Air-water Partition Coefficients Research Articles

Environmental impact of PFAS: Filling data gaps using theoretical quantum chemistry and QSPR modeling

Per- and polyfluorinated alkyl substances (PFAS), known for their widespread environmental presence and slow degradation, pose significant concerns. Of the approximately 10,000 known PFAS, only a few have undergone comprehensive testing, resulting in limited experimental data. In this study, we employed a combination of physics-based methods and data-driven models to address gaps in PFAS bioaccumulation potential. Using the COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) method, we predicted n-octanol/water partition coefficients (logKOW), crucial for PFAS bioaccumulation. Our developed Quantitative Structure-Property Relationship (QSPR) model exhibited high accuracy (R2 = 0.95, RMSEC = 0.75) and strong predictive ability (Q2LOO = 0.93, RMSECV = 0.83). Leveraging the extensive NORMAN, we predicted logKOW for over 4,000 compounds, identifying 244 outliers out of 4519. Further categorizing the database into eight Organisation for Economic Co-operation and Development (OECD) categories, we confirmed fluorine atoms role in enhanced bioaccumulation. Utilizing predicted logKOW, water solubility logSW, and vapor pressure logVP values, we calculated additional physicochemical properties that are responsible for the transport and dispersion of PFAS in the environment. Parameters such as Henry’s Law (kH), air–water partition coefficient (KAW), octanol–air coefficient (KOA), and soil adsorption coefficient (KOC) exhibited favorable correlations with literature data (R2 > 0.66). Our study successfully filled data gaps, contributing to the understanding of ubiquitous PFAS in the environment and estimating missing physicochemical data for these compounds.

Evaluation of Physicochemical Property Data in the ECHA Database

The database of the European Chemicals Agency (ECHA) is one of the most important databases that contains physicochemical properties, also because these data are used for the regulation of chemicals in the European Economic Area. The present study investigates the availability and quality of the data in the ECHA database for the logarithmic octanol–water partition coefficient (log10 KOW), solubility in water (SW), vapor pressure (pV), air–water partition coefficient, boiling point (Tb), second-order rate constant for the degradation with OH radicals, and the soil adsorption coefficient. For the evaluation of the data, calculations were run with COSMOtherm for the majority of the mono-constituent, neutral organic substances that are fully registered under the EU Regulation on the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH). The COSMOtherm data were evaluated against data from the PHYSPROP database, a manually curated database of experimental property data, to ensure that the COSMOtherm data were free of systematic errors. The comparison between COSMOtherm and the experimental data in the ECHA database showed that the data agree (within some variability) for many of the endpoints. However, there are also certain ranges with substantial discrepancies. These include log10 KOW > 8, SW < 10−3 mg/l, pV < 10−6 Pa, and Tb > 400 °C. The deviations between the non-experimental data and the COSMOtherm values are for all endpoints on average higher than the deviations between the experimental data and the COSMOtherm values. With this study, we provide COSMOtherm data for more than 4400 substances that can be used in the future for the hazard and risk assessment of these chemicals.

Effect of inoculum type, packing material and operational conditions on the biofiltration of a mixture of hydrophobic volatile organic compounds in air

The emission of volatile organic compounds (VOCs) into the atmosphere causes negative environmental and health effects. Biofiltration is known to be an efficient and cost-effective treatment technology for the removal of VOCs in waste gas streams. However, little is known on the removal of VOC mixtures and the effect of operational conditions, particularly for hydrophobic VOCs, and on the microbial populations governing the biofiltration process. In this study, we evaluated the effect of inoculum type (acclimated activated sludge (A-AS) versus Rhodococcus erythropolis) and packing material (mixture of compost and wood chips (C + WC) versus expanded perlite) on the removal of a mixture of hydrophobic VOCs (toluene, cyclohexane and hexane) in three biofilters (BFs), i.e., BF1: C + WC and R. erythropolis; BF2: C + WC and A-AS; and BF3: expanded perlite and R. erythropolis. The BFs were operated for 374 days at varying inlet loads (ILs) and empty bed residence times (EBRTs). The results showed that the VOCs were removed in the following order: toluene > cyclohexane > hexane, which corresponds to their air-water partitioning coefficient and thus bioavailability of each VOC. Toluene is the most hydrophilic VOC, while hexane is the most hydrophobic. BF2 outperformed BF1 and BF3 in each operational phase, with average maximum elimination capacities (ECmax) of 21 ± 3 g toluene m−3 h−1 (removal efficiency (RE): 100 %; EBRT: 82 s), 11 ± 2 g cyclohexane m−3 h−1 (RE: 86 ± 6 %; EBRT: 163 s) and 6.2 ± 0.9 g hexane m−3 h−1 (RE: 96 ± 4 %; EBRT: 245 s). Microbial analysis showed that despite having different inocula, the genera Rhodococcus, Mycobacterium and/or Pseudonocardia dominated in all BFs but at different relative abundances. This study provides new insights into the removal of difficult-to-degrade VOC mixtures with limited research to date on biofiltration.

Understanding the Environmental Distribution and Potential Health Risks of Pollutants from Deodorant Products: A Review

Deodorants are frequently used personal care products; however, questions have been raised concerning their possible toxicity to cause air and water pollution, and their potential impact on human health. The degree to which deodorant ingredients, such as fragrance chemicals, antibacterial compounds, aluminium compounds, and preservatives, are toxic depends on their chemical composition. Many of these chemicals have been connected to adverse health effects, such as skin rashes, allergic reactions, endocrine disruption, and respiratory problems. Understanding these chemicals’ toxicity is crucial for determining any potential risks to human health. Spray formulations have the potential to release volatile organic compounds into the air, such as propellants and fragrance chemicals, which can be harmful to human respiratory health and lead to indoor and outdoor air pollution. Improper disposal and wastewater treatment can lead to the contamination of water bodies, potentially impacting aquatic ecosystems and human water supplies. This review provides an overview of the toxicity of deodorant ingredients in various formulations, including sprays, roll-ons, and sticks. The partition coefficients Log Kaw (air-water partition coefficient), Log Koa (airorganic carbon partition coefficient), and Log Kow (octanol-water partition coefficient), values of deodorant ingredients were summarized for assessing their potential for long-range transport, persistence in the environment, and bioaccumulation in organisms.

Exploring the role of octanol-water partition coefficient and Henry’s law constant in predicting the lipid-water partition coefficients of organic chemicals

Partition coefficients for storage lipid-water (logKlw) and phospholipid-water (logKpw) phases are key parameters to understand the bioaccumulation and toxicity of organic contaminants. However, the published experimental databases of these properties are dwarfs and current estimation approaches are cumbersome. Here, we present partition models that exploit the correlations of logKlw, and of logKpw with the linear combinations of the octanol-water partition coefficient (logKow) and the dimensionless Henry’s law constant (air–water partition coefficient, logKaw). The calibrated partition models successfully describe the variations in logKlw data (n = 305, R2 = 0.971, root-mean-square-error (rmse) = 0.375), and in logKpw data (n = 131, R2 = 0.953, rmse = 0.413). With the inputs of logKow and logKaw estimated from the U.S. EPA’s EPI Suite, our models of logKlw and logKpw have exhibited rmse = 0.52 with respect to experimental values indicating suitability of these models for inclusion in the EPI Suite. Our models perform similar to or better than the previously reported models such as one parameter partition models, Abraham solvation models, and models based on quantum-chemical calculations. Taken together, our models are robust, easy-to-use, and provide insight into variations of logKlw and logKpw in terms of hydrophobicity and volatility trait of chemicals.

Sonolytic destruction of Per- and polyfluoroalkyl substances in groundwater, aqueous Film-Forming Foams, and investigation derived waste

Per- and polyfluoroalkyl substances (PFASs) are anthropogenic amphipathic heat-resistant materials found in some household products and Aqueous Film-Forming Foams (AFFFs) used to extinguish hydrocarbon fires. There is a critical need for developing destructive technologies for the treatment of PFAS-impacted waters because several PFASs are classified as probable carcinogens and endocrine disruptors. We tested the destruction of 7 individual PFASs, a mix of 24 native PFASs (24Mix), and samples of AFFF and concentrated Investigation Derived Waste (IDW) by high-frequency ultrasound (700 kHz – 1040 W) in deionized water, groundwater containing low total dissolved solids (TDS) (388 mg L−1), and high-TDS groundwater (10.2 g L−1). This study demonstrated the degradation of novel PFASs, hexafluoropropylene oxide dimer acid (HFPO-DA) and 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB), with near-stoichiometric fluoride release. The salts and surfactants affect the air-water partitioning coefficients of PFASs and their availability at the ultrasonic cavity, thereby affecting the degradation rates. The degradation rates of sulfonates and short-chain PFASs were 30% to 60% higher in low TDS groundwater than those in deionized water, while the rates were lower in high TDS groundwater. The degradation rates of sulfonates in AFFF were 40% to 60% higher as compared to the 24Mix. The treatment of concentrated, high-TDS IDW resulted in significant defluorination of 41 PFASs, consuming 3 kWh g−1 – 76 kWh g−1 whereas dilute AFFF degradation utilized 5900 kWh g−1. The results inform important parameters for designing and operating ultrasonic reactors for the degradation of PFASs and verify that sonolytic treatment of concentrated PFAS mixtures and AFFF IDWs can effectively degrade and defluorinate PFASs without the formation of disinfection by-products.

Exploring the Environmental Exposure to Methoxychlor, α-HCH and Endosulfan-sulfate Residues in Lake Naivasha (Kenya) Using a Multimedia Fate Modeling Approach.

Distribution of pesticide residues in the environment and their transport to surface water bodies is one of the most important environmental challenges. Fate of pesticides in the complex environments, especially in aquatic phases such as lakes and rivers, is governed by the main properties of the contaminants and the environmental properties. In this study, a multimedia mass modeling approach using the Quantitative Water Air Sediment Interaction (QWASI) model was applied to explore the fate of organochlorine pesticide residues of methoxychlor, α-HCH and endosulfan–sulfate in the lake Naivasha (Kenya). The required physicochemical data of the pesticides such as molar mass, vapor pressure, air–water partitioning coefficient (KAW), solubility, and the Henry’s law constant were provided as the inputs of the model. The environment data also were collected using field measurements and taken from the literature. The sensitivity analysis of the model was applied using One At a Time (OAT) approach and calibrated using measured pesticide residues by passive sampling method. Finally, the calibrated model was used to estimate the fate and distribution of the pesticide residues in different media of the lake. The result of sensitivity analysis showed that the five most sensitive parameters were KOC, logKow, half-life of the pollutants in water, half-life of the pollutants in sediment, and KAW. The variations of outputs for the three studied pesticide residues against inputs were noticeably different. For example, the range of changes in the concentration of α-HCH residue was between 96% to 102%, while for methoxychlor and endosulfan-sulfate it was between 65% to 125%. The results of calibration demonstrated that the model was calibrated reasonably with the R2 of 0.65 and RMSE of 16.4. It was found that methoxychlor had a mass fraction of almost 70% in water column and almost 30% of mass fraction in the sediment. In contrast, endosulfan–sulfate had highest most fraction in the water column (>99%) and just a negligible percentage in the sediment compartment. α-HCH also had the same situation like endosulfan–sulfate (e.g., 99% and 1% in water and sediment, respectively). Finally, it was concluded that the application of QWASI in combination with passive sampling technique allowed an insight to the fate process of the studied OCPs and helped actual concentration predictions. Therefore, the results of this study can also be used to perform risk assessment and investigate the environmental exposure of pesticide residues.

Air-Water Partitioning of Biomass-Burning Phenols and the Effects of Temperature and Salinity.

Biomass burning (BB) emits organic gases that, with chemical aging, can form secondary organic aerosol (SOA) in both the gas and aqueous phases. One class of biomass-burning emissions, phenols, are of interest because they react rapidly in the aqueous phase to efficiently form SOA, which might affect climate and human health. However, while measurements exist for the air-water partitioning constants of some simple phenols, Henry's law constants (KH) are unknown for more complex BB phenols. In this work, we use a custom-built apparatus to measure KH for a suite of biomass-burning phenols that span a wide range of air-water partitioning coefficients. Comparing our measurements to predicted values from EPI Suite shows that this model consistently overestimates KH unless a suitable measured phenol KH value is included to adjust the calculations. In addition, we determine the effect of five salts on phenol partitioning by measuring the Setschenow coefficients (KS). Across the eight phenols we examined, values of KS depend primarily on salt identity and descend in the order (NH4)2SO4 > NaCl > NH4Cl ≥ KNO3 > NH4NO3. Lastly, we use our KH and KS results to discuss the aqueous processing of biomass-burning phenols in cloud/fog water versus aerosol liquid water.

Density Functional Theory Calculation of Molecular Descriptors for Simple Coumarins in Gas and Different Solvents

The primary aim of this study is to show the importance of molecular structure analysis of pharmaceutical active coumarins compounds using quantum chemistry methods based on density functional theory. To explore the theoretical calculations for global descriptors, the standard Gaussian 09W program was used for coumarins compounds. The full geometry optimization was carried out by the B3LYP/6-311G level of theory. The octanol-water and air-water partition coefficients were also estimated using functional density theory. The order of the HOMO-LUMO energy gap for studied coumarins in the gas phase is umbelliferone (UBA) < (herniarin) HNR ~ (crenulatin) CNT < (scopoletin) SCT < (scoparone) SCO < (isoscopoletin) IST < (4-methylesculetin) MST < (umbelliferone-2- carboxylic acid) UCA < (isofraxidin) IFD < (fraxetin) FXT < (aesculetine) ACT < (dapnetine) DPT. Therefore, UBA molecule in gas phase is less stable. Compared to the measured index of electrophilicity (DE). The MST molecule is stronger, more reactive, nucleophile electrophile at the gas phase and in solvents. In all solvent phases, CNT and UCA molecules have lower values, which mean they are strong nucleophiles. From the log P values of ACT and MST coumarins are in between 1.35-1.8, so ACT and MST coumarins use oral and intestinal absorptions.

Air–Water Partitioning of C5 and C6 Alkanones: Measurement, Critical Compilation, Correlation, and Recommended Data

Air–water partitioning of all nine C5 and C6 isomeric alkanones (namely, pentan-2-one, pentan-3-one, 3-methylbutan-2-one, hexan-2-one, hexan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 2-methylpentan-3-one, and 3,3-dimethylbutan-2-one) in water was examined at several temperatures in the range from (273 to 333) K using the inert gas stripping technique. Results are reported in the form of air–water partition coefficients Kaw and limiting (infinite dilution) activity coefficients γ1∞. A comprehensive critical review is further presented for such literature data as well as data on respective derivative thermal properties (enthalpies and heat capacities of hydration and dissolution). For each alkanone, the data measured in this work together with those reported previously in the literature were correlated with a suitable model equation providing an adequate simultaneous description of the equilibrium measurements and the calorimetric information. As a result, recommended Kaw(T) and γ1∞(T) temperature ...

A new method for the determination of Henry's law constants (air-water-partition coefficients)

We set out a method for the determination of Henry's Law constants or air-water-partition coefficients at 298.15 K that does not require a knowledge of either the vapor pressure or the aqueous solubility of a compound, but is derived from experimental solubilities in non-aqueous solvents, or from experimental water-solvent partition coefficients. The method is applicable to a wide range of compound, from volatile organic compounds to very hydrophobic compounds with low vapor pressures and low aqueous solubilities. Using equations that we have developed previously, our obtained air-water partition coefficients at 298.15 K can be corrected to any temperature between 273 K and 573 K.

Descriptors for terpene esters from chromatographic and partition measurements: Estimation of human odor detection thresholds

We have used gas chromatographic retention data together with other data to obtain Abraham descriptors for 30 terpene esters. These include the air-water partition coefficient, as log Kw, for which no experimental values are available for any terpene ester. The other descriptors are the ester dipolarity, S, the hydrogen bond basicity, B, (the ester hydrogen bond acidity is zero for the esters studied), and L the logarithm of the air-hexadecane partition coefficient. Both S and B are larger than those for simple aliphatic esters, as expected from the terpene ester structures that include ring systems and ethylenic double bonds. These descriptors can then be used to obtain a large number of physicochemical and environmental properties of terpene esters. We have analyzed experimental results on human odor detection thresholds and have constructed another equation for the calculation of these thresholds, to go with a previous equation that we have reported. Then the descriptors for terpene esters can be used to estimate the important odor detection thresholds.

Effect of Ethanol and Temperature on Partition Coefficients of Ethyl Acetate, Isoamyl Acetate, and Isoamyl Alcohol: Instrumental and Predictive Investigation

For alcoholic beverages such as beer, downstream processing for either dealcoholization or off-flavor removal requires both quantitative data and suitable predictive methods. Along with experimental investigations, we use a method initially developed for studying the solubility of gases in two or more miscible liquid solvents to monitor the effect of ethanol on air–water partition coefficients of three major flavors found in beer, namely, isoamyl alcohol, ethyl acetate, and isoamyl acetate. In the ethanol concentration range between 0 and 0.1 mole fraction, a slight, rather linear increase in the Henry’s solubility coefficient was observed. This overall behavior can be captured well using Henry coefficients for aqueous binary and ternary systems together with the Wohl expansion for excess Gibbs free energy coupled with the one-parameter Margules equation. Based on the developed model, the Wohl’s expansion parameter for ethanol–water is introduced as the solvent–solvent interaction parameter. The van ’t Hoff parameters for temperature dependence of Henry coefficients for binary water–flavor solutions are determined in the range of 30 to 60 °C.

Influence of deep water formation by open-sea convection on the transport of low hydrophobicity organic pollutants in the NW Mediterranean Sea

The significance of the offshore vertical convection currents in the transport and sinking of water-soluble organic pollutants into marine deep basins has been evaluated. For this purpose, sediment cores were collected in the Gulf of Lion (GoL) at sites between 26 and 2330 m water depth. The top core layers were analyzed for aromatic and aliphatic hydrocarbons and organochlorine compounds. Organic compounds with logKAW (air water partition coefficient) between −2 and −4, e.g. lindane, PCB 28, PCB 52, phenanthrene, methylphenanthrenes, dimethylphenanthrenes, C14–C23n-alkanes, are found in higher concentrations or exhibit relative concentration increases in the sediments deposited in the continental rise as consequence of the open-sea convection processes associated with the formation of Western Mediterranean Deep Water (WMDW). In contrast, the organic pollutants with intermediate air-water distribution coefficients, logKAW between −2 and 0, and high octanol water distribution coefficients (logKow > 6), e.g. highly chlorinated PCBs, DDTs, DDEs, DDDs, C25–C35n-alkanes, and polycyclic aromatic hydrocarbons with molecular weight higher than 200, occur in association to sediment particles, which are mainly transported by the Northern current along the continental shelf forming the mud belt. The Rhône prodelta is therefore the area of the GoL showing the highest concentrations of this group of organic compounds, which are preferentially associated with water particles. Overall, the results show that vertical open-sea convection processes related with offshore formation of WMDW may have an important role in the transport and accumulation of water soluble pollutants to deep marine environments of the GoL (>2000 m water depth).

Thermodynamic properties of five biofuel-relevant compounds at infinite dilution in water

In this work, thermodynamic behavior of five biomass-derived compounds, namely furfural, 2-methylfuran, 2,5-dimethylfuran, methyl vinyl ketone, and allyl alcohol, in highly dilute aqueous solutions has been experimentally investigated. Using the inert gas stripping technique, their air-water partition coefficients (Kaw) and limiting activity coefficients γ1∞ were measured at several temperatures in the range from (273 to 333) K. Except for the furans, infinite dilution partial molar excess enthalpies and volumes were further determined as functions of temperature from (288 to 318) K by tandem flow mixing calorimetry and vibrating-tube densimetry, which in turn allowed reliable derivation of respective heat capacities and expansivities. In addition, densities of all five pure liquids and viscosities of furfural and allyl alcohol were also measured in the range from (288 to 318) K. For each compound, the vapor-liquid equilibrium and (when measured) calorimetric data of this work together with some relevant data reported previously in the literature were simultaneously correlated by a three-parameter model equation providing adequate simultaneous description of all information involved. As a result, recommended thermodynamically consistent temperature dependences of Kaw and γ1∞ of superior accuracy were thus established in the range from the melting point to the normal boiling point of water. The variation of Kaw and γ1∞ with temperature and solute molecular structure along with related energetic functions of dissolution and hydration of the examined compounds were overviewed and briefly discussed.

Evaluation of Long‐Range Transport Potential of Selected Brominated Flame Retardants with Measured 1‐Octanol–Air Partition Coefficients

Various alternative flame retardants are used in many countries since polybrominated diphenyl ethers (PBDEs) were classified as persistent organic pollutants (POPs). However, difficulties in the evaluation of the long‐range transport potential (LRTP) of the alternatives are related to the lack of information on their physicochemical properties, which govern their environmental fates and transport. Based on the simulation of LRTP using OECD POV and LRTP Screening Tool, five alternative brominated flame retardants (BFRs) (hexabromobenzene [HBB], 2,3,4,5,6‐pentabromotoluene [PBT], 2,3,4,5,6‐pentabromoethylbenzene [PBEB], 2‐ethylhexyl 2,3,4,5‐tetrabromobenzoate [TBB], and 1,2,4,5‐tetrabromo‐3,6‐dimethylbenzene [TBX]), and 3 PBDEs (BDE‐28, BDE‐47, and BDE‐99) were chosen to perform a refined assessment. This was done using an experimentally measured 1‐octanol–air partition coefficient (KOA) for the calculation of the air–water partition coefficient (KAW) required for the model. The four selected alternative BFRs (HBB, PBT, PBEB, TBX) have KOA values close to the in silico estimation used in the screening evaluation. On the other hand, the measured KOA value for TBB was two orders of magnitude lower than the estimated value used in the screening simulation. The refined simulation showed that characteristic travel distance (CTD) and transfer efficiency (TE) for HBB, PBT, PBEB, and TBX were greater than those for BDE‐28, whereas CTD and TE for TBB were lower than those for BDE‐28. This suggested that TBB has a lower LRTP than BDE‐28, considering the refined partition coefficients.

Aqueous solubility, vapor pressure and octanol-water partition coefficient of two phthalate isomers dibutyl phthalate and di-isobutyl phthalate contaminants of recycled food packages

In this work, we studied the aqueous solubility, vapor pressures of dibutylphthalate (DBP) and di-isobutylphthalate (DIBP) as a function of temperature between 298.15 and 328.15 K and between 313.15 and 423.15 K respectively. The octanol-water partition coefficient was measured at 298.15 K using shake-flask method. For aqueous solubility, measurements were carried out using the dynamic saturation method and values ranges in 10−7 mol fraction with a relative higher solubility for DIBP regarding DBP. Solubility results are in good agreement with the octanol-water partition coefficient measurement showing that DBP is more hydrophobic than its isomer DIBP. For vapor pressure, after an interlaboratory validation step using static method performed with DBP in a temperature range between 381 and 421 K, measurements for both compounds DBP and DIBP using the gas saturation method presented a standard relative deviation lower than 2% and values ranged from 10−2 and 102 Pa. By combining vapor pressure and solubility results, we calculated Henry's law constant and air-water partition coefficient and showed an important deviation between the two isomers even at low temperature.

Air–water partition coefficients for a suite of polycyclic aromatic and other C10 through C20 unsaturated hydrocarbons

ABSTRACTThe air–water partition coefficients (Kaw) for 86 large polycyclic aromatic hydrocarbons and their unsaturated relatives were estimated using high-level G4(MP2) gas and aqueous phase calculations with the SMD, IEFPCM-UFF, and CPCM solvation models. An extensive method validation effort was undertaken which involved confirming that, via comparisons to experimental enthalpies of formation, gas-phase energies at the G4(MP2) level for the compounds of interest were at or near thermochemical accuracy. Investigations of the three solvation models using a range of neutral and ionic compounds suggested that while no clear preferential solvation model could be chosen in advance for accurate Kaw estimates of the target compounds, the employment of increasingly higher levels of theory would result in lower Kaw errors. Subsequent calculations on the polycyclic aromatic and unsaturated hydrocarbons at the G4(MP2) level revealed excellent agreement for the IEFPCM-UFF and CPCM models against limited available experimental data. The IEFPCM-UFF-G4(MP2) and CPCM-G4(MP2) solvation energy calculation approaches are anticipated to give Kaw estimates within typical experimental ranges, each having general Kaw errors of less than 0.5 log10 units. When applied to other large organic compounds, the method should allow development of a broad and reliable Kaw database for multimedia environmental modeling efforts on various contaminants.

Effect of additives on volatility of aroma compounds from dilute aqueous solutions

Volatility of fragrance and flavor substances from food and cosmetic products or intermediates is influenced by admixtures of various nonvolatile substances which occur in these basically aqueous matrices naturally or are added on purpose. For control of the production process and formulation of a final product, it is important to know how such admixtures affect the air–water partitioning of aroma substances. In this work, using an effective headspace gas chromatography method, we studied the effect of salts (NaCl, NaHCO3), saccharides (glucose, sucrose), macrocyclic polysaccharides (α-cyclodextrin, β-cyclodextrin), polyalcohols (ethylene glycol, glycerol) and protein denaturants (urea, guanidine hydrochloride) on the air–water partition coefficient of two isomeric esters ethyl butanoate and butyl ethanoate as typical representatives of aroma substances. The strongest effect was observed for cyclodextrins (aroma retention by inclusion complexation) and for inorganic salts (aroma release by salting-out). For other additives, a weaker salting-in (denaturants, ethylene glycol) or salting-out (saccharides, glycerol) was found. The dependence of these effects on the additive concentration was in all cases well correlated by Setschenow equation and for cyclodextrins also by the 1:1 complex formation model. Determination of the temperature dependence of these effects gave a useful insight into the thermodynamics of the ester–cyclodextrin inclusion binding. Considerations of guest–host size matching supported by simple molecular modeling proved useful to rationalize different binding affinities observed for individual ester–cyclodextrin pairs and suggest their possible binding modes.

Measurement of activity coefficient at infinite dilution for some bio-oil components in water and mass transfer study of bubbles in the dilutor

Activity coefficients at infinite dilution (γ∞) values are of great importance when designing separation processes like distillation, liquid–liquid extraction and gas stripping. In this study the γ∞ values were determined for four compounds in water that are present in bio-oil. Henry’s law constants (H12), Partial molar excess enthalpies at infinite dilution (H¯iE,∞) and air–water partition coefficients (Kaw) are also reported. The measurements were performed using inert gas stripping equipment (dilutor) in the 298–340K temperature range. Mass transfer study was also performed to investigate the equilibrium between the solution and the gas leaving the cell.