Alkane-water system

Caron, G Ermondi, G. Calculating virmal log P in the alkane/water system (logPait) and its derived parameters AlogP/i ait and logDJ. /. Med. Chem. 2005, 48, 3269-3279. 

It is our opinion that, among isotropic systems, alongside the standard octanol-water, the alkane-water system (partihoning between water and different alkanes is relahvely independent of the alkane used [14]) is the only system that can be successfuUy used in ADMET predichon, because of its completely different nature from octanol-water. The situahon is much more confused for arhsohopic systems (see Ref. [7] for a brief review) since no standard system has been defined to date. 

One of the likely reasons octanol-water gained such a widespread use is its amphiprotic character, i.e. its abiUty to serve as an H-bond donor and acceptor while, for example, alkane-water systems are inert in that sense, from the point... 

The difficulties and low-throughput nature of the experimental dual determination, especially in alkane-water systems, the development of other techniques more amenable to automation, as well as more refined computational approaches for octanol-water systems, aU have contributed to Umit the use of the alkane-water system as a second bulk-phase system. However, efforts have been devoted to the development of log (alkane) computational prediction methods by Rekker et al. [13] as well as Caron and Ermondi [14]. 

Mackay, D., Shiu, W.Y., Wolkoff, A.W. (1975) Gas chromatographic determination of low concentrations of hydrocarbons in water by vapor phase extraction. ASTM STP 573, pp. 251-258, Am. Soc. Testing and Materials, Philadelphia, Pennsylvania. Macknick, A.B., Prausnitz, J.M. (1979) Vapor pressures of high-molecular-weight hydrocarbons.. /. Chem. Eng. Data 24, 175-178. Mac/ynski. A., Wioeniewska-Goclowska, B., Goral, M. (2004) Recommended liquid-liquid equilibrium data. Part 1. Binary alkane-water systems. J. Phys. Chem. Ref. Data 33, 549-577. 

J. As with the alkane - water systems, the interaction parameters for the aqueous liquid phase were found to be temperature - dependent. However, the compositions for the benzene - rich phases could not be accurately represented using any single value for the constant interaction parameter. The calculated water mole fractions in the hydrocarbon - rich phases were always greater than the experimental values as reported by Rebert and Kay (35). The final value for the constant interaction parameter was chosen to fit the three phase locus of this system. Nevertheless, the calculated three-phase critical point was about 9°C lower than the experimental value. 

Experimental solubility data are available for some higher alkane - water systems (see, for example, Skripka et al., (38)). However, these data either cover only a very limited temperature range or contain results for one phase only. No attempt has been made to determine the interaction parameters for water - hydrocarbon systems where the hydrocarbon is larger than n-octane. 

Three-Phase Loci. Figure 11 shows the three-phase loci for the alkane - water systems. No experimental three-phase data were available in the literature for the ethane - water binary. 

Where A was derived from experimental log P measurements in an alkane-water system (i.e., cyclohexane/water) and the computed molar volumes (Eq. 9) ... 

Zeppieri, S., Rodriguez, J., and Edpez de Ramos, A.L. Interfacial tension of alkane + water systems, J. Chem. Eng. Data, 46(5) 1086-1088, 2001. 

Among the large number of existing lipophilicity parameters [31], the descriptor frequently estimated by in silica methods is the partition coefficient of a solute between 1-octanol and water, expressed as log Poet [32]. However, lipophilicity determination in different solvent systems, such as alkane/water system, proved its utility in (Q)SAR studies and therefore some predictive methods also emerged in this field. Many publically available databases include numerous experimental values collected through the literature the quality of the experimental data represents the cornerstone of most of the models developed to predict lipophilicity. 

In the same way, o-nitrophenyl octyl ether (o-NPOE) was immobilized on polycarbonate (PC) filters and the apparent permeability measured after 5 h incubation time was correlated to log Pnpoe for a series of reference compounds (log Pnpoe ranging from —1 to 3.6) [90]. Lipophilicity values in the alkane/water system were also determined using PAMPA with hexadecane-PC coated filters [89]. In this case, a correlation was found between intrinsic permeability (log Pq, permeability corrected for ionization and for unstirred water layer contribution, which particularly affects permeability of lipophilic compounds) and log P ik. However, log Pq is obtained from the knowledge of the pJC, value(s) and the permeability pH profile and therefore requires the full permeability pH profile to be measured for each compound, which negatively impacts the assay throughput. 

Caron, G. and Ermondi, G. (2005) Calculating virtual log P in the alkane/ water system (log PNalk) and its derived parameters Dlog PNoct-alk and log DpHalk. Journal of Medicinal Chemistry, 48, 3269-3279. 

Many reports are available where the cationic surfactant CTAB has been used to prepare gold nanoparticles [127-129]. Giustini et al. [130] have characterized the quaternary w/o micro emulsion of CTAB/n-pentanol/ n-hexane/water. Some salient features of CTAB/co-surfactant/alkane/water system are (1) formation of nearly spherical droplets in the L2 region (a liquid isotropic phase formed by disconnected aqueous domains dispersed in a continuous organic bulk) stabilized by a surfactant/co-surfactant interfacial film. (2) With an increase in water content, L2 is followed up to the water solubilization failure, without any transition to bicontinuous structure, and (3) at low Wo, the droplet radius is smaller than R° (spontaneous radius of curvature of the interfacial film) but when the droplet radius tends to become larger than R° (i.e., increasing Wo), the microemulsion phase separates into a Winsor II system. 

Finally, in the discussion of reverse microemulsion systems, mention should be made of one of the most widely studied systems. The surfactant, sodium bis(2-ethylhexyl) sulfosuccinate or Aerosol-OT (AOT), is one of the most thoroughly studied reverse micelleforming surfactants since it readily forms reverse micelle and microemulsion phases in a multitude of different solvents without the addition of cosurfactants or other solvent modifiers. The phase behavior of AOT in liquid alkane/water systems is already well documented. Indeed, the first report of the existence of the formation of microemulsions in a supercritical fluid involved an AOT/alkane/ water system. A The spherical structure of an AOT/nonpolar-fluid/ water microemulsion droplet is shown in Fig. 1. In the now well-known structure, it can be seen that the two hydrocarbon tails of each AOT molecule point outward into the nonpolar phase (e g., supercritical fluid). These tails are lipophilic and are solvated by the nonpolar continuous phase solvent whereas the hydrophilic head groups are always positioned in the aqueous core. 

Antibodies can be utifized under a variety of non-physiological conditions and are excellently suited for preparative applications due to their intrinsic stability. We have found that antibodies catalyzing the retro-Diels-Alder reaction of 63 function equally well between pH 4 and pH 11. Aldolase antibody 72D4 operates in the presence of 10% acetone. Janda et al. have used an immobilized esterase antibody with up to 40% dimethylsulfoxide [110]. Esterase catalytic antibodies have been used in reverse micelles and in lipid-coated form to transform lipophilic substrates [111]. Catalytic antibodies can also be used in a biphasic alkane/water system [112]. The lipophilic substrate remains in the alkane phase where it does not undergo any reaction, which suppresses any uncatalyzed reaction. In case that the reaction product is still lipophilic and returns to the alkane phase, product inhibition is also suppressed under these conditions. 

Data concerning the interfacial tension of an alkane-water system deserves detailed analysis for various basic theoretical reasons. Not only are these systems of fundamental importance in oil recovery processes and emulsion formation, but such molecules also form the basis of structures in complex biological and industrial molecules. 

An explanation of the discrepancies was offered by the results from some experiments made by Johannsson et al. [30], employing a more long lived probe, Crfbpy) (t 25 /is), in the AOT-alkane-water system. From the observation of two decay processes, well separated in time as shown in Fig. 7, the authors concluded that small clusters of reverse micelles were present in the microemulsions. The initial fast process, the intramicellar quenching, occurs on the submicrosecond time scale and appears only as an initial drop since it is not resolved on the time scale used with Cr(bpy)3. It is this part of the deactivation that is possible to monitor in normal TRLQ measurements with short-lived probes. The initial drop is followed by a second decay with a characteristic time of a few microseconds before the final, very slow deactivation occurs. The results suggest that the fast exchange... 

Phenomena in Fluid (n-alkane+Water) Systems at High Pressures and Temperatures, Fluid Phase Equilibria 10, 279-287... 

Several reviews have been devoted to a detailed presentation of the fragmental method of Rekker." This method, which was the first of its kind, was revised recently, leading to more precise hydrophobic fragmental increments for the octanol/water system as well as for the alkane/water system." ... 

It was discussed elsewhere 16 that in nonionogenic solid/n-alkane - water systems, determinations of zeta potential as a function of the film specific volume may be used for studies of energetic changes. 

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