Applications of nano-baskets in drug development: high solubility and low toxicity

New Supramolecular Hypoxia-Sensitive Complexes Based on Azo-Thiacalixarene

Hypoxia accompanies many human diseases and is an indicator of tumor aggressiveness. Therefore, measuring hypoxia in vivo is clinically important. Recently, complexes of calix[4]arene were identified as potent hypoxia markers. The subject of this paper is new hypoxia-sensitive host-guest complexes of thiacalix[4]arene. We report a new high-yield synthesis method for thiacalix[4]arene with four anionic carboxyl azo fragments on the upper rim (thiacalixarene L) and an assessment of the complexes of thiacalixarene L with the most widespread cationic rhodamine dyes (6G, B, and 123) sensitivity to hypoxia. Moreover, 1D and 2D NMR spectroscopy data support the ability of the macrocycles to form complexes with dyes. Rhodamines B and 123 formed host-guest complexes of 1:1 stoichiometry. Complexes of mixed composition were formed with rhodamine 6G. The association constant between thiacalixarene L and rhodamine 6G is higher than for other dyes. Thiacalixarene L-dye complexes with rhodamine 6G and rhodamine B are stable in the presence of various substances present in a biological environment. The UV-VIS spectrometry and fluorescence showed hypoxia responsiveness of the complexes. Our results demonstrate that thiacalixarene L has a stronger binding with dyes compared with the previously reported azo-calix[4]arene carboxylic derivative. Thus, these results suggest higher selective visualization of hypoxia for the complexes with thiacalixarene L.

Membrane-Active Antibacterial Agents Based on Calix[4]arene Derivatives: Synthesis and Biological Evaluation

Bacteria have developed increasing resistance to currently used antimicrobial agents. New classes of antimicrobial drugs are urgently required to fight drug-resistant pathogens. Here, we designed and synthesized a series of calix[4]arene derivatives as antibacterial agents by biomimicking the structural properties and biological functions of antibacterial peptides. After introducing cationic hydrophilic moieties and preliminary structural optimization, we obtained a lead compound (16) that exhibited excellent antibacterial activity against Gram-positive bacteria, low toxicity toward mammalian cells and poor hemolytic activity. The antibacterial mechanism studies showed that compound 16 can destroy bacterial cell membrane directly, leading to bacterial death and a low tendency to develop bacterial resistance.

A General Hypoxia-Responsive Molecular Container for Tumor-Targeted Therapy

Enhanced drug delivery can improve the therapeutic efficacy of drugs and help overcome side effects. However, many reported drug-delivery systems are too complex and irreproducible for practical use. In this work, the design of a hypoxia-responsive molecular container based on calixarene, called CAC4A, which presents a significant advance in practical, hypoxia-targeted drug-delivery, is reported. CAC4A enables a wide variety of clinical drugs to be quantitatively loaded to improve their solubility and stability, as well as enable the administration of reduced doses. Furthermore, as a result of its azo functional groups, which are sensitive to reduction within a hypoxic environment, it is possible to achieve tumor-targeted drug-release with reduced side effects. CAC4A fulfils all essential requirements for a drug-delivery system in addition to multiple advantages, including facile preparation, well-defined molecular weight, and structure, and universal applicability. Such features collectively enable supramolecular prodrugs to be formulated simply and reproducibly, with potential for bench-to-bedside translation. Moreover, CAC4A is amenable to other therapy modalities and can be facilely decorated with functional groups and hybridized with nanomaterials, providing ample possibilities for its role in future drug-delivery systems.

Carrier-mediated extraction: Applications in extraction and microextraction methods

The present review is mainly focused on the overview of carrier mediated extraction (principles and applications) being reported over the last two decades and discusses the extraction process through carriers in various extraction methods such as Bulk liquid membranes, supported liquid membranes, emulsion liquid membranes and polymer inclusion membranes. Several types of carriers such as neutral, anionic, cationic, macrocyclic and supramulecular carriers are discussed. Also their application for metal, anions, drugs and environmental compounds are investigated. Carriers have been demonstrated to be useful for the selective extraction and recovery of numerous cations and anions enhancing the extraction properties of traditional solvent extraction and ion-exchange processes. Several types of carriers have different transport mechanisms. In these mechanisms, transport configurations are addressed and emphasized and the detailed information on the type of carrier are presented along with their specific separation modes. The performance of different carriers in terms of selectivity as well as efficiency are also discussed. Finally, the application of different carriers for the extraction of various compounds are compared and reviewed. To our best knowledge no reviews have been published on carrier-mediated extraction methods.

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.

Extraction of s-block metals by nano-baskets of calix[4]crown-3

Three kinds of nano-baskets including 1,2-alternate and cone conformers of di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 and the cone conformer of p-tert-butylcalix[4]arene-1,2-thiacrown-3 were synthesized and the competitive solvent extractions of alkali and alkaline earth metal cations were studied. The novelty of this study is including three binding units of the calixarene’s bowl, the crown ether’s ring, and electron-donor ionizable moieties in a unique scaffold, in which their sizes were selected based upon their complexation ability to show equal binding tendency towards the cations. The objective of this work is to assess the extraction efficiency, selectivity, and pH1/2 of such complexes. The results of solvent extraction experiments indicated that these compounds were effective extractants of alkali and alkaline earth metal cations. Their selectivities were greatly influenced by the acidity of the solution and the conformations of the calixcrown. One conformer was highly selective to Na+ and the other to Ba2+ in acidic and basic solutions, respectively.