Acetylcholinesterase-induced fluorescence turn-off of an oligothiophene-grafted quartz surface sensitive to myristoylcholine.

Conjugated polyelectrolytes (CPEs) have recently emerged as label-free materials for biosensing due to their intrinsic ability to transduce an amplified optical signal in response to interactions with different analytes. Herein, the conformational change of an anionic oligothiophene is exploited to generate a unique fluorescent response upon interaction with myristoylcholine (MyrCh). The variations observed in spectroscopic signals are explained in terms of a synergistic combination of hydrophobic and electrostatic forces involving the oligothiophene chains and MyrCh molecules, inducing the disassembling of oligothiophene chains. The enzyme acetylcholinesterase (AChE) is able to reverse this effect by catalyzing the hydrolysis of MyrCh; hence, its enzymatic activity can be monitored through the variation of fluorescence emission of the system. The oligothiophene sensing probe retains its conformational sensitivity with regard to the AChE-mediated cleavage of MyrCh upon immobilization onto a quartz substrate, which is accomplished by a "grafting onto" approach based on click chemistry. These results are encouraging for the further development of such a label-free system towards the fabrication of sensing devices that would incorporate CPEs and would be potentially useful for the specific detection of a wide range of bioanalytes.

Hyaluronan derivatives bearing variable densities of ferulic acid residues.

A synthetic procedure has been developed to conjugate ferulic acid (FA) to an important natural polysaccharide derivative such as hyaluronic acid (HA). The activation of FA with 1,1'-carbonyldiimidazole (CDI) has been investigated. Two reactive intermediates, namely monoimidazolide 2 [i.e. (E)-3-(4-hydroxy-3-methoxyphenyl)-1-(1H-imidazol-1-yl)prop-2-en-1-one] and bisimidazolide 3 [i.e. (E)-4-(3-(1H-imidazol-1-yl)-3-oxoprop-1-enyl)-2-methoxyphenyl 1H-imidazole-1-carboxylate] were characterized from the point of view of their structure and reactivity. The ready isolation of bisimidazolide 3 and its reactivity support its potential usefulness in the feruloylation of molecular or macromolecular materials bearing hydroxyl moieties. Bisimidazolide derivative 3 has been found to be an effective reagent in the feruloylation of HA to give HAFA graft copolymers showing different grafting degrees (GD), which could be modulated by varying the reaction conditions. A series of HAFA derivatives showing different GD values has been prepared and submitted to an extensive macromolecular and rheological characterization in order to ascertain that the grafting of HA with FA does not degrade the polysaccharide backbone and to evaluate the role of GD in affecting solubility and rheological properties. The results suggested that relatively low GD values were sufficient to confer physical cross-linking capabilities resulting in the features of a strong gel of HAFA dispersions.