Turning Supramolecular Receptors into Chemosensors by Nanoparticle-Assisted “NMR Chemosensing”

By exploiting a magnetization transfer between monolayer-protected nanoparticles and interacting analytes, the NMR chemosensing protocol provides a general approach to convert supramolecular receptors into chemosensors via their conjugation with nanoparticles. In this context, the nanoparticles provide the supramolecular receptor not only with the “bulkiness” necessary for the NMR chemosensing approach but also with a different selectivity as compared to the parent receptor. We here demonstrate that gold nanoparticles of 1.8 nm core coated with a monolayer of 18-crown-6 ether derivatives can detect and identify protonated primary amines in methanol and in water, and even discriminate between two biogenic diamines that are selectively detected over monoamines and α-amino acids

Structural Investigation of the Ligand Exchange Reaction with Rigid Dithiol on Doped (Pt, Pd) Au₂₅ Clusters

The ligand exchange reaction between heteroatom doped (Pd, Pt) Au₂₅(2-PET)₁₈ (2-PET = 2-phenylethylthiolate) clusters and enantiopure 1,1′-binaphthyl-2,2′-dithiol (BINAS) was monitored in situ using chiral high-performance liquid chromatography (HPLC). During the ligand exchange reactions, replacement of two protecting thiols (2-PET) with one new entering BINAS ligand on the cluster surface occurs. The rigid dithiol BINAS adsorbs in a specific mode that bridges the apex and one core site of two adjacent S­(R)–Au–S­(R)–Au–S­(R) units. This is the most favorable binding mode and theoretically preserves the original structure. A kinetic investigation on these in situ ligand exchange reactions revealed a decrease in reactivity after multiple exchange. A comparison of relative rate constants demonstrates a similar exchange rate toward BINAS for both (Pd, Pt) systems. The possible structural deformation after incorporation of BINAS was investigated by X-ray absorption spectroscopy (XAS) at the S K-edge and Au L₃-edge. First, a thorough assignment of all sulfur contributions to the XANES spectrum was performed, distinguishing for the first time long and short staple motifs. Following that, a structural comparison of doped systems using XANES and EXAFS confirmed the unaltered Au₂₅ structure, except for some slight influence on the Au–S bonds. Additionally, an intact staple motif was confirmed after incorporation of rigid dithiol BINAS by both XANES and EXAFS. This finding agrees with a BINAS interstaple binding mode predicted by calculation, which does not perturb the cluster structure

Extremely Strong Self-Assembly of a Bimetallic Salen Complex Visualized at the Single-Molecule Level

A bis-Zn­(salphen) structure shows extremely strong self-assembly both in solution as well as at the solid–liquid interface as evidenced by scanning tunneling microscopy, competitive UV–vis and fluorescence titrations, dynamic light scattering, and transmission electron microscopy. Density functional theory analysis on the Zn₂ complex rationalizes the very high stability of the self-assembled structures provoked by unusual oligomeric (Zn–O)_<i>n</i> coordination motifs within the assembly. This coordination mode is strikingly different when compared with mononuclear Zn­(salphen) analogues that form dimeric structures having a typical Zn₂O₂ central unit. The high stability of the multinuclear structure therefore holds great promise for the development of stable self-assembled monolayers with potential for new opto-electronic materials