3 research outputs found
Turning Supramolecular Receptors into Chemosensors by Nanoparticle-Assisted āNMR Chemosensingā
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 ābulkinessā 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 Ī±-amino acids
Structural Investigation of the Ligand Exchange Reaction with Rigid Dithiol on Doped (Pt, Pd) Au<sub>25</sub> Clusters
The
ligand exchange reaction between heteroatom doped (Pd, Pt)
Au<sub>25</sub>(2-PET)<sub>18</sub> (2-PET = 2-phenylethylthiolate)
clusters and enantiopure 1,1ā²-binaphthyl-2,2ā²-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
SĀ(R)āAuāSĀ(R)āAuāSĀ(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 L<sub>3</sub>-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 Au<sub>25</sub> structure, except for some slight influence on the AuāS
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-ZnĀ(salphen) structure shows extremely strong self-assembly
both in solution as well as at the solidāliquid interface as
evidenced by scanning tunneling microscopy, competitive UVāvis
and fluorescence titrations, dynamic light scattering, and transmission
electron microscopy. Density functional theory analysis on the Zn<sub>2</sub> complex rationalizes the very high stability of the self-assembled
structures provoked by unusual oligomeric (ZnāO)<sub><i>n</i></sub> coordination motifs within the assembly. This coordination
mode is strikingly different when compared with mononuclear ZnĀ(salphen)
analogues that form dimeric structures having a typical Zn<sub>2</sub>O<sub>2</sub> 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