Datta Markad

The selective separation of enantiomers is important for industrial technologies such as pharmaceuticals, biotechnology, and agrochemicals. Chiral porous materials have been used as the stationary phase for the chromatographic separation of enantiomers; however, they lack synthetic and performance designability. Here we present a new chiral metal‐organic framework with excellent chromatographic enantioseparation performance for a family of aromatic chiral molecules. This material has been developed by diversifying the amino acid sidechains appended to an underlying common structural framework. The structure of the framework places the bulky isopropyl sidechain of L ‐valine in the one‐dimensional pore channels characteristic of the materials family, modulating the accessible space to emphasize the helical shape of the channels. The dimensions of the pores are adapted to those of guests, through conformational flexibility directed by the sidechain, creating appropriate adsorption sites for functionalized aromatic guests. This porous framework affords superior enantioseparation performance compared to the same underlying framework decorated with the shorter methyl sidechain. These results demonstrate that the structure and porosity of dynamic chiral metal‐organic frameworks can be tailored using amino acid‐derived linkers and enhance the enantiomeric separations through stimulation of conformational flexibility.

The selective separation of enantiomers is important for industrial technologies such as pharmaceuticals, biotechnology, and agrochemicals. Chiral porous materials have been used as the stationary phase for the chromatographic separation of enantiomers; however, they lack synthetic and performance designability. Here we present a new chiral metal‐organic framework with excellent chromatographic enantioseparation performance for a family of aromatic chiral molecules. This material has been developed by diversifying the amino acid sidechains appended to an underlying common structural framework. The structure of the framework places the bulky isopropyl sidechain of L ‐valine in the one‐dimensional pore channels characteristic of the materials family, modulating the accessible space to emphasize the helical shape of the channels. The dimensions of the pores are adapted to those of guests, through conformational flexibility directed by the sidechain, creating appropriate adsorption sites for functionalized aromatic guests. This porous framework affords superior enantioseparation performance compared to the same underlying framework decorated with the shorter methyl sidechain. These results demonstrate that the structure and porosity of dynamic chiral metal‐organic frameworks can be tailored using amino acid‐derived linkers and enhance the enantiomeric separations through stimulation of conformational flexibility.

The ordering of multiple organic linkers with different sizes and geometries on metal-organic frameworks (MOFs) offers structures with advanced complexity and functionality for enhanced properties. The selection of the components and the number of synthesis steps are commonly rationalized to match existing structural motifs in order to increase the probability of producing the designed new frameworks. Alternatively, combining multiple components, without a preconceived structural model, allows for the exploration of unprecedented structural characteristics. However, this approach requires a large number of experiments to identify both the composition and conditions for a successful synthesis. Here, we report a new Zr-MOF containing ordered straight and bent dicarboxylate linkers prepared by a one-pot synthesis. The discovery was made by high-throughput exploration of the chemical space composed of two linkers, the source of Zr, and the modulator. The linkers and the Zr₆ cluster are ordered on an fcu framework that is tetragonally distorted from its typical cubic symmetry. The arrangement of linkers with different sizes and geometries affords cages and windows with shapes that have not been reported previously, despite the plethora of known fcu-based MOFs. The new MOF exhibits chromatographic separation of the n-hexane/benzene/cyclohexane mixture and demonstrates reversible unbinding and rebinding of the bent linkers upon the addition and removal of protic solvents. The unusual structural properties of the new MOF arise from ordering linkers in a non-predetermined manner following high-throughput synthesis exploration.

The Oxygen Evolution Reaction (OER) is considered to be one of the most important processes for energy storage and conversion applications. However, due to its sluggish kinetics it becomes extremely crucial to design and develop cost‐effective, stable and highly efficient electrocatalysts. Herein, we report two lead(II) based coordination polymers (CPs) {[Pb ₂ (TPBN)(TDC) ₂ ].3H ₂ O} _n ( CP1 ), and {[Pb ₂ (TPBN)(FDC) ₂ ].H ₂ O} _n ( CP2 ) synthesized via self‐assembly at ambient conditions in good yields (where TPBN= N,N′,N′′′,N′′′′‐tetrakis‐(2‐pyridylmethyl)‐1,4‐diaminobutane, H ₂ TDC=2,5‐2,5‐thiophenedicarboxylic acid, and H ₂ FDC=2,5‐furandicarboxylic acid. Their 3D structures were determined by Single‐crystal X‐ray diffraction (SCXRD) studies. The bulk purity and thermal stability of CP1 and CP2 were studied by powder X‐ray diffraction studies and thermogravimetric analysis, respectively. Both the CPs showed remarkable catalytic activity for the OER. With a current density of 15 mA cm ⁻² , for both CP1 and CP2 , overpotentials of 570 mV and 630 mV with tafel slope values of 112 mV dec ⁻¹ , and 178 mV dec ⁻¹ respectively for CP1 and CP2 in 1.0 M alkaline (KOH) solution was obtained. It is notable that the difference in their catalytic performance – CP1 is better than CP2 , can be attributed to the subtle single heteroatom in the dicarboxylate ring (S in thiophene and O in furan, respectively).

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal–organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognize and order multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level.

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal–organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognize and order multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level.

Mechanical properties of drug molecules largely affect pharmaceutical processing into a finished product. Structural insights together with computational prediction tools help develop a crystal engineering approach to modulate crystal mechanical parameters. This study focuses on mechanical anisotropy in ambrisentan polymorphs (form I and II). Nanoindentation experiments revealed higher hardness (H) and elastic modulus I of form I as compared to form II, while form II showed lower H/E (0.03) as compared to form I (0.08). These properties were rationalized based on the potential slip plane in form II, which exhibited relatively larger d-spacing and lack of hydrogen bonding interaction across plane. On the contrary, form I revealed the presence of an interlocked 3D clustering network that may retard the gliding of the slip planes under the indention stress. These features were found to be consistent with the predicted mechanical parameters. Besides, the energy framework calculation displays relatively higher interlayer energy in form I, which is attributed to the cohesive crystal lattice. However, in form II, a smaller number of intertwined cylinders resulted in a smaller energetic barrier for sliding molecular layer under applied load during the nanoindentation experiment. In addition, AFM studies have indicated higher surface roughness in form II pointing towards softer and less brittle crystal than form I responsible for ease of elasticity under external stress. Hence, in-depth knowledge of structural features together with mechanical properties helps to establish structure–mechanical property relationships. Overall, form II (metastable form) exhibited higher plasticity and good tabletability than form I, which is attributed to the differential crystal packing, slip systems, strength of intermolecular interactions, surface contacts, and surface roughness. The present study showcases the implications of the crystal structure anisotropy on the mechanical performances that would aid in the selection of the right solid form in formulation development.

The α-aminonitriles are versatile building blocks in the synthesis of natural or artificial amino acids as well as important intermediates in organic synthesis. For their synthesis, the three-component Strecker reaction involving an aldehyde or a ketone together with amines and trimethylsilyl cyanide is used. In the literature, hydrothermally produced metal-based heterogeneous Lewis acid catalysts have been utilized in various solvents. In this work, we aimed at a greener approach toward such catalysis by (a) making two precatalysts with d¹⁰ metal centers, {[Zn(hipamifba)(H₂O)]·2H₂O}_n (1) and {[Cd(hipamifba)(H₂O)₂]·2H₂O}_n (2) (where H₂hipamifba = 4-(((4-((carboxymethyl) carbamoyl)phenyl)amino)methyl)benzoic acid), via an easy and scalable room-temperature method, and (b) showcasing the use of these coordination polymers (CPs) as very efficient, recyclable, and heterogeneous catalysts for the Strecker reaction to form α-aminonitriles in high yields under solvent-free reaction at ambient conditions. This has also allowed us to demonstrate the importance of open metal sites in such catalysis through an efficiency comparison between activated 1 and 2. In addition, activated 2 exhibited a wide substrate scope including a natural product Girgensohnine, providing an example of a natural product synthesis by a CP catalyst via an organic transformation such as the Strecker reaction.

A well-organized worldwide effort in providing remedies to sustainable clean energy generation and storage has focused on the strategic design and development of stable and efficient earth-abundant metal (Fe, Co, Ni, Pb, etc.)-based electrocatalysts for the oxygen evolution reaction (OER). Unfortunately, examples of Pb-based catalysts for such a process are rare. In this work, based on the dual-linker strategy, we have designed and synthesized two new two-dimensional (2D) coordination polymers of Pb with the hcb topology, [Pb₂(tpbn)(adc)₂]·4H₂O·0.5CH₃OH}_n (CP1) and {[Pb₂(tpbn)(fum)₂]·7H₂O}_n (CP2), in excellent yields by the room-temperature self-assembly of Pb(OAc)₂, tpbn, and H₂adc or H₂fum (where tpbn = N,N',N‴,N‴'-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane, H₂adc = acetylene dicarboxylic acid, and H₂fum = fumaric acid). In addition to determining their X-ray single crystal structures, the phase purity and thermal stability were established by powder X-ray diffraction and thermogravimetric analysis, respectively. Furthermore, these were also characterized by the microscopic techniques (SEM/EDX and TEM/HRTEM). For their conductive and highly stable nature in alkaline medium, both CP1 and CP2 were tested for their suitability in the OER process. Interestingly, with a subtle change from adc in CP1 to fumarate in CP2 as the dicarboxylate linker, the latter performed much better than the former and displayed an excellent electrochemical stability in basic medium. Remarkably, CP2 has one of the lowest Tafel values (35 mV dec^-1) and a low overpotential value (140 mV vs RHE) in 0.5 M KOH compared to those reported for any materials. Such a comparative study with CP1 and CP2, which are the simplest CPs and made with green-chemistry protocols for an easy making in large quantities, provides an outlook to developing the next-generation Pb-based electrocatalysts.