Nonpolar Substances Research Articles

Development of an universal group contribution equation of state: I. Prediction of liquid densities for pure compounds with a volume translated Peng–Robinson equation of state

With a view to the development of an universal group contribution equation of state, the Peng–Robinson (PR) equation of state (EOS) has been modified to obtain a better description of saturated liquid densities for the pure compounds. A simple improved volume translation together with a temperature dependent volume correction deliver an accurate representation of this property near and far from the critical point for polar and non-polar substances. The fitted parameters have been generalized as a function of the critical compressibility factor. The results are compared with the results of the original PR and the Soave–Redlich–Kwong (SRK) EOS.

A new quartic equation of state

A new quartic equation of state (EOS) is presented, which consists of the repulsive term of CCOR EOS and the attractive term of PT EOS, coupled with new parameters, the general forms of which are given for non-polar substances. The new EOS can be solved algebraically like a cubic EOS. Calculated vapor pressures, specific volumes and evaporation enthalpies are compared with experimental data and with that calculated by CCOR EOS and PT EOS for a variety of fluids. In low temperature region, the new quartic EOS produces more reliable results than commonly-used cubic EOS. One important character of the new EOS is that it is capable of calculating specific volume of solid and sublimation pressure. The vapor–liquid equilibria (VLE), including volume properties, of binary mixtures are also well presented by the new EOS with van der Waals one-fluids mixing rules containing one adjustable parameter.

Polar and non-polar aromatic micropollutants in water (drinking-water) resources

Aromatic compounds are important contaminants that limit the intended uses of water resources. Both polar and non-polar substances, such as phenols, aromatic sulfonates, lignin-sulfonic acids, humic and fulvic substances (acids) and mono- and poly-aromatic hydrocarbons, their alkyl-substituted derivatives, respectively, are among the potential aromatic micropollutants. During the last 5 - 10 years, an analytical approach has been developed on the basis of total fluorescence measurement of the original water sample and its organic solvent (cyclohexane) extract. It has been demonstrated and verified that polar aromatic compounds fluoresce only in the original water sample, whereas non-polar (hydrophobic) compounds fluoresce in an organic solvent (e.g. cyclohexane) extract. During extraction, polar compounds remain in the water sample. This method has been used in a country-wide survey in drinking water aquifers, as well as in several environmental impact assessment studies, particularly for petroleum-related pollution. It is a very convenient method to determine the naturally occurring humic and fulvic substances in water and has proved to be an appropriate substitute of the infrared spectrophotometric method for oil pollution assessment in the environment, also having the advantage of signalling more harmful, toxic aromatic petroleum hydrocarbons.

Hydrophilic interaction chromatography using amino and silica columns for the determination of polar pharmaceuticals and impurities

Hydrophilic interaction chromatography (HILIC) is described as a useful alternative to reversed-phase chromatography for applications involving polar compounds. In the HILIC mode, an aqueous–organic mobile phase is used with a polar stationary phase to provide normal-phase retention behavior. Silica and amino columns with aqueous–acetonitrile mobile phases offer potential for use in the HILIC mode. An examination of the retention and separation of several pyrimidines, purines, and amides on silica and amino columns from three manufacturers revealed that mobile phases should contain a buffer or acid for pH control to achieve similar and reproducible results among columns from different sources. Amino columns may also be used in an anion-exchange mode, which provides an advantage for some applications. In some cases, silica can provide different selectivity and better separation than an amino column. Example applications include: low-molecular-mass organic acids and amides as impurities in non-polar drug substances, 5-fluorouracil in 5-fluorocytosine, guanine in acyclovir, and different selectivity for polar basic compounds compared to an ion-pairing system.

An Equation for Prediction and/or Correlation of Second Virial Coefficients

We present a simple expression that satisfies known limits for correlating and/or predicting the second virial coefficient. For prediction, we utilize a generalized function that can provide the second virial coefficient of nonpolar and polar substances, as well as for molecules with association and quantum effects. The expression does not require additional terms to encompass these effects.

Thermodynamics of the Hydrophobic Effect

A thermodynamic theory is developed describing the transfer process of nonpolar substances from water to their pure state and the micellization process. The basis of the theory is the consideration, experimentally supported, that to a first-order approximation the change in the standard molar entropy (ΔS°) can be consider proportional to the standard molar heat capacity (ΔCpo) with proportionality constant, r, independent of the temperature and the pressure. In general it is found that the value of the magnitude of r decreases with the size of the solute molecule until a limiting value. This level of approximation is sufficient to predict observations such as linear plots between TΔS° and ΔH°, reduced behavior for surfactants with the temperature, and an important part of accepted phenomenology in the literature about the hydrophobic effect.

Crystalline Molecular Complexes Generated between Surfactants and Various Additive Compounds: An Attempt to Modify Sparingly Water Soluble Drugs to Easily Water Soluble Drugs.

It has been established that ionic surfactants, whether cationic or anionic, provide crystalline molecular complexes stably with various aromatic compounds as additives. Among various additives phenolic compounds are especially favorable for both surfactant species. Other than these additives, cationic surfactants easily provide crystalline molecular complexes with basic materials and even with non-polar substances such as biphenyl and phenanthrene. The isolated surfactant molecular complexes were analyzed by X-ray. To date the number of the obtained surfactant molecular complexes exceeds two hundred species or more and thirty or more of them were structurally analyzed. These surfactant molecular complexes were shown to be novel surfactant species different from their mother species, supplied with enhanced solubility to the complex additives. We applied these characteristics to sparingly water soluble drugs as the complex additive to modify them into easily water soluble drugs. The obtained complex drugs revealed an improved behavior in solubility and dissolution rate compared with pure drugs.

Hydrophilicity of Polar and Apolar Domains of Amphiphiles

The hydrophilicity of polar and apolar domains of various amphiphiles was systematically estimated for their homologues and analogues by measuring the molar adiabatic compressibility of an aqueous solution at infinite dilution. The homologues of protic alkyl H(CH2)n–, perfluoroalkyl F(CF2)n–, and alkylphenyl H(CH2)n(C6H5)– groups (n=0–10) were chosen to represent apolar hydrophobic domains. The polar hydrophilic domains tested were –SO4Na, –SO3Na, –COONH4, –N(CH3)3Br, N(CmH2m+1)4Br (m=1–5), and –NH(CH2)nSO3 (n=3, 4) groups. Also tested were the tetraphenyl ionic compounds (C6H5)4MX (M=B/X=Na, M=P/X=Cl, M=As/X=Cl) to study the effect of the ionic sign of the core atom across the tetraphenyl apolar shell, the polyethylene glycols H(OCH2CH2)mOH (m=1–4) to study the role of apolar –CH2– units in the hydrophilic oxyethylene group, and the zwitterionic dimethylaminoalkylsulfonate (CH3)2NH(CH2)nSO3 homologues to study the effect of intramolecular salt formation on the hydrophilicity of the zwitterion. The adiabatic compressibility of the solution was calculated from measurement of the sound velocity and density of solutions. The introduction of laboratory automation and the numerical control of the system improved the accuracies and efficiencies of the measurements a great deal. The range of the temperature scan was 0–40°C with an effective accuracy of ±0.001°C and the concentration was automatically scanned down to far below the cmc of the surfactant. The hydrophilicity of various polar and apolar substances was estimated as the decrease of molar adiabatic compressibility of the aqueous solution with increased concentration of their homologues and analogues. The hydrophobic hydration of nonpolar substances was found to be very small at room temperature and was barely detected above 40°C; however, it became large as the temperature was lowered and attained a maximum at 0°C. The cationic charge of quaternary ammonium N+(CnH2n+1)4 was found to enhance the hydrophobic hydration of methylene groups located at a distance of 4 to 6 Å from the core nitrogen atom, while the terminal negative charge of the anionic surfactant R–SO4−, R–SO3−, or R–COO− was found to decrease the hydrophobic hydration of –CH2– units within the same range. The hydrophilicity of quaternary ammonium and the tetraphenyl ions should be synergistically given by both hydrophobic and ionic hydrations. The hydrophilicity of the perfluoromethylene unit –CF2– was found to have a value comparable to that of the protic methylene unit –CH2–. The hydrophobic hydration seems to offer a good measure of the hydrophilicity of apolar substances; however, it does not necessarily represent the “hydrophobicity” of the apolar segment when the “surface activity” of the amphiphile is concerned.

Calculation of surface properties of pure fluids using density gradient theory and SAFT-EOS

The Cahn–Hilliard theory was combined with three equations of state (EOS) (the Peng–Robinson (PR), the Sanchez–Lacombe (SL) lattice fluid model, and the original Statistical Associating Fluid Model) in order to describe both the phase behaviour and the surface properties of different types of molecules, namely nonpolar substances ( n-alkanes and aromatic compounds), alcohols and water. Experimental surface tensions for nonpolar compounds could be correlated accurately and comparably by all EOS, adjusting one temperature-independent influence parameter. Despite the limitation in the critical region, the Statistical Association Fluid Theory (SAFT)-EOS successfully predicts the saturated liquid density and the degree of hydrogen bonding for methanol. The implementation of the SAFT-EOS into the Cahn–Hilliard framework leads to a useful possibility to calculate surface tensions which are in satisfactory agreement with experimental data, if the temperature-independent influence parameter was fitted to experimental surface tensions. The non-ideal behaviour of water is reflected in its phase behaviour and also in its surface tension. Some noticeable improvements of the association model 4C (four association sites) over the model 3B (three association sites) are found for the calculation of liquid–vapour equilibrium, the monomer concentration and the surface tension of water. Unfortunately, the SAFT-approach for associating compounds did not generally result in accurate calculations, especially near the critical region. Under comparable conditions the SAFT-EOS gives better surface tensions of water at low temperatures than the Associated-Perturbed-Anisotropic-Chain Theory (APACT)-EOS. At high temperatures, the opposite behaviour was observed.

HYDROPHOBIC EFFECT: SOLUBILITY OF NON-POLAR SUBSTANCES IN WATER, PROTEIN DENATURATION AND MICELLE FORMATION

The 'hydrophobic effect' of the dissolution process of non-polar substances in water has been analysed under the light of a statistical thermodynamic molecular model. The model, based on the distinction between non-reacting and reacting systems explains the changes of the thermodynamic functions with temperature in aqueous systems. In the dissolution of non-polar substances in water, it follows from the model that the enthalpy change can be expressed as a linear function of the temperature (ΔH app =ΔH o +n w C p,w T ). Experimental solubility and calorimetric data of a large number of non-polar substances nicely agree with the expected function. The specific contribution of n w solvent molecules depends on the size of solute and is related to destructuring (n w >0) of water molecules around the solute. Then the study of 'hydrophobic effect' has been extended to the protein denaturation and micelle formation. Denaturation enthalpy either obtained by van't Hoff equation or by calorimetric determinations again depends linearly upon denaturation temperature, with denaturation enthalpy, ΔH den , increasing with T . A portion of reaction enthalpy is absorbed by a number n w of water molecules (n w >0) relaxed in space around the denatured moieties. In micellization, an opposite process takes place with negative number of restructured water molecules (n w <0) because the hydrophobic moieties of the molecules joined by hydrophobic affinity occupy a smaller cavity.

Coupling of capillary electrochromatography to coordination ion spray mass spectrometry, a novel detection method.

Miniaturized separation techniques such as capillary electrochromatography (CEC), pressurized capillary electrochromatography (pCEC) and capillary high performance liquid chromatography (CHPLC) have been coupled to a new detection technique: coordination ion spray mass spectrometry (CIS-MS). Electrospray ionization (ESI) has found widespread applications in mass spectrometry (MS) for the analysis of polar compounds such as peptides or nucleotides. However, for weakly polar or nonpolar substances, ESI-MS yields poor sensitivity since, in the absence of basic or acidic groups, protonation or deprotonation is not possible. CIS is a universal ionization technique capable of detecting these compounds. Through the addition of a central complexing ion, charged coordination compounds are formed, enabling the detection with good sensitivity. Using the coaxial sheath flow interface commonly employed in CE-MS coupling, we were able to separate and detect various important natural compounds such as unsaturated fatty acid methyl esters, vitamins D2 and D3, and four different estrogens. A central ion solution of 100 microg/mL AgNO3 in water was used as sheath flow liquid, resulting in the formation of positively charged coordination compounds.

Functionalized coating materials based on inorganic-organic polymers

ORMOCER®s (ORMOCER® Trademark of Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.) as inorganic-organic polymers synthesized by a two-step sol-gel processing method can be applied as thin transparent coatings on various substrates (polymers, metals, ceramics). The curing of ORMOCER®s is performed thermally (at temperatures below 200°C) or by UV-radiation. Their high abrasion resistance and good chemical stability led to several actual industrial applications. Beside mechanical protection functions (e.g. for sensitive polymer substrates) additional functionalities of ORMOCER® surfaces are investigated to find new application areas. This paper presents two additional surface functions of abrasion resistant ORMOCER® coatings: Antiadhesive and antistatic properties. Incorporation of perfluorinated alkoxysilane compounds via sol-gel processing decreases the surface energy of the cured layer. Water as well as non-polar substances lose their adhesion to the surface, wetting is reduced, solutions are drained off and particles can be removed easily.By addition of polar and/or ionic compounds bearing hydrolyzable alkoxysilyl groups a scratch resistant antistatic coating for polycarbonate was developed. Compared to the uncoated substrate, the specific surface resistance was decreased from 1015 to 108 Ω. Electrostatic charging is decreased and attraction of particles inhibited or reduced. The coatings are abrasion resistant and show very good adhesion even in a wet climate.

Interactions of dissolved organic matter with xenobiotic compounds: Molecular modeling in water

AbstractAn hypothesis for the structure of dissolved organic matter (DOM) in water is proposed. It is based on previously published humic acid and soil organic matter (SOM) models. Personal computer (PC)‐based molecular modeling and geometry optimization of DOM and humic/xenobiotic complexes in vacuo and water were performed using modern PC software in order to determine low energy conformations and to simulate site‐specific processes such as trapping and binding of biological and anthropogenic substances. Nanochemistry (10−9 m level) allows the evaluation of atomic and molecular space requirements, voids, inter‐ and intramolecular hydrogen bonds, and interactions with water, metal cations, and xenobiotics. The described modeling approach in general allows hydrophilic and hydrophobic reactions to be examined. Structural, molecular, and environmental properties of DOM and its xenobiotic complexes were determined by quantitative structure‐activity relationship software. Focal points were molecular properties, such as solvent accessibility as well as van der Waals surface areas and volumes, partial charges, hydration energy (peptides), hydrophobicity (log P), refractivity, and polarizabilities of humic/xenobiotic complexes were determined. Molecular mechanics calculations show that nonbonded forces (e.g., van der Waals) and hydrogen bonds were the main reasons for temporary immobility of xenobiotic substances retained in DOM. Preliminary experiments to simulate the acidity of water molecules by protonation‐enhanced reactions with polar xenobiotics (e.g., hydroxyatrazine) but left nonpolar substances (e.g., DDT) unchanged.

Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection

In this paper the application of on-line HPLC–UV–APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of β-carotene is reported. All HPLC separations were carried out under RP conditions on self-synthesized polymeric C30 phases. The analysis of a carotenoid mixture containing astaxanthin, canthaxanthin, zeaxanthin, echinenone and β-carotene by HPLC–APCI-MS was achieved by scanning the mass range from m/z 200 to 700. For the characterization of a sample containing cis/trans isomers of β-carotene as well as their oxidation products, a photodiode-array UV–visible absorbance detector was used in addition between the column and the mass spectrometer for structural elucidation of the geometrical isomers. The detection limit for β-carotene in positive-ion APCI–MS was determined to be 1 pmol. In addition, an extract of non-polar substances in vegetable juice has been analyzed by HPLC–APCI-MS. The included carotenoids could be identified by their masses and their retention times.

In Vitro Investigation of the Synthetic Sebum Adsorbing Efficacy of Acrylate Copolymer as an Excipient And In Clinac ™ Oc

Abstract While sebum provides several functions in the integument, there is considerable interest in the control of excess sebum on the human skin. The primary function of sebum is to lubricate and waterproof the stratum cornenum layer, in addition to preventing hair from becoming brittle. In several cases, the secretion of sebum is inhibited as a result of blockage of the drainage pathway for the sebaceous glands which may result in abnormal skin conduction (1,2). Clinac™ OC (Oil Control) has been developed with a special oil adsorbing polymer, DVB/lsobornyl Methacrylate/Lautyl Methacrylate Copolymer (3). This particular copolymer posses the capacity to adsorb oils because of its high affinity for hydrophobic nonpolar substances. The purpose of this investigation is to show the adsorptive capacity of the acrylate copolymer in Clinac™ OC preparation and in buffer. The acrylate polymer was incubated in artificial sebum for 4 hrs and 8 hrs at 37 C.

Separation and Identification of Tocotrienol Isomers by HPLC−MS and HPLC−NMR Coupling

A crude palm-oil extract rich in vitamin E homologues was investigated by HPLC-MS and HPLC-NMR coupling. For mass spectrometry a newly introduced ionization technique called Coordination Ion Spray (CIS) was used. Through the addition of silver ions to the HPLC eluent, the ionization process of nonpolar substances is facilitated. Chromatography and all coupling experiments were conducted on a C(30) column which exhibited an extraordinary shape selectivity and overwhelming sample-loading capability. Experiments were performed with pure methanol as an eluent which proved to be ideal for NMR spectroscopy as well as mass spectrometry. All necessary information for unambiguous structural assignment was collected within 45 min of the LC-NMR experiment and 15 min of the LC-MS experiment. Six compounds were identified, i.e., α-, β-, γ-, and δ-tocotrienol, α-tocoenol, and α-tocopherol.

INTERACTIONS OF DISSOLVED ORGANIC MATTER WITH XENOBIOTIC COMPOUNDS: MOLECULAR MODELING IN WATER

An hypothesis for the structure of dissolved organic matter (DOM) in water is proposed. It is based on previously published humic acid and soil organic matter (SOM) models. Personal computer (PC)-based molecular modeling and geometry optimization of DOM and humic/xenobiotic complexes in vacuo and water were performed using modern PC software in order to determine low energy conformations and to simulate site-specific processes such as trapping and binding of biological and anthropogenic substances. Nanochemistry (10−9 m level) allows the evaluation of atomic and molecular space requirements, voids, inter- and intramolecular hydrogen bonds, and interactions with water, metal cations, and xenobiotics. The described modeling approach in general allows hydrophilic and hydrophobic reactions to be examined. Structural, molecular, and environmental properties of DOM and its xenobiotic complexes were determined by quantitative structure-activity relationship software. Focal points were molecular properties, such as solvent accessibility as well as van der Waals surface areas and volumes, partial charges, hydration energy (peptides), hydrophobicity (log P), refractivity, and polarizabilities of humic/xenobiotic complexes were determined. Molecular mechanics calculations show that nonbonded forces (e.g., van der Waals) and hydrogen bonds were the main reasons for temporary immobility of xenobiotic substances retained in DOM. Preliminary experiments to simulate the acidity of water molecules by protonation-enhanced reactions with polar xenobiotics (e.g., hydroxyatrazine) but left nonpolar substances (e.g., DDT) unchanged.

Characterization of a Fiber-Optic System for the Distributed Measurement of Leakages in Tanks and Pipelines

A fiber-optic sensor system for the distributed measurement of organic chemicals is presented in this paper. The system uses the technique of optical time-domain reflectometry (OTDR) and a polymerclad optical fiber that is sensitive to nonpolar substances. The location of the chemicals is attained by measuring the time delay between a short laser light pulse entering the fiber and a discrete change in the backscatter signal caused by the enrichment of the analyte in the fiber cladding. Chemical substances enriched in the cladding of the sensor fiber lead to changes in the OTDR response signal, because the light-guiding properties of the fiber are affected through the evanescent wave. The enrichment of an analyte with a higher refractive index than the fiber cladding, for example, will induce a light loss because of mode stripping. This light loss is followed by a step drop in the OTDR response signal. If the analyte penetrating into the fiber cladding absorbs the emitted laser light pulse, a step drop also occurs in the backscatter signal because of the light loss due to the absorption. A fluorescent substance in the fiber cladding leads to a characteristic peak in the OTDR response signal. The intensity of the different signals is correlated with the refractive index and the concentration of the analyte, the interaction length between analyte and sensing fiber, and the temperature, fiber diameter, and bend radius of the fiber.

Silver-plated vitamins: a method of detecting tocopherols and carotenoids in LC/ESI-MS coupling.

In LC/MS, nonpolar substances in the majority of cases cannot be ionized by standard electrospray ionization (ESI) because they obviously lack a site for protonation or deprotonation. The ionization of carotenoids and tocopherols can be greatly enhanced by the addition of silver ions. The Ag(+)-carotenoid and Ag(+)-tocopherol adducts thus formed render these substances amenable to MS. alpha-, beta-, gamma-, and delta-tocopherol, alpha-tocopherol acetate, and the various isomers of lycopene and beta-carotene were separated by C30 RP-HPLC and could be identified by online ESI-MS. A mixture of six different carotenoids was analyzed by scanning the mass range from m/z 500 to 800. The mass spectra of the peaks revealed that all carotenoids and most tocopherols were partially oxidized to radical cations. The detection limit for canthaxanthin was approximately 500 fmol while that of beta-carotene was below 300 fmol. An increase in sensitivity in the MRM mode can be attained by monitoring ions formed by loss of elemental silver from the adducts in the CID cell. Dichloromethane extracts of tomato, carrot, and vegetable juices, a vitamin drink, and a commercial infant food product were analyzed by LC/MS. After postcolumn argentation, from the mass-selective extracts of the TIC, the carotenoids and tocopherols present could be identified by their masses and their retention times. For all studies, a silver perchlorate solution with an overall concentration of 50 micrograms/mL was used.

A systematic study of cubic three-parameter equations of state for deriving a structurally optimized PVT relation

The characteristics of a variety of two- and three-parameter cubic equations of state (C2EOS and C3EOS) have been analyzed by a systematic consideration of possible relations between the parameters of a general four-parameter equation. The PVT behaviour of oxygen and water as popular examples of nonpolar and polar substances and other compounds has been studied with different C3EOS. From these results conclusions for suitable structures of C3EOS can be drawn.