Anion complexation and transport by isophthalamide and dipicolinamide derivatives: DNA plasmid transformation in E. coli

Small Molecule-Based Highly Active and Selective K+ Transporters with Potent Anticancer Activities

We report here a novel class of cation transporters with extreme simplicity, opening a whole new dimension of scientific research for finding small molecule-based cation transporters for therapeutic applications. Comprising three modular components (a headgroup, a flexible alkyl chain-derived body, and a crown ether-derived foot for ion binding), these transporters efficiently (EC₅₀ = 0.18-0.41 mol % relative to lipid) and selectively (K⁺/Na⁺ selectivity = 7.0-9.5) move K⁺ ions across the membrane. Importantly, the most active (EC₅₀ = 0.18-0.22 mol %) and highly selective series of transporters A12, B12, and C12 concurrently possess potent anticancer activities with IC₅₀ values as low as 4.35 ± 0.91 and 6.00 ± 0.13 μM toward HeLa and PC3 cells, respectively. Notably, a mere replacement of the 18-crown-6 unit in the structure with 12-crown-4 or 15-crown-5 units completely annihilates the cation-transporting ability.

From Interaction to Function in DNA-Templated Supramolecular Self-Assemblies

DNA-templated self-assembly represents a rich and growing subset of supramolecular chemistry where functional self-assemblies are programmed in a versatile manner using nucleic acids as readily-available and readily-tunable templates. In this review, we summarize the different DNA recognition modes and the basic supramolecular interactions at play in this context. We discuss the recent results that report the DNA-templated self-assembly of small molecules into complex yet precise nanoarrays, going from 1D to 3D architectures. Finally, we show their emerging functions as photonic/electronic nanowires, sensors, gene delivery vectors, and supramolecular catalysts, and their growing applications in a wide range of area from materials to biological sciences.

Molecular architectonics of DNA for functional nanoarchitectures

DNA is the key biomolecule central to almost all processes in living organisms. The eccentric idea of utilizing DNA as a material building block in molecular and structural engineering led to the creation of numerous molecular-assembly systems and materials at the nanoscale. The molecular structure of DNA is believed to have evolved over billions of years, with structure and stability optimizations that allow life forms to sustain through the storage and transmission of genetic information with fidelity. The nanoscale structural characteristics of DNA (2 nm thickness and ca. 40-50 nm persistence length) have inspired the creation of numerous functional patterns and architectures through noncovalent conventional and unconventional base pairings as well as through mutual templating-interactions with small organic molecules and metal ions. The recent advancements in structural DNA nanotechnology allowed researchers to design new DNA-based functional materials with chemical and biological properties distinct from their parent components. The modulation of structural and functional properties of hybrid DNA ensembles of small functional molecules (SFMs) and short oligonucleotides by adapting the principles of molecular architectonics enabled the creation of novel DNA nanoarchitectures with potential applications, which has been termed as templated DNA nanotechnology or functional DNA nanoarchitectonics. This review highlights the molecular architectonics-guided design principles and applications of the derived DNA nanoarchitectures. The advantages and ability of functional DNA nanoarchitectonics to overcome the trivial drawbacks of classical DNA nanotechnology to fulfill realistic and practical applications are highlighted, and an outlook on future developments is presented.

Dynamics and Molecular Mechanism of Phosphate Binding to a Biomimetic Hexapeptide

Phosphorus (P) recovery from wastewater is essential for sustainable P management. A biomimetic hexapeptide (SGAGKT) has been demonstrated to bind inorganic P in P-rich environments, however the dynamics and molecular mechanisms of P-binding to the hexapeptide still remain largely unknown. We used dynamic force spectroscopy (DFS) to directly distinguish the P-unbound and P-bound SGAGKT adsorbed to a mica (001) surface by measuring the single-molecule binding free energy (Δ G_b). Using atomic force microscopy (AFM) to determine real-time step retreat velocities of triangular etch pits formed at the nanoscale on the dissolving (010) face of brushite (CaHPO₄·2H₂O) in the presence of SGAGKT, we observed that SGAGKT peptides promoted in situ dissolution through an enhanced P-binding driven by hydrogen bonds in a P-loop being capable of discriminating phosphate over arsenate, concomitantly forming a thermodynamically favored SGAGKT-HPO₄^2- complexation at pH 8.0 and relatively low ionic strength, consistent with the DFS and isothermal titration calorimetry (ITC) determinations. The findings reveal the thermodynamic and kinetic basis for binding of phosphate to SGAGKT and provide direct evidence for phosphate discrimination in phosphate/arsenate-rich environments.

Aromatic isophthalamides aggregate in lipid bilayers: evidence for a cooperative transport mechanism

The synthesis and anion transport properties of a series of transmembrane anion transporters based on an isophthalamide scaffold with phenyl, naphthyl or anthracenyl central rings are reported. Anion transport studies using POPC vesicles, showed that the compounds have Hill coefficients >1. This is indicative of higher order complex formation, evidence that leads us to suggest that the compounds are not functioning solely as mobile carriers but rather that a cooperative transport mechanism is being observed. Fluorescence spectroscopy was used to show that the compounds aggregate in the phospholipid bilayer, which provides evidence that these compounds function as a self-assembled anion-conducting aggregate.

Anion Recognition in Water: Recent Advances from a Supramolecular and Macromolecular Perspective

The recognition of anions in water remains a key challenge in modern supramolecular chemistry, and is essential if proposed applications in biological, medical, and environmental arenas that typically require aqueous conditions are to be achieved. However, synthetic anion receptors that operate in water have, in general, been the exception rather than the norm to date. Nevertheless, a significant step change towards routinely conducting anion recognition in water has been achieved in the past few years, and this Review highlights these approaches, with particular focus on controlling and using the hydrophobic effect, as well as more exotic interactions such as C-H hydrogen bonding and halogen bonding. We also look beyond the field of small-molecule recognition into the macromolecular domain, covering recent advances in anion recognition based on biomolecules, polymers, and nanoparticles.

QSAR analysis of substituent effects on tambjamine anion transporters

The transmembrane anion transport activity of 43 synthetic molecules based on the structure of marine alkaloid tambjamine were assessed in model phospholipid (POPC) liposomes. The anionophoric activity of these molecules showed a parabolic dependence with lipophilicity, with an optimum range for transport efficiency. Using a quantitative structure-transport activity (QSAR) approach it was possible to rationalize these results and to quantify the contribution of lipophilicity to the transport activity of these derivatives. While the optimal value of log P and the curvature of the parabolic dependence is a property of the membrane (and so similar for the different series of substituents) we found that for relatively simple substituents in certain locations on the tambjamine core, hydrophobic interactions clearly dominate, but for others, more specific interactions are present that change the position of the membrane hydrophobicity parabolic envelope.

Synthetic ion channels: from pores to biological applications

In this Account, we describe the development of several diverse families of synthetic, membrane-active amphiphiles that form pores and facilitate transport within membrane bilayers. For the most part, the compounds are amphiphiles that insert into the bilayer and form pores either on their own or by self-assembly. The first family of synthetic ion channels prepared in our lab, the hydraphiles, used crown ethers as head groups and as a polar central element. In a range of biophysical studies, we showed that the hydraphiles formed unimolecular pores that spanned the bilayer. They mediated the transport of Na(+) and K(+) but were blocked by Ag(+). The hydraphiles are nonrectifying and disrupt ion homeostasis. As a result, these synthetic ion channels are toxic to various bacteria and yeast, a feature that has been used therapeutically in direct injection chemotherapy. We also developed a family of amphiphilic heptapeptide ion transporters that selected Cl(-) >10-fold over K(+) and showed voltage dependent gating. The formed pores were approximately dimeric, and variations in the N- and C-terminal anchor chains and the acids affected transport rates. Surprisingly, the longer N-terminal anchor chains led to less transport but greater Cl(-) selectivity. A proline residue, which is present in the ClC protein channel's conductance pore, proved to be critical for Cl(-) transport selectivity. Pyrogallol[4]arenes are macrocycles formed by acid-catalyzed condensation of four 1,2,3- trihydroxybenzenes with four aldehydes. The combination of 12 hydroxyl groups on one face of the macrocycle and four pendant alkyl chains conferred considerable amphiphilicity to these compounds. The pyrogallol[4]arenes inserted into bilayer membranes and conducted ions. Based on our experimental evidence, the ions passed through a self-assembled pore comprising four or five amphiphiles rather than passing through the central opening of a single macrocycle. Pyrogallol[4]arenes constructed with branched chains are also amphiphilic and active in membranes. The pyrogallol[4]arene with 3-pentyl sidechains formed a unique nanotube assembly and functioned as an ion channel in bilayer membranes. Finally, we showed that dianilides of either isophthalic or dipicolinic acids, compounds which have been extensively studied as anion binders, can self-assemble to form pores within bilayers. We called these dianilides tris-arenes and have shown that they readily bind to phosphate anions. These structures also mediated the transport of DNA plasmids through vital bilayer membranes in the bacterium Escherichia coli and in the yeast Saccharomyces cerevisiae . This transformation or transfection process occurred readily and without any apparent toxicity or mutagenicity.

How do amphiphiles form ion-conducting channels in membranes? Lessons from linear oligoesters

The X-ray crystal structures of biological ion channels are exquisitely complex, but not all natural products capable of forming ion-conducting channels are equally elaborate. Examples such as the peptides gramicidin or alamethicin or the polyene antibiotics amphotericin and nystatin clearly form well-defined channels without requiring a massive protein superstructure. These molecules form the starting point for a supramolecular chemistry challenge: how to create synthetic compounds and systems that catalyze the translocation of ionic species across bilayer membranes mimicking naturally occurring channels. Over the past three decades, supramolecular chemists have developed numerous examples of systems with transport rates and efficiencies that rival natural channels. As the field developed, researchers discovered many compounds that are functional for ion transport but bear very little resemblance to any imagined architectures of ion channels. We and others have followed these lead compounds extensively in a quest to focus on the mechanisms such simple compounds use to achieve their function. These compounds show all the hallmarks of ion channels including high activity, ion specificity, regular time-dependent conductance changes, and in some cases higher-order phenomena such as voltage-dependent activity. In this Account, we summarize experimental evidence derived from an extensive class of oligoester bolaamphiphiles that illustrates how amphiphilic molecules can form ion-conducting channels in membranes. Examination of increasingly simple compounds over the past two decades has shifted the focus away from biological paradigms towards alternative modes for transmembrane ion transport. We have developed new tools to move beyond simple on-off channel openings to complex bursts of high activity. From the perspective of flux, the highly conducting bursts clearly move ions more efficiently than simple on-off openings. High and sustained conductance, whatever its structural origin, has direct applications in amplification of chemical signals or membrane-disrupting biological activity. These results ensure that simple transporters will continue to fascinate and puzzle for a long time to come.

Anion receptor chemistry: highlights from 2011 and 2012

This review covers advances in anion complexation in the years 2011 and 2012. The review covers both organic and inorganic systems and also highlights the applications to which anion receptors can be applied such as self-assembly and molecular architecture, sensing, catalysis and anion transport.

"Unclosed cryptands": a point of departure for developing potent neutral anion receptors

Six macrocyclic lariat-type compounds, representing a new class of anion receptors, were synthesized in a simple approach. We identified the optimal macroring size and the position of the hydrogen bond donating center in the lariat arm offering the best affinities toward chloride and carboxylate anions. The anion-binding properties of such systems were investigated by applying (1)H NMR titrations in DMSO/water and methanol/DMSO mixtures.