Preparation and evaluation of 1,3-alternate 25,27-bis-(pentafluorobenzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene-bonded silica gel high performance liquid chromatography stationary phase

Unexpected Role of pH and Microenvironment on the Antioxidant and Synergistic Activity of Resveratrol in Model Micellar and Liposomal Systems

Experimental and theoretical studies indicate that resveratrol (RSV, dietary polyphenol that effectively reduces cellular oxidative stress) is a good scavenger of hydroxyl, alkoxyl, and peroxyl radicals in homogeneous systems. However, the role of RSV as a chain-breaking antioxidant is still questioned. Here, we describe pH dependent effectiveness of RSV as an inhibitor of peroxidation of methyl linoleate in Triton X-100 micelles and in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes, with the best effectiveness at pH 6 (stoichiometric factors, n, are 4.9 and 5.6, and the rate constants for reaction with peroxyl radicals, k_inh, are 1200 and 3300 M^–1 s^–1 in micellar and liposomal systems, respectively). We propose the mechanism in which RSV-derived radicals are coupled to dimers with recovered ability to trap lipidperoxyl radicals. The formation of such dimers is facilitated due to increased local concentration of RSV at the lipid–water interface. Good synergy of RSV with α-tocopherol analogue in micelles and liposomes is in contrast to the previously reported lack of synergy in non-polar solvents; however, the increased persistency of tocopheroxyl radicals in dispersed lipid/water systems and proximal localization of both antioxidants greatly facilitate the possible recovery of α-TOH by RSV.

Recent progress to construct calixarene-based polymers using covalent bonds: synthesis and applications

The combination of supramolecular chemistry and polymer sciences creates a great possibility to afford calixarene-based polymers offering unique features and applications. The enhancement of calixarene's versatility in this manner has made chemists better able to achieve different objectives in host-guest chemistry. The calixarene-based polymers can be divided into covalent polymers and supramolecular polymers regarding the interactions. Although there are several studies available on the calixarene-based supramolecular polymers, there is a paucity of studies on the calixarene-based covalent polymers. In this paper, the most recent developments and applications of the calixarene-based covalent polymers in the last two decades have been reviewed. We have particularly focused on the polymers, including those where the calixarene molecules have been used as macromonomers and polymerize through covalent bonds. Moreover, covalent polymers or solid supports functionalized with calixarenes are highlighted as well.

Emerging or Underestimated Silica-Based Stationary Phases in Liquid Chromatography

Several newly synthesized or forgotten silica-based stationary phases proposed for liquid chromatography are described, including non-endcapped, short-chain alkyl phases; hydrophilic and polar-endcapped stationary phases; polar-embedded alkyl phases; long-chain alkyl phases. Stationary phases with aromatic, cyanopropyl, diol and aminopropyl functionalities are also reviewed. Stationary phases of particular interest are biomolecular materials - based on immobilized cholesterol, aminoacids, peptides, proteins or lipoproteins. Packing materials involving macrocyclic chemistry (crown ethers; calixarenes; aza-macrocycles; oligo-and polysaccharides including these of marine origin - chitin- or chitosan-based; macrocyclic antibiotics) are discussed. Since many stationary phases developed for one type of applications (e.g. chiral separation) have been found useful in solving other analytical problems (e.g. drug's plasma protein binding ability), it seemed reasonable to discuss particular chemistries behind the stationary phases presented in this review rather than specific types of interactions or chromatographic modes.

Preparation and evaluation of a chiral HPLC stationary phase based on cone calix[4]arene functionalized at the upper rim with l-alanine units

Here we report a new chiral stationary phase (CSP) immobilized on silica gel based on cone calix[4]arene functionalized at the upper rim with two l-alanine units as new chiral selector that has been used in high-performance liquid chromatography. The CSP was prepared by covalently bonding the allyl groups at the lower rim of calix[4]arene to silica gel by thiol-ene click chemistry reaction. Elemental analysis of the CSP showed that 120 μmol of chiral selector bonded per gram of silica gel. 1-Hexene was used for end-capping of unreacted mercapto groups on silica gel. Since the CSP is chemically bonded to the silica, it can be used in the normal-phase and reversed-phase mode and with halogenated solvents as mobile phases, if desired. The chromatographic performance of the CSP was evaluated in the enantioseparation of the 3,5-dinitrobenzoyl derivatives of some amino acids, diclofop-methyl and dl-mandelic acid.

Chromatographic separation of clenbuterol by bonded phases bearing nano-baskets of p-tert-calix[4]-1,2-crown-3, -crown-4, -crown-5 and -crown-6

BACKGROUND

Clenbuterol (salbutamol), which increases muscle mass and decreases adipose tissue, is misused as a nutrient-repartitioning agent in livestock. In this paper a new sensitive method for determining clenbuterol in livestock is presented. The novelty of this approach is the separation and determination of salbutamol enantiomers with marked quantitative merits.

RESULTS

Four proton di-ionisable Nano-baskets, namely 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26-bis(carboxy-methoxy)calix[4]arene-27,28-crown-3, -crown-4, -crown-5 and -crown-6 in the cone conformation, were synthesised and used to prepare bonded phases for high-performance liquid chromatography separation. The new synthesised bonded phases were characterised and optimised. The bonding interactions of solute/bonded phases were examined and the main interactions are reported.

CONCLUSION

The clenbuterol levels in six samples of livestock meat (pork, pork casing, beef, beef casing, mutton and mutton casing) were analysed and the results revealed that for the best bonded phases the limits of detection and quantitation were 0.06 and 0.2 µg mL(-1) respectively.

Preparation and chromatographic performance of calix[4]crown-5 macrocycle-bonded silica stationary phase

A new calix[4]crown-5 macrocycle-bonded silica stationary phase (CL-CIMS) was prepared and applied at the same time to develop a chromatographic procedure to separate aromatic amines, phenols and drugs in this study. The chromatographic behaviors of the prepared stationary phase for these analytes were studied and compared with those of ODS (octadecylsilane). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were investigated. Some aromatic amines, phenols or drugs on CL-CIMS were successfully separated. The results show that CL-CIMS exhibits high selectivities for the above analytes in high aqueous mobile phases and a bright prospect in routine, fast separation of aromatic amines, phenols and drug compounds. From chromatographic data, it can be concluded that hydrophobic interaction is mainly responsible for the retention behavior as well as hydrogen-bonding interaction, π-π and dipole-dipole interaction.