N-hexane Solution Research Articles

UPS, XPS, and NEXAFS Study of Self-Assembly of Standing 1,4-Benzenedimethanethiol SAMs on Gold

We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 °C for 30 min and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free -SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24° with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units.

ZnO hierarchical nanostructures grown at room temperature and their C 2H 5OH sensor applications

Highly crystalline ZnO hierarchical nanostructures were prepared at room temperature through the alkaline hydrolysis of zinc salt by the forced mixing of two immiscible solutions: Zn-nitrate aqueous solution and oleic-acid-dissolved n-hexane solution. The oleic acid acted as a surfactant in the room-temperature formation of well-defined ZnO hierarchical nanostructures, which subsequently demonstrated a sensitive and selective detection of C 2H 5OH. The responses of these hierarchical nanostructures to 10–100 ppm C 2H 5OH ranged from 15.7 to 177.7, which were 7–9 times higher than those of the agglomerated nanoparticles.

Assessment of carcinogenic risk due to inhalation of polycyclic aromatic hydrocarbons in PM 10 from an industrial city: A Korean case-study

This study investigated the effects of meteorological conditions and spatial variations on the toxicity of polycyclic aromatic hydrocarbons (PAHs) in airborne PM 10 in Ulsan, the largest industrial city in Korea. Daily PM 10 samples were collected on quartz microfiber filters using high volume samplers located in a downtown area, a residential area and an industrial area of Ulsan during spring and summer sampling periods. Sixteen individual PAHs were extracted into a mixture solution of dichloromethane and n-hexane (1:1, v/v) in an ultrasonic bath and were analyzed using a high performance liquid chromatography system with an ultra-violet detector (HPLC-UVD). The average total PAH concentrations from the three representative sampling sites of Ulsan ranged from 16.15 to 57.12 ng/m 3 in spring and from 11.11 to 34.56 ng/m 3 in summer. The toxicity equivalent concentrations (TEQs) of the PAHs in PM 10 of Ulsan ranged from 1.82 to 13.1 ng/m 3, with an average level of 4.17 ng/m 3. The highest TEQs were found in the downtown area, which had an average value of 6.30 ng/m 3 in spring and 5.52 ng/m 3 in summer. BaP and DahA were identified as the major carcinogenic PAHs that contributed to 34.8 and 59.4% of the total carcinogenic potency of PAHs in PM 10 in Ulsan. The identified TEQs were highly correlated ( r 2 = 0.73–0.90, p < 0.01) with the total PAH concentrations for each area. The TEQs showed a significant correlation ( p < 0.01) with the concentration of air pollutants, including PM 10, PM 2.5 and NO 2.

Hydrophobic Ceramic Surface by Sol-Gel Method

The sol-gel method was chosen in the experiment to make nano-structured coatings on the ceramics. In this experiment the TEOS, ETOH were chosen as the main reagents and the two group formulas whose scale were 3:50 and 18:25 were chosen to make the sol of silica by the way of sol-gel, and the two formula were mixed on some scale. The sols of the three formulas would be spread on the ceramics separately; and then burned in different temperatures of 500°C, 800°C, 900°C and 1000°C, last the samples were put into the 10% of trim ethyl chlorosilane of n-hexane solution to adorn the surface of spread the gel ceramics. The result of the samples, which are uncalcined, calcined and black and calcined and the surface adorned compared, shows that the contact angle of samples that have been calcined and the surface adorned becomes bigger. So the hydrophic effect is the best when there are all of the microstructure and the low-surface power on the ceramics surface.

Typing of unknown microorganisms based on quantitative analysis of fatty acids by mass spectrometry and hierarchical clustering

Rapid identification of unknown microorganisms of clinical and agricultural importance is not only critical for accurate diagnosis of infections but also essential for appropriate and prompt treatment. We describe here a rapid method for microorganisms typing based on quantitative analysis of fatty acids by iFAT approach (Isotope-coded Fatty Acid Transmethylation). In this work, lyophilized cell lysates were directly mixed with 0.5 M NaOH solution in d3-methanol and n-hexane. After 1 min of ultrasonication, the top n-hexane layer was combined with a mixture of standard d0-methanol derived fatty acid methylesters with known concentration. Measurement of intensity ratios of d3/d0 labeled fragment ion and molecular ion pairs at the corresponding target fatty acids provides a quantitative basis for hierarchical clustering. In the resultant dendrogram, the Euclidean distance between unknown species and known species quantitatively reveals their differences or shared similarities in fatty acid related pathways. It is of particular interest to apply this method for typing fungal species because fungi has distinguished lipid biosynthetic pathways that have been targeted for lots of drugs or fungicides compared with bacteria and animals. The proposed method has no dependence on the availability of genome or proteome databases. Therefore, it is can be applicable for a broad range of unknown microorganisms or mutant species.

Synthesis of hydrophilic and hydrophobic xerogels with superior properties using sodium silicate

Highly porous hydrophilic and hydrophobic silica xerogels were synthesized by surface modification of silica hydrogels at ambient pressure drying. The silica hydrogels were prepared by a sol–gel polymerization of an inexpensive silica precursor (sodium silicate) under atmospheric conditions. In order to minimize shrinkage due to drying, the hydrogel surface was modified using trimethylchlorosilane (TMCS) in the presence of ethanol/ n-hexane solution before ambient pressure drying (APD). Properties of the final product were investigated using Field-Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Analysis (TG–DTA), and nitrogen physisorption studies. The final product was observed to have an extremely high specific surface area (783 m 2/g) and a large cumulative pore volume (2.74 cm 3/g). Highly porous hydrophilic xerogels were obtained after heat-treating the modified xerogels. At temperatures above 450 °C the surface alkyl groups ( CH 3) were significantly oxidized and, consequently, the properties of the resulting xerogels were altered. Products obtained via the proposed inexpensive approach have superior properties and the method exploits an inexpensive silica source (sodium silicate). Thus it is feasible for large-scale economic industrial production.

Disorder, solvent effects and substitutional self-assembly of alkane dithiols from alkane thiol SAMs

Substitutional self-assembly of nonanedithiol from a hexanethiol self-assembled monolayer and the effects of use of ethanol and n-hexane as solvents were investigated. It was found that presence of original solvents in the HT SAM allowed easy replacement, while dried SAMs were more resilient to substitution and much longer times are necessary for substitution to occur. In general substitution in ethanol leads to production of a disordered dithiol SAM, with existence of extra molecules bonded to the SAM. Well ordered substituted SAMs were obtained with degassed n-hexane solutions and in absence of ambient light.

Effects of co-existed proteins on measurement of pesticide residues in blood by gas chromatography–mass spectrometry

Accurate measurement of pesticides in biological fluids such as blood is important for quantifying environmental exposures. Beyond sample enrichment and separation, the method presented here is focused on studies of interactions between pesticides and co-existed proteins. It was experimentally demonstrated that entrapped or adsorbed pesticide residues within the folded native structures of proteins were poorly recovered using direct solvent extraction solely. We described here an effective approach termed Enzymatic Digestion-Organic Solvent Extraction (eDOSE) that utilizes the enzymatic approach to disrupt the folded structures of proteins and release entrapped or adsorbed pesticide residues. In this approach, samples were first reduced, alkylated, tryptically digested and then diluted 10 times before the subsequent extraction using an n-hexane solution. Resultant pesticide residues were determined by capillary gas chromatography coupled with a mass spectrometer. Mean recoveries of the 5 organophosphorus pesticides pre-spiked in fish blood including diazinon, parathion-methyl, malathion, parathion-ethyl and ethion were 85%, 95%, 84%, 103%, and 43% respectively using eDOSE strategy but only 24%, 45%, 40%, 27%, and 29% respectively using direct solvent extraction approach. The eDOSE approach was effective for demonstrating the critical role of folded native structure of serum albumin in adsorption of exogenous chemicals. It provides an alterative means for denaturation of proteins when the target analytes are not stable in acidic solution or entrapped within the protein aggregates caused by organic solvents such as acetone that have been applied for protein denaturation. The eDOSE approach should be able to combine with other advanced techniques of enrichment and separation for more efficient and accurate measurement of target compounds present in the context of complex biological systems. This approach can provide wide applications to the analysis of a variety of small molecules including environmental pesticide residues and metabolites as well as other toxins present in cells, tissues and biofluids.

Adsorption of β-carotene onto mesoporous carbon coated monolith in isopropyl alcohol and n-hexane solution: equilibrium and thermodynamic study

Mesoporous carbon coated monolith prepared from furfuryl alcohol by the dip-coating method was utilized as an adsorbent for adsorption of β-carotene from crude palm oil. The effect of temperature on the adsorption was investigated by batch adsorption experiments. The adsorption quantity increased with increasing temperature. The adsorption was performed using two different solvents, isopropyl alcohol and n-hexane. The maximum adsorption capacity of β-carotene was 62.118 mg/g for isopropyl alcohol at 50 °C. The experimental results were fitted using the Langmuir and Freundlich isotherms. The Langmuir described the adsorption process better. The negative values of Gibbs free energy change suggested that the adsorption was a spontaneous process. The positive values of heat of enthalpy and entropy change confirmed the endothermic nature of the adsorption.

ChemInform Abstract: Photolysis of 1-Bromo-2,2-bis(p-methoxyphenyl)ethene in Solution

UV irradiation (λinc= 254 nm) of 1-bromo-2,2-bis(p-methoxyphenyl)ethene (AAHVB) in acetonitrile solution results in its decomposition: ϕ(–AAHVB)= 0.18 both in the absence and presence of O2. Apart from the isomers [(E)-1-bromo-1,2-bis(p-methoxyphenyl)ethene (HAAVB) and (Z)-1-bromo-1,2-bis(p-methoxyphenyl) ethene (AHAVB)] the main photoproducts are 1,2-bis(p-methoxyphenyl)ethine (P-2) and HBr (ϕ≈ 0.1). Flash photolysis studies in acetonitrile, dichloromethane and n-hexane solution at 266 nm revealed that P-2 is formed with a halflife of less than a few ns via a singlet route involving vinyl cations which rapidly rearrange and split off protons. Part of the vinyl cations decay via a different route forming an ionic species with an optical absorption band at ca. 350 nm. The decay of the latter is not correlated with the formation of P-2. This ionic species probably results from an interaction of vinyl cations with solvent or AAHVB. AAHVB quenches triplet states of various compounds X (e.g. benzophenone, chrysene, benzil, pyrene) provided that ET(X) > 200 kJ mol–1. The energy transfer from these compounds to AAHVB does not result in the formation of P-2 or vinyl cations.

Development of superparamagnetic high-magnetization C 18-functionalized magnetic silica nanoparticles as sorbents for enrichment and determination of methylprednisolone in rat plasma by high performance liquid chromatography

In this study, a novel extraction and enrichment technique based on superparamagnetic high-magnetization C 18-functionalized magnetic silica nanoparticles (C 18-MNPs) as sorbents was successfully developed for the determination of methylprednisolone (MP) in rat plasma by high performance liquid chromatography (HPLC). The synthesized silica-coated magnetite modified with chlorodimethyl-n-octadecylsilane was about 320 nm in diameter with strong magnetism and high surface area. It provided an efficient way for extraction and concentration of MP in the samples through hydrophobic interaction by the interior C 18 groups. Moreover, MP adsorbed with C 18-MNPs could be simply and rapidly isolated through placing a strong magnet on the bottom of container, and then easily eluted from C 18-MNPs by n-hexane solution. Extraction conditions such as amounts of C 18-MNPs added, adsorption time and desorption solvent, were investigated. Method validations including linear range, detection limit, precision, and recovery were also studied. The results showed that the proposed method based on C 18-MNPs was a simple, accurate and high efficient approach for the analysis of MP in the complex plasma samples.

Nonadiabatic Excited-State Dynamics with Hybrid ab Initio Quantum-Mechanical/Molecular-Mechanical Methods: Solvation of the Pentadieniminium Cation in Apolar Media

A new implementation of nonadiabatic excited-state dynamics using hybrid methods is presented. The current approach is aimed at the simulation of photoexcited molecules in solution. The chromophore is treated at the ab initio level, and its interaction with the solvent is approximated by point charges within the electrostatic embedding approach and by a Lennard-Jones potential for the nonbonded interactions. Multireference configuration interaction (MRCI) and multiconfiguration self-consistent field (MCSCF) methods can be used. The program implementation has been performed on the basis of the Columbus and Newton-X program systems. For example, the dynamics of penta-2,4-dien-1-iminium (PSB3) and 4-methyl-penta-2,4-dien-1-iminium cations (MePSB3) was investigated in gas phase and in n-hexane solution. The excited-state (S(1)) lifetime and temporal evolution of geometrical parameters were computed. In the case of PSB3 the n-hexane results resemble closely the gas phase data. MePSB3, however, shows a distinct extension of lifetime due to steric hindering of the torsion around the central bond because of solute-solvent interactions.

Conformational preferences for some 2-substituted N-methoxy- N-methylacetamides through spectroscopic and theoretical studies

The analysis of the IR carbonyl band of the 2-substituted N-methoxy- N-methylacetamides Y–CH 2C(O)N(OMe)Me (Y = F 1, OMe 2, OPh 3, Cl 4), supported by B3LYP/6-311++G(3df, 3pd) calculations along with the NBO analysis for 1– 4, indicated the existence of cis– gauche conformers i.e. ( c) and ( g) for 1 and 3, ( c 1 , c 2) and ( g 1 , g 2) for 2, and ( c) and ( g 1 , g 2) for 4. In the gas phase, the g conformer population prevails over the c one, for 1 and 3, the ( c 1 + c 2) population prevails over the ( g 1 + g 2) one for 2, and the ( g 1 + g 2) conformer population is more abundant than ( c) one for 4. In n-hexane solution, the cis conformer is more abundant for 1– 3. The occurrence of Fermi resonance in the ν CO region, in n-hexane, precludes the estimative of relative populations of the ( c, g 1, g 2) conformers for 4. The SCI-PCM calculations agree with the solvent effect on the ν CO band component relative intensities for 1– 3. NBO analysis showed that the n N → π co ∗ orbital interaction is the main factor which stabilizes the gauche ( g, g 1, g 2) conformers for 1– 4 into a larger extent relative to the cis ( c, c 1, c 2) ones. The n Y → π co ∗ , σ C Y → π co ∗ , π co → σ C Y ∗ and π co ∗ → σ C Y ∗ orbital interactions still contribute, but into a minor extent for the stabilization of the gauche conformers relative to the cis ones. The existence of some pyramidalization at the nitrogen atom of the Weinreb amides 1– 4 is responsible for the occurrence of Y δ −(4)···O δ −(9) and Y δ −(4)···N δ −(7) short contacts in the gauche ( g, g 1, g 2) conformers, which originates strong repulsive Coulombic interactions, acting in opposition to the large orbital stabilization of the gauche conformer with respect to the cis one. Therefore, a delicate balance of the Coulombic and orbital interactions seems to be responsible for the observed stabilization of the gauche ( g, g 1, g 2) and cis ( c, c 1, c 2) conformers, both in the gas phase and in the solution for 1– 4. However, the cis conformer predominance, in non polar solvents, for the 2-substituted N-methoxy- N-methyl acetamides 1– 3, bearing in α first raw (fluorine and oxygen) atoms, is in the opposite direction to the gauche conformer preference for the corresponding 2-substituted N, N-dialkyl-acetamides.

Liquid Membrane Permeation of Nitrogen Heterocyclic Compounds Contained in Model Coal Tar Fraction

We investigated the separation of nitrogen heterocyclic compound (NHC) contained in a model coal tar fraction comprising four kinds of NHC [indole (In), quinoline (Q), iso-quinoline (iQ), quinaldine (Qu)], three kinds of bicyclic aromatic compound (BAC) [1-methylnaphthalene (1MN), 2-methylnaphthalene (2MN), dimethylnaphthalene (DMN) mixture with ten structural isomers (DMNs; regarded as one component)], biphenyl (Bp) and phenyl ether (Pe) by liquid membrane permeation (LMP). A batch-stirred tank was used as the permeation unit. An aqueous solution of saponin and n-hexane were used as the liquid membrane and the outer oil phase, respectively. Yield and selectivity of individual NHC was much larger than that of BAC, Bp and Pe. Increasing the initial mass fraction of the saponin to the membrane solution () and the initial volume fraction of O/W emulsion to total liquid in a stirred tank () resulted in deteriorating the yield of individual NHC, but increasing the stirring speed (N) resulted in improving the yield of each NHC. With increasing , the selectivity of each NHC based on DMNs increased. Increasing and N resulted in decreasing the selectivity of individual NHC based on DMNs. At an experimental condition fixed, the sequence of the yield and selectivity in reference to DMNs for each NHC was Q > Qu = iQ > In. Furthermore, we compared LPM method with methanol extraction method in view of the separation efficiency (yield, selectivity) of NHC.

Quantitative Determination of Cyfluthrin in N-Hexane by Terahertz Time-Domain Spectroscopy With Chemometrics Methods

This paper presents the preliminary research in detecting pesticide residues with the newly developed terahertz technique. Experiments were carried out on cyfluthrin n-hexane solutions in the concentration range of 1-20 ?g/ml with terahertz time-domain spectroscopy (THz-TDS). We employed four calibration methods for the regression between the absorbance and the concentration of the solutions, i.e., linear regression methods of simple linear regression (SLR), partial least squares (PLS), and nonlinear regression methods of simple least-squares support vector machine (LS-SVM), and the combination of PLS and LS-SVM (PLS-LS-SVM), which utilizes the features extracted by PLS from the original absorbance spectra as the input of LS-SVM. To analyze the antinoise abilities of these models, we collected two data sets of the same series of samples on two different days, i.e., one with higher signal-to-noise ratio (SNR) and the other with lower SNR. Separate models were built on them. We find that the PLS and PLS-LS-SVM models present much better prediction and antinoise abilities than the SLR and simple LS-SVM models, whereas PLS-LS-SVM outperforms PLS, showing much less dependence on the selection of the number of the features extracted. To further analyze the influence of the selection of the frequency range, we built different PLS-LS-SVM models by varying the frequency ranges between 0.5 and 1.5 THz, and find that the model performance dramatically varies with the selection of different frequency ranges, which may be due to the unevenly distributed SNR and the spectroscopic interaction variations in different frequency ranges. The selection of the whole frequency range of 0.5-1.5 THz results in relatively low prediction error with either the higher or the lower SNR spectra and will thus be selected for further modeling. The overall results indicate that the THz-TDS plus PLS-LS-SVM method proves to be an effective tool for the quantitative analysis of cyfluthrin n-hexane solutions and may provide a new technique for further pesticide residue detection.

Preparation of biodiesel from Jatropha curcas L. oil produced by two-phase solvent extraction

In the present work the preparation of biodiesel from Jatropha curcas L. oil produced by two-phase solvent extraction (TSE) was studied. The experimental results of TSE process showed that the optimal extraction conditions were 30 g samples, 240 mL of extraction solvent mixture and methanol/ n-hexane volume ratio 60:40, extraction temperature 35 °C, extraction time 30 min. Further, the effect of methanol recycling on the TSE process was also investigated. After TSE process, the investigations were carried out on transesterification of methanol with oil– n-hexane solution coming from TSE process in the presence of sodium hydroxide as the catalyst. The conversion could achieve 98% with 3:1 n-hexane/oil weight ratio, 60 °C reaction temperature, 7:1 methanol/oil mole ratio, 1.1% alkali catalyst concentration and 120 min reaction time. The properties of fatty acid methyl ester (FAME) product prepared from Jatropha curcas L. oil produced by two-phase solvent extraction met the ASTM specifications for biodiesel.

Re-examination of 7,7′-dimethyl-7-germanorbornadiene photocleavage in solution and in organic glasses

Dimethylgermylene and its Ge=Ge doubly bonded dimer, tetramethyldigermene, have been characterized directly in solution by 308-nm laser flash photolysis in n-hexane solution, as well as 254-nm photolysis in hydrocarbon glasses at t = 77 K. An absorption band maximum of λmax ≈ 430 nm and molar absorption coefficient of e ≈ 2,700 M−1 cm−1 have been shown to be attributable to low-temperature glasses, while the absorption band maximum of λmax ≈ 480 nm and molar absorption coefficient of e ≈ 2,400 M−1 cm−1 have been shown to be related to dimethylgermylene in n-hexane solution. The molar absorption coefficient of tetramethyldigermene (λmax ≈ 380 nm) was determined to be e ≈ 84,000 M−1 cm−1. The germylene is formed via (formal) cheletropic photocycloreversion of 7,7′-dimethylgerma-1,4,5,6-tetraphenyl-2,3-benzo-norbornadiene. Tetramethyldigermene and 1,2,3,4-tetraphenylnaphthalene in the triplet state were formed, together with dimethylgermylene. We attempted to explain the various contradictory interpretations of experimental data existing in the literature on this reaction.

Synthesis, structure, and catalytic activity of group 4 complexes with new chiral biaryl-based NO 2 ligands

A new series of chiral bis-ligated group 4 complexes have been prepared from the reaction between M(NMe 2) 4 (M = Ti, Zr) and C 1-symmetric biaryl-based NO 2 ligands, ( R)-2-(mesitoylamino)-2′-methoxy-1,1′-binaphthyl ( 1H), ( R)-2-(mesitoylamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl ( 2H), ( S)-5,5′,6,6′,7,7′,8,8′-octahydro-2-(mesitoylamino)-2′-methoxy-1,1′-binaphthyl ( 3H), ( R)-2-(3,5-di- tert-butyl-2-hydroxyphenylmethyleneamino)-2′-methoxy-1,1′-binaphthyl ( 4H), ( R)-2-(3- tert-butyl-2-hydroxyphenylmethyleneamino)-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl ( 5H), which are derived from ( R)-2-amino-2′-methoxy-1,1′-binaphthyl, ( R)-2-amino-2′-methoxy-6,6′-dimethyl-1,1′-biphenyl or ( S)-5,5′,6,6′,7,7′,8,8′-octahydro-2-amino-2′-methoxy-1,1′-binaphthyl. Treatment of M(NMe 2) 4 with 2 equiv. of mesitoylamides 1H, 2H or 3H gives, after recrystallization from a toluene or n-hexane solution, the bis-ligated chiral titanium amides ( 1) 2Ti(NMe 2) 2 ( 6), ( 2) 2Ti(NMe 2) 2 ( 8), ( 3) 2Ti(NMe 2) 2 ( 10), and zirconium amides ( 1) 2Zr(NMe 2) 2 ( 7), ( 2) 2Zr(NMe 2) 2 ( 9), ( 3) 2Zr(NMe 2) 2 ( 11), respectively, in good yields. Under similar reaction conditions, treatment of M(NMe 2) 4 with 2 equiv. of Schiff base ligands 4H or 5H gives, after recrystallization from a toluene solution, the chiral bis-ligated titanium complex {( R)-2-[3,5-(Me 3C) 2-2-O-C 6H 2CH(NMe 2)N]-2′-(MeO)-1,1′-C 20H 12} 2Ti ( 12) and zirconium complex {( R)-2-[3-Me 3C-2-O-C 6H 3CH(NMe 2)N]-2′-(MeO)-1,1′-(6-Me-C 6H 3) 2}( 5)ZrNMe 2 ( 13), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 1H, 6, 8, 9, 12 and 13 have further been confirmed by X-ray diffraction analyses. The titanium and zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to excellent yields with good ee values.

Interaction of Oxidized Copper Surfaces with Alkanethiols in Organic and Aqueous Solvents. The Mechanism of Cu2O Reduction

The interaction of 1-octanethiol, 1,8-octanedithiol, 1-hexadecanethiol, and 16-mercaptohexadecanoic acid with polycrystalline copper surfaces was investigated comparatively using forming solutions with polar (0.05 M NaOH solution) and apolar (n-hexane) solvents. The thiol layers were formed on the freshly chemically polished copper surface as well as on the anodically oxidized surface. The effects of the alkanethiol chain length and terminal group on the blocking properties of the surface were investigated. We show for the first time that compact monolayers and multilayers can be obtained from an alkaline forming solution. Copper oxides are completely reduced in the alkaline forming solution for all of the thiols investigated after an immersion time of 45 min. On the contrary, the presence of a surface oxide was always detected after the formation of the thiol layer in the n-hexane solution. The mechanism of Cu2O reduction by thiols was investigated by means of density functional theory calculations. The ...

Peculiarities of asphaltene precipitation in n-alkane-oil systems

n-Pentane-, n-hexane-, and n-heptane-insoluble asphaltenes obtained via a standard procedure by precipitating from oil solutions in n-pentane, n-hexane, and n-heptane, respectively, as well as n-pentane/n-hexane/n-heptane-insoluble and n-heptane/n-hexane/n-pentane-insoluble asphaltene constituents prepared through successive washing (fractional dissolution) of n-pentane-insoluble asphaltenes with n-hexane and n-heptane and n-heptane-insoluble asphaltenes with n-hexane and n-pentane, respectively, are studied. Asphaltenes and their constituents extracted from three oils distinguished by high contents of asphaltenes, resins, and paraffins, respectively, are investigated by 1H NMR spectroscopy in carbon tetrachloride solutions. It is established that the mass fractions and the fragment compositions of asphaltenes and their constituents depend on both the type of oil and the procedure of their preparation; i.e., the precipitation from n-alkane-oil systems or the extraction through the successive washing with a series of n-alkanes. The obtained experimental data made it possible to formulate a hypothesis according to which the precipitation of asphaltenes from oils is controlled by not only the dissolving power of a solvent with respect to molecular components of initial oils, but also (and primarily) by the dissolving power of a solvent with respect to supramolecular structures of asphaltenes formed in n-alkane-oil systems.