Small Molecule Model Compounds Research Articles

Malleable, Ultrastrong Antibacterial Thermosets Enabled by Guanidine Urea Structure.

Dynamic covalent polymers (DCPs) that strike a balance between high performance and rapid reconfiguration have been a challenging task. For this purpose, a solution is proposed in the form of a new dynamic covalent supramolecular motif-guanidine urea structure (GUAs). GUAs contain complex and diverse chemical structures as well as unique bonding characteristics, allowing guanidine urea supramolecular polymers to demonstrate advanced physical properties. Noncovalent interaction aggregates (NIAs) have been confirmed to form in GUA-DCPs through multistage H-bonding and π-π stacking, resulting in an extremely high Young's modulus of 14 GPa, suggesting remarkable mechanical strength. Additionally, guanamine urea linkages in GUAs, a new type of dynamic covalent bond, provide resins with excellent malleability and reprocessability. Guanamine urea metathesis is validated using small molecule model compounds, and the temperature dependent infrared and rheological behavior of GUA-DCPs following the dissociative exchange mechanism. Moreover, the inherent photodynamic antibacterial properties are extensively verified by antibacterial experiments. Even after undergoing three reprocessing cycles, the antibacterial rate of GUA-DCPs remains above 99% after 24 h, highlighting their long-lasting antibacterial effectiveness. GUA-DCPs with dynamic nature, tuneable composition, and unique combination of properties make them promising candidates for various technological advancements.

Radical Attack and Damage Mitigation in Hydrocarbon-Based Ionomers

In an operating polymer electrolyte fuel cell (PEFC) radical intermediates are formed as a result of the interaction of H2 and O2 on the surface of the Pt-based electrocatalyst. Of the various radical intermediates, •OH is of particular concern owing to its high oxidative strength, E°(•OH,H+/H2O) = 2.72 V) [1]. In PFSA ionomers, •OH reacts relatively slowly with the polymer and has a lifetime on the order of microseconds. This leaves sufficient time for additives, such as Ce(III), to scavenge the radicals and thus mitigate radical induced damage of the ionomer. In hydrocarbon-based ionomers containing aromatic units, •OH reacts within nanoseconds with polymer constituents [2]. Radical scavenging can therefore not be effective.In the development of alternative antioxidant strategies for hydrocarbon-based ionomers, it is crucial to elucidate polymer degradation mechanisms triggered by radical attack. In addition to studying the initial reactions of primary radicals, i.e. •OH, it is equally important to characterize the nature of the formed polymer intermediates, their lifetime, stability and reactivity. Sufficiently long-lived intermediates can be repaired by suitable additives, thereby restoring the original ionomer [3]. In the fuel cell, the thus protected membranes show a much lower rate of degradation in an accelerated stress test (AST) at open circuit voltage (OCV) [4].In this contribution, we provide an overview of methods to study reaction of radicals with small-molecule model compounds and ionomer constituents [5, 6]. The interaction of ionizing radiation (MeV electrons or photons) with water leads to the formation of radicals, such as •OH, at known rates. Water radiolysis can therefore be used to study the kinetics of radical attack and follow-up reactions as a function of pH, electron density of the aromatic ring, and presence of additives. Examples relevant to the acidic conditions in the proton exchange membrane (see Figure, Panel a) as well as the alkaline conditions in an anion exchange membrane (AEM) will be given. Moreover, the use of suitable antioxidants to mitigate degradation through the repair of intermediates will be discussed. Fuel cell tests with hydrocarbon-based membranes containing polymer-bound antioxidants will be shown (see Figure, Panel b) and prospects for long-term stability of non-fluorinated ionomers assessed.Figure caption: a) Analysis of the effect of Ce(III) ions on the extent of degradation of 1 mM of 4-cumenesulfonate (4CS) and 4-(tert-butyl)phenylsulfonate (BPS) at pH 0 (1 M H2SO4) in 1 mM H2O2 upon exposure to a radiolytic dose provided by a 60Co-source of 800 Gy (corresponding to a cumulative amount of •OH of 0.22 mM). ‘Excess degradation’ indicates the difference to the extent of degradation in the absence of Ce(III) and H2O2. Data for BPS from [5]. b) Ohmic resistance of single cells (average of several experiments) with partially fluorinated membrane containing a tethered crown ether with and without Ce(III) metal center during an accelerated stress test. Ion exchange capacity at the end of test was measured to represent remaining membrane state of health. Conditions: open circuit voltage (OCV), H2/O2, 80 °C, 2.5 bara, and 100% R.H. [4].

Tandem Suzuki Polymerization/Heck Cyclization Reaction to Form Ladder-Type 9,9'-Bifluorenylidene-Based Conjugated Polymer.

The synthesis of ladder-type 9,9'-bifluorenylidene-based conjugated polymer is reported. Unlike the typical synthetic strategy, the new designed ladder-type conjugated polymer is achieved via tandem Suzuki polymerization/Heck cyclization reaction in one-pot. In the preparation process, Suzuki polymerization reaction occurred first and then the intramolecular Heck cyclization followed smoothly under the same catalyst Pd(PPh3)4. The model reaction proved that the introduction of iodine (I) for this tandem reaction can effectively control the sequential bond-forming process and inhibit the additional competitive side reactions. Thus, small-molecule model compounds could be obtained in high yields. The successes of the synthesized small molecule and polymer compounds indicate that the Pd-catalyzed tandem reaction may be an effective strategy for improving extended π-conjugated materials.

Stable cysteine sulfenic acid: synthesis by direct oxidation of a thiol, crystallographic analysis, and elucidation of reactivities

A small-molecule cysteine sulfenic acid (Cys–SOH) was synthesized and isolated as stable crystals, for the first time, by utilizing a nanosized molecular cavity as a protective cradle. The cradled Cys–SOH was synthesized by direct oxidation of the corresponding cysteine thiol with H2O2 under basic conditions and its structure was established by X-ray crystallographic analysis. In the reaction of the cradled Cys–SOH with a thiol to produce the disulfide, a remarkable acceleration was observed upon the addition of an amine base. This suggests the important role of base in the reaction of Cys–SOH with thiols in biological systems. The cradled Cys–SOH was reduced to the cysteine thiol by dithiothreitol or triphenylphosphine. The high stability and sufficient reactivity of the cradled Cys–SOH indicate its usefulness as a small-molecule model compound for better understanding the chemical behavior of Cys–SOH in biological systems.

Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle.

In the biological functions of selenoproteins, various highly reactive species formed by oxidative modification of selenocysteine residues have been postulated to play crucial roles. Representative examples of such species are selenocysteine selenenic acids (Sec-SeOHs) and selenocysteine selenenyl iodides (Sec-SeIs), which have been widely recognized as important intermediates in the catalytic cycle of glutathione peroxidase (GPx) and iodothyronine deiodinase, respectively. However, examples of even spectroscopic observation of Sec-SeOHs and Sec-SeIs in either protein or small-molecule model systems remain elusive so far, most likely due to their notorious instability. For the synthesis of small-molecule model compounds of these reactive species, it is essential to suppress their very facile bimolecular decomposition such as self-condensation and disproportionation. Here we outline a novel method for the synthesis of stable small-molecule model compounds of the selenocysteine-derived reactive species, in which a nano-sized molecular cavity is used as a protective cradle to accommodate the reactive selenocysteine unit. Stabilization by the molecular cradle led to the successful synthesis of Sec-SeOHs, which are stable in solution at low temperatures, and a Sec-SeI, which can be isolated as crystals. The catalytic cycle of GPx was investigated using the NMR-observable Sec-SeOH models, and all the chemical processes proposed for the catalytic cycle of GPx, including the bypass process from Sec-SeOH to the corresponding cyclic selenenyl amide, were experimentally confirmed. Detailed protocols for the syntheses of selenopeptide derivatives bearing the molecular cradle and for the spectroscopic monitoring of their reactions are provided.

Alkaline Stability Evaluation of Polymerizable Hexyl-Tethered Ammonium Cations.

One of the important challenges in designing robust alkaline anion exchange membranes is the difficulty associated with the chemical stability of covalently bound cationic units. Here, a systematic study exploring alkaline stabilities of polymerizable hexyltrimethylammonium cations is presented, where the hexyl chain is linked to a phenyl ring through a direct carbon-carbon, phenyl ether, or benzyl ether functionality. For this work, small molecule model compounds, styrenic monomer analogs, and their homopolymers are synthesized. Alkaline stabilities of the small molecule cations and their homopolymers are compared to alkaline stability of benzyltrimethylammonium (BTMA) cation and its homopolymer poly(BTMA), respectively. All the hexyl-tethered cations and their homopolymers are significantly more stable under strongly alkaline conditions (2 m KOD at 80 °C). Moreover, ether-linked cations show comparable stability to the direct carbon-carbon linked cation. Via 1 H NMR analyses, possible degradation mechanisms are investigated for each small molecule cation. Findings of this study strongly suggest that the alkaline stability is dictated by the steric hindrance around the β-hydrogen. This study expands beyond the limits of general knowledge on alkaline stability of alkyl-tethered ammonium cations via the Hofmann elimination route, highlights important design parameters for stable ammonium cations, and demonstrates accessible directly polymerizable alkaline stable ammonium cations.

Utilizing in situ spectroscopic tools to monitor ketal deprotection processes

The use of protection groups to shield a functional group during a synthesis is employed throughout many reactions and organic syntheses. The role of a protection group can be vital to the success of a reaction, as well as increase reaction yield and selectivity. Although much work has been done to investigate the addition of a protection group, the removal of the protection group is just as important – however, there is a lack of methods employed within the literature for monitoring the removal of a protection group in real time. In this work, the process of removing, or deprotecting, a ketal protecting group is investigated. Process analytical technology tools are incorporated for in situ analysis of the deprotection reaction of a small molecule model compound. Specifically, Raman spectroscopy and Fourier transform infrared spectroscopy show that characteristic bands can be used to track the decrease of the reactant and the increase of the expected products over time. To the best of our knowledge, this is the first report of process analytical technology being used to monitor a ketal deprotection reaction in real time. This information can be capitalized on in the future for understanding and optimizing pharmaceutically-relevant deprotection processes and downstream reactions.

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Polyether-Based Diblock Terpolymer Micelles with Pendant Anthracene Units-Light-Induced Crosslinking and Limitations Regarding Reversibility.

The synthesis of 9-methylanthracenyl glycidyl ether (AnthGE) as a crosslinkable monomer that can be applied in anionic ring opening polymerization is reported. Diblock terpolymers of the composition methoxy-poly(ethylene oxide)-block-poly(2-ethylhexyl glycidyl ether-co-9-methylanthracenyl glycidyl ether) (mPEO-b-P(EHGE-co-AnthGE) with 10 to 24 wt% of AnthGE are synthesized and characterized. Their micellization behavior, as well as their light-induced core-crosslinking via irradiation with UV light (λ = 365nm) is studied. The results are compared with studies on the dimerization, and the dimer cleavage via irradiation with UV-C light (λ = 254nm), of the same diblock terpolymer in organic solution, and the small-molecule model compound 9-methoxymethylanthracene. Differences in 1 H NMR spectra of the crosslinked or dimerized compounds and reaction kinetics of the dimerization reactions under different conditions suggest possible side reactions for the case of the core-crosslinking of micelles in aqueous solution. These side reactions limit the reversibility of the anthracene dimerization reaction in aqueous solutions, even if the anthracene molecule is encapsulated within the hydrophobic core of a polymeric micelle.

Desirability of position 2, 2’-bipyridine group into COFs for the fluorescence sensing of Ni (II)

Covalent organic frameworks (COFs) with predesigned bipyridine recognition sites (donated as BPD-COFs) were prepared by using 2, 2’-bipyridine-5, 5’-diamine and benzene-1, 3, 5-tricarbaldehyde as monomers, and the corresponding small molecule model compound (2, 2’-bipyridine-5, 5’-diiminebenzene, donated as BPDB) was synthesized by using benzaldehyde and 2, 2’-bipyridine-5, 5’-diamine. The fluorescence sensing property between BPD-COFs and BPDB were compared as the fluorescence sensing platform for the sensitive, selective and rapid detection of Ni2+. The unique structure characteristics such as large conjugated structure, high surface area, regularity pore canals and predesigned bipyridine link endow BPD-COFs with prominent fluorescence emission, enough space and strong specificity for Ni2+. The fluorescence quenching degree of BPD-COFs is four times more than that of BPDB. Besides better selectivity, BPD-COFs also displays the prominent advantages, such as the wider concentration range (4.20 × 10−10∼1.26 × 10-6 M) and lower limit of detection (6.80 × 10-11 M) compared to that of BPDB (1.00 × 10-7∼5.00 × 10-7 M, 4.50 × 10-8 M). Good spiked recoveries (>92.0 %) in chocolate and tea support that BPD-COFs is competent to detect Ni2+ in real samples. All these results indicate that BPD-COFs is potential as a fast, sensitive, and accurate fluorescence sensing platform for the selective detection of Ni2+ in complex system.

Stable, Dual Redox Unit Organic Electrodes.

The development of organic materials for electrochemical energy storage has attracted great attention because of their high natural abundance and relatively low toxicity. The bulk of these studies focus on small molecules, polymers, or porous/framework-type materials that employ one type of redox moiety. Here, we report the synthesis and testing of organic materials that incorporate two distinct types of redox units: triptycene-based quinones and perylene diimides. We examine this “dual redox” concept through the synthesis of both frameworks and small molecule model compounds with the redox units positioned at the vertices and connection points. Such a design increases the theoretical capacity of the material. It also imparts high stability because both examples are relatively rigid and highly insoluble in the electrolyte. Lithium-ion batteries consisting of the framework and the small molecule have an excellent cycling retention of 75 and 77%, respectively, over 500 cycles at 1 C. Our work emphasizes the advantages of using multiple redox units in the design of the cathodic materials and redox-active triptycene linkages to achieve high cycling stability.

Accelerating the Coupling of Maleated Polyolefins with Polyesters via Tin Compounds

Poly(ethylene terephthalate) (PET) and polyethylene (PE) are two of the most commonly used polymers in the packaging industry, and they make up a large portion of the recycling stream. Adhesion between these two immiscible polymers is poor without compatibilization. Maleic anhydride (MAH) grafted PE is a popular compatibilizer for PET/PE but is limited by the slow rate of reaction. In this study, we propose tin additives for improving adhesion and explore the mechanism of that improvement. We demonstrate that either dibutyltin oxide (DBTO) or di-n-octyltin oxide (DOTO) can dramatically enhance adhesion with only 60 s of contact time during lamination. A range of MAH and DOTO concentrations are examined, yielding adhesion up to 1300 J/m2. Possible reactions at the interface are investigated with small molecule model compounds, namely 1-hexadecanol, octylsuccinic anhydride (OSA), and ethylene glycol dibenzoate. DOTO does not improve the reaction rate in the hexadecanol–OSA system. This suggests that another...

Bulk Acyclic Diene Metathesis Polycondensation

AbstractBulk acyclic diene metathesis (ADMET) polymerization performed in the melt at temperatures up to 175 °C is completed using a cyclic (alkyl)(amino) carbene (CAAC) ruthenium‐based Grubbs catalyst. High temperature stability is investigated at temperatures well above conventional ADMET chemistry, leading to the highest weight‐average molecular weights ever achieved for any ADMET polymer. A study of isomerization tendency (double bond migration) is done via self‐metathesis of a small molecule model compound using CAAC catalysts. Minimal olefin isomerization is observed using appropriate catalyst ratios and temperatures.

NMR Analysis of Hydroxyl‐Terminated Polybutadiene End Groups and Reactivity Differences with Monoisocyanates

ABSTRACTNuclear magnetic resonance (NMR) spectroscopy was employed to investigate both the end group microstructure of R‐45HTLO hydroxyl‐terminated polybutadiene (HTPB) and reactivity rate differences among the different types of end groups. There is some conflict in the literature about the exact nature of the end groups and which resonance frequencies represent the three main types of methylene‐hydroxyl end groups (cis, trans, or vinyl) and other possible branch point end groups (geraniol). NMR spectral analysis of small molecule model compounds supports the cis, trans, and vinyl end groups model. A model reaction scheme is proposed that produces branch points without the requirement of any “geraniol” structures. The reaction, with and without catalyst, of the various HTPB end groups with three different monoisocyanates (2‐fluorophenyl isocyanate, phenyl isocyanate, and tert‐butyl isocyanate) monitored by NMR spectroscopy, revealed different reactivity rates that are correlated with the assigned structures. In both the catalyzed and uncatalyzed reactions, the vinyl end groups reacted slower than the cis or trans end groups. As expected, the bulky isocyanates were the slowest to react, while the isocyanate group with electron withdrawing groups reacted the fastest. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2665–2671

Anion exchange membranes with well-developed conductive channels: Effect of the functional groups

To explore the alkaline stability of cationic groups, several investigations have been reported via small molecule model compounds, theoretical calculations or grafting cations to the benzylic positions of the polymer backbones. In this work, anion exchange membranes (AEMs) with various head groups of trimethylammonium (TMA), 1-methylpyrrolidinium (MPY), 1-methylpiperidinium (MPRD), 1-methylimidazolium (Im1) and 1,2-dimethylimidazolium (Im1,2)) flexibly linked to poly(ether sulfone) (PES) backbones are prepared to explore the effect of pendent functional groups. The AEMs tethering MPRD groups are found to exhibit the highest Br− conductivity of 60.4 ± 2.1 mS cm−1 at 80 °C. PES-MPY exhibits the best relative stability and maintains 90.7% and 83.1% of the original ionic exchange capacity (IEC) and conductivity, respectively, after immersed into 2 M NaOH at 60 °C for 672 h. Meanwhile, the alkaline stability is in the order of PES-MPY > PES-MPRD > PES-TMA > PES-Im1,2 > PES-Im1. The maximum power density of a H2/O2 fuel cell using PES-MPRD (109.0 mW cm−2) and PES-MPY (106.5 mW cm−2) is larger than that using PES-Im1 (65.1 mW cm−2). The results provide a guidance for designing high-performance AEMs.

Coordination environment changes of the vanadium in vanadium-dependent haloperoxidase enzymes

Vanadium-dependent haloperoxidases are a class of enzymes that catalyze oxidation reactions with halides to form halogenated organic products and water. These enzymes include chloroperoxidase and bromoperoxidase, which have very different protein sequences and sizes, but regardless the coordination environment of the active sites is surprisingly constant. In this manuscript, the comparison of the coordination chemistry of V-containing-haloperoxidases of the trigonal bipyramidal geometry was done by data mining. The catalytic cycle imposes changes in the coordination geometry of the vanadium to accommodate the peroxidovanadium(V) intermediate in an environment we describe as a distorted square pyramidal geometry. During the catalytic cycle, this intermediate converts to a trigonal bipyramidal intermediate before losing the halogen and forming a tetrahedral vanadium-protein intermediate. Importantly, the catalysis is facilitated by a proton-relay system supplied by the second sphere coordination environment and the changes in the coordination environment of the vanadium(V) making this process unique among protein catalyzed processes. The analysis of the coordination chemistry shows that the active site is very tightly regulated with only minor changes in the coordination geometry. The coordination geometry in the protein structures deviates from that found for both small molecules crystalized in the absence of protein and the reported functional small molecule model compounds. At this time there are no examples reported of a structurally similar small molecule with the geometry observed for the peroxidovanadium(V) in the active site of the vanadium-containing haloperoxidases.

Regioisomeric Preference in Ring-Opening Polymerization of 3',5'-Cyclic Phosphoesters of Functional Thymidine DNA Analogues.

Regioregularity is a crucial property in the synthesis of DNA analogues, as natural DNA is synthesized exclusively in the 5' to 3' direction. We have focused our attention on the determination of the regioisomeric distribution of poly(3',5'-cyclic 3-(3-butenyl) thymidine ethylphosphate)s obtained from the ring-opening polymerization of (R)-3',5'-cyclic 3-(3-butenyl) thymidine ethylphosphate. The regioisomeric preference was investigated by comparison to synthesized model compounds of 3',3'-, 3',5'-, and 5',5'-linkages, where the model 3'-phosphoester linkages were to the secondary alcohol of 3-hydroxytetrahydrofuran and the model 5'-linkages derived from coupling to the primary alcohol of tetrahydrofurfuryl alcohol. From the 31P resonance frequency assignments of those small molecule model compounds, 31P NMR spectra revealed the major connectivity in the polymer backbone to be 3',5'-linkages, with ≤30% of other isomeric forms. Model reactions employing a series of alcohol initiators imparting various degrees of steric hindrance, to mimic the increased steric hindrance of the propagating alcohol relative to the initiator, were then conducted to afford the corresponding ring-opened unimer adducts and to gain understanding of the regioselectivity during the ring-opening polymerization. 1H-31P heteronuclear multiple-bond correlation spectroscopy showed ethanol and 4-methoxybenzyl alcohol initiation to yield only the P-O5' bond cleavage product, whereas attack by isopropyl alcohol upon (R)-3',5'-cyclic 3-(3-butenyl) thymidine ethylphosphate afforded both P-O3' and P-O5' bond cleavage products, supporting our hypothesis that the increased steric hindrance of the propagating species dictates the regioselectivity of the P-O bond cleavage. Further model reactions suggested that the P-O5' bond cleavage products can be detected upon the formation of dimers during the ring-opening polymerization. Overall, this work provides a fundamental understanding of the polymerization behavior of six-membered cyclic phosphoesters and broadens the scope of DNA analogues from the ring-opening polymerization of 3',5'-cyclic phosphoesters.

Oxidation-Responsive Aliphatic Polycarbonates from N-Substituted Eight-Membered Cyclic Carbonate: Synthesis and Degradation Study.

Oxidation-responsive aliphatic polycarbonates represent a promising branch of functional biodegradable polymers. This paper reports the synthesis and ring-opening polymerization (ROP) of an eight-membered cyclic carbonate possessing phenylboronic pinacol ester (C3) and the H2 O2 -triggered degradation of its polymer (PC3). C3 is prepared from the inexpensive and readily available diethanolamine with a moderate yield and undergoes the well-controlled anionic ROP with a living character under catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene. It can also be copolymerized with l-lactide, trimethylene carbonate, and 5-ter-butyloxycarbonylamino trimethylene carbonate, affording the copolymers with a varied distribution of the repeating units. To clearly demonstrate the oxidative degradation mechanism of PC3, this paper first investigates the H2 O2 -induced decomposition of small-molecule model compounds by proton nuclear magnetic resonance (1 H NMR). It is found that the adduct products formed by the in-situ-generated secondary amines and p-quinone methide (QM) are thermodynamically unstable and can decompose slowly back to QM and the amines. On this basis, this paper further studies the H2 O2 -accelerated degradation of PC3 nanoparticles that are prepared by the o/w emulsion method. A sequential process of oxidation of the phenylboronic ester, 1,6-elimination of the in-situ-generated phenol, releasing CO2 and intramolecular cyclization or isomerization is proposed as the degradation mechanism of PC3.

A Schiff-base cross-linked supramolecular polymer containing diiminophenol compartments and its interaction with copper(II) ions

We report here the preparation of a Schiff-base linked organic polymer 1 based on linkages containing the potent supramolecular aggregator benzene-1,3,5-tricarboxamide, connected through 2,6-diiminophenol metal binding pockets into a cross-linked polymer. The morphological and physical properties of this material are studied using electron microscopy techniques, thermal analysis, NMR, fluorescence spectroscopy and gas adsorption studies. The interaction of the polymer 1 with CuII ions is then investigated by soaking the material with methanolic copper acetate solution, and studying the resulting aggregates using EDX microscopy and FTIR spectroscopy. A small-molecule model compound 2 is also prepared and crystallographically characterised to act as a spectroscopic comparison, providing strong evidence that 1 interacts with copper ions through a nucleation/seeding mechanism for the growth of microcrystalline copper acetate deposits, rather than via chemisorption of the copper ions within the diiminophenol binding pockets. Preliminary results suggest a similar mechanism for CoII adsorption, while ZnII ions exhibit a separate interaction mode.

Thermochemical Stability Study of Alkyl-Tethered Quaternary Ammonium Cations for Anion Exchange Membrane Fuel Cells

The increased interest in the use of anion exchange membranes (AEMs) for applications in electrochemical devices has prompted significant efforts in designing materials with robust stability in alkaline media. Most reported AEMs suffer from polymer backbone degradation as well as cation functional group degradation. In this report, we provide comprehensive experimental investigations for the analysis of cation functional group stability under alkaline media. A silver oxide-mediated ion exchange method and an accelerated stability test in aqueous KOH solutions at elevated temperatures using a Parr reactor were used to evaluate a broad scope of quaternary ammonium (QA) cationic model compound structures, particularly focusing on alkyl-tethered cations. Additionally, byproduct analysis was employed to gain better understanding of degradation pathways and trends of alkaline stability. Experimental results under different conditions gave consistent trends in the order of cation stability of various QA small molecule model compounds. Overall, cations that are benzyl-substituted or that are near to electronegative atoms (such as oxygen) degrade faster in alkaline media in comparison to alkyl-tethered QAs. These comprehensive model compound stability studies provide valuable information regarding the relative stability of various cation structures and can help guide researchers towards designing new and promising candidates for AEM materials.