The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging method offers the first approach for evaluating the antioxidant potential of a compound, an extract or other biological sources. This is the simplest method, wherein the prospective compound or extract is mixed with DPPH solution and absorbance is recorded after a defined period. However, with the advancement and sophistication in instrumental techniques, the method has undergone various modifications to suit the requirements, even though the basic approach remains same in all of them. This article presents a critical review on various developments to the DPPH method.

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Genesis and development of DPPH method of antioxidant assay

Intermolecular static and dynamic fluorescence quenching constants of eight coumarin derivatives by nucleobase derivatives have been determined in aqueous media. One common sequence of the quenching efficiency has been found for the nucleobases. The feasibility of a photoinduced electron transfer reaction for the nucleobase-specific quenching of fluorescent dyes is investigated by the calculation of the standard free energy changes with the Rehm−Weller equation. A complete set of one-electron redox potential data for the nucleobases are determined electrochemically in aprotic solvents for the first time, which are compared with values obtained by various other methods. Depending on the redox properties of the fluorescent dyes, the sequences of the quenching efficiencies can be rationalized by the orders of electrochemical oxidation potentials (vs NHE) of nucleosides (dG (+1.47 V) < dA < dC ≈ dT < U (≥ +2.39 V)) and reduction potentials (dG (< −2.76 V) < dA < dC < dT < U (−2.07 V)). The correlation between...

Nucleobase-specific quenching of fluorescent dyes. 1. nucleobase one-electron redox potentials and their correlation with static and dynamic quenching efficiencies

Different methods of preparing lipases for use in organic media are critically reviewed. Solid lipase preparations can be made by typical immobilisation methods such as adsorption, entrapment, covalent coupling or cross-linking. Immobilisation is especially attractive for lipases because, in addition to the normal benefits of enzyme immobilisation, it can also lead to a considerable increase in catalytic activity, probably caused by conformational changes in the lipase molecules. Activation can be achieved, for example, using hydrophobic support materials or surfactants during the immobilisation procedure. Surfactants can also be used to solubilise lipases in organic media via the formation of hydrophobic ion pairs, surfactant-coated lipase or reversed micelles. Lipase preparation methods are discussed with regard to potential lipase inactivation and activation effects, mass transfer limitations, lipase stability and other features important for applications. The practical applications of lipases in organic media reviewed include ester synthesis, modification of triacylglycerols and phospholipids, fatty acid enrichment, enantiomer resolution, biodiesel production and acylation of carbohydrates and bioactive compounds.

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Immobilisation and application of lipases in organic media.

Ion Binding and Reactivity at Charged Aqueous Interfaces

Interactions of small molecules with reverse micelles

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

The aggregation numbers of sodium dodecyl sulfate micelles formed in water solutions of poly(ethylene oxide) and poly(vinyl pyrrolidone) were determined from fluorescence quenching experiments, employing ruthenium tris(bipyridyl) chloride as donor and 9-methyl anthracene as quencher. It was found that sodium dodecyl sulfate aggregates comprise 35 ± 5 monomers when formed on poly(ethylene oxide) chains and 28 ± 6 when formed on poly(vinyl pyrrolidone). The aggregation numbers were the same for surfactant/polymer ratios from ca. 40% of coverage up to saturation, and they were also independent of the polymers molecular weight (from 6 × 103 to 10 × 105 for poly(ethylene oxide) and 4 × 104 to 4 × 105 for poly(vinyl pyrrolidone). On the other hand, the sodium dodecyl sulfate aggregation number of the micelles formed on poly(ethylene oxide) chains increases in the presence of added salt. A value of 46 ± 5 was found in a 0.1 M sodium chloride solution.

Aggregation numbers of sodium dodecyl sulfate micelles formed on poly(ethylene oxide) and poly(vinyl pyrrolidone) chains

A fluorescence method was employed to determine the partitioning of n-hexanol and n-heptanol between sodium dodecyl sulfate micelles and the intermicellar phase from dilute to saturated solutions of the alcohols. Pyrene was used as a fluorescent probe. The method employed takes advantage of the change in the rate of pyrene fluorescence quenching by oxygen that occurs when the alcohols are incorporated into the micelles. The results obtained show that the partition constants of the alcohols suddenly decrease when the mole fraction of the alcohols in the micellar phase is about 0.5. This change is probably due to saturation of the micellar surface.

Partitioning of n-hexanol and n-heptanol in micellar solutions of sodium dodecyl sulfate

Etude de la reaction d'echange entre des anions monovalents et divalents dans des solutions micellaires d'un agent de surface cationique (palmityltrimethylammonium) a l'aide de 2 methodes differentes: l'extinction de la fluorescence des echantillons solubilises dans les micelles et l'ultrafiltration

Elsa Abuin

Papers

Interactions of small molecules with reverse micelles

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

Aggregation numbers of sodium dodecyl sulfate micelles formed on poly(ethylene oxide) and poly(vinyl pyrrolidone) chains

Partitioning of n-hexanol and n-heptanol in micellar solutions of sodium dodecyl sulfate

Ion exchange between monovalent and divalent counterions in cationic micellar solution