Ernestina Dubini-Paglia

Characterization of a poly(3-hydroxybutyrate) depolymerase fromaureobacterium saperdae: Active site and kinetics of hydrolysis studies

An extracellular poly(3-hydroxybutyrate) (PHB) depolymerase was purified fromAureobacterium saperdae cultural medium by using hydrophobic interaction chromatography. The isolated enzyme was composed of a single polypeptide chain with a molecular mass of 42.7 kDa as determined by SDS-PAGE and by native gel filtration on TSK-HW-55S. The enzyme was not a glycoprotein. Its optimum activity occurred at pH 8.0 and it showed a broad pH stability, ranging from pH 3 to pH 11.N-Bromosuccinamide and 2-hydroxy-5-nitrobenzyl bromide completely inactivated the enzyme, suggesting the involvement of tryptophan residues at the active site of the protein. The enzyme was very sensitive to diisopropyl fluorophosphate and diazo-dl-norleucine methyl ester, showing the importance of serine and carboxyl groups. The modification of cysteine residues byp-hydroxy mercuricbenzoate did not cause a loss of activity, whereas dithiothreitol rapidly inactivated the enzyme, revealing the presence of disulfide bonds.A saperdae depolymerase acted on the surface layer of PHB films and the degradation proceeded by surface erosion releasing monomers and dimers of 3-hydroxybutric acid. The degradation of PHB films byA. saperdae depolymerase was partially inhibited in the presence of excess amounts of enzyme. This phenomenon, already observed by Mukaiet al. with poly(hydroxyalkanoates) depolymerases fromAlcaligenes faecalis, Pseudomonas pickettii, andComamonas testosteroni, was analyzed according to the kinetic model proposed by these authors. The experimental data evidenced a general agreement with the kinetic model, although higher initial degradation rates were found withA. saperdae depolymerase.

Thermodynamic analysis of proton dissociation equilibria of some 4-diethylaminoazobenzenes in 20 wt% aqueous methanol solution

Proton dissociation of XC6H4NCNH6H3YNHEt2(X = H, CO2H, NO2, OMe; Y = H, Me, OEt) has been examined at 293.15 K in aqueous sulphuric acid solutions. Equilibrium constants for the proton dissociation of XC6H4NHNC6H3YNEt2(X = H, CO2H, NO2, OMe; Y = H, Me, OEt) have been measured as a function of temperature, in the range 293–323 K, in 20 wt% aqueous methanol solution. Thermodynamic functions (ΔG°, ΔH°, ΔS°) have been calculated. Experimental data have been discussed and interpreted in terms of linear free energy relationships. Tautomeric equilibrium constants have been evaluated and apparent equilibrium constants separated into the separate contributions of ammonium and azonium forms.

The thermal cis—trans isomerization of azo dyes dispersed in polymeric blends as a probe for characterizing their morphology

Abstract The thermal cis-trans isomerization of some 4-diethylaminoazobenzenes was studied kinetically as a function of temperature in various polymeric matrices. Blends of isotactic polypropylene mixed with various weight fractions of hydrogenated oligocyclopentadiene or oligo-β-pinene were used. Kinetics experiments confirmed that the isomerization reaction is a sound probe for characterizing the transition from rubbery to glassy state of the medium with the appearance of a multiplicity of first-order reactions. The isomerization rates were found to be dependent on the position of the substituents, but no marked influence of the composition of the polymeric blend was detected, even in the presence of considerable changes in the glass transition temperature or in the crystallinity of the samples. This behavior confirms that the isomerization reaction takes place essentially in the amorphous regions which appear to be quite similar for the various blends examined.

The cis-trans isomerization and lightfastness of azo dyes dispersed in thermoplastic fibers with different structural features

Abstract The cis-trans isomerization of 4-N,N-diethylaminoazobenzene dispersed in two polyamidic fibers has been studied. The fibers were obtained by blending polyamide 6 with appropriate amounts of an aromatic copolyamide, which allowed a controlled enhancement of the Tg value of the polyamide. The different fastness properties of the dyed materials could be explained in terms of the observed fifferent structural features of the blends.