An ESI/MS study of the formation of ternary 25,27-bis(dihydroxy-phosphoryloxy) calixarene-metal ion-aminoacid complexes

Promises of anionic calix[n]arenes in life science: State of the art in 2023

Because they hold together molecules by means of non-covalent interactions - relatively weak and thus, potentially reversible - the anionic calixarenes have become an interesting tool for efficiently binding a large range of ligands - from gases to large organic molecules. Being highly water soluble and conveniently biocompatible, they showed growing interest for many interdisciplinary fields, particularly in biology and medicine. Thanks to their intrinsic conical shape, they provide suitable platforms, from vesicles to bilayers. This is a valuable characteristic, as so they mimic the biologically functional architectures. The anionic calixarenes propose efficient alternatives for overcoming the limitations linked to drug delivery and bioavailability, as well as drug resistance along with limiting the undesirable side effects. Moreover, the dynamic non-covalent binding with the drugs enables predictable and on demand drug release, controlled by the stimuli present in the targeted environment. This particular feature instigated the use of these versatile, stimuli-responsive compounds for sensing biomarkers of diverse pathologies. The present review describes the recent achievements of the anionic calixarenes in the field of life science, from drug carriers to biomedical engineering, with a particular outlook on their applications for the diagnosis and treatment of different pathologies.

Elucidating the mechanism of the considerable mechanical stiffening of DNA induced by the couple Zn2+/Calix[4]arene-1,3-O-diphosphorous acid

The couple Calix[4]arene-1,3-O-diphosphorous acid (C4diP) and zinc ions (Zn²⁺) acts as a synergistic DNA binder. Silicon NanoTweezer (SNT) measurements show an increase in the mechanical stiffness of DNA bundles by a factor of >150, at Zn²⁺ to C4diP ratios above 8, as compared to Zinc alone whereas C4diP alone decreases the stiffness of DNA. Electroanalytical measurements using 3D printed devices demonstrate a progression of events in the assembly of C4diP on DNA promoted by zinc ions. A mechanism at the molecular level can be deduced in which C4diP initially coordinates to DNA by phosphate-phosphate hydrogen bonds or in the presence of Zn²⁺ by Zn²⁺ bridging coordination of the phosphate groups. Then, at high ratios of Zn²⁺ to C4diP, interdigitated dimerization of C4diP is followed by cross coordination of DNA strands through Zn²⁺/C4diP inter-strand interaction. The sum of these interactions leads to strong stiffening of the DNA bundles and increased inter-strand binding.

Fluorescent calix[4]arene chemosensor for acidic and basic amino acids in pure aqueous media

A fluorescent calix[4]arene chemosensor 2 displays high sensitivity toward acidic and basic amino acids in aqueous media through multiple H-bond interactions.

Anionic calixarene-capped silver nanoparticles show species-dependent binding to serum albumins

The anionic calixarenes para-sulphonatocalix[4]arene and 1,3-di-O-phosphonatocalix[4]arene, have been used to cap silver nanoparticles. The binding of these functional particles with regard to various serum albumins (bovine serum albumin, human serum albumin, porcine serum albumin and sheep serum albumin) has been studied by variable temperature fluorescence spectroscopy. The quenching of the fluorescence of the proteins was shown to vary as a function of the anionic calixarene capping molecule and also as a function of the origin of the serum albumin. It is thus possible to discriminate between the different species.

A Zn2+ specific triazole based calix[4]arene conjugate (L) as a fluorescence sensor for histidine and cysteine in HEPES buffer milieu

A highly fluorescent Zn(2+) complex of the triazole linked salicyl-imino-thiophenyl conjugate of calix[4]arene, [ZnL] has been demonstrated to be a chemo-sensing ensemble for the recognition of His and Cys among the naturally occurring amino acids in HEPES buffer milieu. The recognition behaviour of the [ZnL] towards these amino acids has been shown on the basis of fluorescence, absorption and visual fluorescent colour changes. The species of recognition were shown by ESI MS titrations, AFM & TEM microscopy and cell studies.

Cd2+ complex of a triazole-based calix[4]arene conjugate as a selective fluorescent chemosensor for Cys

An N,N-Dimethylamine ethylimino-appended triazole-linked calix[4]arene conjugate, L, has been synthesized and characterized, and its Cd(2+) complex has been isolated and characterized. The structure of [CdL] was established by computational calculation using B3LYP/LANL2DZ. Time-dependent density functional theory calculations were performed to demonstrate the electronic properties of [CdL]. This highly fluorescing [CdL] has been used to recognize Cys selectively among the 20 naturally occurring amino acids. [CdL] exhibits a minimum detection limit of 58 ppb for Cys, with reusability and reversibility being imparted to the system during sensing. Thus, the sensing of Cys was well demonstrated using various techniques, viz., fluorescence, absorption, visual color change, electrospray ionization MS, (1)H NMR, and live cell imaging experiments.

Biochemistry of anionic calix[n]arenes

This review treats the biological properties of the various anionic calix[n]arenes, both as soluble forms and in the colloidal state. The complexation of these molecules with amino-acids, peptides and proteins is discussed, as is their interaction with model membranes. The complexations with various Active Pharmaceutical Ingredients as complexes, for tamoxifen as solid state and colloidal structures, are treated in depth. Two sections deal with the direct biological action of the calix[n]arenes and their use as biosensors. A final section deals with the toxicity, in reality the lack of toxicity of the calix[n]arenes.

An electrospray ionization tandem mass spectrometric study of p-tert-butylcalix[6]arene complexation with ammonium hydroxide, and ammonium and sodium ions

The formation of complexes involving p-tert-butylcalix[6]arene with neutral and charged species has been investigated by tandem mass spectrometry combined with electrospray ionization. Complexes of p-tert-butylcalix[6]arene with NH4+ ions were observed in the ratios 1:1, 2:1, and 3:1, together with the complexes of p-tert-butylcalix[6]arene with NH4OH and Na+ ions in the ratios 1:1:1, 2:1:1, and 3:1:1. A single 1:1 complex of p-tert-butylcalix[6]arene with Na+ ions was observed. In addition, a doubly charged complex of p-tert-butylcalix[6]arene with NH4OH, Na+, and NH4+ ions in the ratio 6:1:1:1 was observed. The identity of each complex was determined by mass analysis of product ions formed by the application of a declustering potential over the range 20-220 V and by observation of product ion mass spectra wherein the collision energy was varied from 5 to 50 eV. Fragmentation of the complexes is characterized by the facile loss of the ammonia molecule, sodium and ammonium ions, loss of neutral p-tert-butylcalix[6]arene, and successive neutral losses of C4H8 from the six tert-butyl groups in each p-tert-butylcalix[6]arene molecule.

Investigation of disulfonamide ligands derived from o-phenylenediamine and their Pb(II) complexes by electrospray ionization mass spectrometry

An electrospray ionization mass spectrometry (ESI-MS) method, in both positive and negative ion modes, was developed for characterization of disulfonamide ligands derived from o-phenylenediamine and their Pb(II) complexes. For the ligands, negative ion mode ESI-MS in methanolic solutions gave simple and easily interpretable mass spectra. However, the spectra of Pb complexes were not readily interpretable under the same conditions. Protonated ligands and their Pb(II) complexes were observed in methanolic solutions by ESI-MS in positive ion mode. The formation of Na(+), K(+), or NH(4) (+) adducts was also observed, complicating the mass spectra and decreasing the signal intensity. In order to optimize the detection of the ligands and the Pb complexes, a method was developed by adding NaOAc in the solutions. The presence of 0.2 mM NaOAc simplified the mass spectra of the ligands and the Pb complexes, and significantly increased sensitivity in both negative and positive ion modes. This modification makes ESI-MS in both modes suitable for characterization of sulfonamide ligands and their Pb complexes, thus providing a potentially powerful tool for evaluating formation of metal complexes and screening combinatorial ligand libraries.