Effect of copolymerization and semi-interpenetration with conducting polyanilines on the physicochemical properties of poly(N-isopropylacrylamide) based thermosensitive hydrogels

Thermosensitive hydrogels are made by radical homopolymerization of N-isopropylacrylamide (NIPAAM) or copolymerization of NIPAAM with 2-acrylamido-2-methyl-propane sulfonic acid (AMPS). The networks are semi-interpenetrated (s-IPN) with linear conducting polymers: polyaniline (PANI) or poly(N-methylaniline) (PNMANI). The semi-interpenetration affect slightly the phase transition temperature (measured by DSC) of the hydrogels, while water uptake capacity is strongly affected and depends on the relative hydrophobicity of the conducting polymer. Since polyanilines can be protonated in aqueous media, the swelling capacity of the s-IPN hydrogel depends strongly on pH unlike the unmodified hydrogel. The release of a model compound (tris(2,2′-bipyridine)ruthenium (II), ), driven by swelling or temperature, is also strongly affected both by the introduction of sulfonic groups, by copolymerization of NIPAAM with AMPS, semi-interpenetration and on the hydrophobicity of the conducting polymer. In that way, composite materials with quite different ion exchange behavior can be made by copolymerization and conducting polymer interpenetration.     

Conformational Selection in Glycomimetics: Human Galectin‐1 Only Recognizes syn‐Ψ‐Type Conformations of β‐1,3‐Linked Lactose and Its C‐Glycosyl Derivative

The human lectin galectin‐1 (hGal‐1) translates sugar signals, that is, β‐galactosides, into effects on the level of cells, for example, growth regulation, and has become a model for studying binding of biopharmaceutically relevant derivatives. Bound‐state conformations of Galβ‐C‐(1→3)‐Glcβ‐OMe ( 1 ) and its βGal‐(1→3)‐βGlc‐OMe disaccharide parent compound were studied by using NMR spectroscopy (transferred (TR)‐NOESY data), assisted by docking experiments and molecular dynamics (MD) simulations. The molecular recognition process involves a conformational selection event. Although free C‐glycoside access four distinct conformers in solution, hGal‐1 recognizes shape of a local minimum of compound 1 , the syn‐Φ/syn‐Ψ conformer, not the structure at global minimum. MD simulations were run to explain, in structural terms, the observed geometry of the complex.     

Delineating Binding Modes of Gal/GalNAc and Structural Elements of the Molecular Recognition of Tumor‐Associated Mucin Glycopeptides by the Human Macrophage Galactose‐Type Lectin

The human macrophage galactose‐type lectin (MGL) is a key physiological receptor for the carcinoma‐associated Tn antigen (GalNAc‐α‐1‐O‐Ser/Thr) in mucins. NMR and modeling‐based data on the molecular recognition features of synthetic Tn‐bearing glycopeptides by MGL are presented. Cognate epitopes on the sugar and matching key amino acids involved in the interaction were identified by saturation transfer difference (STD) NMR spectroscopy. Only the amino acids close to the glycosylation site in the peptides are involved in lectin contact. Moreover, control experiments with non‐glycosylated MUC1 peptides unequivocally showed that the sugar residue is essential for MGL binding, as is Ca²⁺. NMR data were complemented with molecular dynamics simulations and Corcema‐ST to establish a 3D view on the molecular recognition process between Gal, GalNAc, and the Tn‐presenting glycopeptides and MGL. Gal and GalNAc have a dual binding mode with opposite trend of the main interaction pattern and the differences in affinity can be explained by additional hydrogen bonds and CH–π contacts involving exclusively the NHAc moiety.     

Systematic Dissection of an Aminopyrrolic Cage Receptor for β‐Glucopyranosides Reveals the Essentials for Effective Recognition

A set of structures designed for the recognition of glucosides has been obtained by systematically destructuring a tripodal aminopyrrolic cage receptor that selectively recognizes octyl‐β‐D ‐glucopyranoside (OctβGlc). NMR spectroscopy and isothermal titration calorimetry binding measurements showed that cleavage of one pillar of the cage was beneficial to the binding properties of the receptor, as long as two residual amino groups of the cleaved pillar were present. Removal of these two residual amino groups produced a dramatic loss of affinity for OctβGlc of the resulting monocyclic analogue of the parent cage receptor. A significant improvement in the binding ability was achieved by replacing one pillar with two aminopyrrolic hydrogen‐bonding arms, despite the loss of a preorganized structure. In contrast to the cage receptor, recognition of OctβGlc was observed, even in a competitive medium (30 % DMF in chloroform). Structural studies in solution, carried out through NMR spectroscopy and molecular modeling calculations, led to the elucidation of the 3D binding modes of the side‐armed monocyclic receptors; this highlighted the key role of the amino groups and demonstrated the occurrence of a rotaxane‐like complex, which featured the octyl chain of the glucoside threaded through the macrocyclic ring.     

Second order elasticity in nematics: A new anchoring source

By considering, in the expression of the nematic free energy density, an additional term in the square of the director second derivatives, an unexpected anchoring source results, due only to surface and bulk elastic constants. As an example, the case of a planar homogeneous and of a homeotropic nematic cell, equally anchored on both walls, is discussed. In both situations the new anchoring source has a destabilizing effect.     

Role of the linear elastic term in the spatial derivatives of the nematic director in a 1D geometry

The role of the linear elastic term in the spatial derivatives of the nematic director on the director field is analysed. We consider a nematic sample in the shape of a slab, confined by two surfaces treated to induce homeotropic alignment. It is shown that this term can be responsible for spontaneous Fréedericksz transitions. The connection between the linear term and the flexoelectric contribution, associated with a surface field, to the bulk energy density, is discussed. The importance of dielectric anisotropy on the spontaneous Fréedericksz transition is also investigated.     

Small-signal ac response of an electrolytic cell with recombining space charge

A simple model to evaluate the impedance of a cell in the presence of the generation and recombination of charges is proposed. The analysis is performed by considering a typical asymmetric cell having one electrode perfectly blocking and the other electrode perfectly transparent. The dependence of the impedance of the cell, in the shape of a slab, on the recombination coefficient is investigated. We obtain approximated expressions for the impedance of the cell valid in the low and high frequency regions. The frequencies defining the regions where approximated expressions hold are deduced by means of the asymptotic expansions for the real and imaginary parts of the electrical impedance of the cell.     

Advanced design of conductive polymeric arrays with controlled electrical resistance using direct laser interference patterning

In this work, we report a simple method for the fabrication of regular conducting polyanliline periodic arrays on large areas of glass or gold substrates using direct laser interference patterning. Additionally, by controlling the laser intensity it is possible to precisely tune the width of the periodic arrays and consequently the electrical resistance of the polyanliline strips. The periodic arrays were characterized using scanning electron microscopy, white light interferometry and cyclic voltametry. The great importance of the method reported lies both in its versatility and the ability to control the properties of the modified polymer electrodes with high precision. This is important for prospective applications such as electrochemical sensors. PACS 79.20.Ds; 42.25.Hz; 73.61.Ph; 81.65.Cf     

Hemicarbasucrose: Turning off the Exoanomeric Effect Induces Less Flexibility

Hemicarbasucrose, a close congener of sucrose in which the endocyclic oxygen atom of the glucose moiety is replaced by a methylene group was synthesized for the first time. The conformational behaviour of hemicarbasucrose was studied by a combination of molecular mechanics and NMR spectroscopy (J and NOE data). It was shown that the carbadisaccharide populates two distinct conformational families in solution, the normal syn‐ψ conformation, which is the predominating conformation of the parent natural O‐glycoside, and the anti‐ψ conformation, which has not been detected for the O‐disaccharide. Interestingly, the hemicarbasucrose is less flexible than its natural congener.