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Poly­(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) hydrogels are attractive materials for various application areas due to their pH-independent large swelling capacities. However, their covalently cross-linked network structure leads to a brittle behavior even at low strains. We present here for the first time highly stretchable superabsorbent PAMPS hydrogels formed via H-bonds entirely that are stable in water. UV polymerization of AMPS in aqueous solutions at 23 ± 2 °C without a chemical cross-linker produces hydrogels with large swelling capacities exceeding 1000 times their original mass. Although the hydrogels are stable in water, they easily dissolve in chaotropic solvents, suggesting that they form via H-bonding interactions between PAMPS chains. We show that the high molecular weight of the primary chains of PAMPS hydrogels formed via UV polymerization contributes to the H-bonding cooperativity and hence is responsible for their stability in water. Incorporation of N,N-dimethylacrylamide (DMAA) segments into the physical PAMPS network further increases the molecular weight of the primary chains, leading to enhanced mechanical strength of the hydrogels. PAMPS/DMAA hydrogels in their as-prepared states exhibit a high modulus (up to 0.41 MPa), tensile fracture stress (up to 0.57 MPa), and high stretchability (∼1000%) together with an extraordinary swelling capacity (up to ∼1700 g·g–1) and complete self-healing efficiency.

Variational MonteCarlo and Diffusion MonteCarlo calculations have been carried out for cations like Li + , Na + and K + as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms.The interaction has been modelled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab-initio calculations over a broad range of interatomic distances.This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are here discussed in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the clusters features.

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Homology model structures of the dopamine D2 receptor (D2R) were generated starting from the active and inactive states of β2-adrenergic crystal structure templates. To the best of our knowledge, the active conformation of D2R was modeled for the first time in this study. The homology models are built and refined using MODELLER and ROSETTA programs. Top-ranked models have been validated with ligand docking simulations and in silico Alanine-scanning mutagenesis studies. The derived extra-cellular loop region of the protein models is directed toward the binding site cavity which is often involved in ligand binding. The binding sites of protein models were refined using induced fit docking to enable the side-chain refinement during ligand docking simulations. The derived models were then tested using molecular modeling techniques on several marketed drugs for schizophrenia. Alanine-scanning mutagenesis and molecular docking studies gave similar results for marketed drugs tested. We believe that these new D2 receptor models will be very useful for a better understanding of the mechanisms of action of drugs to be targeted to the binding sites of D2Rs and they will contribute significantly to drug design studies involving G-protein-coupled receptors in the future.

We have recently reported G-protein coupled receptor (GPCR) model structures for the active and inactive states of the human dopamine D2 receptor (D2R) using adrenergic crystal structures as templates. Since the therapeutic concentrations of dopamine agonists that suppress the release of prolactin are the same as those that act at the high-affinity state of the D2 receptor (D2High), D2High in the anterior pituitary gland is considered to be the functional state of the receptor. In addition, the therapeutic concentrations of anti-Parkinson drugs are also related to the dissociation constants in the D2High form of the receptor. The discrimination between the high- and low-affinity (D2Low) components of the D2R is not obvious and requires advanced computer-assisted structural biology investigations. Therefore, in this work, the derived D2High and D2Low receptor models (GPCR monomer and dimer three-dimensional structures) are used as drug-binding targets to investigate binding interactions of dopamine and apomorphine. The study reveals a match between the experimental dissociation constants of dopamine and apomorphine at their high- and low-affinity sites of the D2 receptor in monomer and dimer and their calculated dissociation constants. The allosteric receptor-receptor interaction for dopamine D2R dimer is associated with the accessibility of adjacent residues of transmembrane region 4. The measured negative cooperativity between agonist ligand at dopamine D2 receptor is also correctly predicted using the D2R homodimerization model.

We present post Hartree-Fock calculations of the potential energy surfaces (PESs) for the ground electronic states of the three alkali dimer ions Li(2) (+),Na(2) (+), and K(2) (+) interacting with neutral helium. The calculations were carried out for the frozen molecular equilibrium geometries and for an extensive range of the remaining two Jacobi coordinates, R and theta, for which a total of about 1000 points is generated for each surface. The corresponding raw data were then fitted numerically to produce analytic expressions for the three PESs, which were in turn employed to evaluate the bound states of the three trimers for their J=0 configurations: The final spatial features of such bound states are also discussed in detail. The possible behavior of additional systems with more helium atoms surrounding the ionic dopants is gleaned from further calculations on the structural stability of aggregates with up to six He atoms. The validity of a sum-of-potential approximation to yield realistic total energies of the smaller cluster is briefly discussed vis-a-vis the results from many-body calculations.

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