Vincent Nierstrasz

Enzymatic surface modification and functionalization 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. Biotechnol. Bioeng. 2009;103: 845–856.

Thermodynamically controlled synthesis of β-lactam antibiotics. Equilibrium concentrations and side-chain properties

For the enzymatic synthesis of the antibiotic cephalexin, an activated acyl donor is generally used as one of the substrates (kinetically controlled approach); however, the thermodynamically controlled approach might be of interest since there is no need for activation of the acyl donor and less waste is produced. If the synthesis reaction can be combined with an effective product removal step, the thermodynamic approach can be beneficial. The thermodynamically controlled synthesis of cephalexin was studied at various pH values, solvent concentrations, and temperatures. With direct synthesis in water, only small amounts of cephalexin were formed (0.1 mm from 20 mm starting material by the Xanthomonas citri enzyme). Addition of water-miscible organic solvent had a positive effect on synthesis (by the Escherichia coli enzyme); the equilibrium concentration of cephalexin, however, was at best increased by a factor of 2-3 (in methanol and triglyme). The equilibrium antibiotic concentrations reported in this study were notably lower than the values reported in the literature. These differences originate from the improved analytical methods that are available nowadays. Low product concentrations were also found for other side-chains with an amino group at the α-position. Side-chains without this group can be coupled and give acceptable product concentrations. For these antibiotics, a thermodynamically controlled process may be an alternative to kinetically controlled coupling. Copyright (C) 1999 Elsevier Science Inc. All rights reserved. | For the enzymatic synthesis of the antibiotic cephalexin, an activated acyl donor is generally used as one of the substrates (kinetically controlled approach); however, the thermodynamically controlled approach might be of interest since there is no need for activation of the acyl donor and less waste is produced. If the synthesis reaction can be combined with an effective product removal step, the thermodynamic approach can be beneficial. The thermodynamically controlled synthesis of cephalexin was studied at various pH values, solvent concentrations, and temperatures. With direct synthesis in water, only small amounts of cephalexin were formed (0.1 mM from 20 mM starting material by the Xanthomonas citri enzyme). Addition of water-miscible organic solvent had a positive effect on synthesis (by the Escherichia coli enzyme); the equilibrium concentration of cephalexin, however, was at best increased by a factor of 2-3 (in methanol and triglyme). The equilibrium antibiotic concentrations reported in this study were notably lower than the values reported in the literature. These differences originate from the improved analytical methods that are available nowadays. Low product concentrations were also found for other side-chains with an amino group at the α-position. Side-chains without this group can be coupled and give acceptable product concentrations. For these antibiotics, a thermodynamically controlled process may be an alternative to kinetically controlled coupling.

Thermodynamically controlled synthesis of cefamandole

The direct enzymatic synthesis of the antibiotic cefamandole is presented as an alternative for the current processes based on either chemical synthesis or kinetic enzymatic synthesis. The influence of pH and temperature on the apparent equilibrium constant was measured; from these data, the maximum cefamandole concentration was predicted. In spite of a beneficial apparent equilibrium constant at pH 3.75, less product was formed as compared to the concentration at the optimum pH (4.25). This effect is caused by the low solubility of one of the substrates at pH 3.75.The maximum product concentration (at the optimum pH of 4.25) was found to be 22 mM which is a significant concentration. The thermodynamically controlled synthesis may prove to be an alternative for the currently used processes if it can be combined with an effective in-situ cefamandole removal step.

Ultrasound-boosted enzymatic cotton scouring process with cutinase and pectate lyase

Abstract The synergistic effect between power ultrasound and enzymes in an enzymatic scouring process has been studied. The scouring enzymes were Fusarium solani pisi cutinase (EC 3.1.1.74) and pectate lyase (EC 4.2.2.2). In different stages of the scouring process, power ultrasound with a pre-optimized power of 0.57 W cm−2 and a frequency of 30 kHz was applied. It was found that ultrasound shortens the enzymatic scouring process time dramatically; less than 5 min was required to achieve the desired scouring expressed in terms of hydrophilicity of the cotton fiber. The results obtained have been explained in terms of mass transfer intensification by ultrasound (so-called ‘sono-mechanics’) and its effect on the enzyme kinetics (so-called ‘sono-chemistry’). This latter effect has been found by applying ultrasound in a homogeneous enzymatic reaction in which mass transfer did not play any role. The kinetics of product formation in a homogeneous system was carried out using poly-d-galacturonic acid as a model substrate.

Enzymatic hydrolysis and modification of core polymer fibres for textile and other applications

Abstract: Recent progress and new developments in enzymatic surface hydrolysis of the core textile polymers poly(ethylene terephthalate) (PET) and polyamide (PA) are discussed. The process produces modifications that yield charged functional groups at the surface of these synthetic materials. The use of cutinases, proteases and amidases for modification of the surface of fibres is described and possible applications for the bio-modified PET and PA are explored.

Enzyme surface modification of textiles

Abstract: The chapter discusses recent progress and new developments in the enzymatic surface modification of textiles. Enzymatic surface modification of textile materials involves processing of fibres or (bio)polymers to modify the physical and chemical surface properties or the introduction of functional groups on the surface. In this chapter the focus is on cellulases, pectinases, xyloglucan endotransglycosylase, tyrosinases and cutinases in the surface modification of textile materials to demonstrate the potential and different applications of enzyme technology in this area. Research on the enzymatic surface modification of textiles contributes to bio-based economy through the development of novel processes for textiles exhibiting targeted functionalities and through development of novel enzyme technology for structuring and functionalisation of surfaces.