Jara Morante, Eliana

Profile Picture

Filters

20041
Reset filters

Settings

Citations

Publication Search Results

Now showing 1 - 1 of 1
  • Thumbnail Image
    Publication
    Reverse micelles in supercritical carbon dioxide for pharmacological applications: a spectroscopic characterization
    (2004) Jara Morante, Eliana; Suleiman Rosado, David; College of Engineering; Colón Burgos, Guillermo; Estévez, L. Antonio; Velázquez, Carlos; Department of Chemical Engineering; Romañach, Rodolfo
    The aim of this research is to characterize microemulsions in supercritical (sc) CO2 using two spectroscopic techniques (UV-Vis and FT-IR) and apply the microemulsion approach to extract impurities from a pharmacological drug, hydroxy ethyl starch (HES). Nonionic pluronic (PL92, PL31, and P17R2), perfluorinated (Zonyl) and polyethylene glycols ethers (Gele) surfactants with known solubility in scCO2 have been used to form microemulsions. Aqueous solutions of pharmacological drugs (acetaminophen and imipramine HCl) have been added to the systems in an attempt to capture the polar solute in the core of the microemulsion formed in scCO2. The indicator (N,N,-dimethyl-4-nitroaniline) was used to characterize microemulsions with UV-Vis spectroscopy, due to its large solvatochromic shift. The maximum absorbance shifted to lower energy (red shift) due to the specific hydrogen bonding interactions when the polarizability/dipolarity (π*) of the solvent increased. The π* values for the five indicator-H2O-surfactant-scCO2 systems indicated the formation of a changing microenvironment as pressure increased, achieving values comparable to those of linear hydrocarbons. The higher π* values corresponded to P17R2-IndicatorH2O-scCO2 (from -0.22 to 0.05) at pressures and temperatures ranging 91-221 bar and 313-323 K, respectively. Compared to the other surfactants, P17R2 has demonstrated to be more stable, perhaps due to its structure (PPO-EO-PPO), which gives it more ability to trap H2O through stronger hydrogen-bonding interactions. The systems evaluated have shown to be solute sensitive. Even though the π* values suggested a constant water-like surrounding, different behaviors were observed for acetaminophen and imipramine HCl. This suggested different intermolecular interactions among the components that compromised the stability and performance of the surfactants. Data taken with this technique also provided the possibility to evaluate the systems through other parameters used to characterize the supercritical state, such as the local density augmentation, dielectric constant, and second virial coefficient. FT-IR spectroscopy was used to study the intermolecular interactions of microemulsions in scCO2. The effect of pressure and H2O addition to the systems was evaluated at 313 K. This effect was analyzed through the inspection of characteristic peaks that have been proven to be sensitive to micellization (e.g., the variation of the ratio CH2 asymmetric to CH3 symmetric stretching vibration, deformation around the CH3 asymmetric bending vibration, the C–O stretching, and the C=O region) and gave evidence of hydrogen bonding interactions. The formation of different hydration states was also used to characterize the microemulsions. The four (OH) regions evaluated (free, hydrogen bonded, non-hydrogen bonded, and monomeric H2O) denote the interactions with the hydrophilic portion of the surfactants. P17R2-Acetaminophen-H2O-scCO2 system showed the best performance with H2O loaded up to 4% prior to phase separation or destabilization. However, I can not assure a one-phase micellar system because the cloud point was only verified by visual inspection through the high-pressure cell. The values of water-to-surfactant molar ratio (W0) calculated showed variation with pressure and H2O addition. According to the low W0 values (W0 values (<15), it can be concluded that with Gele reverse micelles have been formed. Again, the performance of the surfactants was affected by the pharmacological drugs used in this study, which agrees with the UV-Vis spectroscopic conclusions. Microemulsions and other extraction strategies (pure scCO2 and cosolvents-scCO2) were applied in the extraction of ethylene glycol from HES. Two HES lots with different amounts of impurities were treated with scCO2, obtaining a 48% and 96% extraction. The 3-5 hours supercritical extraction processes were performed at 200 bar and 313 K. Based on extraction percentage, the performance of the cosolvent-scCO2 agrees with its dielectric constants. Since the extraction process is H2O-composition dependent, the formation of reverse micelles to trap the polar compounds (e.g., ethylene glycol, H2O) in the micelles core seemed to be adequate. With 75% extraction, Gele-scCO2 showed a solvent capacity comparable to polar modified acetonitrile-scCO2 system (87%) and higher than acetone-scCO2 (65%). Zonyl was able to trap H2O and hence the ethylene glycol. This was verified through the detection of the broad band situated around 3300cm-1 assigned to hydrogen bonded (OH). The low level composition did not destabilize the microemulsions formed in scCO2. This leads to the conclusion that these surfactants can be used to extract organic compounds in a ppm-level composition, through the formation of reverse micelles or microemulsion. This can be a useful application of commercial and non-expensive surfactants and an attempt to replace the use of environmentally undesirable and expensive organic solvents.