The fragile nature of most enzymes is a major hindrance to their use in industrial processes. Herein, we describe a synthetic chemical strategy to produce hybrid organic/inorganic nanobiocatalysts; it exploits the self-assembly of silane building blocks at the surface of enzymes to grow an organosilica layer, of controlled thickness, that fully shields the enzyme. Remarkably, the enzyme triggers a rearrangement of this organosilica layer into a significantly soft structure. We demonstrate that this change in stiffness correlates with the biocatalytic turnover rate, and that the organosilica layer shields the enzyme in a soft environment with a markedly enhanced resistance to denaturing stresses.

The design and synthesis of a novel linear thioether-based ligand subunit with a tetraphenylmethane core used in the stabilisation of gold nanoparticles (AuNPs) are presented. Mono-, tri, penta- and heptamers of the ligand have been synthesised and used to stabilise AuNPs by enwrapping. With the exception of the monomer, all ligands provide reliable long-term stability and redispersibility for the coated nanoparticles in common organic solvents. Despite variation of the oligomer length, all stable particles were of the same size within error tolerance (1.16±0.32 nm for the trimer, 1.15±0.30 nm for the pentamer, 1.17±0.34 nm for the heptamer), as investigated by transmission electron microscopy (TEM). These findings suggest that not only the number of sulfur atoms in the ligand, but also its bulkiness play a crucial role in stabilising the AuNPs. These findings are supported by thermogravimetric analysis (TGA), showing that AuNPs stabilised by the penta- or heptamer are passivated by a single ligand. Thermal stability measurements suggest a correlation between ligand coverage and thermal stability, further supporting these findings.

Using a tripodal, thioether‐based ligand comprising a remote protected acetylene, we efficiently stabilize small gold nanoparticles (Ø ≈ 1.2 nm) which are isolated and purified by chromatography. The 1:1 ligand‐to‐particle ratio is obtained by comparing the particles' dimensions measured by transmission electron microscopy with the weight fraction of the coating ligand determined by thermogravimetric analysis. The single ligand coating of the gold particle guarantees the presence of a single masked alkyne per particle. It can be addressed by wet chemical protocols providing the particles with the properties of “massive molecules”. The “massive molecule” nature of the particles is demonstrated by involving them in wet chemical coupling protocols like oxidative acetylene coupling providing gold nanoparticle dimers (34 % isolated yield) or alkyne‐azide “click”‐chemistry with a suitable triazide, giving trimeric particle architectures (30 % determined by transmission electron microscopy). The particle stabilization obtained by the coating ligand allows, for the first time, to treat these multi‐particle architectures by size exclusion chromatography.

The fragile nature of most enzymes is am ajor hindrance to their use in industrial processes.H erein, we describe as ynthetic chemical strategy to produce hybrid organic/inorganic nanobiocatalysts;i te xploits the self-assembly of silane building blocks at the surface of enzymes to grow an organosilica layer,ofcontrolled thickness,that fully shields the enzyme.Remarkably,the enzyme triggers arearrangement of this organosilica layer into asignificantly soft structure.W e demonstrate that this changei ns tiffness correlates with the biocatalytic turnover rate,a nd that the organosilica layer shields the enzyme in as oft environment with am arkedly enhanced resistance to denaturing stresses.

have been investigated, ranging from oligomeric, [28][29][30][31][32][33] tripodal, [34,35] and dendrimeric [36][37][38][39][40][41] to even cage-like [42] thioether-based ligands, most of them yielding AuNPs with narrow size distributions. Cages controlling the size of the nanoparticles were also developed for other noble metals like palladium, displaying catalytic activity. [43][44][45] Also, the periodically arranged cavities of a covalent organic framework were used as "caging" structure for catalytically active palladium and platinum particles. [46] It has furthermore been shown that such oligomeric benzyl sulfide ligand-stabilized AuNPs are accessible by wet chemical procedures, and ligand-coated AuNPs exposing reactive functional groups have been interlinked forming nanoarchitectures. [29][30][31]37,38] In the approach, the ligand not only controls the particles' sizes, but also the number and the spatial orientation of exposed functional groups.While rather complex and synthetically demanding dentritic ligands already displayed their ability to stabilize an entire AuNP, [36][37][38][39] a more recent ligand design showed that also linear oligomers are able to stabilize an entire particle when bulky enough to sterically protect the surface of the ligand-coated AuNP. [32] With a series of linear oligomers of various sulfursulfur distances, a correlation between the size of the stabilized AuNP and both parameters, the distance between coordination points of these multivalent ligand structures and the equivalents of gold salt used has been observed. [33] The study, however, also unraveled some limitations of the approach, namely an increasing loss over the control of the NP's size going along with a decrease in the stability of these AuNPs with increasing size.An alternative approach to increase both the number of coordinating sulfide groups and the AuNP surface covered by the ligand is the use of suitable branching points, increasing the number of oligomeric branches per ligand. Further, such architectures break the linearity of the ligand, enabling better coverage of the surface of AuNPs upon passivation. Of particular interest was to which extent a local density of concave, pre-organized coordinating sites might steer the dimensions of the stabilized particle.Already slightly larger AuNPs with diameters in the order of about 2 nm display surface plasmon bands and are thus interesting target structures opening the door for sensing and labeling applications. [3] The here reported research is motivated by our interest in optically active, ligand-stabilized AuNPs with a controlled exposition of functional groups as potential building blocks for hybrid nanoarchitectures interacting with optical signals.In order to benefit from surficial rather than linear coverage, we introduce a central tetraphenylmethane-based tripodal unit, which interlinks three oligomeric side-chains. In addition, the In order to coat the entire surface of gold nanoparticles (AuNPs) by a single ligand, tripodal macromolecules comprising be...

A systematic investigation of two parameters steering the size of linear octadentate heptamer‐coated gold nanoparticles (AuNPs) is presented, being i) the chemical structure (sulfur‐sulfur distance) of the coating thioether heptamer ligand and ii) the ratio of ligand to tetrachloroauric acid (HAuCl4) reduced during the formation of the AuNPs. For this purpose, a novel terphenyl‐based thioether heptamer (Ter) is synthesized via an end‐capping oligomerization strategy, comprising an increased distance between neighboring sulfur atoms in the ligand backbone compared to the meta‐xylene‐ (Xyl) and tetraphenylmethane‐ (TPM) based heptamers. While for both investigated parameters a clear trend to various‐sized NPs is shown, a stronger influence in the resulting sizes is observed by alteration of ligand to gold‐ratio. Remarkable processability‐ and long‐term stability‐features were observed for AuNPs stabilized by the bulky tetraphenylmethane‐based heptamer (TPM).

An overview of various approaches to synthesize gold nanoparticles (AuNPs) bearing one single chemically addressable unit and their diverse fields of application is presented. This comprehensive review not only describes the strategies pursued to obtain monofunctionalized AuNPs, but also reports their behavior as 'massive' molecules in wet chemical protocols and the scope of their applications. The latter reaches from site-specific labels in biomolecules over mechanical barriers in superstructures to building blocks in hybrid nano-architectures. The complementing physical properties of AuNPs combined with precise chemical control of their attachment makes these objects promising building blocks for numerous proof-of-concept experiments and applications.

A molecular cage encapsulating gold nanoparticles is presented. Six benzylic thioethers are pointing into its cavity, stabilizing the particles in a 1:1 ligand-to-particle-ratio in excellent yields. They are bench stable...