David L. Compton

Comparison of peroxidase activities of hemin, cytochrome c and microperoxidase-11 in molecular solvents and imidazolium-based ionic liquids

The ability of Fe(III)protoporphyrin(IX) chloride (hemin), microperoxidase-11 (MP-11), and cytochrome c (cyt-c) to oxidize 2-methoxyphenol (guaiacol) was examined in the room-temperature ionic liquids (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) and the hexafluorophosphates of 1-butyl- and 1-octyl-3-methylimidazolium, ([bmim][PF6] and [omim][PF6]), respectively. All three biocatalysts displayed peroxidase activity when activated by an electron acceptor, tert-butyl hydroperoxide for hemin and hydrogen peroxide for MP-11 and cyt-c. Hemin required the addition of a coordinating base, pyridine or N-methylimidazole (NMI), to produce an active complex. Cyt-c did not require exogenous ligands for activity in IL, although their addition increased peroxidase activity. MP-11 could not be solubilized without an exogenous ligand, therefore, whether MP-11 was active in the absence of such ligands was not determined. Pyridine provided higher activities than NMI for the three catalysts. Hemin and MP-11 peroxidase activities were markedly higher in IL compared to molecular solvents of similar polarity, as characterized by probe solvatochromic behavior, while cyt-c activity was comparable between both types of solvents. There was no consistent preference by the catalysts for a particular IL. These observations indicate that IL are suitable media for bioelectrocatalysis.

Direct electrochemical reduction of hemin in imidazolium-based ionic liquids

The direct electrochemical reduction of hemin, protoporphyrin(IX) iron(III) chloride, ligated with strong or weak heterocyclic bases, was investigated in the ionic liquids (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-octyl-3methylimidazolium hexafluorophosphate ([omim][PF6]), using cyclic voltammetry and chronocoulometry. Hemin complexed with N-methylimidazole (NMI) or with pyridine had E1/2 values slightly (4–59 mV) more positive in IL (without electrolyte) than in methanol (1.0 M electrolyte) using a gold electrode. NMI-ligated hemin had a lower E1/2 than pyridine-ligated hemin in either IL, consistent with the stronger electron donor characteristic of NMI. [Bmim][PF6] solutions consistently yielded E1/2 values 30 mV more negative than [omim][PF6] solutions. The diffusion coefficients Do of hemin in the IL ranged between 1.50 and 2.80 ×10 −7 cm 2 s −1 , while the heterogeneous electron-transfer rate constants ks ranged between 3.7 and 14.3 × 10 − 3 cm s − 1 . Cyclic voltammetry of hemin adsorbed to a gold surface through 4,4-bispyridyl disulfide (AT4) linkages showed a large positive shift in the oxidation wave, indicating that adsorption stabilizes the reduced hemin state. The surface concentration o of the adsorbed hemin was determined to be 1.21 ×10 − 10 mol cm − 2 , indicating the presence of one or more complete monolayers of hemin. These findings suggest that while hemin is electrochemically active in IL, its behavior is modified by the ligand field strength and surface adsorption phenomena. Published by Elsevier Science B.V.

Packed-bed bioreactor synthesis of feruloylated monoacyl- and diacylglycerols: clean production of a “green” sunscreen

A biocatalytic process for covalent incorporation of ferulic acid onto the glycerol backbone of vegetable oil proceeds efficiently, although rather slowly, with Candida antarctica lipase B in a packed-bed reactor. The bioreactor shows considerable long-term stability. Product yield is influenced by the water content of the fluid phase and enzyme support. The enzyme support modulates substrate concentrations through adsorption and subsequent release of reactants over the course of the reaction. The resulting product has excellent UVA/UVB absorbing properties, making it a potential substitute for conventional petroleum-based sunscreen active agents.

Loss of cytochrome c Fe(III)/Fe(II) redox couple in ionic liquids

Abstract The electrochemical behavior of cytochrome c (cyt- c ) adsorbed to gold electrodes through mercaptoalkanoic acid/mercaptoalcohol monolayers was investigated in the 1-butyl-3-methylimidazolium salts of bis(trifluoromethylsulfonyl)imide and hexafluorophosphate. Cyt- c does not retain its Fe(III)/Fe(II) redox activity in dry ionic liquids (ILs); however, the redox signal of the modified electrodes can be reconstituted upon subsequent treatment with aqueous buffer. Water saturated ILs, 1.4 wt.%, failed to support the redox activity of the adsorbed cyt- c ; therefore, the ILs’ deleterious effects on the redox behavior of the cyt- c modified electrodes cannot be attributed solely to the stripping of essential water from the enzymes polypeptide lattice.

Evaluation of Soyscreen in an Oil-Based Formulation for UV Protection of Beauveria bassiana Conidia

ABSTRACT Soyscreen oil was studied as a formulation ingredient to protect Beauveria bassiana (Balsamo) Vuillemin conidia from UV degradation. Feruloylated soy glycerides, referred to as Soyscreen oil, are biobased UV-absorbing molecules made by combining molecules of soybean oil with ferulic acid. Conidia stored in Soyscreen oil for 28 wk at 25, 30, and 35°C retained viability as well as conidia stored in sunflower oil, demonstrating that Soyscreen did not adversely affect viability with prolonged storage. For samples applied to glass and exposed to simulated sunlight (xenon light), conidia in sunflower oil with or without sunscreens (Soyscreen or oxyl methoxycinnimate) had similar conidia viability after exposure. These oil formulations retained conidia viability better than conidia applied as an aqueous treatment. However, the 10% Soyscreen oil formulation applied to field grown cabbage (Brassica oleracea L.) and bean (Phaseolus vulgaris L.) plants, did not improve residual insecticidal activity compared with aqueous applications of unformulated conidia or two commercial formulations when assayed against Trichoplusia ni (Hübner) larvae. Our results suggest that the oil applications lose UV protection because the oil was absorbed by the leaf. This conclusion was supported in subsequent laboratory exposures of conidia in oil-based formulations with UV screens applied to cabbage leaves or balsa wood, which lost protection as measured by decreased viability of conidia when exposed to simulated sunlight. As a result, additional formulation techniques such as encapsulation to prevent separation of the protective oil from the conidia may be required to extend protection when oil formulations are applied in the field.

Synthesis and tribological investigation of lipoyl glycerides.

Lipoyl glycerides were synthesized by enzymatic transesterification of lipoic acid with high-oleic sunflower oil in 2-methyl-2-butanol solvent. The synthesis gave a crude product mixture comprising unreacted lipoic acid, free fatty acids, and several lipoyl glyceride structures of varying lipoic acid substitution. A more purified product mixture, devoid of unreacted lipoic acid and free fatty acids, was obtained in 61% yield. The crude and purified product mixtures were thoroughly characterized and their components positively identified. The tribological properties of the product mixtures were further investigated using a variety of methods. The product mixtures displayed significantly improved oxidation stability, cold-flow, and extreme pressure properties over those of the parent high-oleic sunflower oil. The extreme pressure results for the neat products showed a higher weld point for the crude than for the purified mixture. This was attributed to differences in the chemical properties of the components in the two product mixtures.

Carboxyl-terminated PAMAM dendrimer interaction with 1-palmitoyl-2-oleoyl phosphocholine bilayers.

Polyanionic polymers and liposomes have a great potential use as individual drug delivery systems and greater potential as a combined drug delivery system. Thus, it is important to better understand the interactions of polymers with phospholipid bilayers. A mechanistic study of the interaction between carboxyl-terminated poly(amidoamine) (PAMAM) dendrimers with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer using fluorescence leakage and quartz crystal microbalance with dissipation monitoring (QCMD) was conducted. Fluorescence leakage experiments demonstrated that carboxyl-terminated generation 2 (G2-COOH) dendrimers caused increased liposome leakage with increasing dendrimer concentration over a 0 to 20μM range. Generation 5 (G5-COOH), on the other hand, reduced leakage over the same concentration range, presumably by increasing lipid packing. QCMD and atomic force microscopy (AFM) measurements demonstrated that G2-COOH interacting with supported bilayers resulted in small defects with some mass loss and no adsorption. In contrast, G5-COOH interaction with a bilayer resulted in adsorption and local bilayer swelling.

Formation of inclusion complexes between high amylose starch and octadecyl ferulate via steam jet cooking.

Amylose-ligand inclusion complexes represent an interesting approach to deliver bioactive molecules. However, ferulic acid has been shown not to form single helical inclusion complexes with amylose from high amylose maize starch. To overcome this problem a lipophilic ferulic acid ester, octadecyl ferulate, was prepared and complexed with amylose via excess steam jet cooking. Jet-cooking octadecyl ferulate and high amylose starch gave an amylose-octadecyl ferulate inclusion complex in 51.0% isolated yield. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed that a 61 V-type inclusion complex was formed. Amylose and extraction assays showed the complex to be enriched in amylose (91.9±4.3%) and contain 70.6±5.6mgg(-1) octadecyl ferulate, although, minor hydrolysis (∼4%) of the octadecyl ferulate was observed under the excess steam jet-cooking conditions utilized. This study demonstrates that steam jet cooking is a rapid and scalable process in which to prepare amylose-octadecyl ferulate inclusion complexes.

Octadecyl ferulate behavior in 1,2-Dioleoylphosphocholine liposomes.

Octadecyl ferulate was prepared using solid acid catalyst, monitored using Supercritical Fluid Chromatography and purified to a 42% yield. Differential scanning calorimetry measurements determined octadecyl ferulate to have melting/solidification phase transitions at 67 and 39°C, respectively. AFM imaging shows that 5-mol% present in a lipid bilayer induced domains to form. Phase behavior measurements confirmed that octadecyl ferulate increased transition temperature of phospholipids. Fluorescence measurements demonstrated that octadecyl ferulate stabilized liposomes against leakage, maintained antioxidant capacity within liposomes, and oriented such that the feruloyl moiety remained in the hydrophilic region of the bilayer. Molecular modeling calculation indicated that antioxidant activity was mostly influenced by interactions within the bilayer.

Phenol Esterase Activity of Porcine Skin

The alkyl esters of plant-derived phenols may serve as slow-release sources for cutaneous delivery of antioxidants. The ability of skin esterases to hydrolyze phenolic esters was examined. Esters of tyrosol and hydroxytyrosol were prepared from decanoic and lipoic acids. Ferulic acid was esterified with octadecanol, glycerol, and dioleoylglycerol. These phenolic derivatives were treated in taurodeoxycholate microemulsion and unilamellar liposomes with ex vivo porcine skin and an aqueous extract of the skin. Extracted esterases hydrolyzed the microemulsions at rates in the order: tyrosyl lipoate > tyrosyl decanoate > hydroxytyrosyl lipoate > hydroxytyrosyl decanoate. The tyrosyl decanoate was subject to comparatively little hydrolysis (10-30% after 24h) when incorporated into liposomes, while hydroxytyrosyl decanoate in liposomes was not hydrolyzed at all by the skin extract. Ferulate esters were not hydrolyzed by the extract in aqueous buffer, microemulsion, nor liposomes. Tyrosyl decanoate applied topically to skin explants in microemulsion were readily hydrolyzed within 4h, while hydrolysis was minimal when applied in liposomes. These findings indicate that porcine skin displays a general esterase activity toward medium-chain esters of tyrosol and hydroxytyrosol, which can be moderated by the physiochemical properties of the lipid vehicle, but no feruloyl esterase activity.