o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.

Molecular self-assembly can be described as the thermodynamically controlled association of molecules into structurally well defined, stable aggregates through noncovalent interactions. 1 Selfassembly is an essential process in biological systems, providing the diverse range of highly ordered structures observed in living organisms. The controlled application of noncovalent interactions also provides a powerful tool for the engineering of man-made systems, allowing the construction of structures spanning the nanoto macroscale range. 2 Adaptation of self-assembly processes to the controlled aggregation of synthetic polymers provides a useful method for the creation of novel, higher order architectures. 3 We have recently incorporated specific recognition elements into polystyrene-based polymers. 4 Unlike biopolymers such as DNA and RNA, 5 these synthetic polymers are highly flexible and randomly substituted. This combination of randomness and flexibility provides a platform for the creation of highly structured extended systems: in recent studies, we have demonstrated a polymer-mediated selfassembly of gold nanoparticles into highly ordered spherical arrays incorporating up to 5 × 10 6 individual particles. 6 We report here the extension of this approach to the self-assembly of complementary polymer strands into giant vesicles 7 through specific interchain hydrogen bonding.Complementarity between polymers was achieved using a diaminopyridine-thymine three-point hydrogen-bonding interaction. 8 The desired random dispersion of functionality in the polymers was obtained via functionalization of a 1:1 random copolymer of styrene and 4-(chloromethyl)styrene. 9 Reaction of this polymer with a diacyldiaminopyridine derivative 10 in the presence of potassium carbonate provided diaminopyridinefunctionalized polymer 1 (Figure 1). The complementary thyminefunctionalized polymer 2 was synthesized in a similar fashion using thymine-1-acetic acid.Formation of the aggregates was achieved by mixing equal volumes of polymer 1 (3 mg/mL) and polymer 2 (3 mg/mL) in CHCl 3 (Figure 2). Light scattering was observed immediately upon mixing of the clear solutions of polymers 1 and 2, indicating rapid complexation-mediated aggregation. The resulting aggregates were stable indefinitely (>7 days) in solution; however, they dissociated rapidly at elevated temperatures (60°C).Preliminary insight into structures of mixed-polymer aggregates was obtained through differential interference contrast (DIC) optical microscopy. Micrographs of mixed solutions of polymers 1 and 2 in CHCl 3 clearly show the formation of spherical aggregates (Figure 3). These vesicle-like structures are 3.3 ( 0.9 µm in diameter 11 with a size distribution characteristic of vesicle (1) Whitesides, G. M.; Mathias, J. P.; Seto, C. T. Science 1991, 254, 1312. (2) For examples of self-assembly-based man-made systems, see: Breen, T. L.; Tien, J.; Oliver, S. R. J.; Hadzic, T.; Whitesides, G. M. Science 1999, 284, 948. Fyfe, M. C. T.; Stoddart, J. F. The average diameter was obt...

Polystyrene-based systems with varying donor−acceptor−donor (D−A−D) hydrogen bonding side chains were synthesized. Recognition interactions between these polymers and guest flavin 5 were studied through 1H NMR titration experiments. Using these systems, we have shown that the efficiency of recognition between the polymer and guest can be controlled through the choice of recognition element on the polymer by adjusting the balance between intra- and intermolecular interactions. The versatility of this “plug and play” strategy was readily extended to bulk materials. Using spin casting, we kinetically trapped these host−guest complexes in polystyrene films, resulting in highly efficient recognition processes, a key prerequisite for creation of supramolecular devices.

Bis-thymine units were used to noncovalently cross-link a complementary diamidopyridine-functionalized copolymer. Upon combination in noncompetitive solvents, discrete micron-scale spherical aggregates were formed arising from specific three-point polymer-cross-linker hydrogen bonding interactions. The diameter of these microspheres could be controlled through spacer structure. The cross-linking process was fully thermally reversible, with complete dissolution observed at 50 degrees C and reformation of the aggregates upon return to ambient temperature. This process could be repeated multiply, with lower particle dispersity observed arising from the annealing process.

Monolayer modification of alkylamine-protected γ-Fe 2 O 3 nanoparticles using functionalized alcohols and diols is presented. the stability of the modified nanoparticles was found to be dependent on the nature of the introduced alcohol: both bidentate surface-ligand bonding and steric blocking by bulky tail groups were necessary to produce systems resistant to agglomeration. EPR, UV-vis, and powder XRD analyses of the pre-and post-modified nanoparticles demonstrated that the core γ-Fe 2 O 3 functionality was unaffected by the change in monolayer composition. Finally, multiple ligands could be readily incorporated into the monolayer using a simultaneous displacement reaction.