Increasing Alkyl Chain Length Research Articles

Ionic Liquids: Emerging Antimicrobial Agents.

Antimicrobial resistance has become a serious threat to global health. New antimicrobials are thus urgently needed. Ionic liquids (ILs), salts consisting of organic cations and anions with melting points less than 100°C, have been recently found to be promising in antimicrobial field as they may disrupt the bacterial wall and membrane and consequently lead to cell leakage and death. Different types of antimicrobial ILs are introduced in the review, including cationic, polymeric, and anionic ILs. Being the main type of the antimicrobial ILs, the review focuses on the structure and the antimicrobial mechanisms of cationic ILs. The quantitative structure-activity relationship (QSAR) models of the cationic ILs are also included. Increase in alkyl chain length and lipophilicity is beneficial to increase the antimicrobial effects of cationic ILs. Polymeric ILs are homopolymers of monomer ILs or copolymers of ILs and other monomers. They have great potential in the field of antibiotics as they provide stronger antimicrobial effects than the sum of the monomer ILs. Anionic ILs are composed of existing anionic antibiotics and organic cations, being capable to enhance the solubility and bioavailability of the original form. Nonetheless, the medical application of antimicrobial ILs is limited by the toxicity. The structural optimization aided by QSAR model and combination with existing antibiotics may provide a solution to this problem and expand the application range of ILs in antimicrobial field.

Surface Activity of Amines Provides Evidence for the Combined ESI Mechanism of Charge Reduction for Protein Complexes.

Charge reduction reactions are important for native mass spectrometry (nMS) because lower charge states help retain native-like conformations and preserve noncovalent interactions of protein complexes. While mechanisms of charge reduction reactions are not well understood, they are generally achieved through the addition of small molecules, such as polyamines, to traditional nMS buffers. Here, we present new evidence that surface-active, charge reducing reagents carry away excess charge from the droplet after being emitted due to Coulombic repulsion, thereby reducing the overall charge of the droplet. Furthermore, these processes are directly linked to two mechanisms for electrospray ionization, specifically the charge residue and ion evaporation models (CRM and IEM). Selected protein complexes were analyzed in solutions containing ammonium acetate and selected trialkylamines or diaminoalkanes of increasing alkyl chain lengths. Results show that amines with higher surface activity have increased propensities for promoting charge reduction of the protein ions. The electrospray ionization (ESI) emitter potential was also found to be a major contributing parameter to the prevalence of charge reduction; higher emitter potentials consistently coincided with lower average charge states among all protein complexes analyzed. These results offer experimental evidence for the mechanism of charge reduction in ESI and also provide insight into the final stages of the ESI and their impact on biological ions.

Thermodynamic analysis of nucleation of alcohol molecules with the varied alkyl chain length in nanoconfined solution

Combining the molecular dynamics (MD) simulations and the free-energy-based thermodynamic analysis, we analyze the role of alkyl chain length on the nucleation of alcohol molecules with the mono-hydroxyl in nanoconfined solution. The free energy formulae and thermodynamic equilibrium equation are parameterized by fitting the theoretical equilibrium equation to MD simulation results. We find that alcohol molecules with the varied alkyl chain length show different nucleation states, i.e., dispersion, reversible and aggregation states, corresponding to the total free energy Gconfine(n, N) with a single minimum at n∼ 1, two minima at n∼ 1 and N separated by a maximum, and a local minimum at n∼N, respectively. The alcohol molecule with a longer alkyl chain tends to aggregate into a cluster at a lower solute number in nanoconfined solution. Besides, the free energy of cluster formation in nanoconfined solution Gcluster(n) also depends on the alkyl chain length, and three regions can be identified: For the shorter alkyl chain, such as ethanol, there is no local maximum on Gcluster(n), indicating that alcohol molecules tend to be dispersed in water; For the intermediate alkyl chain length, such as 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol, the critical nucleation number nc and nucleation barrier Gb monotonically decrease with the increase of alkyl chain length; For the longer alkyl chain, nc∼ 1 and Gb∼0kBT suggest that alcohol molecules, such as 1-heptanol, can aggregate into clusters easily. Our work deepens the understanding of the alkyl chain length effect on the nucleation behavior of alcohol molecules in nanoconfined solution.

Effect of alkyl chain length on the antioxidant activity of alkylresorcinol homologs in low-moisture crackers

Alkylresorcinols (ARs) are a naturally occurring homologous series of phenolipids extracted from rye bran which have previously shown antioxidant activity in lipid-containing foods. This study extends previous work to consider their use in low-moisture foods using crackers as a model system. ARs (153 μmol) were capable of inhibiting lipid oxidation reactions based on the delayed generation of lipid hydroperoxides and headspace hexanal compared to a control treatment and were more effective than α-tocopherol which displayed prooxidant behavior. The antioxidant activity of ARs was observed to increase as a function of increasing alkyl chain length, with optimum activity at an alkyl chain length of C23:0; however, ARs were lost at a rate independent of alkyl chain length. A mixture of ARs displayed comparable antioxidant activity to the C23:0 and C25:0 homologs, all of which exerted stronger activity than butylated hydroxytoluene providing an effective alternative to synthetic antioxidants. These findings suggest that ARs are effective antioxidants in low-moisture foods likely because of their hydrophobicity, which allowed them to localize in the lipid phase, the purported site of lipid oxidation in the model cracker system.

Both alkyl chain length and V-amylose structure affect the structural and digestive stability of amylose-alkylresorcinols inclusion complexes

Alkylresorcinols (ARs) are a group of bioactive phenolic lipids and mostly concentrated in the bran of whole grains. In this study, the influences of alkyl chain length of ARs and V-amylose structure on the stability of V-amylose-ARs inclusion complexes were characterized. On the one hand, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and in vitro digestion studies of complexes showed that the crystallinity, thermo-stability, and digestion resistance of V-amylose-ARs inclusion complexes increased with increasing alkyl chain length of ARs. On the other hand, V6-amylose-ARs inclusion complexes displayed the strongest thermostability, the highest crystallinity, and the lowest digestibility compared to V7-amylose-ARs inclusion complexes and V8-amylose-ARs inclusion complexes. It could be concluded that both the helical structure of hydrated V6-amylose and ARs with longer alkyl chain stabilized the structure and stability of the inclusion complexes. This work could pave a way to develop bioactive cereal foods with high bioaccessibility of ARs.

Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy and advanced calorimetry

Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n = 5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a γ-relaxation due to localized fluctuations as well as two glassy dynamics, the αcore- and αalkyl-relaxation, were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n = 8 from a rigid constrained (n = 5,6) to a softer system (n = 10,12) was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene-like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition.

Synthesis and properties of different alkyl alcohol polyethers as the defoamers for concrete

In this study, we report the synthesis and properties of different alkyl alcohol polyethers as the defoamers for concrete. A series of alkyl alcohol polyethers with the same ethylene oxide unit amount (8 EO) but different alkyl chain lengths (C14~22) were obtained. The surface activities and defoaming properties of them in aqueous solutions were studied. Using them as the concrete defoamers, the defoaming properties in both fresh and hardened cement mortars were investigated, and the structure-property relationships of the polyethers were fully discussed. The results indicate that the C14 polyether showed obvious air-entraining property and the C16~22 polyethers showed effective defoaming property. As the alkyl chain length increases, the HLB value of polyether decreases (hydrophobicity increases), and the defoaming effect of polyether increases in both solutions and mortars. The results also indicate that the polyether containing longer alkyl chain length improved the mechanical performance of the hardened mortar more effectively. The study found great potential of alkyl alcohol polyethers for the practical applications as high performance defoamers.

Complexation thermodynamics of UO22+/diglycolamide complex in a room temperature ionic liquid: A study by optical spectroscopy and microcalorimetry

Complexation thermodynamics of UO22+ and a series of N,N,N’,N’-tetraalkyl diglycolamide (TRDGA) ligands having alkyl chains –CH3 to –C6H13 were investigated in an ionic liquid (IL). The complexation constant for UO22+/DGA complex increased linearly with increasing alkyl chain length of DGA from tetramethyl (logβ1 = 4.52, logβ2 = 8.01) to tetrahexyl (logβ1 = 5.62, logβ2 = 10.3). There were two types of species recorded in the calorimetric titration for all the four ligands, one having endothermic complexation, and other exothermic. This observation was in contrast with those observed for aqueous medium, where both the stepwise complexation enthalpies were endothermic. The structural feature indicated the formation of [UO2L2]2+ type of complex without water or Tf2N− anion in the primary coordination sphere of the uranyl cation.

Delineating molecular interactions within surface active ionic liquids + tartrazine dye solutions: A comparative study with conventional surfactant-DTAC

Surface active ionic liquids (SAILs) have been used in various technological fields. Moreover, the deep understanding of interactions exist in SAIL and dye systems will enhance their utility in various fields. In this study, the interactions of cationic Ionic liquids/surfactant 1-Methyl-3-octylimidazoilum chloride [C8mim][Cl], 1-Methyl-3-decylimidazolium chloride[C10mim][Cl], Dodecyl trimethylammonium chloride (DTAC) with anionic dye tartrazine were investigated by state of the art techniques i.e., conductivity, UV–visible spectroscopy, fluorescence spectroscopy and surface tension. The Critical micelle concentration (CMC) of tartrazine-added aqueous ILs/surfactant solutions were obtained, and a decrease is observed after addition of dye. Further, with the increase in alkyl chain length of ILs, the CMC is considerably reduced. Spectroscopic studies reveal a change in spectra of dye which hints ILs/surfactant dye interaction. The binding constant (Kb) is calculated by conductivity, UV-visible, fluorescence methods, which follows the order DTAC>[C10mim][Cl]>[C8mim][Cl]. Computational studies give an idea of the HOMO – LUMO energy gap between the donor and acceptor orbitals of ILs/surfactant and dye, which can be useful in the prediction of the feasibility of interaction between two entities.

INVESTIGATION OF THE INFLUENCE OF THE SUBSTITUTE IN THE THIRD POSITION ON THE ELECTRONIC STRUCTURE OF 1,3-THIAZOLO[2,3-c][1,2,4]TRIAZOLE

Condensed 1,2,4-triazole derivatives exhibit a wide range of biological activity. In particular, triazolam, alprazolam and estazolam, which contain [1,2,4]triazolo[4,3-a][1,4]benzodiazepine system, are used as tranquilizers. Brotizolam is another tranquilizer, a derivative of thieno[3,2-f][1,2,4]triazolo [4,3-a][1,4]diazepine. The oral hypoglycemic drug sitagliptin contains the [1,2,4]triazolo[4,3-a]pyrazine system. In addition, pesticides such as flumetsulam, metosulam, cloransulam, diclosulam, florasulam, are derivatives of [1,2,4]triazolo[1,5-a]pyrimidine, [1,2,4]triazolo[1,5-c]pyrimidine and [1,2,4]triazolo[4,3-a]pyrimidine. Also, the search for anticancer drugs is based on the nucleus of 1,2,4-triazole. The popularity of the use of 1,2,4-triazole derivatives is primarily due to the high pharmacological action and relatively low toxicity of these compounds.
 The calculations were performed in the software package ORCA 4.2.1, by the method of density functional theory using the B3LYP/def2-TZVP method. After optimizing the geometry, to confirm the finding of the true local minimum, we calculated the matrix of the second derived energy from the coordinates of the atoms - in all cases, no imaginary frequencies were detected, indicating the finding of the true minimum. The magnetic characteristics of the compounds were calculated by the GIAO method. Using the method of density functional theory, the geometric and electronic structures of five compounds of the [1,3]thiazolo[2,3-c][1,2,4]triazole class were simulated, namely: unsubstituted [1,3]thiazolo[2,3-c][1,2,4]triazole, 3-methyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-ethyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-butyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-hexyl-[1,3]thiazolo[2,3-c][1,2,4]triazole. It is established that the length of the alkyl substituent in the third position has almost no effect on the shape and localization of the frontal molecular orbitals. In all cases, the isosurfaces are localized on the condensed system [1,3]thiazolo[2,3-c][1,2,4]triazole. The length of the alkyl substituent in the third position affects the ionization energy and electron affinity of [1,3]thiazolo[2,3-c][1,2,4]triazoles. Moreover, both the ionization energy and the electron affinity decrease with increasing alkyl chain length. The change in aromaticity with the change in the length of the alkyl substituent in the third position of the [1,3]thiazolo[2,3-c][1,2,4]triazole system is irregular, but the change is insignificant. It is established that both triazole and thiazole cycles are more aromatic than benzene, and the aromaticity of the triazole cycle is greater than thiazole.
 Keywords: 1,2,4-triazole; 1,3-thiazole, thiazolo[2,3-c][1,2,4]triazole, frontal molecular orbitals; aromaticity.

Investigating bolalipids as solubilizing agents for poorly soluble drugs: Effects of alkyl chain length on solubilization and cytotoxicity

Synthetic single-chain bolalipids with symmetrical headgroups have shown potential in various pharmaceutical applications, such as the stabilization of liposome bilayers. Despite their amphiphilic character, synthetic bolalipids have not yet been investigated for their suitability as solubilizing agents for poorly soluble drug compounds. In this study, three synthetic single-chain bolalipids with increasing alkyl chain lengths (C22, C24 and C26) were investigated. All three bolalipids were able to achieve an increased solubility of the model drug, mefenamic acid, by approximately 180% in a pH 7.4 buffer compared to only a 102–105% increase achieved by sodium dodecyl sulfate (SDS) or the non-ionic surfactant pegylated hydroxystearate (PEG-HS). Subsequently, interfacial activity of bolalipids and their ability to destabilize liposomal bilayers were investigated. The C22 bolalipid exhibited a consistently lower interfacial activity, which was consistent with its significantly lower cytotoxicity in the macrophage-like cell line, J774. A1, compared to C24 and C26 counterparts. The mean IC50 values of the bolalipids tested (0.035–0.093 mM) were approximately 4–100-fold lower than that of SDS (0.401 mM) or PEG-HS (0.922 mM), with the mechanism of toxicity linked to increased cell membrane permeability, as is expected for surfactants. In summary, evidence from this study shows that decreasing the length of the bolalipid alkyl linker from C26 to C22 resulted in a significantly decreased cytotoxicity with no loss in drug solubilization efficiency.

Intercalation of montmorillonite with dialkylammonium cationic surfactants

Three montmorillonite (Mt) clays with different cation exchange capacity (CEC) were intercalated by a series of dialkyl ammonium cations with carbon numbers (Nc=) 8, 10, 12 and 18 in each alkyl chain. The intercalated clays were characterized by X-ray Diffraction, Thermogravimetric Analysis, Fourier Transform Infrared Spectroscopy and Transmission Electron Microscopy. The basal spacing of intercalated Mts increased gradually with increasing chain length. Interlayer arrangement of dialkyl surfactant cations in the intercalated clay gallery changed from flat bilayer to paraffinic and reached as high as 3.57 nm for the highest CEC clay intercalated with cations having Nc= 18 in each alkyl chain. For dialkylammonium intercalants, the increase in basal spacing was predominantly guided by the intercalant's structure and organic loading values lacked such direct correlation. Mt with low CEC showed large expansion in the clay interlayer with increasing alkyl chain length even with marginal increment in the organic loading. The highest basal spacing was observed always with the highest CEC clay for every intercalant irrespective of alkyl chain length. The wide expansion of clay gallery for the longest dialkyl intercalant in this series for all clays might be attributed to presence of intercalated surfactant molecules along with physically adsorbed surfactant cations in the clay interlayer. The change in conformations of intercalated dialkyl ammonium intercalants with increasing alkyl chain length was analyzed from FTIR study. With increasing alkyl chain length, methylene symmetric and asymmetric stretching frequency shifted to lower wavenumber for all Mt clays- which indicated greater ordered conformations obtained with increasing alkyl chain length.

Implementation of Artificial Neural Networks in the assessment of CO2 solubility in deep eutectic and ionic liquid solvents – Performance and cost comparison

In order to counteract the economic and environmental issues presented by Ionic Liquids (ILs) for carbon capture in post-combustion processes, Deep eutectic solvents (DESs) are being researched as potential absorbents. These are an emerging class of ILs that have a strong contribution from hydrogen bonding and have shown promising trends in CO 2 absorption in recent times. In this study, three hydrogen bond acceptors (HBA), along with 2-hydroxypropanoic acid (Lactic Acid (LA)) as the hydrogen bond donor (HBD), have been identified and analyzed as CO 2 absorbents. Considering their structural properties, thermodynamic behavior, and experimental conditions as input parameters, a backpropagation neural network (BPNN) has been implemented to analyze and predict the extent of CO 2 solubility within each of the DES mixtures. BPNN successfully predicted trends in the solubility as a function of the alkyl chain length, temperature, and pressure. It was observed that the solubility of CO 2 increased with increasing alkyl chain length and pressure but decreased with increasing values of temperature. DES is found to be more economical than other ionic liquid solvents used for CO 2 absorption.

Imidazolium-based ionic liquids with increasing alkyl chain length of cations decrease the stability and fibrillation propensity of lysozyme

Imidazolium ionic liquids with longer alkyl side chains show a larger destabilization effect on lysozyme. Increased hydrophobicity of the IL increases its binding affinity and inhibits the fibril formation of lysozyme.

Solubility of carbon dioxide in some imidazolium and pyridinium-based ionic liquids and correlation with NRTL model

In this study, the solubility of carbon dioxide gas in a series of 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids with various anions, viz. thiocyanate ([SCN]−), chloride ([Cl]−) and bromide ([Br]−) was investigated using a quartz crystal microbalance at 298.15 K and pressures up to 0.4 MPa. CO2 solubility in the ionic liquids correlates well with the non-random two-liquid (NRTL) model. The results indicate that the cation alkyl chain length and the type of anion have the main effects on the solubility of carbon dioxide in ionic liquids. CO2 solubility in both 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids increased with increasing alkyl chain length of the cation. Also, CO2 solubility was strongly dependent on the selection of the anion. CO2 solubility in both 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids increased as follows: [SCN]− > [Cl]− > [Br]−.

Effect of alkyl chain length on the corrosion inhibition of mild steel in a simulated hydrochloric acid medium by a phosphonium based inhibitor

The corrosion inhibiting effect of three synthesised phosphonium containing ionic liquids of varying alkyl chain length, namely, butyltriphenyl phosphonium bromide (BTPPB), hexyltriphenyl phosphonium bromide (HTPPB) and hexadecyltriphenyl phosphonium bromide (HDTPPB) on mild steel, was evaluated in 1 M HCl medium. The corrosion inhibition performance was studied by gravimetric method, potentiodynamic polarization studies, electrochemical impedance spectroscopy and quantum chemical studies (DFT). However, the results of the SEM, AFM and contact angle tests confirmed that the protective layer formed on the mild steel. Furthermore, assessed the theoretical calculations for exploring the inhibition mechanism. A maximum of 95.77% inhibition efficiency was achieved using 250 ppm of HDTPPB. The obtained results showed that HDTPPB has greater inhibition ability than BTPPB and HTPPB. Adsorption studies obeyed the Langmuir adsorption isotherm. Moreover, the increased alkyl chain length of ionic liquids did increase their inhibition efficiency.

Transition from antagonistic to synergistic interaction in mixed micellar system by increase in alkyl chain length of alkyl trimethylammonium bromide

Herein, the electrical conductivity technique used to measure the critical micelle concentration (cmc) for pure cationic surfactants (Dodecyl/cetyltrimethylammonium bromides) and phenothiazine drug (Promethazine hydrochloride), as well as their different mole fractions in 10−3 ​mol/kg 1-methyl-3-octylimidazolium chloride (C8mim.Cl) at different temperatures. By using the cmc values the regular solution theory used to evaluate the micellar mole fraction for DTAB/CTAB-PMT mixed systems. The clint's model used to calculate the ideal critical micelle concentration (cmc∗) that helps to evaluate the ideal micellar mole fraction for studied mixed systems, both explain the deviation from ideality. In addition, interaction parameter βm helps to confirm the nature of interaction (either antagonistic or synergistic) for the studied systems. The calculated parameters confirm a transition in the binding nature from antagonistic to synergistic with the increase in alkyl chain length of cationic surfactant i.e., component of the binary mixed system. The ease of micellization for the studied systems discussed by the standard Gibb's energy of micellization (ΔGm0), as well as the standard enthalpy and standard entropy of micellization were (ΔHm0) and (ΔSm0), respectively to discuss the stability of the studied systems.

Mechanism responsible for the reduction of interfacial tension by extended surfactants

The dynamic interfacial tensions (IFTs) of four extended surfactants (S-C12PO13S, L-C12PO4S, L-C16PO4S and L-C12PO11S) with different alkyl chain length and polypropylene oxide (PO) group against hydrocarbons were investigated. The mechanism responsible for the IFT reduction for extended surfactant has been detected. According to experimental results, we found that only when the size of hydrophobic part is enlarged to match the size of anionic head, the ultralow IFT will appear at optimized hydrophilic-lipophilic balance. For extended surfactants, with an increase of PO number, the curled PO chains occupy larger spaces at interface and match the size of anionic head. As a result, the ultralow IFT appears against alkanes when PO number is 13. The increase of alkyl chain length shows little effect on the size of hydrophobic part and ability of reducing IFT. Moreover, with an increase of n-alkane carbon number (ACN), the size of hydrophobic part increases as a function of ACN. Therefore, the increase of size of hydrophobic part compensates the decrease of adsorbed amount when ACN is higher than nmin value (the n-alkanes carbon number when the IFTs reach the minimum), which results in the “L” shape of IFT curve with a function of ACN.

Ultrafast vibrational dynamics of a solute correlates with dynamics of the solvent.

Two-dimensional infrared (2D-IR) spectroscopy is used to measure the spectral dynamics of the metal carbonyl complex cyclopentadienyl manganese tricarbonyl (CMT) in a series of linear alkyl nitriles. 2D-IR spectroscopy provides direct readout of solvation dynamics through spectral diffusion, probing the decay of frequency correlation induced by fluctuations of the solvent environment. 2D-IR simultaneously monitors intramolecular vibrational energy redistribution (IVR) among excited vibrations, which can also be influenced by the solvent through the spectral density rather than the dynamical friction underlying solvation. Here, we report that the CMT vibrational probe reveals solvent dependences in both the spectral diffusion and the IVR time scales, where each slows with increased alkyl chain length. In order to assess the degree to which solute-solvent interactions can be correlated with bulk solvent properties, we compared our results with low-frequency dynamics obtained from optical Kerr effect (OKE) spectroscopy-performed by others-on the same nitrile solvent series. We find excellent correlation between our spectral diffusion results and the orientational dynamics time scales from OKE. We also find a correlation between our IVR time scales and the amplitudes of the low-frequency spectral densities evaluated at the 90-cm-1 energy difference, corresponding to the gap between the two strong vibrational modes of the carbonyl probe. 2D-IR and OKE provide complementary perspectives on condensed phase dynamics, and these findings provide experimental evidence that at least at the level of dynamical correlations, some aspects of a solute vibrational dynamics can be inferred from properties of the solvent.

N-Butane, iso-Butane and 1-Butene Adsorption on Imidazolium-Based Ionic Liquids Studied with Molecular Beam Techniques.

The interaction of molecules, especially hydrocarbons, at the gas/ionic liquid (IL) surface plays a crucial role in supported IL catalysis. The dynamics of this process is investigated by measuring the trapping probabilities of n‐butane, iso‐butane and 1‐butene on a set of frozen 1‐alkyl‐3‐methylimidazolium‐based ILs [C n C1Im]X, where n=4, 8 and X−=Cl−, Br−, [PF6]− and [Tf2N]−. The decrease of the initial trapping probability with increasing surface temperature is used to determine the desorption energy of the hydrocarbons at the IL surfaces. It increases with increasing alkyl chain length n and decreasing anion size for the ILs studied. We attribute these effects to different degrees of alkyl chain surface enrichment, while interactions between the adsorbate and the anion do not play a significant role. The adsorption energy also depends on the adsorbing molecule: It decreases in the order n‐butane>1‐butene>iso‐butane, which can be explained by different dispersion interactions.