Effect of nicotinamide and urea on the solubility of riboflavin in various solvents

Parallel stacking of caffeine with riboflavin in aqueous solutions: the potential mechanism for hydrotropic solubilization of riboflavin

Hydrotropy is a phenomenon where the presence of a large quantity of one solute enhances the solubility of another solute. The mechanism of this phenomenon remains elusive and a topic of debate. This study employed molecular dynamics simulation to investigate solute interactions of a model system consisting of a hydrotropic agent, caffeine (CAF), a poorly water-soluble solute, riboflavin (RBF), and water. The study demonstrates that CAF and RBF undergo molecular parallel stacking in the aqueous solution, a result correlating closely to the self-stacking of CAF under the same conditions. The correlations are found both structurally and dynamically, suggesting that the self-stacking of CAF is the primary effect, and incorporation of RBF is the secondary effect. The solute stacking gives rise to the partitioning of solutes and water, which helps restoring the normal water structure and drives down the system energy. The interactions between the solutes are found insignificant to the solute clustering. The dynamic data confirm that the solute stacks are dynamically active. These results suggest that hydrotropic effect of CAF may be attributed to solute parallel stacking.

Temperature-responsive properties and drug solubilization capacity of amphiphilic copolymers based on N-vinylpyrrolidone and vinyl propyl ether

A series of amphiphilic copolymers were synthesized by free-radical copolymerization of N-vinylpyrrolidone (NVP) with vinyl propyl ether (VPE), and the structure of the copolymers was characterized by elemental analysis and gel permeation chromatography. The reactivity of VPE in copolymerization was found to be significantly lower than the reactivity of NVP, which resulted in a decrease of copolymers' yields and molecular weights with higher content of VPE in the feed mixture. An investigation of the behavior of the copolymers in aqueous solutions at different temperatures by dynamic light scattering revealed the presence of lower critical solution temperature, which depending on the content of VPE ranged within 23-38 degrees C. Aqueous solutions of these copolymers were studied by fluorescent spectroscopy with pyrene as a polarity probe to reveal the formation of hydrophobic domains. The copolymers were found to be useful for enhancing the solubility of riboflavin in water.

Ethyl-paraben and nicotinamide mixtures: apparent solubility, thermal behavior and X-ray structure of the 1:1 co-crystal

This work aims at investigating the nicotinamide (NA)-ethyl-paraben (EP) binary system both in solution and in the solid state. In particular, the apparent EP solubility in water was studied in the presence of different NA concentrations (between 0.28 and 1.64 M). It was found that the apparent EP solubility increase (nearly twofold) observed at the highest NA concentration tested can be ascribed to a change in the polarity of the solvent mixture, rather than to a direct effect of NA on EP. The effect of fusion and re-crystallization from water or ethanol solutions on EP and NA mixtures was investigated by means of differential scanning calorimetry, elemental analysis and X-ray diffraction both on powder and single crystal. It was discovered that EP and NA form a co-crystal having a 1:1 molar composition that can be easily crystallized from ethanol. Single crystal X-ray analysis of this species revealed that the NA and EP molecules form corrugated layers within which the two components are intimately associated by a dense network of hydrogen bonds. In the presence of an excess NA in solution, the EP-NA co-crystal has lower water solubility with respect to both the single co-crystal formers and precipitates in aqueous solutions at ambient temperature.

Effect of a mixture of caffeine and nicotinamide on the solubility of vitamin (B2) in aqueous solution

The effect of caffeine (CAF) and nicotinamide (NMD) on the solubility of a vitamin B2 derivative (FMN) has been evaluated for mixtures containing either a single hydrotrope (CAF or NMD) or the two hydrotropes simultaneously. A model for analysis of ternary systems, which takes into account all possible complexes between the molecules, has been developed and tested with experimental NMR data on the three-component mixture FMN-CAF-NMD. The results indicate that special attention should be given to the concentration of a hydrotropic agent used to enhance the solubility of a particular drug. A decrease in the efficacy of solubility of the vitamin on addition of large amounts of hydrotropic agent is expected in the two-component systems due to the increased proportion of self-association of the hydrotrope. It is found that a mixture of two hydrotropic agents leads to an increase in the solubility of the vitamin in three-component compared to the two-component system. Rather than using just one hydrotropic agent, it is proposed that a strategy for optimising the solubility of aromatic drugs is to use a mixture of hydrotropic agents.

Rapid, small-scale determination of organic solvent solubility using a thermogravimetric analyzer

A rapid gravimetric method for determining drug candidate solubility in organic solvents has been developed. The scale, speed, precision, and accuracy of the method make it ideal for solubility screening of pharmaceutical compounds during early development. The method utilizes a thermogravimetric analyzer to automate drying and weighing. Results for model compounds compare favorably with literature values.

Caffeine and nicotinamide enhances the aqueous solubility of the antimalarial agent halofantrine

The aqueous solubility of the antimalarial agent halofantrine in phosphate buffers pH 5.9 and 7.0 (ionic strength 0.08) is increased by the addition of caffeine and nicotinamide. Solubility is increased to a greater extent in the presence of caffeine (12.5-125 mM) than nicotinamide (125 mM -2.0 M). The greatest increase in solubility was observed at pH 5.9 where the basal solubility of halofantrine rose from 0.91 to 435 microM when 125 mM caffeine was added. Phase solubility studies support the formation of a 1:1 complex between caffeine and halofantrine which is characterised by a K(1:1) constant of 2.75x10(3) M(-1) (pH 5.9). A less stable 1:1 complex is formed at pH 7.0 (K(1:1)=6.37x10(3) M(-1)). Differential scanning calorimetry of solid mixtures of caffeine and halofantrine showed the absence of the endotherms of the two drugs and the appearance of a distinct endotherm (with a smaller enthalpy) characteristic of the complex. An analysis of the 1H-NMR spectra of mixtures of caffeine and halofantrine revealed perturbations in the chemical shifts of the methyl group and proton at positions 4 and 8 of caffeine, and a change in splitting pattern of the H(9) proton of the phenanthrene ring in halofantrine.