Surface structure and properties of poly-(ethylene terephthalate) hydrolyzed by alkali and cutinase

This study was aimed at comparatively investigating the hydrolysis of crystalline and amorphous poly-(ethylene terephthalate) films by alkali and cutinase. Changes of surface properties were investigated by FTIR spectroscopy (ATR mode). The A1341/A1410 and I1120/I1100 absorbance ratios, and the full width at half maximum of the carbonyl stretching band (FWHM1715) were used to evaluate the polymer crystallinity and its changes upon hydrolysis. The effect of different treatments on chain orientation was evaluated by calculating R ratios of appropriate bands. The spectroscopic indexes showed that both alkali and enzyme treatments induced structural and conformational rearrangements with a consequent increase in crystallinity in both amorphous and crystalline films. The crystalline PET film was modified more strongly by alkali than by cutinase, while the opposite occurred for the amorphous one. The trend of the water contact angle (WCA) clearly indicates that alkali is more effective than cutinase in enhancing hydrophilicity of PET films and that the effect is stronger on amorphous than on crystalline films. The values of WCA correlate well with the FTIR indexes calculated from the spectra of hydrolyzed crystalline PET films. The mechanism of the surface hydrolysis of PET by alkali and cutinase is discussed

Protein disulphide isomerase-induced refolding of sonochemically prepared Ribonuclease A microspheres

The present communication describes for the first time the development of Ribonuclease A (RNase A) microspheres using the sonochemical method followed by an enzymatic treatment with protein disulphide isomerase (PDI). Ultrasound application induced changes on the protein physicochemical and biological properties: the enzymatic activity of RNase A was decreased in 35% and the free thiol groups content was significantly increased, probably due to the breakage of protein disulphide bonds and assembly of RNase A monomers. The deconvolution of amide I band, from Fourier Transform Infrared Spectroscopy, showed that the secondary structure of RNase A was slightly changed after microspherization. The PDI application on microspheres promoted the recovery of RNase A biological activity and induced the release of active protein into solution in its native state. These results were promoted by different states of PDI active site: oxidized and reduced, respectively. The PDI aptitude to catalyze the refolding of a protein substrate in the form of spheres is here reported.Margarida Fernandes thanks FCT "Fundacao para a Ciencia e Tecnologia" for providing the grant for PhD studies (SFRH/BD/38363/2007). Helena Ferreira thanks POPH/FSE for co-financing and FCT for fellowship SFRH/BPD/38939/2007

Enzymatic surface modification and functionalisation of PET: a water contact angle, FTIR, and fluorescence spectroscopy study

The purpose of this study was to investigate the changes induced by a lypolytic enzyme on the surface properties of polyethylene terephthalate (PET). Changes in surface hydrophilicity were monitored by means of water contact angle (WCA) measurements. Fourier Transform Infrared spectroscopy (FTIR) in the Attenuated Total Reflectance mode (ATR) was used to investigate the structural and conformational changes of the ethylene glycol and benzene moieties of PET. Amorphous and crystalline PET membranes were used as substrate. The lipolytic enzyme displayed higher hydrolytic activity towards the amorphous PET substrate, as demonstrated by the decrease of the WCA values. Minor changes were observed on the crystalline PET membrane. The effect of enzyme adhesion was addressed by applying a protease after-treatment which was able to remove the residual enzyme protein adhering to the surface of PET, as demonstrated by the behavior of WCA values. Significant spectral changes were observed by FTIR-ATR analysis in the spectral regions characteristic of the crystalline and amorphous PET domains. The intensity of the crystalline marker bands increased while that of the amorphous ones decreased. Accordingly, the crystallinity indexes calculated as band intensity ratios (1,341/1,410 cm(-1) and 1,120/1,100 cm(-1)) increased. Finally, the free carboxyl groups formed at the surface of PET by enzyme hydrolysis were esterified with a fluorescent alkyl bromide, 2-(bromomethyl)naphthalene (BrNP). WCA measurements confirmed that the reaction proceeded effectively. The fluorescence results indicate that the enzymatically treated PET films are more reactive towards BrNP. FTIR analysis showed that the surface of BrNP-modified PET acquired a more crystalline character

Effects of a multi-step sol-gel process of inorganic silica coatings on cotton fabrics

In this work the sol-gel synthesis of silica thin films and a novel multistep process consisting of 1-6 consecutive depositions of tetraethoxysilane (TEOS) onto cotton fabric are presented: samples with a different number of silica layers, with the last one alternately consisting of DBTA (Dibutyltindiacetate) catalyst, were obtained. The interaction of sol–gel derived silica coatings and the textiles fabrics were studied by changing two process variables: the TEOS concentration and the presence or absence of the catalyst