Encapsulation and Functionalization of Nanoparticles in Crosslinked Resorcinarene Shells

A giant hybrid organic–inorganic octahedron from a narrow rim carboxylate calixarene

Here we discovered an unprecedented giant octahedral coordination compound bearing 16 Zn²⁺, 12 Na⁺, 8 O²⁻, 4 OH⁻, 13 H₂O and 6 L⁴⁻ ligands [L⁴⁻ = fully deprotonated tetra(carboxymethoxy)calix[4]arene].

Surface Functionalization and Patterning by Multifunctional Resorcinarenes

Plant phenolic compounds and catecholamines have been widely used to obtain substrate-independent precursor nanocoatings and adhesives. Nevertheless, there are downsides in using such phenolic compounds for surface modification such as formation of nonuniform coatings, need for multistep modification, and restricted possibilities for postfunctionalization. In this study, inspired by a strong binding ability of natural polyphenols found in plants, we used three different macrocyclic polyphenols, known as resorcin[4]arenes, to modify the surface of different substrates by simple dip-coating into the dilute solution of these compounds. Eight hydroxyl groups on the large rim of these resorcin[4]arenes provide multiple anchoring points to the surface, whereas the lower rim decorated with different appending groups introduces the desired chemical and physical functionalities to the substrate's surface. Deposition of a uniform and transparent resorcinarene layer on the surface was confirmed by several surface characterization techniques. Incubation of the modified substrates in different environments indicated that the stability of the resorcinarene layer was dependent on the type of substrate and the pH value. The most stable resorcinarene layer was formed on amine-functionalized substrates. The surface was modified with alkenyl functional groups in one step using a resorcinarene compound possessing four alkenyl appending groups on its small rim. Thiol-ene photoclick chemistry was used to site-selectively postfunctionalize the surface with hydrophilic and hydrophobic micropatterns, which was confirmed by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Thus, we demonstrate that resorcin[4]arenes extend the scope of applications of plant polyphenol and mussel-inspired precursors to tailor-made multifunctional nanocoatings, suitable for a variety of potential applications in biotechnology, biology, and material science.

Highly fluorescent resorcinarene cavitand nanocapsules with efficient renal clearance

Nanomaterial based imaging approaches hold substantial promise in addressing current diagnostic and therapeutic challenges. One of the key requirements for the successful clinical translation of nanomaterials is their complete clearance from the body within a reasonable time period preferably via the renal filtration route. This article describes the synthesis of highly fluorescent, water soluble, resorcinarene cavitand nanocapsules and demonstrates their effective renal clearance in mice. The synthesis and functionalization of nanocapsules was accomplished in a one-pot operation via thiol-ene reactions without involving self-assembly, sacrificial templates or emulsions. Water soluble resorcinarene cavitand nanocapsules obtained by this approach were covalently functionalized with Alexa Fluor 750. Highly fluorescent nanocapsules with hydrodynamic diameters of 122 nm and 68 nm and extinction coefficients of 1.3 × 10(9) M(-1) cm(-1) and 1.5 × 10(8) M(-1) cm(-1) respectively were prepared by varying the reaction conditions. The in vivo biodistribution and clearance of these nanocapsules in mice followed by whole-body fluorescence imaging showed that they were both cleared renally within a few hours. Given the inherent encapsulation capabilities of nanocapsules, the renal clearance demonstrated in this work opens up new opportunities for their theranostic applications especially for targeting and treating the urinary tract.

Chemical Control over Cellular Uptake of Organic Nanoparticles by Fine Tuning Surface Functional Groups

The functional groups displayed on the surface of nanoparticles (NP) are known to play an important role in NP cellular uptake. However, only a few systematic studies have been reported to address their role, in large part because of the difficulty in regularly varying the number and structure of the functional groups on the NP surface. We employ a bottom-up strategy for the synthesis of water-soluble organic nanoparticles (ONPs) with different sizes and functional groups, using readily available monomers. Utilizing flow cytometry, we measured the HeLa cell uptake efficiency of ONPs that contain side-chains with a different (a) length, (b) number of hydroxyl groups, and (c) number of methyl groups. We have also investigated ONPs with the same functional groups but different sizes. The potential formation and influence of protein corona was examined using the same approach but in the presence of serum. The results demonstrate that under both serum and serum-free conditions the surface-exposed functional groups determine the efficiency of cellular uptake of the particles, and that the trend can be partially predicted by the lipophilicity of the polymeric ONP's repeating units. Also, by using a "masking" strategy, these particles' cellular uptake behavior could be altered conveniently.

4,10,16,22-Tetra-kis(2-chloro-acet-oxy)-6,12,18,24-tetra-meth-oxy-2,8,14,20-tetra-pentyl-resorcin[4]arene

The title compound, C₆₀H₇₆Cl₄O₁₂, has a macrocyclic structure and both the upper and lower rim have disordered atoms. There are no hydrogen bonds or π–π stacking inter­actions in the crystal.

Selective decoration of metal nanoparticles inside or outside of organic microstructures via self-assembly of resorcinarene

A facile template method was described for the decoration of organic microtubes with various nanoparticles (NPs), which was achieved in a straightforward "mix" process in the presence of templates and resorcinarene-functionalized nanoparticles (AuNPs, AgNPs, PtNPs, and PdNPs). A combination of UV-visible spectra and Fourier transform-infrared spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction measurements, contact angle experiment, and energy dispersive X-ray spectroscopy was used for analysis. Interestingly, it was found that NPs could be encapsulated into the microtubes during the process of resorcinarene self-assembly. As a model system, AuNP-loaded microtubes were investigated and discussed, and loaded nanoparticles with a narrow size distribution were observed. Furthermore, AuNP-decorated microsheets could also be obtained by the assembly of resorcinarene with hydrazide groups. Remarkably, it was also observed that the incorporated NPs could be redispersed by treating the NP-loaded microtubes, which made it possible to realize the uptake and release of given nanoparticles. This procedure was scalable to diverse resorcinarene-based self-assemblies and applicable to various metal nanoparticles that decorate by resorcinarenes.

Self-assembled monolayers of thiols and dithiols on gold: new challenges for a well-known system

Self-assembled monolayers (SAMs) of alkanethiols and dialkanethiols on gold are key elements for building many systems and devices with applications in the wide field of nanotechnology. Despite the progress made in the knowledge of these fascinating two-dimensional molecular systems, there are still several "hot topics" that deserve special attention in order to understand and to control their physical and chemistry properties at the molecular level. This critical review focuses on some of these topics, including the nature of the molecule-gold interface, whose chemistry and structure remain elusive, the self-assembly process on planar and irregular surfaces, and on nanometre-sized objects, and the chemical reactivity and thermal stability of these systems in ambient and aqueous solutions, an issue which seriously limits their technological applications (375 references).

Postsynthetic modification of gold nanoparticles with calix[4]arene enantiomers: origin of chiral surface plasmon resonance

Gold nanoparticles postsynthetically modified with chiral 1,3-disubstituted diamino calix[4]arene ligands 2a and 2b are shown to exhibit a circular dichroism (CD)-active surface plasmon resonance absorption (SPR) band. Electronic communication between adsorbed ligand and the gold nanoparticle surface is evidenced in an almost 10-fold increase in the ligand molar ellipticity in the pi-pi* transition spectral range when bound to the gold surface relative to free solution. The footprint of ligand on the gold nanoparticle surface at saturation is measured to be 91 A(2) via monitoring the red shift in the SPR band accompanying ligand adsorption. At ligand concentrations above that required for surface saturation, the ellipticity of the band in the SPR spectral range plateaus to a constant value, whereas the ellipticity of the band in the pi-pi* transition spectral range continues to increase in a manner that corresponds to free ligand in solution. This critical observation correlates ligand adsorption and the onset of the CD-active SPR band. On the basis of the packing characteristics of the bulky calixarene ligand, which are controlled by achiral tert-butyl groups, and the postsynthetic nature of nanoaprticle surface modification of 4.7 nm gold cores used in this study, which precludes synthesis of chiral arrangements of gold atoms, a mechanism responsible for the CD-active SPR bands is proposed, which is based upon the influence of the asymmetric center of the chiral adsorbate on the electronic states of the metal nanoparticle core-an explanation supported by the observed interactions between the gold surface and adsorbed ligand.

Synthesis and self-assembly of thio derivatives of calix[4]arene on noble metal surfaces

Self-assembled monolayers (SAMs) provide a simple route to functionalize electrode surfaces with organic molecules. Herein we use cavity-containing derivatives of calix[4]arenes in SAMs. Bound to noble metal surface, the assembled molecules are candidates to serve as molecular sieves for H 2 molecules and H (+) ions, which could have relevance for fuel cell applications. Tetra- O-alkylated calix[4]arenes with thiolacetate and thiolamide wide-rim anchoring groups in cone and partial-cone conformations were designed, synthesized and self-assembled onto Au, Pt, and Pd surfaces. The resulting SAMs were systematically examined. Single crystal X-ray diffraction of 5,11,17,23-tetrakis(thioacetyl)-25,26,27,28-tetra- i-propoxycalix[4]arene confirmed the cone conformation and revealed the cavity dimensions of the SAMs that were formed by immersing noble metal substrates (Au, Pt and Pd deposited on Si-wafers) in solutions of calix[4]arenes. Surface characterization techniques including ellipsometry, cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) were used, indicating that the metal surface is terminated with a monomolecular layer. Experimental thicknesses obtained from the ellipsometry are consistent with the calculated values. CV results showed 50 to 80% physical passivation against the Fe(CN) 6 (3-/4-) couple, implying an overall relatively low concentration of defects and pinholes in the films. The binding energies of the S2p core level in the XPS were consistent with the literature values and revealed that up to 3.2 out of four anchoring groups were bonded to the noble metal surface.

Resorcinarene-Encapsulated Gold Nanorods: Solvatochromatism and Magnetic Nanoshell Formation

Gold nanorods (GNRs) were encapsulated and dispersed into organic solvents by tetrabenzylthiol resorcinarene (TBTR) and by a poly(dithiocarbamate) derived from tetra- N-methyl(aminomethyl)resorcinarene (TMAR-DTC), formed by the in situ condensation of TMAR with carbon disulfide. The latter proved to be highly effective at enabling the redispersion of GNRs in various organic solvents. GNRs encapsulated in TMAR-DTC exhibited a strong solvatochromic response, with a refractive index sensitivity of over 300 nm/RIU. The resorcinarene-encapsulated GNRs could withstand high temperatures for a short period of time, and could be used to nucleate the growth of magnetic nanoshells.