Postsynthetic Functionalization Research Articles

Tandem catalysis by ultrathin metal-organic nanosheets formed through post-synthetic functionalisation of a layered framework.

Covalent post-synthetic functionalisation of layered metal-organic frameworks is demonstrated as a new approach to forming ultrathin nanosheets for use in catalysis. An aminoterephthalate framework was partially functionalised with sulfonate chains and exfoliated to form predominantly monolayer nanosheets able to catalyse a two-step acid-base reaction in one pot.

Making Prussian blue analogues nanoparticles luminescent: effect of the luminophore confinement over the properties.

In this communication, we report the post-synthetic functionalization of K+/Ni2+/[Cr(CN)6]3- Prussian blue analogue (PBA) nanoparticles by the 2-aminoanthracene luminophore to yield a bifunctional magneto-luminescent nanosystem. The photoluminescence properties of the fluorophore are found modified by the confinement effect upon adsorption, while the magnetic behavior of PBA is preserved.

A new catechol-functionalized polyamidoamine as an effective SPION stabilizer

A synthetic strategy was established for decorating and stabilizing superparamagnetic iron oxide nanoparticles (SPIONs) with a zwitterionic linear polyamidoamine (PAA). The strategy was successfully tested with a PAA coded ISA23 previously found endowed with interesting biological properties, such as biocompatibility, degradability in aqueous media and stealth-like properties when injected in test animals. A post-synthetic functionalization with catechol-bearing moieties of a preformed PAA was successfully carried out. ISA23 was obtained by polyaddition reactions of methyl-piperazine and 2,2-bis(acrylamidoacetic) acid. It was functionalized using nitrodopamine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling agent, to randomly form amide bonds with 17% of ISA23 carboxylic groups (ISA23-ND). SPIONs were prepared by a thermal decomposition synthesis in 1-octadecene with oleic acid, and then transferred in water by two distinct ligand exchange procedures: i) the direct displacement of oleate molecules from SPION surface by ISA23 in a biphasic (n-hexane/water) environment; ii) the two-step method involving an intermediate small molecule, tetramethylammonium hydroxide, used as a transient transfer agent, which was in turn exchanged with ISA23-ND in a second exchange step occurring in water. The two-step procedure provided a SPION@PAA nanocomposite more stable than that obtained by the one-step procedure in the presence of an applied external magnetic field. ATR-FTIR spectroscopy, ζ-potential and thermogravimetric analysis (TGA) showed the presence of the ISA23 on the SPION surface. In particular, TGA showed that the ISA23-ND amount on the NPs accounted for 26% of the overall nanocomposite mass. The nanocomposite size was determined by both TEM (21.1±2.9 nm) and DLS measurements (hydrodynamic size 100±28 nm). SPION@ISA23-ND were re-suspended after lyophilization reverting to their pristine dimensions. The SPION@ISA23-ND adsorption of BSA in water, considered as the first stage of phagocytosis, was very low, suggesting that ISA23 could impart stealthiness to SPION@ISA23-ND. 1H-NMR relaxivity measurements showed an r2 value of 158 s-1 mmol-1 L (vs 100 s-1 mmol-1L for Endorem®) at relevant clinical fields for magnetic resonance imaging (from 0.2 to 1.5 T). SPION@ISA23-ND was tested on HeLa cells and their internalization was visualized by reflectance microscopy. Finally, with the aim of prepare a new dual magneto-optical system, a synthetic procedure to decorate SPION@ISA23-ND with a fluorescent dye was devised, even though the emission intensity of the resultant conjugate was lower than expected, possibly due to luminescence quenching caused by the closeness of emitting moieties to the SPION surface.

Synthesis of Phosphonic Acid Ligands for Nanocrystal Surface Functionalization and Solution Processed Memristors

Here, we synthesized 2-ethylhexyl, 2-hexyldecyl, 2-[2-(2-methoxyethoxy)ethoxy]ethyl, oleyl, and n-octadecyl phosphonic acid and used them to functionalize CdSe and HfO2 nanocrystals. In contrast to branched carboxylic acids, postsynthetic surface functionalization of CdSe and HfO2 nanocrystals was readily achieved with branched phosphonic acids. Phosphonic acid capped HfO2 nanocrystals were subsequently evaluated as memristors using conductive atomic force microscopy. We found that 2-ethylhexyl phosphonic acid is a superior ligand, combining a high colloidal stability with a compact ligand shell that results in a record-low operating voltage that is promising for application in flexible electronics.

Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization.

Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust and magnetic functionalized monolayers of coordination polymers. A series of five isostructural layered magnetic coordination polymers based on Fe(II) centres and different benzimidazole derivatives (bearing a Cl, H, CH3, Br or NH2 side group) were first prepared. On mechanical exfoliation, 2D materials are obtained that retain their long-range structural order and exhibit good mechanical and magnetic properties. This combination, together with the possibility to functionalize their surface at will, makes them good candidates to explore magnetism in the 2D limit and to fabricate mechanical resonators for selective gas sensing.

Site Isolation in Metal-Organic Frameworks Enables Novel Transition Metal Catalysis.

Comprising periodically repeating inorganic nodes and organic linkers, metal-organic frameworks (MOFs) represent a novel class of porous molecular solids with well-defined pores and channels. Over the past two decades, a large array of organic linkers have been combined with many inorganic nodes to afford a vast library of MOFs. The synthetic tunability of MOFs distinguishes them from traditional porous inorganic materials and has allowed the rational design of many interesting properties, such as porosity, chirality, and chemical functionality, for potential applications in diverse areas including gas storage and separation, catalysis, light harvesting, chiral separation, and chemical sensing. In particular, the molecular functionality and intrinsic porosity of MOFs have rendered them attractive candidates as porous single-site solid catalysts for a large number of organic transformations. MOF catalysts offer several advantages over their homogeneous counterparts, including enhanced stability, recyclability and reusability, and facile removal of the toxic catalyst components from the organic products. Additionally, the highly ordered nature of MOFs leads to the generation of single-site solid catalysts, allowing for precise characterization of the catalytic sites through X-ray diffraction, X-ray absorption, and other spectroscopic interrogations and facilitating the elucidation of reaction mechanisms. Thus, MOF catalysis represents a fertile research area that is expected to witness continued growth in the foreseeable future. In this Account, we present our recent research progress in developing ligand-supported single-site MOF catalysts for challenging organic reactions. We present two complementary approaches to the design of ligand-supported MOF catalysts: direct incorporation of prefunctionalized organic linkers into MOFs and postsynthetic functionalization of orthogonal secondary functional groups of the organic linkers in MOFs. Monophosphine-, bipyridine-, β-diketimine-, and salicylaldimine-based ligands have been used to support both precious (Pd, Pt, Ir, Ru) and earth-abundant (Cu, Co, Fe) metals for a number of interesting catalytic reactions. The resulting MOF catalysts feature stable low-coordination species with minimum steric bulk around the active site-a feat that remains a challenge for homogeneous catalysts. For each ligand, we describe types of reactions catalyzed by the MOF in comparison with its homogeneous counterpart. In all cases, MOF catalysts outperformed their homogeneous counterparts in terms of catalyst stability, catalytic activity, and recyclability and reusability. Interestingly, several bipyridine- and salicylaldimine-ligated earth-abundant-metal-based MOF catalysts do not have homogeneous counterparts because the molecular compounds disproportionate or oligomerize to form inactive species in solution. This Account not only presents several interesting designs of ligand-supported single-site MOF catalysts but also provides illustrative examples of how site isolation in MOF catalysts shuts down deactivation pathways experienced by homogeneous systems. With precise knowledge of MOF structures and catalytically active sites, we envision the development of practically useful MOF catalysts comprising tailor-made building blocks that rationally optimize catalytic activities and selectivities.

Postsynthetic Covalent Modification in Covalent Organic Frameworks

AbstractThe modification of covalent organic frameworks (COFs) based on postsynthetic covalent linkages is discussed in this review. In this strategy, the COF is preparedas scaffold and then assembled with functional groups with preservation of structural skeleton. Recent studies indicate that a number of COFs, such as COF‐5 and 3D‐OH‐COOF, are controllable to postsynthetic modification. Furthermore, covalentmodifications including triazole, ester, amide, sulfide, o‐carbamate, ether, and oxime are suitable for postsynthetic functionalization. The rapid development of postsynthetic modification demonstrates that this approach will provide a general platform to create COFs as robust functional porous materials for wide applications.

Uio-66 As an Effective Support of Metal Oxides for Oxygen Evolution Catalysis

The most well-known electrocatalyst for oxygen evolution reaction (OER) have been noble metals or combination of them such as ruthenium, and/or iridium.1 Due to their cost and scarcity, however, there is a persistent search for alternative materials. Metal organic frameworks (MOFs) have recently attracted significant attention due to their versatility and stability in wide range of environments that allow for post-synthetic modifications and functionalization. This tunability of MOFs has given way to the development of exceptional electrocatalyst that can have comparable performance to noble metals, and mitigate the issues found in them.2 In this study we investigated the OER performance of the zirconia-based MOF, UiO-66, as a support for metal oxides such as CoOx, MnOx and TiOx. UiO-66 has previously been used as a support for catalyst such as molybdenum, and has rendered comparable catalytic performance to that of platinum carbon for the hydrogen evolution reaction (HER).3 Having a MOF support for catalysts, such as metal oxides, can be ideal due to the well-defined MOF surrounding that will allow them to function as catalyst, but protect them from agglomeration at high temperatures. We synthesized samples containing UiO-66, graphene oxide (GO) and cobalt oxide (CoOx) using the solvothermal method. Electrochemical characterization revealed that the hybrid CoOx@UiO-66/GO affords an excellent catalytic activity for OER with an onset potential of 1.6 V versus RHE, comparable to that of Ir and Ru-based catalysts.2 Additionally, this study contains discussions on the factors of the high OER activity through a series of physical characterizations of the hybrid catalyst.

Multifunctional Cyclopentadienes as a Scaffold for Combinatorial Bioorganometallics in [(η5 -C5 H2 R1 R2 R3 )M(CO)3 ] (M=Re, 99m Tc) Piano-Stool Complexes.

Multifunctional cyclopentadiene (Cp) ligands and their rhenium and 99m Tc complexes were prepared by a versatile synthetic route. The properties of these Cp ligands can be tuned on demand, either during their synthesis (variation of R1 ) or through post-synthetic functionalization with two equal or different vectors (V1 and V2 ). Variation of these groups enables a combinatorial approach in the synthesis of bioorganometallic complexes. This is demonstrated by the preparation of Cp ligands containing both electron-donating and electron-withdrawing groups at the R1 position and their subsequent homo- or heterofunctionalization with biovector models (benzylamine and phenylalanine) under standard amide bond-formation conditions. All ligands can be coordinated to the fac-[Re(CO)3 ]+ and fac-[99m Tc(CO)3 ]+ cores to give tetrafunctional complexes in straightforward and functional-group-tolerant procedures. The 99m Tc complexes were prepared in one step, in 30 min, and under aqueous conditions from generator-eluted [99m TcO4 ]- .

Flexible Alkyne-Linked Thymidine Phosphoramidites and Triphosphates for Chemical or Polymerase Synthesis and Fast Postsynthetic DNA Functionalization through Copper-Catalyzed Alkyne-Azide 1,3-Dipolar Cycloaddition.

Two alternative flexible alkyne-linked thymine nucleosides (propargyl-diethylene glycol- or undecyn-linked 5-hydroxymethyluracil derivatives), as well as their phosphoramidites and triphosphates, were designed and synthesized. The nucleoside 3'- O-phosphoramidites were successfully incorporated into oligonucleotides on a solid support, whereas the nucleoside triphosphates served as good substrates for polymerase synthesis of modified DNA, which underwent fast and efficient copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) reactions.

Metal-Organic Framework Nanoparticles.

Due to their well-defined 3D architectures, permanent porosity, and diverse chemical functionalities, metal-organic framework nanoparticles (MOF NPs) are an emerging class of modular nanomaterials. Herein, recent developments in the synthesis and postsynthetic surface functionalization of MOF NPs that strengthen the fundamental understanding of how such structures form and grow are highlighted; the internal structure and external surface properties of these novel nanomaterials are highlighted as well. These fundamental advances have resulted in MOF NPs being used as components in chemical sensors, biological probes, and membrane separation materials, as well as building blocks for colloidal crystal engineering.

Gulf-Selective Postsynthetic Functionalization of a Soluble Hexabenzoovalene.

The interest in 2D-annulated polycyclic aromatic hydrocarbons (PAHs) has risen in recent years due to promising applications in using PAHs for organic electronics. The larger the PAHs, the more insoluble they are, making their characterization and especially selective functionalization difficult. Triptycene end-capping has been introduced to circumvent the problem of low solubility of a hexabenzoovalene (HBO). Additionally, the tendency to form single-crystals for X-ray diffraction is preserved. The good solubility of the HBO makes it possible to selectively difunctionalize the compound in the "gulf" region to change electronic properties of the π-system, which has been investigated photophysically as well as electrochemically.

Frontispiece: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiece: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiz: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiz: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Post-transcriptional labeling by using Suzuki-Miyaura cross-coupling generates functional RNA probes.

Pd-catalyzed C-C bond formation, an important vertebra in the spine of synthetic chemistry, is emerging as a valuable chemoselective transformation for post-synthetic functionalization of biomacromolecules. While methods are available for labeling protein and DNA, development of an analogous procedure to label RNA by cross-coupling reactions remains a major challenge. Herein, we describe a new Pd-mediated RNA oligonucleotide (ON) labeling method that involves post-transcriptional functionalization of iodouridine-labeled RNA transcripts by using Suzuki–Miyaura cross-coupling reaction. 5-Iodouridine triphosphate (IUTP) is efficiently incorporated into RNA ONs at one or more sites by T7 RNA polymerase. Further, using a catalytic system made of Pd(OAc)2 and 2-aminopyrimidine-4,6-diol (ADHP) or dimethylamino-substituted ADHP (DMADHP), we established a modular method to functionalize iodouridine-labeled RNA ONs in the presence of various boronic acid and ester substrates under very mild conditions (37°C and pH 8.5). This method is highly chemoselective, and offers direct access to RNA ONs labeled with commonly used fluorescent and affinity tags and new fluorogenic environment-sensitive nucleoside probes in a ligand-controlled stereoselective fashion. Taken together, this simple approach of generating functional RNA ON probes by Suzuki–Miyaura coupling will be a very important addition to the resources and tools available for analyzing RNA motifs.

Postsynthetic Functionalization of Three-Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions.

Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three-dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy-functionalized COF through postsynthetic modification of a hydroxy-functionalized COF, and for the first time exploration of the 3D carboxy-functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy-functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd3+ over Sr2+ and Fe3+ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.

Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

AbstractChemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three‐dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy‐functionalized COF through postsynthetic modification of a hydroxy‐functionalized COF, and for the first time exploration of the 3D carboxy‐functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy‐functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd3+ over Sr2+ and Fe3+ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.

A Novel and Versatile Grafting Procedure: Toward the Highest Possible Sulfonation Degree of Mesoporous Silica

AbstractA unique method for the postsynthetic functionalization of ordered mesoporous silica materials is described. The functionalization is done via a chemical vapor deposition‐type method and leads to the quantitative reaction of isolated surface silanol groups of mesoporous silica materials with organosilane molecules. The result is a highly sulfonated material by anchorage of 3‐mercaptopropyltrimethoxysilane molecules and subsequent oxidation of the thiol groups to sulfonic acid groups. Ordered mesoporous KIT‐6 and SBA‐15 are chosen as model systems. The sulfonated material exhibits a functionalization degree of 1.05 resp. 1.32 molecules nm−2, which is on the maximum of the theoretical achievable functionalization density resulting in high ion exchange capacities of 1.22 and 1.12 mmol g−1. The versatility and mildness of this method opens up functionalization possibilities for a wide range of other materials, which could be sulfonated or otherwise modified with silanes, and tailored for the further application in catalysis or as solid‐state proton conductors.

Functionalized biochar derived from heavy metal rich feedstock: Phosphate recovery and reusing the exhausted biochar as an enriched soil amendment

This paper provides a circular win-win approach for recycling rhizofiltration biomass into multifunctional engineered biochar for various environmental applications (e.g. phosphate recovery) with a potential reuse of the exhausted biochar as an enriched soil amendment. Functionalized biochars were derived from the disposals of water hyacinth (Eichhornia crassipes) plants grown in synthetic contaminated water spiked with either Fe2+ (Fe-B), Mn2+ (Mn-B), Zn2+ (Zn-B) or Cu2+ (Cu-B) comparing with the original drainage water as a control treatment (O-B). The in-situ functionalization of biochar via the inherently heavy metal-rich feedstock produced homogenous organo-mineral complexes on biochar matrix without environmental hazards (e.g. volatilization or chemical sludge formation) associated with other post-synthetic functionalization methods. Physicochemical analyses (SEM-EDS, XRD, FTIR, BET and zeta potential (ζ)) confirmed the functionalization of Fe-B, Zn-B and Cu-B due to organo-mineral complexes formation, maximizing specific surface area, lowering the electronegativity, originating positively charged functional groups, and thus improving the anion exchange capacity (AEC) comparing with O-B. In contrary, physicochemical characteristics of Mn-B was in similarity with those of O-B. Phosphate recovery by the functionalized biochar was much greater than that of the unfunctionalized forms (O-B and Mn-B). Precipitation was the dominant chemisorption mechanisms for phosphate sorption onto biochar compared to other mechanisms (ion exchange, electrostatic attraction and complexation with active functional groups). The exhausted biochar showed an ameliorating effect on the low water and nutrient supply potentials of sandy soil, and thus improved fresh biomass yield and nutritional status of maize seedlings with some restrictions on its high micronutrient content.

Hybrid Postsynthetic Functionalization of Tetraethylenepentamine onto MIL-101(Cr) for Separation of CO2from CH4

To remove CO2 from CH4, tetraethylenepentamine was grafted onto coordinatively unsaturated centers of MIL-101(Cr) by postsynthetic functionalization: wet impregnation at 298 K, followed by grafting, drying, and washing. Compared to MIL-101(Cr), TEPA–MIL-101(Cr) showed 54% higher CO2 adsorption at 1 bar and 98% reduction of CH4 adsorption at 60 bar. The ideal adsorption solution theory (IAST) selectivity of CO2/CH4 for a binary gas mixture of 2% CO2 + 98% CH4 at 298 K and 60 bar predicted by the Toth equation was found to be 11 and 598 for ungrafted and grafted MIL-101(Cr), respectively. Single column breakthrough tests were performed for upgrading the 2% CO2 + 98% CH4 mixture to liquefied quality of natural gas (CO2 < 50 ppm) under various operating conditions including different temperatures and total amount of purge gas at the fixed pressure of 60 bar and temperature of 298 K. At the feed flow rate of 1000 sccm, the TEPA–MIL-101(Cr) extrudates obtained 0.89 mmol/g CO2 adsorption capacity and nearly 83% ...