Cyanophenyl vs. pyridine substituent: impact on the adlayer structure and formation on HOPG and Au(111).

A new cyano substituted bis(terpyridine) derivative CN-BTP was synthesized and its adsorption on highly oriented pyrolytic graphite (HOPG) and Au(111) was investigated. CN-BTP is closely related to the previously investigated 2,4'-BTP, where the cyanophenyl groups are replaced by pyridine moieties. The scanning tunneling microscopy (STM) investigation of CN-BTP at the liquid|HOPG interface shows a highly ordered herringbone structure that is stabilized by double weak intermolecular C-HN hydrogen bonds, partially through the -CN substituents, which is different from the most stable square structure of 2,4'-BTP. The adsorption processes were investigated using cyclic voltammetry (CV) on Au(111) in a neutral phosphate buffer. A fast and full adlayer formation could be observed with CN-BTP, whereas an extremely slow process with 2,4'-BTP under the same conditions was found. Our data show that the CN substituents on BTP not only change the structure of the monolayer at the liquid|HOPG interface, but also accelerate the phase transition process in the electrolyte dramatically. This could be explained by the adlayer-substrate interactions, which is supported by DFT calculations. Our findings might be extended more generally to further pyridine comprising self-assembling molecules to fine-tune the adlayer structure and phase transition/adsorption kinetics by replacing pyridine by cyanophenyl moieties.

Binding performance of pepsin surface-imprinted polymer particles in protein mixtures.

Surface-imprinted polymer particles facilitate the accessibility of synthetic selective binding sites for proteins. Given their volume-to-surface ratio, submicron particles offer a potentially large surface area facilitating fast rebinding kinetics and high binding capacities, as investigated herein by batch rebinding experiments. Polymer particles were prepared with (3-acrylamidopropyl)trimethylammonium chloride as functional monomer, and ethylene glycol dimethacrylate as cross-linker in the presence of pepsin as template molecule via miniemulsion polymerization. The obtained polymer particles had an average particle diameter of 623 nm, and a specific surface area of 50 m2 g-1. The dissociation constant and maximum binding capacity were obtained by fitting the Langmuir equation to the corresponding binding isotherm. The dissociation constant was 7.94 µM, thereby indicating a high affinity; the binding capacity was 0.72 µmol m-2. The binding process was remarkably fast, as equilibrium binding was observed after just 1 min of incubation. The previously determined selectivity of the molecularly imprinted polymer for pepsin was for the first time confirmed during competitive binding studies with pepsin, bovine serum albumin, and ß-lactoglobulin. Since pepsin has an exceptionally high content in acidic amino acids enabling strong interactions with positively charged quaternary ammonium groups of the functional monomers, another competitive protein, i.e., α1-acid glycoprotein, was furthermore introduced. This protein has a similarly high content in acidic amino acids, and was used for demonstrating the implications of ionic interactions on the achieved selectivity.

Recognition-directed supramolecular assemblies of metal complexes of terpyridine derived ligands with self-complementary hydrogen bonding sites.

The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but partially broken grid with a quarter of the H-bonding sites unsaturated (d(N-H-N)=2.984-3.206 A). In the case of the Zn complex 12 with triflate anions, half of the hydrogen bonds are formed. Only one of the two orthogonal ligands has hydrogen bonds (d(N-H-N) = 3.082, 3.096 A) to the neighbouring complexes and thus builds linear, supramolecular, polymeric chains. These structural differences are mainly attributed to crystal-packing effects caused by the different anions. The data presented here may also be regarded as a prototype for the generation of organised arrays through sequential self-assembly processes.