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Metal-support interactions have been widely utilized for optimizing the catalytic reactivity of oxide-supported Au nanoparticles. Optimized reactivity was mainly detected with small (1-5 nm) oxide-supported Au nanoparticles and correlated to highly reactive sites at the oxide-metal interface. However, catalytically active sites are not necessarily restricted to the interface but reside as well on the Au surface. Uncovering the interconnection between reactive sites located at the interface and those situated at the metal surface is of crucial importance for understanding the reaction mechanism on Au nanoparticles. Herein, high-spatial-resolution IR nanospectroscopy measurements were conducted to map the localized reactivity in hydrogenation reactions on oxide-supported Au particles while using nitro-functionalized ligands as probes molecules. Comparative analysis of the reactivity pattern on single particles supported on various oxides revealed that oxide-dependent reactivity enhancement was not limited to the oxide-metal interface but was detected throughout the Au particle, leading to site-independent reactivity. These results indicate that reactive Au sites on both the oxide-metal interface and metal surface can activate the nitro groups toward hydrogenation reactions. The observed influence of oxide support (TiO2 > SiO2 > Al2O3) on the overall reactivity pattern specified that hydrogen dissociation occurred at the oxide-metal interface, followed by highly efficient intraparticle hydrogen atom diffusion to the interior parts of the Au particle. In contrast to Au particles, the oxide-metal interface had only a minor impact on the reactivity of supported Pt particles in which hydrogen dissociation and nitro group reduction were effectively activated on Pt sites. Single-particle measurements provided insights into the relative reactivity pattern of oxide-supported Au particles, revealing that the less-reactive Au metal sites can activate hydrogenation reactions in the presence of hydrogen atoms that diffuse from the Au/oxide boundary.

N-heterocyclic carbenes (NHCs) have been widely utilized for the formation of self-assembled monolayers (SAMs) on various surfaces. The main methodologies for preparation of NHCs-based SAMs either requires inert atmosphere and strong base for deprotonation of imidazolium precursors or the use of specifically-synthesized precursors such as NHC(H)[HCO3] salts or NHC-CO2 adducts. Herein, we demonstrate an electrochemical approach for surface-anchoring of NHCs which overcomes the need for dry environment, addition of exogenous strong base or restricting synthetic steps. In the electrochemical deposition, water reduction reaction is used to generate high concentration of hydroxide ions in proximity to a metal electrode. Imidazolium cations were deprotonated by hydroxide ions, leading to carbenes formation that self-assembled on the electrode's surface. SAMs of NO2-functionalized NHCs and dimethyl-benzimidazole were electrochemically deposited on Au films. SAMs of NHCs were also electrochemically deposited on Pt, Pd and Ag films, demonstrating the wide metal scope of this deposition technique.

Catalytic nanoparticles are heterogeneous in their nature and even within the simplest particle various surface sites exist and influence the catalytic reactivity. Thus, detailed chemical information at the nanoscale is essential for understanding how surface properties and reaction conditions direct the reactivity of different surface sites of catalytic nanoparticles. In this work, hydroxyl-functionalized N-heterocyclic carbene molecules (NHCs) were anchored to the surface of Pt particles and utilized as chemical markers to detect reactivity variations between different surface sites under liquid and gas phase oxidizing conditions. Differences in the chemical reactivity of surface-anchored NHCs were identified using synchrotron-radiation-based infrared nanospectroscopy with a spatial resolution of 20 nanometers. By conducting IR nanospectroscopy measurements, along with complementary spatially averaged IR and X-ray spectroscopy measurements, we identified that enhanced reactivity occurred on the particles periphery under both gas and liquid phase oxidizing conditions. Under gas phase reaction conditions the NHCs hydroxyl functional groups underwent preferential oxidization to the acid along the perimeter of the particle. Exposure of the sample to harsher, liquid phase oxidizing conditions induced modification of the NHCs, which was mostly identified at the particles periphery. Analysis of X-ray absorption spectroscopy measurements revealed that exposure of the sample to oxidizing conditions induced aromatization of the NHCs, presumably due to oxidative dehydrogenation reaction, along with reorientation of the NHCs from perpendicular to parallel to the Pt surface. These results, based on single particle measurements, demonstrate the high reactivity of surface sites that are located at the nanoparticles periphery and the influence of reaction conditions on site-dependent reactivity.

The performance of catalysts depends on their nanoscale properties, and local variations in structure and composition can have a dramatic impact on the catalytic reactivity. Therefore, probing the localized reactivity of catalytic surfaces using high spatial resolution vibrational spectroscopy, such as infrared (IR) nanospectroscopy and tip-enhanced Raman spectroscopy, is essential for mapping their reactivity pattern. Two fundamentally different scanning probe IR nanospectroscopy techniques, namely, scattering-type scanning near-field optical microscopy (s-SNOM) and atomic force microscopy-infrared spectroscopy (AFM-IR), provide the capabilities for mapping the reactivity pattern of catalytic surfaces with a spatial resolution of ∼20 nm. Herein, we compare these two techniques with regard to their applicability for probing the vibrational signature of reactive molecules on catalytic nanoparticles. For this purpose, we use chemically addressable self-assembled molecules on Au nanoparticles as model systems. We identified significant spectral differences depending on the measurement technique, which originate from the fundamentally different working principles of the applied methods. While AFM-IR spectra provided information from all the molecules that were positioned underneath the tip, the s-SNOM spectra were more orientation-sensitive. Due to its field-enhancement factor, the s-SNOM spectra showed higher vibrational signals for dipoles that were perpendicularly oriented to the surface. The s-SNOM sensitivity to the molecular orientation influenced the amplitude, position, and signal-to-noise ratio of the collected spectra. Ensemble-based IR measurements verified that differences in the localized IR spectra stem from the enhanced sensitivity of s-SNOM measurements to the adsorption geometry of the probed molecules. [ABSTRACT FROM AUTHOR]

Atomic and molecular layer deposition (ALD and MLD) are techniques based on surface‐directed self‐limiting reactions that afford deposition of films controlled at the monolayer level and with extreme conformality, even on ultra‐high‐aspect‐ratio and porous substrates. These methodologies are typically used to deposit thin films with desirable physical properties and functionality. Here, the MLD process is harnessed to demonstrate the growth of molecularly thin chiral films that inherit a desirable chemical property directly from the source precursor: using this innovative technique, enantioselective nanosurfaces are managed to be grown. Specifically, the formation of a Zn/Cysteine nanostructure by MLD is demonstrated for both the l‐ and d‐ enantiomers. The reaction and growth mechanism of these chiral hybrid inorganic‐organic nanosurfaces are studied via various experimental procedures; their enantioselectivity is also demonstrated. The findings contribute to the understanding of the structure and chiral nature of hybrid inorganic‐organic nanosurfaces and open the path to the bottom‐up synthesis of diverse chiral nanosurfaces. These chiral nanostructures may play a key role in many aspects of chiral chemistry and are valuable for both fundamental science and practical applications. [ABSTRACT FROM AUTHOR]

Nanoparticle-imprinted matrices (NAIMs) are an innovative approach for the efficient and selective recognition of nanoparticles (NPs). The NAIM system comprises the preparation of thin films in which NPs are embedded as a template. The removal of the template forms nanometric voids, which are subsequently used for the selective reuptake of NPs identical to those imprinted. The recognition ability depends on several parameters such as the geometrical compatibility between the voids and imprinted NPs, the thickness of the matrix, and the supramolecular interactions between the matrix and the NP capping agents. Herein, we studied carefully the NP–matrix interactions in three NAIM systems, which were prepared by imprinting identical-sized AuNPs, bearing different carboxylic acid-functionalized thiols as capping agents, in a carboxylic acid-functionalized matrix. This experimental setup has enabled us to meticulously examine the selectivity of the NAIM systems driven by matrix–shell interactions. The three studied NAIM systems have shown high and selective reuptake ability once exposed to solutions of NPs stabilized with the same capping agent used for the imprinting process. In particular, the reuptake percentage of the originally imprinted AuNPs ranges from 50 to 80%, whereas the reuptake of AuNPs bearing different carboxylic capping agents than those imprinted was substantially lower (1–11%). Surface-sensitive polarization-modulation infrared reflection-absorption spectroscopy was utilized to correlate the selectivity of the NAIM systems and hydrogen bonding detected between the capping agents and the matrix. This study paves the way for the rational design of NAIM systems, which can be tuned according to the desired shell–matrix interactions and eventually applied in sensing and separation technologies. [ABSTRACT FROM AUTHOR]

The formation of flexible self‐assembled monolayers (SAMs) in which an external trigger modifies the geometry of surface‐anchored molecules is essential for the development of functional materials with tunable properties. In this work, it is demonstrated that NO2‐functionalized N‐heterocyclic carbene molecules (NHCs), which were anchored on Au (111) surface, change their orientation from tilted into flat‐lying position following trigger‐induced reduction of their nitro groups. DFT calculations identified that the energetic driving force for reorientation was the lower steric hindrance and stronger interactions between the chemically reduced NHCs and the Au surface. The trigger‐induced changes in the NHCs′ anchoring geometry and chemical functionality modified the work function and the hydrophobicity of the NHC‐decorated Au surface, demonstrating the impact of a chemically tunable NHC‐based SAM on the properties of the metal surface. [ABSTRACT FROM AUTHOR]

Although native chemical ligation has enabled the synthesis of hundreds of proteins, not all proteins are accessible through typical ligation conditions. The challenging protein, 125-residue human phosphohistidine phosphatase 1 (PHPT1), has three cysteines near the C-terminus, which are not strategically placed for ligation. Herein, we report the first sequential native chemical ligation/deselenization reaction. PHPT1 was prepared from three unprotected peptide segments using two ligation reactions at cysteine and alanine junctions. Selenazolidine was utilized as a masked precursor for Nterminal selenocysteine in the middle segment, and, following ligation, deselenization provided the native alanine residue. This approach was used to synthesize both the wild-type PHPT1 and an analogue in which the active-site histidine was substituted with the unnatural and isosteric amino acid βthienyl- l-alanine. The activity of both proteins was studied and compared, providing insights into the enzyme active site. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue are Elad Gross, F. Dean Toste, and co‐workers at The Hebrew University and UC Berkeley. The image depicts the flexible anchoring geometry of addressable carbene molecules on Au surface, which upon exposure to reducing conditions changed their orientation from a standing into a flat‐lying position. Read the full text of the article at 10.1002/chem.201903434. [ABSTRACT FROM AUTHOR]

The development of chemically addressable N-heterocyclic carbene (NHC) based self-assembled monolayers (SAMs) requires in-depth understanding of the influence of NHC's anchoring geometry on its chemical functionality. Herein, it is demonstrated that the chemical reactivity of surface-anchored NO 2 -functionalized NHCs (NO 2 -NHCs) can be tuned by modifying the distance between the functional group and the reactive surface, which is governed by the deposition technique. Liquid deposition of NO 2 -NHCs on Pt(111) induced a SAM in which the NO 2 -aryl groups were flat-lying on the surface. The high proximity between the NO 2 groups and the Pt surface led to high reactivity, and 85% of the NO 2 groups were reduced at room temperature. Lower reactivity was obtained with vapor-deposited NO 2 -NHCs that assumed a preferred upright geometry. The separation between the NO 2 groups in the vapor-deposited NO 2 -NHCs and the reactive surface circumvented their surface-induced reduction, which was facilitated only after exposure to harsher reducing conditions.