Polyethylenimine Functionalized with Dopamine: Characterization and Electrocatalytic Properties

We report the chemical modification of polyethylenimine (PEI) by functionalization with dopamine (Do) using glutaraldehyde (Glu) as a linker (PEI‐Glu‐Do). The new polymer was characterized by FT‐IR spectroscopy, by derivative UV‐vis spectroscopy, and Cyclic Voltammetry. The PEI‐Glu‐Do demonstrated to have an important electrocatalytic activity allowing an important decrease in the overvoltages for the oxidation of NADH and a significant increase in its oxidation peaks currents. Different ratios of PEI:Do were assayed and the best response was obtained using PEI : Glu : Do 1 : 2 : 1. The new polymer represents an interesting and promising alternative for the electrochemical quantification of NADH and other analytes of clinical interest, as well as for the development of new electrochemical (bio)sensors.     

Semiinvariants for hopf algebra actions

LetH be a Hopf algebra andM a representation or a corepresentation ofH. In this paper we study semiinvariants ofM. This notion generalizes the known concept of weight spaces in the context of representations of Lie algebras. Our best results are attained for pointed Hopf algebras, and semiinvariants which are related to the coradical filtration ofH.     

pH-induced changes in the fabrication of multilayers of poly(acrylic acid) and chitosan: fabrication, properties, and tests as a drug storage and delivery system

Multilayers of poly(acrylic acid), PAA, and chitosan, CHI, have been built by the layer-by-layer (LbL) method from aqueous solutions at different pH values and analyzed by the dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results showed that under all of the assembly conditions considered the growth of the films is nonlinear. The thickness of the PAA layers increases as the pH of the assembling solutions decreases, whereas the adsorption of CHI is almost unaffected by the pH conditions. The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films, showing that the multilayers are highly hydrated, with an average water content higher than 20%. The analysis of D-QCM data has provided high-frequency values of the complex shear modulus that are in the megapascal range and shows a transition from mainly viscous to mainly elastic behavior for the added PAA layers, depending on the pH. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the monomer density depends on the assembly conditions. It was found that the adsorption kinetics is a bimodal process, with characteristic times that depend on the number and nature of the layers. Finally, the possibility of using of these multilayers as a drug storage and delivery system has been evaluated.     

Dihydroxy(4-thiomorpholinomethyl)benzoic acid: from molecular asymmetry to diode characteristics

One of the challenges in molecular electronics is to design molecules which can be used as functional units in electronic devices. The subject of our investigations is an asymmetrical molecule, dihydroxy(4-thiomorpholinomethyl)benzoic acid (TMBA), whose structural and electronic properties are characterized. The self-assembly behavior of TMBA on Au(111) surfaces resulting in highly ordered monolayers is obtained using scanning tunneling microscopy (STM). Furthermore, investigations on the electronic properties of the combined metal/molecule system reveal an orbital mediated tunneling process and tunneling decay constants for the carboxylic and thiomorpholino group. Thus, a diode-like character of TMBA is shown to be caused by intrinsic electronic properties of different molecular moieties.     

New dendronized polymers from acrylate Behera amine and their ability to produce visco-elastic structured fluids when mixed with CTAT worm-like micelles

Two new water soluble dendronized polymers (PLn) from acrylate Behera amine monomer of different molecular weights were successfully synthesized. The polymers were characterized by FTIR, NMR, GPC and DLS. Both GPC and DLS results indicated that these PLn have a remarkable tendency to form aggregates in solution that lead to apparent molecular weights that are much higher than their theoretical values, as well as large diameters in solution. However, the addition of any PLn to water did not cause any increase in viscosity up to concentrations of 1000 ppm. The possible interactions of PLn with the cationic surfactant CTAT were explored by solution rheometry. A synergistic viscosity enhancement was found by adding small amounts of dendronized PLn polymers to a CTAT solution composed of entangled worm-like micelles. The highest association tendency with CTAT was found for PL1 at the maximum polymer concentration before phase separation (i.e., 100 ppm). The solution viscosity at low-shear rates could be increased by an order of magnitude upon addition of 100 ppm of PL1 to a 20mM CTAT solution. For this mixture, the fluid obtained was highly structured and exhibited only shear thinning behavior from the smallest shear rates employed. These PL1/CTAT mixtures exhibited an improved elastic character (as determined by dynamic rheometry) that translated in a much longer value of the cross-over relaxation time and a pronounced thixotropic behavior which are indicative of a strong intermolecular interaction. In the case of the polymer with a higher theoretical molecular weight, PL2, its association with CTAT leads to an extraordinary doubling of solution viscosity with just 0.25 ppm polymer addition to a 20mM CTAT solution. However, such synergistic viscosity enhancement saturated at rather low concentrations (25 ppm) indicating an apparent lower solubility as compared to PL1, a fact that may be related to its higher molecular weight.