Nonideal behavior of alkylammonium salts in organic solvents at elevated temperatures

Osmometric vapor-pressure-lowering measurements on toluene, butylbenzene, chlorobenzene, and chloronaphthalene solutions of several secondary, tertiary, and quaternary long-chain (at least five carbon atoms per chain) alkylammonium chlorides, bromides, thiocyanates, nitrates, and perrhenates in the temperature range between 50–130°C show an appreciable amount of molecular association. The extent (number of aggregated units) and/or the degree (size of aggregated units) of aggregation decreases with the number of carbon atoms per chain, the polarity of the solvent, and the temperature, but increases with the size of the anions and the solute concentration. The data were treated quantitatively in terms of activity coefficients via the Gibbs-Duhem relation and also in terms of specific oligomer formation. The latter treatment shows the salts to form a dimer and one (exceptionally two) higher oligomer, for which the association constants have been calculated.     

Bacterial adhesion inhibition of the quaternary ammonium functionalized silica nanoparticles

Quaternary ammonium compounds have been considered as excellent antibacterial agents due to their effective biocidal activity, long term durability and environmentally friendly performance. In this work, 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride as a quaternary ammonium silane was applied for the surface modification of silica nanoparticles. The quaternary ammonium silane provided silica surface with hydrophobicity and antibacterial properties. In addition, the glass surface which was coated with the surface modified silica nanoparticles presented bacterial growth inhibition activity. For comparison of bacterial growth resistance, hydrophobic silane (alkyl functionalized silane) modified silica nanoparticles and pristine silica nanoparticles were prepared. As a result of bacterial adhesion test, the quaternary ammonium functionalized silica nanoparticles exhibited the enhanced inhibition performance against growth of Gram-negative Escherichia coli (96.6%), Gram-positive Staphylococcus aureus (98.5%) and Deinococcus geothermalis (99.6%) compared to pristine silica nanoparticles. These bacteria resistances also were stronger than that of hydrophobically modified silica nanoparticles. It could be explained that the improved bacteria inhibition performance originated from the synergistic effect of hydrophobicity and antibacterial property of quaternary ammonium silane. Additionally, the antimicrobial efficacy of the fabricated nanoparticles increased with decreasing size of the nanoparticles.     

Chromatographic retention behaviour, modelling and separation optimisation of the quaternary ammonium salt isometamidium chloride and related compounds on a range of reversed-phase liquid chromatographic stationary phases

This paper describes the reversed-phase liquid chromatographic behaviour of the trypanocidal quaternary ammonium salt isometamidium chloride and its related compounds on a range of liquid chromatographic phases possessing alkyl and phenyl ligands on the same inert silica. In a parallel study with various extended polar selectivity phases which possessed different hydrophobic/silanophilic (hydrogen bonding) activity ratios, the chromatographic retention/selectivities of the quaternary ammonium salts was shown to be due to a co-operative mechanism between hydrophobic and silanophilic interactions. The highly aromatic and planar isometamidium compounds were found to be substantially retained on stationary phases containing aromatic functionality via strong π-π interactions. The chemometric approach of principal component analysis was used to characterise the chromatographic behaviour of the isometamidium compounds on the differing phases and to help identify the dominant retention mechanism(s). Two-dimensional (temperature/gradient) retention modelling was employed to develop and optimise a rapid liquid chromatography method for the separation of the six quaternary ammonium salts within 2.5 min which would be suitable for bioanalysis using liquid chromatography-mass spectrometry. This is the first reported systematic study of the relationship between stationary phase chemistries and retention/selectivity for a group of quaternary ammonium salts.     

Surfing silica surfaces superciliously

The present mini-review summarizes the experience gathered by our group in developing different classes of novel quaternarized heterocyclic compounds able to modulate and reverse the electroendoosmotic flow (EOF) in a most peculiar manner. The first class comprises mono-salt compounds, with the determinant omega-iodoalkyl chains of different lengths (typically C4-C8), able to be adsorbed by silicas, at alkaline pH, and spontaneously alkylate ionised silanols, thus becoming covalently affixed to it. The second class is constituted by di-salt compounds, attached at the termini of an alkyl chain of variable lengths (here too, typically, C4-C8). This second class is unable to bind covalently silica surfaces, although, in thin-layer chromatography, it exhibits an extraordinary affinity for silica beads, contrary to the first one. On the basis of the strikingly different behaviour, structural rules are derived for the minimum requirements for general classes of amines to bind to silica walls and modify EOF. For compounds unable to bind covalently to the wall, the most important structural motif is two quaternary nitrogens spaced apart by a C4 chain: this seems to be the average distance (i.e., 0.8 nm) between two adjacent, ionized silanols for a snug fit. The other structural binding motif is the "hydrophobic decoration", i.e., the ratio of charged groups to alkyl residue in the various amines; amines with high levels of such alkane groups (i.e., with higher hydrophobicity), seem to bind more tenaciously to the wall, probably due to hydrophobic interaction not to the wall but among the amine derivatives themselves, when carpeting the silica.     

Supercritical fluid chromatography of metoprolol and analogues on aminopropyl and ethylpyridine silica without any additives

Metoprolol and a number of related amino alcohols and similar analytes have been chromatographed on aminopropyl (APS) and ethylpyridine (EPS) silica columns. The mobile phase was carbon dioxide with methanol as modifier and no amine additive was present. Optimal isocratic conditions for the selectivity were evaluated based on experiments using design of experiments. A central composite circumscribed model for each column was used. Factors were column temperature, back-pressure and % (v/v) of modifier. The responses were retention and selectivity versus metoprolol. The % of modifier mainly controlled the retention on both columns but pressure and temperature could also be important for optimizing the selectivity between the amino alcohols. The compounds could be divided into four and five groups on both columns, with respect to the selectivity. Furthermore, on the aminopropyl silica the analytes were more spread out whereas on the ethylpyridine silica, due to its aromaticity, retention and selectivity were closer. For optimal conditions the column temperature and back-pressure should be high and the modifier concentration low. A comparison of the selectivity using optimized conditions show a few switches of retention order between the two columns. On aminopropyl silica an aldehyde failed to be eluted owing to Schiff-base formation. Peak symmetry and column efficiency were briefly studied for some structurally close analogues. This revealed some activity from the columns that affected analytes that had less protected amino groups, a methyl group instead of isopropyl. The tailing was more marked with the ethylpyridine column even with the more bulky alkyl substituents. Plate number N was a better measure than the asymmetry factor since some analyte peaks broadened without serious deterioration of symmetry compared to homologues.     

Adsorption of alkyl polyglucosides on the solid/water interface: equilibrium effects of alkyl chain length and head group polymerization

The equilibrium adsorption behavior of two n-alkyl-beta-D-glucosides (octyl (C8G1) and decyl (C10G1)) and four n-alkyl-beta-D-maltosides (octyl (C8G2), decyl (C10G2), dodecyl (C12G2), and tetradecyl (C14G2)) from aqueous solution on a titania surface, as measured by ellipsometry, has been investigated. The main focus has been on the effect of changes in the alkyl chain length and headgroup polymerization, but a comparison with their adsorption on the silica/water and air/water interfaces is also presented. Some comparison with the corresponding adsorption of ethylene oxide surfactants, in particular C10E6 and C12E6, is given as well. For all alkyl polyglucosides, the maximum adsorbed amount on titania is reached slightly below the critical micelle concentration (cmc), where it levels off to a plateau and the amount adsorbed corresponds roughly to a bilayer. However, there is no evidence that this is the actual conformation of the surfactant assemblies on the surface, but the surfactants could also be arranged in a micellar network. On hydrophilic silica, the adsorbed amount is a magnitude lower than on titania, corresponding roughly to a layer of surfactants lying flat on the surface. A change in the alkyl chain length does not result in any change in the plateau molar adsorbed amount at equilibrium; however, the isotherm slope for the alkyl maltosides increases with increasing chain length. Headgroup polymerization on the other hand affects the adsorbed amount. The alkyl glucosides start adsorbing at lower bulk concentrations than the maltosides and equilibrate at higher adsorbed amounts above the cmc. When compared with the ethylene oxide (EO) surfactants, it is confirmed that the EO surfactants hardly adsorb on titania, since the measured changes in the ellipsometric angles are within the noise level. They do, however, adsorb strongly on silica.     

Rapid determination of bromide in seawater samples by capillary ion chromatography using monolithic silica columns modified with cetyltrimethylammonium ion

Monolithic silica capillary columns dynamically modified with quaternary ammonium ions were evaluated for the determination of bromide in seawater samples. A quaternary ammonium ion such as cetyltrimethylammonium ion was dynamically introduced onto monolithic silica surfaces. The first layer of the modifier was introduced by electrostatic interaction, whereas the second layer was introduced by hydrophobic interaction. The latter layer worked as the anion-exchange sites. The modified monolithic silica capillary columns could be used for rapid separation of inorganic anions. Separation of authentic mixture of five anions was achieved within a few minutes. The addition of small amount of the modifier in the eluent improved the repeatability of the retention time. Seawater samples could be directly injected onto the prepared capillary columns, and bromide could be determined to be 63 mg/L.     

硫脲基咪唑啉季铵盐的合成及其缓蚀作用

用戊酸、羊蜡酸、油酸、二乙烯三胺、氯化苄和硫脲为原料,合成了6种咪唑啉季铵盐化合物。 采用静态失重法和极化曲线法,比较了硫脲基烷基咪唑啉型季铵盐和烷基咪唑啉型季铵盐在80 ℃、1 mol/L的HCl溶液中对碳钢的缓蚀性能,研究了这两类缓蚀剂与无机阴离子和阴离子表面活性剂的协同作用。 结果表明,硫脲基烷基咪唑啉季铵盐类的缓蚀效果明显优于烷基咪唑啉季铵盐类,硫脲基羊脂酸咪唑啉缓蚀剂的缓蚀率可达98.3%。 当以羊脂酸、二乙烯三胺、氯化苄和硫脲为原料合成的硫脲基烷基咪唑啉型季铵盐化合物与I-质量比为1∶1复配时,缓蚀效果最佳,比单独使用硫脲基烷基咪唑啉季铵盐化合物的缓蚀率提高了1.5%。     

High-performance liquid chromatography on dynamically modified silica : II. Modification of various silica packings with cetyltrimethylammonium bromide

High-performance liquid chromatography on silica using eluents containing cetyltrimethylammonium (CTMA) bromide was investigated, and adsorption isotherms were determined for two silica packings of different pore diameter and surface area. It was found that about one CTMA ion was adsorbed per square nanometer of the silica surface at pH 7.5 and at a concentration of 6 mM CTMA bromide in 50% of methanol.Fourteen different silica packings were compared using a test mixture, and thirteen were found to exhibit the same selectivity towards the test mixture, which included acids, bases and non-ionic compounds, thus providing a chromatographic system that is largely independent of the origin of the column material.The retention mechanisms for the five test compounds are discussed.     

N-烷基-N,N-二(2-羟乙基)-N-甲基溴化铵与牛血清白蛋白的相互作用

用荧光光谱法在298K研究了Tris-HCl缓冲溶液(pH=7.1)中系列N-烷基-N,N-二(2-羟乙基)-N-甲基溴化铵(烷基链长为C12到C16)与牛血清白蛋白(BSA)的结合作用,考察了表面活性剂结构、BSA浓度对结合作用的影响,分别用Stern-Volmer方程、虚拟结合常数模型探讨了表面活性剂在浓度较低区域与BSA的作用机制.结果表明:三种季铵盐表面活性剂均对BSA内源荧光有猝灭作用,并导致其最大发射波长蓝移;表面活性剂的烷基链越长,Stern-Volmer猝灭常数和虚拟结合常数越大,表面活性剂与BSA的结合作用也越强.     

High-performance liquid chromatographic analysis of basic drugs on silica columns using non-aqueous ionic eluents. I. Factors influencing retention, peak shape and detector response

The use of silica columns together with non-aqueous ionic eluents provides a stable yet flexible system for the high-performance liquid chromatographic analysis of basic drugs. At constant ionic strength, eluent pH influences retention via ionisation of surface silanols and protonation of basic analytes, pKa values indicating the pH of maximum retention. At constant pH, retention is proportional to the reciprocal of the eluent ionic strength for fully protonated analytes and quaternary ammonium compounds. The addition of water up to 10% (v/v) has little effect on retention if the protonation of the analytes is unaffected. Thus, it is likely that retention is mediated primarily via cation exchange with surface silanols. However, additional factors must play a part with compounds such as morphine which give tailing peaks at acidic or neutral eluent pHs.     

Adsorption of alkyl trimethylammonium bromides at the air/water interface

A number of features of the adsorption of alkyl trimethylammonium bromides with nc=10,12,14, and 16 at the air/water interface were studied. First, the adsorption isotherms were calculated from experimental surface tension vs concentration curves by means of the Gibbs equation. Second, a novel method was used to estimate the adsorption free energy change. From the analysis of these data it was concluded that the hydrophobic driving force for the adsorption first increases with increasing adsorbed amount and then levels off in a plateau, which holds true for all four homologues. This peculiar behavior was interpreted by the formation of a thin liquid-like alkane film at the air/water interface once a certain adsorbed amount is exceeded. The hydrophobic contribution to the standard free energy change of adsorption was compared with those values previously determined for alkyl sulfate homologues. This comparison suggests that the alkyl trimethylammonium type surfactants behave as if their alkyl chain was approximately one methylene group shorter than those of the corresponding alkyl sulfates.     

Comparison of Anion-Exchange and Hydrophobic Interactions between Two New Silica-Based Long-Chain Alkylimidazolium Stationary Phases for LC

Two new silica-based long-chain alkylimidazolium stationary phases were prepared and characterized for their use in high-performance liquid chromatography. The stationary phases were both prepared by the reaction of chloropropyl silica with long-chain alkylimidazoles and were used to separate common inorganic anions. Hydrophobic interactions were also studied by the comparison of differential retention of various organic compounds. The alkyl chain length did not show an impact on the anion-exchange process but affected the hydrophobic interaction of the stationary phases.     

Microwave‐assisted synthesis of 1,3′‐diaza‐flavanone/flavone and their alkyl derivatives with antimicrobial activity

A simple environmentally friendly solid‐phase microwave‐assisted method was used to synthesis of the 1,3′‐diazaflavanone ( 2 ) and 1,3′‐diazaflavone ( 3 ) from the cyclization of 2′‐amino (E)‐3″‐azachalcone ( 1 ). Ten new N‐alkyl (C_5–12,14,15)‐substituted 1,3′‐diazaflavanonium bromides ( 2a–j ) were prepared from compound 2 with corresponding alkyl halides in acetonitrile under reflux. In addition, nine new N,N′‐dialkyl (C_5–12,14)‐substituted 1,3′‐diazaflavonium bromides ( 3a–i ) were also synthesized from compound 3 with corresponding alkyl halides using basic silica in acetonitrile. The antimicrobial activities of compounds 1–3 , 2a–j , and 3a–i were tested against Gram‐positive (G+) (Bacillus subtilis, Staphylococcus epidermidis, Staphylococcus aureus, and Enterococcus faecalis) and Gram‐negative (G?) (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus vulgaris, Salmonella typhimirium, Yersinia pseudotuberculosis, and Enterobacter cloaceae) microorganisms. They showed good antimicrobial activity against the Gram‐positive bacteria tested with the minimal inhibitory concentration values less than 7.8 μg/mL in most cases. The optimum length of the alkyl chain for better and broader activity is situated in the range of 9–12 carbon atoms in the series of compounds 2a–j and five to six carbon atoms in the series of compounds 3a–i . The nonalkylated compounds 1–3 were not effective, as were the ones alkylated with five or six C alkyl groups ( 2a and 2b ) and 8–13 C alkyl groups for N,N′‐dialkyl compounds ( 3c–3i ). The antimicrobial activity increased as the length of the alkyl substitution increased from 8 to 12 carbons in compounds 2a–j . However, antimicrobial activity decreased as the length of the alkyl substitution increased from 7 to 13 carbons in compounds 3c–i . J. Heterocyclic Chem., (2012)     

Macroporous silica in chromatography and immobilization of biopolymers

Macroporous silicas--silica gel (xerogels) and silochroms--are used for the chromatography of proteins and viruses and for the immobilization of several enzymes. The stabilization of silica by aluminum and zirconium salts was investigated. The hydrolytic stability of silica in alkaline media can be significantly increased by the substitution of aluminum ions for hydrogen atoms of the surface silanol groups. The aluminum modification also enhances the stability of glucose isomerase immobilized on silica. The maximum capacity for the immobilization of enzymes is found with silicas having average pore sizes of 5 to 10 times those of the protein globules. A thin layer of pyrolytic carbon deposited on silica enhances the retention of the adsorbed enzyme by the carrier. The original, aluminated and modified by γ-aminopropyltriethoxysilane and carbohydrates silica gels and silochroms are applicable in the liquid chromatography of acid and neutral proteins and in the purification of viruses. Adsorption and steric and ionic exclusion were observed in the chromatography of biopolymers.     

Piperazine quaternary diammonium salts as additives to background electrolytes in capillary zone electrophoresis

The differential behavior of five different quaternary mono- and diammonium salts, among the 18 investigated, in modulating the electroendoosmotic flow (EOF) and analyte separations in capillary zone electrophoresis is evaluated. It is found that quaternary diammonium salts with positive charges separated by more than four carbon atoms, while exhibiting a very strong affinity for chromatographic silica beads, to the point of exhibiting Rf values close to zero, display, on the contrary, a very poor affinity for the silica wall of capillaries. Compounds separated only by a C2 unit (i.e., 1,4-dialkyl-1,4-diazoniabicyclo[2,2,2,]octane, salts 17 and 18) show high Rf values due to strong ion pair association. The unique behavior of quaternary monoammonium salts possessing an iodinated alkyl (butyl or octyl) tail (i.e., 1, 6, and 7) is attributed to their ability to be covalently affixed to the silica wall via alkylation of ionized silanols at alkaline pH values. They thus strongly modulate and typically invert the EOF, even when not present in the background electrolyte. On the contrary, all diammonium salts, devoid of such alkyl tails, are unable to modulate the EOF and to prevent analyte binding to the silica wall, since they are rapidly removed from the wall by the voltage gradient. However, if added in small amount to the background electrolyte, they offer excellent separations of mixtures of very similar organic acids and prevent any interaction with the capillary wall.     

Dynamically modified silica — the use of bare silica in reversed-phase high-performance liquid chromatography

A new approach to reversed-phase high-performance liquid chromatography has been developed and investigated in some detail. Bare silica is used as the column packing material with an aqueous eluent containing a buffer, an organic solvent as the modifier and a long-chain quaternary ammonium ion. The eluent exhibits a high affinity to the silica surface at pH values above 5, thus, dynamically, forming a nonpolar stationary phase.     

Estimation of the dissociation constants for functional groups on modified and unmodified silica gel supports from the relationship between electroosmotic flow velocity and pH

Electroosmotic volume flow was directly observed in a simple instrument consisting of 1 cm long a home-made support, packed between two polyethylene frits in the polypropylene tube. Equations relating electroosmotic flow (EOF) velocity and pH for two functional groups on the surface of the solid materials were developed. With these equations, we can estimate the dissociation constants of two different kinds of functional groups on modified silica gel materials simultaneously. The dissociation constants of silanol groups, benzene sulfonic acid groups, and alkyl quaternary ammonium groups on the modified and unmodified silica gel supports were estimated. The estimated pK values of the silanol groups on the silica gel and modified silica gel surfaces are between 4.0 and 4.3. The estimated pK values of the benzene sulfonic acid groups and alkyl quaternary ammonium groups on the surface of the modified silica gel are 2.6 and 8.6, respectively.     

有机磷化合物的研究 VIII. 酸性有机磷化合物的气相色谱

Acidic organophosphorus compounds may be identified by GLC via their methyl esters, usually prepared from diazomethane. The wide applications of this mthod are, however, limited by the toxicity of diazomethane. Tetramethyl ammonium hydroxide in methanol solution reacted rapidly with acidic organophosphorus compounds at room temperature to form tetramethyl ammonium salts, which were then converted to the corresponding methyl esters by pyrolysis at 300-350 deg.C. A simple and convenient method for separation and identification of various types of acidic phosphates, phosphonates and phosphinates by GLC has been developed. The GLC behaviours of phosphoric acid dialkyl esters, mono-esters of phenyl-and cyclohexyl-phosphonic acids as well as dialkylphosphinic acids can be represented by corrected retention time (t'R) which correlates linearly with the number of carbon atoms of the alkyl groups in these organophosphorus compounds. The influence of number of carbon atoms and isomerization of alkyl group on t'R values and retention index (I) calculated by Kovats equation was discussed. As shown by our experiments the change in retention index (ΔI) in the homologous series of phosphoric acid dialkyl esters is nearly a constant on lengthening the alkyl group of the esters with methylene linkages.     

Silver-catalyzed benzylation and allylation reactions of tertiary and secondary alkyl halides with grignard reagents

Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers.