G4-Quartet·M+Borate Hydrogels

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 1H NMR and rheology. Data from powder XRD, 1H 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 viscosit

Divergent Synthesis of Alternant Bisanthenequinone and Nonalternant Heptalenodifluorenedione Ring Systems via a Concentration-Dependent Rearrangement

The synthesis of a diol containing a nonalternant aromatic core was investigated to access a nonalternant isomer of bisanthene with functional groups suitable for two-dimensional polymerization. An alternant diol and its nonalternant isomer were prepared in a short synthetic route from the same bifluorenylidene starting material. The bifluorenylidene reactant undergoes a Stone–Wales rearrangement in neat triflic acid, which unexpectedly provided both an alternant and nonalternant dione. The rearrangement was characterized by spectroscopy and single crystal X-ray diffraction of Grignard addition products of both isomers. The relative yield of the rearranged, alternant product increased along with the initial concentration of its polycyclic aromatic hydrocarbon (PAH) precursor, implicating a bimolecular rearrangement mechanism and enabling the divergent synthesis of both the nonalternant and alternant products. These findings offer convenient access to functional derivatives of two PAH classes of interest for their optoelectronic properties and serve as yet another warning about the importance of characterizing these materials with care, especially when insoluble products must be carried forward in a multistep synthetic route

A G4·K+Hydrogel stabilized by an anion

Supramolecular hydrogels derived from natural products have promising applications in diagnostics, drug delivery, and tissue engineering. We studied the formation of a long-lived hydrogel made by mixing guanosine (G, 1) with 0.5 equiv of KB(OH)4. This ratio of borate anion to ligand is crucial for gelation as it links two molecules of 1, which facilitates cation-templated assembly of G4·K+ quartets. The guanosine–borate (GB) hydrogel, which was characterized by cryogenic transmission electron microscopy and circular dichroism and 11B magic-angle-spinning NMR spectroscopy, is stable in water that contains physiologically relevant concentrations of K+. Furthermore, non-covalent interactions, such as electrostatics, π-stacking, and hydrogen bonding, enable the incorporation of a cationic dye and nucleosides into the GB hydrogel

A Molecular Chaperone for G4-Quartet Hydrogels

Thioflavin T (ThT) functions as a molecular chaperone for gelation of water by guanosine and lithium borate. Substoichiometric ThT (1 mol % relative to hydrogelator) results in faster hydrogelation as monitored by ¹H NMR and visual comparison. Vial-inversion tests and rheology show that ThT increases the stiffness of the Li⁺ guanosine-borate (GB) hydrogel. In addition, the dye promotes relatively rapid and complete repair of a Li⁺ GB hydrogel destroyed by shearing. We used rheology to show that other planar aromatics, some cationic and one neutral dye (methylene violet), also stiffened the Li⁺ GB hydrogel. Data from powder X-ray diffraction, UV, and circular dichroism spectroscopy and ThT fluorescence indicate that G4 quartets are formed by the Li⁺ GB system. We observed a species in solution by ¹H NMR that was intermediate in size between monomeric gelator and NMR-invisible hydrogel. The concentration of this intermediate decreased much faster when ThT was present in solution, again showing that the dye can accelerate hydrogel formation. We propose that ThT functions as a molecular chaperone by end stacking on terminal G4-quartets and promoting the assembly of these smaller fragments into longer G4-based structures that can then provide more cross-linking sites needed for hydrogelation

Total body irradiation must be delivered at high dose for efficient engraftment and tolerance in a rhesus stem cell gene therapy model

Reduced intensity conditioning (RIC) is desirable for hematopoietic stem cell (HSC) gene therapy applications. However, low gene marking was previously observed in gene therapy trials, suggesting that RIC might be insufficient for (i) opening niches for efficient engraftment and/or (ii) inducing immunological tolerance for transgene-encoded proteins. Therefore, we evaluated both engraftment and tolerance for gene-modified cells using our rhesus HSC gene therapy model following RIC. We investigated a dose de-escalation of total body irradiation (TBI) from our standard dose of 10Gy (10, 8, 6, and 4Gy), in which rhesus CD34+ cells were transduced with a VSVG-pseudotyped chimeric HIV-1 vector encoding enhanced green fluorescent protein (GFP) (or enhanced yellow fluorescent protein (YFP)). At ∼6 months after transplantation, higher-dose TBI resulted in higher gene marking with logarithmic regression in peripheral blood cells. We then evaluated immunological tolerance for gene-modified cells, and found that lower-dose TBI allowed vigorous anti-GFP antibody production with logarithmic regression, while no significant anti-VSVG antibody formation was observed among all TBI groups. These data suggest that higher-dose TBI improves both engraftment and immunological tolerance for gene-modified cells. Additional immunosuppression might be required in RIC to induce tolerance for transgene products. Our findings should be valuable for developing conditioning regimens for HSC gene therapy applications

A G₄·K⁺ Hydrogel Stabilized by an Anion

Supramolecular hydrogels derived from natural products have promising applications in diagnostics, drug delivery, and tissue engineering. We studied the formation of a long-lived hydrogel made by mixing guanosine (G, <b>1</b>) with 0.5 equiv of KB­(OH)₄. This ratio of borate anion to ligand is crucial for gelation as it links two molecules of <b>1</b>, which facilitates cation-templated assembly of G₄·K⁺ quartets. The guanosine–borate (GB) hydrogel, which was characterized by cryogenic transmission electron microscopy and circular dichroism and ¹¹B magic-angle-spinning NMR spectroscopy, is stable in water that contains physiologically relevant concentrations of K⁺. Furthermore, non-covalent interactions, such as electrostatics, π-stacking, and hydrogen bonding, enable the incorporation of a cationic dye and nucleosides into the GB hydrogel

G4-Quartet·M⁺ Borate Hydrogels

The ability to modulate the physical properties of a supramolecular hydrogel may be beneficial for biomaterial and biomedical applications. We find that guanosine (G <b>1</b>), 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 <b>1</b> and KB­(OH)₄ formed the strongest hydrogel, while the weakest system was obtained with LiB­(OH)₄, as judged by ¹H NMR and rheology. Data from powder XRD, ¹H 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 <b>1</b> 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 <b>1</b> 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 viscosit