Experimental and Theoretical Study for the Assessment of the Conformational Stability of Polymethylene-Bridged Heteroaromatic Dimers: A Case of Unprecedented Folding (original) (raw)
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ChemistrySelect, 2017
Present manuscript reports three tripodal molecules for their special structural and conformational properties. Interestingly, X-ray structure revealed that all these molecules adopt folded conformation in solid state. Further, these molecules are flexible due to linker, may exist in various conformations, the studies have been carried out with different conformers through theoretical calculation in gaseous state.
This paper reports conformational studies of pyridazinone-based flexible dimer connected through diethylamine linker. The conformational studies have been done by X-ray crystal structure and DFT calculation. Further, after crystallization, the compound has shown two types of crystals, one is hydrated and another one is non-hydrated. The hydrated and non-hydrated crystals showed difference in their conformation due to the presence of water in crystal lattice of hydrated crystal. The difference in their conformation has been proved by crystallographic studies, DSC curves and detailed analysis of Hirshfeld surfaces and fingerprint plots facilitating a comparison of intermolecular interactions. Along with conformational studies, this compound also showed DNA binding, as revealed in docking simulation studies.
Macromolecules
Anfinsen's famous experiment showed that the restoration of catalytic activity of a completely unfolded ribonuclease A is only possible when the correct order of events is followed during the refolding process. Inspired by this work, the effect of structural constraints induced by covalent cross-links on the folding of a synthetic polymer chain via hydrogen-bonding interactions is investigated. Hereto, methacrylate-based monomers comprising either benzene-1,3,5tricarboxamide (BTA)-based or coumarin-based pendants are copolymerized with n-butyl methacrylate in various ratios via reversible addition−fragmentation chain-transfer (RAFT) polymerization. To assess whether the folding and single-chain polymeric nanoparticle (SCPN) formation depend on the order of events, we compare two folding pathways. In the one case, we first covalently cross-link the coumarin pendants within the polymers in a solvent that prevents hydrogen bonding, after which hydrogen bonding is activated, inducing folding of the polymer. In the other case, we induce hydrogen-bonding interactions between tethered BTAs prior to covalent cross-linking of the coumarin pendants. A combination of circular dichroism (CD) spectroscopy, UV−vis spectroscopy, size-exclusion chromatography (SEC), and dynamic light scattering (DLS) is employed to understand the effect of the structural constraints on the folding behavior of these synthetic polymers. The results show that like in ribonuclease A, the order of events matters greatly and determines the outcome. Importantly, a hydrogen-bond-promoting solvent prevents the formation of SCPNs upon covalent cross-linking and results in multichain aggregates. In contrast, covalently cross-linking the polymer when no hydrogen bonds are present followed by inducing hydrogen bonding favors the formation of SCPNs above the UCST of the methacrylate-based polymer. To our surprise, the two systems show a fundamentally different response to changes in temperature, indicating that also in synthetic polymers differences in the folding pathway induce differences in the properties of the resultant nanostructures.
This paper describes the results of X-ray crystallography of 4-methyl-2-oxo-6-phenyl-1,2-dihydropyridine-3-carbonitrile ( 1) and its propylene bridged dimers 2 and 3. Influence of inter- and intramolecular interactions on the conformation of propylene linker have been studied through single crystal X-ray crystallography and density functional theory studies. Hirshfeld surface analysis has been employed for the study of intermolecular interactions. However, differential scanning calorimetry analysis of compounds 2 and 3, and thermogravimetric analysis of compound 3 has been performed to determine the thermal stability. Along with molecular packing and thermal analysis, molecular docking has also been performed in the catalytic site of cyclooxygenase-2 to identify the potential anti-inflammatory activity of dimer 2 and 3. The above results suggest that the supramolecular aggregate structures which are formed in solution are of lowest energy. However, cyclooxygenase-2 active site prefers the higher energy conformers.
Cooperative Folding of Linear Poly(dimethyl siloxane)s via Supramolecular Interactions
Macromolecular Rapid Communications
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Structural Tuning and Conformational Stability of Aromatic Oligoamide Foldamers
Chemistry (Weinheim an der Bergstrasse, Germany), 2017
A series of aromatic oligoamide foldamers with two or three pyridine-2,6-dicarboxamide units as their main folding motifs and varying aromatic building blocks as linkers have been synthetized to study the effects of the structural variation on the folding properties and conformational stability. Crystallographic studies showed that in the solid state the central linker unit either elongates the helices and more open S-shaped conformations, compresses the helices to more compact conformations, or acts as a rigid spacer separating the pyridine-2,6-dicarboxamide units, which for their part add the predictability of the conformational properties. Multidimensional NMR studies showed that, even in solution, foldamers show conformational stability and folded conformations comparable to the solid-state structures.
Toward folding control in oligomers and polymers
Tetrahedron Letters, 1999
A facile synthetic route affording polycondensable monomers containing alkyl chains connected to a rigid aromatic core allowing chain folding was developed. The stepwise condensation of the monomer was shown to afford dimer, tetramer and was further proved to be applicable to higher oligomers. Such oligomers composed of "tinker toy" building blocks may be of interest for inducing controlled conformations in nanostructured materials. 6