Receptor for Anionic Pyrene Derivatives Provides the Basis for New Biomembrane Assays

Abstract

This study describes a new receptor cyclen 1 capable of strong selective binding of pyrene-based anionic dyes under near-physiological conditions. This receptor comprises four naphthylthiourea groups tethered to a cyclen core via an ester linkage. The complexation behavior of cyclen 1 receptor is characterized by a series of (1)H NMR, microcalorimetry, UV-vis, and fluorometry experiments. The relevance of structural features of this receptor to its recognition function is assessed using control compounds that lack some of the groups found in cyclen 1. The specificity of cyclen 1 toward pyrene-based dyes is assessed through experiments using dyes with different molecular organization. The most important finding was the ability of cyclen 1 to bind efficiently to a pH-sensitive dye pyranine, a dye that is commonly used in various biomembrane assays. The high affinity of cyclen 1 to pyranine, its impermeability to the lipid bilayer membrane, fast kinetics of binding, and ability to quench the pyranine's fluorescence were used as a basis for a new membrane leakage assay. This membrane leakage assay is fully compatible with the commonly applied pH-stat transport assay, and therefore it allows for differentiation of the ion transport and nonselective leakage mechanisms within a single set of experiments. The ability of cyclen 1 to quench the fluorescence of pyranine also finds limited applicability to the detection of endovesiculation.

Enantio‐ and Chemoselective Differentiation of Protected α‐Amino Acids and β‐Homoamino Acids with a Single Copper(II) Host

“…[22][23][24][25][26][27] It is expected that host 1 rapidly interconverts between these kinds of M and P helices in solution, as has been shown for other similar molecules. [15,28,29] There are several reasons why we chose to apply host 1 to the differentiation of amino acids. First, it can be rapidly and easily synthesized from commercially available starting materials.…”

Chemoselective precipitation of lactose from a lactose/sucrose mixture: proof of concept for a new separation methodology

“…While the physical properties of these sugars are very similar (28), which makes their separation by common techniques difficult (29,30), the presence of a reducing end in lactose allows a test of our principle. APTS is the dye that forms a stable complex (K a ¼ 8 £ 10 5 M 21 ) with the naphthyl thiourea cyclen receptor (cyclen 1, Scheme 1) (26). The presence of an amino group in this dye implies that it can be readily tethered to the reducing end of lactose via reductive amination reaction.…”

“…Recently, we have identified a family of artificial cyclen-thiourea receptors that form complexes with the pyrene-based dyes under near-physiological conditions (26,27). These complexes feature micromolar stability and diminished solubility in water and methanol compared to the intrinsic solubility of the dye and receptor alone (26).…”

“…These complexes feature micromolar stability and diminished solubility in water and methanol compared to the intrinsic solubility of the dye and receptor alone (26). More interestingly, the cyclen-based artificial receptors were highly selective for the pyrene scaffold, while at the same time tolerating considerable structural variations in peripheral positions on the dye.…”

A Controlled Cyclization of Functionalized Thioureas and Unprecedented Termolecular Decyclization of Iminothiazolidinones

“…Thiourea function incorporated into complex molecules was shown to serve as the basic unit in recognition of anionic substrates . The latter compounds were used for the detection of membrane leakage and lipid flip in cellular assays, separation of isomeric saccharides and photosensing . Similar compounds facilitated development of a drug delivery system potentially useful for the treatment of type 1 diabetes …”