title: G4-quartet·M(+) borate hydrogels.
abstract: The ability to modulate the physical properties of a supramolecular hydrogel may be beneficial for biomaterial and biomedical applications. We find that guanosine (G 1), when combined with 0.5 equiv of potassium borate, forms a strong, self-supporting hydrogel with elastic moduli >10 kPa. The countercation in the borate salt (MB(OH)4) significantly alters the physical properties of the hydrogel. The gelator combination of G 1 and KB(OH)4 formed the strongest hydrogel, while the weakest system was obtained with LiB(OH)4, as judged by (1)H NMR and rheology. Data from powder XRD, (1)H double-quantum solid-state magic-angle spinning (MAS) NMR and small-angle neutron scattering (SANS) were consistent with a structural model that involves formation of borate dimers and G4·K(+) quartets by G 1 and KB(OH)4. Stacking of these G4·M(+) quartets into G4-nanowires gives a hydrogel. We found that the M(+) cation helps stabilize the anionic guanosine-borate (GB) diesters, as well as the G4-quartets. Supplementing the standard gelator mixture of G 1 and 0.5 equiv of KB(OH)4 with additional KCl or KNO3 increased the strength of the hydrogel. We found that thioflavin T fluoresces in the presence of G4·M(+) precursor structures. This fluorescence response for thioflavin T was the greatest for the K(+) GB system, presumably due to the enhanced interaction of the dye with the more stable G4·K(+) quartets. The fluorescence of thioflavin T increased as a function of gelator concentration with an increase that correlated with the system's gel point, as measured by solution viscosity.
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Gretchen Marie
authors: GM
authors: Peters
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Luke P
authors: LP
authors: Skala
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Taylor N
authors: TN
authors: Plank
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Hyuntaek
authors: H
authors: Oh
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: G N Manjunatha
authors: GN
authors: Reddy
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Andrew
authors: A
authors: Marsh
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Steven P
authors: SP
authors: Brown
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Srinivasa R
authors: SR
authors: Raghavan
authors: §Department of Physics and #Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
authors: Jeffery T
authors: JT
authors: Davis
mesh_terms: D052160:Benzothiazoles; D001881:Borates / Q000737:chemistry*; D005453:Fluorescence; D006151:Guanosine / Q000737:chemistry*; D020100:Hydrogels / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008672:Metals, Alkali / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011522:Protons; D013844:Thiazoles / Q000737:chemistry*
chemical_list: D052160:Benzothiazoles; D001881:Borates; D020100:Hydrogels; D008672:Metals, Alkali; D009942:Organometallic Compounds; D011522:Protons; D013844:Thiazoles; D006151:Guanosine; C009462:thioflavin T