A.M. Gumel

Biosynthesis and Characterization of Polyhydroxyalkanoates Copolymers Produced by Pseudomonas putida Bet001 Isolated from Palm Oil Mill Effluent

The biosynthesis and characterization of medium chain length poly-3-hydroxyalkanoates (mcl-PHA) produced by Pseudomonas putida Bet001 isolated from palm oil mill effluent was studied. The biosynthesis of mcl-PHA in this newly isolated microorganism follows a growth-associated trend. Mcl-PHA accumulation ranging from 49.7 to 68.9% on cell dry weight (CDW) basis were observed when fatty acids ranging from octanoic acid (C8∶0) to oleic acid (C18∶1) were used as sole carbon and energy source. Molecular weight of the polymer was found to be ranging from 55.7 to 77.7 kDa. Depending on the type of fatty acid used, the 1H NMR and GCMSMS analyses of the chiral polymer showed a composition of even and odd carbon atom chain with monomer length of C4 to C14 with C8 and C10 as the principal monomers. No unsaturated monomer was detected. Thermo-chemical analyses showed the accumulated PHA to be semi-crystalline polymer with good thermal stability, having a thermal degradation temperature (T d) of 264.6 to 318.8 (±0.2) oC, melting temperature (T m) of 43. (±0.2) oC, glass transition temperature (T g) of −1.0 (±0.2) oC and apparent melting enthalpy of fusion (ΔH f) of 100.9 (±0.1) J g−1.

Ultrasound assisted lipase catalyzed synthesis of poly-6-hydroxyhexanoate

Ultrasonic irradiation greatly improved the Candida antarctica lipase B mediated ring opening polymerization of ε-caprolactone to poly-6-hydroxyhexanoate in the ionic liquid 1-ethyl-3-methylimidazolium tetraflouroborate. Compared to the conventional nonsonicated reaction, sonication improved the monomer conversion by 63% and afforded a polymer product of a narrower molecular weight distribution and a higher degree of crystallinity. Under sonication, the polydispersity index of the product was ~1.44 compared to a value of ~2.55 for the product of the conventional reaction. With sonication, nearly 75% of the monomer was converted to product, but the conversion was only ~16% for the reaction carried out conventionally. Compared to conventional operation, sonication enhanced the rate of polymer propagation by >2-fold and the turnover number of the lipase by >3-fold.

Thermo-kinetics of lipase-catalyzed synthesis of 6-O-glucosyldecanoate.

Lipase-catalyzed synthesis of 6-O-glucosyldecanoate from d-glucose and decanoic acid was performed in dimethyl sulfoxide (DMSO), a mixture of DMSO and tert-butanol and tert-butanol alone with a decreasing order of polarity. The highest conversion yield (> 65%) of decanoic acid was obtained in the blended solvent of intermediate polarity mainly because it could dissolve relatively large amounts of both the reactants. The reaction obeyed Michaelis-Menten type of kinetics. The affinity of the enzyme towards the limiting substrate (decanoic acid) was not affected by the polarity of the solvent, but increased significantly with temperature. The esterification reaction was endothermic with activation energy in the range of 60-67 kJ mol⁻¹. Based on the Gibbs energy values, in the solvent blend of DMSO and tert-butanol the position of the equilibrium was shifted more towards the products compared to the position in pure solvents. Monoester of glucose was the main product of the reaction.

Lipase catalyzed ultrasonic synthesis of poly-4-hydroxybutyrate-co-6-hydroxyhexanoate

Four different lipases were compared for ultrasound-mediated synthesis of the biodegradable copolymer poly-4-hydroxybutyrate-co-6-hydroxyhexanoate. The copolymerization was carried out in chloroform. Of the enzymes tested, Novozym 435 exhibited the highest copolymerization rate, in fact the reaction rate was observed to increase with about 26-fold from 30 to 50°C (7.9×10(-3)Ms(-1)), sonic power intensity of 2.6×10(3)Wm(-2) and dissipated energy of 130.4Jml(-1). Copolymerization rates with the Candida antarctica lipase A, Candida rugosa lipase, and Lecitase Ultra™ were lower at 2.4×10(-4), 1.3×10(-4) and 3.5×10(-4)Ms(-1), respectively. The catalytic efficiency depended on the enzyme. The efficiency ranged from 4.15×10(-3)s(-1)M(-1) for Novozym 435-1.48×10(-3)s(-1)M(-1) for C. rugosa lipase. Depending on the enzyme and sonication intensity, the monomer conversion ranged from 8.2% to 48.5%. The sonication power, time and temperature were found to affect the rate of copolymerization. Increasing sonication power intensity from 1.9×10(3) to 4.5×10(3)Wm(-2) resulted in an increased in acoustic pressure (P(a)) from 3.7×10(8) to 5.7×10(8)Nm(-2) almost 2.4-3.7 times greater than the acoustic pressure (1.5×10(8)Nm(-2)) that is required to cause cavitation in water. A corresponding acoustic particle acceleration (a) of 9.6×10(3)-1.5×10(4)ms(-2) was calculated i.e. approximately 984-1500 times greater than under the action of gravity.

Growth kinetics, effect of carbon substrate in biosynthesis of mcl-PHA by Pseudomonas putida Bet001.

Growth associated biosynthesis of medium chain length poly-3-hydroxyalkanoates (mcl-PHA) in Pseudomonas putida Bet001 isolated from palm oil mill effluent was studied. Models with substrate inhibition terms described well the kinetics of its growth. Selected fatty acids (C8:0 to C18:1) and ammonium were used as carbon and nitrogen sources during growth and PHA biosynthesis, resulting in PHA accumulation of about 50 to 69% (w/w) and PHA yields ranging from 10.12 g L−1 to 15.45 g L−1, respectively. The monomer composition of the PHA ranges from C4 to C14, and was strongly influenced by the type of carbon substrate fed. Interestingly, an odd carbon chain length (C7) monomer was also detected when C18:1 was fed. Polymer showed melting temperature (Tm) of 42.0 (± 0.2) °C, glass transition temperature (Tg) of −1.0 (± 0.2) °C and endothermic melting enthalpy of fusion (ΔHf) of 110.3 (± 0.1) J g−1. The molecular weight (Mw) range of the polymer was relatively narrow between 55 to 77 kDa.

Enzymatic synthesis of 6-O-glucosyl-poly(3-hydroxyalkanoate) in organic solvents and their binary mixture

The effects of organic solvents and their binary mixture in the glucose functionalization of bacterial poly-3-hydroxyalkanoates catalyzed by Lecitase™ Ultra were studied. Equal volume binary mixture of DMSO and chloroform with moderate polarity was more effective for the enzyme catalyzed synthesis of the carbohydrate polymer at ≈38.2 (±0.8)% reactant conversion as compared to the mono-phasic and other binary solvents studied. The apparent reaction rate constant as a function of medium water activity (aw) was observed to increase with increasing solvent polarity, with optimum aw of 0.2, 0.4 and 0.7 (±0.1) observed in hydrophilic DMSO, binary mixture DMSO:isooctane and hydrophobic isooctane, respectively. Molecular sieve loading between 13 to 15gL(-1) (±0.2) and reaction temperature between 40 to 50°C were found optimal. Functionalized PHA polymer showed potential characteristics and biodegradability.

Carbon nanofibers-poly-3-hydroxyalkanoates nanocomposite: ultrasound-assisted dispersion and thermostructural properties

The conductivity and high surface-to-volume ratio of carbon nanofibers (CNFs) composited with the medium-chain-length poly- 3-hydroxyalkanoate (mcl-PHA) have attracted much attention as smart biomaterial. However, poor CNF dispersion leads to tactoid agglomerated composite with poor crystallite morphology resulting in inferior thermomechanical properties. We employed acoustic sonication to enhance the construction of exfoliated PHA/CNFs nanocomposites. The effects of CNF loading and the insonation variables (power intensity, frequency, and time) on the stability and microscopic morphology of the nanocomposites were studied. Sonication improved the dispersion of CNFs into the polymer matrix, thereby improving the physical morphology, crystallinity, and thermomechanical properties of the nanocomposites. For example, compositing the polymer with 10% w/w CNF resulted in 66% increase in crystallite size, 46% increase in micromolecular elastic strain, and 17% increase in lattice strain. Nevertheless, polymer degradation was observed following the ultrasound exposure. The constructed bionanocomposite could potentially be applied for organic electroconductive materials, biosensors and stimuli-responsive drug delivery devices.

Ultrasound-assisted enzymatic synthesis of poly-ε-caprolactone: kinetic behavior and reactor design

Abstract Lipase-mediated, ultrasound-assisted synthesis of poly-ε-caprolactone was investigated. It was found that ultrasound irradiation helped to improve the rate constant of poly-ε-caprolactone chain propagation (kp) at high initial monomer (ε-caprolactone) concentration. The enhancement of kp ranged from 34% to 46% at 22.5–18.0 M initial monomer concentration, respectively. In a system proned to time-dependent mass-transfer limitation due to polymer chain extension, the acoustic effects could have also allowed the reaction to continue longer compared to non-sonicated process until it became impossible at highly elevated reaction mixture viscosity(>2,000 times increase from initial viscosity). Consequently, it also helped to improve monomer conversion. In a continuous flow polymerization system, a plug flow reactor system is recommended due to its lowest volume for maximum conversion compared to a continuously stirred tank reactor system.

Lipase-catalyzed synthesis of 6-o-d-glucosyldecanoate in tert-butanol: reaction optimization and effect of mixing power input

ABSTRACT Enzymatic synthesis of 6-O-D-glucosyldecanoate in tert-butanol was performed using substrates D-glucose as acyl acceptor and decanoic acid as acyl donor Candida antarctica lipase B (Novozyme 435) was used as the catalyst in the esterification process. Box Behnken of response surface methodology (RSM) was used in the optimization of selected parameters viz. reaction temperature, reaction time, substrate ratio and amount of enzyme loading. Substrate ratio was found to be the sole significant main effect while the second-order interaction between reaction time and immobilized enzyme loading was found to be a significant interaction factor. Optimized conditions for the process were: substrate molar ratio 1 (mole acyl donor-to-mole acyl acceptor), 7.5 g-L−1 immobilized enzyme loading, reaction temperature 55°C and time of 14.2 hours. When a mixed-flow impeller with downward pumping mode was used in a stirred tank reactor, minimum power input at 6.8 kW-kg−1 solvent was sufficient for an improved yield of 0.77 g glucosyl decanoate per g glucose. The reaction product composed solely of monoester with sugar acylation occurring at 6-OH primary group of D-glucose where 60% (mole) of the product was 6-O-β-D-glucosyldecanoate and 40% (mole) 6-O-α-D-glucosyldecanoate.

Perspectives on the emerging applications of multifaceted biomedical polymeric nanomaterials

Biodegradable and biocompatible polymeric nanomaterials, serving as biomedical devices have garnered significant attention as a promising solution to therapeutic management of many chronic diseases. Despite their potentials, majority of the synthetic nanomaterials used in biomedical applications lack crucial properties, for example, ligand binding sites, responsiveness, and switchability to efficiently deliver intended drugs to the target site. Advancements in manipulating nanoscale geometry have incurred the incorporation of triggered release mechanism within the nanomaterials design. This expanded their potential applications beyond nanocarriers to theranostics exhibiting both tandem drug delivery and diagnostic capabilities. Additionally, it highlights possibilities to design nanomaterials that could translate chemical response(s) to photometric display, thus making affordable biosensors and actuators readily available for biomedical exploitation. It is anticipated that, in the near future, these implementations could be made to access some of the most difficult therapy locations, for example, blood brain barrier to provide efficient management of Alzheimer, Huntington, and other neurodegenerative diseases. This review aims to serve as a reference platform by providing the readers with the overview of the recent advancements and cutting-edge techniques employed in the production and instrumentation of such nanomaterials.