Recognition of carboxylates by synthetic receptors – from structure-affinity studies to solid-contact anion-selective electrode prototyping
Date
2024-07-11
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Abstract
Huvipakkuvate anioonide sisalduse reaalajas määramiseks erinevate tootmisprotsesside käigus, kaugel asuvates kohtades või miks mitte meie enda randmelt, on vaja arendada lihtsaid ja miniaturiseeritavaid analüsaatoreid. Sellisteks seadmeteks sobivad oma omaduste poolest hästi ioonselektiivsed elektroodid – need on lihtsad, odavad, kiired, miniaturiseeritavad ja need saab asetada otse mõõdetavasse lahusesse, ilma et peaks selleks proovi eeltöötlema või laborisse viima. Kuigi väikeste mõõtmetega katioone on polümeerse membraaniga ioonselektiivsete elektroodidega määratud juba üle 40 aasta, on keerukamate ioonide, iseäranis orgaaniliste anioonide määramine jätkuvalt lahendamata probleem, kuna ei ole leitud piisavalt häid ionofoore, millega elektroodi membraani valmistada.
Käesolev väitekiri keskendub olulise orgaaniliste anioonide perekonna – monokarboksülaatide – vastasmõjude uurimisele potentsiaalsete uute ionofooridega. Selleks mõõdeti suhtelise tuumamagnetresonants-spektromeetrilise meetodiga 44 sünteetilise retseptormolekuli seondumisafiinsused kaheksa karboksülaatiooniga (formaat, atsetaat, pivalaat, laktaat, ibuprofeen, ketoprofeen, glükuronaat ja bensoaat). Koostati seondumisskaalad, kus kõik retseptor-anioon seondumisafiinsused on omavahel võrreldavad. Leiti, et karbüksülaatanioonide sidumiseks on kõige sobivamad planaarsed tetradentaatsed retseptorid. Lisaks kirjeldati, kuidas retseptori mittepolaarsed asendusrühmad, molekulide steerika, võimalikud lisainteraktsioonid ja solvofoobsed efektid konkreetsete karboksülaatide seondumist mõjutavad. Tulemustest ilmnes, et tekkivate seondumismustrite tõttu on mitme retseptori koosmõjul võimalik erineva struktuuriga karboksülaate üksteisest eristada.
Seondumisuurimuse tulemusena valiti välja üks sobivaimate omadustega retseptormolekul, 1,3-biskarbasolüüluurea derivaat, mida kasutati ionofoorina tahke kontaktiga atsetaatselektiivsete elektroodide valmistamiseks. Valmistatud elektroodidel oli väikeste karboksülaatide (atsetaat, formaat) ja bikarbonaadi suhtes kõrgem selektiivsus kui kloriidiooni suhtes. Lisaks leiti, et valitud ionofoori lisamine membraani vähendab oluliselt tüüpiliste segavate ioonide (SCN-, I-, NO3- ja Br-) mõju, mis on oluline samm edasi karboksülaate siduvate ionofooride disainis.
To address the need for precise anion detection in various production processes, remote locations, and even wearable devices, the development of simple and miniaturisable analysers is essential. Potentiometric ion-selective electrodes (ISEs) are well-suited for this purpose due to their favourable characteristics: simplicity, affordability, speed, miniaturisation, and direct placement in the measured solution without extensive sample preparation or laboratory handling. While polymer membrane ISEs have been effective for detecting small cations for over four decades, determining more complex ions, such as organic anions, remains a challenge. Finding suitable ionophores to prepare electrode membranes for these anions has proven difficult. This dissertation presents a study of the interactions between small monocarboxylates and potential new ionophores. By measuring the binding constants of eight carboxylates (formate, acetate, pivalate, lactate, ibuprofen, ketoprofen, glucuronate, and benzoate) to 44 synthetic receptor molecules using nuclear magnetic resonance, eight binding affinity scales where constructed where all the binding affinities are comparable. Planar tetradentate receptors were identified as particularly effective for binding carboxylate anions. Additionally, it is explored how non-polar substituents, steric effects, additional interactions, and solvophobic effects impact the binding of specific carboxylates. The results revealed that the selected synthetic hydrogen-bond donor receptors can distinguish carboxylates with different structures. As a result of this binding study, a 1,3-bis(carbazolyl)urea derivative was selected as a hydrogen-bonding ionophore to create prototypes of electrodes that can detect acetate. These electrodes showed a unique selectivity pattern of different anions, preferring smaller carboxylates like acetate and formate, as well as bicarbonate, over chloride. The addition of this ionophore to the electrode’s membrane also reduced the interference from other common ions like SCN-, I-, NO3-, and Br-. This discovery is an important step forward in designing ionophores that can specifically bind carboxylates.
To address the need for precise anion detection in various production processes, remote locations, and even wearable devices, the development of simple and miniaturisable analysers is essential. Potentiometric ion-selective electrodes (ISEs) are well-suited for this purpose due to their favourable characteristics: simplicity, affordability, speed, miniaturisation, and direct placement in the measured solution without extensive sample preparation or laboratory handling. While polymer membrane ISEs have been effective for detecting small cations for over four decades, determining more complex ions, such as organic anions, remains a challenge. Finding suitable ionophores to prepare electrode membranes for these anions has proven difficult. This dissertation presents a study of the interactions between small monocarboxylates and potential new ionophores. By measuring the binding constants of eight carboxylates (formate, acetate, pivalate, lactate, ibuprofen, ketoprofen, glucuronate, and benzoate) to 44 synthetic receptor molecules using nuclear magnetic resonance, eight binding affinity scales where constructed where all the binding affinities are comparable. Planar tetradentate receptors were identified as particularly effective for binding carboxylate anions. Additionally, it is explored how non-polar substituents, steric effects, additional interactions, and solvophobic effects impact the binding of specific carboxylates. The results revealed that the selected synthetic hydrogen-bond donor receptors can distinguish carboxylates with different structures. As a result of this binding study, a 1,3-bis(carbazolyl)urea derivative was selected as a hydrogen-bonding ionophore to create prototypes of electrodes that can detect acetate. These electrodes showed a unique selectivity pattern of different anions, preferring smaller carboxylates like acetate and formate, as well as bicarbonate, over chloride. The addition of this ionophore to the electrode’s membrane also reduced the interference from other common ions like SCN-, I-, NO3-, and Br-. This discovery is an important step forward in designing ionophores that can specifically bind carboxylates.
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Väitekirja elektrooniline versioon ei sisalda publikatsioone