Structural analysis of poly[(R,S)-3-hydroxybutyrate-co-L-lactide] copolyesters by electrospray ionization ion trap mass spectrometry

Matrix-Assisted Laser Desorption and Electrospray Ionization Tandem Mass Spectrometry of Microbial and Synthetic Biodegradable Polymers

The in-depth structural and compositional investigation of biodegradable polymeric materials, neat or partly degraded, is crucial for their successful applications. Obviously, an exhaustive structural analysis of all synthetic macromolecules is essential in polymer chemistry to confirm the accomplishment of a preparation procedure, identify degradation products originating from side reactions, and monitor chemical-physical properties. Advanced mass spectrometry (MS) techniques have been increasingly applied in biodegradable polymer studies with a relevant role in their further development, valuation, and extension of application fields. However, single-stage MS is not always sufficient to identify unambiguously the polymer structure. Thus, tandem mass spectrometry (MS/MS) has more recently been employed for detailed structure characterization and in degradation and drug release monitoring of polymeric samples, among which are biodegradable polymers. This review aims to run through the investigations carried out by the soft ionization technique matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) MS/MS in biodegradable polymers and present the resulting information.

From Anionic Ring-Opening Polymerization of β-Butyrolactone to Biodegradable Poly(hydroxyalkanoate)s: Our Contributions in This Field

The feasibility of synthesis of functionalized poly(3-hydroxybutanoic acid) analogue and its copolymers via ring-opening polymerization of β-butyrolactone mediated by activated anionic initiators is presented. Using these new synthetic approaches, polyesters with a defined chemical structure of the end groups, as well as block, graft, and random copolymers, have been obtained and characterized by modern instrumental techniques, with special emphasis on ESI-MS. The relationship between the structure and properties of the prepared polymeric materials is also discussed.

Mass Spectrometry Reveals Molecular Structure of Polyhydroxyalkanoates Attained by Bioconversion of Oxidized Polypropylene Waste Fragments

This study investigated the molecular structure of the polyhydroxyalkanoate (PHA) produced via a microbiological shake flask experiment utilizing oxidized polypropylene (PP) waste as an additional carbon source. The bacterial strain Cupriavidus necator H16 was selected as it is non-pathogenic, genetically stable, robust, and one of the best known producers of PHA. Making use of PHA oligomers, formed by controlled moderate-temperature degradation induced by carboxylate moieties, by examination of both the parent and fragmentation ions, the ESI-MS/MS analysis revealed the 3-hydroxybutyrate and randomly distributed 3-hydroxyvalerate as well as 3-hydroxyhexanoate repeat units. Thus, the bioconversion of PP solid waste to a value-added product such as PHA tert-polymer was demonstrated.

Sequencing of Side-Chain Liquid Crystalline Copolymers by Matrix-Assisted Laser Desorption/Ionization Tandem Mass Spectrometry

Polyether based side-chain liquid crystalline (SCLC) copolymers with distinct microstructures were prepared using living anionic polymerization techniques. The composition, end groups, purity, and sequence of the resulting copolymers were elucidated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and tandem mass spectrometry (MS/MS). MALDI-MS analysis confirmed the presence of (CH₃)₃CO– and –H end groups at the initiating (α) and terminating (ω) chain end, respectively, and allowed determination of the molecular weight distribution and comonomer content of the copolymers. The comonomer positions along the polymer chain were identified by MS/MS, from the fragments formed via C–O and C–C bond cleavages in the polyether backbone. Random and block architectures could readily be distinguished by the contiguous fragment series formed in these reactions. Notably, backbone C–C bond scission was promoted by a radical formed via initial C–O bond cleavage in the mesogenic side chain. This result documents the ability of a properly substituted side chain to induce sequence indicative bond cleavages in the polyether backbone.

Analysis of monodisperse, sequence-defined, and POSS-functionalized polyester copolymers by MALDI tandem mass spectrometry

Monodisperse, sequence-defined polymers can be potentially used for digital data storage. This study reports the sequence analysis and differentiation of monodisperse polyester copolymers carrying side chains functionalized in a specific order by polyhedral oligomeric silsesquioxane (POSS) nanoparticles. Steglich esterification and succinic anhydride ring-opening chemistries were utilized iteratively to synthesize the intended sequences, which were characterized by matrix-assisted laser desorption ionization tandem mass spectrometry (MALDI-MS²). Isomeric oligomers were readily distinguished based on their different fragmentation patterns. The sequences embedded in the oligomers were decrypted by their specific backbone dissociation pathways. The robustness of using MALDI-MS² as a sequencing method for monodisperse synthetic macromolecules was assessed and validated by the characterization of longer oligomers.

Prediction studies of environment-friendly biodegradable polymeric packaging based on PLA. Influence of specimens' thickness on the hydrolytic degradation profile

Application of new biodegradable polymer packaging based on polylactide (PLA), susceptible to organic recycling, can help in the waste reduction in landfills. In this paper, the results of the study on abiotic degradation of PLA and its blend containing 15 mol% of poly[(R,S)-3-hydroxybutyrate], as a model for the first step of organic recycling were presented. The samples used for this study have different shapes and thicknesses: rigid films and cuboid-bars. Particular emphasis was placed on determining the pattern of degradation products released into the medium. Originally, the results of present study revealed that the application of electrospray ionization mass spectrometry supported by high performance liquid chromatography allowed envisaging the differences in the degradation products pattern released from the studied PLA-based samples differing in thickness. The significant differences in degradation products pattern were predominately observed in the first steps of incubation process and are caused by an autocatalytic effect, which occurs mainly during degradation of the large size PLA samples. Although, the thickness of PLA-based packaging changes the degradation product patterns, however this does not increase the total amounts of acids released to the medium. Thus, it may be concluded that thickness should not affect significantly organic recycling of the packaging.

Adduction of ammonium to polylactides to modify their dissociation behavior in collision-induced dissociation

RATIONALE

The goal of this work was to modify the dissociation pathways of polylactide (PLA) holding benzyl and hydroxyl terminations, in order to circumvent coincidence of product ions generated during collisional activation of sodiated chains, which prevented their reliable characterization.

METHODS

Benzyl-, hydroxyl-terminated PLAs were ionized as ammonium adducts in positive ion mode electrospray and subjected to collision-induced dissociation (CID). Tandem mass spectrometry (MS/MS) experiments were conducted in a quadrupole time-of-flight (QTOF) instrument for safe assignment of product ions based on their elemental composition derived from accurate mass measurements.

RESULTS

Adduction of ammonium to PLAs was found to induce chain fragmentation via charge-assisted processes, in great contrast to the charge-remote mechanisms experienced by sodiated molecules. The main reaction produced ions containing the ω termination only, hence allowing straightforward end-group determination. Other minor pathways were studied in detail to establish dissociation rules for ammoniated PLAs. Some reactions were found to be end-group specific, highlighting the higher reactivity of ammonium than alkali ion adducts.

CONCLUSIONS

Changing the usually employed sodium-cationizing agent to ammonium was shown to induce dramatic changes in the CID behavior of PLAs. This was a simple and efficient approach to address issues encountered for end-group analysis of the particular PLA studied here.

Multidimensional Mass Spectrometry of Synthetic Polymers and Advanced Materials

Multidimensional mass spectrometry interfaces a suitable ionization technique and mass analysis (MS) with fragmentation by tandem mass spectrometry (MS² ) and an orthogonal online separation method. Separation choices include liquid chromatography (LC) and ion-mobility spectrometry (IMS), in which separation takes place pre-ionization in the solution state or post-ionization in the gas phase, respectively. The MS step provides elemental composition information, while MS² exploits differences in the bond stabilities of a polymer, yielding connectivity and sequence information. LC conditions can be tuned to separate by polarity, end-group functionality, or hydrodynamic volume, whereas IMS adds selectivity by macromolecular shape and architecture. This Minireview discusses how selected combinations of the MS, MS² , LC, and IMS dimensions can be applied, together with the appropriate ionization method, to determine the constituents, structures, end groups, sequences, and architectures of a wide variety of homo- and copolymeric materials, including multicomponent blends, supramolecular assemblies, novel hybrid materials, and large cross-linked or nonionizable polymers.

Designing of Biodegradable and Biocompatible Release and Delivery Systems of Selected Antioxidants Used in Cosmetology

Conjugates of antioxidants p-anisic (p-AA) and vanillic (VA) acids with nontoxic, biocompatible, and biodegradedable oligo-(R,S)-(3-hydoxybutyrate) carrier were synthesized, and their structural and biological characterization was performed. The molecular structure of the bioconjugates, in which antioxidants are covalently bonded with oligo(3-hydroxybutyrate) (OHB) chains, has been proven by mass spectrometry supported by NMR. The bioconjugate hydrolytic degradation studies allowed gaining thorough insight into the hydrolysis process and confirmed the release of p-AA and VA. In vitro studies demonstrated that all of the conjugates studied were well tolerated by KB and HaCaT cell lines, as they had no marked cytotoxicity, while conjugates with a relatively short OHB carrier are optimal to support keratinocyte function. The preliminary study of the biological activity confirmed the protective effect of VA-OHB conjugates against H2O2-induced lipid peroxidation in human keratinocytes (HaCaT). It was also demonstrated that the selected bioconjugates can penetrate all layers of the skin, which shows their functionality and opens up their potential application in cosmetology.

Tandem mass spectrometry and ion mobility mass spectrometry for the analysis of molecular sequence and architecture of hyperbranched glycopolymers

Multidimensional mass spectrometry techniques, combining matrix-assisted laser desorption/ionization (MALDI) or electrospray ionization (ESI) with tandem mass spectrometry (MS(2)), multistage mass spectrometry (MS(n)) or ion mobility mass spectrometry (IM-MS), have been employed to gain precise structural insight on the compositions, sequences and architectures of small oligomers of a hyperbranched glycopolymer, prepared by atom transfer radical copolymerization of an acrylate monomer (A) and an acrylate inimer (B), both carrying mannose ester pendants. The MS data confirmed the incorporation of multiple inimer repeat units, which ultimately lead to the hyperbranched material. The various possible structures of n-mers with the same composition were subsequently elucidated based on MS(2) and MS(n) studies. The characteristic elimination of bromomethane molecule provided definitive information about the comonomer connectivity in the copolymeric AB2 trimer and A2B2 tetramer, identifying as present only one of the three possible trimeric isomers (viz. sequence BBA) and only two of the six possible tetrameric isomers (viz. sequences BBA2 and BABA). Complementary IM-MS studies confirmed that only one of the tetrameric structures is formed. Comparison of the experimentally determined collision cross-section of the detected isomer with those predicted by molecular simulations for the two possible sequences ascertained BBA2 as the predominant tetrameric architecture. The multidimensional MS approaches presented provide connectivity information at the atomic level without requiring high product purity (due to the dispersive nature of MS) and, hence, should be particularly useful for the microstructure characterization of novel glycopolymers and other types of complex copolymers.

Molecular level structure of novel synthetic analogues of aliphatic biopolyesters as revealed by multistage mass spectrometry

The present study focuses on electrospray ionisation (ESI) tandem mass spectrometry of novel copolyesters obtained by anionic ring-opening copolymerisation of β-substituted β-lactones. Detailed analysis of these copolyesters, including molecular chain architecture as well as the structures of the end groups, was performed using ESI-MS/MS collision-induced dissociation spectra. The random arrangement of comonomeric units along the copolyester chains was demonstrated by comparison of ESI-MS(n) fragmentation spectra and fragmentation pathways. Sequence distribution analysis of comonomeric units confirmed the copolymer's random structure. ESI-MS(n) proved to be a promising technique for structural analysis of copolyesters obtained via anionic ROP.

Structural characterization of biocompatible lipoic acid-oligo-(3-hydroxybutyrate) conjugates by electrospray ionization mass spectrometry

RATIONALE

Currently, most of the antioxidants and free radical neutralizers used in cosmetic compositions are absorbed quickly into deeper layers of skin, and then carried away by the blood stream. It would be beneficial to delay the penetration of antioxidants to the deeper layers of skin to control their delivery and release.

METHODS

Recently, growing attention has been paid to the attachment of cosmetics to specific polymer carriers. Biodegradable and biocompatible conjugates of oligo-3-hydroxybutyrate with lipoic acid were obtained via the anionic ring-opening oligomerization of (R,S)-β-butyrolactone initiated by lipoic acid potassium salt. The structure of the resulting conjugates as well as their water-soluble hydrolytic degradation products were established at the molecular level by electrospray ionization mass spectrometry (ESI-MS(n)) supported by (1)H NMR analyses.

RESULTS

The structural studies, performed with the aid of ESI-MS(n), confirmed that the lipoic acid was covalently bound to oligo-3-hydroxybutyrate chains through hydrolyzable ester bonds. Furthermore, hydrolytic degradation studies of the bioconjugates provided detailed insight into the hydrolysis process, allowing the identification of the degradation products and confirming the release of α-lipoic acid. Cytotoxicity tests demonstrated that the conjugates were non-toxic.

CONCLUSIONS

Detailed molecular structural studies of new polymeric delivery systems of lipoic acid were performed by ESI-MS. ESI-MS proved to be an excellent technique for the evaluation of hydrolytic degradation products of the conjugates and for monitoring the release of lipoic acid. The results obtained contribute significantly to the characterization of biocompatible LA-OHB conjugates with potential applications in cosmetology.

Selective reduction of PHA biopolyesters and their synthetic analogues to corresponding PHA oligodiols proved by structural studies

A highly selective method is described for controlling the degradation of polyhydroxyalkanoates, PHA, via a reduction reaction that uses lithium borohydride. Using this method, oligo(hydroxyalkanoate)diols derived from a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) biopolyester [poly(3HB-co-4HB)] and from synthetic atactic poly[(R,S)-3-hydroxybutyrate] (a-PHB) were obtained. The structural characterization of the oligo(hydroxyalkanoate)diols was conducted using NMR and ESI-mass spectrometry analyses, which confirmed that oligomers that were terminated by two hydroxyl end groups were formed. The reduction of the ester groups occurred in a statistical way regardless of the chemical structure of the comonomer units or of the microstructure of the polyester chain. The presented method can be used to synthesize various PHA oligodiols that are potentially useful in the further synthesis of tailor-made biodegradable materials.

Electrospray ionisation mass spectrometry molecular-level structural characterisation of novel phenoxycarboxylic acid-oligo(3-hydroxybutyrate) conjugates with potential agricultural applications

RATIONALE

Due to the low resistance of forms of pesticides to environmental conditions, agrochemicals frequently do not reach their objective, which may cause environmental pollution. The minimisation of the adverse effects of pesticides requires the development of a system for their long-term controlled release. In the present work, we report the synthesis and structural studies of novel controlled-release pesticide-oligo-3-hydroxybutyrate systems with potential agricultural applications.

METHODS

The novel controlled-release pesticide-oligo(3-hydroxybutyrate) systems were obtained via the anionic ring-opening oligomerisation of (R,S)-β-butyrolactone initiated by the potassium salt of selected pesticides. Electrospray ionisation mass spectrometry (ESI-MS(n)) analyses in positive-ion mode, supported by (1)H NMR results, were used for the structural characterisation of the obtained conjugates. The presence of the respective pesticides in an unchanged form associated with oligo-3-hydroxybutyrate chains was confirmed by ESI-MS/MS experiments performed for selected pesticide-oligo(3-hydroxybutyrate) ions and by the subsequent investigation of their fragmentation pathways.

RESULTS

The structures of the resulting conjugates were established at the molecular level with the aid of ESI-MS(n). The presence of one and two chlorine atoms (derived from MCPA and 2,4-D pesticides) in the conjugates studied was confirmed by comparison of the calculated and experimental isotopic profiles for the selected ions of the respective conjugates. The fragmentation of the selected ions of the resulting conjugates confirmed that the respective pesticides are covalently bonded with oligo(3-hydroxybutyrate) through a hydrolysable ester bond.

CONCLUSIONS

An analytical method has been developed for the characterisation of new pesticide-oligo(3-hydroxybutyrate) conjugates. A detailed NMR and MS structural characterisation of the designed controlled-release system of the pesticides was performed. These results are important in the analysis of designed biodegradable polymeric conjugates with potential agricultural applications.

Mechanistic study of the collision-induced dissociation of sodium-cationized polylactide oligomers: a joint experimental and theoretical investigation

The low-kinetic energy collision-induced dissociation (CID) behavior of different sodium-cationized polylactide (PLA) oligomers was thoroughly investigated to shed some light on the analytical potentialities of CID experiments in the context of polymer characterization. Indeed, investigation of several end-groups modified PLA reveals that, in addition to the expected end-group specific dissociations, collisionally-excited PLA.Na(+) suffer from a backbone cleavage. The so-obtained sodium-bound dimer cations consecutively undergo the loss of a monomeric residue that corresponds to neutral acrylic acid. The experimental observations, performed on a hybrid Q-ToF instrument, were totally corroborated by a theoretical study involving DFT calculations, molecular mechanics, and molecular dynamics calculations.

Tandem mass spectrometry of synthetic polymers

The detailed characterization of macromolecules plays an important role for synthetic chemists to define and specify the structure and properties of the successfully synthesized polymers. The search for new characterization techniques for polymers is essential for the continuation of the development of improved synthesis methods. The application of tandem mass spectrometry for the detailed characterization of synthetic polymers using the soft ionization techniques matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS), which became the basic tools in proteomics, has greatly been increased in recent years and is summarized in this perspective. Examples of a variety of homopolymers, such as poly(methyl methacrylate), poly(ethylene glycol), as well as copolymers, e.g. copolyesters, are given. The advanced mass spectrometric techniques described in this review will presumably become one of the basic tools in polymer chemistry in the near future.

Metastable processes investigated on an orthogonal-axis time-of-flight instrument: mass-scale calibration and application

In this letter, the authors would like to present a rapid method for mass-scale calibration of metastable dissociation in an orthogonalaxis time-of-flight instrument. The calibrating ion is a protonated polyhedral oligomeric silsesquioxane (POSS) generated in electrospray ionization. In addition, dissociation mechanisms for protonated POSS are proposed. Finally, the interest of the method is illustrated in the context of a collision-induced dissociation investigation of sodium-cationized polylactide.