A polyelectrolyte-surfactant complex as support layer for membrane functionalization.

A polyelectrolyte-surfactant complex, polyallylamine-dodecylsulfate system, is presented as an alternative method for the modification of membranes. Due its chemical structure, the complex, once casted on a surface, is highly stable in aqueous solutions. This allows modifying with the same method different types of membranes, exemplified here by alumina and polycarbonate. Using different strategies, the complex system can also incorporate other elements useful for catalysis, biorecognition, or separation. Two applications are presented: the incorporation of gold nanoparticles to catalyze the reduction of 4-nitrophenol using a polycarbonate membrane, and the modification of alumina with a biotin derivative for the recognition of avidin in label-free sensors.

Self-assembled monolayers of disulfide Cu porphyrins on Au surfaces: adsorption induced reduction and demetalation.

Metalloporphyrin molecules have a wide range of potential applications in diverse technological areas ranging from electronics to optoelectronics, electrochemistry, photophysics, chemical sensors, and catalysis. In particular, self-assembled monolayers of porphyrin molecules have recently attracted considerable interest. In this work we have studied for the first time the self-assembly of a novel Cu deutero porphyrin functionalized with disulfide moieties using electrochemical techniques, UV-vis absorption spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and photoelectron spectroscopies (XPS and UPS). Experimental results indicate that the molecule adsorbs retaining its molecular integrity without forming molecular aggregates via the formation of Au-S covalent bonds. Furthermore, the monolayer consists of a packed array of molecules adsorbed with the plane of the porphyrin molecule at an angle of around 30° with respect to the surface normal. Interestingly, adsorption induces reduction of the Cu center and its consequent removal from the center of the porphyrin ring resulting in porphyrin demetalation. Our results are important in the design of self-assembled monolayers of metallo porphyrins where not only blocking of the metal center by the functional groups that drive the self-assembly should be considered but also possible adsorption induced demetalation with the consequent loss in the properties imparted by the metal center.