Amides do not always work: observation of guest binding in an amide-functionalised porous host

An amide-functionalised metal organic frame-work (MOF) material, MFM-136, shows a high CO2 uptake of 12.6 mmol g-1 at 20 bar and 298 K. MFM-136 is the first example of acylamide pyrimidyl isophthalate MOF without open metal sites, and thus provides a unique platform to study guest bind-ing, particularly the role of free amides. Neutron diffraction reveals that, surprisingly, there is no direct binding between the adsorbed CO2/CH4 molecules and the pendant amide group in the pore. This observation has been confirmed un-ambiguously by inelastic neutron spectroscopy. This suggests that introduction of functional groups solely may not neces-sarily induce specific guest-host binding in porous materials, but it is a combination of pore size, geometry, and functional group that leads to enhanced gas adsorption properties

Analysis of high and selective uptake of CO2 in an oxamide-containing {Cu2(OOCR)4}-based metal-organic framework

The porous framework [Cu2(H2O)2L].4H2O.2DMA ((H¬4¬L = oxalylbis(azanediyl)diisophthalic acid; DMA = N,N-dimethylacetamide), denoted NOTT-125, is formed by connection of {Cu2(RCOO)4} paddlewheels with the isophthalate linkers in L4-. A single crystal structure determination reveals that NOTT-125 crystallises in monoclinic cell with a = 27.9161(6) Å, b = 18.6627(4) Å and c = 32.3643(8) Å, space group P2 (1)/c. The structure of this material shows fof topology, which can be viewed as the packing of two types of cages (Cage A and Cage B) in 3-dimensional space. Cage A is constructed by twelve {Cu2(OOCR)4} paddlewheels and six linkers to form an ellipsoid-shaped cavity approximately 24.0 Å along its long axis and 9.6 Å across the central diameter. Cage B consists of six {Cu2(OOCR)4} units and twelve linkers with a spherical diameter of 12.7 Å taking into account the van der Waals radii of the atoms. NOTT-125 incorporates oxamide functionality within the pore walls, and this, combined with high porosity in the desolvated NOTT-125a, is responsible for excellent CO2 uptake (40.1 wt% at 273 K and 1 bar) and selectivity for CO2 over CH4 or N2. Grand canonical Monte Carlo (GCMC) simulations show excellent agreement with the experimental gas isotherm data, and a computational study into the specific interactions and binding energies of both CO2 and CH4 with the linkers in NOTT-125 reveals a set of strong interactions between CO2 and the oxamide motif, which are not possible with a single amide

Efficient Automated Solid-Phase Synthesis of Recognition- Encoded Melamine Oligomers

Recognition-encoded melamine oligomers (REMO) are synthetic polymers with an alternating 1,3,5-triazine-piperazine backbone and side chains equipped with either a phenol or phosphine oxide recognition unit. Here, we describe an automated method for highly efficient solid-phase synthesis (SPS) of REMO of any specified length and sequence. These SPS protocols are amongst the most robust reported to date, as demonstrated by the synthesis of a mixed-sequence 42-mer, which was obtained in excellent crude purity on a 100 mg scale. Starting from loaded Wang resin and dichlorotriazine monomer building blocks, the SPS methods were automated and optimised on a commercial peptide synthesiser. Major side products were identified using LCMS, and the undesired side reactions were suppressed by the choice of resin, solvent and coupling conditions. REMO have been shown to form high-fidelity length- and sequence-selective H-bonded duplexes, analogous to nucleic acids, and automated synthesis will facilitate exploration of related functional properties, such as molecular replication and programmable self-assembly.ERC (ERC-2020-AdG-101018984-InfoMols) and EPSR

Efficient automated solid-phase synthesis of recognition-encoded melamine oligomers

Acknowledgements: We thank the ERC (ERC-2020-AdG-101018984-InfoMols) and EPSRC (EP/N509620/1) for funding.An automated solid-phase synthesis route has been developed to rapidly synthesise recognition-encoded melamine oligomer sequences up to 42 monomer units long in remarkably high yield and excellent crude purity.</jats:p

Behavior of Constitutional Dynamic Networks: Competition, Selection, Self‐sorting in Cryptate Systems

Funder: University of Strasbourg Institute for Advanced Study (USIAS)Understanding dynamic systems is a crucial step toward the design of complex matter. Here, we aim to study the behavior of Constitutional Dynamic Networks (CDNs) in conditions of dynamic competition, taking cryptands and metal cations as a test bed. The CDNs of cryptates were analyzed by NMR spectroscopy. The experimental results were complemented by extensive numerical simulations, based on a large amount of thermodynamic and kinetic data available in the literature for cryptates. Although the CDN′s output is a result of the interplay between the individual stability constants of the complexes in a mixture, the overall effect may be governed by only one – the most thermodynamically stable member of a network. Significantly, these findings indicate that an increase in complexity (multiplicity and connectivity) of a system may, in conditions of dynamic competition, result in “simplexity”, i. e. a simplification of the output of the system

Selective Duplex Formation in Mixed Sequence Libraries of Synthetic Polymers

Publication status: PublishedRecognition-encoded melamine oligomers (REMO) are synthetic polymers that feature an alternating 1,3,5-triazine-piperazine backbone and side-chains equipped with either a phenol or phosphine oxide recognition unit. An automated method for the solid-phase synthesis (SPS) of REMO of any specified sequence has been developed starting from dichlorotriazine monomer building blocks. Complementary homo-oligomers with either six phenols or six phosphine oxides were synthesized and shown to form a stable duplex in nonpolar solvents by NMR denaturation experiments. The duplex was covalently trapped by equipping the ends of the oligomers with an azide and an alkyne group and using a copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction. The SPS methodology was adapted to synthesize mixed sequence libraries by using a mixture of two different dichlorotriazine building blocks in each coupling cycle of an oligomer synthesis. The resulting libraries contain statistical mixtures of all possible sequences. The self-assembly properties of these libraries were screened by using the CuAAC reaction to trap any duplexes present. In mixed sequence libraries of 6-mers, the trapping experiments showed that only sequence-complementary oligomers formed duplexes at micromolar concentrations in dichloromethane. The automated synthesis approach developed here provides access to large libraries of mixed sequence synthetic polymers, and the covalent trapping experiment provides a convenient tool for screening functional properties of mixtures. The results suggest high-fidelity sequence-selective duplex formation in mixtures of 6-mer sequences of the REMO architecture

Behavior of Constitutional Dynamic Networks: Competition, Selection, Self‐sorting in Cryptate Systems

Abstract Understanding dynamic systems is a crucial step toward the design of complex matter. Here, we aim to study the behavior of Constitutional Dynamic Networks (CDNs) in conditions of dynamic competition, taking cryptands and metal cations as a test bed. The CDNs of cryptates were analyzed by NMR spectroscopy. The experimental results were complemented by extensive numerical simulations, based on a large amount of thermodynamic and kinetic data available in the literature for cryptates. Although the CDN′s output is a result of the interplay between the individual stability constants of the complexes in a mixture, the overall effect may be governed by only one – the most thermodynamically stable member of a network. Significantly, these findings indicate that an increase in complexity (multiplicity and connectivity) of a system may, in conditions of dynamic competition, result in “simplexity”, i. e. a simplification of the output of the system