Electrochemical studies of orthophthaladehyde (OPA) in aqueous solutions, equilibria and kinetics

Part one. Orthophthalaldehyde (1,2-dicarboxaldehyde) (OPA) forms in the presence of a strong nucleophile with amino acids isoindole derivatives. The reaction is used in fluorometric determination of amino acids. The mechanism of these processes is not understood. OPA is present in aqueous solutions in three forms: hydrated (Ia), monohydrated acyclic (I b) and cyclic hemiacetal (Ic). Absence of data for molar absorptivities of these forms, together with overlaps of their absorption bands, limits the application of spectrophotometry. Measurement of polarographic limiting currents of forms Ia and Ib enables determination of equilibrium constants K1 (formation of Ib) and K 2 (for the ring formation). Presence of these forms was supported by 1H-NMR and 13C-NMR. Rate of hydration of OPA is general acid-base catalyzed, but that of dehydration show only specific acid-base catalysis. The rate of hydration is controlled by general acid-base catalyzed addition of water to Ia. The rate of dehydration depends on the opening of the ring in Ic, which is specific acid-base catalyzed. At pH > 10 OPA undergoes a complex set of acid-base reactions. Presence of polarographic anodic waves and oxidation on the gold electrode indicates the importance of the presence of a geminal diol form (IIa). Establishment of equilibria between the three forms of OPA together with reactions at pH > 10 have to be considered in elucidating the reaction scheme of procedures using OPA as a reagent in determination of amino acids.; Part two. Reversible addition fragmentation chain transfer (RAFT) polymerizations were performed in the presence of organically modified clays and successfully prepared polystyrene-, poly (methyl methacrylate)-, and poly (n-butyl acrylate)-layered silicate nanocomposites. The polymers had well-defined molecular weights and low polydispersities, as expected from RAFT polymerizations. The morphology of polystyrene-, and poly(n-butyl acrylate)-nanocomposites were found to be exfoliated using montmorillonite modified with N,N-dimethyl- n-hexadecyl-(4-vinylbenzyl) ammonium (MMT-VB16). In the case of PMMA nanocomposite, the structure was a mixture of intercalated and exfoliated when MMT-VB 16 was used, while the use of montmorillonite modified with 2-methacryloyloxyethyl-hexadecyldimethyl ammonium (MMT-MA16) resulted in exfoliation.