Hybrid xerogel films as novel coatings for antifouling and fouling release

Hybrid sol-gel-derived xerogel films prepared from 45/55 (mol ratio) n-propyltrimethoxysilane (C3-TMOS)/tetramethylorthosilane (TMOS), 2/98 (mol ratio) bis[3-(trimethoxysilyl)propyl]-ethylenediamine (enTMOS)/tetraethylorthosilane (TEOS), 50/50 (mol ratio) n-octyltriethoxysilane (C8-TEOS)/TMOS, and 50/50 (mol ratio) 3,3,3-trifluoropropyltrimethoxysilane (TFP-TMOS)/TMOS were found to inhibit settlement of zoospores of the marine fouling alga Ulva (syn. Enteromorpha) relative to settlement on acid-washed glass and give greater release of settled zoospores relative to glass upon exposure to pressure from a water jet. The more hydrophobic 50/50 C8-TEOS/TMOS xerogel films had the lowest critical surface tension by comprehensive contact angle analysis and gave significantly greater release of 8-day Ulva sporeling biomass after exposure to turbulent flow generated by a flow channel than the other xerogel surfaces or glass. The 50/50 C8-TEOS/TMOS xerogel was also a fouling release surface for juveniles of the tropical barnacle Balanus amphitrite. X-ray photon electron data indicated that the alkylsilyl residues of the C3-TMOS-, C8-TEOS-, and TFP-TMOS-containing xerogels were located on the surface of the xerogel films (in a vacuum), which contributes to the film hydrophobicity. Similarly, the amine-containing silyl residues of the enTMOS/TEOS films were located at the surface of the xerogel films, which contributes to the more hydrophilic character and increased critical surface tension of these films.     

A patch coating method for preparing biocatalytic films of Escherichia coli

A method has been developed for immobilizing viable but nongrowing Escherichia coli in highly uniform patches. The patches consist of a thin layer of bacteria in acrylate vinyl acetate covered with a thin layer of the same polymer devoid of bacteria and sealed by the edges. This method permits study of immobilized cell physiology in biocatalytic films by the assay methods used for suspended cells. Large numbers of patches of immobilized E. coli can be generated on metal or polyester sheets. Those described here are 12.7 mm in diameter; in them the cell layer is 30 microm thick and contains more than 5 x 10(8) viable cells. The method allows the cell-plus-polymer layer and the polymer sealant to be varied in thickness from 5 to 60 microm and from 7 to 80 microm, respectively. No leakage of cells was detected from 87% of the patches during 15 days of rehydration. Culturability of the immobilized cells, released by shaking the cells out of the porous polymer layer, was 80% of pre coating culturability. E. coli beta-galactosidase activity and measurements of total RNA and DNA from immobilized and suspended cells indicated that cells immobilized in the thin polymer layer have higher specific beta-galactosidase activity and a slower total RNA degradation rate than suspended cells over 15 days.     

Comparison of lignin derivatives as substrates for laccase-catalyzed scavenging of oxygen in coatings and films

Background

Lignin derivatives are phenylpropanoid biopolymers derived from pulping and biorefinery processes. The possibility to utilize lignin derivatives from different types of processes in advanced enzyme-catalyzed oxygen-scavenging systems intended for active packaging was explored. Laccase-catalyzed oxidation of alkali lignin (LA), hydrolytic lignin (LH), organosolv lignin (LO), and lignosulfonates (LS) was compared using oxygen-scavenging coatings and films in liquid and gas phase systems.

Results

When coatings containing lignin derivatives and laccase were immersed in a buffered aqueous solution, the oxygen-scavenging capability increased in the order LO?<?LH?<?LA?<?LS. Experiments with coatings containing laccase and LO, LH or LA incubated in oxygen-containing gas in air-tight chambers and at a relative humidity (RH) of 100% showed that paperboard coated with LO and laccase reduced the oxygen content from 1.0% to 0.4% during a four-day period, which was far better than the results obtained with LA or LH. LO-containing coatings incubated at 92% RH also displayed activity, with a decrease in oxygen from 1.0% to 0.7% during a four-day period. The oxygen scavenging was not related to the content of free phenolic hydroxyl groups, which increased in the order LO?<?LS?<?LH?<?LA. LO and LS were selected for further studies and films containing starch, clay, glycerol, laccase and LO or LS were characterized using gel permeation chromatograpy, dynamic mechanical analysis, and wet stability.

Conclusions

The investigation shows that different lignin derivatives exhibit widely different properties as a part of active coatings and films. Results indicate that LS and LO were most suitable for the application studied and differences between them were attributed to a higher degree of laccase-catalyzed cross-linking of LS than of LO. Inclusion in active-packaging systems offers a new way to utilize some types of lignin derivatives from biorefining processes.     

Development of environmentally friendly coatings and paints using medium-chain-length poly(3-hydroxyalkanoates) as the polymer binder.

Unsaturated medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHAs) produced by Pseudomonas putida from linseed oil fatty acids (LOFA) and tall oil fatty acids (TOFA), were used as the polymer binder in the formulation of high solid alkyd-like paints. The relatively high concentration of unsaturated alkyl side chains incorporated into the PHA resins resulted in oxidative drying PHA paints having excellent coating properties. The homogeneously pigmented PHA coatings yielded high-gloss, smooth and strong films upon curing and showed an excellent flexibility, a good adhesion to different substrates, cohesive film properties and resistance to chipping.     

Preparation of biodegradable porous films for use as wound coverings

We studied the preparation of polymeric films formed from solutions of poly-3-hydroxybutyrate and poly-ε-caprolactone in chloroform and methylene chloride. A morphological study of film chips (electron microscopy) showed that solvent evaporation results in the formation of a heterogeneous structure with interpenetrating pores (1–20 μm). We proposed a new method for introducing the proteolytic enzyme and the aminopolysaccharide chitosan into the composition of polyester films. Composite films possessed necrolytic activity and were characterized by increased hydrophilicity. Properties of enzyme-containing films from a mixture of polymers (proteolytic activity, porous structure, and increased hydrophilicity) account for their use in the preparation of biodegradable wound coverings.     

The use of microscale processing technologies for quantification of biocatalytic Baeyer-Villiger oxidation kinetics

Microscale processing techniques would be a useful tool for the rapid and efficient collection of biotransformation kinetic data as a basis for bioprocess design. Automated liquid handling systems can reduce labor intensity while the small scale reduces the demand for scarce materials such as substrate, product, and biocatalyst. Here we illustrate this concept by establishing the use of several microwell formats (96-round, 96-deep square and 24-round well microtiter plates) for quantification of the kinetics of the E. coli TOP10 [pQR239] resting cell catalyzed Baeyer-Villiger oxidation of bicyclo[3.2.0]hept-2en-6-one using glycerol as a source of reducing power. By increasing the biocatalyst concentration until the biotransformation rate was oxygen mass-transfer limited we can ensure that kinetic data collected are in the region away from oxygen limitation. Using a 96-round well plate the effect of substrate (bicyclo[3.2.0]hept-2en-6-one) concentration on the volumetric CHMO activity was examined and compared to data collected from 1.5-L stirred-tank experiments. The phenomenon and magnitude of substrate inhibition, observed at the larger scale, was accurately reproduced in the microwell format. We have used this as an illustrative example to demonstrate that under adequately defined conditions, automated microscale processing technologies can be used for the collection of quantitative kinetic data. Additionally, by using the experimentally determined stoichiometry for product formation and glycerol oxidation, we have estimated the maximum oxygen transfer rates as a function of well geometry and agitation rate. Oxygen-transfer rates with an upper limit of between 33 mmol. L(-1). h(-1) (based solely on product formation) and 390 mmol. L(-1). h(-1) (based on product formation and glycerol oxidation) were achieved using a 96-square well format plate shaken at 1300 rpm operated with a static surface area to volume ratio of 320 m(2). m(-3).     

Polymersomes as nanoreactors for preparative biocatalytic applications: current challenges and future perspectives

Bioprocess and Biosystems Engineering - Polymersomes are hollow, spherical vesicles that are surrounded by a polymer membrane. The applied polymer must be amphiphilic to promote self-assembly in...     

Water-soluble carbon nanotube-enzyme conjugates as functional biocatalytic formulations

We report the activity, stability, and reusability of enzyme-carbon nanotube conjugates in aqueous solutions. A variety of enzymes were covalently attached to oxidized multi-walled carbon nanotubes (MWNTs). These conjugates were soluble in aqueous buffer, retained a high fraction of their native activity, and were stable at higher temperatures relative to their solution phase counterparts. Furthermore, the high surface area of MWNTs afforded high enzyme loadings, yet the intrinsic high length of the MWNT led to facile filtration. These water-soluble carbon nanotube-enzyme conjugates represent novel preparations that possess the virtues of both soluble and immobilized enzymes, thus providing a unique combination of useful attributes such as low mass transfer resistance, high activity and stability, and reusability.     

GMA grafted sago starch as a reactive component in ultra violet radiation curable coatings

Glycidyl methacrylate (GMA) was successfully grafted onto sago starch using ceric ammonium nitrate as initiator in aqueous medium. The percentage of grafting increased with increasing concentration of GMA monomer in the range studied. A core-shell configuration had been suggested to account for the hydrophobic behavior of the starch-g-GMA. Fourier transform infrared spectral analysis provided evidence of the grafting of GMA onto the starch. The acrylic double bond participated in the grafting onto the polysaccharide backbone with the glycidyl groups remaining unaffected.

The graft copolymer of starch and glycidyl methacrylate (starch-g-GMA) was incorporated into UV curable formulations using a cationic photoinitiator. In general, the addition of starch-g-GMA increased the flexibility of the cured film. The increasing of starch-g-GMA concentration in the coatings formulation increased the hardness of cured films. Gel content of the cured epoxy resin remained unimpaired by the addition of starch-g-GMA. Increasing the photoinitiator concentration in the coating formulations increased the hardness and as expected decreased the flexibility of the cured film. The gel content increased with increasing photoinitiator concentration. Further experiments are in progress to study the biodegradability of coatings.     

Selection of organic substrates as potential reactive materials for use in a denitrification permeable reactive barrier (PRB)

The aim of the present study was to select a suitable natural organic substrate as a potential carbon source for use in a denitrification permeable reactive barrier (PRB). A number of seven organic substrates were first tested in batch tests. The materials attained varying degrees of success at promoting denitrification. Some of the organic substrates performed very well, achieving complete nitrate removal (>98%), while others were considered unsuitable for a variety of reasons, including: insufficient nitrate or nitrogen removal, excessive release of leachable nitrogen from the substrate or excessive reduction of nitrate to ammonium rather than removing it as gaseous N2. The top performing substrate in terms of denitrification extent (>98%) and rate (0.067 mgNO3(-)-N dm(-3)d(-1)g(sub)(-1)) was then selected for two bench-scale column experiments in an attempt to simulate the PRB. The inlet concentration was 50 mg dm(-3) NO3(-)-N and the columns operated at two different flow rates: 0.3 cm3 min(-1) (Column 1) and 1.1cm3 min(-1) (Column 2). The two columns showed different general patterns, making it clear that the flow rate was a key factor at the nitrate removal. Nitrate was completely removed (>96%) by the passage through Column 1, while only partially removed in Column 2 (66%). The results indicated that the selected organic substrate (Softwood) was applicable for further use as a filling material for a PRB.     

Engineering the microstructure and permeability of thin multilayer latex biocatalytic coatings containing E. coli.

The microstructure and permeability of rehydrated 20-100 microm thick partially coalesced (vinyl-actetate acrylic copolymer) SF091 latex coatings and a 118 microm thick model trilayer biocatalytic coating consisting of two sealant SF091 layers containing a middle layer of viable E. coli HB101 + latex were studied as delaminated films in a diffusion apparatus with KNO(3) as the diffussant. The permeability of the hydrated coatings is due to diffusive transport through the pore space between the partially coalesced SF091 latex particles. Coating microstructure was visualized by fast freeze cryogenic scanning electron microscopy (cryo-SEM). The effective diffusion coefficient of SF091 latex coatings (diffusive permeability/film thickness) was determined as the ratio of the effective diffusivity of KNO(3) to its diffusivity in water (D(eff)/D). Polymer particle coalescence was arrested by two methods to increase coating permeability. The first used glycerol with coating drying at 4 degrees C, near the glass transition temperature (T(g)). The second method used sucrose or trehalose as a filler to arrest coalescence; the filler was then dissolved away. D(eff)/D was measured as a function of film thickness; content of glycerol, sucrose, and trehalose; drying time; and rehydration time. D(eff)/D varied from 3 x 10(-4) for unmodified SF091 coatings to 6.8 x 10(-2) for coatings containing sucrose. D(eff)/D was reduced by the flattening of latex particles against the surface of the solid substrate, as well as by the presence of the colloid stabilizer hydroxyethylcellulose (HEC). When corrected for the flattened particle layer, D(eff)/D of HEC-free coatings was as high as 0.20, which agreed with the value predicted from analysis of cryo-SEM images of the coat surface. D(eff)/D decreased by one-half in approximately 5 days in rehydrated SF091 coatings, indicating that significant wet coalescence occurs after glycerol, sucrose, or trehalose are leached from the films. D(eff)/D of SF091 latex trilayer coatings containing viable E. coli HB101 cells decreased as cell loading was increased from 2.2 x 10(-2) for 64 g dry cell weight per liter of coat volume to 5 x 10(-3) for 151 g DCW/L of coat volume. The reduction in coating permeability with increasing cell loading is predicted by Maxwell's equation for D(eff)/D in periodic composites.     

Painting and printing living bacteria: engineering nanoporous biocatalytic coatings to preserve microbial viability and intensify reactivity

Latex biocatalytic coatings containing approximately 50% by volume of microorganisms stabilize, concentrate and preserve cell viability on surfaces at ambient temperature. Coatings can be formed on a variety of surfaces, delaminated to generate stand-alone membranes or formulated as reactive inks for piezoelectric deposition of viable microbes. As the latex emulsion dries, cell preservation by partial desiccation occurs simultaneously with the formation of pores and adhesion to the substrate. The result is living cells permanently entrapped, surrounded by nanopores generated by partially coalesced polymer particles. Nanoporosity is essential for preserving microbial viability and coating reactivity. Cryo-SEM methods have been developed to visualize hydrated coating microstructure, confocal microscopy and dispersible coating methods have been developed to quantify the activity of the entrapped cells, and FTIR methods are being developed to determine the structure of vitrified biomolecules within and surrounding the cells in dry coatings. Coating microstructure, stability and reactivity are investigated using small patch or strip coatings where bacteria are concentrated 102- to 103-fold in 5-75 microm thick layers with pores formed by carbohydrate porogens. The carbohydrate porogens also function as osmoprotectants and are postulated to preserve microbial viability by formation of glasses inside the microbes during coat drying; however, the molecular mechanism of cell preservation by latex coatings is not known. Emerging applications include coatings for multistep oxidations, photoreactive coatings, stabilization of hyperthermophiles, environmental biosensors, microbial fuel cells, as reaction zones in microfluidic devices, or as very high intensity (>100 g.L-1 coating volume.h-1) industrial or environmental biocatalysts. We anticipate expanded use of nanoporous adhesive coatings for prokaryotic and eukaryotic cell preservation at ambient temperature and the design of highly reactive "living" paints and inks.     

Sustainable biocatalytic synthesis of L-homophenylalanine as pharmaceutical drug precursor

Over the past decade, L-homophenylalanine is extensively used in the pharmaceutical industry as a precursor for production of angiotensin-converting enzyme (ACE) inhibitor, which possesses significant clinical application in the management of hypertension and congestive heart failure (CHF). A number of chemical methods have been reported thus far for the synthesis of L-homophenylalanine. However, chemical methods generally suffer from process complexity, high cost, and environmental pollution. On the other hand, enantiomerically pure L-homophenylalanine can be obtained elegantly and efficiently by employing biocatalytic methods, where it appears to be the most attractive process in terms of potential industrial applications, green chemistry and sustainability. Herein we review the biocatalytic synthesis of vital L-homophenylalanine as potentially useful intermediate in the production of pharmaceutical drugs in environmentally friendly conditions, using membrane bioreactor for sustainable biotransformation process. One envisages the future prospects of developing an integrated membrane bioreactor system with improved performance for L-homophenylalanine production.     

The use of fungicidal paints and gels to treat existing apple cankers

Four paints containing mercuric oxide, octhilinone, thiophanate-methyl or triad-imefon and five gel formulations (carbendazim/triadimefon in sodium alginate or xanthan gum, carbendazim/triadimefon/hypophosphorous acid and thiophanate-methyl/oxycarboxin in xanthan or PP969/alginate) were tested on natural cankers caused by Nectria galligena on apple trees. Scraping cankers decreased their size 7–9 months later due to stimulation of callus formation, even where no fungicide was applied, and decreased perithecial, but not conidial production. Only the paints were applied to scraped cankers and that containing mercuric oxide was the most effective in decreasing canker size and restricting new canker growth. All formulations except the octhilinone paint were applied to unscraped cankers. Only mercuric oxide paint and acidic carbendazim/triadimefon/xanthan gel stimulated callus formation and only the former caused a decrease in canker size. Every treatment, except triadimefon paint and PP969/alginate, reduced conidial production. Bioassay with TV. galligena showed that the carbendazim and thiophanate-methyl gels achieved some movement of fungitoxicant into plant tissue.     

Oxygen-scavenging coatings and films based on lignosulfonates and laccase

Laccase and lignosulfonates were included in coating colors and embedded in latex-based or starch-based films and coatings on foil or board. After 6 days at 23 °C and 100% relative humidity, the oxygen content in airtight chambers decreased from 1.0% (synthetic gas consisting of 99% N(2) and 1% O(2)) to 0.3% in the presence of board coated with lignosulfonate and laccase, while the oxygen content remained unchanged in control experiments without enzyme. The water stability of lignosulfonate-containing latex-based coatings and starch-based films was improved after laccase-catalyzed oxidation of lignosulfonates, which indicates polymerization to products with lower solubility in water. Furthermore, the E' modulus of starch-based films increased with 30%, which indicates laccase-catalyzed polymerization of lignosulfonates resulting in increased stiffness of the film. The results suggest that laccases and lignosulfonates can be used as an oxygen-scavenging system in active packaging and that enzyme-catalyzed polymerization of lignosulfonates contributes to improved water stability and mechanical properties.     

Enzyme evolution for industrial biocatalytic cascades

1. Download : Download high-res image (122KB)
2. Download : Download full-size image

     

Sustainable films and coatings from hemicelluloses: a review

This review summarizes the results of past research on films and coatings from hemicelluloses, biopolymers that are as yet relatively unexploited commercially. The targeted uses of hemicelluloses have primarily been packaging films and coatings for foodstuffs as well as biomedical applications. Oxygen permeability of hemicellulose films, an important characteristic for food packaging, was typically comparable to values found for other biopolymer films such as amylose and amylopectin. As expected, the modification of hemicelluloses to create more hydrophobic films reduced the water vapor permeability. However, modified hemicellulose coatings intended for food still exhibited water vapor permeabilities several magnitudes higher than those of other polymers currently used for this purpose. Research on hemicelluloses for biomedical applications has included biocompatible hydrogels and coatings and material surfaces with enhanced cell affinity. Numerous possibilities exist for chemically modifying hemicelluloses, and fundamental studies of films from modified hemicelluloses have identified other potential applications, including selective membranes.     

Process implementation aspects for biocatalytic hydrocarbon oxyfunctionalization

Oxidoreductases catalyze a large variety of regio-, stereo-, and chemoselective hydrocarbon oxyfunctionalizations, reactions, which are important in industrial organic synthesis but difficult to achieve by chemical means. This review summarizes process implementation aspects for the in vivo application of the especially versatile enzyme class of oxygenases, capable of specifically introducing oxygen from molecular oxygen into a large range of organic molecules. Critical issues such as reaching high enzyme activity and specificity, product degradation, cofactor recycling, reactant toxicity, and substrate and oxygen mass transfer can be overcome by biochemical process engineering and biocatalyst engineering. Both strategies provide a growing toolset to facilitate process implementation, optimization, and scale-up. Major advances were achieved via heterologous overexpression of oxygenase genes, directed evolution, metabolic engineering, and in situ product removal. Process examples from industry and academia show that the combined use of different concepts enables efficient oxygenase-based whole-cell catalysis of various commercially interesting reactions such as the biosynthesis of chiral compounds, the specific oxyfunctionalization of complex molecules, and also the synthesis of medium-priced chemicals. Better understanding of the cell metabolism and future developments in both biocatalyst and bioprocess engineering are expected to promote the implementation of many and various industrial biooxidation processes.