title: Disaggregation is a Mechanism for Emission Turn-On of ortho-Aminomethylphenylboronic Acid-Based Saccharide Sensors.
abstract: ortho-Aminomethylphenylboronic acid-based receptors with appended fluorophores are commonly used as molecular sensors for saccharides in aqueous media. The mechanism for fluorescence modulation in these sensors has been attributed to some form of photoinduced electron transfer (PET) quenching, which is diminished in the presence of saccharides. Using a well-known boronic acid-based saccharide sensor (3), this work reveals a new mechanism for fluorescence turn-on in these types of sensors. Compound 3 exhibits an excimer, and the associated ground-state aggregation is responsible for fluorescence modulation under certain conditions. When fructose was titrated into a solution of 3 in 2:1 water/methanol with NaCl, the fluorescence intensity increased. Yet, when the same titration was repeated in pure methanol, a solvent in which the sensor does not aggregate, no fluorescence response to fructose was observed. This reveals that the fluorescence increase is not fully associated with fructose binding, but instead disaggregation of the sensor in the presence of fructose. Further, an analogue of the sensor that does not contain a boronic acid (4) responded nearly identically to 3 in the presence of fructose, despite having no functional group with which to bind the saccharide. This further supports the claim that fluorescence modulation is not primarily a result of binding, but of disaggregation. Using an indicator displacement assay and isothermal titration calorimetry, it was confirmed that fructose does indeed bind to the sensor. Thus, our evidence reveals that while binding occurs with fructose in the aqueous solvent system used, it is not related to the majority of the fluorescence modulation. Instead, disaggregation dominates the signal turn-on, and is thus a mechanism that should be investigated in other ortho-aminomethylphenylboronic acid-based sensors.
authors.affiliation: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Brette M
authors.initials: BM
authors.lastname: Chapin
authors.affiliation: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Pedro
authors.initials: P
authors.lastname: Metola
authors.affiliation: Department of Chemistry, University of South Florida , Tampa, Florida 33620, United States.
authors.forename: Sai Lakshmana
authors.initials: SL
authors.lastname: Vankayala
authors.affiliation: Department of Chemistry, University of South Florida , Tampa, Florida 33620, United States.
authors.forename: H Lee
authors.initials: HL
authors.lastname: Woodcock
authors.affiliation: Van't Hoff Institute for Molecular Sciences, University of Amsterdam , 1098 XH Amsterdam, Netherlands.
authors.forename: Tiddo J
authors.initials: TJ
authors.lastname: Mooibroek
authors.affiliation: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.affiliation: Department of Chemistry, University of South Florida , Tampa, Florida 33620, United States.|Department of Chemistry, Eckerd College , St. Petersburg, Florida 33711, United States.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Larkin
authors.affiliation: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Eric V
authors.identifier: 0000-0002-5137-8797
authors.initials: EV
authors.lastname: Anslyn
mesh_terms: D002241:Carbohydrates / Q000032:analysis*; D004579:Electron Transport; D005453:Fluorescence; D000432:Methanol / Q000737:chemistry; D008744:Methylamines / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D055668:Photochemical Processes; D012965:Sodium Chloride / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry
chemical_list: D002241:Carbohydrates; D008744:Methylamines; D014867:Water; D012965:Sodium Chloride; D000432:Methanol