Recent Advances in Bioactive Artificial Ionophores

Several life-threatening diseases, also known as 'Channelopathies' are linked to irregularities in ion transport proteins. Significant research efforts have fostered the development of artificial transport systems that facilitates to restore the functions of impaired natural transport proteins. Indeed, a few of these artificial ionophores demonstrate the rare combination of transmembrane ion transport and important biological activity, offering early promises of suitability in 'channel replacement therapy'. In this review, structural facets and functions of both cationophores and anionophores are discussed. Ionophores that are toxic to various bacteria and yeast, could be exploited as antimicrobial agent. Nevertheless, few non-toxic ionophores offer the likelihood of treating a wide range of genetic diseases caused by the gene mutations. In addition, their ability to disrupt cellular homeostasis and to alter lysosomal pH endow ionophores as promising candidates for cancer treatment. Overall, critically outlining the advances in artificial ionophores in terms of in vitro ion transport, possible modes of action and biological activities enables us to propose possible future roadmaps in this research area.

Sequence-function relationship within water-soluble Peptoid Chelators for Cu2

Chelation of Cu²⁺ by synthetic molecules is an emerging therapeutic approach for treating several illnesses in human body such as Wilson disease, cancer and more. Among synthetic metal chelators, those based on peptoids - N-substituted glycine oligomers - are advantageous due to their structural similarity to peptides, ease of synthesis on solid support and versatile controlled sequences. Tuning peptoid sequences, via systematically changing at least one side chain, can facilitate and control their function. Along these lines, this work aims to explore the role of the non-coordinating side chain within peptoid chelators in order to understand the factors that control the selectivity of these chelators to Cu²⁺ in water medium. To this aim, a set of peptoid trimers having a pyridine group at the acetylated N-terminal, a 2,2'-bipyridine group at the second position and a non-coordinating group at the C-terminus, where the latter is systematically varied between aromatic, aliphatic, chiral or non-chiral, were investigated as selective chelators for Cu²⁺. The effect of the position of the non-coordinating group on the selectivity of the peptoid to Cu²⁺ was also tested. Based on extensive spectroscopic data, we found that the choice of the non-coordinating group along with its position dramatically influences the selectivity of the peptoids to Cu²⁺. We showed that peptoids having bulky chiral groups at the C-terminus enable high selectivity to Cu²⁺. We further demonstrated the ability of one of the selective chelators to remove Cu²⁺ from the natural copper binding protein metallothionein in HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) buffer medium.

Solid-State Conformational Flexibility at Work: Energetic Landscape of a Single Crystal-to-Single Crystal Transformation in a Cyclic Hexapeptoid

We describe the energetic landscape beyond the solid-state dynamic behavior of a cyclic hexapeptoid decorated with four propargyl and two methoxyethyl side chains, namely, cyclo-(Nme-Npa₂)₂, Nme = N-(methoxyethyl)glycine, Npa = N-(propargyl)glycine. By increasing the temperature above 40 °C, the acetonitrile solvate form 1A starts to release acetonitrile molecules and undergoes a reversible single crystal-to-single crystal transformation into crystal form 1B with a remarkable conformational change in the macrocycle: two propargyl side chains move by 113° to form an unprecedented "CH-π zipper". Then, upon acetonitrile adsorption, the "CH-π zipper" opens and the crystal form 1B transforms back to 1A. By conformational energy and lattice energy calculations, we demonstrate that the dramatic side-chain movement is a peculiar feature of the solid-state assembly and is determined by a backbone conformational change that leads to stabilizing CH···OC backbone-to-backbone interactions tightening the framework upon acetonitrile release. Weak interactions as CH···OC and CH-π bonds with the guest molecules are able to reverse the transformation, providing the energy contribution to unzip the framework. We believe that the underlined mechanism could be used as a model system to understand how external stimuli (as temperature, humidity, or volatile compounds) could determine conformational changes in the solid state.

Cyclic hexapeptoids with N-alkyl side chains: solid-state assembly and thermal behaviour

The solid state assembly of two cyclic hexapeptoids decorated respectively with five and six carbon N-alkyl side chains is analyzed by X-ray diffraction, intermolecular energies and lattice energy calculations.

Peptoids as tools and sensors

A review of molecular tools and sensors assembled on N-substituted glycine, or α-peptoid, oligomers between 2013 and November 2018 with the following sections: (a) Peptoids as crystal growth modifiers, (b) Peptoids as catalysts, (c) Ion and molecule sequestration and transport, (d) Peptoid sensors, (e) Macromolecule recognition, (f) Cellular transporters, (g) Medical imaging, (h) Future direction and (i) Summary and outlook. Peptoids are a promising class of peptide mimic making them an excellent platform for functional molecule preparation. Attributes of peptoid oligomers include: (a) the ease of precise sequence definition and mono-dispersity; (b) access to a vast chemical space within simple and repeating chemical preparative steps and (c) thermal, chemical and biological stability all lending support for their application in a number of areas, with some that have been realised to date. The peptoid tool and sensor examples selected have realised practical utility. They serve to illustrate the rapidity of new insight that can generate in many disparate areas of science and technology, enabling the quick assembly of design criteria for efficient peptoid molecular tools and sensors.