Two new Schiff base-like ligands bearing a heteroaromatic fluorophore were synthesised and converted into the corresponding Ni(II), Cu(II) and Zn(II) square planar complexes. The Ni(II) complexes were studied with regard to a coordination change-induced spin state change upon addition of pyridine in solution. An inverse correlation between the fluorescence properties and the spin state of the metal centre was observed, and investigated with steady state fluorescence and time-resolved spectroscopy. RESULTS SynthesesAll metal complexes were synthesised in two steps. Starting with the diamines 1 and 4, firstly a condensation with a ketoenol ether forms the chelate cycles, which then react with metal acetate to give the respective complexes [ML1] and [ML2] (M = Ni II , Cu II , Zn II ), the counter anionic acetates acting as bases for deprotonation of the ligand. The molecular structures and the synthetic pathway are given in Scheme 1. All complexes were obtained as pure powder with the general formula [ML1] or [ML2]. All ligands and intermediates were characterised with IR, CHN and 1 H-NMR. All complexes were characterised with IR, CHN analysis and mass spectrometry. Scheme 1. Pathway of synthesis of the metal complexes described in this work and used abbreviations. Crystal structure analysisSingle crystals suitable for X-ray diffraction analysis of [NiL1] and [CuL1] were obtained from a vapour-vapour slow diffusion setup between a trichloromethane solution of the complex and ethanol. All crystallographic data are given in the Supporting Information: Table S1. While the complex [NiL1] crystallises with the same composition as the bulk material, the structure of compound [CuL1] was determined as [CuL1(EtOH)]•2 CHCl 3 . Both compounds crystallise in the triclinic space group P-1, and the asymmetric units contain one complex molecule. ORTEP drawings of the asymmetric units are displayed in Figure 1. The nickel(II) centre in [NiL1] lies in a N 2 O 2 square planar coordination sphere. Ni-N (1.83 Å) and Ni-O eq (1.85 Å) bond lengths are in agreement with other complexes with similar coordination sphere. 16,17 The sum of the angles is with Σ = 717°, not far from a perfect square planar coordination sphere (Σ = 720°). In the case of [CuL1(EtOH)]•2 CHCl 3 , the copper(II) lies in a N 2 O 3 square pyramidal geometry. Cu-N (1.92 Å), Cu-O eq (1.92 Å) and Cu-O EtOH (2.378(5) Å) bond lengths are generally longer than for the nickel complex, due to the different geometry of the coordination sphere and the increase of the covalent radius from 124 pm (Ni) to 132 pm (Cu). Selected bond lengths and angles are presented in Table 1.The crystal packing of [NiL1] shows the complexes stacked over each other, forming columns along the vector [100]. π-π interactions between the aromatic rings of the ligand, as well as metal-aromatic interactions between the nickel centre and the chelate rings of neighbouring complexes lead to the formation of the columns in the packing. Illustrations of the packing are shown in Figure 2, and selected distance...

Glyco-functionalized gold nanoparticles have great potential as biosensors and as inhibitors due to their increased binding to carbohydrate-recognizing receptors such as the lectins. Here we apply previously developed solid phase polymer synthesis to obtain a series of precision glycomacromolecules that allows for straightforward variation of their chemical structure as well as functionalization of gold nanoparticles by ligand exchange. A novel building block is introduced allowing for the change of spacer building blocks within the macromolecular scaffold going from an ethylene glycol unit to an aliphatic spacer. Furthermore, the valency and overall length of the glycomacromolecule is varied. All glyco-functionalized gold nanoparticles show high degree of functionalization along with high stability in buffer solution. Therefore, a series of measurements applying UV-Vis spectroscopy, dynamic light scattering (DLS) and surface plasmon resonance (SPR) were performed studying the aggregation behavior of the glyco-functionalized gold nanoparticles in presence of model lectin Concanavalin A. While the multivalent presentation of glycomacromolecules on gold nanoparticles (AuNPs) showed a strong increase in binding compared to the free ligands, we also observed an influence of the chemical structure of the ligand such as its valency or hydrophobicity on the resulting lectin interactions. The straightforward variation of the chemical structure of the precision glycomacromolecule thus gives access to tailor-made glyco-gold nanoparticles (glyco-AuNPs) and fine-tuning of their lectin binding properties.

Ligand exchange with end-functionalized polymers is often applied to render nanoparticles with enhanced colloidal stability, to change the solubility in various environments, and/or to introduce new functionalities. Here we show that exchange of citrate molecules with α-trithiocarbonate-ω-carboxyl-terminated poly(N-isopropylacrylamide) can successfully stabilize spherical gold particles of different diameters ranging from 15 to 53 nm. This is verified by transmission electron microscopy, dynamic light scattering, and extinction spectroscopy. We show that the polymer-decorated nanoparticles respond to temperature and pH allowing access to control interparticle interactions. In a range of pH slightly below the pK of the terminal carboxyl groups, phase transfer of the particles from water to chloroform can be mediated by increasing the dispersion temperature above the lower critical solution temperature of poly(N-isopropylacrylamide). Upon cooling, fully reversible phase transfer to the water phase is observed. Extinction spectroscopy reveals phase transfer efficiencies close to 100% for every system under investigation.