Octanol-water System Research Articles

Lipid-Based Catalysis Demonstrated by Bilayer-Enabled Ester Hydrolysis.

Lipids have not traditionally been considered likely candidates for catalyzing reactions in biological systems. However, there is significant evidence that aggregates of amphiphilic compounds are capable of catalyzing reactions in synthetic organic chemistry. Here, we demonstrate the potential for the hydrophobic region of a lipid bilayer to provide an environment suitable for catalysis by means of a lipid aggregate capable of speeding up a chemical reaction. By bringing organic molecules into the nonpolar or hydrophobic region of a lipid bilayer, reactions can be catalyzed by individual or collections of small, nonpolar, or amphiphilic molecules. We demonstrate this concept by the ester hydrolysis of calcein-AM to produce a fluorescent product, which is a widely used assay for esterase activity in cells. The reaction was first carried out in a two-phase octanol-water system, with the organic phase containing the cationic amphiphiles cetyltrimethylammonium bromide (CTAB) or octadecylamine. The octanol phase was then replaced with phospholipid vesicles in water, where the reaction was also found to be carried out. The reaction was monitored using quantitative fluorescence, which revealed catalytic turnover numbers on a scale of 10-7 to 10-8 s-1 for each system, which is much slower than enzymatic catalysis. The reaction product was characterized by 1H-NMR measurements, which were consistent with ester hydrolysis. The implications of thinking about lipids and lipid aggregates as catalytic entities are discussed in the context of biochemistry, pharmacology, and synthetic biology.

Evaluation of Distribution and Partition Coefficients of Levulinic Acid in Octanol-Water System at 298.15 K

Evaluation of Distribution and Partition Coefficients of Levulinic Acid in Octanol-Water System at 298.15 K

Controlled synthesis and solution properties of copolymers of methacrylic esters and ammonium-containing methacrylamide

Copolymers based on oligo(ethylene glycol) methacrylate, dodecyl methacrylate, and the cationic monomer N-methacryloylaminopropyl-N,N-dimethyl-N-propylammonium bromide have been obtained by reversible addition−fragmentation chain-transfer polymerization in high yields and in a controlled mode. The influence of the composition of the obtained polymers on the solubility in water and organic solvents, distribution in the water-octanol system, and interfacial tension at the water-oil interface is shown. The presence of thermoresponsive properties for polymers in water was found, and their aggregation in aqueous media was also studied.

Pure Graphene Acts as an "Entropic Surfactant" at the Octanol-Water Interface.

Graphene oxide (GO) has proved itself as a nanomaterial capable of acting as a surfactant by lowering the interfacial tension of the oil-water interface due to its polar oxygen groups. However, the surfactant behavior of the pure graphene sheet─since prevention of edge oxidation in experimental setups is nontrivial─is still an unresolved issue in graphene research despite significant progress in the field in recent years. Here, we conduct both atomistic and coarse-grained simulations to demonstrate that─surprisingly─even pristine graphene, which only consists of hydrophobic carbon atoms, is attracted to the octanol-water interface and consequently reduces its surface tension by 2.3 kBT/nm2 or about 10 mN/m. Interestingly, the location of the free energy minimum is not precisely at the oil-water interface itself but is rather buried about two octanol layers into the octanol phase, being about 0.9 nm from the water phase. We demonstrate that the observed surfactant behavior is purely entropically driven and can be attributed to the unfavorable lipid-like structuring of octanol molecules at the free octanol-water interface. In essence, graphene enhances the inherent lipid-like behavior of octanol at the water interface rather than directly acting as a surfactant. Importantly, graphene does not display surfactant-like behavior in corresponding Martini coarse-grained simulations of the octanol-water system since the free liquid-liquid interface loses essential structure at the lower coarse-grained resolution. However, a similar surfactant behavior is recovered in coarse-grained simulations of longer alcohols such as dodecan-1-ol and hexadecan-1-ol. The observed discrepancies at different model resolutions enable us to construct a comprehensive model of the surfactant behavior of graphene at the octanol-water interface. The here-gained insights may facilitate the broader utilization of graphene in numerous domains of nanotechnology. Furthermore, since a drug's octanol-water partition coefficient is a crucial physicochemical parameter in rational drug discovery, we also believe that the universality of the here-illustrated entropic surfactant behavior of planar molecules deserves special attention in the drug design and development field.

МОЛЕКУЛЯРНАЯ СТРУКТУРА И РАДИОЗАЩИТНАЯ АКТИВНОСТЬ ПРОИЗВОДНЫХ АМИНОЭТИЛТИОСУЛЬФАТОВ И АМИНОТИОЛОВ

An analysis of the relationship of radioprotective properties in the series of derivatives of S-2-aminoethylthiosulphates and S-2-aminothiols with their electronic characteristics and physicochemical parameters was performed. The result indicates the existence of a statistically significant relationship between the radioprotective activity and the value of the parameters of the radioprotector molecule: the lower free molecular orbital, the product of the ionization potential and polarizability, and the distribution coefficient in the octanol-water system. In the process of implementing the protective properties of a radioprotector, the ability of the drug to participate in the formation of charge transfer complexes for temporary inhibition of biochemical processes is of great importance. It was shown that the protective effect correlates with the ability of these compounds to participate in the electron transfer process, the energy of intermolecular interaction in the drug-damaged biomolecule system, and the transport properties of radioprotector molecules in the body. It was established that protection can be carried out through the formation of complexes in which molecules of S-2-aminoethylthiosulphate and S-2-aminothiol derivatives act as ligands, and the protective effect increases with an increase in the bond of the complexes and the mobility of the radioprotector molecules.

Preparation of covalently bonded liposome capillary column and its application in evaluation of drug membrane permeability

Two liposomes, including 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) + 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (PE) + cholesterol (Chol) (DSPC/PE/Chol liposomes) and soybean lecithin (SPC) + PE + Chol (SPC/PE/Chol liposomes), were prepared and fixed on the inner wall of capillary column by using the adhesion of polydopamine (PDA) membrane and the cross-linking property of glutaraldehyde (GA). The immobilized liposome capillary column (ILCC) has good repeatability and stability based on the electrophoretic mobility of analyte. A CE method based on the immobilized liposome capillary column chromatography (ILCCC) was successfully developed to study the retention behavior of drugs on ILCC, and the logarithm of retention factor (log k) of neutral and ionic drugs were determined. The results show that the log k measured by the ILCCC based on two liposomes have a good linear fitting (R2 = 0.86). Moreover, the linear relationship between ILCCC system and other related research systems (octanol-water system and immobilized artificial membrane (IAM)) was analyzed, and the results indicate that SPC/PE/Chol ILCCC, DSPC/PE/Chol ILCCC and IAM systems have good fitting results, R2 values are 0.86 and 0.78, respectively. In addition, the normalization coefficients of ILCCC and IAM systems obtained by the linear free energy relationship (LFER) analysis are close and the d value is small. In short, the ILCCC is a simple and feasible method for studying drug membrane permeability.

The use of biomimetic chromatography to predict acute aquatic toxicity of pharmaceutical compounds

The potential of biomimetic chromatography to predict ecotoxicological endpoints of pharmaceutical compounds was investigated. For this purpose, a data set of previously and newly measured chromatographic retention data for 36 structurally diverse drugs was used. Standardized retention times were measured on the immobilized artificial membrane, human serum albumin, and alpha-1-acid glycoprotein stationary phases. As ecotoxicological endpoints, half-maximal lethal concentration values of fish and half-maximal effective concentration (immobilization) values of a water flea (Daphnia magna spp.) determined with a two-day static method were considered. Ecotoxicity values correlated with octanol-water partitioning and the positive charge of compounds contributed even more to the toxicity. Models based on membrane partition exhibited the best statistics and predictive performance, attributed to lipophilicity and membrane electrostatic interactions. Alpha-1-acid glycoprotein binding led to satisfactory models, owing to its function as a binder of neutral and basic lipophilic compounds. Albumin binding, however, did not result in sound models, as it is governed by lipophilicity and the negative charge of compounds, contrary to the mechanism of toxicity. Both membrane and alpha-1-acid glycoprotein models were superior statistically from those derived from the octanol-water system. Overall, membrane and alpha-1-acid glycoprotein retention can be suggested as promising indices to assess the ecotoxicological risk of drugs.

Determination of lipid–water partition coefficient of neutral and ionic drugs by liposome electrokinetic chromatography

Profiling of lipid-water partition coefficients (KL/W ) of drugs is an essential issue during the early stage of drug development. In this study, two liposomes, including 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) + cholesterol (Chol) (DSPC/Chol liposomes) and soybean lecithin (SPC) + Chol (SPC/Chol liposomes), were prepared for the liposome electrokinetic chromatography (LEKC) analysis, and the logarithm of lipid-water partition coefficients (log KL/W ) of neutral and ionic drugs were determined based on an iterative method. The log KL/W values determined by the SPC/Chol or DSPC/Chol liposomes LEKC were linearly fitted, which showed a good fitting coefficient (R2 = 0.89). Furthermore, the linear relationship between the data obtained from LEKC system and octanol-water system, immobilized artificial membrane, Caco-2 cell model, and software prediction was analyzed, respectively. Results illustrated that DSPC/Chol liposomes or SPC/Chol liposomes had a good linear relationship with Caco-2 cell model, and R2 was 0.81 and 0.72, respectively. Moreover, the linear free energy relationship analysis suggested that the solute volume, hydrogen bond basicity, and J- were the main descriptors that drove the partition process of solutes in the SPC/Chol or DSPC/Chol LEKC system. In addition, the normalized properties of the SPC/Chol and DSPC/Chol LEKC systems through linear free energy relationship analysis were very close. In short, DSPC/Chol liposomes are more suitable for simulating cell membranes than SPC/Chol liposomes, and the developed LEKC is an effective partitioning model for measuring the log KL/W of drugs.

Estimation of the octanol-water distribution coefficient of basic compounds by a cationic microemulsion electrokinetic chromatography system.

The octanol-water partition coefficient (Po/w), or the octanol-water distribution coefficient (Do/w) for ionized compounds, is a key parameter in the drug development process. In a previous work, this parameter was estimated through the retention factor measurements in a sodium dodecyl sulfate (SDS) - microemulsion electrokinetic chromatography (MEEKC) system for acidic compounds. Nonetheless, when ionized basic compounds were analyzed, undesirable ion pairs were formed with the anionic surfactant and avoided a good estimation of log Do/w. For this reason, an alternative MEEKC system based on a cationic surfactant has been evaluated to estimate Po/w or Do/w of neutral compounds and ionized bases. To this end, it has been characterized through the solvation parameter model (SPM) and compared to the octanol-water partition system. Results pointed out that both systems show a similar partition behavior. Hence, the log Po/w of a set of neutral compounds has been successfully correlated against the logarithm of the retention factor (log k) determined in this MEEKC system. Then, the log Do/w of 6 model bases have been estimated at different pH values and they have been compared to data from the literature, determined by the reference shake-flask and potentiometric methods. Good agreement has been observed between the literature and the estimated values when the base is neutral or partially ionized (up to 99% of ionization).

Partitioning of Catechol Derivatives in Lipid Membranes: Implications for Substrate Specificity to Catechol-O-methyltransferase.

We have utilized multiparametric surface plasmon resonance and impendance-based quartz crystal microbalance instruments to study the distribution coefficients of catechol derivatives in cell model membranes. Our findings verify that the octanol–water partitioning coefficient is a poor descriptor of the total lipid affinity for small molecules which show limited lipophilicity in the octanol–water system. Notably, 3-methoxytyramine, the methylated derivative of the neurotransmitter dopamine, showed substantial affinity to the lipids despite its nonlipophilic nature predicted by octanol–water partitioning. The average ratio of distribution coefficients between 3-methoxytyramine and dopamine was 8.0. We also found that the interactions between the catechols and the membranes modeling the cell membrane outer leaflet are very weak, suggesting a mechanism other than the membrane-mediated mechanism of action for the neurotransmitters at the postsynaptic site. The average distribution coefficient for these membranes was one-third of the average value for pure phosphatidylcholine membranes, calculated using all compounds. In the context of our previous work, we further theorize that membrane-bound enzymes can utilize membrane headgroup partitioning to find their substrates. This could explain the differences in enzyme affinity between soluble and membrane-bound isoforms of catechol-O-methyltransferase, an essential enzyme in catechol metabolism.

Preparation and evaluation of 99mTc-labeled porphyrin complexes prepared using PNP and HYNIC cores: studying the effects of core selection on pharmacokinetics and tumor uptake in a mouse model.

Porphyrins are tetrapyrrolic macrocyclic ligands known for their affinity towards neoplastic tissues and once radiolabeled with a suitable diagnostic radioisotope could potentially be used for the imaging of tumorous lesions. In the present study, an unsymmetrically substituted porphyrin derivative namely 5-(p-amino-propyloxyphenyl)-10,15,20-tris(carboxymethyleneoxyphenyl)-porphyrin was synthesized and modified further to enable radiolabeling with 99mTc using two different 99mTc-cores viz. 99mTc-HYNIC (hydrazino nicotinic acid) and 99mTc(N)PNP2 (PNP2 = bis-[(2-dimethylphosphino)ethyl]-methoxy-ethylamine) in order to study the effect of employing different 99mTc-cores on tumor affinity and pharmacokinetic behavior of the resultant 99mTc-labeled porphyrin complexes. 99mTc-Porphyrin complexes were characterized by reversed phase HPLC studies and could be prepared with >95% radiochemical purity under optimized radiolabeling conditions. Both 99mTc-complexes were found to be adequately stable in human blood serum till 3 h post-preparation. Bio-distribution studies, carried out in Swiss mice bearing fibrosarcoma tumors, revealed relatively higher tumor uptake for the 99mTc-HYNIC-porphyrin complex (3.95 ± 1.42 and 3.28 ± 0.27% IA per g) compared to that exhibited by the 99mTc(N)PNP-DTC-porphyrin complex (1.52 ± 0.53 and 1.56 ± 0.10% IA per g) at 1.5 and 3 h post-administration, although the former complex exhibited comparatively lower lipophilicity in the octanol-water system. Higher uptake and longer retention in the blood were observed for the 99mTc-HYNIC-porphyrin complex (6.63 ± 0.75 and 4.36 ± 0.25% IA per g) compared to that exhibited by the 99mTc(N)PNP-DTC-porphyrin complex (2.41 ± 0.54 and 2.30 ± 0.16% IA per g) at both 1.5 and 3 h post-administration. However, relatively lower liver uptake was observed for the former complex (19.26 ± 3.48 and 18.45 ± 1.05% IA per g) than that exhibited by the latter one (39.37 ± 3.88 and 34.15 ± 8.25% IA per g) at both 1.5 and 3 h post-administration. This study indicates that the in vivo behavior exhibited by the 99mTc-labeled porphyrins not only depends on their lipophilicity/hydrophilicity but is also governed by the Tc-cores employed for radiolabeling.

An evaluation of in-silico methods for predicting solute partition in multiphase complex fluids – A case study of octanol/water partition coefficient

Solute partition in multiphase fluids is an important thermodynamic phenomenon and performance attribute for a wide range of product formulations of foods, pharmaceuticals and cosmetics. Experimental evaluation of partition coefficients in complex product formulations is empirical, difficult and time consuming. In-silico methods such as fragment constant method and group contribution method require parameter fitting to the experimental data and are limited to relatively simple fluids. Recently, a method combining molecular dynamics (MD) and quantum chemical (QC) calculation of screening charge density function has been reported. The method does not only use fundamental properties of intermolecular force and charge density function, which does not require parameter fitting to the experimental data, but also applies to complex fluid structures such as micelles. In this work, the predictive accuracy of the combined method of MD and QC is evaluated. Using widely available octanol-water partition coefficients as a case study, the performance of the combined MD and COSMOmic for predicting octanol/water partition coefficients has been compared with those of the EPI Suite™ fragment constant method, UNIFAC group contribution method and COSMOtherm. The prediction of the combined MD/COSMOmic method is the closest to the best performing fragment constant method which was specifically designed for the octanol-water system. The combined MD/QC method proves to be the most promising and robust method applicable to a wide range of complex structures of multiphase fluid systems.

Differential Partitioning of Bioantioxidants in Edible Oil–Water and Octanol–Water Systems: Linear Free Energy Relationships

Partition coefficients, PWO, of antioxidants (AOs) between edible oils and water are scarce in the literature, despite that AOs are widely used to control lipid oxidation and the oxidative stress in cells. PWO values have a great importance to predict the efficiency and distribution of bioactives at different levels of biological organization from binary oil–water systems to living cells. Here, we determined the partition coefficients, PWO, of four series of potent, natural AOs of increasing lipophilicity between vegetable oils (olive, soybean, and corn) and water and, for the sake of comparison, between octanol–water, PWOCT. Results indicate that the contribution of the −CH2 groups to the overall lipophilicity of the AO is the same irrespective of the oil employed. The PWO values were compared with PWOCT values, and linear relationships were obtained for each series of AOs. Results indicate that, in general, PWO values cannot be predicted from the PWOCT values, making necessary to determine the PWO value...

ДОСЛІДЖЕННЯ АМФІФІЛЬНИХ ВЛАСТИВОСТЕЙ КОПОЛІЕСТЕРІВ З ХРОМОФОРНИМИ ГРУПАМИ В СИСТЕМІ ВОДА-ОКТАНОЛ

ДОСЛІДЖЕННЯ АМФІФІЛЬНИХ ВЛАСТИВОСТЕЙ КОПОЛІЕСТЕРІВ З ХРОМОФОРНИМИ ГРУПАМИ В СИСТЕМІ ВОДА-ОКТАНОЛ

Substituted benzotriazoles as inhibitors of copper corrosion in borate buffer solutions

The adsorption of substituted 1,2,3-benzotriazoles (R-BTAs) onto copper is measured via ellipsometry in a pure borate buffer (pH 7.4) and satisfactorily described by Temkin’s isotherm. The adsorption free energy (−ΔG a 0 ) values of these azoles are determined. The (−ΔG a 0 ) values are found to rise as their hydrophobicity, characterized by the logarithm of the partition coefficient of a substituted BTA in a model octanol–water system (logP), grows. The minimum concentration sufficient for the spontaneous passivation of copper (C min) and a shift in the potential of local copper depassivation with chlorides (E pt) after an azole is added to the solution (i.e., ΔE = E pt in − E pt backgr characterizing the ability of its adsorption to stabilize passivation) are determined in the same solution containing a corrosion additive (0.01М NaCl) for each azole under study. Both criteria of the passivating properties of azoles (logC min and ΔE) are shown to correlate linearly with logP, testifying to the role played by surface activity of this family of organic inhibitors in protecting copper in an aqueous solution.

Effect of complex formation by taxifolin and naringenin with Cu(i) ions on the distribution of the components of complexes in the octanol–water system

The interaction of two structurally close flavanones: taxifolin and naringenin with copper(I) ions and its effect on the distribution of flavonoids and the corresponding ions in a biphasic system octanol–water have been studied. It has been shown that these polyphenols form complexes with copper ions of different stoichiometric ratio depending on the pH of medium (5.4, 7.4, and 9.0). The interaction of the flavonoids with copper ions leads to an increase in the fraction of polyphenols in the water phase at all pH values examined. The fraction of metal ions in octanol in the presence of both taxifolin and naringenin is maximal in the range of neutral pH values. The parameters obtained in the study, such as the partition coefficient and the coefficient of distribution in a biphasic system octanol–water (logP and logD) form the physicochemical basis necessary for the estimation of the bioavailability of flavonoids and the corresponding metal ions upon their combined consumption.

Experience in the Use of Solid-Phase Extraction in the Screening of Pharmaceuticals and Narcotics in the Blood by Gas Chromatography with Mass Spectrometric Detection

Studies using 224 blood samples as examples showed that the use of solid-phase extraction and gas chromatography with mass spectrometric detection for screening blood provides reliable identification of a wide range of narcotic and pharmaceutical substances of forensic medical interest, including “designer” synthetic narcotics – methylenedioxypyrovalerone (MDPV), pyrrolidinovalerophenone (PVP), and their metabolites; cannabimimetic metabolites N-(1-carbamoyl-2-methylpropyl)-1-pentyl-1H-indazole-3-carboxamide (ABPINACA) and/or N-[(1-pentyl-1H-indazol-3-yl)carbonyl]valine methyl ester (AMB). The distribution of substances in different elusion fractions is given and dissociation constants (pKa) and coefficients of distribution in an octanol-water system (log P) are calculated.

Predicting solvent-water partitioning of charged organic species using quantum-chemically estimated Abraham pp-LFER solute parameters

Methods for obtaining accurate predictions of solvent-water partitioning for neutral organic chemicals (e.g., Kow) are well-established. However, methods that provide comparable accuracy are not available for predicting the solvent-water partitioning of ionic species. Previous methods for addressing charge contributions to solvent-water partitioning rely on charged solute descriptors which are obtained from regressions to neutral species descriptors as well as charged descriptors which are specific to unique charge-functionalities and structural moieties. This paper presents a method for obtaining Abraham poly-parameter linear free energy relationship (pp-LFER) descriptors using quantum chemical calculations and molecular structure, only. The method utilizes a large number of solvent-water systems to overcome large errors in individual quantum chemical computations of ionic solvent-water partition coefficients. The result is a single set of quantum-chemically estimated Abraham solute parameters (QCAP) which are solvent-independent, and can be used to predict the solvent-water partitioning of ionic species.Predictions of solvent-water partition coefficients for ionic species using quantum-chemically estimated Abraham parameters (QCAPs) are shown to provide improved accuracy compared over both existing Absolv-estimated Abraham solute parameters (AAP) as well as direct a priori quantum chemical (QC) calculations for partitioning of anionic solutes in 4 organic solvent-water systems (RMS = 0.740, 2.48 and 0.426 for the Absolv, QC and QCAP methods, respectively). For quaternary amine cations in the octanol-water system the RMS errors of the solvent-water partition coefficients were larger and similar between the two Abraham models (RMSE = 0.997 and 1.16, for the AAP and QCAP methods, respectively). Both methods showed significant improvement over direct QC calculations (RMSE = 2.82).

A linear free energy analysis of PAMPA models for biological systems

Equation coefficients in the Abraham linear free energy relationship have been obtained for a number of parallel artificial membrane permeability assays, PAMPA, and have been compared to equation coefficients for several biological processes and a large number of water-solvent partitions. From a principal component analysis of the equation coefficients we show that one particular PAMPA (Wohnsland and Faller, 2001) is a good model for human intestinal absorption, but we could find no PAMPA that was a good model for rat brain permeation, mouse brain permeation, blood–brain distribution, skin permeation or water–skin partition, although models that include PAMPA and other descriptors may be useful. The water–octanol system is a poor model for all the biological process we have studied, but water-nonpolar solvent partitions are good models for permeation through egg lecithin membranes.

Analysis of Metformin Applied Different Tools Computationals for Determine All the Characteristics of Drug

The metformin structure was analyzed using Hyperchem software to determine the structural properties for absorption process in chitosan cross linking with genipin for medical applications The theoretical calculations were Gibbs free energy electrostatic potential and FTIR spectroscopy Optimized structures and their molecular electrostatic potentials were calculated using the AM and PM method and the results were used to calculate the molecular interactions of metformin The quantitative structure property relationship model was also used to estimate the activity of the chemicals on the basis their molecular structures Fourier transform infrared FTIR spectroscopy reveals information about the metformin properties The molecular electrostatic potential MESP is a powerful tool that has provided insights into intermolecular association and molecular properties of small molecules for example actions of drug molecules and their analogs The nucleophilic and electrophilic regions were calculated using the MESP The Log P value P is the partition coefficient of the molecule in the water ndash octanol system showed the hydrophobic character of drug