Analytical and Bioanalytical Chemistry (v.409, #24)

Social impact of analytical chemistry by Günter Gauglitz (5613-5614).
is Senior Professor at the Eberhard Karls University of Tübingen working in analytical and physical chemistry. He was Chairman of the Division of Analytical Chemistry of the German Chemical Society, and chaired the Europt(r)ode VIII meeting. For more than 15 years, his main scientific interests have centered on research and development in chemical and biochemical sensors with special focus on the characterization of interfaces of polymers and biomembrane surfaces, spectroscopic techniques, use of spectral interferometry to monitor changes in the optical thickness of thin layers, and the effects of Fresnel reflectivity at interfaces. He has been an editor of Analytical and Bioanalytical Chemistry since 2002.

is a postgraduate student in the Department of Environmental Science and Analytical Chemistry, Stockholm University, and has worked on method development for polycyclic aromatic hydrocarbon analysis using multidimensional chromatographic and mass spectrometric techniques. has a PhD degree in analytical chemistry from Stockholm University. She has been working on the development and validation of analytical chemical methods for trace analysis of carcinogenic organic compounds using multidimensional chromatographic methods consisting of liquid chromatography coupled with gas chromatography/mass spectrometry. She is a chemist at the Swedish National Food Agency. is an analytical chemist. He studied and obtained his PhD degree in the Department of Analytical Chemistry at Stockholm University. His research interest is the development and validation of methods for the determination of polycyclic aromatic compounds. Special focus has been on the use of highly automated and multidimensional methods consisting of liquid chromatography coupled with gas chromatography/mass spectrometry. is Professor of Analytical Chemistry in the Department of Environmental Science and Analytical Chemistry, Stockholm University. His research covers a broad spectrum of analytical methods, from sampling techniques to online analytical techniques of liquid/gas chromatography coupled with mass spectrometry. The compounds of interest are polycyclic aromatic compounds in general. An online two-dimensional (2D) liquid chromatography/2D gas chromatography system with two mass-selective detectors has been developed on the basis of a previous system with two flame ionization detectors. The method translation involved the change of carrier gas from hydrogen to helium, column dimension and detectors. The 2D system with two mass-selective detectors was validated with use of polycyclic aromatic hydrocarbon (PAH) standards and two standard reference materials from air and diesel exhaust. Furthermore, the system was applied to a real sample, wood smoke particulates. The PAH values determined correlated well with the previous data and those from the National Institute of Standards and Technology. The system enhanced the benefits of the previous system, which were limited by the low detectability and lack of mass selectivity. This study shows an automated 2D system that is valid for PAH analysis of complex environmental samples directly from crude extracts. Graphical Abstract Schematic illustration showing on-line clean-up, separation and detection using 2D-LC/2D-GC/MS
Keywords: Polycyclic aromatic hydrocarbon; Multidimensional gas chromatography; Standard reference material; Wood smoke particulates; Long-term stability

Exploring the peptide retention mechanism in molecularly imprinted polymers by Cecilia Rossetti; Odd Gøran Ore; Börje Sellergren; Trine Grønhaug Halvorsen; Léon Reubsaet (5631-5643).
The authors would like to call the reader’s attention to the fact that unfortunately due to the file formatting during the exporting of the data matrix from the program Unscrambler (used for the development of the statistical model) to the Word office file.is a PhD candidate in the School of Pharmacy, University of Oslo, Norway. Her research interests have focused on targeted proteomics with the development of liquid chromatography–tandem mass spectrometry methods for the analysis of peptides and antibodies. She has been studying the implementation of affinity-based materials such as molecularly imprinted polymers in multiple sample preparation platforms for the analysis of biological fluids. has a master degree in pharmacy from the School of Pharmacy, University of Oslo, Norway. During his master research, he evaluated retention mechanisms of tryptic peptides in molecularly imprinted polymers using a micro solid-phase extraction format and liquid chromatography–tandem mass spectrometry. is Professor of Biomedical Technology in the Department of Biomedical Sciences, Malmö University, Sweden, and Vice President of the Society of Molecular Imprinting. His research is focused on molecular imprinting, biomimetic systems and molecular self-assembly, and applications of artificial receptors in the life sciences. is Associate Professor of Pharmaceutical Analysis in the School of Pharmacy, University of Oslo, Norway. Her background is in bioanalysis of drugs and protein biomarkers using liquid chromatography–tandem mass spectrometry. She focuses on novel sampling materials for dried blood spot analysis of proteins and affinity-based sample preparation of proteins and peptides from biological matrices. is Professor of Drug Analysis in the School of Pharmacy, University of Oslo, Norway, and Chair of the Norwegian Society of Mass Spectrometry. He has more than two decades of experience with liquid chromatography–tandem mass spectrometry based peptide and protein analysis. For the past 10 years he also focused on affinity extractions based on antibodies and molecular imprints of peptides and proteins with diagnostic value from biological matrices. Molecularly imprinted polymers (MIPs) have been used as useful sorbents in solid-phase extraction for a wide range of molecules and sample matrices. Their unique selectivity can be fine-tuned in the imprinting process and is crucial for the extraction of macromolecules from complex matrices such as serum. A relevant example of this is the application of MIPs to peptides in diagnostic assays. In this article the selectivity of MIPs, previously implemented in a quantitative mass-spectrometric assay for the biomarker pro-gastrin-releasing peptide, is investigated. Partial least squares regression was used to generate models for the evaluation and prediction of the retention mechanism of MIPs. A hypothesis on interactions of MIPs with the target peptide was verified by ad hoc experiments considering the relevant peptide physicochemical properties highlighted from the multivariate analysis. Novel insights into and knowledge of the driving forces responsible for the MIP selectivity have been obtained and can be directly used for further optimization of MIP imprinting strategies. Graphical Abstract Applied analytical strategy: the Solid Phase Extraction (SPE) of digested Bovin Serum Albumin (BSA), using Molecularly Imprinted Polymers (MIP), is followed by the liquid chromatography-mass spectrometry (LC-MS) analysis for the identification of the retained peptides. The further application of multivariate analysis allows setting up a Partial Least Square (PLS) model, which describes the peptide retention into the MIP and gives additional knowledge to be used in the optimization of the MIP and the whole SPE method
Keywords: Peptide enrichment; Pro-gastrin-releasing peptide; Molecularly imprinted polymers; Liquid chromatography–mass spectrometry; Partial least squares; Solid-phase extraction

Novel ribonuclease activity of cusativin from Cucumis sativus for mapping nucleoside modifications in RNA by Balasubrahmanyam Addepalli; Sarah Venus; Priti Thakur; Patrick A. Limbach (5645-5654).
A recombinant ribonuclease, cusativin, was characterized for its cytidine-specific cleavage ability of RNA to map chemical modifications. Following purification of native cusativin protein as described before (Rojo et al. Planta 194:328, 17), partial amino acid sequencing was carried out to identify the corresponding protein coding gene in cucumber genome. Cloning and heterologous expression of the identified gene in Escherichia coli resulted in successful production of active protein as a C-terminal His-tag fusion protein. The ribonuclease activity and cleavage specificity of the fusion protein were confirmed with a variety of tRNA isoacceptors and total tRNA. Characterization of cusativin digestion products by ion-pairing reverse-phase liquid chromatography coupled with mass spectrometry (IP-RP-LC-MS) analysis revealed cleavage of CpA, CpG, and CpU phosphodiester bonds at the 3′-terminus of cytidine under optimal digestion conditions. Ribose methylation or acetylation of cytosine inhibited RNA cleavage. The CpC phosphodiester bond was also resistant to cusativin-mediated RNA cleavage; a feature to our knowledge has not been reported for other nucleobase-specific ribonucleases. Here, we demonstrate the analytical utility of such a novel feature for obtaining high-sequence coverage and accurate mapping of modified residues in substrate RNAs. Graphical abstract Cytidine-specific novel ribonuclease activity of cusativin
Keywords: Cusativin; Cytidine-specific; Modification mapping; Acetylation; LC-MS

Development of a lateral flow dipstick immunoassay for evaluation of folate levels in maize by Qiuju Liang; Chen Yi; Ling Jiang; Guiyu Tan; Chunyi Zhang; Baomin Wang (5655-5660).
Folates (vitamin B9) are essential for all organisms as cofactors for one-carbon metabolism. However, measurement of folates is technically complicated and time-consuming. In this study, we developed a dipstick immunoassay using a folate-specific monoclonal antibody (mAb), allowing rapid and low-cost detection of folates. The indicator range of the dipstick for 5-formylterahydrofolate (5-CHO-THF), 5-methyltetrahydrofolate (5-CH3-THF) and their polyglutamyl forms was 100–200 ng mL−1; moreover, no cross-reactivity was observed with tetrahydrofolate (THF) or 5,10-methenyltetrahydrofolate (5,10-CH=THF) at 500 ng mL–1, or with the folate precursors pterin-6-COOH, p-aminobenzoate (pABA), and L-glutamate, or with the folate analogues methotrexate and 10-formyltetrahydrofolate (10-CHO-THF) at up to 1000 ng mL−1. The dipstick immunoassay was tested in maize seeds; the results classified the seeds into those with low, moderate, and high levels of folates, and were in agreement with those of liquid chromatography-mass spectrometry. Thus, we conclude that the dipstick assay will provide a versatile tool to facilitate large-scale screening of maize rich in folates. Graphical Abstract The dipstick based immunoassay for analyzing folate level in maize
Keywords: Folates; Dipstick; Immunoassay; Maize

TLC surface integrity affects the detection of alkali adduct ions in TLC-MALDI analysis by Yonghui Dong; Ruggero Ferrazza; Andrea Anesi; Graziano Guella; Pietro Franceschi (5661-5666).
Direct coupling of thin-layer chromatography (TLC) with matrix-assisted laser desorption ionization (MALDI) mass spectrometry allows fast and detailed characterization of a large variety of analytes. The use of this technique, however, presents great challenges in semiquantitative applications because of the complex phenomena occurring at the TLC surface. In our laboratory, we recently observed that the ion intensities of several alkali adduct ions were significantly different between the top and interior layer of the TLC plate. This indicates that the integrity of the TLC surface can have an important effect on the reproducibility of TLC- MALDI analyses. Graphical Abstract MALDI imaging reveals that surface integrity affects the detection of alkali adductions in TLC-MALDI.
Keywords: TLC-MALDI; MS imaging; Alkali-metal ions; Lipid

Disposable electrochemical immunosensor for Brettanomyces bruxellensis based on nanogold-reduced graphene oxide hybrid nanomaterial by Boryana Borisova; María L. Villalonga; María Arévalo-Villena; Abderrahmane Boujakhrout; Alfredo Sánchez; Concepción Parrado; José M. Pingarrón; Ana Briones-Pérez; Reynaldo Villalonga (5667-5674).
The assembly of a novel disposable amperometric immunosensor for the detection of the red wine spoilage yeast Brettanomyces bruxellensis is reported. The nanostructured sensing interface was prepared by first coating carbon screen printed electrodes with a gold nanoparticles-reduced graphene oxide hybrid nanomaterial, which was then modified with 3-mercaptopropionic acid to further immobilize specific antibodies for B. bruxellensis via a carbodiimide-coupling reaction. The functionalized electrode allowed the amperometric detection of B. bruxellensis in buffered solutions and red wine samples in the range of 10–106 CFU/mL and 102–106 CFU/mL, with low detection limits of 8 CFU/mL and 56 CFU/mL, respectively. The electrochemical immunosensor also exhibited high reproducibility, selectivity, and storage stability. Graphical abstract A novel disposable electrochemical immunosensor for the detection of the red wine spoilage yeast B. bruxellensis
Keywords: Brettanomyces bruxellensis ; Biosensor; Graphene; Screen printed electrode; Red wine

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for quantitation of paralytic shellfish toxins: validation and application to reference materials by Krista M. Thomas; Daniel G. Beach; Kelley L. Reeves; Ryan S. Gibbs; Elliott S. Kerrin; Pearse McCarron; Michael A. Quilliam (5675-5687).
Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by marine dinoflagellates that are responsible for paralytic shellfish poisoning (PSP) in humans. This work highlights our ongoing efforts to develop quantitative methods for PSTs using hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS). Compared with the commonly used method of liquid chromatography with post-column oxidation and fluorescence detection (LC-ox-FLD), HILIC-MS/MS has the potential of being more robust, sensitive and straightforward to operate, and provides unequivocal confirmation of toxin identity. The main driving force for the present work was the need for a complementary method to LC-ox-FLD to assign values to shellfish tissue matrix reference materials for PSTs. Method parameters that were optimized included LC mobile and stationary phases, electrospray ionization (ESI) conditions, and MS/MS detection parameters. The developed method has been used in the detection and identification of a wide range of PSTs including less common analogues and metabolites in a range of shellfish and algal samples. We have assessed the matrix effects of shellfish samples and have evaluated dilution, standard addition and matrix matched calibration as means of mitigating them. Validation on one LC-MS/MS system for nine common PST analogues (GTX1-4, dcGTX2&3, STX, NEO, and dcSTX) was completed using standard addition. The method was then transferred to a more sensitive LC-MS/MS system, expanded to include five more PSTs (C1&2, dcNEO and GTX5&6) and validated using matrix matched calibration. Limits of detection of the validated method ranged between 6 and 280 nmol/kg tissue using standard addition in extracts of blue mussels, with recoveries between 92 and 108%. Finally, this method was used in combination with the AOAC Official Method based on LC-ox-FLD to measure PSTs in a new mussel tissue matrix reference material.
Keywords: Hydrophilic interaction liquid chromatography; Mass spectrometry; Algal toxins; Paralytic shellfish poisoning; Reference material

Determination of ketones and ethyl acetate—a preliminary study for the discrimination of patients with lung cancer by Patricia Martín Santos; Miguel del Nogal Sánchez; Ángel Pedro Crisolino Pozas; José Luis Pérez Pavón; Bernardo Moreno Cordero (5689-5696).
In this work, ten possible volatile biomarkers of lung cancer (acetone, 2-butanone, ethyl acetate, 2-pentanone, 4-methyl-2-pentanone, 2-hexanone, 3-heptanone, 2-heptanone, 3-octanone, and 2-nonanone) have been analyzed to evaluate their different concentration levels in urine samples from lung cancer patients (n = 12) and healthy controls (n = 12). The volatile compounds were generated with a headspace autosampler and analyzed with a gas chromatograph equipped with a programmed temperature vaporizer and mass spectrometry detector (HS-PTV-GC-MS). With the aim of evaluating the aforementioned differences, a Mann-Whitney U test and box-plots were obtained. Very good discrimination between cancer and control groups was achieved for three (ethyl acetate, 3-heptanone, and 3-octanone) of the ten analytes studied. With a view to assigning samples to the group of healthy or ill individuals, the Wilcoxon signed-rank test has been used. In spite of the small number of urine samples assayed, the results may suggest that the studied compounds could be considered useful tools in order to discern samples and they could be employed as a complementary test in a diagnosis. Graphical abstract Classification of samples (lung cancer patients and controls) with the Wilcoxon signed rank test.
Keywords: Volatile biomarkers; Urine; Lung cancer; Mass spectrometry

A simple and efficient three-step sample preparation method was developed and optimized for the simultaneous analysis of illegal anionic and cationic dyes (acid orange 7, metanil yellow, auramine-O, and chrysoidine) in food samples. A novel solid-phase extraction (SPE) procedure based on nanofibers mat (NFsM) was proposed after solvent extraction and freeze-salting out purification. The preferred SPE sorbent was selected from five functionalized NFsMs by orthogonal experimental design, and the optimization of SPE parameters was achieved through response surface methodology (RSM) based on the Box-Behnken design (BBD). Under the optimal conditions, the target analytes could be completely adsorbed by polypyrrole-functionalized polyacrylonitrile NFsM (PPy/PAN NFsM), and the eluent was directly analyzed by high-performance liquid chromatography-diode array detection (HPLC-DAD). The limits of detection (LODs) were between 0.002 and 0.01 mg kg−1, and satisfactory linearity with correlation coefficients (R > 0.99) for each dye in all samples was achieved. Compared with the Chinese standard method and the published methods, the proposed method was simplified greatly with much lower requirement of sorbent (5.0 mg) and organic solvent (2.8 mL) and higher sample preparation speed (10 min/sample), while higher recovery (83.6–116.5%) and precision (RSDs < 7.1%) were obtained. With this developed method, we have successfully detected illegal ionic dyes in three common representative foods: yellow croaker, soybean products, and chili seasonings. Graphical abstract Schematic representation of the process of the three-step sample preparation.
Keywords: Solid-phase extraction; Functionalized nanofibers mat; Illegal ionic dyes; Food analysis

Optical biosensor optimized for continuous in-line glucose monitoring in animal cell culture by Mircea Tric; Mario Lederle; Lisa Neuner; Igor Dolgowjasow; Philipp Wiedemann; Stefan Wölfl; Tobias Werner (5711-5721).
Biosensors for continuous glucose monitoring in bioreactors could provide a valuable tool for optimizing culture conditions in biotechnological applications. We have developed an optical biosensor for long-term continuous glucose monitoring and demonstrated a tight glucose level control during cell culture in disposable bioreactors. The in-line sensor is based on a commercially available oxygen sensor that is coated with cross-linked glucose oxidase (GOD). The dynamic range of the sensor was tuned by a hydrophilic perforated diffusion membrane with an optimized permeability for glucose and oxygen. The biosensor was thoroughly characterized by experimental data and numerical simulations, which enabled insights into the internal concentration profile of the deactivating by-product hydrogen peroxide. The simulations were carried out with a one-dimensional biosensor model and revealed that, in addition to the internal hydrogen peroxide concentration, the turnover rate of the enzyme GOD plays a crucial role for biosensor stability. In the light of this finding, the glucose sensor was optimized to reach a long functional stability (>52 days) under continuous glucose monitoring conditions with a dynamic range of 0–20 mM and a response time of t 90 ≤ 10 min. In addition, we demonstrated that the sensor was sterilizable with beta and UV irradiation and only subjected to minor cross sensitivity to oxygen, when an oxygen reference sensor was applied. Graphical abstract Measuring setup of a glucose biosensor in a shake flask for continuous glucose monitoring in mammalian cell culture
Keywords: Optical biosensor; Glucose monitoring; Bioreactor; Cell culture

Cereal-based beverages contain a complex mixture of various polymeric macromolecules including polysaccharides, peptides, and polyphenols. The molar mass of polymers and their degradation products affect different technological and especially sensory parameters of beverages. Asymmetrical flow field-flow fractionation (AF4) coupled with multi-angle light scattering (MALS) and refractive index detection (dRI) or UV detection (UV) is a technique for structure and molar mass distribution analysis of macromolecules commonly used for pure compound solutions. The objective of this study was to develop a systematic approach for identifying the polymer classes in an AF4//MALS/dRI/UV fractogram of the complex matrix in beer, a yeast-fermented cereal-based beverage. Assignment of fractogram fractions to polymer substance classes was achieved by targeted precipitations, enzymatic hydrolysis, and alignments with purified polymer standards. Corresponding effects on dRI and UV signals were evaluated according to the detector’s sensitivities. Using these techniques, the AF4 fractogram of beer was classified into different fractions: (1) the low molar mass fraction was assigned to proteinaceous molecules with different degrees of glycosylation, (2) the middle molar mass fraction was attributed to protein–polyphenol complexes with a coelution of non-starch polysaccharides, and (3) the high molar mass fraction was identified as a mixture of the cell wall polysaccharides (i.e., β-glucan and arabinoxylan) with a low content of polysaccharide–protein association. In addition, dextrins derived from incomplete starch hydrolysis were identified in all fractions and over the complete molar mass range. The ability to assess the components of an AF4 fractogram is beneficial for the targeted design and evaluation of polymers in fermented cereal-based beverages and for controlling and monitoring quality parameters.
Keywords: Beer; FFF; AF4; Macromolecules; Protein; Polysaccharide; Polymer

Profiling of cardiolipins and their hydroperoxides in HepG2 cells by LC/MS by Zhen Chen; Yue Wu; Yi-Shing Ma; Yuu Kobayashi; Yao-Yao Zhao; Yusuke Miura; Hitoshi Chiba; Shu-Ping Hui (5735-5745).
Cardiolipin (CL) exists as crucial functional phospholipid in mitochondria. The oxidation of CL is concerned with mitochondrial dysfunction and various diseases. As main oxidation products, CL hydroperoxide (CL-OOH) plays a key role in intermediating oxidative reaction. Thus, direct analysis of CL-OOH is of great interest. In the present study, CL and CL-OOH profiles were analyzed in oxidized HepG2 cell lipid via HPLC-Orbitrap MS/MS. Furthermore, the contents of individual molecular species were compared between intact and AAPH-oxidized HepG2 cells. In total, 46 CL and 18 CL-OOH were identified from oxidized cell lipids, while 21 CL and 9 CL-OOH were detected in AAPH-treated cells. Most CL depleted significantly after AAPH inducement, with percentages varying from 8.3% (CL70:7) to 73.7% (CL72:4), depending on fatty acyl composition. While almost all the CL-OOH remarkably increased, among them 68:6-, 72:6-, and 72:7-OOHs were only detected in AAPH-treated cells. CL68:5- and CL68:4-OOH were the most abundant species, while CL70:5-OOH among all the species expressed the highest oxidation percentage of the corresponding CL. Our results showed practical separation, identification, and semi-quantitation of CL-OOH species, which could contribute to approaches to lipidomic analysis of CL and CL-OOH, as well as tracing biomarkers in mitochondrial oxidative stress diagnosis. Graphical abstract Illustration represents cardiolipin hydroperoxide structure and its content increasing in AAPH-treated HepG2 cells by LC/MS analysis
Keywords: Cardiolipin; Lipid hydroperoxides; CL-OOH; Molecular species; Mitochondria; LC-HR-MS/MS

New approach in evaluation of ceramic-polymer composite bioactivity and biocompatibility by Leszek Borkowski; Anna Sroka-Bartnicka; Izabela Polkowska; Marta Pawlowska; Krzysztof Palka; Emil Zieba; Anna Slosarczyk; Krzysztof Jozwiak; Grazyna Ginalska (5747-5755).
Regeneration of bone defects was promoted by a novel β-glucan/carbonate hydroxyapatite composite and characterized by Raman spectroscopy, microCT and electron microscopy. The elastic biomaterial with an apatite-forming ability was developed for bone tissue engineering and implanted into the critical-size defects of rabbits’ tibiae. The bone repair process was analyzed on non-decalcified bone/implant sections during a 6-month regeneration period. Using spectroscopic methods, we were able to determine the presence of amides, lipids and assign the areas of newly formed bone tissue. Raman spectroscopy was also used to assess the chemical changes in the composite before and after the implantation process. SEM analyses showed the mineralization degree in the defect area and that the gap size decreased significantly. Microscopic images revealed that the implant debris were interconnected to the poorly mineralized inner side of a new bone tissue. Our study demonstrated that the composite may serve as a biocompatible background for collagen ingrowth and exhibits the advantages of applying Raman spectroscopy, SEM and microCT in studying these samples.
Keywords: Bioactivity; Biomaterials; Bone substitutes; Carbonate hydroxyapatite; Mineralization; Raman spectroscopy; SEM

Fluorescent light-up probes based on aggregation-induced emission (AIE)-active molecules have recently attracted great research interest due to the intelligent fluorescence activation mechanism and high sensitivity. In this work, an AIE-silica nanosphere (SiO2 NP)-based label-free fluorescent aptasensor for the sensitive “turn-on” detection of prostate-specific antigen (PSA) is reported for the first time. The positively charged amino-functionalized SiO2 NPs were used as efficient nanocapturer to electrostatically adsorb single-stranded PSA aptamer (PA) to form SiO2 NP-PA nanocomposite as well as adsorb negatively charged tetraphenylethylene derivative 3 (TPE3) to form AIE-SiO2 NP nanocomposite. The binding of the aptamer to the target PSA could induce a rigid aptamer conformation, resulting in the release of the PA away from the surface of SiO2 NPs. This made the AIE molecules TPE3 aggregate on the SiO2 NP surface and emit high fluorescence. With the advantages of simple design and rapid responses, the proposed aptasensor showed high sensitivity and selectivity for PSA with a detection limit of 0.5 ng/mL. The aptasensor was further applied in human serum samples with satisfactory results. Given its versatility, high selectivity, and sensitivity, the proposed method could be extended to other targets by varying the recognition probes. Graphical abstract An AIE-SiO2 NP-based label-free fluorescent aptasensor for the sensitive “turn-on” detection of PSA is reported for the first time
Keywords: Aggregation-induced emission; Silica nanoparticle; Aptasensor; Fluorescence; Prostate-specific antigen

Optimized experimental workflow for tandem mass spectrometry molecular networking in metabolomics by Florent Olivon; Fanny Roussi; Marc Litaudon; David Touboul (5767-5778).
New omics sciences generate massive amounts of data, requiring to be sorted, curated, and statistically analyzed by dedicated software. Data-dependent acquisition mode including inclusion and exclusion rules for tandem mass spectrometry is routinely used to perform such analyses. While acquisition parameters are well described for proteomics, no general rule is currently available to generate reliable metabolomic data for molecular networking analysis on the Global Natural Product Social Molecular Networking platform (GNPS). Following on from an exploration of key parameters influencing the quality of molecular networks, universal optimal acquisition conditions for metabolomic studies are suggested in the present paper. The benefit of data pre-clustering before initiating large datasets for GNPS analyses is also demonstrated. Moreover, an efficient workflow dedicated to Agilent Technologies instruments is described, making the dereplication process easier by unambiguously distinguishing isobaric isomers eluted at different retention times, annotating the molecular networks with chemical formulas, and giving access to semi-quantitative data. This specific workflow foreshadows future developments of the GNPS platform.
Keywords: Tandem mass spectrometry; Metabolomics; Molecular networking; Natural products; Annotation

Zeta potential: a case study of cationic, anionic, and neutral liposomes by Mackensie C. Smith; Rachael M. Crist; Jeffrey D. Clogston; Scott E. McNeil (5779-5787).
Zeta potential is often used to approximate a nanoparticle’s surface charge, i.e., cationic, anionic, or neutral character, and has become a standard characterization technique to evaluate nanoparticle surfaces. While useful, zeta potential values provide only very general conclusions about surface charge character. Without a thorough understanding of the measurement parameters and limitations of the technique, these values can become meaningless. This case study attempts to explore the sensitivity of zeta potential measurement using specifically formulated cationic, anionic, and neutral liposomes. This study examines zeta potential dependence on pH and ionic strength, resolving power, and highlights the sensitivity of zeta potential to charged liposomes. Liposomes were prepared with cholesterol, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), and varying amounts of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS). A strong linear relationship was noted between zeta potential values and the mole percentage of charged lipids within a liposome (e.g., cationic DOTAP or anionic DOPS). This finding could be used to formulate similar liposomes to a specific zeta potential, potentially of importance for systems sensitive to highly charged species. In addition, cationic and anionic liposomes were titrated with up to two mole percent of the neutral lipid 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (lipid-PEG; LP). Very small amounts of the lipid-PEG (<0.2 mol%) were found to impart stability to the DOTAP- and DOPS-containing liposomes without significantly affecting other physicochemical properties of the formulation, providing a simple approach to making stable liposomes with cationic and anionic surface charge.
Keywords: Zeta potential; Liposomes; Surface characterization; Lipid-PEG; Stability