techniques can be used as a facile and powerful tool for quick separation and identification of G4s in solutions, and for effective assessment of DNA sequences and annealing environments on G4 polymorphism. The established protocol provides a novel strategy for evaluating G4 polymorphism, which will facilitate studies on quadruplex structures and their biophysical properties.

The study on nucleic acid retention in ion-pair reversed-phase high-performance liquid chromatography mainly focuses on size-dependence, however, other factors influencing retention behaviors have not been comprehensively clarified up to date. In this present work, the retention behaviors of oligonucleotides and double-stranded DNAs were investigated on silica-based C18 stationary phase by ion-pair reversed-phase high-performance liquid chromatography. It is found that the retention of oligonucleotides was influenced by base composition and base sequence as well as size, and oligonucleotides prone to self-dimerization have weaker retention than those not prone to self-dimerization but with the same base composition. However, homo-oligonucleotides are suitable for the size-dependent separation as a special case of oligonucleotides. For double-stranded DNAs, the retention is also influenced by base composition and base sequence, as well as size. This may be attributed to the interaction of exposed bases in major or minor grooves with the hydrophobic alky chains of stationary phase. In addition, no specific influence of guanine and cytosine content was confirmed on retention of double-stranded DNAs. Notably, the space effect resulted from the stereostructure of nucleic acids also influences the retention behavior in ion-pair reversed-phase high-performance liquid chromatography.

The industrial hemp varieties ‘Yunma 5’ and ‘Bamahuoma,’ which demonstrate growth vigor and environmental adaptability, have been primarily cultivated in Yunnan and Guangxi, China, respectively, for fiber and seeds. The results of physiological measurements showed the phenotypic differences between the two varieties in response to salt stress. RNA-Seq analysis was first performed on leaves of both varieties sampled at four time intervals (0, 2, 4, 6 days) after treatment with salt (500 mM NaCl) We identified 220 co-up-regulated differentially expressed genes (DEGs) in the two varieties, while 26 up-regulated DEGs and 24 down-regulated DEGs were identified exclusively in the single varieties after 2 days of salt stress. Among the 220 DEGs, we identified 22 transcription factors, including key transcription factors involved in salt stress, such as MYB, NAC, GATA, and HSF. We applied gene expression profile analysis and found that ‘Yunma 5’ and ‘Bamahuoma’ have variety-specific pathways for resisting salt stress. The DEGs of ‘Yunma 5’ were enriched in spliceosome and amino acid metabolism genes, while the DEGs of ‘Bamahuoma’ were enriched in fatty acid metabolism, amino acid metabolism, and endoplasmic reticulum protein processing pathway. Although there were common DEGs, such as genes encoding cysteine protease and alpha/beta-hydrolase superfamily, the two varieties’ responses to salt stress impacted different metabolic pathways. The DEGs that were co-expressed in both varieties under stress may provide useful insights into the tolerance of cultivated hemp and other bast fiber crops to saline soil conditions. These transcriptomes also represent reference sequences for industrial hemp.

The amyloid formation of human islet amyloid polypeptide (hIAPP)-an intrinsically disordered peptide, is associated with type II diabetes. Cellular membranes, especially those composed of negatively-charged lipids, accelerate the hIAPP amyloid fibrillation, and their integrity is disrupted during the aggregation process, leading to cell apoptosis. However, the underlying molecular mechanism is not well understood. Herein, we investigated the conformational dynamics during the interactions of hIAPP monomer with POPG membrane bilayer, by carrying out μs-long all-atom molecular dynamics simulations. Starting from the metastable coiled conformations in water, hIAPP monomers tend to adopt transient α-helical and β-sheet structures when adsorbing to the membrane surface. The amphiphilic N-terminal region further inserts into the membrane interior and is located at the lipid head-tail interface, mainly in turn and α-helical structures. In contrast, the β-hairpin structures reside on the membrane surface without insertion, and expand laterally with the hydrophobic residues exposed to the solvent. Moreover, the adsorption and insertion of hIAPP monomers induce two distinct local membrane deformations: (1) the hIAPP adsorption on the membrane surface mainly causes membrane bending; (2) the insertion of both turns and α-helices synchronizes with the formation of hydrophobic defects on the POPG membrane, leading to stronger membrane stretching and a longer coherence length of membrane thinning. Based on the structural and dynamical results, we propose that β-hairpin structures may be a precursor for the fibrillation on the membrane surface due to the flat geometry and hydrophobic regions exposed to solvent, while N-terminal amphiphilic α-helices would facilitate hIAPP assembling into toxic oligomers inside the membrane.

Polydopamine-coated Fe3 O4 magnetic nanoparticles synthesized through a facile solvothermal reaction and the self-polymerization of dopamine have been employed as a magnetic solid-phase extraction sorbent to enrich four phenolic compounds, bisphenol A, tetrabromobisphenol A, (S)-1,1'-bi-2-naphthol and 2,4,6-tribromophenol, from environmental waters followed by high-performance liquid chromatographic detection. Various parameters of the extraction were optimized, including the pH of the sample matrix, the amount of polydopamine-coated Fe3 O4 sorbent, the adsorption time, the enrichment factor of analytes, the elution solvent, and the reusability of the nanoparticles sorbent. The recoveries of these phenols in spiked water samples were 62.0-112.0% with relative standard deviations of 0.8-7.7%, indicating the good reliability of the magnetic solid-phase extraction with high-performance liquid chromatography method. In addition, the extraction characteristics of the magnetic polydopamine-coated Fe3 O4 nanoparticles were elucidated comprehensively. It is found that there are hydrophobic, π-π stacking and hydrogen bonding interactions between phenols and more dispersible polydopamine-coated Fe3 O4 in water, among which hydrophobic interaction dominates the magnetic solid-phase extraction performance.

Graphene-doped Fe3O4 nanocomposites were prepared by a solvothermal reaction of an iron source with graphene. The nanocomposites were characterized by transmission electron microscopy, atomic force microscopy, X-ray diffraction, superconducting quantum interference, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. This nanomaterial has been used as a magnetic solid-phase extraction sorbent to extract trace brominated flame retardants from environmental waters. Various extraction parameters were optimized including dosage and reusability of the nanocomposites, and pH of sample matrix. The reliability of the magnetic solid-phase extraction protocol based on graphene-doped Fe3O4 nanocomposites was evaluated by investigating the recoveries of 2,4,6-tribromophenol, tetrabromobisphenol A, 4-bromodiphenyl ether, and 4,4'-dibromodiphenyl ether in water samples. Good recoveries (85.0-105.0%) were achieved with the relative standard deviation ranging from 1.1-7.1%. Moreover, it is speculated from characterization and magnetic solid-phase extraction experiment that there is not only π-π stacking but also possible hydrophobic interaction between the graphene-doped Fe3O4 nanocomposites and analytes.

Matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry MALDI-(TOF/TOF) MS is a simple, rapid, sensitive, and high-resolution method for the characterization of polypeptides. In this article, bacitracin zinc, which is a polypeptide antibiotic, was characterized by MALDI-(TOF/TOF) MS. The mass spectrometry conditions were comprehensively investigated in this study. Nearly complete sequence coverage of bacitracin A was observed in a single tandem mass spectrum by careful adjustment of the instrumental parameters. The primary sequence of bacitracin A was analyzed by a de novo approach. The vibrations of functional groups in the infrared and electron transitions in the ultraviolet absorption spectra of bacitracin zinc were assigned and interpreted. The zinc stoichiometry was determined by inductively coupled plasma–optical emission spectrometry. This investigation of bacitracin zinc provides provides sequencing and structural characterization of this polypeptide pharmaceutical mate...

The influence of n-octanol additive agent on the retention behavior, the uniformity of the retention mechanism, as well as the quantitative structure–retention relationships (QSRRs) of weak acidic and basic compounds on reversed-phase high performance liquid chromatography (RP-HPLC) was systematically discussed in this paper, especially for the QSRRs of logarithm of apparent n-octanol/water partition coefficient (log K′′ow) and logarithm of retention factor extrapolated to neat aqueous mobile phase (log kw(o)), which have not been discussed in other studies to date. For this purpose, the aqueous fraction of mobile phase was saturated with n-octanol and 0.25% (v/v) n-octanol was added into organic modifier. Eleven substituted benzoic acids, as well as fifteen anilines or pyridines were selected to establish QSRR models by using different types of ion-suppressors. The results indicated that the roles of n-octanol were different in various systems. For acids compounds, if perchloric acid (strong acid) acts as an ion-pair agent, the silanophilic interaction between solutes and residual silanol groups of alkyl-silica stationary phase can be ignored, and n-octanol/water partition and chromatographic process are homo-energetic. In this case, n-octanol acts only as organic modifier. However, if acetic acid (weak acid) or phosphoric acid/potassium dihydrogen phosphate (buffer salt) were used as the ion-suppressor, n-octanol is not only an organic modifier, but also a masking agent of free silanols. For weak bases, if ammonium chloride–ammonia was employed as the ion-suppressor, the addition of n-octanol will make QSRRs correlation significantly worse. Therefore, for studying on QSRRs of lipophilicity and retention behavior of acidic and basic compounds, n-octanol is only recommended for acidic system, and strong monoprotic acids, e.g., perchloric acid, are recommended as the ion-suppressors.

In this paper, a strong halogen bond (XB) donor (iodine) and photoinduced electron transfer (PET) molecule (ciprofloxacin, Cip) were selected with the objective to investigate halogen bonding under weakly alkaline conditions. A series of experimental characterization techniques was employed to elucidate the interaction mechanism of the XB, in combination with theoretical calculations. It is found that new UV-Vis absorption peaks and the fluorescence enhancement with the mixing of Cip and iodine are attributed to the disruption of the PET charge separation process through the halogen bonding interaction. The 2 : 1 stoichiometry of the XB complex (I2 : Cip) was attested using a modified Benesi–Hildebrand method. 1H NMR spectra showed that the iodine molecule can interact with three nitrogen atoms of Cip to form three XBs. FT-IR spectra indicated that the nitrogen atom of the imino group is the preferential interaction site of the XB. Notably, direct analysis in real time-mass spectrometry (DART-MS) gave a distinct quasi-molecular ion of the supramolecular complex (Cip + I) in solution. Meanwhile, density functional theory (DFT), taking into account the dispersion energy, revealed that the formation of an I⋯N XB not only disrupts the PET charge separation process of Cip to enhance fluorescence but also induces the cleavage of an iodine molecule (I–I) to produce a triiodine anion (I3−) XB. This explained why I3− was observed in UV-Vis and DART-MS as well as in the crystal, and how the fourth iodine atom involved in the self-assembly of the XB existed stably. Moreover, a developed optosensor based on halogen bonding has been successfully used to analyze commercial Cip·HCl capsules, suggesting the potential applicability of halogen bonding in real pharmaceutical analyses.

Carbon doped Fe3O4 nanoparticles (Fe3O4/C) prepared by a facile hydrothermal reaction of glucose with iron resource have been applied as magnetic solid-phase extraction (MSPE) sorbent, for the first time, to extract trace brominated flame retardants (BFRs) and pentachlorophenol (PCP) from environmental waters. Various MSPE parameters were optimized including amount of Fe3O4/C nanoparticles, pH of sample solution, enrichment factor of analytes and reusability of Fe3O4/C sorbent. The reliability of the MSPE method was evaluated by the recoveries of BFRs and PCP in spiked water samples. Good recoveries (80.0–110.0%) were achieved with the relative standard deviations range from 0.3% to 6.8%. In this paper, the extraction characteristics of Fe3O4/C sorbent were further elucidated. It is found that the adsorption process of Fe3O4/C to analytes predominates the MSPE efficiency. There is hybrid hydrophobic interaction and hydrogen bonding or dipole–dipole attraction between Fe3O4/C and analytes. Notably, the chemical components of carbon layer on the surface of Fe3O4 nanoparticles were identified by X-ray photoelectron spectroscopy and thermogravimetry-mass spectrometry, and in consequence the covalent bonds between Fe3O4 and the coated carbon have been observed. In addition, the straight influence of synthesis condition of Fe3O4/C nanoparticles including glucose concentration and hydrothermal reaction time on extraction performance for BFRs and PCP has been investigated. It is confirmed that the existence of organic carbon containing functional groups over Fe3O4/C sorbent is responsible for the MSPE extraction.

Cobalt doped TiO 2 nanoparticle prepared by ultrasonic-assisted hydrothermal method was used as the photocatalyst in the degradation of chlorophenols (CPs) and bromophenols (BPs). The doping content of cobalt in this catalyst was optimized as 0.5 wt%. The degradation rates of 2,4,6-trichlorophenol (2,4,6-TCP), 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4,6-tribromophenol (2,4,6-TBP), 2,4-dibromophenol (2,4-DBP), 2,6-dibromophenol (2,6-DBP), 2-bromophenol (2-BP) and 4-bromophenol (4-BP) were estimated based on the quantitative determination of the degradation products. It was found that the degradation of CPs and BPs underwent dehalogenation process with pseudo-first-order kinetics. Moreover, the photodegradation kinetics was compared between CPs and BPs. The degradation rate of BPs was more quickly than CPs due to the difference in bond energy of carbon–halogen, and the degradation rates of BPs and CPs were mainly dependent on the number and the position of substituting halogen atom respectively. In addition, 2,4,6-TCP and 2,4,6-TBP can be effectively degraded by more than 95.1% and 93.5%, respectively, within 240 and 30 min. Tri-substituted phenols were firstly photodegraded to corresponding di-substituted ones, then to mono-substituted ones, and finally to phenol by TiO 2 /Co nano catalyst, although there were some differences in selectivity, rate and yield in the dehalogenation pathway of 2,4,6-TCP and 2,4,6-TBP.

A strategy to utilize neutral model compounds for lipophilicity measurement of ionizable basic compounds by reversed-phase high-performance liquid chromatography is proposed in this paper. The applicability of the novel protocol was justified by theoretical derivation. Meanwhile, the linear relationships between logarithm of apparent n-octanol/water partition coefficients (logKow '') and logarithm of retention factors corresponding to the 100% aqueous fraction of mobile phase (logkw ) were established for a basic training set, a neutral training set and a mixed training set of these two. As proved in theory, the good linearity and external validation results indicated that the logKow ''-logkw relationships obtained from a neutral model training set were always reliable regardless of mobile phase pH. Afterwards, the above relationships were adopted to determine the logKow of harmaline, a weakly dissociable alkaloid. As far as we know, this is the first report on experimental logKow data for harmaline (logKow = 2.28 ± 0.08). Introducing neutral compounds into a basic model training set or using neutral model compounds alone is recommended to measure the lipophilicity of weakly ionizable basic compounds especially those with high hydrophobicity for the advantages of more suitable model compound choices and convenient mobile phase pH control.

Reversed-phase liquid chromatography (RPLC) based octanol-water partition coefficient (logP) or distribution coefficient (logD) determination methods were revisited and assessed comprehensively. Classic isocratic and some gradient RPLC methods were conducted and evaluated for neutral, weak acid and basic compounds. Different lipophilicity indexes in logP or logD determination were discussed in detail, including the retention factor logk w corresponding to neat water as mobile phase extrapolated via linear solvent strength (LSS) model from isocratic runs and calculated with software from gradient runs, the chromatographic hydrophobicity index (CHI), apparent gradient capacity factor (k g ’) and gradient retention time (t g ). Among the lipophilicity indexes discussed, logk w from whether isocratic or gradient elution methods best correlated with logP or logD. Therefore logk w is recommended as the preferred lipophilicity index for logP or logD determination. logk w easily calculated from methanol gradient runs might be the main candidate to replace logk w calculated from classic isocratic run as the ideal lipophilicity index. These revisited RPLC methods were not applicable for strongly ionized compounds that are hardly ion-suppressed. A previously reported imperfect ion-pair RPLC method was attempted and further explored for studying distribution coefficients (logD) of sulfonic acids that totally ionized in the mobile phase. Notably, experimental logD values of sulfonic acids were given for the first time. The IP-RPLC method provided a distinct way to explore logD values of ionized compounds.

Based on a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) sample preparation method with Fe3O4 magnetic nanoparticles (MNPs) as the adsorbing material and gas chromatography-tandem mass spectrometry (GC-MS/MS) determination in multiple reaction monitoring (MRM) mode, we established a new method for the determination of multiple pesticides in vegetables and fruits. It was determined that bare MNPs have excellent function as adsorbent when purified, and it is better to be separated from the extract. The amount of MNPs influenced the clean-up performance and recoveries. To achieve the optimum performance of modified QuEChERS towards the target analytes, several parameters including the amount of the adsorbents and purification time were investigated. Under the optimum conditions, recoveries were evaluated in four representative matrices (tomato, cucumber, orange and apple) with the spiked concentrations of 10 μg kg(-1), 50 μg kg(-1)and 200 μg kg(-1) in all cases. The results showed that the recovery of 101 pesticides ranged between 71.5 and 111.7%, and the relative standard deviation was less than 10.5%. The optimum clean-up system improved the purification efficiency and simultaneously obtained satisfactory recoveries of multiple pesticides, including planar-ring pesticides. In short, the modified QuEChERS method in addition to MNPs used for removing impurities improved the speed of sample pre-treatment and exhibited an enhanced performance and purifying effect.

Cyanobacterial blooms induce important ecological constraints for aquatic organisms and strongly impact the functioning of aquatic ecosystems. In the past decades, the effects of the cyanobacterial secondary metabolites, so called cyanotoxins, have been extensively studied in fish. However, many of these studies have used targeted approaches on specific molecules, which are thought to react to the presence of these specific cyanobacterial compounds. Since a few years, untargeted metabolomic approaches provide a unique opportunity to evaluate the global response of hundreds of metabolites at a glance. In this way, our study provides the first utilization of metabolomic analyses in order to identify the response of fish exposed to bloom-forming cyanobacteria. Three relevant fish species of peri-urban lakes of the European temperate regions were exposed for 96 h either to a microcystin (MC)-producing or to a non-MC-producing strain of Microcystis aeruginosa and metabolome changes were characterized in the liver of fish. The results suggest that a short-term exposure to those cyanobacterial biomasses induces metabolome changes without any response specificity linked to the fish species considered. Candidate metabolites are involved in energy metabolism and antioxidative response, which could potentially traduce a stress response of fish submitted to cyanobacteria. These results are in agreement with the already known information and could additionally bring new insights about the molecular interactions between cyanobacteria and fish.

Amyloid deposits of human islet amyloid polypeptide (hIAPP) are identified in 95% of type II diabetes patients. The oligomers during the early stage of hIAPP aggregation are believed to be more cytotoxic than the mature fibrils. However, the structural details during the initial stage of hIAPP aggregation are still under debate experimentally. To understand its initial nucleation mechanism, we investigate the thermodynamics and kinetics of hIAPP(11–25) dimerization, which is the first manifestation of the interplay between intra- and inter-molecular interactions, via the construction of Markov state models from extensive molecular dynamics simulations. We identified a largely populated metastable dimer state with the antiparallel cross-β structure, although tangled coil states are also observed. The dimerization process consists of two stages kinetically: the initial collision of separate monomers followed by structural rearrangements. During the collapsing stage, hydrophobic interactions are the main driving force, although electrostatic interactions also play a role. In the subsequent structural rearrangement step, there exist heterogeneous pathways from the initial collapsed complexes to the antiparallel cross-β structure, with the transition time-scales around hundreds of microseconds. Our replica-exchange molecular dynamics simulations demonstrate that this antiparallel cross-β state is negligible in the dimer ensemble of the fibril-free S20P mutant, indicating that it is an on-pathway intermediate for hIAPP(11–25) fibrillation. These results, together with those from our previous study of the monomer, prompt us to propose a generalized model with the combination of the induced-fit and conformational-selection mechanisms for this dimerization process. These findings shed light on the understanding of hIAPP(11–25) aggregation mechanisms.

Microcystins (MCs) released during cyanobacterial blooms exert varied toxicity on fish. Up to now, the reproductive toxicity of MCs on fish has rarely been reported. The present study investigated the reproductive toxicity of microcystin-LR (MC-LR) on male and female zebrafish (Danio rerio) by subchronic immersion in 1, 5, 20 μg/L for 30 d. After MC-LR exposure, the hatchability and the 17 beta-estradiol (E2) concentration in gonads significantly decreased in the 20 μg/L group. In the 5 and 20 μg/L groups, the whole body vitellogenin (VTG) levels significantly increased in females, while considerably decreased in males. The VTG1 transcriptional level significantly reduced in the liver of both female and male treated fish. Marked histological lesions were observed in the livers, ovaries and testes in MC-LR treated fish. Apoptotic rate in the ovaries significantly increased. Significant down-regulation of Bcl-2 transcriptional level was found in the gonads of all MC-LR treated fish, while marked up-regulation of Bax transcription level was determined in the 20 μg/L female treatment group, but a significant down-regulation in males. Although the transcriptional level of caspase-3 dropped in ovaries of the 5 and 20 μg/L treatment groups, the significant increase of caspase-3 activation levels in the ovaries and testes were detected. The present findings indicate that MC-LR exposure exerts diverse reproductive toxicity in zebrafish with females exhibiting more sensitivity than males. The present study also confirmed for the first time that MC-LR does not cause any estrogenic effects in adult zebrafish.

A high performance liquid chromatography with ultraviolet detection was proposed for the separation and determination of relative substances in industrial arbutin and its synthetical intermediates 4-acetoxyphenol (ATP) and arbutin pentaacetate (ABPA). Liquid chromatography–mass spectrometry was used for further confirmation of these relative substances. As relative impurities, hydroquione (HQ) and 1,4-diacetoxybenzene (DATB) in industrial ATP, HQ, ATP, and DATB in industrial ABPA, and HQ, ATP, DATB, and ABPA in industrial arbutin were, respectively, quantified. As the results showed, the linearity of standard curves was excellent with relative coefficients of over 0.999 for all the detected components, and the intra- and inter-day precisions of impurities determination were satisfactory, with relative standard deviations of not more than 4.0 %. The distribution and transfer of related substances were elucidated in the synthesis process of arbutin. The established HPLC method not only has great potential in quality control of arbutin but can also be used to instruct the optimization of the synthesis procedure.

Microcystin-LR (MCLR), released by toxic cyanobacterial blooms, has received worldwide concerns in the past decades for its hepatotoxicity. Recent studies show that microcystins (MCs) can be accumulated in immune organs and exert notable immunotoxicity. In order to better understand cellular responses in immune tissues disrupted by MCLR treatment, this work mainly focuses on the spleen impairments of rats. After a subchronic 50 d exposure (1 or 10 mu g/kg body weight per day), spleen index, MCLR accumulation, histological change and plasma lysozyme activity were detected in MCLR-treated rat. Results indicated that prolonged exposure of MCLR led to toxin accumulation and caused severe damage in spleen of rats, and eventually impaired the immune functions. To further our understanding of the toxic effects of MCLR on the spleen and the mechanisms behind it, a proteomic analysis was performed to determine the global effects of MCLR on splenetic protein levels. In total, 48 proteins were identified and showed a significant increase or decrease in abundance compared to the control after MCLR exposure. These proteins are mainly involved in immune response, oxidative stress, energetic metabolism and the cytoskeleton assembly, indicating that MCLR exerts complex toxic effects in rat spleen and jointly results in immunotoxicity. (C) 2012 Elsevier B.V. All rights reserved.

The variation in mobile phase pH and ionizable solute dissociation constant (pK(a)) with the change of organic modifier fraction in hydroorganic mobile phase has seemingly been a troublesome problem in studies and applications of reversed phase high performance liquid chromatography (RP-HPLC). Most of the early studies regarding the RP-HPLC of acid-base compounds have to measure the actual pH of the mixed mobile phase rigorously, sometimes bringing difficulties in the practices of liquid chromatographic separation. In this paper, the effect of this variation on the apparent n-octanol/water partition coefficient (K(ow)″) and the related quantitative structure-retention relationship (QSRR) of logK(ow)″ vs. logk(w), the logarithm of retention factor of analytes in neat aqueous mobile phases, was investigated for weakly acidic compounds. This QSRR is commonly used as a classical method for K(ow) measurement by RP-HPLC. The theoretical and experimental derivation revealed that the variation in mobile phase pH and solute pK(a) will not affect the QSRRs of acidic compounds. This conclusion is proved to be suitable for various types of ion-suppressors, i.e., strong acid (perchloric acid), weak acid (acetic acid) and buffer salt (potassium dihydrogen phosphate/phosphoric acid, PBS). The QSRRs of logK(ow)″ vs. logk(w) were modeled by 11 substituted benzoic acids using different types of ion-suppressors in a binary methanol-water mobile phase to confirm our deduction. Although different types of ion-suppressor all can be used as mobile phase pH modifiers, the QSRR model obtained by using perchloric acid as the ion-suppressor was found to have the best result, and the slightly inferior QSRRs were obtained by using acetic acid or PBS as the ion-suppressor.

Sexual dimorphism describes the features that discriminate between the two sexes at various biological levels. Especially, during the reproductive phase, the liver is one of the most sexually dimorphic organs, because of different metabolic demands between the two sexes. The liver is a key organ that plays fundamental roles in various physiological processes, including digestion, energetic metabolism, xenobiotic detoxification, biosynthesis of serum proteins and also in endocrine or immune response. The sex-dimorphism of the liver is particularly obvious in oviparous animals, as the female liver is the main organ for the synthesis of oocyte constituents. In this work, we are interested in identifying molecular sexual dimorphism in the liver of adult medaka fish and their sex-variation in response to hepatotoxic exposures. By developing an integrative approach combining histology and different high-throughput omic investigations (metabolomics, proteomics and transcriptomics), we were able to globally depict the strong sexual dimorphism that concerns various cellular and molecular processes of hepatocytes comprising protein synthesis, amino acid, lipid and polysaccharide metabolism, along with steroidogenesis and detoxification. The results of this work imply noticeable repercussions on the biology of oviparous organisms environmentally exposed to chemical or toxin issues.

International audience; Cyanobacterial blooms often occur in freshwater lakes and constitute a potential health risk to human populations, as well as to other organisms. However, their overall and specific implications for the health of aquatic organisms that are chronically and environmentally exposed to cyanobacteria producing hepatotoxins, such as microcystins (MCs), together with other bioactive compounds have still not been clearly established and remain difficult to assess. The medaka fish was chosen as the experimental aquatic model for studying the cellular and molecular toxicological effects on the liver after chronic exposures (28 days) to environmentally relevant concentrations of pure MC-LR, complex extracts of MC producing or nonproducing cyanobacterial biomasses, and of a Microcystis aeruginosa natural bloom. Our results showed a higher susceptibility of females to the different treatments compared to males at both the cellular and the molecular levels. Although hepatocyte lysis increased with MC-containing treatments, lysis always appeared more severe in the liver of females compare to males, and the glycogen cellular reserves also appeared to decrease more in the liver of females compared to those in the males. Proteomic investigations reveal divergent responses between males and females exposed to all treatments, especially for proteins involved in metabolic and homeostasis processes. Our observations also highlighted the dysregulation of proteins involved in oogenesis in female livers. These results suggest that fish populations exposed to cyanobacteria blooms may potentially face several ecotoxicological issues.

Self-assembly processes play a key role in the fabrication of functional nano-structures with widespread application in drug delivery and micro-reactors. In addition to the thermodynamics, the kinetics of the self-assembled nano-structures also play an important role in determining the formed structures. However, as the self-assembly process is often highly heterogeneous, systematic elucidation of the dominant kinetic pathways of self-assembly is challenging. Here, based on mass flow, we developed a new method for the construction of kinetic network models and applied it to identify the dominant kinetic pathways for the self-assembly of star-like block copolymers. We found that the dominant pathways are controlled by two competing kinetic parameters: the encounter time Te, characterizing the frequency of collision and the transition time Tt for the aggregate morphology change from rod to sphere. Interestingly, two distinct self-assembly mechanisms, diffusion of an individual copolymer into the aggregate core and membrane closure, both appear at different stages (with different values of Tt) of a single self-assembly process. In particular, the diffusion mechanism dominates the middle-sized semi-vesicle formation stage (with large Tt), while the membrane closure mechanism dominates the large-sized vesicle formation stage (with small Tt). Through the rational design of the hydrophibicity of the copolymer, we successfully tuned the transition time Tt and altered the dominant self-assembly pathways.

The utilization of neutral compounds as model compounds is put forward for determination of the n-octanol/water partition coefficient (K(ow)) of highly hydrophobic, weak acidic compounds by reversed-phase high performance liquid chromatography (RP-HPLC). It is based on a linear relationship between the logarithm of apparent n-octanol/water partition coefficient (log K(ow)″), expressing hydrophobicity of acidic solutes more accurately, and the logarithm of RP-HPLC retention factor of the solutes corresponding to the neat aqueous fraction of mobile phase (log k(w)). The availability of neutral model compounds was theoretically tested for this novel protocol. Moreover, a high consistency of linear log K(ow)″-log k(w) correlations was demonstrated between a mixed training set of neutral and acidic model compounds, and a training set of neutral model compounds. It is proved in theory that for a certain set of compounds investigated, all derived linear relationships between log K(ow)″ and log k(w) have a unit slope and the same intercept, regardless of mobile phase pH. This model was applied to measure log K(ow) of lipophilic aristolochic acid I (AA I) and aristolochic acid II (AA II). Log K(ow) values for AA I and AA II are 4.45±0.07 and 3.99±0.06, respectively. To the best of our knowledge, this is the first report on experimental log K(ow) data for AAs. The proposed strategy solves the problem of lacking suitable acidic model compounds with reliable experimental K(ow) in determining K(ow) of lipophilic acidic solutes by RP-HPLC.

An ion suppression reversed phase high performance liquid chromatography method has been developed for the determination of 2,6-di-tert-butylphenol in Irganox 1425. Separation was carried out on a Welch Material Ultimate XB-C18 column (5 μm, 150 mm × 4.6 mm), using methanol–water (0.1 % HClO4) (75/25, v/v) mixture as the mobile phase in an isocratic elution. Detection was performed by UV absorption at a wavelength of 275 nm, and the limit of detection was 0.2 μg/mL. The method presented excellent repeatability and precision with both intra- and inter-day relative standard deviations (RSDs) of less than 2.0 %, as well as satisfactory accuracy with the recovery of 98.7–102.3 %, and therefore can be applied for the quality control analysis of Irganox 1425 industrial product.

The retention factor corresponding to pure water in reversed-phase high performance liquid chromatography (RP-HPLC), k(w), was commonly obtained by extrapolation of retention factor (k) in a mixture of organic modifier and water as mobile phase in tedious experiments. In this paper, a relationship between logk(w) and logk for directly determining k(w) has been proposed for the first time. With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of k(w) for compounds in question with similar structure to model compounds. Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the logk(w)-logk correlation on both silica-based C(8) and C(18) stationary phases to evaluate logk(w) of sample compounds including seven PCB, six PBB and eight PBDE congeners. These eight model PCBs were subsequently combined with seven structure-similar benzene derivatives possessing reliable experimental K(ow) values as a whole training set for logK(ow)-logk(w) regressions on the two stationary phases. Consequently, the evaluated logk(w) values of sample compounds were used to determine their logK(ow) by the derived logK(ow)-logk(w) models. The logK(ow) values obtained by these evaluated logk(w) were well comparable with those obtained by experimental-extrapolated logk(w), demonstrating that the proposed method for logk(w) evaluation in this present study could be an effective means in lipophilicity study of environmental contaminants with numerous congeners. As a result, logK(ow) data of many PCBs, PBBs and PBDEs could be offered. These contaminants are considered to widely exist in the environment, but there have been no reliable experimental K(ow) data available yet.

In this paper, cobalt (Co(2+))-doped (CoD) ZnS quantum dots (QDs) are synthesised in aqueous solution and characterised for the first time. L-Cysteine (L-Cys) ligands on the surface of CoD ZnS QDs can bind 2,4,6-trinitrotoluene (TNT) to form Meisenheimer complexes (MHCs) mainly through acid-base pairing interactions between TNT and L-Cys and the assistance of hydrogen bonding and electrostatic co-interactions among L-Cys intermolecules. The aggregation of inter-dots induced by MHCs greatly influenced the light scattering property of the QDs in aqueous solution, and Rayleigh scattering (RS) enhancement at the defect-related emission wavelengths as well as its left side was observed with the excitation of CoD ZnS QDs by violet light. RS enhancement, combining with the quenching of the orange transition emission induced by TNT anions, resulted in a change in the ratiometric visualisation of the system being investigated. A novel CoD ZnS QD-based hybrid ratiometric chemosensor has therefore been developed for simple and sensitive analysis of TNT in water. This ratiometric probe can assay down to 25 nM TNT in solution without interference from a matrix of real water sample and other nitroaromatic compounds. Because of the excellent electron-accepting ability and strong affinity of TNT to L-Cys on the surface of CoD ZnS QDs, the CoD photoluminescent nanomaterials reported here are well suited for detecting ultra-trace TNT and for distinguishing different nitro-compounds in aqueous solution.

A reversed-phase high-performance liquid chromatography (RP-HPLC) with ultraviolet detection was established for the determination of phenol, catechol, hydroquinone, and p-benzoquinone in the reaction solution of catalytic oxidation of phenol using hydrogen peroxide as the oxidant and copper-doped FeSBA-15 zeolite as the catalyst. Separation was accomplished on a reversed-phase C18 column, and the elution condition was optimized by changing the composition of the mobile phase. A good resolution of all of the relative components in the reaction solution was achieved when the mobile phase was methanol–water–1% acetic acid aqueous solution = 10:50:40 (v/v/v). The concentrations of phenol, catechol, hydroquinone, and p-benzoquinone were determined in 11 different reaction solutions by the external standard method. The proposed HPLC method was simple, accurate, reliable, and suitable for tracing the amount of target products during the catalytic oxidation reaction of phenol. The results can provide data support for evaluating the properties of catalysts, and, thus, guide the selection of catalysts for the industrial production of dihydric phenol.

n-Octanol/water partition coefficients (P) for DDTs and dicofol were determined by reversed-phase high performance liquid chromatography (RP-HPLC) on a C(18) column using methanol-water mixture as mobile phase. A dual-point retention time correction (DP-RTC) was proposed to rectify chromatographic retention time (t(R)) shift resulted from stationary phase aging. Based on this correction, the relationship between logP and logk(w), the logarithm of the retention factor extrapolated to pure water, was investigated for a set of 12 benzene homologues and DDT-related compounds with reliable experimental P as model compounds. A linear regression logP=(1.10±0.04) logk(w) - (0.60±0.17) was established with correlation coefficient R(2) of 0.988, cross-validated correlation coefficient R(cv)(2) of 0.983 and standard deviation (SD) of 0.156. This model was further validated using four verification compounds, naphthalene, biphenyl, 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (p,p'-DDD) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (p,p'-DDE) with similar structure to DDT. The RP-HPLC-determined P values showed good consistency with shake-flask (SFM) or slow-stirring (SSM) results, especially for highly hydrophobic compounds with logP in the range of 4-7. Then, the P values for five DDT-related compounds, 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1,1-trichloroethane (o,p'-DDT), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethane (o,p'-DDD), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethene (o,p'-DDE), and 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol (dicofol) and its main degradation product 4,4'-dichlorobenzophenone (p,p'-DBP) were evaluated by the improved RP-HPLC method for the first time. The excellent precision with SD less than 0.03 proved that the novel DP-RTC protocol can significantly increases the determination accuracy and reliability of P by RP-HPLC.

A reliable reversed-phase high-performance liquid chromatographic method has been developed for analysis of related impurities in industrial phthalic anhydride (PA). Maleic acid (hydrolysis product of maleic anhydride), phthalimide, and benzoic acid were separated from phthalic acid (Pa, hydrolysis product of PA) on a C18 column by gradient elution with acetonitrile and 0.1% (v/v) aqueous perchloric acid solution. This method is simple, sensitive, and accurate, and has been successfully applied to quality control of PA for industrial use.

A combination of gas chromatography and mass spectrometry (GC-MS) was applied to separate and identify the relative substances in 2-chloroethyl phenyl sulfide (CEPS), an industrial intermediate formed in the synthesis of sulfinpyrazone. Six impurities, including 1,2-dichloroethane, thiophenol, diethylmalonate, tributylamine, diphenyl disulfide, and 1,2-dithiophenylethane, were verified. According to the production technique, the sources of all of these related impurities were analyzed, and some practical suggestions are put forward for their removal from or avoidance in CEPS. Furthermore, a technique involving high-performance liquid chromatography with UV detection (HPLC-UV) was developed to separate and determine thiophenol, the key impurity in CEPS. A linear standard curve was obtained for thiophenol in concentrations between 2.65 × 10−4 and 0.106 mg mL−1, and the detection limit of thiophenol was 1.32 × 10−4 mg mL−1. Excellent precision and accuracy were shown from the method validation, with relative...

A high-performance liquid chromatographic method was proposed for the separation of relative impurities in industrial 3-methylflavone-8-carboxylic acid (MFCA) and its intermediate methyl 3-propionylsalicylate (MPS). Benzoic acid (BA), MPS, 6-chloro-3-methylflavone-8-carboxylic acid (MFCA-Cl) and methyl 5-chloro-3-propionylsalicylate (MPS-Cl) in MFCA, and MPS-Cl in MPS were respectively quantified by an external standard method. As results showed, the linearity of standard curves was excellent with the relative coefficients of over 0.999 for all the detected components, and the intra- and inter-day precisions of impurities determination were satisfactory with the relative standard deviation of not more than 8.0%. Under the selected experimental condition, the chromatographic fingerprints of MFCA and MPS were drawn synthetically, and the transfer of impurities in the stepwise reactions of MFCA manufacture was elucidated. The fingerprints have great potential in instructing the production of MFCA for industrial use and in conducting the conversion of relative impurities.

A high performance liquid chromatography−photodiode array detection−electrospray ionization mass spectrometry (HPLC-PDA-ESIMS) method has been developed for separation and identification of relativ...

Two semi-flexible 4,4′-bispyridyl ligands, N,N′-bis(4-pyridylethyl) pyromellitic diimide (4-pepmd) and N,N′-bis(4-pyridylmethyl)pyromellitic diimide (4-pmpmd), with different linker length, and their coordination polymers obtained by reaction with M(NO3)2 (M = Co or Cd) in mixed CHCl3 and ROH solvents are reported. 2D (6,3) brick-wall networks with Py3M nodes for the isostructural [Co(4-pepmd)1.5(NO3)2]n · nCHCl3 · 2nH2O · nEtOH (1) and [Cd(4-pepmd)1.5(NO3)2]n · nCHCl3 · nH2O · 2nMeOH (2), and 1D zigzag chain with Py2M nodes for [Co(4-pmpmd)(NO3)2]n · nCHCl3 (3) are observed. The ligand 4-pepmd with longer linker –(CH2)2– induces exclusively trispyridyl building blocks and 2D networks in its Co and Cd complexes, while the coordination preference of metal ions works more effectively for shorter linked 4-pmpmd to give either 1D (for Co, 3) or 2D [Cd(4-pmpmd)1.5(NO3)2]n · nCHCl3 (4) [10] polymer depending on the size of the metal ion.

Introduction Osteoarthritis is an inflammatory disorder associated with oxidative stress and apoptosis leading to cartilage destruction and impairment of cartilage formation. In the present study, we studied the protective effect of lutein against monosodium iodoacetate (MIA)-induced osteoarthritis in primary chondrocyte cells. Material and methods Oxidative stress was determined through testing antioxidant status, reactive oxygen species levels and lipid peroxide content. Also, Nrf2 expression and its downstream target genes HO-1 and NQO-1 were determined. Inflammation was analyzed through NF-κB, COX-2 and pro-inflammatory cytokines (IL-6, TNF-α, IL-1β). In addition, the effects of MIA and lutein on mitochondrial membrane potential and caspase-3 levels were analyzed. Results The results showed that lutein treatment significantly increased the cell viability of chondrocytes and offered significant cytoprotection by enhancing the antioxidant defense mechanisms and reducing oxidative stress (reactive oxygen species and lipid peroxidation). Lutein treatment showed anti-inflammatory effects by downregulating inflammatory proteins (NF-κB, COX-2) and pro-inflammatory cytokines (IL-6, TNF-α, IL-1β). Lutein reduced MIA-induced apoptosis through maintaining mitochondrial membrane potential and downregulating caspase-3 activity. Conclusions The present study shows significant cytoprotection offered by lutein against MIA-induced oxidative stress, inflammation and apoptosis by the modulatory effect of NF-κB and Nrf2 activation.

Toxic cyanobacterial blooms, which produce cyclic heptapeptide toxins known as microcystins, are worldwide environmental problems. On the other hand, the cyanobacteria protein (30–50%) has been recommended as substitute protein for aquaculture. The present laboratory study verified the feasibility of cyanobacteria protein substitution and risk assessment. Goldfish were fed diets supplemented lyophilised cyanobacteria powder for 16 weeks with the various doses: 0% (control), 10%, 20%, 30% and 40%. Low doses (10% and 20%) promoted growth whereas high doses (30% and 40%) inhibited growth. In cyanobacteria treated fish, the proximate composition of ash, crude fat content and crude protein content decreased in 16 weeks; the saturated fatty acid (SFA) content significantly increased; the n-3 polyunsaturated fatty acid content, collagen content and muscle pH significantly decreased; cooking loss percents increased significantly. Muscle fiber diameter and myofibril length were negatively correlation. Additionally, flavour compounds (e.g., amino acids, nucleotides, organic acids and carnosine) changed significantly in the treated fish and odour compounds geosmin and 2-methylisoborneol increased significantly. The estimated daily intake (EDI) of microcystins in muscle was close to or exceeded the World Health Organization (WHO) tolerable daily intake (TDI), representing a great health risk. Cyanobacterie is not feasible for protein sources use in aquaculture.