Towards the kinetic resolution of mechanically planar chiral rotaxanes

In this work, we reported the synthesis and characterization of two [2]rotaxanes endowed with a central ammonium group and two triazolium recognition stations on either side, acting as complexation sites for a dibenzo-24-crown-8 ether macrocycle. These mechanically interlocked architectures were obtained through the interlocking of a functionalized achiral macrocycle with Cs symmetry (where the symmetry element is a mirror plane corresponding to plane of the ring) and a C∞v symmetric axle (where a mirror plane and a C∞ principal axis are aligned along the axle length). We took advantage of the reversible acid/base triggered molecular shuttling of the ring between two lateral triazolium units to switch the rotaxanes between prochiral and mechanically planar chiral forms, which exists as two rapidly-interconverting co-conformers. We exploited the reactivity of the central amino group to attach an optically pure chiral substituent, with the goal of demonstrating the enantiomeric nature of the co-conformers and to obtain a non-zero diastereomeric excess in the resulting diastereomeric products through a dynamic kinetic resolution. To this end, two enantiopure reagents were chosen that could perform clean and fast reaction with amines: a sulfonyl chloride and an acyl chloride. Only the acyl chloride successfully produced an amide in high yield with the deprotonated rotaxane. The group added to the central amine station acted as a stopper against the shuttling of the macrocycle along the axis, thus preventing the fast interconversion of the two mechanically planar enantiomers. We analysed the results through static and dynamic NMR spectroscopic techniques by varying temperature and solvent used. Indeed, the presence of diastereomers was recorded alongside the configurational isomers resulting from the slow rotation of the CN-CO bond of the amide moiety, thus paving the way for a dynamic kinetic resolution.

Investigation of gold-based catalysts for liquid phase oxidation of glucose to glucaric acid

Glucaric acid (GA) is one of the building block chemicals derived from sugar biomass with higher added value. Nowadays, GA is produced by oxidation of glucose (Glu) with either stoichiometric oxidants (HNO3), or by means of electrochemical or biochemical synthesis. However, these processes show drawbacks from either the environmental or economic viewpoint. For this reason, gold nanoparticles (Au NPs) supported on activated carbon (AC) have been studied as catalysts for the oxidation of Glu, using O2 as oxidant in the presence of a base. Using sol immobilization technique, Au NPs have been supported on AC following different experimental procedures. UV-Vis spectroscopy, XRD, TEM and TG analysis were utilized in the characterization of the catalysts. The operational conditions were optimized obtaining 24% of yield of GA, 37% to GO and 27% to byproducts in 1 h, 1000 rpm, 10 bar of O2 and Glu:Au:NaOH molar ratio of 1000:1:3000. Under such conditions, catalysts show relatively high Glu conversion (≥82%) with different GA yields. GO+GA yield is around 58-61%. Therefore, the oxidation reaction was performed at 15 min where Au/AC PVA0 reached the highest yield of GA (16%) and Au/AC PVA2.4 gave the lowest (8%). It is evident that the presence of PVA influences to a higher degree the reaction rate than the Au NPs size. Hence, the effect of different heat treatments where applied for the removal of PVA: washing with water at 60℃ or heat treatment (120-250℃) with Air/H2. Washing treatment and heat treatment at 120℃ with Air/H2 may have resulted in the mildest treatments for the removal of PVA. Finally, two different supports have been used in order to study the effect of metal-support interaction in the immobilization of Au NPs: ZrO2 and AC. Au/AC catalyst demonstrated a higher conversion of GO to GA at short reaction times (15.1% yield GA) compared to Au/ZrO2 (2.4% yield GA).

Sensori elettrochimici a base di PEDOT:PSS stampati a getto di inchiostro

Conductive polymers (CPS) are a class of carbon-based materials, capable of conducting electric current, characterized by metallic properties in combination with the intrinsic properties of conventional polymers. The structural model of the CP consists of a system of double π-conjugated on the backbone (polyene structure) which can easily undergo reversible doping reaching a wide range of conductivity. Thanks to their versatility and peculiar properties (mechanical flexibility, biocompatibility, transparency, ease of chemical functionalization, high thermal stability), CPS have revolutionized the science of materials giving rise to Organic Bioelectronics, the discipline resulting from the convergence between biology and electronics. The Poly (3,4-ethylenedioxythiophene) : poly (styrenesulfonate) (PEDOT: PSS), complex polyelectrolyte, in the form of a thin film, currently represents the reference standard in applications concerning Bioelectronics. In this project, two types of electrochemical sensors ink-jet printed on a flexible polymeric substrate, the polyethylene terephthalate, have been developed and characterized. The Drop on Demand (DOD) inkjet technology has allowed to control the positioning of fluid volumes of the order of picoliters with an accuracy of ± 25μm. This resulted in the creation of amperometric sensors and organic electrochemical transistors (OECT) all-PEDOT: PSS with high reproducibility. The sensors have been used for the determination of Ascorbic Acid (AA) which is currently considered an important benchmark in the field of sensors. In Cyclic Voltammetry, the amperometric sensor has detected AA at potentials less than 0.2 V vs. SCE thanks to the electrocatalytic properties of the PEDOT: PSS. On the other hand, the OECT detected AA concentrations equal to 10 nanomolar in Chronoamperometry. Furthermore, a promising new generation of all-printed OECTS, consisting of silver metal contacts, has been created. Preliminary results are presented.