Superchaotropic Boron Clusters as Membrane Carriers for the Transport of Hydrophilic Cargos

Abstract

Design of membrane transporters is important in pharmaceutical drug delivery and bioimaging. Traditionally, the amphiphilic transport mechanism has governed the design of membrane carriers over the last 50 years. Recently, Montenegro, Nau and co‐workers discarded classical amphiphilic models and proposed a new transport principle based on the chaotropic effect. They utilized globular boron clusters as membrane carriers to transport a broad range of hydrophilic cargo. Herein, we highlight this recent pioneering work, which is a landmark for membrane transport.

NMR spectroscopy to study cyclodextrin-based host–guest assemblies with polynuclear clusters

“…These NMR nuclei should then be present in the cluster part of the hybrid assembly, providing additional characterization from the guest's point of view. For example, 31 30 In the binary system γ-CD : [P 2 W 18 O 62 ] 6− , the characteristic signal of the POM appeared similar to that of the free species at −12.3 ppm as an indication of labile dynamic {1 : 1} complex (Fig. 10).…”

“…24,25 Although the chaotropic effect was identified by Hofmeister in 1888 for small ions, 67 this property has been clearly associated with cluster anions only very recently and opens a new avenue for the design of CD-based smart supramolecular materials. 7,[31][32][33][34][35][36] The characterization of CD complexation by polynuclear clusters is of paramount importance to understand the driving forces of the phenomena involved in solutions such as selfassembly, host-guest inclusion, and aggregation process. Various analytical techniques such as calorimetric titration, 37 ESI-mass spectrometry, 38,39 X-ray scattering and diffraction, 1,40 circular dichroism, 21,36,41 voltammetry 41 and fluorescence spectroscopy 42 were applied to study the reactivity of CDs with different guest molecules.…”

Metallacarborane Cluster Anions of the Cobalt Bisdicarbollide-Type as Chaotropic Carriers for Transmembrane and Intracellular Delivery of Cationic Peptides

“…This potential utilization is being inspired by the recent observation of the same activity for dodecaborates. 14,15 The associated applications, ranging from drug delivery and fluorescence staining to therapy, appear particularly attractive, because of promising low (cell) toxicity studies that have already been conducted for COSANs. 3,34,36,42,45−51 Note that membrane carrier activity can be studied in both artificial liposomal model membranes and natural cellular systems, which facilitates systematic physicochemical investigations of structure−activity relationships.…”

“…Boron-containing compounds have application potential in pharmaceutical chemistry, − with boron neutron capture therapy being the most prominent example . Recently, a new cell-biological as well as medicinal-chemical application line has been documented for icosahedral dodecaborates B 12 X 12 2– (X = H, Cl, Br, and I; Figure a), because their superchaotropic ionic character − enables their use as broadband membrane carriers, that is, they enable cellular uptake of a wide range of otherwise impermeable hydrophilic molecules, including amino acids, neurotransmitters, peptides, and drugs. , This, combined with their chemical inertness, ,− high water solubility, ,, and high biocompatibility, ,,,,, defines a new research area in chaotropic inorganic cluster chemistry. Accordingly, it is of interest to investigate how variations in the boron cluster structure and topology affect their chaotropic character and, thus, their potential membrane carrier activity.…”

“…However, while their ability to permeate (nondestructively) through artificial − and natural membranes, either in their free form or as fluorescent derivatives, , is known, their function as transmembrane carriers of biologically interesting targets (“cargos”) has not been investigated. This potential utilization is being inspired by the recent observation of the same activity for dodecaborates. , The associated applications, ranging from drug delivery and fluorescence staining to therapy, appear particularly attractive, because of promising low (cell) toxicity studies that have already been conducted for COSANs. ,,,,− Note that membrane carrier activity can be studied in both artificial liposomal model membranes and natural cellular systems, which facilitates systematic physicochemical investigations of structure–activity relationships. Toward this goal, we have studied the COSAN derivatives 1 – 6 . − (Figure e).…”