Ram R. R. Prasad

The development of materials that mimic the catalytic activity of natural enzymes, so called nanozymes, are of crucial importance in biochemical and biotechnological fields. A Zr‐pyridine tribenzoate metal‐organic framework nanosheet (MON), Zr‐PTB with 6‐connected Zr₆O₈ clusters is synthesized via a formic acid modulated solvothermal synthesis. The catalytic activity of MON, graphene‐like 2D materials which possess large external surface areas and tunable properties, is reported for the first time toward peptide bond hydrolysis of various peptides and proteins. Structure‐reactivity analysis and the comparison with Zr‐BTB (BTB = 1,3,5‐tri(4‐carboxyphenylbenzene)), a structural analogue of Zr‐PTB with a more hydrophobic linker, revealed a delicate interplay between coordination bonds and hydrophobic interactions with the MON's surface as the main driving forces influencing reactivity. Compared to 3D MOFs, Zr‐PTB produced a larger number of peptide fragments, indicating the importance of larger external surface area with easily accessible catalytically active sites for more comprehensive hydrolysis of proteins. The advantage of 2D MONs with respect to 3D MOFs, where pore sizes and diffusion of large substrates is a limiting factor influencing their reactivity, is further reflected by the ability to hydrolyze very large proteins. The exceptional stability of Zr‐PTB allowed for its recyclability for over 5 reaction cycles.

Peptides are important biomarkers for various diseases, however distinguishing specific amino‐acid sequences using artificial receptors remains a major challenge in biomedical sensing. This study introduces a new approach for creating highly selective recognition surfaces using phage display biopanning against metal–organic nanosheets (MONs). Three MONs (ZIF‐7, ZIF‐7‐NH_2, and Hf‐BTB‐NH₂) are added to a solution containing every possible combination of seven‐residue peptides attached to bacteriophage hosts. The highest affinity peptides for each MON are isolated through successive bio‐panning rounds. Comparison of the surface properties of the MONs and high‐affinity peptides provide useful insights into the relative importance of electrostatic, hydrophobic, and co‐ordination bonding interactions in each system, aiding the design of future MONs. Coating of the Hf‐BTB‐NH₂ MONs onto a quartz crystal microbalance (QCM) produced a five‐fold higher signal for phage with the on‐target peptide sequence compared to those with generic sequences. Surface plasmon resonance (SPR) studies produce a 4600‐fold higher equilibrium dissociation constant (K_D) for on‐target sequences and are comparable to those of antibodies (K_D = 4 x 10⁻¹⁰ m). It is anticipated that insights from the biopanning approach, combined with the highly tunable nature of MONs, will lead to a new generation of highly selective recognition surfaces for use in biomedical sensors.

Two-dimensional metal-organic nanosheets (MONs) have emerged as attractive alternatives to their three-dimensional metal-organic framework (MOF) counterparts for heterogeneous catalysis due to their greater external surface areas and higher accessibility of catalytically active sites. Zr MONs are particularly prized because of their chemical stability and high Lewis and Brønsted acidities of the Zr clusters. Herein, we show that careful control over modulated self-assembly and exfoliation conditions allows the isolation of the first example of a two-dimensional nanosheet wherein Zr₆ clusters are linked by dicarboxylate ligands. The hxl topology MOF, termed GUF-14 (GUF = Glasgow University Framework), can be exfoliated into monolayer thickness hns topology MONs, and acid-induced removal of capping modulator units yields MONs with enhanced catalytic activity toward the formation of imines and the hydrolysis of an organophosphate nerve agent mimic. The discovery of GUF-14 serves as a valuable example of the undiscovered MOF/MON structural diversity extant in established metal-ligand systems that can be accessed by harnessing the power of modulated self-assembly protocols.

Two-dimensional metal-organic nanosheets (MONs) have emerged as attractive alternatives to their three-dimensional metal-organic framework (MOF) counterparts for heterogeneous catalysis due to their greater external surface areas and higher accessibility of catalytic active sites. Zr MONs are particularly prized because of their chemical stability and the high Lewis and Brønsted acidities of the Zr clusters. Herein, we show that careful control over modulated self-assembly and exfoliation conditions allows the isolation of the first example of a two-dimensional nanosheet wherein Zr6 clusters are linked by dicarboxylate ligands. The hxl topology MOF, termed GUF-14 (GUF = Glasgow University Framework), can be exfoliated into monolayer thickness hns topology MONs, and acid-induced removal of capping modulator units yields MONs with enhanced catalytic activity towards the formation of imines and the hydrolysis of an organophosphate nerve agent mimic. The discovery of GUF-14 serves as a valuable example of the undiscovered MOF/MON structural diversity extant in established metal-ligand systems that can be accessed by harnessing the power of modulated self-assembly protocols.

Peptides are important biomarkers for a range of diseases, however distinguishing different amino-acid sequences using artificial receptors remains a major challenge in biomedical sensing. Here we present a new approach to creating highly selective recognition surfaces using phage display biopanning against metal-organic nanosheets (MONs) and demonstrate their use as the next-generation of biomolecular recognition surfaces. Three MONs (ZIF-7, ZIF-7-NH2 and Hf-BTB-NH2) were chosen as initial targets to demonstrate how simple synthetic modifications can enhance selectivity towards specific amino acid sequences. Each MON system was added to a solution containing every possible combination of 7-residue peptides attached to bacteriophage hosts and the highest affinity binding peptides for each system was identified via successive biopanning rounds. In each case only a single peptide sequence was isolated (YNYRNLL – ZIF-7, NNWWAPA – ZIF-7-NH2 and FTVRDLS – Hf-BTB-NH2). This indicates that these MONs are highly selective, which is attributed to their 2D nanosheet structure. Zeta potential and contact angle measurements were conducted on each MON and combined with calculated properties for the peptide sequences and binding studies to provide insights into the relative importance of electrostatic, hydrophobic and co-ordination bonding interactions. A quartz crystal microbalance (QCM) was used to model phage binding and the Hf-BTB-NH2 MON coated QCM produced a 5-fold higher signal for FTVRDLS functionalised phage compared to phage with generic peptide sequences. Further studies focusing on Hf-BTB-NH2 confirmed that the VRDL sequence was highly conserved, and on-target binding exhibited equilibrium dissociation constants that are comparable to natural recognition materials. Surface plasmon resonance (SPR) studies indicated a 4600-fold higher equilibrium dissociation constant (KD) for FTVRDLS compared to those obtained for off-target sequences, comparable to those of antibodies (KD = 4 x10-10). We anticipate that the highly tunable nature of MONs will enhance our understanding of binding interactions and enable molecular recognition of biomedically important peptides.

Metal–organic framework nanosheets (MONs) have recently emerged as a distinct class of 2D materials with programmable structures that make them useful in diverse applications. In this review, the breadth of applications that have so far been investigated are surveyed, thanks to the distinct combination of properties afforded by MONs. How: 1) The high surface areas and readily accessible active sites of MONs mean they have been exploited for a variety of heterogeneous, photo‐, and electro‐catalytic applications; 2) their diverse surface chemistry and wide range of optical and electronic responses have been harnessed for the sensing of small molecules, biological molecules, and ions; 3) MONs tunable optoelectronic properties and nanoscopic dimensions have enabled them to be harnessed in light harvesting and emission, energy storage, and other electronic devices; 4) the anisotropic structure and porous nature of MONs mean they have shown great promise in a variety of gas separation and water purification applications; are discussed. The aim is to draw links between the uses of MONs in these different applications in order to highlight the common opportunities and challenges presented by this promising class of nanomaterials.

Interpenetrated multicomponent MIL-142(Sc) MOFs were synthesised using the planar tritopic (4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)tribenzoate, TATB, or 4,4′,4′′-(pyridine-2,4,6-triyl)tribenzoate, PTB) and linear ditopic (1,4-benzenedicarboxylate, BDC, or 2-amino or 2-nitro-1,4-benzenedicarboxylate (NH₂- or NO₂-BDC) linkers. Structure solution of the MIL-142(Sc)-TATB series from single crystal X-ray diffraction in space group Rm reveals regioselective ordering of bulky NO₂ groups in MIL-142(Sc)-TATB-NO₂. Use of 1,3,5-benzenetribenzoate (BTB) favours instead the mesoporous Sc-BTB, the PTB analogue of which forms in the absence of BDC. The materials are highly porous: MIL-142(Sc)-TATB-BDC has a pore volume of 0.70 cm³ g⁻¹.

The scandium-based tetracarboxylate MOF STA-27, which contains a 1D rod SBU comprised of Sc₂O₁₁ dimers, is an effective Lewis acid catalyst.

Post‐synthetic modification of the hafnium metal–organic framework MOF‐808(Hf) to include triarylphosphine ligands is reported. Sulfonated phenylphosphines are incorporated without oxidation to give a “MOF ligand” that can complex late transition metals such as Ir and Rh to give a bifunctional catalyst containing both metal–phosphine complexes and the Lewis acidic framework hafnium metal sites. The metallated phosphine‐bearing MOFs act as fully heterogeneous bifunctional catalysts for tandem reductive amination and hydroaminomethylation reactions.