Joseph A. Laszlo

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.

Preparation of a weakly basic ion exchanger by crosslinking starch with epichlorohydrin in the presence of NH4OH1

Crosslinking of starch with epichlorohydrin in the presence of NH4OH, NaOH and water was studied. The reaction was optimized and the products analysed by solid-state 13C-NMR in the presence of water, acid-base titration and dyebinding measurements. The presence of different types of hydroxypropyl groups was confirmed by NMR, but their linkage to polysaccharide could not be confirmed because of their minor abundance relative to all other CH2 groups, and because the motion of the sidechains is much greater than the starch component, which remains fairly constant despite the presence of water. Yield of crosslinked, water-insoluble product is increased as a greater amount of NH4OH and a lower amount of water is used in the reaction. Product yield using water-insoluble starch is higher than with a water-soluble starch. Closed-vessel (pressurized) reaction conditions increases product exchange capacity. Potentiometric titration of products in Cl−-form or in non-ionized form indicated smaller exchange capacity values than expected from product nitrogen contents, reflecting the difficulty in fully protonating the products. Dye binding by the crosslinked-starch exchangers is pH-dependent, with an increased quantity of dye bound at lower pH, which is consistent with the weak-amine nature of the products. Hydrolyzed Remazol Brilliant Red F3B, a trivalent reactive dye, binds less effectively under acidic conditions, on a molar basis, to the starch-based exchangers than does Alizarin Red S, a monovalent mordant dye. Dye-binding capacities are somewhat lower than the total ion-exchange capacities determined by potentiometric titration, suggesting that a portion of the exchange sites are unavailable to the dyes.

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.

Mineral absorption in the monogastric GI tract

Section I. Mechanisms of Mineral Absorption -- 1. Theoretical and Practical Aspects of Zinc Uptake and Absorption -- 2. Zinc Absorption in Humans Determined Using In Vivo Tracer Studies and Kinetic Analysis -- 3. Mechanisms of Intestinal Brush Border Iron Transport -- 4. Trace Metal Interactions Involving the Intestinal Absorption Mechanisms of Iron and Zinc -- 5. On the Molecular Mechanisms of Intestinal Calcium Transport -- 6. Equilibration Constants for the Complexation of Metal Ions by Serum Transferrin -- Section II. Dietary Influences on Mineral Uptake -- 7. Protein Digestion and the Absorption of Mineral Elements -- 8. The Effect of Dietary Proteins on Iron Bioavailability in Man -- 9. Effect of Gastrointestinal Conditions on the Mineral-Binding Properties of Dietary Fibers -- 10. In Vivo Mineral Contents of Dietary Fiber Determined by EDX Analysis -- 11. Phytic Acid Interactions with Divalent Cations in Foods and in the Gastrointestinal Tract -- 12. Low Gastric Hydrochloric Acid Secretion and Mineral Bioavailability -- 13. Effect of Age and the Milk Sugar Lactose on Calcium Absorption by the Small Intestine -- 14. Dietary Fiber or Bile-Sequestrant Ingestion and Divalent Cation Metabolism.

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.

Modeling the cation-exchange properties of corn bran under simulated gastrointestinal ionic conditions

Abstract Dietary fiber is known to exert many positive health benefits. However, evidence suggests that dietary fiber may decrease mineral bioavailability. In order to test the hypothesis that dietary fiber limits mineral availability through ion-exchange processes, an analytical model was developed which predicts the extent of binding of metal cations in the gastrointestinal tract. Corn bran, representing a typical insoluble dietary fiber, was tested in vitro against solutions of varying H + , Na + , K + , Ca 2+ and Mg 2+ concentrations mimicking the range of gastrointestinal ionic conditions. The model relates solution composition to the extent of metal cation binding through a series of proton/metal exchanges with the dietary fiber carboxyl groups. In addition to equilibrium constants for each proton/metal exchange, solution and solid phase activity coefficients for all ions are required. It was found that an exponential function relating the activity coefficient of protonated exchange sites to their mole fraction was necessary and sufficient to make the model adequately sensitive to solution pH. Introduction of this expression produced a 6-fold improvement in the fit of the model to experimental observations of ion binding. The general nature of the model should permit its application to other dietary fibers, plant cell walls and synthetic ion-exchange resins.

Biodegradability of quaternized, crosslinked sugarcane bagasse

Quaternized, crosslinked sugarcane bagasse can adsorb anionic dyes from textile wastewater. Disposal of dye-saturated adsorbent by composting or land application would require that modifications made to the bagasse do not interfere with its decomposition. The impact of quaternization and crosslinking on bagasse biodegradability was examined. Bagasse in varying states of modification was mixed with soil and monitored for carbon dioxide evolution for four weeks at 27°C. After subtracting the amount of carbon evolved from control soil samples, the net carbon evolved from the bagasse samples was determined and used as a measure of their extent of biodegradation. Biodegradability decreased in the order: bagasse (approx. 60% degraded after four weeks) > quaternized bagasse > quaternized, epichlorohydrin-crosslinked bagasse > quaternized, methylene-bis-acrylamide-crosslinked bagasse > epichlorohydrin-crosslinked bagasse (less than 5% degraded). Crosslinking severely impacted biodegration, probably by preventing the penetration of (hemi)cellulytic and lignolytic enzymes into the interior of the modified bagasse particles. It is concluded that the biodegradability of quaternized, crosslinked bagasse is too low for composting or land application.

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.