Physical properties of pyrimidine and purine antimetabolites. I. The effects of salts and temperature on the solubility of 5-fluorouracil, 1-(2-tetrahydrofuryl)-5-fluorouracil, 6-mercaptopurine, and thrioinosine

Dynamic Tannic Acid Hydrogel with Self-Healing and pH Sensitivity for Controlled Release

Dynamic hydrogels constructed with dynamic chemical bonds often have mechanical strength and self-healing properties. In this paper, tannic acid is combined with lysine-containing F127 through Schiff base. A series of FLaT hydrogels cross-linked by hydrogen bonds and dynamic chemical bonds is prepared, and the influence of Schiff base amount on the performance is discussed. The FLaT hydrogel exhibits reversible sol-gel transition, self-healing, injectability, and pH sensitivity. Increasing the amount of Schiff base can improve the strength, stability, and self-healing ability of the hydrogel. Owing to their low cytotoxicity, linear release pattern, and pH-controlled release rate, the FLaT hydrogels show potential use in drug delivery systems for cancer treatment.

Thermally induced and physically cross-linked hydrogel doped with graphene oxide for controlled release

Graphene oxide (GO) is an ideal hydrogel material because of its water solubility, non-toxicity, and excellent mechanical properties. Here, we added GO to oligo(lysine)-modified F127 to prepare a series of FLGO composite hydrogels. The FLGO hydrogel was thermally induced, stable and injectable. And the content of GO would affect the sol-gel transition, rheological properties and glass transition temperature of the FLGO hydrogel. GO was connected to the matrix through electrostatic interactions and hydrogen bonds. The cross-linking effect of GO enhanced the FLGO hydrogel. We also studied the release properties of the FLGO hydrogel loaded with anticancer drug 5-fluorouracil. Compared with F127 hydrogel, the FLGO hydrogel showed a linear, slower and stable release pattern within one week. The release rate of FLGO hydrogel could be adjusted by the pH and it was faster under acidic conditions. Therefore, the FLGO hydrogel is expected to be used as a drug release system in the field of biomedicine.

Factors Governing the Chemical Stability and NMR Parameters of Uracil Tautomers and Its 5-Halogen Derivatives

We report on the density functional theory (DFT) modelling of structural, energetic and NMR parameters of uracil and its derivatives (5-halogenouracil (5XU), X = F, Cl, Br and I) in vacuum and in water using the polarizable continuum model (PCM) and the solvent model density (SMD) approach. On the basis of the obtained results, we conclude that the intramolecular electrostatic interactions are the main factors governing the stability of the six tautomeric forms of uracil and 5XU. Two indices of aromaticity, the harmonic oscillator model of aromaticity (HOMA), satisfying the geometric criterion, and the nuclear independent chemical shift (NICS), were applied to evaluate the aromaticity of uracil and its derivatives in the gas phase and water. The values of these parameters showed that the most stable tautomer is the least aromatic. A good performance of newly designed xOPBE density functional in combination with both large aug-cc-pVQZ and small STO(1M)-3G basis sets for predicting chemical shifts of uracil and 5-fluorouracil in vacuum and water was observed. As a practical alternative for calculating the chemical shifts of challenging heterocyclic compounds, we also propose B3LYP calculations with small STO(1M)-3G basis set. The indirect spin-spin coupling constants predicted by B3LYP/aug-cc-pVQZ(mixed) method reproduce the experimental data for uracil and 5-fluorouracil well.

Dual responsive oligo(lysine)-modified Pluronic F127 hydrogels for drug release of 5-fluorouracil

Peptide-containing hydrogels have become a research hotspot due to their unique secondary structure and biocompatibility. Herein, we used amino-terminated F127 as a macroinitiator to initiate the ring-opening polymerization of l-lysine(z)-NCA, and the obtained oligo(lysine)-modified F127 (FL) had degrees of polymerization of lysine of 2, 5, and 8. The results showed that the FL hydrogels had reversible temperature-dependent sol–gel transitions, and the introduction of lysine increased the critical gel temperature. In the dilute solution of FL, the micelle size increased and aggregated as the pH increased; the micelle grew into a rod-like shape under alkaline conditions. Scanning electron micrographs showed that the interior of the FL hydrogel had a more complete porous structure. The FL-2 hydrogel loaded with 5-fluorouracil exhibited an approximately linear release trend within 12 h and has good biocompatibility. Therefore, FL hydrogels have potential applications in the field of biomedicine.

Oligo(lysine)-F127 hydrogels have a temperature-responsive sol–gel transition and pH-responsive micelle morphology.

Measurement and Correlation of the Solubility of 5-Fluorouracil in Pure and Binary Solvents

The solubility of 5-ffuorouracil (5-FU), a widely used chemotherapeutic agent to treat solid tumors, which include colorectal, head and neck, breast, and lung cancer, was determined at temperatures ranging from 278.15 to 333.15 K in 11 pure solvents and binary water + ethanol solvent mixtures using the polythermal method. It was demonstrated that the solubility of 5-FU increases with increasing temperature in the pure solvents and at constant solvent composition in the solvent mixtures. Moreover, the solubility of 5-FU in the solvent mixtures exceeds its solubility in pure water and ethanol. The experimental solubility data of 5-FU in the pure solvents and solvent mixtures were correlated using the modified Apelblat and λh model equations. The predicted solubility data obtained agree with the experimental data based on the calculated relative deviation (RD) and the average relative deviation (ARD%) values. The selected solvents are categorized as either Class 2 or 3 (less toxic and lower risk to human health) solvents, and hence the correlated and experimentally derived solubility data of 5-FU presented provide a pathway to develop and engineer enhanced pharmaceutical processes and products based on this compound.

PNIPAM-MAPOSS Hybrid Hydrogels with Excellent Swelling Behavior and Enhanced Mechanical Performance: Preparation and Drug Release of 5-Fluorouracil

Poly(N-isopropylacrylamide) (PNIPAM) is a widely-studied polymers due to its excellent temperature sensitivity. PNIPAM-MAPOSS hybrid hydrogel, based on the introduction of acrylolsobutyl polyhedral oligomeric silsesquioxane (MAPOSS) into the PNIPAM matrix in the presence of polyethylene glycol, was prepared via radical polymerization. The modified hydrogels exhibited a thick, heterogeneous porous structure. PEG was used as a pore-forming agent to adjust the pore size. MAPOSS reduced the swelling ratios of gels, and decreased the LCST, causing the hydrogels to shrink at lower temperatures. However, its hydrophobicity helped to improve the temperature response rate. The incorporation of rigid MAPOSS into the polymer network greatly increased the compressive modulus of the hydrogel. It is worth noting that, by adjusting the amount of MAPOSS and PEG, the hydrogel could have both ideal mechanical properties and swelling behavior. In addition, hydrogel containing 8.33 wt % MAPOSS could achieve stable and sustained drug release. Thus, the prepared PNIPAM-MAPOSS hybrid hydrogel can serve as drug carrier for 5-fluorouracil and may have potential application in other biomedical fields.

Prediction of Setschenow constants

The Setschenow (salting out) constant by sodium chloride is related to molar volume, aqueous solubility, and octanol-water partition coefficient, K(ow), of the drug solute. This study validates a previously proposed relationship between the salting out constant of a solute and its partition coefficient. It also shows that the partition coefficient is a better descriptor of salting out than either molar volume or solubility.

Thermodynamics of mercaptopurine dehydration

The hydrate form of mercaptopurine was shown to undergo peritectic decomposition of its water molecule, localized dissolution, and dehydration around 125 degrees. The anhydrate form was prepared by a thermal method, whose effectiveness was confirmed by X-ray diffraction, NMR spectroscopy, and differential scanning calorimetry. The activation energy for mercaptopurine dehydration calculated by various methods ranged from 45.74 to 63.04 kcal/mole. The dehydration enthalpy was calculated to be 8.27 kcal/mole by differential scanning calorimetry. The solution enthalpy for the hydrate was calculated to be 4.85 kcal/mole from its saturation solubility and differential scanning calorimetry. Anhydrate solubility in water was calculated based on initial dissolution rate data since the anhydrate converts to hydrate in aqueous media. The high degree of stability against interconversion of the hydrate and anhydrate forms and the higher solubility of the anhydrate suggest that use of the anhydrate might improve mercaptopurine bioavailability.