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At least 19 recordsLinked to original sources
PubMed2006

Structural characterization of interfacial n-octanol and 3-octanol using molecular dynamic simulations.

Structurally isomeric octanol interfacial systems, water/vapor, 3-octanol/vapor, n-octanol/vapor, 3-octanol/water, and n-octanol/water are investigated at 298 K using molecular dynamics simulation techniques. The present study is intended to investigate strongly associated liquid/liquid interfaces and probe the atomistic structure of these interfaces. The octanol and water molecules were initially placed randomly into a box and were equilibrated using constant pressure techniques to minimize bias within the initial conditions as well as to fully sample the structural conformations of the interface. An interface formed via phase separation during equilibration and resulted in a slab geometry with a molecularly sharp interface. However, some water molecules remained within the octanol phase with a mole fraction of 0.12 after equilibration. The resulting "wet" octanol interfaces were analyzed using density profiles and orientational order parameters. Our results support the hypothesis of an ordered interface only 1 or 2 molecular layers deep before bulk properties are reached for both the 3-octanol and water systems. However, in contrast to most other interfacial systems studied by molecular dynamics simulations, the n-octanol interface extends for several molecular layers. The octanol hydroxyl groups form a hydrogen-bonding network with water which orders the surface molecules toward a preferred direction and produces a hydrophilic/hydrophobic layering. The ordered n-octanol produces an oscillating low-high density of oxygen atoms out of phase with a high-low density of carbon atoms, consistent with an oscillating dielectric. In contrast, the isomeric 3-octanol has only a single carbon-rich layer directly proximal to the interface, which is a result of the different molecular topology. Both 3-octanol and n-octanol roughen the water interface with respect to the water/vapor interface. The "wet" octanol phases, in the octanol/water systems reach bulk properties in a shorter distance than the "dry" octanol/vapor interfaces.

1-Octanol↗
PubMed2006

Hydrogen bonding in liquid and supercritical 1-octanol and 2-octanol assessed by near and midinfrared spectroscopy.

The near and midinfrared spectra of 1-octanol (and 2-octanol) have been measured along the liquid-gas coexistence curve from room temperature up to the critical point and in the supercritical domain along the isotherm T=385 degrees C (and T=365 degrees C) above the critical point of both 1-octanol and 2-octanol for pressure ranging from 0.5 up to 15 MPa. The density values of SC 1- and 2-octanol have been estimated by analysing the near infrared (NIR) spectra in the 3nu(a)(CH) region. A quantitative analysis of the absorption band associated with the OH stretching vibration [nu(OH)] and its first and second overtones [2nu(OH) and 3nu(OH)] was carried out in order to estimate the percentage of "free" OH groups in both alcohols in the whole thermodynamic domain investigated here. Very consistent results have been obtained from the independent analysis of these three different absorption bands which gave us a good confidence in the degree of hydrogen bonding reported here for 1- and 2-octanol. Thus, the percentage of free OH groups which is around 5% in liquid 1-octanol under ambient conditions strongly increase up to 70%-80% at a temperature of about 340 degrees C. Then, in the supercritical domain, upon a decrease of the density from 0.4 to 0.1 g cm(-3), the fraction of free hydroxyl groups is nearly constant presenting a plateaulike regime around 80%. As the density decreases again, this plateau regime is followed by a further increase of X(nb) which reaches a value of 96% for the system in the gaseous phase (0.01 g cm(-3); P=0.45 MPa). Finally, it comes out from this study that the percentage of free OH groups is always greater in 2-octanol than in 1-octanol at the same density.

Journal Article↗
PubMed2006

Comparison of hydrogen bonding in 1-octanol and 2-octanol as probed by spectroscopic techniques.

Liquid 1-octanol and 2-octanol have been investigated by infrared (IR), Raman, and Brillouin experiments in the 10-90 degrees C temperature range. Self-association properties of the neat liquids are described in terms of a three-state model in which OH oscillators differently implicated in the formation of H-bonds are considered. The results are in quantitative agreement with recent computational studies for 1-octanol. The H-bond probability is obtained by Raman data, and a stochastic model of H-bonded chains gives a consistent picture of the self-association characteristics. Average values of hydrogen bond enthalpy and entropy are evaluated. The H-bond formation enthalpy is ca. -22 kJ/mol and is slightly dependent on the structural isomerism. The different degree of self-association for the two octanols is attributed to entropic factors. The more shielded 2-isomer forms larger fractions of smaller, less cooperative, and more ordered clusters, likely corresponding to cyclic structures. Signatures of a different cluster organization are also evidenced by comparing the H-bond energy dispersion (HBED) of OH stretching IR bands. A limiting cooperative H-bond enthalpy value of 27 kJ/mol is found. It is also proposed that the different H-bonding capabilities may modulate the extent of interaggregate hydrocarbon interactions, which is important in explaining the differences in molar volume, compressibility, and vaporization enthalpy for the two isomers.

1-Octanol↗
PubMed1983

Enthalpies of solution of a series of m-alkoxy phenols in water, n-octanol and water-n-octanol mutually saturated: derivation of the thermodynamic parameters for solute transfer between these solvents.

Enthalpies of solution in both water and n-octanol have been determined for a series of phenols, in a microcalorimeter modified for titration. The thermodynamic data for solution in n-octanol and in water, as well as for transfer between the two, have been calculated from the free energies of transfer, based upon partition coefficients, and the free energies of solution, based upon solubility data. The results are discussed in terms of solute-solvent interactions in both phases and are used to assess, critically, the use of n-octanol as lipid-like solvent in QSAR studies.

1-Octanol↗
PubMed1983

Solubility and partitioning VI: octanol solubility and octanol-water partition coefficients.

A simple equation for the estimation of the aqueous solubility of crystalline solutes was previously derived based on the assumption that the presence of water does not significantly alter the crystal properties of the solute. The data presented verify the solubility equation for a set of 36 nonelectrolytes and weak electrolytes. Using the same set of solutes, the two major assumptions used to derive the equation were also verified: that the octanol solubility of nonelectrolytes is exponentially proportional to the melting point of the solute and that the octanol-water solubility ratio is a good approximation of the octanol-water partition coefficient.

Chemical Phenomena↗
PubMed2005

Estimating octanol-air partition coefficients with octanol-water partition coefficients and Henry's law constants.

The octanol-air partition coefficient (K(OA)) is useful for predicting the partitioning behavior of organic compounds between air and environmental matrices such as soil, vegetation, and aerosol particles. At present, experimentally determined K(OA) values are available for only several hundred compounds. Therefore, the ability to estimate K(OA) is necessary for screening level evaluation of most chemicals. Although it is possible to estimate K(OA) from the octanol-water partition coefficient (K(OW)) and Henry's law constant (HLC), various concerns have been raised in regard to the usability of this estimation methodology. This work examines the accuracy and usability of K(OW) and HLC in application to a comprehensive database set of K(OA) values for screening level environmental assessment. Results indicate that K(OW) and HLC can be used to accurately predict K(OA) even when estimated K(OW) and HLC values are used. For an experimental dataset of 310log K(OA) values for different compounds, the K(OW)-HLC method was statistically accurate as follows: correlation coefficient (r2): 0.972, standard deviation: 0.526, absolute mean error: 0.358 using predominantly experimental K(OW) and HLC values. When K(OW) and HLC values were estimated (using the KOWWIN and HENRYWIN programs), the statistical accuracy was: correlation coefficient (r2): 0.957, standard deviation: 0.668, absolute mean error: 0.479.

1-Octanol↗
PubMed1990

Sensory irritant receptor compartment properties. Equipotent vapour concentrations related to saturated vapour concentrations, octanol-water, and octanol-gas partition coefficients.

Receptor compartments can be hydrophilic or hydrophobic. The hydrophobic character can be revealed from the logarithmic relationship between the octanol-water partition coefficient (Po/w) and the equipotent equilibrium concentration (Cw) measured in the water compartment (Franke: Theoretical Drug Design Methods. Elsevier, Amsterdam 1984). For activation of the sensory irritant receptor during exposure to airborne chemicals the Cw values at equilibrium can be obtained from the gas or vapour concentrations [( A]a) and the water-gas partition coefficients (Pw/g). However, if the octanol-gas partition coefficients (Po/g) are used, the analysis can be carried out directly from the gas or vapour concentrations. The thermodynamic activity can also be used to reveal whether the environment of the receptor is hydrophobic or not. We have adapted Franke's theory to a series of homologous airborne sensory irritants. Our results suggest that the environment of the sensory irritant receptor is likely to be a hydrophobic site within the polar part of the nerve membrane. The extended theory is general and it is therefore suggested that it applies to other airborne exposure concentrations which are in equilibrium with a hydrophobic receptor.

Chemical Phenomena↗
PubMed2004

Adsorption of 1-octanol at the free water surface as studied by Monte Carlo simulation.

The adsorption of 1-octanol at the free water surface has been investigated by Monte Carlo computer simulation. Six different systems, built up by an aqueous and a vapor phase, the latter also containing various number of octanol molecules, have been simulated. The number of the octanol molecules has been chosen in such a way that the octanol surface density varies in a broad range, between 0.27 and 7.83 micromol/m(2) in the six systems simulated. For reference, the interfacial system containing bulk liquid octanol in the apolar phase has also been simulated. The results have shown that the formation of hydrogen bonds between the interfacial water and adsorbed octanol molecules is of key importance in determining the properties of the adsorbed layer. At low octanol surface concentration values all the octanol molecules are strongly (i.e., by hydrogen bonds) bound to the aqueous phase, whereas their interaction with each other is negligibly small. Hence, they are preferentially oriented in such a way that their own binding energy (and thus their own free energy) is minimized. In this preferred orientation the O-H bond of the octanol molecule points flatly toward the aqueous phase, declining by about 30 degrees from the interfacial plane, irrespectively from whether the octanol molecule is the H-donor or the H-acceptor partner in the hydrogen bond. Hence, in its preferred orientation the octanol molecule can form at least two low energy hydrogen bonds with water: one as a H-donor and another one as a H-acceptor. Moreover, the preferred orientation of the hydrogen bonded water partners is close to one of the two preferred interfacial water alignments, in which the plane of the water molecule is parallel with the interface. When increasing the octanol surface density, the water surface gets saturated with hydrogen bonded octanols, and hence any further octanol molecule can just simply condense to the layer of the adsorbed octanols. The surface density value at which this saturation occurs is estimated to be about 1.7 micromol/m(2). Above this surface density value the hydrogen bonded octanols and their water partners are oriented in such a way that the number of the water-octanol hydrogen bonds is maximized. Hence, the preferred alignment of the O...O axes of these hydrogen bonds is perpendicular to the interface. This orientation is far from the optimal alignment of the individual octanol molecules, which is also reflected in the observed fact that, unlike in the case of many other adsorbents, the average molecular binding energy of the adsorbed octanol molecules increases (i.e., becomes less negative) with increasing octanol surface density.

Journal Article↗
PubMed1996

Octanol, a gap junction uncoupling agent, changes intracellular [H+] in rat astrocytes.

Octanol rapidly closes gap junction channels but its mechanism of action is not known. Because intracellular [H+], pHi, also affects the conductance of gap junctions, we studied octanol's effects on pHi in cultured rat astrocytes, which are highly coupled cells. Octanol (1 mM) caused an acid shift in the pHi of 90% of rat hippocampal astrocytes which averaged -0.19 +/- 0.09 pH units in magnitude. In 58% of the cells tested, a biphasic change in pHi was seen; octanol produced an initial acidification lasting approximately 10 min that was followed by a persistent alkalinization. The related gap junction uncoupling agent, heptanol, had similar effects on pHi. Octanol-induced changes in pHi were similar in nominally HCO(3-)-free and HCO(3-)-containing solutions, although the rate of initial acidification was significantly greater in the presence of HCO3-. The initial acidification was inhibited in the presence of the stilbene DIDS, an inhibitor of Na+/HCO3- cotransport, indicating that octanol caused acidification by blocking this powerful acid extruder. The alkalinization was inhibited by amiloride which blocks the Na+/H+ exchanger (NHE), an acid extruder, suggesting that the alkaline shift induced by octanol was caused by stimulation of NHE. As expected, octanol's effects on astrocytic pHi were prevented by removal of external Na+, which blocks both Na+/HCO3- cotransport and NHE. Octanol had only small effects on intracellular Ca2+ (Ca2+i) in astrocytes. Hepatocytes which, like astrocytes, are strongly coupled to one another, showed no change in pHi with octanol application. Fluorescence recovery after photobleaching (FRAP) was used to study the effect of changes in astrocyte pHi on degree of coupling in hippocampal astrocytes. Coupling was decreased by intracellular acid shifts approximately -0.2 pH units in size. Octanol's effects on astrocyte pHi were complex but a prompt initial acidification was nearly always seen and could contribute to the uncoupling action of this drug in astrocytes. Because octanol uncouples hepatocytes without changing their pHi, this compound clearly can influence gap junctional conductance independent of changes in pHi.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1978

Octanol reduces end-plate channel lifetime.

1. Post-synaptic effects of n-octanol at concentrations of 0.1-1 mM were examined in toad sartorius muscles by use of extracellular and voltage-clamp techniques.2. Octanol depressed the amplitude and duration of miniature end-plate currents and hence depressed neuromuscular transmission.3. The decay of miniature end-plate currents remained exponential in octanol solutions even when the time constant of decay (tau(D)) was decreased by 80-90%.4. The lifetime of end-plate channels, obtained by analysis of acetylcholine noise, was also decreased by octanol. The average lifetime measured from noise spectra agreed reasonably well with the time constant of decay of miniature end-plate currents, both in control solution and in octanol solutions.5. Octanol caused a reduction in the conductance of end-plate channels. Single channel conductance was on average about 25 pS in control solution and 20 pS in octanol.6. In most cells the normal voltage sensitivity of the decay of miniature end-plate currents was retained in octanol solutions. The lifetime of end-plate channels measured from acetylcholine noise also remained voltage-sensitive in octanol solutions. In some experiments in which channel lifetime was exceptionally reduced the voltage sensitivity was less than normal.7. In octanol solutions, tau(D) was still very sensitive to temperature changes in most cells although in some the temperature sensitivity of tau(D) was clearly reduced. Changes in tau(D) with temperature could generally be fitted by the Arrhenius equation suggesting that a single step reaction controlled the decay of currents both in control and in octanol solutions. In some cells in which tau(D) became less than 0.3 ms, the relationship between tau(D) and temperature became inconsistent with the Arrhenius equation.8. As the decay of end-plate currents in octanol solutions remains exponential, and the voltage and temperature sensitivity can be unchanged even when tau(D) is significantly reduced, it seems likely that octanol decreases tau(D) by increasing the rate of the reaction which normally controls the lifetime of end-plate channels.

Animals↗
PubMed1999

Octanol blocks fluid secretion by inhibition of capacitative calcium entry in rat mandibular salivary acinar cells.

The aliphatic alcohol octanol is thought to modulate enzyme secretion from the exocrine pancreas by the inhibition of gap junction permeability. We have now investigated the effects of octanol on salivary secretion and intracellular calcium concentration ([Ca2+]i), measured in isolated perfused rat mandibular glands and in isolated mandibular acinar cells respectively. Stimulation of perfused glands with 10 microM carbachol (CCh) evoked a rapid increase in fluid secretion followed by a decrease to a sustained elevated level. Application of 1 mM octanol during CCh stimulation inhibited fluid secretion reversibly. In isolated acini, the CCh-induced [Ca2+]i increase was reversibly inhibited by the same concentration of octanol. However, octanol also inhibited the increase in [Ca2+]i in single acinar cells where gap junctions were no longer functional, indicating that octanol directly affected the intracellular Ca2+ signalling pathway. The initial increase in [Ca2+]i induced by 0.5-10 microM CCh, which is due to Ca2+ release from IP3-sensitive Ca2+ stores, was not affected by pretreatment with octanol. In contrast, CCh-, phenylephrine- or thapsigargin-induced Ca2+ entry was almost completely and reversibly inhibited by octanol. Octanol also blocked agonist-evoked Ca2+ entry in pancreatic acinar cells, and thapsigargin-evoked Ca2+ entry in fibroblasts. These data strongly suggest that octanol blocks salivary secretion from mandibular gland by the inhibition of capacitative Ca2+ entry, and raise the possibility that octanol may be a useful tool for inhibiting agonist-evoked Ca2+ entry pathways.

Animals↗
PubMed1995

Halothane and octanol block Ca2+ oscillations in pancreatic acini by multiple mechanisms.

This study has investigated halothane and octanol, reported inhibitors of gap junction permeability, for their effects on acinar cell intracellular Ca2+ concentration ([Ca2+]i) signaling. Halothane and octanol alone at maximal concentrations induced a sustained rise in [Ca2+]i of 23 +/- 4 and 29 +/- 5 nM, respectively. Cholecystokinin (CCK, 20 pM) induced [Ca2+]i oscillations in single acinar cells within the acinus to a peak of 275 +/- 17 nM, rising from a basal level of 55 +/- 3 nM. These oscillations were completely abolished by superfusion with both halothane (4 mM) and octanol (1 mM), concentrations that blocked the spread of Lucifer yellow from cell to cell within an acinus. Lower concentrations of octanol markedly reduced the oscillation frequency (0.2 and 0.5 mM octanol: reduction in oscillation frequency of 69 +/- 6 and 43 +/- 6%, respectively). These agents however, over the same concentration range, also exhibited similar inhibitory effects on [Ca2+]i oscillations in single cells dispersed from the acinus (reduction in oscillation frequency of 75 +/- 10 and 32 +/- 12% for 0.2 and 0.5 mM octanol, respectively), suggesting additional effects other than on gap junctions. Halothane inhibited inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production in response to both 1 and 10 nM CCK (31 and 40% inhibition, respectively), possibly explaining its effects on [Ca2+]i oscillations, whereas octanol showed no significant inhibition. Octanol, unlike halothane, blocked Ins(1,4,5)P3-induced Ca2+ release from permeabilized acini, an effect that was most pronounced at a more physiological Ins(1,4,5)P3 concentration. Octanol did not affect Ins(1,4,5)P3 binding to Ins(1,4,5)P3 receptor preparation. In conclusion, although halothane and octanol block gap junction permeability in pancreatic acinar cells, these agents also affect Ins(1,4,5)P3 production and Ca2+ mobilization in response to agonist stimulation.

1-Octanol↗
PubMed2006

Microscopic structure and solvation in dry and wet octanol.

Octanol-water partition coefficients are extraordinarily successful for correlating and predicting numerous processes of pharmacological and environmental importance. The amphiphilic nature of the 1-octanol molecules allows the octanol phase to mimic the complexities of many different environments ranging from biomembranes to soil. However, the structural details of the octanol phase and whether its structure is altered upon water saturation are not yet fully understood. Configurational-bias Monte Carlo simulations in the Gibbs ensemble demonstrate that a diverse spectrum of hydrogen-bonded aggregates exists in dry and wet 1-octanol, and that water saturation substantially alters the 1-octanol environment from predominantly linear aggregates in dry octanol to larger cylindrical micelles with water cores in wet octanol. These simulation results are able to reconcile the conflicting views (chain-like or water-centered aggregates vs spherical micelles) of the 1-octanol structure inferred from thermodynamic arguments, spectroscopic measurements, and diffraction experiments. Calculated partition constants quantify the influence of water saturation on the solubility characteristics of the dry and wet octanol phases.

1-Octanol↗
PubMed1999

Agonist and potentiation actions of n-octanol on gamma-aminobutyric acid type A receptors.

The n-octanol effects on the gamma-aminobutyric acid type A (GABAA) receptor were studied in human embryonic kidney 293 cells transfected with alpha1, beta2, and gamma2S subunit cDNAs. GABA-evoked currents had an EC50 of 13.3 +/- 1.7 microM and a Hill coefficient (nH) of 1.4 +/- 0.1. n-Octanol was also capable of evoking a small current with an EC50 of 1000 microM and an nH of 2. In addition, n-octanol modulated GABA-induced currents in a concentration-dependent manner. Coapplications of n-octanol increased peak currents evoked by 3 microM GABA with an EC50 of 190 microM and an nH of 1.8. The extent of potentiation decreased with increasing GABA concentrations and no potentiation was observed when n-octanol was coapplied with 1000 microM GABA. One-minute preapplication of 1000 microM n-octanol slightly potentiated 3 microM GABA-induced current, whereas it suppressed 300 microM GABA-induced current to 16% of the control, suggesting that 84% of the receptors underwent desensitization. Two models were used to explain n-octanol agonistic and potentiating actions on the alpha1beta2gamma2S GABAA receptor: n-octanol binds to multiple sites to exert multiple actions, or n-octanol acts as a partial agonist to manifest these actions. The partial agonist model is unique because it is a simpler model to explain n-octanol actions on the GABAA receptor.

1-Octanol↗
PubMed1985

Blocking and modifying actions of octanol on Na channels in frog myelinated nerve.

The actions of externally applied n-octanol on Na channels in myelinated frog nerve fibres were studied under voltage clamp conditions. Upon octanol application peak Na inward currents declined in two phases: 90% of the reduction occurred in less than 2 min but a steady-state was reached only after 15 min. During washout the currents came to a stable level within 10 min. The reduction of Na inward currents by octanol was dependent on the amplitude and duration of prepotentials. At the resting potential (VH = 0 mV) 0.4 mM octanol reduced peak Na inward currents at V = 60 mV by 50%. After a prepulse of -60 mV and 50 ms duration Na currents decreased only by 20%. At a hyperpolarizing holding potential of VH = -28 mV 0.7 mM octanol reduced peak inward Na currents to one half. Octanol depressed Na currents at all potentials by approximately the same factor. The Na reversal potential VNa remained unchanged. 0.7 mM external octanol shifted the Na activation curve m infinity (V) by 5 mV to more positive and the inactivation curve h infinity (V) by 14 mV to more negative potentials. The midpoint slopes of both curves were reduced. The time constants of Na activation and inactivation at small depolarizations were decreased. The conductance gamma of a single Na channel and the number No of conducting Na channels per node were determined from nonstationary Na current fluctuations. 0.7 mM octanol increased gamma by a factor of 1.6 and reduced No by a factor of 0.34. It is concluded that octanol blocks some Na channels and modifies the remaining unblocked channels.

Animals↗
PubMed2005

Octanol-solubility of dissolved and particulate trace metals in contaminated rivers: implications for metal reactivity and availability.

The lipid-like, amphiphilic solvent, n-octanol, has been used to determine a hydrophobic fraction of dissolved and particulate trace metals (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) in contaminated rivers. In a sample from the River Clyde, southwest Scotland, octanol-solubility was detected for all dissolved metals except Co, with conditional octanol-water partition coefficients, D(ow), ranging from about 0.2 (Al and Cu) to 1.25 (Pb). In a sample taken from the River Mersey, northwest England, octanol-solubility was detected for dissolved Al and Pb, but only after sample aliquots had been spiked with individual ionic metal standards and equilibrated. Spiking of the River Clyde sample revealed competition among different metals for hydrophobic ligands. Metal displacement from hydrophobic complexes was generally most significant following the addition of ionic Al or Pb, although the addition of either of these metals had little effect on the octanol-solubility of the other. In both river water samples hydrophobic metals were detected on the suspended particles retained by filtration following their extraction in n-octanol. In general, particulate Cu and Zn (up to 40%) were most available, and Al, Co and Pb most resistant (<1%) to octanol extraction. Distribution coefficients defining the concentration ratio of octanol-soluble particle-bound metal to octanol-soluble dissolved metal were in the range 10(3.3)-10(5.3)mlg(-1). The presence of hydrophobic dissolved and particulate metal species has implications for our understanding of the biogeochemical behaviour of metals in aquatic environments. Specifically, such species are predicted to exhibit characteristics of non-polar organic contaminants, including the potential to penetrate the lipid bilayer. Current strategies for assessing the bioavailability and toxicity of dissolved and particulate trace metals in natural waters may, therefore, require revision.

Animals↗