New calixarene-bonded stationary phases in high-performance liquid chromatography: comparative studies on the retention behavior and on influences of the eluent

The chromatographic behavior of six calixarene-bonded stationary phases is reported. Varying analyte selectivities (i.e., for phenols, substituted aromatics, polycyclic aromatic hydrocarbons, barbituric acid derivatives, xanthines) exist as a function of the ring-size of the calix[n]arenes (n=4, 6, 8) and the substitution at the "upper rim" with para-tert.-butyl groups. Although eluents with unusually high proportions of water were used, a comparison with conventional reversed-phase (RP) columns shows a predominantly reversed-phase character with remarkable selectivities of these phases. The influences of several organic solvents on retention variations of solutes are compared for RP-C18, phenyl and calixarene phases.     

Synthesis and photochemical reaction of cyclic oligomers: Synthesis and photopolymerization of novel C‐methylcalix[4]resorcinarene and p‐alkylcalix[n]arene derivatives containing spiro ortho ether groups

New photoreactive calixarene derivatives containing spiro ortho ester groups (calixarenes 3a–3c ) were synthesized by the reaction of 2‐bromomethyl‐1,4,6‐trioxaspiro[4.4]nonane with 2,8,14,20‐tetramethyl‐4,6,10,12,16,18,22,24‐octakis(carboxymethoxy)calix[4]resorcinarene, 5,11,17,23,29,35‐hexamethyl‐37,38,39,40,41,42‐hexakis(carboxymethoxy)calix[6]arene, and 5,11,17,23,29,35,41,47‐octa‐tert‐butyl‐49,50,51,52, 53,54,55,56‐octakis‐(carboxymethoxy)calix[8]arene, which were prepared by the reaction of C‐methylcalix[4]resorcinarene, p‐methylcalix[6]arene, and p‐tert‐butylcalix[8]arene, respectively. The thermal stability of the obtained calixarene derivatives containing spiro ortho ester groups was examined with thermogravimetric analysis, and it was found that these calixarene derivatives had good thermal stability. The photoinitiated cationic polymerization of spiro ortho ester groups in calixarene derivatives 3a–3c was examined with certain photoacid generators in the film state. Interestingly enough, the reaction of calixarene derivatives did not proceed with only photoirradiation; however, the reaction proceeded smoothly when the photoirradiation was followed by heating. Furthermore, calixarene 3a , composed of a C‐methylcalix[4]resorcinarene structure, showed the highest photochemical reactivity in this reaction system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1293–1302, 2002     

Polycyclic aromatic hydrocarbons as test probes to investigate the retention behavior of 1,3‐alternate calix[4]arene silica‐bonded stationary phases

A series of polycyclic aromatic hydrocarbons (PAHs) of different size and shape has been used to characterize the chromatographic behavior of five calix[4]arene stationary phases in 1,3‐alternate conformation synthesized in our laboratory. The selection of linear, four‐ring nonlinear, and five‐ring PAHs gave data on selectivity changes across range of the calix[4]arene columns. Retention of the 12 aromatic solutes has been evaluated at various methanol contents in the mobile phase (70–100% v/v) and column temperatures (20–45°C). The thermodynamic parameters underlying the retention mechanisms revealed that each of the five calix[4]arene columns exhibited variation in selectivity and retention of PAHs caused by enthalpy and entropy effects. The calixarene stationary phases substituted with electron‐withdrawing groups exhibit enhanced selectivity toward PAHs in comparison to the rest of the investigated columns. The observed divergences are due to differences in solute–stationary phase interactions and originate in π–π and π‐electron transfer specific to the analytes and the type of calix[4]arene functionalization at the upper rim, as well as steric and sorption phenomena.     

Investigation of the retention mechanism of naphthol and benzenediol on calix[4]arene stationary phase based on quantum chemistry calculations

Calixarenes are macrocyclic oligomers having the shape of a conical vase. Their inner cavity can accommodate various guest molecules, i. e. form supramolecules. Thus, calixarenes can be employed to manipulate selectivity in separation sciences. The essential step of separation is the interaction between calixarene and analytes. Therefore, in the present work, the retention mechanisms of benzenediol and naphthol positional isomers on a calix[4]arene column were investigated. The optimized supramolecular structures showed that there exist hydrogen bonding and pi-pi interactions for benzenediol, and for naphthol the pi-pi interactions dominate. Thermodynamic results from quantum chemistry calculations using DFT-B3LYP/STO-3G** basis set were consistent with the retention behaviors of benzenediol and naphthol positional isomers on the calix[4]arene column. This work will provide theoretical support for the design of new calixarene stationary phases.     

Study of the Calix[4]resorcinarene--dopamine interactions in monolayers by measurement of pressure--area isotherms and Maxwell displacement currents

The mechanisms of interactions between calix[4]resorcinarene and dopamine in monolayers formed at the air-water interface were studied by analyzing their mechanical, thermodynamic, and electrical properties evaluated from measurements of pressure-area isotherms and Maxwell displacement currents (MDCs). An increased concentration of dopamine in the water subphase resulted in an increase in the area per calix[4]resorcinarene molecule, an increase in the collapse pressure, and a shift in the monolayer phase transitions from the gaseous to the liquid state and from the liquid to the solid state toward higher molecular areas. A contactless method of recording MDCs enabled the monitoring of changes in the charge state of the monolayer-constituting molecules and the determination of a relationship between the phase state of the monolayer and the structural transitions of calix[4]resorcinarene. The changes of the MDC recordings started already in the gaseous state of the monolayer. On the basis of MDC values, we determined the normal component of the dipole moment of calix[4]resorcinarene, as well as that of its complex with dopamine. The dipole moment reached a maximum value of 1040 mD in the region of the phase transition from the liquid to the solid state of the monolayer. The results obtained suggest that the binding of dopamine with calix[4]resorcinarene depends on the orientation of the calixarene molecules in the monolayer. The calix[4]resorcinarene-dopamine interactions were also quantified in terms of the excess of Gibbs free energy, thereby allowing the evaluation of the energy of the calix [4]resorcinarene-dopamine bond, which was in the range from 1.95 to 8.54 kJ/mol depending on the surface pressure. This value implies weak interactions between these molecules.     

Preparation and characterization of six calixarene bonded stationary phases for high performance liquid chromatography

Six calixarene bonded silica gel stationary phases were prepared and characterized by elemental analysis, infrared spectroscopy and thermal analysis. Their chromatographic performance was investigated by using PAHs, aromatic positional isomers and E- and Z-ethyl 3-(4-acetylphenyl) acrylate isomers as probes. Separation mechanism based on the different interactions between calixarenes and analytes were discussed. The chromatographic behaviors of those analytes on the calixarene columns were influenced by the supramolecular interaction including pi-pi interaction, space steric hindrance and hydrogen bonding interaction between calixarenes and analytes. Notably, the presence of polar groups (-OH, -NO(2) and -NH(2)) in the aromatic isomers could improve their separation selectivity on calixarene phase columns. The results from quantum chemistry calculation using DFT-B3LYP/STO-3G* base group were consistent with the retention behaviors of PHAs on calix[4]arene column.     

Preparation and study of two polysiloxanes with pendant hand-basket type calixarene stationary phases for capillary gas chromatography

In this study two novel pendant hand-basket type calixarene gas chromatography stationary phases were prepared by hydrosilylation of ω-undecenyloxymethyl dimethyl calix[4]-15C5 and ω-undecenyloxymethyl dimethyl calix[4]-18C6 with dichloromethane followed by condensation reaction with silanol-terminated polydimethylsiloxane. Important stationary phase properties of these two novel stationary phases such as column efficiency, polarity, and selectivity were examined and compared with those of ω-undecyloxymethyl-18-crown-6, 2,3-benzo-9-propyloxymethyl-15-crown-5 and 2,3-benzo-11-propyloxymethyl-18-crown-6. Excellent thermostability from 60 to 330°C with onset bleeding temperatures at 308°C have been found. The mechanism of specific selectivity for position isomers based on the calix[4]crown ether ring, the molecular size of the solute and its shape are discussed.     

Preparation and Evaluation of Calix[8]arene Bonded Silica Stationary Phase for High Performance Liquid Chromatography

In recent years, calix[n]arenes (n=4,5,6,7,8) as stationary phase have been introduced into the field of chromatography. In our previous works, we have synthesized, characterized and evaluated two different silica-bonded calix[n]arenes (n=4,6) stationary phase, on which the chromatographic behavior of PAHs, positional isomers,nucleosides and bases was investigated. In this paper we report the preparation of calix[8]arene bonded silica stationary phase, and characterization of its structure and chromatographic behavior.     

Separation of Positional Isomers on A,C- and A,D-Bridged Calix[6]arene as Stationary Phases in Capillary GC

A,C-Bridged (ACCX) and A,D-bridged isopropyldimethylsilylcalix[6]arene (ADCX) dissolved in OV-1701 were used as stationary phases in isothermal capillary gas chromatographic separation of some positional isomers. Retention factors and separation factors for the isomers were measured. The isomers investigated are well resolved on the two phases. Retention of all the solutes investigated is longer on ACCX than on ADCX. The longer retention on A,C-bridged calix[6]arene is probably due to extra inductive interactions of the solute molecule with the carbonyl moieties in the phase. Separation factors for closely eluting isomer pairs are similar on the two phases. This seems to indicate that the carbonyl moieties do not play an appreciable role in discriminating the isomer molecules on entering the cavity of the calixarene if the solute is retained by the inclusion process.     

Functional modification,self-assembly and application of calix[4]resorcinarenes

As a special subset of calix[4]arene, calix[4]resorcinarene is an excellent molecular platform which could be modified by introducing functional groups to multiple sites at the upper and lower rims. There are mainly three ways to build functionalized calix[4]resorcinarene derivatives: (1) modification on the C-2 sites of calix[4]resorcinarenes; (2) modification on the phenolic hydroxyl groups of calix[4]resorcinarenes; (3) modification on the bridging methylenes at lower rim of calix[4]resorcinarenes. Functionalized calix[4]resorcinarene derivatives play an important role in the development of self-assembly chemistry, among which hydrogen bonding and metal coordination are the two most common interactions to obtain multicomponent structures. Moreover, due to the excellent topological structures and various active substituents of functionalized calix[4]resorcinarene derivatives, their applications in various fields, such as nanoparticles, catalysts, fluorescent materials, and sensors, have been briefly presented in this paper.

     

Structural Characterization of l-proline and Morpholine Appended Chiral Calix[4]resorcinarene Molecules

Calix[4]resorcinarenes serve as host molecules for small guest molecules. Recently calixarenes have been appended to chiral molecules in an attempt to promote chiral recognition. To take advantage of both cavity host and chiral substituent properties the position of the chiral moiety is important. We report the synthesis and structural characterization of two calix[4]resorcinarene based molecules that have helical chirality in the solid state. The calix[4]resorcinarene 1 has chiral l-proline ethyl ester substituents positioned perpendicular to the cavity whereas the calix[4]resorcinarene 2 has morpholines positioned parallel to the cavity which extend the depth of the cavity. Compound 1 is one of the first compounds to show the position of chiral centers with respect to the calixarene cavity. 1H and 13C NMR spectroscopy indicate that the helical chirality of 2 is retained at low temperature in nonpolar solvents.     

对-叔丁基杯[8]芳烃键合固定相的制备及表征

合成了一种新的对-叔丁基杯[8]芳烃的高效液相色谱键合固定相,考察了多环芳烃、苯甲酸酯、邻苯二甲酸酯、苯的单官能团取代物在该键合相上的反相液相色谱保留行为,并以甲醇-水作为流动相分离了氨基苯酚的邻、间、对取代位置异构体．研究结果发现,该键合相具有明显的反相特征,并讨论了可能的分离机理．     

Characterization of 1,3-alternate calix[4]arene-silica bonded stationary phases and their comparison to selected commercial columns by using principal component analysis

Twelve calix[4]arene stationary phases in 1,3-alternate conformation, synthesized in the authors’ laboratory, were characterized in terms of their surface coverage, hydrophobic selectivity, aromatic selectivity, shape selectivity, hydrogen bonding capacity and ion-exchange capacity. The set of tests commonly used for evaluation of commercially available stationary phases was applied to assess fundamental chromatographic properties of the calixarene phases. The new calixarene phases were compared to each other, to Caltrex and LiChrosorb C-18 columns. Principal component analysis has been used to provide comparison between 1,3-alternate calix[4]arene phases and commercially available phenyl, fluorophenyl and fluoroalkyl columns.     

A sulfonated calix[4]resorcinarene with l-pipecolinic acid groups as a water-soluble chiral NMR solvating agent

A water-soluble calix[4]resorcinarene containing l-pipecolinic acid groups is investigated as a chiral NMR solvating agent for aromatic-containing substrates. The substrates form complexes by insertion of the aromatic ring into the cavity of calix[4]resorcinarene. Compounds with phenyl, naphthyl, indole, indoline and pyridyl rings were investigated. The substrates also have ammonium or carboxylate functional groups. The effectiveness of the calix[4]resorcinarene with l-pipecolinic acid groups is compared to similar reagents with proline, hydroxyproline, and α-methylproline moieties that have previously been reported. The derivative with l-pipecolinic acid usually produces better enantiomeric discrimination compared to previous calix[4]resorcinarene reagents.     

硅烷基咪唑双三氟甲烷磺酰亚胺离子液体气相色谱固定相的性能评价

以双三氟甲烷磺酰亚胺离子([NTf₂]^-)为阴离子,合成阳离子烷基取代不同(C1、C2和C4)的硅烷基咪唑离子液体,以其为固定相制备气相色谱填充柱。 硅烷基咪唑离子液体为强极性固定相;阳离子结构影响固定相的热稳定性、极性和分离性能。 在这些离子液体固定相中,1-丁基-3-[(3-三甲氧基硅基)-丙基]咪唑双三氟甲烷磺酰亚胺([PBIM]NTf₂)对Grob试剂分离性能较好。 利用溶剂化作用参数模型,评价[PBIM]NTf₂固定相特性,研究固定相-组分分子之间相互作用机制;同时考察[PBIM]NTf₂色谱柱对不同类型化合物的分离性能。 结果表明,[PBIM]NTf₂固定相主要作用力是氢键碱性和偶极作用,对烷烃、醇、酯和胺等不同类型的样品组分表现出良好的分离能力。     

Supramolecular systems based on aminomethylated calix[4]resorcinarene and a cationic surfactant: Catalysts of the hydrolysis of esters of phosphorus acids

Kinetics of alkaline hydrolysis of 4-nitrophenyl esters of tetracoordinated phosphorus acids in micellar solutions of aminomethylated calix[4]resorcinarene containing sulfonatoethylene groups on the lower rim of the macrocycle, 4-aza-1-hexadecyl-azoniabicyclo[2.2.2]octane bromide and their mixtures was investigated spectrophotometrically. It is established that the catalytic effect of aggregates depends on the concentration of calixarene and surfactants, pH, presence of lanthanum salt and reaches more than two orders of magnitude. The parameters of the catalyzed reactions and their dependence on the composition are determined.     

Development of a decaaza‐cyclophane stationary phase for high‐performance liquid chromatography

A new stationary phase for high‐performance liquid chromatography was prepared by covalently bonding a heteroatom‐bridged cyclophane onto silica gel using 3‐aminopropyltriethoxysilane as the coupling reagent. The structure of the new material was characterized by infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The linear solvation energy relationship method was successfully employed to evaluate the new phase with a set of 25 solutes, and compared with octadecylsilyl and p‐tert‐butyl‐calix[4]arene bonded stationary phases. The retention characteristics of the new phase are similar to the octadecylsilyl and conventional calixarene phases, and it also has distinctive features. In addition, the chromatographic behavior of the phase was illustrated by eluting alkylbenzenes and inorganic anions in the reversed‐phase mode and anion‐exchange mode, respectively. Thus, multi‐interaction mechanisms and mixed‐mode separation of the new phase can very likely guarantee its promising application in the analysis of complex samples. The column has been successfully employed for the analysis of triazines in milk, and it is demonstrated to be a competitive alternative analytical method for the determination of triazine herbicide residues.     

Chromatographic behavior of a new hybrid type RP material containing silica bonded 1,3‐alternate 25,27‐bis‐[cyanopropyloxy]‐26,28‐bis‐[3‐propyloxy]‐calix[4]arene

A novel 1,3‐alternate 25,27‐bis‐[cyanopropyloxy]‐26,28‐bis‐[3‐propyloxy]‐calix[4]arene‐bonded silica gel stationary phase (CalixPrCN) was prepared and its structure was confirmed by ATR‐FTIR spectroscopy and elemental analysis. The CalixPrCN phase was characterized in terms of its surface coverage, hydrophobic selectivity, aromatic selectivity, shape selectivity, hydrogen bonding capacity, residue metal content, and silanol activity based on Tanaka, Lindner, and SMR 870 test protocols. The effect of the acetonitrile content on the retention and selectivity of the selected neutral, basic, and acidic solutes was studied. The neutral and acidic analytes exhibited classical RP behavior, in which retention time decreases with increasing acetonitrile content. In contrast, basic analytes showed an increase in retention at low and high percentages of acetonitrile, forming “U‐shaped” retention profiles. The new calixarene phase was compared with previously reported 1,3‐alternate 25,27‐bis‐[propyloxy]‐26,28‐bis‐[3‐propyloxy]‐calix[4]arene stationary phase and commercial cyanopropyl column. The results indicate that the CalixPrCN stationary phase behaves like RP packing; however, inclusion complex formation, dipole–dipole, and π–π interactions seem to be involved in the separation process. The selectivity of this phase was demonstrated in separation of polynuclear aromatic hydrocarbons, non‐steroidal anti‐inflammatory drugs, and sulfonamides as analytes.     

Selectivity of calixarene‐bonded silica phases in HPLC: Description of special characteristics with a multiple term linear equation at different methanol concentrations

Retention and selectivity characteristics of different calixarene‐, resorcinarene‐ and alkyl‐bonded stationary phases are examined by analyzing a set of test solutes covering the main interactions (hydrophobic, steric, ionic, polar) that apply in HPLC. Therefore Dolan and Snyder's multiple term linear equation has been adapted to fit the properties of calixarene‐bonded columns. The obtained parameters are used to describe retention and selectivity of the novel Caltrex^® phases and to elucidate underlying mechanisms of retention. Here, differences of stationary phase characteristics at different methanol concentrations in the mobile phases are examined. Both selectivity and retention were found to depend on the methanol content. Differences of these dependencies were found for different stationary phases and interactions. The differences between common alkyl‐bonded and novel calixarene‐bonded phases increase with increasing methanol content.     

Liquid chromatographic behavior of two alanine‐substituted calix[4]arene‐bonded silica gel stationary phases

Two new kinds of alanine‐substituted calix[4]arene stationary phases of 5,11,17,23‐p‐tert‐butyl‐25,27‐bis(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐26,28‐dihyroxycalix[4]arene‐bonded silica gel stationary phase (BABS4) and 5, 11, 17, 23‐p‐tert‐butyl‐25,26,27,28‐tetra(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐calix[4]arene‐bonded silica gel stationary phase (TABS4) were prepared and characterized in the present study. They were compared with each other and investigated in terms of their chromatographic performance by using polycyclic aromatic hydrocarbons, disubstituted benzene isomers, and mono‐substituted benzenes as solute probes. The results indicated that both BABS4 and TABS4 exhibited multiple interactions with analytes. In addition, the commonly used Tanaka characterization protocol for the evaluation of commercially available stationary phases was applied to evaluate the properties of these two new functionalized calixarene stationary phases. The Tanaka test results were compared with Zorbax Eclipse XDB C₁₈ and Kromasil phenyl columns, respectively. BABS4 has stronger hydrogen‐bonding capacity and ion‐exchange capacity than TABS4, and features weaker hydrophobicity and hydrophobic selectivity. Both of them behave similarly in stereoselectivity. Both BABS4 and TABS4 are weaker than C₁₈ and phenyl stationary phases in hydrophobicity and hydrophobic selectivity.