Browsing by Author "Morteza G. Khaledi, Committee Chair"

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Characterization and Prediction of Partition Coefficients of Uncharged Solutes into Micelles and Liposomes using Electrokinetic Chromatography
(2002-12-06) Burns, Scott Thomas; Morteza G. Khaledi, Committee Chair
Liposome and micelle electrokinetic chromatography (EKC) were used to determine retention factors (k) that are directly related to partition coefficients (K) and the phase ratio (φ) as: k = K*φ. Linear solvation energy relationship (LSER) models were used to elucidate the contributions of solute partitioning into liposomes. In addition, an LSER model for both MEKC and LEKC was used to determine partition coefficients for solutes without observed partition coefficients. The observed partition coefficients and those determined from LSER were then used to predict partition coefficients with the group contribution approach (GCA) and the fragmental constant approach (FCA) from solute structure. In the GCA, a relatively small number of key monosubstituted aromatic and aliphatic solutes are used to determine the substituent constants of functional groups. These substituent constants as well as the contributions from aromatic and aliphatic carbon plus hydrogen are used to predict partition coefficients of other solutes. Though the GCA is able to predict partition coefficients for simple di-substituted aromatics, predictions for more complicated solutes such as drugs are considerably less accurate. In the FCA, a large database of aromatic and aliphatic solutes is used to determine the fragmental constants of various functional groups as well as carbon and hydrogen. Overall, the FCA was able to predict partition coefficients for more complicated solutes like drugs with more accuracy than the GCA. However, with both the GCA and FCA large solute databases are needed because they are relatively small (˜ 500) in comparison to the 8,000 aromatic and aliphatic solutes analyzed with the octanol-water system.
Characterization of Complex Protein Mixtures from Human Plasma Fractionation by Capillary Electrophoresis and Mass Spectrometry
(2006-08-23) Frantz, Neha Joshi; Morteza G. Khaledi, Committee Chair
The purpose of the research has been to develop a simple, quantitative method for characterizing complex protein mixtures using Cohn Fractionation IV-1 Paste as an example. This process step is the starting material for the plasma fractionation process which leads to purified alpha1-antitrypsin, and is an example of a complex protein matrix. Currently, CE analysis of complex plasma samples involves a Borate-NaCl buffer system which does not provide adequate resolution to quantitate protein composition. The goal of this research is to discover optimum CE separation conditions, which would allow rapid, efficient, and inexpensive characterization of these complex samples. A simple, reproducible system utilizing SDS has been developed which provides better resolution and quantitation of complex protein mixtures. This new method is referred to as 'CE-SDS,' and although it is an improvement over the current method, orthogonal methods such as mass spectrometry can provide additional information not captured by this method.
Development of Micellar Selectivity Triangle for Classification of Pseudo-stationary Phase Selectivity in Electrokinetic Chromatography
(2006-08-16) Fu, Cexiong; Morteza G. Khaledi, Committee Chair
A novel Micellar selectivity triangle (MST) was developed to rationalize and classify the chemical selectivities for a wide variety of pseudo-phases in Electrokinetic Chromatography (EKC). The descriptors of polar selectivities for constructing the MST were derived from the linear solvation energy relationships (LSER). The effects of solvent modification of micelles, mixed-micellar systems along with surfactant type on the pseudo-phase selectivities were investigated using the MST. To quantitatively describe the similarities and differences of the chemical selecitivities, a phase selectivity ranking system was constructed on the basis of the Euclidean distance between objects. Chemometric methods including the principal component analysis (PCA), hierarchical clustering and k-means clustering were used to elucidate the classification and characterization of the micellar phases in different perspectives. The results form the MST and the chemometric methods were in generally good agreement. The micellar selectivity triangle was used as a guideline for optimizing the separation of 20 Phenylthiohydantoin (PTH) amino acids. The effects of the surfactant type and concentration, temperature and organic solvent additives on the PTH amino acids separation were evaluated. Additionally, the substituent constants of these PTH amino side chain obtained from the EKC methods were compared to those obtained from octanol-water partitioning and free energy of transferring amino acid moieties from the globular proteins interior to surface. Finally, the combined use of the unified selectivity triangle (UST), PCA and cluster analysis was explored for the comparison of the chemical selectivity between the two powerful chromatographic techniques, EKC and RPLC. The database consisted of 518 reversed-phase systems and 83 pseudo-phases. The primary factors to influence the phase selectivity of the two techniques were identified and compared. Suggestions for future works are also discussed.
Drug Partitioning and Solvation Environments in Lipid Bilayers
(2004-12-09) Carrozzino, Jennifer Marie; Edmond F. Bowden, Committee Member; Morteza G. Khaledi, Committee Chair; Charles B. Boss, Committee Member; Daniel L. Feldheim, Committee Member
The main goal of this research project was to investigate various factors influencing solute partitioning and solvation in lipid bilayer membranes using liposomes as biomembrane models and applying a combination of spectroscopic and capillary electrophoresis techniques. The first area of investigation involved using a series of polarity sensitive solvatochromic indicators to probe the dipolarity of various phospholipid and synthetic surfactant vesicles. A homologous series of probes of varying hydrophobicity allowed a systematic probing of the dipolarity in the interfacial region of the vesicles and resulted in very specific polarity information for various regions or microenvironments depending on the probes positions. This dipolarity was examined in terms of vesicle size and composition, in addition to indicator partitioning behavior. To develop Liposome Electrokinetic Chromatography (LEKC) as a method for rapidly determining liposome - water distribution coefficients, the effects of various parameters on the retention of basic drugs in liposomes were examined. This included characterizing the electrostatics of interactions between charged drugs and charged lipid membranes by examining the effect of membrane and buffer compositions. Additionally, LEKC was used to determine the effect of pH on the partitioning of basic drugs into liposomes composed of lipids which mimic the composition of natural cell membranes. Drug partitioning as a function of pH is examined in detail in terms of the fractions of charged and neutral drug forms in the aqueous and lipid phases. An increase in pH results in a smaller degree of ionization of the basic drugs and consequently leads to a lower degree of interaction with the negatively charged membranes. Finally, LEKC retention was used in QSAR studies for the evaluation of membrane permeability and intestinal absorption. LEKC retention factor data was correlated with human oral absorption in comparison with other methods such as octanol - water partitioning, total number of hydrogen bonding groups, and polar surface area. LEKC retention data was also related to Caco-2, MDCK, and human jejunal permeability in comparison with the standard model, octanol - water partitioning.
Prediction of Peptide Maps in CZE and MEKC Systems
(2005-04-24) Shen, Yang; Edmond F. Bowden, Committee Member; Charles B. Boss, Committee Member; Morteza G. Khaledi, Committee Chair
A new Quantitative Structure-Migration Relationships(QSMR) model was developed to predict the electrophoretic mobilities of peptides in capillary zone electrophoresis(CZE). A three-step strategy was used: first, select the best charge-size term from the existing models; second, develop a muilti-linear regression(MLR) model to study the linear characteristics of peptide mobility using the best charge-size term and other descriptors; third, generate an artificial neural network(ANN) to investigate the nonlinear behavior of peptide mobility and use this ANN model to predict peptide migration behavior in CZE. To test the robustness of the QSMR model, it was applied to the data published by another research group. Very accurate predictions were achieved. To study the influence of peptide sequence on the migration of a peptide in CZE, a series of 'sequence-related' descriptors were developed. These descriptors were used to develop MLR models for peptide mobility prediction. With the 'sequence-related' descriptor, more accurate mobility could be predicted for peptides with same amino acid composition but different sequences. Group contribution approach(GCA) was used to determine the individual contribution of each amino acid residue and both N-, C- terminal to the peptide mobility in Tween20 system. Data of a relatively small number of peptides were used for this purpose. The sum of individual contributions was calculated for each peptide and used as a new descriptor in developing MLR models for the prediction of peptide mobilities in Tween20 system. Good preliminary results were achieved.
Thermodynamic Study and Prediction of Solute Partitioning into Micelles and Liposomes Using Electrokinetic Chromatography.
(2004-08-22) Bui, Hai Hoang; Morteza G. Khaledi, Committee Chair
Vesicles and micelle electrokinetic chromatography (EKC) were used to study solute partitioning from the aqueous phase into vesicles and micelles. The retention factors (k) of neutral solutes are related to their partition coefficients (K) and the phase ratio (f), k = K*f. Dihexadecyl phosphate (DHP) vesicles used in this study undergo gel to liquid-crystalline phase at the critical temperature. Investigation of thermodynamics of solute partitioning into bilayers would allow separating the enthalpic and entropic contributions to the free energy of transfer. Linear Solvation Energy Relationship (LSER) modeling was used to elucidate the contributions of hydrophobic, hydrogen bond interactions, dipolar, and polarizability to the free energy of transfer of solutes from the aqueous phase into the vesicle phase at above and below Tc. Hydrophobic interaction keeps an important role in solute partitioning into bilayers. Hydrogen bonding, electrostatic, and dipolar are also relative important. Polarity (p*) was directly measured at different locations in the DHP vesicles using different solvatochromic probes over a wide range of temperature. The size of liposomes and vesicles were also examined at different temperatures. In peptide mapping, models for the prediction of electrophoretic mobility and micelle-water partition coefficient of peptides were developed, and thus retention behavior of peptides, which should facilitate method development in MEKC. It allows rapid optimization of separation conditions that can lead to enhance resolution of complex mixtures. Initially, the partition coefficients of a training set of peptides were determined by MEKC. A quantitative structure-partition relationship (QSPR) was established based on the data set that relates partition coefficient (Kmc) to structural descriptors of the peptides. Also, a quantitative structure-migration relationship (QSMR) was developed based on the charge, residue mass, and length of peptide. An advantage of this model is that peptide descriptors can be calculated from the amino acid composition of the peptides. Different statistical methods were then used to determine the most relevant descriptors in the models and to test the accuracy and error for each model. The QSPR and QSMR models were then used to predict Kmc and peptide mobility for several membrane peptides and tryptic digest of horse cytochrome C.