Molecular Level Structure of (R,S)-3-Hydroxybutyrate/(R,S)-3-Hydroxy-4-ethoxybutyrate Copolyesters with Dissimilar Architecture

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

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.

Ring opening copolymerization of δ-valerolactone with 2-methyl-1,3-dioxane-4-one towards poly(3-hydroxypropionate-co-5-hydroxyvalerate) copolyesters

A straightforward strategy of ring-opening copolymerization (ROCOP) toward the synthetic copolyesters is gaining increasing interest. In present work, a novel series of poly(3-hydroxypropionate-co-5-hydroxyvalerate) P(3HP-co-5HV) copolyesters are obtained through ROCOP of...

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.

Towards Advances in Molecular Understanding of Boric Acid Biocatalyzed Ring-Opening (Co)Polymerization of δ-Valerolactone in the Presence of Ethylene Glycol as an Initiator

Following our previous studies on the molecular level structure of (co)oligoesters obtained via anionic homo- and co-polymerization of novel β-substituted β-lactones, prepared by the atmospheric pressure carbonylation reaction of respective epoxides, the boric acid biocatalyzed ring-opening (co)polymerization of δ-valerolactone has been studied. As a co-monomer the 6-methy-ε-caprolactone, prepared by the one-pot oxidation of respective alcohol, and ethylene glycol as polymerization initiator were used. The obtained copolymers were characterized by 1H-NMR, GPC and ESI-MS, respectively in order to confirm their chemical structures and identity. Subsequently, tandem mass spectrometry (MS-MS studies) via collision-induced dissociation were utilized to characterize the fragmentation pattern. ESI-MS and NMR analyses confirmed the formation of random linear copolymer chains composed of different polyester repeat units. MS-MS experiments showed that fragmentation proceeds via ester bound cleavage along the (co)polyester chains. The innovative aspect of this contribution is related to the elaboration of the telechelic (co)polymers end-capped with hydroxyl end groups and well-defined molecular architectures, which could facilitate the development of new flexible macromolecular systems for potential biomedical applications.

Bioactive (Co)oligoesters as Potential Delivery Systems of p-Anisic Acid for Cosmetic Purposes

This article reports the studies on bioactive (co)oligoesters towards their use as controlled delivery systems of p-anisic acid. The objects of the study were oligo[3-hydroxy-3-(4-methoxybenzoyloxymethyl)propionate], (p-AA-CH₂-HP)_n oligoester, and oligo[(3-hydroxy-3-(4-methoxybenzoyloxymethyl)propionate)-co-(3-hydroxybutyrate)] [(p-AA-CH₂-HP)_x-co-(HB)_y (co)oligoesters containing p-anisic acid moiety (p-AA, as the bioactive end and side groups) connected to the polymer backbone through the susceptible to hydrolysis ester bonds. A thorough insight into the hydrolysis process of the bioactive (co)oligoesters studied has allowed us to determine the release profile of p-AA as well as to identify polymer carrier degradation products. The p-AA release profiles determined on the basis of high-performance liquid chromatography (HPLC) measurements showed that the release of the bioactive compound from the developed (co)oligoester systems was regular and no burst effect occurred. Biological studies demonstrated that studied (homo)- and (co)oligoesters were well tolerated by HaCaT cells because none of them showed notable cytotoxicity. They promoted keratinocyte growth at moderate concentrations. Bioactive (co)oligoesters containing p-anisic acid moiety had somewhat decreased cell proliferation at the highest concentration (100 µg/mL). The important practical inference of the current study is that the (co)oligoesters developed have a relatively large load of the biologically active substance (p-AA) per polymer macromolecule, which unlocks their potential application in the cosmetic industry.

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.

Molecular Level Structure of Biodegradable Poly(Delta-Valerolactone) Obtained in the Presence of Boric Acid

In this study, low molecular weight poly(δ-valerolactone) (PVL) was synthesized through bulk-ring openings polymerization of δ-valerolactone with boric acid (B(OH)₃) as a catalyst and benzyl alcohol (BnOH) as an initiator. The resulting homopolymer was characterized with the aid of nuclear magnetic resonance (NMR) and mass spectrometry (MS) techniques to gain further understanding of its molecular structure. The electrospray ionization mass spectrometry (ESI-MS) spectra of poly(δ-valerolactone) showed the presence of two types of homopolyester chains-one terminated by benzyl ester and hydroxyl end groups and one with carboxyl and hydroxyl end groups. Additionally, a small amount of cyclic PVL oligomers was identified. To confirm the structure of PVL oligomers obtained, fragmentation of sodium adducts of individual polyester molecules terminated by various end groups was explored in ESI-MSⁿ by using collision induced dissociation (CID) techniques. The ESI-MSⁿ analyses were conducted both in positive- and negative ion mode. The comparison of the fragmentation spectra obtained with proposed respective theoretical fragmentation pathways allowed the structure of the obtained oligomers to be established at the molecular level. Additionally, using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), it was proven that regardless of the degree of oligomerization, the resulting PVL samples were a mixture of two types of linear PVL oligomers differing in end groups and containing just a small amount of cyclic oligomers that tended to be not visible at higher molar masses.

The Synthesis and Structural Characterization of Graft Copolymers Composed of γ-PGA Backbone and Oligoesters Pendant Chains

The novel copolymers composed of poly-γ-glutamic acid (γ-PGA) and oligoesters have been developed. The structures of the obtained copolymers including variety of end groups were determined at the molecular level with the aid of electrospray ionization multistage mass spectrometry (ESI-MSⁿ). The fragmentation experiment performed for the selected sodium adducts of the copolymers confirmed that the developed methods lead to the formation of graft copolymers composed of poly-γ-glutamic acid (γ-PGA) backbone and oligoesters pendant chains. Moreover, it was established that fragmentation of selected sodium adducts of graft copolymers proceeded via random breakage of amide bonds along the backbone and ester bonds of the oligoesters pendant chains. Considering potential applications of the synthesized copolymers in the area of biomaterials, the hydrolytic degradation under laboratory conditions and in vitro cytotoxicity tests were performed. The ESI-MSⁿ technique applied in this study has been proven to be a useful tool in structural studies of novel graft copolymers as well as their degradation products. Graphical Abstract ᅟ.

The heterogeneous selective reduction of PHB as a useful method for preparation of oligodiols and surface modification

A selective heterogeneous reduction of natural PHB with lithium borohydride as a reducing agent has been described.

Biocompatible terpolyesters containing polyhydroxyalkanoate and sebacic acid structural segments – synthesis and characterization

A convenient synthetic route of poly(3HB-co-3HH-co-SEB) terpolyesters has been reported.

Bioactive (co)oligoesters with antioxidant properties – synthesis and structural characterization at the molecular level

Anionic ring opening (co)polymerization of novel β-substituted β-lactones to bioactive (co)oligoesters with antioxidant properties.

Mass spectrometry for the elucidation of the subtle molecular structure of biodegradable polymers and their degradation products

Contemporary reports by Polish authors on the application of mass spectrometric methods for the elucidation of the subtle molecular structure of biodegradable polymers and their degradation products will be presented. Special emphasis will be given to natural aliphatic (co)polyesters (PHA) and their synthetic analogues, formed through anionic ring-opening polymerization (ROP) of β-substituted β-lactones. Moreover, the application of MS techniques for the evaluation of the structure of biodegradable polymers obtained in ionic and coordination polymerization of cyclic ethers and esters as well as products of step-growth polymerization, in which bifunctional or multifunctional monomers react to form oligomers and eventually long chain polymers, will be discussed. Furthermore, the application of modern MS techniques for the assessment of polymer degradation products, frequently bearing characteristic end groups that can be revealed and differentiated by MS, will be discussed within the context of specific degradation pathways. Finally, recent Polish accomplishments in the area of mass spectrometry will be outlined.

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.

Molecular architecture of novel potentially bioactive (co)oligoesters containing pesticide moieties established by electrospray ionization multistage mass spectrometry

RATIONALE

Pesticides are commonly used in agriculture to ensure high crop yield; however, because of their low resistance to environmental conditions, a large amount of pesticides does not reach target pests and becomes an environmental pollutant. One of the ways to reduce these drawbacks is synthesis of polymeric systems, which allows for controlled release of pesticides for a prolonged period of time. Herein we report the synthesis and characterization of novel potentially bioactive (co)oligoesters with bioactive moieties (selected from pesticides) which are covalently linked along an oligoester backbone.

METHODS

The delivery systems of pesticides were prepared via anionic ring-opening polymerization of β-substituted β-lactones containing bioactive moieties as a pendant group selected from pesticides and their copolymerization with β-butyrolactone in the presence of carboxylates as initiators. Electrospray ionization multistage mass spectrometry (ESI-MS(n)) supported by (1)H NMR were applied in order to establish the structure, at a molecular level, of the new biodegradable oligomeric release system of selected pesticides.

RESULTS

Based on ESI-MS(n) analyses, the structures of the resulting (co)oligoesters were established at the molecular level. The ESI-MS/MS allowed to confirm the structures of end groups and to determine the composition of individual (co)oligoester molecules which contained one, two or three bioactive molecules per (co)oligomer. Additionally, it was shown that fragmentation of selected ions of potentially bioactive (co)oligoesters proceeded via random breakage of ester bonds along the oligomer chain and ester bonds of the bioactive pendant group.

CONCLUSIONS

An analytical method for detailed structural characterization at the molecular level of potentially bioactive (co)oligoesters has been developed. These results are important in the analysis of designed biodegradable polymeric controlled-release systems of pesticides with potential agricultural applications.

Transesterification of PHA to oligomers covalently bonded with (bio)active compounds containing either carboxyl or hydroxyl functionalities

This manuscript presents the synthesis and structural characterisation of novel biodegradable polymeric controlled-release systems of pesticides with potentially higher resistance to weather conditions in comparison to conventional forms of pesticides. Two methods for the preparation of pesticide-oligomer conjugates using the transesterification reaction were developed. The first method of obtaining conjugates, which consist of bioactive compounds with the carboxyl group and polyhydroxyalkanoates (PHAs) oligomers, is "one-pot" transesterification. In the second method, conjugates of bioactive compounds with hydroxyl group and polyhydroxyalkanoates oligomers were obtained in two-step method, through cyclic poly(3-hydroxybutyrate) oligomers. The obtained pesticide-PHA conjugates were comprehensively characterised using GPC, 1H NMR and mass spectrometry techniques. The structural characterisation of the obtained products at the molecular level with the aid of mass spectrometry confirmed that both of the synthetic strategies employed led to the formation of conjugates in which selected pesticides were covalently bonded to PHA oligomers via a hydrolysable ester bond.

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.

Degradation profile and preliminary clinical testing of a resorbable device for ligation of blood vessels

A resorbable device for ligation of blood vessels was developed and tested in vitro to reveal the degradation profile of the device and to predict the clinical performance in terms of adequate mechanical support during a healing period of 1week. In addition, preliminary clinical testing was performed that showed complete hemostasis and good tissue grip of renal arteries in five pigs. The device was made by injection molding of poly(glycolide-co-trimethylene carbonate) triblock copolymer, and it consisted of a case with a locking mechanism connected to a partly perforated flexible band. A hydrolytic degradation study was carried out for 7, 30 and 60days in water and buffer medium, following the changes in mass, water absorption, pH and mechanical properties. A new rapid matrix-free laser desorption ionization-mass spectrometry (LDI-MS) method was developed for direct screening of degradation products released into the degradation medium. The combination of LDI-MS and electrospray ionization-mass spectrometry analyses enabled the comparison of the degradation product patterns in water and buffer medium. The identified degradation products were rich in trimethylene carbonate units, indicating preferential hydrolysis of amorphous regions where trimethylene units are located. The crystallinity of the material was doubled after 60days of hydrolysis, additionally confirming the preferential hydrolysis of trimethylene carbonate units and the enrichment of glycolide units in the remaining solid matrix. The mechanical performance of the perforated band was followed for the first week of hydrolysis and the results suggest that sufficient strength is retained during the healing time of the blood vessels.

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.

LC-multistage mass spectrometry for the characterization of poly(butylene adipate-co-butylene terephthalate) copolyester

A comprehensive study using liquid chromatography electrospray ionization multistage mass spectrometry (LC-ESI MS(n)) was performed to get detailed structural information on poly(butylene adipate-co-butylene terephthalate) co-polyester and its product of partial degradation. LC-MS and LC-MS(n) identified the existence of cyclic structures in the original samples that disappear completely during the degradation. The occurrence of methanol transesterification in the degradation process was confirmed. MS(2) on the first (13)C isotope peak helped to determine the elemental composition of the fragments and facilitated end group determination. The method can be used to provide an alternative for high mass accuracy MS(2) experiments. Sequence information was also revealed for certain copolymeric structures.