Effect of partition coefficient on microsegregation during solidification of aluminium alloys

In the modeling of microsegregation, the partition coefficient is usually calculated using data from the equilibrium phase diagrams. The aim of this study was to experimentally and theoretically analyze the partition coefficient in binary aluminum--copper alloys. The sam- ples were analyzed by differential thermal analysis （DTA）, which were melted and quenched from different temperatures during solidifica- tion. The mass fraction and composition of phases were measured by image processing and scanning electron microscopy （SEM） equipped with an energy-dispersive X-ray spectroscopy （EDS） unit. These data were used to calculate as the experimental partition coefficients with four different methods. The experimental and equilibrium partition coefficients were used to model the concentration profile in the primary phase. The modeling results show that the profiles calculated by the experimental partition coefficients are more consistent with the experi- mental profiles, compared to those calculated using the equilibrium partition coefficients.

Structural Characterization and Octanol/water Partition Coefficients(LogP) Prediction for Oxygen-containing Organic Compounds

New descriptors were constructed and structures of some oxygen-containing organic compounds were parameterized. The multiple linear regression（MLR） and partial least squares regression（PLS） methods were employed to build two relationship models between the structures and octanol/water partition coefficients（LogP） of the compounds. The modeling correlation coefficients（R） were 0.976 and 0.922, and the ＂leave one out＂ cross validation correlation coefficients（R（CV）） were 0.973 and 0.909, respectively. The results showed that the structural descriptors could well characterize the molecular structures of the compounds; the stability and predictive power of the models were good.

The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

Zircon is widely used to simulate melt generation,migration and evolution within the crust and mantle.The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients(D).However,a large range of D_(REE) values for zircon from natural samples and experimental studies has been reported,with values spanning up to 3 orders of magnitude.Unfortunately,a gap of knowledge on this variability is evident.In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon D_(REE) would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon.Nevertheless,compared to zircon D_(REE) values measured from experimental studies,this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon.Combined with recently published studies,this work supports that analysis of natural zircon/host groundmass pairs provides more robust D_(REE) values applicable to natural systems than those measured from experimental studies,which can be used to constrain the provenance of detrital zircons.

DFT and Position of Cl Substitution (PCS) Methods Studies on n-Octanol/water Partition Coefficients (lgK_(ow)) and Aqueous Solubility (–lgS_w) of All PCDD Congeners

Optimized calculations of 75 PCDDs and their parent DD were carded out at the B3LYP/6-31G＊ level by density functional theory （DFT） method. The structural parameters were obtained and significant correlation between the C1 substitution position and some structural parameters was found. Consequently, the number of C1 substitution positions was taken as theoretical descriptors to establish two novel QSPR models for predicting lgKow and -lgSw of all PCDD congeners. The two models achieved in this work contain two variables （Na and Nβ）, of which r = 0.9312, 0.9965 and SD = 0.27, 0.12 respectively, and t values are all large. The variation inflation factors （VIF） of variables in the two models herein are both less than 5.0, suggesting high accuracy of the lgKow and -lgSw predicting models, and the results of cross-validation test also show that the two models exhibit optimum stability and good predictive power. By comparison, the correlation and predictive ability of the present work are more advantageous than those obtained using semi-empirical AM1 and GC-RI methods.

Experimental and QSPR Studies on n-Octanol/water Partition Coefficient (lgK_(ow)) of Substituted Aniline

The n-octanol/water partition coefficients （lgKow） of 18 substituted anilines were determined at 25 ℃ by shake-flask method. The geometrical optimization of substituted anilines has been performed at B3LYP/6-311G^＊＊ level with Gaussian98 program, and the molecular surface areas of substituted anilines were calculated using ChemOffice 2004 program. The calculated structural parameters of substituted anilines were used as theoretical descriptors and the two-parameter （molecular surface area （MA） and the energy of the highest occupied molecular orbital （EaoMo）） quantitative structure-property relationship （QSPR） model of lgKow for substituted aniline with molecular structural parameters was developed by multi-linear regression method. The regression coefficient square （r^2） is 0.990 and the standard deviation SE 0.109. The model was validated by variance inflation factors （VIF） and t-test, and the results show that there exists small self-correlation between variables of the model with perfect stability. The model gives results in good qualitative agreement with experimental data. At last, the model was applied to predict lgKow values of five substituted anilines whose lgKow values have not been determined experimentally.

QSPR of n-Octanol/water Partition Coefficient (lgK_(ow)) for Alkyl(1-phenylsulfonyl) Cycloalkane-carboxylates

Quantum chemistry parameters of 28 alkyl（1-phenylsulfonyl） cycloalkane-carboxy-lates were computed at the 6-31G＊ level in fully optimal manner using B3LYP method of density functional theory （DFT）. With GQSARF2.0 program, the correlation equations that can predict n-octanol/water partition coefficient （lgKow） were developed using the structural and thermodynamic parameters of 28 alkyl（1-phenylsulfonyl） cycloalkane-carboxylates with experimental data of lgKow as theoretical descriptors; the correlation coefficient （R^2） was 0.9452 and the cross-validation squared correlation coefficient （Rcv^2） 0.9312. Furthermore, a four-variable model from MEDV was obtained, of which R2 = 0.9497 and Rov^2 =0.9388. The models were validated by variance inflation factor （VIF） and t-test. Cross-validation indicates that the correlation and predicting ability of the model based on both DFT method and MEDV are more advantageous than those obtained from semi-empirical AM1 method.

Determination of Teicoplanin A2's Partition Coefficient in Different Liquid-Liquid Extraction Systems

Teicoplanin is one of the macrocyclic glycopeptide antibiotics, which is active against Gram-positive bacteria, and has attracted a lot of attention in the field of chiral separation recently. In this work, the partition coefficients and extraction ratio of teicoplanin in three different solvent systems were studied: conventional extraction, reactive extraction and reverse micelle extraction. With conventional solvent extraction, n-butanol demonstrated high partition coefficient for teicoplanin, but low extraction ratio because of its high solubility in water. Reactive extraction of teicoplanin showed the highest partition coefficient with almost 100% recovery in organic phase when tri-n-octylmethyl ammonium chloride (TOMAC) was used as extractant and pH value was above 5.0. A reverse micelle system, consisted of isooctane +10mmol-L-1 TOMAC +1% n-octanol, also offered high separation factor for teicoplanin. The results are beneficial for the design of teicoplanin separation and purification process.

Studies of n-Octanol/water Partition Coefficients (lgK_(ow)) for Organophosphate Compounds by Density Functional Theory

Optimized calculation of 35 dialkyl phenyl phosphate compounds （OPs） was carded out at the B3LYP/6-31G^＊ level in Gaussian 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained parameters were taken as theoretical descriptors to establish the novel QSPR model for predicting n-octanol/water partition coefficients （lgKow） of OPs. The new model achieved in this work contains three variables, i.e., molecular volume （Vm）, dipole moment of the molecules （μ） and enthalpy （H^0）. For this model, R^2 = 0.9167 and SD = 0.31 at large t values. In addition, the variation inflation factors （VIF） of variables are all close to 1.0, suggesting high accuracy of the predicting model. And the results of cross-validation test （q^2 = 0.8993） and method validation also showed the model of this study exhibited optimum stability and better predictive power than that from semi-empirical method. The model achieved can be used to predict IgKow of congeneric compounds.

Measurement and Correlation of Partition Coefficients of Baicalin in EOPO/Salt Aqueous Two-Phase Systems

The partition coefficients of baicalin were measured in ethylene oxide and propylene oxide (EOPO)/salt aqueous two-phase systems at 298.15K. It was found that most of baicalin partitioned into EOPO-rich phase. The partition coefficients of baicalin varied from 10 to 120. The effect of various factors, including tie-line length, salt composition, molecular weight of EOPO, and solution pH, on the partition behavior was investigated in EOPO/salt systems. Furthermore the partition coefficients of baicalin were correlated using the modified Diamond-Hsu model. Good agreement with experimental data is obtained. The average relative deviations are less than 5.0%.

Estimation of Octanol-Water Partition Coefficient of Chloride Hydrocarbon by Group Contribution Method

A novel method named two-level group contribution （GC-K） method for the estimation of octanol-water partition coefficient （Kow） of chloride hydrocarbon is presented. The equation includes only normal boiling points and molecular weight of compounds. Group contribution parameters of 12 first-level groups and 7 second-level groups for Kow are obtained by correlating experimental data of three types including 57 compounds. By comparing the estimation results of the first-level with that of the two-level groups, it was observed that the latter is better with the addition of the modification of proximity effects. When compared with Marrero＇s three-level group contribution approach and atom-fragment contribution method （AFC）, the accuracy of the average relative error of GC-K by first-level groups is 7.20% and is preferred to other methods.

Coprecipitation of metal ions into calcite: an estimation of partition coefficients based on field investigation

Trace elements(and their isotopes)in carbonates are commonly used to reconstruct paleoenvironment and paleoclimate.Understanding the processes and mechanisms of element incorporation into carbonates is thus crucial for using such geochemical parameters as paleoclimate proxies.In contrast to laboratory-based experimental results,the partitioning of trace metals between solid and solution phases in natural carbonate precipitation systems has rarely been reported.In this study,we investigated the partition coefficients of metal ions between solid and solution in the channel of the natural Baishuitai travertine system,Yunnan,China.Our results show that the partition coefficients of Li+,Na+,Mg2+,Sr2+and Ba2+are<1,that of Ni2+is approximately 1,and those of Co2+,Mn2+,Zn2+and Cu2+are>1,consistent with the results found in previous experimental studies.Although the substitution for Ca2+is likely the main uptake process of these metals into calcite,depending on their ionic radius and charge,trace elements may also be incorporated by adsorption or physical entrapment.Our study shows that unlike laboratory experiments performed under specific conditions,the partitioning of metals between two phases in the natural travertine system could be controlled by several,even multiple,environmental factors(e.g.,carbonate deposition rate,temperature,and pH),which should be taken into account when using trace metals(and their isotopes)in carbonate archives as a paleoclimate proxy.

QSPR Study on Octanol/water Partition Coefficient (lgK_(ow)) of Substituted Naphthalin Compounds

Structural parameters of 24 substituted naphthalin compounds were computed at four levels using Hartree-Fock and DFT methods. Based on the experimental data of octanol/water partition coefficient （lgKow）, three-parameter （energy of the highest occupied molecular orbital （EHOMO）, the most positive, atomic net charges of molecule （q^＋） and molecular average polarizability （α）） dependent equations were developed using structural parameters as theoretical descriptors. Especially, lgKow dependent equation calculated at the HF/6-311G^＊＊ level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors （VIF） and t-test methods and used to predict lgKow of eight designed compounds. Upon comparison, the predictive abilities of our work are all more advantageous than those calculated from molecular property calculator program.

Calculation and application of partition coefficients of light hydrocarbons in oil-based mud system

To find out the relationship between the oil-based mud,the formation fluid and the extracted gas,we use a thermodynamic approach based on static headspace gas chromatography technique to calculate the partition coefficients of 47 kinds of light hydrocarbons compounds between nC5 and nC8 in two kinds of oil-based mud-air systems,and reconstruct the original formation fluid composition under thermodynamic equilibrium.The oil-based drilling mud has little effect on the formation fluid compositions in the range of nC5-nC8(less than 1%for low-toxicity oil-based mud and less than 10%for oil-based mud).For most light hydrocarbon compositions,the partition coefficients obtained by vapor phase calibration and the direct quantitative methods have errors of less than 10%,and the partition coefficients obtained by direct quantitative method are more accurate.The reconstructed compositions of the two kinds of crude oil have match degrees of 91%and 89%with their real compositions,proving the feasibility and accuracy of reconstructing the composition of original formation fluid by using partition coefficients of light hydrocarbon compositions between nC5 and nC8.

Determination and Correlation of 1-Octanol/Water Partition Coefficients for Six Quinolones from 293.15 K to 323.15 K

A shake-flask method was used to determine 1-octanol/water partition coefficients of ofloxacin, norfloxacin, lomefloxacin, ciprofloxacin, pefloxacin and pipemidic acid from 293.15 K to 323.15 K. The results show that 1-octanol/water partition coefficient of each quinolone increased with the increase of temperature. Based on the fluid phase equilibrium theory, the thermodynamic relationship of 1-octanol/water partition coefficient depending on the temperature was proposed, and the changes of enthalpy, entropy, and Gibbs free energy for quinolones partitioning in 1-octanol/water were determined, respectively. Quinolones molecules partitioning in 1-octanol/water was mainly an entropy driving process, during which the order degree of system decreased. The temperature effects of 1-octanol/water partition coefficient were investigated. The results show that its magnitude is the same as the values in the literature.

QSPR Studies on the Octanol/water Partition Coefficient (lgK_(ow)) of Substituted Anilines with 2D and 3D Methods

Octanol/water partition coefficient （Kow） is a crucial property for evaluating the environmental behavior and fate of organic compound. Herein, some quantitative structure-property relationship （QSPR） studies were performed to estimate and predict the lgK ow of substituted anilines. 2D method （multiple linear regression, MLR） and 3D method （comparative molecular field analysis, CoMFA） were applied in this study. Successful 2D and 3D models yielded the correlation coefficient （R2） values of 0.981 and 0.966 and the Leave-One-Out （LOO） cross-validated correlation coefficient （q2） values of 0.933 and 0.820, respectively. The developed models have a highly predictive ability in both internal and external validation. In addition, the results were interpreted in terms of physical and chemical meanings of descriptors and field contribution maps. It showed that the steric and electrostatic properties are the primary factors that govern the lgK ow of substituted anilines. The information obtained from the QSPR models would be helpful to the interpretation of structural features pertinent to the lgK ow of substituted anilines, which may be helpful in estimating the organic compounds＇ potential harm to the environment.

Estimation of Partition Coefficients of Fe-S Protein Models： Se Substitutions in Fe4S4Cysn

The SCAP method allows a semiquantitative estimation of the partitioning of many solutes between numerous pairs of solvents. The organic solvent-water partition coefficients P are calculated. For FeaS4Cysn, the organic solvent-water partition coefficients for l-octanol Po, cyclohexane Pch and chloroform Pcf decay 4.46, 6.25 and 4.60 log units per Cys, respectively. The Po is of the same order of magnitude as CDHI （conformationally dependent hydrophobic index） calculations and Pch-cf as computations performed with a method by Leo and Hansch. The logPo-ch-cf mean relative errors are 17%, 25% and-17%, which represent mean and unsigned relative errors of -3% and 20%. On varying the number of Cys, the structures show hydrophobic moments indicative of amphipathic compounds. For Se substitutions in Fe4SeaCys,, Po-ch-cf drop 4.52, 6.30 and 4.66 exponents per Cys. With the reference calculations, Po-ch-cf decay 4.03, 4.80 and 5.76 exponents per Cys. For FeaS4 mSemCys4, the calculated similar partition coefficients and hydrophobic moments, and lower distance in dendrogram suggest a role of Fe-Se clusters in physiological processes. The analysis is extended to lysozyme and its secondary structures.

Enhanced flushing of polychlorinated biphenyls contaminated sands using surfactant foam: Effect of partition coefficient and sweep efficiency

Foam flushing is an in situ soil remediation technology based on the traditional surfactant flushing method. The contribution of mobility control to contaminant removal by foam is helpful for improving this technology. Foam flushing of polychlorinated biphenyl （PCB）- contaminated unconsolidated media was performed to evaluate the effect of the partition coefficient （PC） and sweep efficiency （SE） on PCB removal. Column flushing with surfactant solution and foam with different types and concentrations of surfactant was carried out for PCB removal. Two types of quartz sand were investigated to evaluate the Jamin effect on the SE value of the washing agent. The results demonstrate that a small PC value and large SE value are necessary to achieve high PCB removal for foam flushing. Compared with solution flushing, the introduction of foam can effectively control the mobility of the washing agent. Similar to solution flushing, solubilization is a key factor which dominates the removal of PCBs in foam flushing, In addition, the SE value and PCB removal by foam flushing is less affected by particle size. Therefore, foam flushing was proved to be more effective in porous media with low hydraulic conductivity and high porosity. An integrated flushing with water, surfactant solution and foam was performed and the results prove that this technology successfully combines the advantages of solution solubilization and mobility control by foam, and thus further increases the remediation efficiency of PCBs to 94.7% for coarse sand.

Displacement characteristics of CO_(2)flooding in extra-high water-cut reservoirs

Carbon dioxide(CO_(2))flooding is a widely applied recovery method during the tertiary recovery of oil and gas.A high water saturation condition in reservoirs could induce a‘water shielding’phenomenon after the injection of CO_(2).This would prevent contact between the injected gas and the residual oil,restricting the development of the miscible zone.A micro-visual experiment of dead-end models,used to observe the effect of a film of water on the miscibility process,indicates that CO_(2)can penetrate the water film and come into contact with the residual oil,although the mixing is significantly delayed.However,the dissolution loss of CO_(2)at high water-cut conditions is not negligible.The oil-water partition coefficient,defined as the ratio of CO_(2)solubility in an oil-brine/two-phase system,keeps constant for specific reservoir conditions and changes little with an injection gas.The NMR device shows that when CO_(2)flooding follows water flooding,the residual oil decreasesdnot only in medium and large pores but also in small and micro pores.At levels of higher water saturation,CO_(2)displacement is characterized initially by a low oil production rate and high water-cut.After the CO_(2)breakthrough,the water-cut decreases sharply and the oil production rate increases gradually.The response time of CO_(2)flooding at high watercut reservoirs is typically delayed and prolonged.These results were confirmed in a pilot test for CO_(2)flooding at the P1-1 well group of the Pucheng Oilfield.Observations from this pilot study also suggest that a larger injection gas pore volume available for CO_(2)injection is required to offset the dissolution loss in high water saturation conditions.

Copper partitioning between granitic silicate melt and coexisting aqueous fluid at 850°C and 100 MPa

Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 ℃, 100 MPa and oxygen fugacity （fO2） buffered at approaching Ni-NiO （NNO）. Partition coefficients of Cu （Dcu = Cfluid/Cmelt） were varied with different alumina/alkali mole ratios [Al2O3/（Na2O ＋ K2O）, abbreviated as Al/ Alk], Na/K mole ratios, and SiO2 mole contents. The DCu increased from 1.28 ± 0.01 to 22.18 ±0.22 with the increase of Al/Alk mole ratios （ranging from 0.64 to 1.20） and Na/K mole ratios （ranging from 0.58 to 2.56）. The experimental results also showed that Dcu was positively correlated with the HCl concentration of the starting fluid. The Dcu was independent of the SiO2 mole content in the range of SiO2 content considered. No Dcu value was less than 1 in our experiments at 850 ℃ and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatichydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than the melt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl^- fluid.

Solid-solution partitioning of arsenic(As) in the paddy soil profiles in Chengdu Plain,Southwest China

To predict the long-term behavior of arsenic （As） in soil profiles, the solid-solution partitioning of As was studied in four paddy soil profiles obtained from agricultural areas in Chengdu Plain, Southwest China. Paddy soil profile samples were collected and soil solution samples were extracted. Total As contents in soil solution and soil solid were analyzed, along with the soil solid phase properties. The As in soil solu- tion was significantly higher in the upper layer （0--20 cm） and had a definite tendency to decrease towards 40 cm regardless of the sampling locations. When the concentration of arsenic in soil solution decreased, its content in solid phase increased. Field-based partition coefficient （Kd） for As was determined by calculating the ratio of the amount of As in the soil solid phase to the As concentration in the soil solution. Kj values varied widely in vertical samples and correlated well with soil pH, total organic carbon （TOC） and total As. The results of this study would be useful for evaluating the accumulation trends of hrsenic in soil profiles and in improving the management of the agricultural soils.