Molecular Characterization of High Molecular Weight Polyesters by Matrix-Assisted Laser Desorption/Ionization High-Resolution Time-of-Flight Mass Spectrometry Combined with On-plate Alkaline Degradation and Mass Defect Analysis

Atomic-Scale Imaging of Polymers and Precision Molecular Weight Analysis

Polymer design requires fine control over syntheses and a thorough understanding of their macromolecular structure. Herein, near-atomic level imaging of polymers is achieved, enabling the precise determination of one of the most important macromolecular characteristics: molecular weight. By judiciously designing and synthesizing different linear metal(loid)-rich homopolymers, subnanoscale polymer imaging is achieved through annular dark field-scanning transmission electron microscopy (ADF-STEM), owing to the incorporation of high Z atoms in the side chain of the monomeric units. The molecular weight of these polymers can be precisely determined by detecting and counting their metal(loid) atoms upon ADF-STEM imaging, at sample concentrations as low as 10 μg·mL-1. Notably, a commonly used C, H, and O-containing polymer (i.e., poly(methyl acrylate)) that was thus far inaccessible at the atomic scale is derivatized to allow for subnano-level imaging, thus expanding the scope of our approach toward the atomic-level visualization of commodity polymers.

Development and ELISA Characterization of Antibodies against the Colistin, Vancomycin, Daptomycin, and Meropenem: A Therapeutic Drug Monitoring Approach

More than 70% of bacteria are resistant to all or nearly all known antimicrobials, creating the need for the development of new types of antimicrobials or the use of "last-line" antimicrobial therapies for the treatment of multi-resistant bacteria. These antibiotics include Glycopeptide (Vancomycin), Polymyxin (Colistin), Lipopeptide (Daptomycin), and Carbapenem (Meropenem). However, due to the toxicity of these types of molecules, it is necessary to develop new rapid methodologies to be used in Therapeutic Drug Monitoring (TDM). TDM could improve patient outcomes and reduce healthcare costs by enabling a favorable clinical outcome. In this way, personalized antibiotic therapy emerges as a viable option, offering optimal dosing for each patient according to pharmacokinetic (PK) and pharmacodynamic (PD) parameters. Various techniques are used for this monitoring, including high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and immunoassays. The objective of this study is the development and characterization by ELISA of specific polyclonal antibodies for the recognition of the antibiotics Vancomycin (glycopeptide), Colistin (polymyxin), Daptomycin (lipopeptide), and Meropenem (carbapenem) for future applications in the monitoring of these antibiotics in different fluids, such as human plasma. The developed antibodies are capable of recognizing the antibiotic molecules with good detectability, showing an IC50 of 0.05 nM for Vancomycin, 7.56 nM for Colistin, 183.6 nM for Meropenem, and 13.82 nM for Daptomycin. These antibodies offer a promising tool for the precise and effective therapeutic monitoring of these critical antibiotics, potentially enhancing treatment efficacy and patient safety.

MALINTO: A New MALDI Interpretation Tool for Enhanced Peak Assignment and Semiquantitative Studies of Complex Synthetic Polymers

The newly developed MALDI interpretation tool ("MALINTO") allows for the accelerated characterization of complex synthetic polymers via MALDI mass spectrometry. While existing software provides solutions for simple polymers like poly(ethylene glycol), polystyrene, etc., they are limited in their application on polycondensates synthesized from two different kinds of monomers (e.g., diacid and diol in polyesters). In addition to such A₂ + B₂ polycondensates, MALINTO covers branched and even multicyclic polymer systems. Since the MALINTO software works based on input data of monomers/repeating units, end groups, and adducts, it can be applied on polymers whose components are previously known or elucidated. Using these input data, a list with theoretically possible polymer compositions and resulting m/z values is calculated, which is further compared to experimental mass spectrometry data. For optional semiquantitative studies, peak areas are allocated according to their assigned polymer composition to evaluate both comonomer and terminating group ratios. Several tools are implemented to avoid mistakes, for example, during peak assignment. In the present publication, the functions of MALINTO are described in detail and its broad applicability on different linear polymers as well as branched and multicyclic polycondensates is demonstrated. Fellow researchers will benefit from the accelerated peak assignment using the freely available MALINTO software and might be encouraged to explore the potential of MALDI mass spectrometry for (semi)quantitative applications.

Synthesis and Phase Behavior of a Platform of CO2-Soluble Functional Gradient Copolymers Bearing Metal-Complexing Units

The synthesis and characterization of a platform of novel functional fluorinated gradient copolymers soluble in liquid and supercritical CO₂ is reported. These functional copolymers are bearing different types of complexing units (pyridine, triphenylphosphine, acetylacetate, thioacetate, and thiol) which are well-known ligands for various metals. They have been prepared by reversible addition–fragmentation chain-transfer (RAFT) polymerization in order to obtain well-defined gradient copolymers. The copolymers have been characterized by proton nuclear magnetic resonance (¹H-NMR) spectroscopy, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, thermal gravimetric analysis (TGA), dynamical scanning calorimetry (DSC) and cloud point measurements in dense CO₂. All the investigated metal-complexing copolymers are soluble in dense CO₂ under mild conditions (pressure lower than 30 MPa up to 65 °C), confirming their potential applications in processes such as metal-catalyzed reactions in dense CO₂, metal impregnation, (e.g., preparation of supported catalysts) or metal extraction from various substrates (solid or liquid effluents). Particularly, it opens the door to greener and less energy-demanding processes for the recovery of metals from spent catalysts compared to more conventional pyro- and hydro-metallurgical methods.

Approaches to Heterogeneity in Native Mass Spectrometry

Native mass spectrometry (MS) is aimed at preserving and determining the native structure, composition, and stoichiometry of biomolecules and their complexes from solution after they are transferred into the gas phase. Major improvements in native MS instrumentation and experimental methods over the past few decades have led to a concomitant increase in the complexity and heterogeneity of samples that can be analyzed, including protein-ligand complexes, protein complexes with multiple coexisting stoichiometries, and membrane protein-lipid assemblies. Heterogeneous features of these biomolecular samples can be important for understanding structure and function. However, sample heterogeneity can make assignment of ion mass, charge, composition, and structure very challenging due to the overlap of tens or even hundreds of peaks in the mass spectrum. In this review, we cover data analysis, experimental, and instrumental advances and strategies aimed at solving this problem, with an in-depth discussion of theoretical and practical aspects of the use of available deconvolution algorithms and tools. We also reflect upon current challenges and provide a view of the future of this exciting field.

Mass Defect Filter for Removing Noise and Detector Oscillation Artifacts in Centroided Time-of-Flight Mass Spectra

Spurious peaks in centroided mass spectra resulting from detector oscillation or "ringing" can be identified by their unusual mass defects. Mass defect plots (fractional m/z vs measured m/z) for the single-charge mass spectrum of a pure compound show data points falling along lines with well-defined slopes. Detector oscillation and electronic noise peaks were removed from database spectra of pure compounds and mixtures by eliminating points outside two standard deviations of the slope of the major peaks. No loss of chemical information was observed, even for compounds with isobaric fragment peaks.

Roles of RcsA, an AhpD Family Protein, in Reactive Chlorine Stress Resistance and Virulence in Pseudomonas aeruginosa

Reactive chlorine species (RCS), particularly hypochlorous acid (HOCl), are powerful antimicrobial oxidants generated by biological pathways and chemical syntheses. Pseudomonas aeruginosa is an important opportunistic pathogen that has adapted mechanisms for protection and survival in harsh environments, including RCS exposure. Based on previous transcriptomic studies of HOCl exposure in P. aeruginosa, we found that the expression of PA0565, or rcsA, which encodes an alkyl hydroperoxidase D-like protein, exhibited the highest induction among the RCS-induced genes. In this study, rcsA expression was dominant under HOCl stress and greatly increased under HOCl-related stress conditions. Functional analysis of RcsA showed that the distinguishing core amino acid residues Cys60, Cys63, and His67 were required for the degradation of sodium hypochlorite (NaOCl), suggesting an extended motif in the AhpD family. After allelic exchange mutagenesis in the P. aeruginosa rcsA, the P. aeruginosa rcsA deletion mutant showed significantly decreased HOCl resistance. Ectopic expression of P. aeruginosa rcsA led to significantly increased NaOCl resistance in Escherichia coli Moreover, the pathogenicity of the rcsA mutant decreased dramatically in both Caenorhabditis elegans and Drosophila melanogaster host model systems compared to the wild type (WT). Finally, the Cys60, Cys63, and His67 variants of RcsA were unsuccessful at complementing phenotypes of the rcsA mutant. Overall, our data indicate the importance of P. aeruginosa RcsA in defense against HOCl stress under disinfections and during infections of hosts, which involves the catalytic Cys60, Cys63, and His67 residues.IMPORTANCE Pseudomonas aeruginosa is a common pathogen that is a major cause of serious infections in many hosts. Hypochlorous acid (HOCl) is a potent antimicrobial agent found in household bleach and is a widely used disinfectant. P. aeruginosa has evolved adaptive mechanisms for protection and survival during HOCl exposure. We identified P. aeruginosa rcsA as a HOCl-responsive gene encoding an antioxidant protein that may be involved in HOCl degradation. RcsA has a distinguishing core motif containing functional Cys60, Cys63, and His67 residues. P. aeruginosa rcsA plays an important role in bleach tolerance, with expression of P. aeruginosa rcsA in Escherichia coli also conferring HOCl resistance. Interestingly, RcsA is required for full virulence in worm and fruit fly infection models, indicating a correlation between mechanisms of bleach toxicity and host immunity during infection. This provides new insights into the mechanisms used by P. aeruginosa to persist in harsh environments such as hospitals.

A mass spectrometry imaging method for visualizing synthetic polymers by using average molecular weight and dispersity as indices

RATIONALE

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MSI) is considered to be a powerful tool for visualizing the spatial distribution of synthetic polymers. However, a conventional method extracting an image of a specific m/z value is not suitable for polymers, which have a mass distribution. It is necessary to develop the visualization method to show the spatial distribution of entire polymer series.

METHODS

The mass peaks included in polymer series were specified from the average mass spectrum of the entire MSI measurement region by using Kendrick mass defect analysis. The images of those mass peaks were extracted and the number average molecular weight (M_n ), the weight average molecular weight (M_w ) and dispersity (Đ) were calculated for each pixel. Finally, the spatial distribution of the polymer series was summarized to images using M_n , M_w and Đ as indices.

RESULTS

The effects of the methods were investigated by (i) polymers with different mass distributions and (ii) polymers with different repeat units and end-groups. In both cases, the spatial distribution of specific polymer series including several dozens to hundreds of mass peaks was summarized into three images related to M_n , M_w and Đ, which are familiar indices in polymer analysis. The results are able to provide an overview of the spatial variation of each polymer more intuitively.

CONCLUSIONS

The visualization of M_n , M_w and Đ will help provide an overview of the spatial distribution of polymer series combined with ion intensity distribution made by conventional methods. It can be also applied to other mass spectrometric imaging methods such as desorption electrospray ionization (DESI) or time-of-flight secondary ion mass spectrometry (TOF-SIMS).

Multistep Analysis of Diol-LC-ESI-HRMS Data Reveals Proanthocyanidin Composition of Complex Plant Extracts (PAComics)

Proanthocyanidins (PACs) are complex oligomeric or polymeric phenolic biopolymers composed of flavan-3-ol building blocks. PACs exert manifold functional bioactivities and are assessed as bioactive ingredients in a variety of food products, beverages, medicinal plants, and phytopharmaceuticals. Although analytical methods for PACs with low degree of polymerization (DP) are well established, a lack of methods for the detailed analysis of higher oligomers and polymers from complex plant extracts is obvious. For this, the present study investigated PAC-enriched extracts from four different plants, traditionally used for medical purpose (Lime flower, Hawthorn leaf and flower, Japanese Wisteria fruits without seeds, and Common Sorrel herb). PACs were separated on diol stationary-phase high-performance liquid chromatography according to the respective DP and detected by fluorescence and quadrupole time-of-flight mass spectrometry (qTOF-MS). The qTOF-MS contour plots [t_R → m/z] provided a sufficient overview on the respective PAC distribution. Subsequently, high-resolution mass spectrometry data were used for Kendrick mass defect (KMD) analysis, with (epi)catechin, the main flavan-3-ol unit in PACs, as the reference unit. The resulting KMD plots enabled an elucidation of the general polymer chain composition with regard to DP, building blocks, and potential secondary modifications (e.g., galloylation). Subsequently, analysis of MS² fragmentation patterns of PAC oligomers confirmed the structural features obtained from the KMD plots. While Lime flower contained oligomeric A- and B-type PACs, composed of (epi)catechin and (epi)afzelechin, Japanese Wisteria fruit contained PACs consisting of three different hydroxylated flavan-3-ols. Cinchonains, A-type PACs, and B-type PACs were detected in the Hawthorn plant material. Galloylated oligo- and polymeric PACs were detected in Common Sorrel herb. This multistep analysis reveals collective insights into the PAC composition of the extracts. The protocol offers a fast and reliable methodology to be used in a standard laboratory. On the other hand, this methodology reaches its limits for higher oligomeric PACs, and further optimization is necessary for a better detection of the polymers, as the optimal DP cluster detection depends on the resolution of diol stationary-phase chromatography and is therefore limited.

Kendrick Analysis and Complex Isotopic Patterns: A Case Study of the Compositional Analysis of Pristine and Heated Polybrominated Flame Retardants by High-Resolution MALDI Mass Spectrometry

The Kendrick analysis is used for the processing and visualization of mass spectra obtained from polymers containing C, H, O and/or Si with simple isotopic patterns (monoisotope=lightest isotope=most intense isotope for short chains). In the case of heteroatoms with complex isotopic patterns, the impact of the chosen isotope on point alignments in Kendrick plots has not been examined extensively. Rich isotopic patterns also make the evaluation of the mass and nature of the repeating unit and end-groups more difficult from the mass spectrum in the case of unknown samples due to the number of peaks and the absence of a monoisotopic peak. Using a polybrominated polycarbonate as running example, we report that horizontal point alignments can be obtained in a Kendrick plot using the mass of the most abundant isotope instead of the monoisotopic mass as is usually done. Rotating the plot (“reverse Kendrick analysis”) helps to accurately evaluate the mass of the most abundant isotope of the repeating unit, as well as the nature of the brominated neutral expelled upon gentle heating (debromination or dehydrobromination). The whole procedure is then applied to the characterization of an unknown polybrominated flame retardant in an industrial formulation before and after heating.

Mass spectrometry as a tool to advance polymer science

In contrast to natural polymers, which have existed for billions of years, the first well-understood synthetic polymers date back to just over one century ago. Nevertheless, this relatively short period has seen vast progress in synthetic polymer chemistry, which can now afford diverse macromolecules with varying structural complexities. To keep pace with this synthetic progress, there have been commensurate developments in analytical chemistry, where mass spectrometry has emerged as the pre-eminent technique for polymer analysis. This Perspective describes present challenges associated with the mass-spectrometric analysis of synthetic polymers, in particular the desorption, ionization and structural interrogation of high-molar-mass macromolecules, as well as strategies to lower spectral complexity. We critically evaluate recent advances in technology in the context of these challenges and suggest how to push the field beyond its current limitations. In this context, the increasingly important role of high-resolution mass spectrometry is emphasized because of its unrivalled ability to describe unique species within polymer ensembles, rather than to report the average properties of the ensemble.

The Kendrick analysis for polymer mass spectrometry

The mass spectrum of a polymer often displays repetitive patterns with peak series spaced by the repeating unit(s) of the polymeric backbones, sometimes complexified with different adducts, chain terminations, or charge states. Exploring the complex mass spectral data or filtering the unwanted signal is tedious whether performed manually or automatically. In contrast, the now 60-year-old Kendrick (mass defect) analysis, when adapted to polymer ions, produces visual two-dimensional maps with intuitive alignments of the repetitive patterns and favourable deconvolution of features overlaid in the one-dimensional mass spectrum. This special feature article reports on an up-to-date and theoretically sound use of Kendrick plots as a data processing tool. The approach requires no prior knowledge of the sample but offers promising dynamic capabilities for visualizing, filtering, and sometimes assigning congested mass spectra. Examples of applications of the approach to polymers are discussed throughout the text, but the same tools can be readily extended to other applications, including the analysis of polymers present as pollutants/contaminants, and to other analytes incorporating a repetitive moiety, for example, oils or lipids. In each of these instances, data processing can benefit from the application of an updated and interactive Kendrick analysis.

Studying the catalytic activity of DBU and TBD upon water-initiated ROP of ε-caprolactone under different thermodynamic conditions

Studies performed revealed that a novel catalytic system for water-initiated ε-CL ROP based on DBU protonation showed enhanced performance under high-pressure/high-temperature conditions.