Relative hydrophobicity of organic compounds measured by partitioning in aqueous two-phase systems

Solvent polarity and hydrophobicity of solutes are two sides of the same coin

The hydrophobicity of solutes measures the intensity of a solute's interaction with aqueous environment. The aqueous environment may change with its composition, leading to changes in its solvent properties largely characterized by polarity. As a result, the relative hydrophobicity of a solute is a function of the solute structure and the properties of the water-based solvent determined by the total composition of the aqueous phase. This aspect is commonly ignored by medicinal chemists even though it is essential for drug distribution between different biological tissues. Partitioning of solutes in aqueous two-phase systems provides the relative hydrophobicity estimates for any water-soluble compounds that can be used to improve predictions of the toxicity and other biological effects of these compounds.

Immunostaining Extracellular Vesicles Based on an Aqueous Two-Phase System: For Analysis of Tetraspanins

Immunostaining of extracellular vesicles (EVs) has become necessary for the characterization of EV subtypes, clarification of the EV biogenesis/cellular uptake pathway, drug delivery, etc. Immunostained EVs must be in suspension for further downstream analyses or uses. However, conventional EV immunostaining methods yielding EVs in suspension lack either sufficient recovery or staining specificity because of the washing steps. In this study, we have devised and tested a method to wash immunostained EVs with successive aqueous two-phase system (ATPS) separations. The ATPS is a liquid-liquid extraction procedure that ensures a gentle separation of target molecules. The ATPS has been successfully employed to separate EVs from other impurities with high yield and high purity. Immunostained EVs were washed with the ATPS and compared with other immunostaining methods to confirm the proposed method's high EV recovery and staining accuracy. According to the result, the ATPS-based EV immunostaining method required as low as ∼1 μg without compromise of accuracy and recovery.

Physiologically Based Pharmacokinetic Modeling of Renally Cleared Drugs in Pregnant Women

BACKGROUND

Since pregnant women are considerably underrepresented in clinical trials, information on optimal dosing in pregnancy is widely lacking. Physiologically based pharmacokinetic (PBPK) modeling may provide a method for predicting pharmacokinetic changes in pregnancy to guide subsequent in vivo pharmacokinetic trials in pregnant women, minimizing associated risks.

OBJECTIVES

The goal of this study was to build and verify a population PBPK model that predicts the maternal pharmacokinetics of three predominantly renally cleared drugs (namely cefazolin, cefuroxime, and cefradine) at different stages of pregnancy. It was further evaluated whether the fraction unbound (f _u) could be estimated in pregnant women using a proposed scaling approach.

METHODS

Based on a recent literature review on anatomical and physiological changes during pregnancy, a pregnancy population PBPK model was built using the software PK-Sim^®/MoBi^®. This model comprised 27 compartments, including nine pregnancy-specific compartments. The PBPK model was verified by comparing the predicted maternal pharmacokinetics of cefazolin, cefuroxime, and cefradine with observed in vivo data taken from the literature. The proposed scaling approach for estimating the f _u in pregnancy was evaluated by comparing the predicted f _u with experimentally observed f _u values of 32 drugs taken from the literature.

RESULTS

The pregnancy population PBPK model successfully predicted the pharmacokinetics of cefazolin, cefuroxime, and cefradine at all tested stages of pregnancy. All predicted plasma concentrations fell within a 2-fold error range and 85% of the predicted concentrations within a 1.25-fold error range. The f _u in pregnancy could be adequately predicted using the proposed scaling approach, although a slight underestimation was evident in case of drugs bound to α₁-acidic glycoprotein.

CONCLUSION

Pregnancy population PBPK models can provide a valuable tool to predict a priori the pharmacokinetics of predominantly renally cleared drugs in pregnant women. These models can ultimately support informed decision making regarding optimal dosing regimens in this vulnerable special population.

A simple method for point-of-need extraction, concentration and rapid multi-mycotoxin immunodetection in feeds using aqueous two-phase systems

The rapid detection of mycotoxins in feed samples is becoming an increasingly relevant challenge for the food production sector, in order to effectively enforce current regulations and assure food and feed safety. To achieve rapid mycotoxin detection, several biosensing strategies have been published, many reaching assay times of the order of a few minutes. However, the vast majority of these rely on sample preparation based on volatile organic solvents, often comprising complex multi-step procedures and devoid of clean-up and/or concentration effects. Here, a novel sample preparation methodology based on a green, non-toxic and inexpensive polyethylene glycol-sodium citrate aqueous two-phase system is reported, providing single-step extraction and concentration of three target mycotoxins within 20min: aflatoxin B1 (AFB1), ochratoxin A (OTA) and deoxynivalenol (DON). With point-of-need applications in mind, the extraction procedure was optimized and validated using a rapid multi-toxin microfluidic competitive immunoassay. The assay was successfully tested with spiked complex solid matrices including corn, soy, chickpea and sunflower-based feeds and limits of detection of 4.6ngg-1±15.8%, 24.1ngg-1±8.1% and 129.7ngg-1±53.1% (±CV) were obtained in corn for AFB1, OTA and DON, respectively. These sensitivities are fit-for-purpose at the required regulatory and recommended limits for animal feed, providing an effective and safe semi-quantitative mycotoxin analysis that can be performed in the field.

Relative hydrophobicity between the phases and partition of cytochrome-c in glycine ionic liquids aqueous two-phase systems

In this work, glycine ionic liquids tetramethylammonium glycine ([N1111][Gly]), tetraethylammonium glycine ([N2222][Gly]), tetra-n-butylammonium glycine ([N4444][Gly]), tetra-n-butylphosphonium glycine ([P4444][Gly]) and tetra-n-pentylammonium glycine ([N5555][Gly]) were synthesized and used to prepare aqueous two-phase systems (ATPSs) in the presence of K2HPO4. Binodal curves of such ATPSs and partition coefficients of a series of dinitrophenylated (DNP) amino acids in these ATPSs were determined at 298.15K to understand the effect of cationic structure of the ionic liquids on the phase-forming ability of glycine ionic liquids, relative hydrophobicity between the phases in the ionic liquids ATPSs, and polarity of the ionic liquids-rich phases. With the attempt to correlate the relative hydrophobicity of the phases in the ATPSs with their extraction capability for proteins, partition coefficients of cytochrome-c in the ATPSs were also determined. It was shown that partition coefficients of cytochrome-c were in the range from 2.83 to 20.7 under the studied pH conditions. Then, hydrophobic interactions between cytochrome-c and the ionic liquid are suggested to be the main driving force for the preferential partition of cytochrome-c in the glycine ionic liquid-rich phases of the ATPSs. Result derived from polarity of the ionic liquids-rich phases supports this mechanism.

Partitioning features of bovine trypsin and α-chymotrypsin in polyethyleneglycol-sodium citrate aqueous two-phase systems

The partitioning of bovine trypsin and alpha-chymotrypsin--proteases of similar physico-chemical properties--in different polyethyleneglycol/sodium citrate aqueous two-phase systems was investigated. The effect of different factors such as polyethyleneglycol molecular weight, pH, tie line length, temperature and the presence of an inorganic salt on the protein partition coefficient were analysed. Both a decrease in PEG molecular weight and an increase in pH led to a higher partition coefficient for both enzymes. Aqueous two-phase systems formed by PEG of molecular weight 3350 and citrate pH 5.2 showed the best separation capability which was enhanced in presence of sodium chloride 3%. The transfer of both proteins to the top phase was associated with negative enthalpic and entropic changes.

Relative hydrophobicity and lipophilicity of drugs measured by aqueous two-phase partitioning, octanol-buffer partitioning and HPLC. A simple model for predicting blood-brain distribution

Relative hydrophobicity and lipophilicity of 63 compounds with known permeability through the blood-brain barrier (BBB) was examined by partitioning in aqueous dextran-poly(ethylene glycol) two-phase system and octanol-buffer system, and by gradient RP-HPLC at pH 7.4. Combination of the relative hydrophobicity estimates, N(CH(2)) obtained by aqueous two-phase partitioning and the lipophilicity (logD(exp) or logD(HPLC)) values obtained by the shake-flask technique or HPLC technique allows one to differentiate between compounds capable of crossing the BBB and those that cannot. A simple model for predicting blood-brain distribution is proposed.

Relative hydrophobicity of di- to hexapeptides as measured by aqueous two-phase partitioning

Partitioning of 153 di- to hexapeptides in an aqueous dextran-PEG two-phase system containing 0.15 m NaCl in 0.01 m sodium phosphate buffer, pH 7.4 was examined. The relative hydrophobicity of the peptides was estimated and expressed in equivalent numbers of methylene units. Analysis of the data shows that the additivity principle applies for the relative hydrophobicity of up to hexapeptides. The relative hydrophobicities of Trp, Glu, and Asp residues in heterooligopeptides are noticeably different from those in corresponding homooligopeptides. The relative hydrophobicity of peptides can be calculated and used as a structural descriptor in quantitative structure-activity relationship analysis. The peptide bitterness threshold is shown to be quantitatively related to the peptide structure described as a combination of the relative hydrophobicity and lipophilicity (logD) of peptides.

pH dependence of the relative hydrophobicity and lipophilicity of amino acids and peptides measured by aqueous two-phase and octanol-buffer partitioning

Partitioning of a series of free amino acids, their derivatives, and homo-oligopeptides in aqueous dextran-PEG two-phase systems and octanol buffer systems was examined at pH values from 2.0 up to 12.5. The pH-dependent partition behavior of free amino acids and peptides in the two-phase systems was compared with that of monofunctional drug-like compounds and found to be clearly different. The differences observed indicate that the information provided by the techniques of partitioning in octanol buffer (log(D)(pH)) and in aqueous two-phase systems, N(CH2), is different. It is suggested that the combination of the two descriptors, log(D) (lipophilicity) and N(CH2) (relative hydrophobicity), may be useful for QSAR analysis of the biological activities involving distribution and/or transport of chemical compounds in biological systems.

Separation and enantioseparation of derivatized amino acids and biogenic amines by high-performance liquid chromatography with reversed and chiral stationary phases

This study demonstrates that an amino-beta-cyclodextrin-bonded phase column exhibits enantioselectivity for various amino acid derivatives. Mixtures of methanol, acetonitrile, tetrahydrofuran or dioxan and triethylamine buffers (pH 4.0-7.0) were used as mobile phases. The effect of the mobile phase on the resolution process was studied by varying the mobile phase composition (type and percentage of organic modifiers, pH, and ionic strength of the buffer solution). The 1-octanol-water partition coefficients are calculated and tabulated for 16 derivatized amino acids. The chromatographic data for 42 pairs of derivatized amino acids resolved on the amino-beta-cyclodextrin-bonded phase are summarised. The separation of adrenaline, noradrenaline and amphetamine on a novel vancomycin stationary phase is demonstrated.

Relative hydrophobicity and lipophilicity of beta-blockers and related compounds as measured by aqueous two-phase partitioning, octanol-buffer partitioning, and HPLC

Partitioning of 15 beta-blockers and structurally related compounds was examined in aqueous dextran-PEG two-phase systems and octanol-buffer systems at pH from 2.0 up to 12.5. The same compounds were examined by gradient RP-HPLC at pH 2.0, 7.4, and 11.0. The differences between the hydrophobic character of the phases in all three systems at different pH values were characterized using a homologous series of dinitrophenyl-amino acids by measuring the free energy of transfer of a methylene group. Estimates of the relative hydrophobicity, N(CH(2)), and lipophilicity, logD, of the compounds obtained by the three techniques employed were compared. The data indicate that while similar pH profiles for a given compound were established by all these techniques, the information provided is different. It is suggested that the combination of the two descriptors, logD and N(CH(2)), may be useful for quantitative structure-activity relationship analysis of the biological activities involving distribution and/or transport of chemical compounds in biological systems.

Relative hydrophobicity of amino acid residues in homooligopeptides as measured by aqueous two-phase partitioning

Partitioning of 17 amino acids and their homooligopeptides of different lengths in an aqueous dextran-PEG two-phase system containing 0.15 m NaCl in 0.01 M sodium phosphate buffer, pH 7.4 and 0.11 m sodium phosphate buffer, pH 7.4 was examined. The relative hydrophobicity of the amino acid residues was estimated and expressed in equivalent numbers of methylene units. Analysis of the data shows that the additivity principle does hold for the hydrophobicity of homooligopeptides. The relative hydrophobicity of essentially all amino acid residues is noticeably affected by the ionic composition of aqueous media.

Measurement of the relative hydrophobicity of organic compounds without organic solvent. Effects of salt composition and pH on organic acids and nonionic compounds

Partitioning of a variety of nonionic and acidic organic compounds was examined in aqueous dextran-poly(ethylene glycol) (PEG) two-phase systems of different ionic composition at pH 2.00 and 7.40. Relative hydrophobicity of the compounds was estimated in terms of equivalent numbers of methylene units. Effect of the ionic composition and pH of aqueous media on the relative hydrophobicity of organic compounds was established and described quantitatively. The results obtained indicate that the ionic composition affects the relative hydrophobicity of ionized compounds and has no effect on that of nonionic compounds and ionizable compounds in the undissociated state. Ionization of a given ionic group seems to bring about a constant change in the relative hydrophobicity of a compound. This result supports the applicability of the additivity principle to the relative hydrophobicity estimates obtained with the aqueous two-phase partitioning technique.