Water-saturated 1-octanol Research Articles

Predicting octanol/water partition coefficients for the SAMPL6 challenge using the SM12, SM8, and SMD solvation models.

Blind predictions of octanol/water partition coefficients at 298 K for 11 kinase inhibitor fragment like compounds were made for the SAMPL6 challenge. We used the conventional, "untrained", free energy based approach wherein the octanol/water partition coefficient was computed directly as the difference in solvation free energy in water and 1-octanol. We additionally proposed and used two different forms of a "trained" approach. Physically, the goal of the trained approach is to relate the partition coefficient computed using pure 1-octanol to that using water-saturated 1-octanol. In the first case, we assumed the partition coefficient using water-saturated 1-octanol and pure 1-octanol are linearly correlated. In the second approach, we assume the solvation free energy in water-saturated 1-octanol can be written as a linear combination of the solvation free energy in pure water and 1-octanol. In all cases here, the solvation free energies were computed using electronic structure calculations in the SM12, SM8, and SMD universal solvent models. In the context of the present study, our results in general do not support the additional effort of the trained approach.

Computational Observation of Pockets of Enhanced Water Concentration at the 1-Octanol/Water Interface

Molecular dynamics simulations with polarizable potentials were carried out to investigate the 1-octanol-water interface in which a significant amount of water migrated into the 1-octanol phase. A region of enhanced water concentration, around three times the average concentration in water saturated 1-octanol, was present 18 Å from the Gibbs dividing surface into the 1-octanol phase. This coincided with two layers of 1-octanol molecules, forming a somewhat ordered bilayer with the first layer having its hydroxyl group pointed toward the water phase. The second layer of 1-octanol had hydroxy groups pointed in the opposite direction on average. A consequence of this was a region of high alkyl concentration and reduced polarity, as has been previously observed. Water structure in the octanol phase contracted as it approached the 1-octanol phase, opposite what was observed at the n-octane-water interface with polarizable potentials. In contrast, 1-octanol hydroxy structure expanded as it came in contact with water.

Certification of the reference material of water content in water saturated 1-octanol by Karl Fischer coulometry, Karl Fischer volumetry and quantitative nuclear magnetic resonance

Certified reference materials (CRMs) of water content are widely used in the calibration and validation of Karl Fischer coulometry and volumetry. In this study, the water content of the water saturated 1-octanol (WSO) CRM was certified by Karl Fischer coulometry, volumetry and quantitative nuclear magnetic resonance (Q NMR). The water content recovery by coulometry was 99.76% with a diaphragm-less electrode and Coulomat AG anolyte. The relative bias between the coulometry and volumetry results was 0.06%. In Q NMR, the water content of WSO is traceable to the International System (SI) of units through the purity of internal standard. The relative bias of water content in WSO between Q NMR and volumetry was 0.50%. The consistency of results for these three independent methods improves the accuracy of the certification of the RM. The certified water content of the WSO CRM was 4.76% with an expanded uncertainty of 0.09%.

Elucidating the Association of Water in Wet 1-Octanol from Normal to High Temperature by Near- and Mid-Infrared Spectroscopy

Near- (NIR) and mid-infrared (MIR) absorption spectra of pure and water-saturated 1-octanol were measured along the liquid-gas coexistence curve from ambient temperature and pressure up to 300 degrees C and 10 MPa. Density of the mixture as a function of temperature was assessed by spectral analysis in the NIR region. Two distinct regimes of temperature were identified in the evolution of solvent-subtracted spectra: at normal conditions and up to 180 degrees C, water is organized in multimeric H-bonded aggregates, while at higher temperature, mainly dimers and monomers exist. Water-water and alcohol-alcohol H-bonding interactions play a major role in wet octanol at low temperature, with resulting microheterogeneity and water segregation at a molecular level; on the other hand, water-alcohol interactions are relevant at higher temperature, as also revealed by the estimated density. At low temperature, water dissolved in octanol shows features which are comparable to those of interfacial water obtained by vibrational sum frequency (VSF) spectroscopy, while at high temperature the spectra generally reproduce those of water in the supercritical phase. Overall spectral assignment was supported by ab initio calculations at the MP2 level on small water clusters.

Gibbs Energies of Transfer of Alkali Metal Cations between Mutually Saturated Water−Solvent Systems Determined from Extraction Experiments with Radiotracer 137Cs

Thermodynamic standard Gibbs energies of transfer of alkali metal cations related to Cs+ cation [DeltatG degrees*,(Cs+)-[DeltatG degrees*,(M+)] between several mutually saturated solvents of the type water-solvent were calculated from determined extraction exchange constants Kexch degrees,*(Cs+/M+). The used liquid-liquid extraction method with radioactive tracing by 137Cs permits attaining higher precision of the values as compared to the methods used up to now. The data for o-nitrophenyloctyl ether, 1,2-dichloroethane, and 1-octanol were compared with literature sources and recommended absolute values of DeltatG degrees,*M+) are reported. For dissociating solvents, the dependences of [DeltatG degrees,*(Cs+) - [DeltatG degrees,*(M+)] on Gibbs energy of hydration of an ion, DeltaGhydr degrees are straight lines either for four cations Cs+, Rb+, K+, and Na+ (nitrosolvents) or for three cations Cs+, Rb+, and K+ (1,2-dichloroethane and 1-octanol). The hydration of Na+ and still more of Li+ in the water-saturated organic phase is apparent from the results. This manifests for high-water-content equilibrium 1-octanol even in a reversal of the values [i.e., DeltatG degrees*,(Li+) being more negative than DeltatG degrees,*(Na+)], although for Cs+, Rb+, and K+, the general trend is conserved. Water-saturated 1-octanol is thus slightly less basic than water, but the overall selectivity is very low. For one studied nondissociating solvent, dioctyl sebacate, the trend of the dependences of log Kexch degrees,*(CsB/M+) on DeltaGhydr degrees is similar to that of Kexch degrees,*(Cs+/M+) for polar solvents, but different for different anions B, thus reflecting ion association in the organic phase.

Water/Alcohol Mixtures: A Spectroscopic Study of the Water-Saturated 1-Octanol Solution

The properties of the water-saturated 1-octanol solution in the 10−75 °C temperature range have been investigated by means of different scattering spectroscopies. The results of Raman, depolarized-Rayleigh, and Rayleigh−Brillouin experiments have been compared to the corresponding results recently obtained for the pure alcohol in our laboratory. Spectroscopic findings obtained for the temperature behavior of vibrational, rotational, and translational degrees of freedom are analyzed according to a single, unifying picture of this liquid system. Differences and analogies between pure and water-saturated 1-octanol suggest the key for interpreting the structural properties connected to the amphiphilic nature of n-alcohols. In a wider perspective, the same arguments can be applied to the study of larger and more complicated systems such as phospholipids for which 1-octanol represents a simple model.

Measurement of water by oven evaporation using a novel oven design. 1. Water in water-saturated 1-octanol, coal, cement, and refined oils.

Using an automated oven evaporation technique combined with the coulometric Karl Fischer method, the mass fraction of water has been measured in cement, coal, and refined oil samples. The accuracy of this method was established by using SRM 2890, water-saturated 1-octanol that was added to white oil. The samples were analyzed for total reactive Karl Fischer reagent (KFR) material, for interfering materials, and for material that does not react with the aldehyde-ketone KFR. All of the samples yielded volatile material that reacted with the standard KFR. None of the samples contained significant masses of material that reacted with iodine. The cement and coal SRMs contained no material that reacted with methanol and very little material that did not volatilize at 107 degrees C. The refined oils contained some material that was volatile at 107 degrees C and some at 160 degrees C. However, none of this material reacted with the aldehyde-ketone reagent. These results show that the material in the solid samples is water and that the material in the refined oils is a material other than water which reacts with methanol to form water.

The determination of water in crude oil and transformer oil reference materials.

The measurement of the amount of water in oils is of significant economic importance to the industrial community, particularly to the electric power and crude oil industries. The amount of water in transformer oils is critical to their normal function and the amount of water in crude oils affects the cost of the crude oil at the well head, the pipeline, and the refinery. Water in oil Certified Reference Materials (CRM) are essential for the accurate calibration of instruments that are used by these industries. Three NIST Standard Reference Materials (SRMs) have been prepared for this purpose. The water in these oils has been measured by both coulometric and volumetric Karl Fischer methods. The compounds (such as sulfur compounds) that interfere with the Karl Fischer reaction (interfering substances) and inflate the values for water by also reacting with iodine have been measured coulometrically. The measured water content of Reference Material (RM) 8506a Transformer Oil is 12.1+/-1.9 mg kg(-1) (plus an additional 6.2+/-0.9 mg kg(-1) of interfering substances). The measured water content of SRM 2722 Sweet Crude Oil, is 99+/-6 mg kg(-1) (plus an additional 5+/-2 mg kg(-1) of interfering substances). The measured water content of SRM 2721 Sour Crude Oil, is 134+/-18 mg kg(-1) plus an additional 807+/-43 mg kg(-1) of interfering substances. Interlaboratory studies conducted with these oil samples (using SRM 2890, water saturated 1-octanol, as a calibrant) are reported. Some of the possible sources of bias in these measurements were identified, These include: improperly calibrated instruments, inability to measure the calibrant accurately, Karl Fischer reagent selection, and volatilization of the interfering substances in SRM 2721.

Interlaboratory assessment of measurement precision and bias in the coulometric Karl Fischer determination of water.

The precision and bias of the coulometric Karl Fischer ASTM method D1533-00 have been assessed in a collaborative ASTM round robin program for a group of 34 laboratories. The test materials used in this study included water saturated 1-octanol (WSO), water saturated 1-butanol (WSB), and a series of new and used transformer oil samples. Fundamental systematic biases have been demonstrated in the accuracy of the measurement of water in the WSO, WSB, and transformer oil samples. The systematic bias in the measurement of the WSO and WSB standards indicates that for some laboratories either the instruments were not accurate or the quantity of the standard was not measured accurately. A second type of systematic bias consisted of measurement errors associated with the selection of the Karl Fischer solvent that was used with each instrument, and this was superimposed upon the error in the measurement of the water in the standards. Using the statistical calculation method ASTM D 6300 the repeatability and reproducibility for water in transformer oil were found to be 7 mg/kg and 14 mg/kg respectively. The method detection limit of water was 8 mg/kg oil. The method bias was estimated based on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2890, WSO, since no suitable reference material for water in transformer oil was available for this study.

Monte Carlo calculations for the phase equilibria of alkanes, alcohols, water, and their mixtures

Configurational-bias Monte Carlo simulations were carried out to investigate (i) the self-aggregation of 1-hexanol in n-hexane rich binary solutions; (ii) the partitioning of normal alkane and primary alkanol solutes between water, neat or water-saturated 1-octanol, n-octane, and vapour phases, and (iii) the vapour–liquid phase diagram of the binary mixture of methanol and n-hexane at a temperature of 448 K. The optimized potentials for liquid simulations (OPLS) united-atom force field was used to describe the interactions of the alkanes and alcohols, and the transferable intermolecular potentials 4 point (TIP4P) model was used for water. Analysis of radial distribution functions and their corresponding number integrals supports a micro-heterogenous picture of the 1-hexanol/hexane solutions with the majority of the 1-hexanol molecules being part of hydrogen-bonded clusters with four to six molecules. The OPLS force field yields Gibbs free energies of transfer that are in qualitative, albeit not quantitative agreement with experimental results. Comparison of the partitioning between a helium vapour phase and dry and wet (water-saturated) 1-octanol established that water saturation affects mostly the partitioning of polar solutes, while differences for alkane partitioning were found to be negligible. The vapour pressure of OPLS n-hexane is too low and that of methanol too high, resulting in a binary vapour–liquid phase diagram that deviates significantly from experiment.

Chloroperoxidase-catalyzed enantioselective oxidations in hydrophobic organic media

Chloroperoxidase from Caldariomyces fumago, a peroxidase that performs P450-like chemistry, was immobilized via covalent attachment into polyurethane foam as well as conjugated with a surfactant or polymer via colyophilization. The resulting preparations catalyzed enantio- and regioselective oxidations in hydrophobic organic media with tert-butyl hydroperoxide as the oxidant. Dried PUR-foam immobilized CPO mediated the selective oxidation of indole to 2-oxindole (regioselectivity: 99%) in water-saturated isooctane or 1-octanol. Thioanisole was converted into the corresponding (R)-sulfoxide (ee > 99%) in isooctane medium. The complexes of CPO with sodium octadecylsulphate or ethyl cellulose mediated the oxidation of thioanisole in water-immiscible organic media with variable enantioselectivity due to radical side-reactions. In the presence of α-tocopherol, acting as radical scavenger, the (R)-sulfoxide was formed with ee > 90%. The effect of the water activity on the catalytic activity of the complexes was investigated. The CPO complexes likewise mediated the regioselctive oxidation of indole into 2-oxindole in water-saturated isooctane or 1-octanol and its kinetics were investigated. The reaction suffered from substrate inhibition when carried out in isooctane. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 72: 523–529, 2001.

Chloroperoxidase‐catalyzed enantioselective oxidations in hydrophobic organic media

Chloroperoxidase from Caldariomyces fumago, a peroxidase that performs P450-like chemistry, was immobilized via covalent attachment into polyurethane foam as well as conjugated with a surfactant or polymer via colyophilization. The resulting preparations catalyzed enantio- and regioselective oxidations in hydrophobic organic media with tert-butyl hydroperoxide as the oxidant. Dried PUR-foam immobilized CPO mediated the selective oxidation of indole to 2-oxindole (regioselectivity: 99%) in water-saturated isooctane or 1-octanol. Thioanisole was converted into the corresponding (R)-sulfoxide (ee > 99%) in isooctane medium. The complexes of CPO with sodium octadecylsulphate or ethyl cellulose mediated the oxidation of thioanisole in water-immiscible organic media with variable enantioselectivity due to radical side-reactions. In the presence of alpha-tocopherol, acting as radical scavenger, the (R)-sulfoxide was formed with ee > 90%. The effect of the water activity on the catalytic activity of the complexes was investigated. The CPO complexes likewise mediated the regioselective oxidation of indole into 2-oxindole in water-saturated isooctane or 1-octanol and its kinetics were investigated. The reaction suffered from substrate inhibition when carried out in isooctane.

Partitioning of Alkane and Alcohol Solutes between Water and (Dry or Wet) 1-Octanol

Configurational-bias Monte Carlo simulations in the Gibbs ensemble using the OPLS (optimized potentials for liquid simulations) force field were performed to study the partitioning of normal alkane and primary alcohol solutes between water, neat or water-saturated 1-octanol, and helium vapor phases. Precise values of the Gibbs free energy of transfer were calculated directly from the ratio of the solute number densities in the two co-existing phases. It is observed that the OPLS force field yields Gibbs free energies of transfer that are in qualitative, albeit not quantitative, agreement with experimental results. Comparison of the partitioning between a helium vapor and dry or wet 1-octanol phases established that water saturation affects mostly the partitioning of polar solutes, while differences for alkane partitioning were found to be negligible. In addition, the analysis of radial distribution functions of alcohol solutes in wet 1-octanol shows preferential partitioning into water-rich regions of the...

Certification by the Karl Fischer method of the water content in SRM 2890, Water Saturated 1-Octanol, and the analysis of associated interlaboratory bias in the measurement process.

The calibration of Karl Fischer instruments and reagents and the compensation for instrumental bias are essential to the accurate measurement of trace levels of water in organic and inorganic chemicals. A stable, nonhygroscopic standard, Water Saturated Octanol, which is compatible with the Karl Fischer reagents, has been prepared. This material, Standard Reference Material (SRM) 2890, is homogeneous and is certified to contain 39.24 +/- 0.85 mg water/mL (expanded uncertainty) of solution (47.3 +/- 1.0 mg water/g solution, expanded uncertainty) at 21.5 degrees C. The solubility of water in -octanol has been shown to be nearly constant between 10 degrees C and 30 degrees C (i.e., within 1% of the value at 21.5 degrees C). The results of an interlaboratory comparison exercise illustrate the utility of SRM 2890 in assessing the accuracy and bias of Karl Fischer instruments and measurements.

Free Energy Perturbation Study of Octanol/Water Partition Coefficients: Comparison with Continuum GB/SA Calculations

Molecular dynamics (MD) free energy perturbation (FEP) simulations were carried out in order to obtain insights into the structures and dynamics of a series of small organic solutes in water and water-saturated 1-octanol. Relative free energies of solvation were computed for each solute in both solvents, and these results were used to estimate the relative octanol/water partition coefficients (log P o w). The relative octanol/water partition coefficients were in good agreement with experimental log P o w values (average unsigned error = 0.74 log units), if one omits the acetamide−acetone simulation which proved problematic. Partition coefficients were also calculated using the newly developed GB/SA octanol continuum solvation model in order to compare the MD-FEP and continuum model results. Interestingly, the computationally much more efficient GB/SA calculations proved to be more accurate (average unsigned error in log P o w = 0.50 log units) than FEP for this set of 12 solutes.

Structural aspects of water in 1-octanol

Water-saturated 1-octanol, extensively used for studies of the distribution of organic solutes, is subjected to structural analysis in terms of the neighbors each molecule has. This is based on thermodynamic information on the system from the literature. The local composition of a given water molecule is richer in water than the bulk composition, and, conversely, for the local composition near a 1-octanol molecule. At saturation (mole fraction of water of 0.275 in the organic phase) the excess (deficiency) of the mole fraction of water is 0.197 (−0.075) near water (1-octanol) molecules.

Ion transport mediated by inverted micellar aggregates across a phosphatidylcholine-octanol liquid membrane

The ionophoretic activity of dipalmitoyl-DL-α-phosphatidylcholine (DPPC) was investigated on the system in which two aqueous NaCl solutions are separated by a porous support membrane impregnated with a 1-octanol solution of DPPC. Transmembrane potential and conductance measurements were carried out with changing temperature to estimate the membrane permeability to ions. To clarify the mechanism of ion transport through an immobilized DPPC-1-ctanol membrane, differential scanning calorimetry and photon correlation spectroscopy were employed to investigate the molecular properties of DPPC in a water-saturated 1-octanol system. An endothermic peak was detected at around 18°C in the water-saturated 1-octanol system, but not in the pure 1-ctanol system. Laser light scattering study indicated that DPPC molecules form aggregates, ca. 0.1 μm in diameter, in water-saturated 1-octanol, but not in pure 1-octanol. Temperature dependences of the relaxation time estimated by the light scattering study changed above and below 18°C. The critical temperature, 18°C, correlates well with that at which modes of the temperature dependences of membrane permeability are altered. Results obtained by these three types of experiments indicate that inverted micellar aggregates of DPPC function as an ionophore.

Phospholipid Inverted Micellar Aggregate as an Ionophore in Liquid Membrane System

Abstract Electrochemical, thermochemical, and light scattering investigations were performed on the 1-octanol liquid membrane systems containing dipalmitoyl-Dl-phosphatidylcholine (DPPC) as an ionophore. It was suggested that DPPC molecules form inverted micellar aggregate in water saturated 1-octanol and that the membrane processes can be regulated by an endothermic phase transition of the DPPC multimolecular cation carrier.