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Molecular recognition of organic and inorganic phosphates at the aqueous interface

Neal, Jennifer Frances
http://rave.ohiolink.edu/etdc/view?acc_num=osu158760097781108

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Chemistry.
The air‒water interface is a unique microenvironment to explore host‒guest chemistry. In the following chapters, molecular recognition of a diverse set of organic and inorganic phosphates were explored at the aqueous interface. Chapter 1 provides a brief introduction to interfacial molecular recognition across synthetic, environmental, and biological systems. This literature review provides a background on supramolecular chemistry at the aqueous interface and the unique properties driving these interactions at the surface of water. Chapter 2 explores a biologically relevant phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphatidic acid, binding to the amino acid arginine. Through a systematic evaluation of the binding sites by testing glycine and guanidinium chloride as control molecules, we determined that the guanidinium moiety was binding to the phosphate headgroup of the phospholipid. Interestingly, the interfacial binding affinity was 10,000-fold greater than the binding affinity determined through bulk solution measurements. The surface binding affinity was determined using infrared reflection absorption spectroscopy and the surface pressure-mean molecular area isotherms. Chapter 3 is a systematic evaluation of the driving forces of interfacial phosphate recognition using synthetic receptors. Four surface receptors were synthesized with long octadecyl chain(s) and different functional groups at the binding site in which guanidinium, thiouronium, and thiourea headgroups were tested. The number of alkyl chains was modulated (single chain versus double chain) to determine their effect on the supramolecular packing and binding affinity. Overall, we determined the driving forces influencing interfacial phosphate recognition as the chemical, physical, and supramolecular superstructural. The chemical nature of the headgroup influenced binding where the guanidinium > thiouronium > thiourea for phosphate affinity. The physical environment of the aqueous subphase influenced the binding selectivity over chloride in which high ionic strength with addition of sodium chloride hindered phosphate selectivity for the double chain guanidinium receptor. The supramolecular superstructural packing arrangement influenced phosphate binding because the single chain guanidinium did not bind to phosphate whereas the double chain guanidinium strongly bound to phosphate. These driving forces are crucial to developing the rational design principles of surface receptors that are selective towards aqueous phosphates. Chapter 4 explores the double chain guanidinium receptor’s selectivity towards various anions. We found that the guanidinium receptor binds to sulfate> phosphate> iodide> nitrate >chloride~ bromide~ nitrite. Interestingly, the guanidinium receptor is selective for sulfate over phosphate even though the dehydration penalty for the sulfate anion is significant. Sulfate is a (-2) anion and the phosphate is a (-1) anion and charge differences could be influencing both the binding affinity and binding stoichiometry of the guanidinium interactions to either phosphate or sulfate. It was already previously shown in Chapter 3 that electrostatic interactions dominate over hydrogen bonding interactions alone because the charged guanidinium receptor had a stronger phosphate affinity than the neutral thiourea receptor. Therefore, it is not surprising that a (-2) anion would outcompete a (-1) anion at the surface of water. Infrared reflection absorption spectroscopy and vibrational sum frequency generation spectroscopy were both used to determine the guanidinium selectivity and essentially provide an order of the relative anion affinities. Lastly, Chapter 5 explores a series of semi-soluble phosphoric and phosphonic acids at the aqueous interface. The relative protonation state and sodium binding properties were determined by systematically controlling the pH and sodium concentrations. Also, competitive binding interactions between protonation state and sodium complexation were explored by increasing amounts of sodium chloride at low pH. We have determined a critical sodium chloride concentration at pH 2 necessary to outcompete the acid-base equilibrium for the phosphonic acid semi-soluble species. The following chapters explore supramolecular chemistry at the air‒water interface and provide new insights into studying these interactions. Each chapter is a diverse look into molecular recognition at the aqueous surface in which Chapter 2 is a biologically relevant system, Chapters 3 and 4 are synthetic receptors, and Chapter 5 is relevant for atmospheric and oceanic chemistries.
Heather Allen (Advisor)
Jovica Badjić (Committee Member)
L. Robert Baker (Committee Member)
Andrew May (Committee Member)
128 p.
Analytical Chemistry; Chemistry

Recommended Citations

Citations

  • Neal, J. F. (2020). Molecular recognition of organic and inorganic phosphates at the aqueous interface [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu158760097781108

    APA Style (7th edition)

  • Neal, Jennifer. Molecular recognition of organic and inorganic phosphates at the aqueous interface. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu158760097781108.

    MLA Style (8th edition)

  • Neal, Jennifer. " Molecular recognition of organic and inorganic phosphates at the aqueous interface." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu158760097781108

    Chicago Manual of Style (17th edition)

osu158760097781108
102
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