Supramolecular ZwitterionicPolymers: Dynamic TraitsImparted by Ionic Interactions

The structures of zinc carbene ZnCH 2 and zinc carbyne HZnCH, and the conversion transition states between them are optimized at B3LYP/aug‐cc‐pVTZ, MP2/aug‐cc‐pVTZ, and CCSD/aug‐cc‐pVTZ levels of theory. The thermodynamic energies with CCSD(T) method are further extrapolated to basis set limit through a series of basis sets of aug‐cc‐pVXZ (X=D, T, Q, 5). The Zn−C bonding characteristics are interpreted by molecular plots, Laplacian of density plots, the integrated delocalization indices, net atomic charges, and derived atomic hardness. On the one hand, the studies demonstrated the efficiency of DFT method in structure optimizations and the accuracy of CBS method in obtaining thermodynamic energies; On the other hand, the density analysis of CCSD/aug‐cc‐pVDZ density demonstrates that both the sharing interaction and ionic interaction are important in ZnCH 2 ad HZnCH. The 3 B 1 state of ZnCH 2 is the global minimum and formed in visible light, but its small bond dissociation energy (47.0 kcal/mol) cannot keep the complex intact under UV light (79.4–102.1 kcal/mol). However, the 3 Σ − state of HZnCH can survive the UV light due to the greater Zn−C dissociation energy (100.7 kcal/mol). The delocalization indices of Zn…C in both 3 B 1 of ZnCH 2 (0.777) and the 3 Σ − state of HZnCH (0.785) are close to the delocalization index of the single C−C bond of ethane (0.841), i. e. the nomenclature of Zinc carbene and Zinc carbyne is incorrect. The stronger Zn−C bond in the 3 Σ − state of HZnCH than in the 3 B 1 state of ZnCH 2 can be attributed to the larger charge separation in the former. It was found that the Zn−C bonds in related Zinc organic compounds were also single bonds no matter whether the organic groups are CR, CR 2 , or CR 3 . The ionic interactions were discussed in terms of the atomic hardness that were in turn related to ionization energy and electron affinity. The unique combination of covalent and ionic characteristics in the Zn−C bonds of organic Zinc compounds could be the origin of many interesting applications of organic Zinc reagents.

The taper-shaped monoesters of mono-3a, di-3c, tri-3d, and tetra-3f ethylene glycol with 3,4,5-tris(p-dodecyloxybenzyloxy)benzoic acid 1 and their corresponding polymethacrylates, 6a, b, c and d, respectively, self-assemble into a tubular supramolecular architecture displaying an enantiotropic columnar hexagonal (Φh) mesophase. Characterization of this supramolecular architecture by a combination of differential scanning calorimetry, wide- and small-angle X-ray scattering, thermal optical polarized microscopy, and molecular modelling suggests a model in which the stratum of the column is formed by in between 3.9 and 5.4 molecules of 3 or 4.5 and 5.9 repeat units of 6 with their oligo(oxyethylenic) segments melted and segregated in the centre of the column and their melted alkyl tails radiating towards the columns periphery. 2-(2-Methoxyethyl) 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate 3b(the model compound of 3a in which the hydroxy group has been replaced by a methoxy group) is only crystalline, while bis(2-{2-[3,4,5-tris(p-dodecyloxybenzyloxy)benzoyloxy]ethoxy}ethyl) ether 3g(which is the dimer of 3c) displays a monotropic Φh phase. These results support that endo-recognition by H-bonding of the oligo(oxyethylenic)receptor of 3 and exo-recognition provided by the tapered 3,4,5-tris(p-dodecyloxybenzyloxy)benzoate fragment of 3(most probably functioning by hydrophobic–hydrophobic interactions) provide the driving force for the self-assembly of this tubular supramolecular architecture. In the case of the supramolecular architectures derived from 6, the H-bonding interaction is replaced by the poly(methacrylate) backbone which leads to a Φh mesophase that undergoes isotropization at temperatures that are 40 °C higher than those of 3. The channel penetrating the middle of the supramolecular cylinders derived from both 3 and 6 dissolves alkali-metal triflates and the ionic interaction generated by the dissolved ion-pairs enhances the thermal stability of their Φh phase. These results allowed for the first time a comparison between a 'molecular' polymer backbone effect (polymethacrylate) and a 'supramolecular' polymer backbone effect (generated by way of H-bonding and ionic interactions) to be made.

Trajectory model for collision‐induced dissociation of two molecules with ionic bond is developed on the base of potential energy surface, which ensure quantitative agreement of calculated data with experimental results. Dynamics of interaction is discussed on the bases of the most typical trajectories and angular distributions of the products of interaction.

Polymeric supramolecular assemblies based on multivalent ionic interactions for biomedical applications

Peptide fragments corresponding to the N- and C-terminal portions of bovine ubiquitin, U(1-35) and U(36-76), are shown by NMR to associate in solution to form a complex of modest stability (Kassn approximately 1.4 x 10(5) M(-1) at pH 7.0), with NMR features characteristic of a nativelike structure. The complex undergoes cold denaturation, with temperature-dependent estimates of stability from NMR indicating a DeltaC(p) degrees for fragment complexation in good agreement with that determined for native ubiquitin, suggesting that fragment association results in the burial of a similar hydrophobic surface area. The stability of the complex shows appreciable pH dependence, suggesting that ionic interactions on the surface of the protein contribute significantly. However, denaturation studies of native ubiquitin in the presence of guanidine hydrochloride (Gdn.HCl) show little pH dependence, suggesting that ionic interactions may be "screened" by the denaturant, as recently suggested. Examination of the conformation of the isolated peptide fragments has shown evidence for a low population of nativelike structure in the N-terminal beta-hairpin (residues 1-17) and weak nascent helical propensity in the helical fragment (residues 21-35). In contrast, the C-terminal peptide (36-76) shows evidence in aqueous solution, from some Halpha chemical shifts, for nonnative phi and psi angles; nonnative alpha-helical structure is readily induced in the presence of organic cosolvents, indicating that tertiary interactions in both native ubiquitin and the folded fragment complex strongly dictate its structural preference. The data suggest that the N-terminal fragment (1-35), where interaction between the helix and hairpin requires the minimum loss of conformational entropy, may provide the nucleation site for fragment complexation.

We have synthesized novel water-soluble anionic porphyrin monomers that undergo pH-regulated ionic supramolecular polymerization in aqueous media. By tuning the total charge of the monomer, we selectively produced two different supramolecular polymers: J- and H-stacked. The main driving force toward the J-aggregated supramolecular polymers was the ionic interactions between the sulfonate and protonated pyrrole groups, ultimately affording neutral supramolecular polymers. In these J-aggregated supramolecular polymers, amide groups were aligned regularly along polymer wedges, which further assembled in an edge-to-edge manner to afford nanosheets. In contrast, the H-aggregated supramolecular polymers remained anionic, with their amide NH moieties acting as anion receptors along the polymer chains, thereby minimizing repulsion. For both polymers, varying the steric bulk of the peripheral ethylene glycol (EG) units controlled the rates of self-assembly as well as the degrees of polymerization. This steric effect was further tunable, depending on the solvation state of the EG chains. Accordingly, this new family of supramolecular polymers was created by taking advantage of unique driving forces that depended on both the pH and solvent.

Non-covalent interactions play an important role for the framework formation of two-dimensional covalent organic frameworks. Until now, π–π interactions and hydrogen bonding are the main reported forces facilitating the stacking of framework layers. Here, we present a two-dimensional anionic covalent organic framework based on tetratopic borate linkages, where layers are connected by ionic interactions between the linkage site and counter cations. The crystalline covalent organic framework is accessed through the formation of an amorphous borate-based polymer and subsequent solvothermal treatment. The progress of crystallization is investigated, revealing the crystallite growth and morphological change from agglomerated dense particles to hollow crystallite spheres. Due to the pillared nature, the crystallites can be exfoliated into nanosheets by sonication of the material in the presence of methanol. The crystallization and ordered arrangement of the lithium ions in the interlayer space is shown to benefit the conductivity tenfold compared to the amorphous material.

Ionic interactions and multilayer structures on self-assembled surfaces of calix[4]resorcinarene

Phytic acid is an antinutritional factor in cereal feeds, and the use of phytases increases the bioavailability of nutrients bound to this molecule. However, the application of these enzymes depends on their thermal stability and activity at acidic pH. Therefore, in this study we created a database composed of 59 phytase sequences and analyzed the interactions that stabilize their structures in order to understand whether they contribute to the biochemical properties observed. The sequences were aligned and grouped at 30 % similarity, generating 5 clusters, which highlights the high variability among them. A comparative structural analysis of the cluster 3 phytases revealed conserved catalytic domains, as well as eight cysteine residues along the primary sequence, forming disulfide bonds for stabilizing the three-dimensional structure. However, the number of Van der Waals, ionic, and hydrogen interactions, and disulfide bonds was not determinant for the biochemical characteristics presented by these enzymes. The phytase KM873028, from cluster 3, was selected for characterization studies, but its expression in Pichia pastoris generated a protein with properties distinct from those derived from the same sequence expressed in a prokaryotic system. It is likely that the differences observed are associated with the location of the interactions in the structures, non-conserved amino acid residues found around the catalytic site, and post-translational modifications inherent to the expression systems. These possibilities highlight the relevance of strategic choices related to enzyme expression aiming at its production and industrial feasibility.

Polyoxometalates (POMs) are discrete anionic metal-oxide nanoclusters which exhibit unrivalled structural diversity, exceptional physical properties, and have many potential applications. Nonetheless, possessing high crystalline energy and hydrophilic nature, the assembly of POM clusters into rationally design architectures has been a long-standing bottleneck for their ultimate use in advanced materials and devices. To confront this challenge, both covalent and non-covalent modifications of POM nanoclusters are increasingly considered. This perspective reviews recent progress in the assembly of non-covalently modified surfactant-encapsulated POM nanoclusters with particular emphasis on our research work. The described solution-based assembly approach provides an excellent control on size, shape, and stability of the assembly structures. By effective exploitation of non-covalent interactions between the POM hybrid nanobuilding blocks, several unprecedented assembly structures including disks, cones, tubes, fullerene-like spheres, multiple shape flowers, wires, and thin films can be achieved. The assembly structures are highly robust and tunable in terms of size and shape and can act as hosts for guest nanomaterials to develop composite materials of combinatorial properties. In the last section of this manuscript, we present the catalytic properties of the assembly structures and their remote controlled manipulation in the reaction system.

Ionic hydrogels suit ionic skins, but advanced hydrogels are challenging. Inspired by jellyfish, we developed an ionic hydrogel with ultrastretchability, conductivity, adhesion, self-healing, and photoswitchable fluorescence via a supramolecular zwitterionic network. This hydrogel consists of silk fibroin, zwitterionic betaine analogue, biomineral calcium salts, and spiropyran in a dynamically cross-linked macromolecular network. Calcium ions facilitate electrical signal transmission and ionic interactions, while spiropyran enables photoswitchable color and fluorescence. Density functional theory and Fourier transform infrared analysis reveal abundant hydrogen bonding, ionic associations, and van der Waals forces, contributing to stretchability, adhesion, and self-healing, making them ideal for epidermal electrodes. The hydrogel also shows potential in optical printing and anti-counterfeiting applications due to spiropyran's reversible photochromic and photoluminescent behaviors. Moreover, a jellyfish-like robot capable of electric-driven movement is created by using these features. This study enhances understanding of dynamic noncovalent interactions in zwitterionic networks, enriching hydrogel design principles and advancing intelligent ionic skins.

ConspectusMolecular association of proteins with nucleicacids is requiredfor many biological processes essential to life. Electrostatic interactionsvia ion pairs (salt bridges) of nucleic acid phosphates and proteinside chains are crucial for proteins to bind to DNA or RNA. Counterionsaround the macromolecules are also key constituents for the thermodynamicsof protein–nucleic acid association. Until recently, therehad been only a limited amount of experiment-based information abouthow ions and ionic moieties behave in biological macromolecular processes.In the past decade, there has been significant progress in quantitativeexperimental research on ionic interactions with nucleic acids andtheir complexes with proteins. The highly negatively charged surfacesof DNA and RNA electrostatically attract and condense cations, creatinga zone called the ion atmosphere. Recent experimental studies wereable to examine and validate theoretical models on ions and theirmobility and interactions with macromolecules. The ionic interactionsare highly dynamic. The counterions rapidly diffuse within the ionatmosphere. Some of the ions are released from the ion atmospherewhen proteins bind to nucleic acids, balancing the charge via intermolecularion pairs of positively charged side chains and negatively chargedbackbone phosphates. Previously, the release of counterions had beenimplicated indirectly by the salt-concentration dependence of theassociation constant.Recently, direct detection of counterionrelease by NMR spectroscopyhas become possible and enabled more accurate and quantitative analysisof the counterion release and its entropic impact on the thermodynamicsof protein–nucleic acid association. Recent studies also revealedthe dynamic nature of ion pairs of protein side chains and nucleicacid phosphates. These ion pairs undergo transitions between two majorstates. In one of the major states, the cation and the anion are indirect contact and form hydrogen bonds. In the other major state,the cation and the anion are separated by water. Transitions betweenthese states rapidly occur on a picosecond to nanosecond time scale.When proteins interact with nucleic acids, interfacial arginine (Arg)and lysine (Lys) side chains exhibit considerably different behaviors.Arg side chains show a higher propensity to form rigid contacts withnucleotide bases, whereas Lys side chains tend to be more mobile atthe molecular interfaces. The dynamic ionic interactions may facilitateadaptive molecular recognition and play both thermodynamic and kineticroles in protein–nucleic acid interactions.

The first part of this paper discusses the molecular design of selected examples of structural units containing taper shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self-assemble via a delicate combination of exo- and endo-recognition processes will be presented. A comparison between various supramolecular (generated via H-bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The formation of columnar hexagonal (Φh), nematic and re-entrant isotropic phases by selected self-assembled systems will be discussed. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel-like architectures and some possible novel material functions derived fiom them will be briefly mentioned. The seco...

Effect of pH on characterization and coagulation performance of poly-silicic-cation coagulant

We report the transformation of [(BPEH2)(H2BTC)2(H3BTC)2·(H2O)] (I) (the first organic salt of trimesic acid with 1,2-bis(4-pyridyl)-ethane recently reported by us), into [(BPEH2)2(H2BTC)2(H3BTC)2·(H2O)14] (II), a new salt which was characterized structurally using single-crystal X-ray diffraction. II has increased crystal symmetry (monoclinic P21/n) when compared to I, and is formed by an extensive and very complex hydrogen bond network containing both homo- and heteronuclear neutral and ionic interactions. Water molecules play an important role in the hydrogen-bonding network, linking together adjacent zigzag ionic trimesic acid tapes leading to the formation of a 2D supramolecular anionic layer; connecting the BPEH22+ cations to the layers, and also acting as bridges between adjacent, close-packed layers.