(b) Chemical structures of molecular tube 1 and long hydrocarbons 4a, 4b, 5a, 6a and 6c.
Herein we report the synthesis and host properties of molecular tube 1 which presents a hydrophobic cavity encircled by polyaromatic anthracene panels (Fig. The tube is obtained by the transition-metal-free cross-coupling reaction of end-functionalized, bent compounds with two embedded anthracene rings.
The tubular structure provides a well-defined hydrophobic nanospace and hydrophilic pyridinium and methoxyethoxy groups so that we examined the host capability of the amphiphilic tube 1 for long hydrocarbons in aqueous solutions.) but shows selectivity for a multiply branched alkane over nonbranched alkanes.For example, when branched 2,2,4,4,6,8,8-heptamethylnonane (4a; 2.2 μmol) and linear n-nonane (4b; 2.2 μmol) were suspended in a 1:1 D=−2.08 p.p.m., due to shielding effects from the encircling anthracene rings.The rigidly bent conformation of 2b facilitates the formation of supramolecular assemblies such as (i) capsular structures through noncovalent, coordinative transition-metal linkages) of 2a were found at considerable downfield (8.64–9.87 p.p.m.), indicating the formation of N-phenylpyridinium units (Fig. The signals (Δδ=−0.4 p.p.m.) indicate a tubular structure, in which the interior aromatic protons are shielded by the adjacent anthracene panels.Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) analysis confirmed the formation of 1 with a molecular weight of 1,532.67 Da: a prominent signal was observed at m/z=730.9, assigned to the [1−2Cl species.However, the recognition of long hydrocarbons by synthetic hosts is a challenging task due to their conformational flexibility and the lack of distinguishing recognition sites.
Thus it is not surprising that the selective binding of simple or functionalized (for example, branched methyl groups or unsaturated carbon–carbon double bonds) long hydrocarbon chains, essential components for biological function(a) Schematic representation of the binding of a long hydrocarbon by a molecular tube with polyaromatic frameworks.The selective recognition and effective binding of hydrocarbons within synthetic host compounds are problematic owing to their conformational flexibility and the lack of specific binding sites.Here we report a molecular tube with polyaromatic frameworks prepared by the Zincke cross-coupling reaction.The girded cylindrical cavity (~1 nm in diameter and length) of tube 1 selectively binds long hydrocarbons with branched methyl groups and/or unsaturated moieties, such as 2,2,4,4,6,8,8-heptamethylnonane (4a), nervonic acid methyl ester (5a), squalene (6a) and coenzyme Q4 (6c) (Fig.1b) through hydrophobic aromatic–aliphatic and/or aromatic–olefinic interactions in 1:1 water/methanol solutions. 2a) with two embedded anthracene panels to design molecular tube 1. 26) were reacted in 1-propanol at 85 °C over 7 days, molecular tube 1 formed and was isolated as a yellow solid (9% yield).The NOESY NMR spectrum showed several sets of correlation signals between the tube and the bound guest (for example, H).